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The future multi-terminal direct-current (MTDC) grid will require the interconnection of point-to-point high-voltage (HV) DC links with different specifications such as DC voltage level, system grounding configuration and HVDC technology. To adapt these differences, it is obligatory for DC/DC converters to interconnect HVDC links. Additionally, they are capable of providing supplementary functionalities as they are highly controllable devices. In this article, a primary virtual resistance DC voltage controller associated with DC/DC converter is proposed for managing DC grid voltages of the interconnected HVDC grids, increasing the reliability of the system. The commonly known topology, Front-to-Front Modular Multilevel Converter (F2F-MMC) is adopted for DC/DC converter. Time-domain simulations are performed using EMTP software for validating the controller behaviour under power disturbances and large events of loss of one converter in a MMC-based MTDC system. The converters are modelled using reduced order modelling (ROM) methodology. Apart from this, dynamic studies have been carried out using a linear state space model for small-signal stability analysis of a HVDC system integrating DC/DC converter with a virtual resistance DC voltage controller. The results are examined through parametric sensitivity analysis.

With the increasing penetration of power electronic converters in the power system induced by the energy transition, Grid Forming (GFM) technology emerges as crucial for complementing traditional synchronous generators in fulfilling system needs. All over the world, TSOs have started introducing performance-based requirements to define the desired behaviour of GFM units without prescribing specific technical solutions. Based on these specifications, manufacturers design their grid-connected equipment. However, depending on requirements, challenges may arise in optimizing control strategies without hardware modifications, potentially becoming cost-driving factors. Intellectual property protection limits information disclosure, restricting the guidance available to TSOs during cost–benefit assessments. Academic contributions on GFM control and generic models can bridge the gap, providing a fair portrayal of the general behaviour and then facilitates an open discussion on their ability to meet the requirements and contribute to fulfil system needs. This survey paper provides a comprehensive overview of the perspectives offered by these diverse stakeholders.

Networked microgrids is a cluster of local grids that can be connected through a weak network and can provide ancillary services. On a system point of view, it is desirable that every microgrid exhibits a behaviour at the Point of Common Coupling (PCC) which enables to share active and reactive powers with other grids. This paper proposes a Model Predictive Supervisor that encompasses internal objectives and enforces a virtual droop control at the PCC. The supervisor uses a prediction module based on a model of the microgrid and an outer loop which supplies the PCC powers with respect to the aggregated capability diagram at the PCC. For a weak network, this diagram depends on the PCC voltage that varies with time, generating a set of time varying non-linear constraints. The supervisor generates the references to control the local distributed generators which are inside the microgrid. Through the three steps developed in this paper, the need for model based control is highlighted and a Model Predictive based Controller proposed and validated from simulations.

Greater numbers of power electronics (PEs) converters are being connected to energy systems due to the development of renewable energy sources, high-voltage transmission, and PE-interfaced loads. Given that power electronics-based devices and synchronous machines have very different dynamic behaviours, some modelling approximations, which may commonly be applied to run transient simulations of transmission systems, may not be optimal for future grids. Indeed, the systematic utilisation of the phasor approximation for power lines, implemented in most transient simulation programs, is increasingly not appropriate anymore. In order to avoid the requirement for full electromagnetic transient simulations, which can be resource-demanding and time-consuming, this paper proposes a combination of an event-based state residualisation approximation and the Kron reduction technique. The proposed technique has the advantage of allowing accurate transient simulations based on the optimal reduction of the number of state variables, depending on the observed variables, the considered events, and the tolerated approximation error, along with simplifying power systems equations for accelerated simulations.

The fast development of renewable energies leads to an increase in the power electronics penetration in transmission systems. This is particularly true if one considers a 100% renewable energies power system, where wind and solar photovoltaic energies, which make most of the renewable energies connections today, are connected to the grid through power electronics converters. Because power electronics-based generators and synchronous machines-based generators have very different dynamic behaviours, some approximations usually used to run transient simulations of transmission systems might not be optimal for future grids. The systematic use of the phasor approximation applied to the power lines, implemented in most of the Transient Simulation Programs, is indeed not relevant any more. To avoid the use of Electromagnetic Transient simulations, that are resource-demanding and time-consuming, this paper presents a novel Model Order Reduction technique for large grids with a high penetration of power electronic devices. Compared to the classical phasor approximation, this event-based state residualization approximation allows accurate transient simulations and at the same time an optimal reduction of the number of the system's state variables depending on the observed variables, the considered events and the tolerated approximation error.

In this paper, a reliable methodology is proposed in order to implement and validate a Model Predictive Control (MPC) scheme on an actual Voltage Source Converter (VSC) integrated in a scale-down multi-terminal DC grid. The objective of the investigated MPC controller is to enable AC frequency support among two asynchronous AC areas through a High Voltage Direct Current (HVDC) grid, while considering physical constraints, such as maximum and minimum DC voltage. A systematic and accurate implementation strategy is proposed, based mainly on the Hardware In the Loop (HIL) and Power Hardware In the Loop (PHIL), leading to the real-life testing on VSC, controlled by a classical microcontroller. The technical problems during the implementation process, as well as the proposed solutions, are described in detail through this paper. This procedure is deemed valuable to bridge the gap between offline simulation and the actual implementation of such advanced control scheme on experimental test rig.

In this paper, it is identified that unstable weak grid connection of voltage source inverters (VSIs) is dominantly caused by the current control. In particular, it is found the proportional gain k p of conventional PI controller cannot balance the grid voltage impact and damping capability when a weak grid with short circuit ratio (SCR) < 1.3 is connected. This issue is solved in this paper by simply restructuring the PI controller as an IP controller for current control. This IP controller will not change the tuning method of current control and make this VSI indeed connect to a very weak grid with rated power injection.

The increasing development of storage systems connected to electrical networks is stimulated by network management issues related to recent energetic landscape evolutions such as the increasing integration of renewable production sources. Hydro-pneumatic systems seem to offer a clean and cheap energy storage solution among the set of existing storage techniques. The present study analyses an air–water direct contact accumulation system, in closed cycle, using a rotodynamic reversible pump/turbine. The use of a unique energy conversion machine and easy-to-recycle materials could lead to cost-effective, environmentally friendly storage technique with long service life. The paper is focused on the experimental implementation and analysis of the system in a Lab environment, and the modeling of its multi-physic dynamic behavior. To deal with the variable operating conditions of the system, two different real time control strategies of the hydraulic machine were successfully tested. Finally, the global system efficiency is discussed. The efficiency control strategy was achieved with a 31% round trip efficiency and the power control strategy lead to 5% and 23% precision on exchanged power in charge and discharge modes respectively. The multi-physic dynamic model led to a 4% error of turbine mode acceleration prediction showing the interest of such a modeling method for such transient systems.

This paper presents an evolution of control systems of Modular Multilevel Converters (MMCs) focusing on the internal voltages and currents dynamics. MMCs have passive components that create extra dynamics compared to conventional VSCs. Some control schemes that do not consider these internal dynamics may still stabilize the system asymptotically thanks to the linearisation in the modulation step. However these control schemes are less robust because they are prone to poor damped oscillations on the dc side of the converter. The MMC circuit and energy relationships are presented in this paper. Along with a gradual development of the energy based control, the important roles of each internal dynamics are clearly demonstrated. Experimental results are presented to show the impacts of the linearisation in the modulation step on the system behaviour.

Modular Multilevel Converter (MMC) is an established technology for HVDC or Multi-Terminal DC (MTDC) systems, due to its advantages over classical Voltage Source Converters (VSCs) such as two or three level VSCs. To achieve a full control of all state variables, it is essential to implement energy-based method in which a cascade control loop is employed to regulate all state variables including ac and differential currents, and stored energy within MMC arms. In addition to normal operation control, dc Fault Ride Through (DC-FRT) capability of the MMC is a crucial and challenging control issue especially for overhead line HVDC system where non-permanent dc fault occurrence is statistically more probable. Furthermore, the main problematic technical obstacle to develop HVDC/MTDC grids is the lack of mature dc fault protection. Since conventional control in normal operation cannot be employed in case of dc fault, an efficient control strategy is indispensable. The principal objectives of the novel control methodology are to (i) obtain DC-FRT capability, (ii) decay short circuit current to zero, (iii) secure the MMC through leg and arm energy balancing, (iv) support ac grid as a Static Synchronous Compensator (STATCOM) and (v) resume normal operation after dc fault clearance. The simulation results verify the validity of proposed control strategy to fulfill the abovementioned objectives in dc fault operation of the hybrid MMC.

Volatile productions and consumptions generate a stochastic behavior of distribution grids and make its supervision difficult to achieve. Usually, the Distributed Generators reactive powers are adjusted to perform decentralized voltage control. Industrial controllers are generally equipped with a local affine feedback law, which settings are tuned at early stage using local data. A centralized and more efficient tuning method should aim to maximize the probability that all the node voltages of distribution grids remain within prescribed bounds. When the characteristics of the stochastic power forecasts are known, the centralized algorithm allows to update the settings on a regular time basis. However, the method requires to solve stochastic optimization problem. Assuming that stochastic variables have Gaussian distributions, a procedure is given which guarantees the convergence of the stochastic optimization. Convex problems drastically reduce the difficulty and the computational time required to reach the global minimum, compared to nonconvex optimal power flow problems. The linear controllers with optimized parameters are compared to traditional control laws using simulations of a real distribution grid model. The results show that the algorithm is reliable and moreover fast enough. Hence, the proposed method can be used to update periodically the control parameters.

The M2DC exploits the interleaving between the three legs of an MMC to realize a promising uninsulated DC/DC converter to interconnect HVDC grids. This paper details a current and energies decoupled model of the M2DC. The major idea proposed in this paper is focused on the full energy control generating optimal current references to minimize the internal currents magnitude. The energy sum and difference models are fully detailled. Both current and energy control loops are based on the model inversion principle in order to control all the state variables. The proposed control is based a dynamic control developed with the model inversion principle associated on an optimization of the current magnitude deduced from a quasi static analysis. All dynamics of the system are then explicitly controlled, which guarantee a good dynamic behavior during the transient. Therefore, current and energy controls are presented in details. Simulation results show the dynamic behavior of the converter for various operating points.

The present paper deals with the post-fault synchronization of a voltage source converter based on the droop control. In case of large disturbances on the grid, the current is limited via current limitation algorithms such as the virtual impedance. During the fault, the power converter internal frequency deviates resulting in a converter angle divergence. Thereby, the system may lose the synchronism after fault clearing and which may lead to instability. Hence, this paper proposes a theoretical approach to explain the dynamic behavior of the grid forming converter subject to a three phase bolted fault. A literal expression of the critical clearing time is defined. Due to the precise analysis of the phenomenon, a simple algorithm can be derived to enhance the transient stability. It is based on adaptive gain included in the droop control. These objectives have been achieved with no external information and without switching from one control to the other. To prove the effectiveness of the developed control, experimental test cases have been performed in different faulted conditions.

Grid-forming inverters usually use inner cascaded controllers in order to regulate the output AC voltage and the converter output current. Yet, at the power transmission system level where the power inverter bandwidth is limited (i.e.; low switching frequency), it is difficult to tune its controller parameters to achieve the desired performances because of the control loops interactions. In this paper, a direct AC voltage control based state-feedback control is applied. Its control gains are tuned using the linear quadratic regulator. In this paper, a sensitivity analysis is proposed in order to choose the right cost factors that allow the system to achieve the imposed specifications. Conventionally, the system based on direct AC voltage control has no restriction on the inverter current. Hence, in this paper, threshold virtual impedance has been added to the state-feedback control in order to protect the inverter against overcurrent. The robustness of the proposed control is assessed for different short circuit ratio using small signal stability analysis, then, checked in different grid topologies using time domain simulations. An experimental test bench is developed in order to validate the proposed control.

This paper addresses the volt-var control of distribution grids embedding many distributed generators (DGs). Specifically, it focuses on the compliance of powers to specified PQ diagrams at the high voltage/medium voltage (HV/MV) interface while the voltages remain well controlled. This is achieved using a two-stage optimization corresponding to two different classes of actuators. The tap position of capacitor banks is selected on a daily basis, given a stochastic model of the input powers prediction, which allows infrequent actuation and increases the device lifespan. In a second stage, a confidence level optimization problem allows to tune on an hourly basis the parameters of the DGs reactive power affine control laws. Results on a real-size grid show that the combined tuning of these actuators allows the ability to comply with European grid codes while the control effort remains reasonable.

The dq impedance stability analysis for a grid-connected current-control inverter is based on the impedance ratio matrix. However, the coupled matrix brings the difficulties to derive its eigenvalues for the analysis based on the General Nyquist Criterion. If the couplings are ignored for simplification, the unacceptable errors will present in the analysis. In this paper, the influence of the couplings on the dq impedance stability analysis is studied. For taking the couplings into account simply, the determinant-based impedance stability analysis is used. The mechanism between the determinant of the impedance-ratio matrix and the inverter stability is unveiled. Compared to the eigenvalues-based analysis, only one determinant rather than two eigenvalue s-function is required for the stability analysis. One Nyquist plot or polemap can be applied to the determinant for checking the right-half-plane poles. The accuracy of the determinant-based stability analysis is also checked by comparing with the state-space stability analysis method. For the stability analysis, the coupling influence on the current control, phase-locked loop and the grid impedance are studied. The errors can be 10% in the stability analysis if the couplings are ignored.

Distributed generators (DG) reactive powers are controlled to mitigate voltage overshoots in distribution grids with stochastic power production and consumption. Classical DGs controllers may embed piecewise affine laws with dead-band terms. Their settings are usually tuned using a decentralized method which uses local data and optimizes only the DG node behavior. It is shown that when short-term forecasts of stochastic powers are Gaussian and the grid model is assumed to be linear, nodes voltages can either be approximated by Gaussian or sums of truncated Gaussian variables. In the latter case, the voltages probability density functions (pdf) that are needed to compute the overvoltage risks or DG control effort are less straightforward than for normal distributions. These pdf are used into a centralized optimization problem which tunes all DGs control parameters. The objectives consist in maximizing the confidence levels for which voltages and powers remain in prescribed domains and minimizing voltage variances and DG efforts. Simulations on a real distribution grid model show that the truncated Gaussian representation is relevant and that control parameters can easily be updated even when extra DGs are added to the grid. The DG reactive power can be reduced down to 50 % or node voltages variances can be reduced down to 30 %.

This article deals with DC voltage dynamics of Multi-Terminal HVDC grids with energy-based controlled Mo\-dular Multilevel Converters (MMC) adopting the commonly used power-voltage droop control technique for power flow dispatch. Special focus is given on the energy management strategies of the MMCs and their ability to influence on the DC voltage dynamics. First, it is shown that decoupling the MMC energy from the DC side by controlling the energy to a fixed value, regardless of the DC voltage level, causes large and undesired DC voltage transient after a sudden power flow change. Second, the Virtual Capacitor Control technique is implemented in order to improve the results, however, its limitations on droop-based MTDC grids are highlighted. Finally, a novel energy management approach is proposed to improve the performance of the later method. These studies are performed with detailed MMC models suitable for the use of linear analysis techniques. The derived MTDC models are validated against time-domain simulations using detailed EMT MMC models with 400 sub-modules per arm.

This paper addresses the relevance of using reactive power from Medium Voltage (MV) networks to support the voltages of a High Voltage (HV) rural network in real-time. The selection and analysis of different optimal coordination strategies between the HV and several MV grids is investigated. The algorithms will control the reactive powers that can flow between HV/MV networks after a request from the Transmission Network Operator in case of an emergency situation such as a line outage. From a case study, the relevance of the coordination is enlightened and recommendations are given on how to tune and to combine the optimal algorithms with the advanced Volt Var Controllers of the distribution grids.

The Modular Multilevel Converter (MMC) is a power electronic structure used for high voltage adjustable speed drives applications as well as power transmission applications and high-voltage direct current (HVDC). MMC structure presents many advantages such as modularity, the absence of a high voltage DC bus and very low switching frequency. It presents also some disadvantages such as modeling complexity and control due to the large number of semiconductors to control. The objectives of this paper are to present the methodology to design a laboratory MMC converter and its control system. This methodology is based on an intensive used of real-time simulation, to develop and test the control algorithm is proposed. This MMC prototype must be as realistic as possible to a full scale MMC, with a large number of SM (i.e. 640kV on the DC side, a rated power of 1GW and 400 sub-modules). A control hardware integrating distributed processors (one for each arm) and a master control is presented. The protocols to validate sub-modules, arms and the converter are explained.

This paper presents the design, development, control and supervision of a hardware-based laboratory Multi- Terminal-Direct-Current (MTDC) test-bed. This work is a part of the TWENTIES (Transmission system operation with large penetration of Wind and other renewable Electricity sources in Networks by means of innovative Tools and Integrated Energy Solutions) DEMO 3 European project which aims to demonstrate the feasibility of a DC grid through experimental tests. This is a hardware-in-the-loop DC system test-bed with simulated AC systems in real time simulation; the DC cables and some converters are actual, at laboratory scale. The laboratory scale test-bed is homothetic to a full scale high voltage direct current (HVDC) system: electrical elements are the same in per unit. The test-bed is supervised by a Supervisory Control And Data Acquisition (SCADA) system based on PcVue. Primary control based droop control method to provide DC grid power balance and coordinated control methods to dispatch power as scheduled by transmission system operator (TSO) are implemented. Since primary control acts as converter level by using local measurements, a coordinated control is proposed to manage the DC grid power flow. The implemented system is innovative and achievable for real-time, real-world MTDC-HVDC grid applications.

The modular multilevel converter (MMC) is be- coming a promising converter technology for HVDC transmission systems. Contrary to the conventional two- or three-level VSC-HVDC links, no capacitors are connected directly on the dc bus in an MMC-HVDC link. Therefore, in such an HVDC link, the dc bus voltage may be much more volatile than in a conventional VSC-HVDC link. In this paper, a connection between the dc bus voltage level and the stored energy inside the MMC is proposed in order to greatly improve the dynamic behavior in case of transients. EMT simulation results illustrate this interesting property on an HVDC link study case.

This work deals with the development of an economic supervisory predictive control method for the management of a hybrid renewable energy system. The hybrid cell integrates solar panels, a gas microturbine and a storage unit. Tuning the predictive controller is easy: the optimal criterion encompasses the environmental, fuel, energy delivery and storage costs. Short time predictions of the solar power are embedded in the supervisor which yields smoother battery control and better power management. Real-time experiments are driven in a Hardware-in-the-Loop framework illustrating the relevance of the proposed supervisory predictive control design.

The supervision of a hybrid power plant, including solar panels, a gas microturbine and a storage unit operating under varying solar power profiles is considered. The Economic Supervisory Predictive controller assigns the power references to the controlled subsystems of the hybrid cell using a financial criterion. A prediction of the renewable sources power is embedded into the supervisor. Results deteriorate when the solar power is unsteady, owing to the inaccuracy of the predictions for a long-range horizon of 10 s. The receding horizon is switched between an upper and a lower value according to the amplitude of the solar power trend. Theoretical results show the relevance of horizon switching, according to a tradeoff between performance and prediction accuracy. Experimental results, obtained in a Hardware In the Loop (HIL) framework, show the relevance of the variable horizon approach. Power amplifiers allow us to simulate virtual components, such as a gas microturbine, and to blend their powers with that of real devices (storage unit, real solar panels). In this case, fuel savings, reaching 15%, obtained under unsteady operating conditions lead to a better overall performance of the hybrid cell. The overall savings obtained in the experiments amount to 12%.

This paper presents an energy management strategy for a commercial building in supermarket application. Some objectives are established as load shedding, to reduce the electricity bill and the CO2 emissions of commercial building, using photovoltaic (PV) and storage systems. An energy management supervision strategy based on the rules of the electricity bill will be presented. This paper focuses on the supervision strategy with the help of fuzzy logic and a graphical methodology to build it. It is shown, with the help of simulations and some economic and ecological indicators that the energy bill cost and the CO2 emissions can be reduced by using the proposed solution

The development of energy management tools for next-generation PhotoVoltaic (PV) installations, including storage units, provides flexibility to distribution system operators. In this paper, the aggregation and implementation of these determinist energy management methods for business customers in a microgrid power system are presented. This paper proposes a determinist energy management system for a microgrid, including advanced PV generators with embedded storage units and a gas microturbine. The system is organized according to different functions and is implemented in two parts: a central energy management of the microgrid and a local power management at the customer side. The power planning is designed according to the prediction for PV power production and the load forecasting. The central and local management systems exchange data and order through a communication network. According to received grid power references, additional functions are also designed to manage locally the power flows between the various sources. Application to the case of a hybrid supercapacitor battery-based PV active generator is presented.

Adequate Path Planning design is an important stage for controlling flexible axes because it may allow to cancel vibrations induced by oscillating modes. Among bang-bang profiles which are linked to optimal control, jerk assignment (acceleration derivative) and input shapers have been investigated. Theoretical results show the performance and robustness with respect to natural frequency mismatch. Practical validations on a real robot arm show the relevance of the jerk algorithm which is more robust with the same productivity performances as input shaping techniques.

Abstract. A controller using acceleration feedback has been applied to a flexible cartesian robot for which the position and velocity of the load are not measured. It is shown that acceleration feedback allows an exact tracking of the motor position, irrespective of the non-linear flexibilities of the axes and of the measurement disturbances. This easy-to-tune algorithm which main control parameters are the modal masses of the motor and load part, and only consists of a positive acceleration feedback plus a PD controller, has been validated on an industrial pick-and-place robot.

Cette deuxième partie généralise le concept d’inversion de modèle.Nous proposons une méthode systématique d’élaboration de la commande des processus électromécaniques à partir d’un modèle utilisant le concept d’énergies localisées et décrit par le formalisme du Graphe Informationnel Causal.Les limites d’utilisation de ces techniques sont évoquées en fonction de critères tels que :les performances en poursuite et en régulation,l’influence des bruits de mesure,les limites énergétiques, les performances en suivi de trajectoire, la réalité technologique. On montre que certaines solutions, classiques ou particulières, sont retrouvées formellement. L’intérêt est de montrer l’aspect déductif systématique de la démarche,visant à une recopie fidèle des trajectoires souhaitées.Ces principes d’inversion sont ensuite appliqués à la synthèse de commande d’un axe de robot cartésien pour en déduire une commande par retour accélérométrique qui permet de compenser directement l’effet d’un mode souple.

Le but de cet article est de proposer une méthodologie de conception générique de la commande des axes linéaires flexibles. Cette première partie s’intéresse plus précisément à la modélisation mécanique d’un robot cartésien utilisé principalement dans la décharge de presse à injection plastique. Dans un premier temps, le comportement de ce robot est analysé à partir de son modèle éléments-finis pour obtenir ses principaux modes de déformation. Les résultats obtenus sont ensuite validés par analyse modale expérimentale. Un modèle mathématique entièrement continu du comportement d’un axe de ce robot est déduit de ces analyses. La discrétisation de ce modèle permet d’obtenir des modèles à paramètres localisés utilisés, dans la deuxième partie, pour la conception de stratégies de commande en appliquant les principes d’inversion sur leurs représentations par Graphe Informationnel Causal.

The evolving energy mix increasingly integrates variable renewable energy systems into power grids, prompting the exploration of alternative black-start approaches at the distribution network. This study focuses on the use of distributed resources connected via power electronics converters to supply loads at the distribution level through transformers, following a blackout of the transmission system. Energizing transformers generates high unbalanced inrush currents with harmonics due to iron core saturation, posing a significant challenge. Unlike synchronous machines, power electronic converters cannot support large inrush currents. This paper demonstrates a grid-forming control that provides high-quality voltage while protecting the converter by limiting the inrush current. A benchmark is then implemented to illustrate the use of grid-forming to energize multiple transformers during a distributed black-start. It also demonstrates the ability of the proposed grid-forming to synchronize with an existing grid.

This paper presents an MTDC test case integrating a DC/DC converter where the converter is working with a DC voltage controller and participating in the DC voltage management system. The influence of voltage-controlled DC/DC converter is studied by introducing power disturbances in the MTDC system.

The development of multi-terminal DC (MTDC) networks has various challenges as interconnecting grids of different voltages and grounding schemes, DC grid protection and power flow. DC/DC converter has emerged as the solution for interconnecting HVDC links with different specifications. In this paper, the Front-to-Front Modular Multilevel Converter (F2F-MMC) topology is adopted for DC/DC converter, which can act as a firewall between the healthy and faulty grid during DC faults. Along with this, DC/DC converters when operated in DC voltage control mode can provide supplementary functionalities such as participating in DC grid voltage management and increasing the reliability of the system. In this study, the F2F-MMC converter is operated with a virtual resistance DC voltage controller integrated into an MTDC system. A pole-to-pole DC fault is applied on the MTDC grid and the influence of the virtual resistance controller associated with the DC/DC converter is studied for re-establishing the power flow after DC faults.

Grid-forming control plays an essential role in the modernization of HV electrical transmission grids, particularly in mitigating challenges imposed by large voltage disturbances. In this context, the concept of virtual power has gained prominence as a potential approach that improves stability following such disturbances. This paper illustrates the use of virtual power method in enhancing the large disturbance stability given by the grid-forming control. An adaptive virtual impedance is also proposed to further improve system dynamics. The methods are evaluated through large disturbance stability analysis and time-domain simulations.

The Modular Multi-Level DC-DC Converter (M2DC) is an attractive non-isolated DC-DC converter topology for HVDC grid. In order to carry out MTDC grid stability studies, the development of reduce order models of converters is necessary. This article first presents the M2DC converter. Then, the reduce order model will be developed in the second part. The development of the control of this model will be carried out in the third part. Atlast, the comparison of the reduce order model and its control with the average arm model will be performed in the later section of the paper.

The Modular Multilevel DC Converter is an attractive non-isolated topology to interconnect High Voltage DC Links. This paper presents the interaction among control, component design and efficiency of this converter. The impact of the two degrees of freedom on the design and the efficiency is analyzed.

In recent years, several works on grid-forming converters in transmission networks have been performed. Since these high voltage grids are mainly inductive, a natural decoupling exists between active and reactive power controls. This decoupling facilitates the design and the performance of the grid-forming controllers. However, in distribution applications, it is well known that the R/X ratio of the line impedance is substantially higher, preventing the system from a natural decoupling effect. This paper proposes an original solution to decouple the control and gives an application to a low voltage connection of a grid-forming converter.

Nowadays, the production of electric energy is evolving towards decentralized systems by an increasingly advanced integration of new active loads such as electric vehicles and renewable energy sources. This energy transition involves the use of power electronics converters to regulate energy exchanges. In this context, this paper brings the L2EP knowledge on grid-forming control developed in a high-voltage context to the ValeoSiemens reversible charger. This comprises two significant differences in the sizing of the system: a lower grid connection impedance and a resistive aspect of the distribution network. To overcome these challenges, this paper proposes two techniques: the virtual impedance to compensate the low value of connection impedance and dynamic decoupling of active and reactive power to consider the resistive effect of the distribution network.

This paper introduces a Type-IV wind turbine interfaced to a grid-forming converter. In order to retain the stable operation of a wind turbine in the presence of a grid-forming control, the classical control of a back-to-back converter has to be modified. The modification of this control creates a strong link between a wind turbine and grid dynamics. From the grid side perspective, this link allows provision of the inertial response from a wind turbine during transient events. On the wind turbine side, this coupling causes the appearance of the torsional vibrations within the drivetrain structure. These vibrations are then propagated to the grid as power oscillations. As a result, there is a negative impact on the mechanical components of a wind turbine as well as on the power system operation. In this work, a solution is introduced in order to suppress the undesired vibrations by applying a damping technique to the control of a back-to-back converter combined with a grid-forming control. Based on the conducted analysis, the addition of a damping filter results in the mitigation of torsional vibrations.

This paper proposes the analysis of the frequency support from a Type-IV wind turbine interfaced to the grid via a grid-forming converter. The frequency support including the inertial response and the fast primary frequency support is implemented by integrating a grid-forming control to the control a back-to-back converter. Knowing that the inertial response from a grid-forming converter can be tuned by varying the inertia constant of a grid-forming control, it is possible to extract different amounts of kinetic energy from the rotating masses of a wind turbine and positively impact the grid frequency dynamics during a grid frequency event. However, the increased inertial response may lead to an increased loading imposed on the mechanical components of a wind turbine. To elaborate and verify these statements, the analysis is aimed at two objectives. Firstly, it is estimated through time domain simulations whether the inertial response from a grid-forming control-based wind turbine has a significant active power contribution or can be neglected compared to the share of the primary frequency support. Secondly, based on the analyzed impact of the inertial response on the grid frequency and the mechanical loading, a value of the inertia required from a wind turbine with a grid-forming converter is recommended.

In this paper, the development of a high bandwidth power amplifier for power hardware-in-the-loop system is proposed. This amplifier consists of a multilevel interleaved converter, controlled by a real time model of a studied system that is implemented in a field programmable gate array. The accuracy of the proposed topology is illustrated with the design of a test bench for PV inverter testing. This topology is able to emulate both sides (AC and DC) of PV inverter. With this scheme it is possible to analyze the behavior of the complete photovoltaic system under special conditions like partial shading and disturbed grid voltage. The simulation and experimental results verify that the proposed topology exhibits good performance compared with classical topology.

The question of grid forming control is very different depending on the connection to a low voltage or high voltage grid. In case of higher power application, the low switching frequency may induce some stability issues. This question has been studied and some solutions have been proposed through new inner current and voltage control tuning methods. However, the possible interactions between the inner and the outer controls have not been discussed yet. Actually, in large power system, the phasor modeling approximation is used in order to ease the analysis and reduce the time computations. It assumes a good decoupling between the control loops, which allows neglecting the inner loop dynamics. This paper investigates the effectiveness of this assumption by taking some examples of tuning methods proposed in the literature and showing the ability of each method to guarantee the decoupling between controllers. In this paper, small-signal analysis tool, participation factors and parametric sensitivities are used.

The MMC is the solution today to connect HVDC grids to the current HVAC grid. This paper proposes to evaluate the impact of Zero Sequence Voltage Injection variants, which until now, have not been extensively studied. Such techniques can involve, for example, a reduction of the SM capacitor value, the number of SM requirement and converter losses. The paper presents MMC current model, control and highlights the implication of the zero-sequence voltage. Grid current control structure with the introduction of the zero-sequence voltage is presented in different techniques. These modulation schemes are compared through two main quantities in MMC, the energy requirement defining the SM capacitance value and the power losses.

In this paper a Power Hardware in the loop simulation has been realized to test in a safely way the performances and reliability of a device called “PowerCorner” used to supply an islanded microgrid. A real-time model has been developed in order to simulate the microgrid, batteries and photovoltaic panels. Some modeling criterions have been proposed to reduce time-step simulation and enhancing the Power Hardware in the loop simulation stability. Power Hardware in the loop simulation is used to emulate the AC and DC environments around the power inverters. On the DC side, DC power amplifier is used to emulate photovoltaic power plants and storage devices made on Lithium batteries. On the AC side, AC power amplifier is used to emulate the behavior of the microgrid. These two power amplifiers are controlled by a digital real time simulator which embeds the dynamic behavior of both DC and AC sides.

The insertion of stochastic renewable energies in distribution grids generates important voltage fluctuations and reactive power exchange between distribution grids and transmission grids. These variations need to comply with European grid codes. The control strategy involves the actuation of the On Load Tap Changer and Capacitor Banks tap position, and the reactive powers of the DGs. This paper focuses on the stochastic estimation of the powers at the interface and the influence of the Capacitor Bank tap position. The main results are that, using a simplified stochastic model of the grid, one can obtain the distribution of the powers, and select, on a daily basis, the tap position which minimizes the level of the prescribed PQ diagram violation risk. This study paves the way for a volt-var stochastic optimization of the distribution grid.

Because of the throng of control strategies based Voltage Source Converters (VSC) recently proposed in the literature; their classification and characterization are becoming a trending topic. The high similarities of the proposed control strategies may lead to confusions and a misunderstanding of vocabulary. Therefore, this paper seeks first to highlight the possible features fulfilled by power converters in a large power system. The combination of these features is used to classify power converters. Furthermore, power converters can be seen by a power transmission system operators as black boxes, and they may have the same inputs and outputs, which makes their characterizations more difficult. This paper looks to show that only the fundamental nature of the source has an influence on the system dynamic behavior, thus, power converter can be characterized from their transient behavior in response to grid disturbances.

The Modular Multilevel Converter (MMC) represents the recent development among the diverse available topologies of VSC and is allegedly the most suitable solution for converters in HVDC transmission systems. This paper investigates the stability of modular multi-level converters based HVDC system connected to a weak ac grid. Small signal stability based on eigenvalues analysis is used to study the interaction between the weak ac grid and the converter. The impact of control parameters, mainly the synchronization system (i.e., Phase Locked Loop) on the stability of the MMC is also considered in frequency domain. Finally, time-domain simulations and frequency domain analysis are carried out using MATLAB/Simulink and symbolic toolbox to validate the effectiveness of the proposed study.

This paper proposes to optimize the real time operation of a microgrid controlled with a two-layer Model Predictive Controller supervisor. Based on the classical decomposition of control level, the proposed supervisor tracks long-term economic references from a classical economic optimization routine. The optimization problem is formulated as a Mixed Integer Quadratic Problem and uses the different power references as levers to reach this optimum and maintain the state of the microgrid within limitations. In addition, it is able to minimize the grid losses.

The modular multilevel converter (MMC) is recognized for many advantages over conventional 2-level or 3-level voltage source converters (VSC). One of the features is that it is possible to control the stored energy in the distributed submodule (SM) capacitors. The aim of this paper is to propose a methodology to develop the control system implemented on a 21-level MMC mock-up. This control must be first validated in a real-time (RT) simulation environment with an accurate MMC model representing the behaviour of the physical MMC mock-up. Then it is performed in the hardware-in-the-loop (HIL) simulation before the implementation. The power system is emulated in a real time simulator from Opal-RT Technologies, which is connected to an external control system programmed in a dual-core microcontroller. The developed HIL platform facilitates the tests of the control and protection system in all possible scenarios.

This paper deals with the conception and the development of a detailed EMT Model for MMC based on experimental results obtained from a mock-up. The main purpose is to illustrate how to exploit the performances of EMT simulation tools to develop a detailed model that represents accurately the behaviour of a physical MMC. According to step-by-step identification of the MMC element parameters, the idea is to perform a systematic method, which allows expanding an accurate EMT model considering the behaviour of the prototype and its environment. The first part depicts the MMC topology and the modelling approach of the Half-bridge Sub-Module (SM) using a detailed IGBT-based model. The second part of the simulation model conception concerns both control levels such as high-level and low-level controllers. The last part of the EMT model conception involves the modelling of measurement process, ADC (Analogue Digital Converter), sensors dynamics, the communication delays and especially the quantization effect. Finally, the obtained results from the final detailed EMT model is compared to the experimental behaviour for different active and reactive powers operating points in order to prove the effectiveness and the capability of the EMT modelling to reach a detailed and accurate model.

In the near future, power converters will be massively introduced in transmission grids due to renewable energy sources and high voltage direct current (HVDC) increase. Voltage Source Converter (VSC) control laws assume that Synchronous Generators (SGs) build a stiff AC voltage which allows the synchronization of converters. This is one of the major reasons that limit the high integration of currentsource converters in transmission grid. This constraint is no longer relevant when power converters operate as a voltage source based on the grid-forming concept. This concept uses an inner cascaded PI controllers in order to regulate the output AC voltage. However, it is difficult to tune its controller parameters for stable operation in grid-connected mode. This paper proposes an alternative state-feedback control with integral compensator based linear quadratic regulation (LQR) in order to ensure a stable operation and to get a better AC voltage transient and good decoupling between reactive and active power. The proposed control will be fully analyzed and compared to conventional methods.

The subject of this paper is the experimental validation of a recently proposed advanced control scheme for Voltage Source Converters (VSC) based on Model Predictive Control (MPC). The main purpose of the investigated advanced controller is the frequency support from an AC grid to another after significant disturbance through HVDC Grid. The paper reports on the implementation methodology on a small-scale 3-terminal DC mock-up grid consisting of several physical low-scale VSCs, actual DC cables. These components are coupled with realtime simulation tools simulating the adjacent AC grids. The different steps for the validation process of the MPC strategy are illustrated, starting from offline simulation based on a model of the DC grid, up to the actual implementation of the controller in the mock-up of the DC grid.

The virtual synchronous machine concept (VSM) has been developed initially to reproduce the synchronous machine stabilizing effect by providing inertia with the emulation of swing equation, whereas droop control is developed initially to ensure load sharing and has no inertia. An introduction of a low pass filter to droop control has been motivated to filter the active power measurement and ensures a time decoupling with the inner control loops, whereas, this low-pass filter can also provide inertia to the system. This functionality is limited due to its negative impact on the active power dynamic. This paper proposes an analysis of the conventional droop control by showing its limitations and proposes an improved inertial droop control that allows providing the inertia to the system and ensures a good dynamic behavior of the active power at once in simple manner, and without modifying the load sharing capability. The results obtained are compared to the conventional method (Droop control and VSM) in various topologies in order to show the relevance of the proposed method.

Over the last 15 years, VSC-based HVDC (High Voltage Direct Current) has become a mature technology for HVDC transmission schemes. The Modular Multilevel Converter (MMC) represents the recent development among the diverse available topologies of VSC and is allegedly the most promising solution today. In fact, the MMC topology offers significant benefits compared to the traditional two-level VSC (Voltage Source Converter), such as lower losses, distributed storage of capacitive energy, improved scalability to higher voltage ratings, a modular design, low total harmonic distortion and, hence, the potential lack of passive fillers on the AC-side of the converter. For the control design, some simplifying assumptions are made to derive an energy based Average Arm Model (AAM) that takes into account the internal dynamics (i.e. the total energy stored in the converter) which do not exist in the 2-level VSC, as well as the AC and DC side dynamics. This additional internal dynamics implies that the control system of the converter must possess additional control loops that govern the DC current and the total amount of stored energy in the SM capacitors of the MMC. The total stored energy in the MMC is then decoupled from the DC bus, but can also be potentially shared depending on the reference signal of the energy control loop. So, the Energy-based controller strategy is introduced, where extra control loops in cascade are added to regulate the dynamics of interest. In this work, an energy based control method is developed for the OPAL-RT’s 10 levels MMC prototype model (5 kW – 400 V). Only the high-level control is proposed and implemented thanks to real time simulation model on the CPU and ARTEMiS solver based on State-Space Nodal Solver. As mentioned above, the energy-based control is based on the possibility to control the AC and DC power separately. Thus, if the power that flowing through the converter is controlled by the AC (resp. DC) power reference, it will be possible to drive the energy level thanks to the other power reference DC (resp. AC). Therefore, to control globally the MMC inner dynamics and state space variables, additional controllers should be added. Thereby, energy based controls have been developed where all the state variables are controlled. In this configuration, the high-level control is composed of outer and inner closed loop controls, which allow controlling the power and the internal MMC energy. Then, based on the designed energy-based controller, the OPAL-RT’s MMC prototype model has been simulated under different operation conditions arising a good performance in steady state as well as during transients. Moreover, the advantages of the Per-unit approach such as the control design as well as the power converter sizing have been carried out across this work. Thus, the per-unit approach is performed on one hand for high voltage characteristic of MMC where the per-unit parameters are derived from EMTP library (based on INELFE project) and on the other hand for the low scale OPAL-RT mockup. As conclusion, the per-unit approach can be used for designing the control as previously said but it can be also very useful for the sizing process of the converter. While the per-unit approach has been used for many years for the classical power system elements (transformer, synchronous machines), it can be extended also to the sizing of power converter. So, in this work, the per-unit quantities of the main elements (capacitor, inductances) will be highlighted. Then, the high voltage characteristic will be considered as a reference and the low voltage characteristics will be compared and some conclusions will be underlined.

The insertion of stochastic renewable energies in distribution grids generates important voltage fluctuations. However, the influence of the On Load Tap Changer and Distributed Generators (DGs) controllers, and specifically the existence of dead-bands in the control laws, has been seldom evaluated. Under the assumptions of Gaussian inputs and a linear model of the grid, it is shown that node voltages can be approximated either by Gaussian variables or sums of truncated Gaussian variables. A procedure is necessary to select the Probability Density Function (PDF) which fits best each node voltage. A signal based method and another algorithm relying on the grid topology are presented and compared when the modeling is applied to a real distribution grid. The model is accurate and can be used for confidence level or chance-constrained optimization of control parameters.

The use of DC transmission is particularly advantageous for long-distance transmission and interconnection of asynchronous AC networks. Several converter topologies can be used for HVDC. Multilevel Modular Converters (MMCs) are the most favored given their technological advantages over other converters topologies. Due to their industrial maturity, they have become essential for all AC / DC conversion. So far, they have always been studied with a voltage source on DC side. However, when the converter is equipped with DC breaker, a series inductor is associated to limit current variations. This has consequences in terms of modeling and control determination. This article aims to propose a modification of the control law in order to take into account this inductor. To facilitate the control organization, the Energetic Macroscopic Representation (EMR) is used.

From the origin of the grid, energy has been delivered to electrical loads mainly by synchronous machines. All the main rules to manage the grid have been based on the electromechanical behavior of these machines which have been extensively studied for many years. Due to the increase of HVDC link and renewable energy sources as wind turbine and PV, power converters are massively introduced in the grid with a fundamentally different dynamic behavior. Some years ago, they were connected as simple power injector. Then, they were asked to provide some ancillary services to the grid, in the future, grid forming capability will be required. Even if gridforming converters had been extensively studied for microgrids and offshore grids, it has to be adapted to transmission grid where the topology may be largely modified. This paper presents an algorithm for calculating the controller parameters of a gridforming converter which guarantee a stable behavior for many different configurations of the grid.

The interconnections of offshore wind farms have raised the interest of Multi-Terminal DC (MTDC) grids with voltage source converters, specifically with the Modular Multilevel Converter (MMC) topology. For controlling the DC bus voltage, the droop control strategy proves to be one of the most effective since it allows a shared effort between the different converters connected to the DC grid. Furthermore, these MTDC grids may likely result in multivendor schemes, where each converter could have different control strategies among them. Specially on the way that the internal energy of the MMC is managed, which may have an important impact on the DC voltage dynamics. This paper proposes a simplified model to represent the dynamic behavior of the DC grid including converters which highlights the droop gain and the energy management of the converter as main influential parameters. The performance of this model was assessed by comparisons with EMT simulations on a representative case study with different parameters.

The frequency support provided by a DC grid to an interconnected AC grid and integrated in VSC-HVDC controller is studied in this paper. The advantages of a combined control of voltage droop and frequency droop are investigated on a hybrid AC/DC system for the case of a sudden loss of large generation unit in the AC grid. The coupling between both droops control and the correction factor of the frequency droop coefficient are discussed. An experimental validation on VSC converter prototypes and under realistic operation conditions is conducted using Power-Hardware-In-the-Loop simulation. The practical results showed a good match with the theoretical calculation and confirmed the offline simulation results presented in previous work.

This paper deals with a centralized tuning of the local controllers parameters in a distribution grid with many Distributed Generators. The optimal controllers settings are obtained by minimizing the confidence level of voltage specification violations. The confidence level optimization problem uses Gaussian uncertainties of short-term forecasting and OLTC errors along with an accurate linear power flow approximation. Considering these assumptions, the optimization problem is shown to be convex and the characteristics of uncertainties are reduced to their means and standard deviations. The proposed method optimizes the full network while keeping the droop-like industrial structure of the controllers and allows to consider feeders which can have low and high voltages. The merits of the method are illustrated via a modified real distribution network showing a decrease of voltage variances and violations.

European Grid codes define new network management rules. In order to answer these decrees, it is important to estimate accurately the voltages and powers inside distribution networks. The intermittent nature of renewable sources leads to consider stochastic variables in power flow algorithms. A review of power flow methods and their ability to comply with these requirements is done, which shows that computationally demanding nonlinear methods have to be discarded when dealing with stochastic data and considering limited calculation time. A combination of linear methods is proposed, for which average errors in power and voltage are quite low, when applied to a real-life distribution network. The validity domain of the method is also presented.

Voltage Source Converter-based transmission grids might be the future of power system with the increasing share of interfaced electricity generation. These systems should be able to support the utility grid autonomously. The present paper focuses on the VSC output filter design and internal control of filter states. Nested AC current and voltage loops are the state of the art for power converters, controlled as voltage sources, in Microgrid or UPS applications. These internal controls are candidates for future industrial implementation at high power level. However, in a VSC based transmission system, those controls will face various topologies while requiring robustness against transient events (load changes, line tripping, etc.). The following development aims at providing keys for designing a versatile internal control suitable for VSC-based transmission system.

The multiplication of interfaced generation units connected to the utility grid might form VSC-based transmission grids in a near future. To support the utility grid autonomously, the converters must provide grid-forming capabilities and be connected in parallel. As the structure of a transmission grid is changing and unknown, these requirements presume a robust local voltage control for each highpower VSC, to face various network topologies. Indeed, the stability is challenged when voltagecontrolled VSCs are close to each other, namely, when the tie-impedance is low. The present contribution describes an impedance-based criterion method as a convenient and effective tool for assessing the stability of the voltage control of converters in a VSC-based transmission grid. The method is successfully applied to a typical two-VSC system to anticipate unstable situations

The Modular Multilevel Converter (MMC) has enhanced the feasibility of Multi-Terminal DC grids (MTDC). For controlling the DC bus voltage in the MTDC grids, the droop control is the most promised technique. This paper evaluates the dynamic impact of the way of controlling the MMC on the MTDC grids. Results are compared with a simplified model that highlights the key elements for the dynamic behavior of the DC bus voltage, the droop parameter and the equivalent DC bus capacitor.

This paper proposes an advanced control strategy for Modular Multilevel Converters (MMC) integrated in Multiterminal DC grid. In this present work, a three terminal MMC-MTDC system connecting onshore AC systems with an offshore wind farm is setup. Firstly, the voltage droop control associated to the conventional cascaded controllers for MMC stations is studied, the dynamic behavior of the DC voltage is analyzed and some drawbacks are outlined. In order to improve the dynamic behavior of the controlled DC bus voltage and the stability of MTDC system, an optimal multivariable control strategy of each MMC converter is proposed and integrated in a voltage droop controller strategy. The designed advanced controller allows to improve the overall DC grid stability and to reach the droop values designed on static considerations with acceptable dynamic behavior. By means of numerical simulations in EMTP-RV software, it is shown that the proposed control strategy performs well the stability of MTDC grid with 400- level model for MMC compared with the classic existing control methods.

This article deals with power flow coordination of a HVDC grid used to connect offshore wind farms to several mainland grids. The coordination of the DC grid is achieved thanks to a centralized control which monitors and sends proper setpoints to manage power flow. This controller is equipped with a dedicated algorithm which enables to guarantee as much as possible the desired power transfer and cope with wind power forecast errors. Moreover, this HVDC grid controller is used as interface for the AC transmission system operator to redistribute power flow among grid side converter stations in order to de-risk AC contingencies and avoid wind power spillage. Simulations results obtained from an EMT model of a five-terminal MTDC grid with Modular Multilevel Converters prove the effectiveness of the proposed methodology in normal operation as well as the system restoration after a wind farm disconnection.

The modular multilevel converter (MMC) is the most promising solution to connect HVDC grids to an HVAC one. The installation of new equipment in the HVDC transmission systems requires an economic study where the power losses play an important role. Since the MMC is composed of a high number of semiconductors elements, the losses estimation becomes complex. This paper proposes a simulation-based method for the losses estimation that combines the MMC averaged and instantaneous model in a modular way. The method brings the possibility to compare performances for different modules technologies as well as different high and low level control techniques. The losses characteristics within the MMC are also discussed. The passive losses are taken into account for the first time.

Modular Multilevel Converters (MMC) are becoming increasingly popular with the development of HVDC connection and, in the future, Multi Terminal DC grid. A lot of publications have been published about this topology these last years since it was first proposed. Many of them deal with converter control methods, other address the method of estimating losses. Usually, the proposed losses estimation techniques are associated to simple control methods For VSC (Voltage Sources Converters) topology, the losses minimization is based on the limitation of the RMS currents values. This hypothesis is usually extended to the control of MMC, by limiting the differential currents to their DC component, without really being checked.

In the near future, transmission grids will include an increasing share of directly connected voltage source converters. These systems should be able to support the utility grid autonomously. The present paper reviews the most popular approaches to address the challenge of proper load sharing amongst multiple parallel inverters applied to the utility grid case. Originally developed for Microgrid or UPS applications, these decentralized controls mimic a conventional synchronous generator based system steady-state behavior and showed suitable effectiveness to reach the desired operating point. However, the operations at the transmission grid level bring additional stress on the converters and require transient capabilities. Physical limitations of semi-conductor based converters fundamentally differ from a conventional synchronous generator. Therefore the paper illustrates how the usual real power controls may lead to undesirable behavior during transient events. This raises new issues for reliable operations of interconnected VSCs at transmission level.

This paper analyses the evolution of reactive power flows at the interface of French transmission and distribution systems. The influence of the insertion of distributed generation (DG), the replacement of medium voltage (MV) overhead lines by underground cables as well as the evolution of the reactive part of the load are investigated. Numerical simulations are performed with a real French HV/MV substation for illustrative purpose. The technical consequences of such evolutions are investigated, e.g. the saturation of On Load Tap Changers (OLTC). The use of DGs connected to the MV network to regulate reactive power exchange between Transmission System Operator (TSO) and Distribution System Operator (DSO) is also discussed.

This article deals with the evolution of voltage and reactive power control strategies in distribution networks with distributed generation. First a comprehensive review of voltage control and reactive power management techniques is given. The gap between actual or short-term industrial possibilities of distribution grids and techniques proposed in literature is highlighted. A realistic control based on local rules using the reactive power capabilities of distributed generators, capacitor banks and on load tap changer (OLTC) voltage setpoint is then presented. Its objective is to control both distribution network voltages and reactive power flows at the Transport System Operator (TSO) - Distribution System Operator (DSO) interface. The proposed control allows limiting OLTC bounds and conflicts between local rules. At last, this paper presents simulations results based on French MV distribution network in order to depict the efficiency of such a control.

The main objective of this work is to design a supervisory predictive controller which optimizes the power flow of a renewable hybrid system (solar panels, microturbine and battery. Short time predictions of the solar power and the power reference will be embedded in the supervisor. Unlike expertise-based algorithms, the design of a generic and flexible strategy based on dynamic models is proposed. The performance index integrates the environmental impact, the cost of fuel, battery cycling and the energy delivery. Simulations and a real-time application in a Hardware-in-the-Loop plant are carried out to illustrate the applicability and effectiveness of the proposed supervisory predictive control design.

A general algorithm of a Space Vector approach is implemented on a 6-leg VSI controlling a PM synchronous machine with three independent phases. In this last case, the necessity of controlling the zero-sequence current motivates the choice of a special family of vectors, different of this one used in Pulse Width Modulation (PWM) intersective strategy and in common Space Vector PWM (SVPWM). To preserve the parallelism of the algorithm and fulfill the execution time constraints, the implementation is made on a Field Programmable Gate Array (FPGA). Comparisons with more classical 2-level and 3-level PWM are provided. Keywords – FPGA, Modulation strategies, Space vector, Multiphase machine, Multiphase, Multi-leg.

This paper deals with the technical feasibility of a multi-terminal VSC-HVDC (MTDC) grid in the North Sea, connecting several offshore wind farms to several substations of the onshore AC grid. A topology of meshed DC grid with five terminals is chosen. Normal operations as well as fault events are investigated in order to estimate the flexibility and the reliability of the MTDC grid. Therefore, this study will comprise two distinct parts. First, the paper goes through the control performance of the system and then, the protection scheme is discussed. The simulation of the considered model is developed and will be computed using EMTP-RV.

This paper describes a design process of advanced grid equipment including both dynamic simulations and power-hardware-in-the-loop. A case study concerning the insertion of an energy storage system in a large isolated grid is used as an illustrative example. First, the methodology developed to achieve a real-time simulation of the studied grid from its original dynamic model is presented. The real-time platform used within the framework of this project is based on the RT-LAB environment and is interfaced with real ultracapacitors through a power amplifier. Some experimental results are analyzed in the final part. The advantages of this methodology including power-hardware-in-the-loop are emphasized by illustrating its contribution to dynamic model validation and the obtained improvement in control system performances.

An indirect Iterative Learning algorithm has shown to be able to update the parameters of an acceleration feedback controller for flexible manipulators. The fine estimation of the masses of a chain of mass-spring-dampers units allows the simultaneous tuning of both the feedback controller and the trajectory generation. This algorithm has been validated on an industrial robot arm.

Abstract - The non-minimum phase phenomena of a robot’s arm modelled by a set of Euler-Bernoulli beams clamped on a moving cart is demonstrated. Modal analysis is used to derive the exact eigensolutions which verify the described geometric boundary conditions. The equations of motion are determined using the Assumed Mode Method. The influence of geometrical and mechanical parameters such as the thickness of the cross sections of the beams, or the beam length, is discussed using numerical simulations. The overall results, with an application to a real robot, show that one has to take the non-minimum phase problem into consideration when designing a flexible mechanical structure.

Afin de réaliser des études de stabilité des réseaux MTDC, le développement de modèles d’ordre réduit des convertisseurs s’avère nécessaire. Cet article présente un modèle réduit du convertisseur DC/DC modulaire multiniveaux (M2DC) : une topologie de convertisseur DC-DC non isolée attrayante pour le réseau HVDC. Cet article présente d’abord le convertisseur M2DC. Dans un second temps, le modèle réduit sera développé. Le développement de la commande de ce modèle sera effectué dans la troisième partie. Enfin, la comparaison du modèle réduit et de son contrôle avec le modèle moyen des bras sera effectuée dans la dernière section de l’article.

Le convertisseur DC-DC Modulaire Multi-niveaux (M2DC) est une topologie attrayante de convertisseur DC-DC non isolée pour les réseaux haute tension à courant continu (HVDC). Cet article présente dans un premier temps, le modèle et la commande du M2DC. Une étude de l’utilisation des degrés de liberté phares est menée dans un second temps pour réaliser une analyse de leurs impacts sur le dimensionnement des éléments du convertisseur tels que les condensateurs de sous modules ainsi que sur les pertes liées aux semi-conducteurs

L'utilisation de la transmission DC est particulièrement avantageuse pour la transmission à longue distance et l'interconnexion des réseaux AC asynchrones. Plusieurs topologies de convertisseur peuvent être utilisées pour le HVDC. Les convertisseurs modulaires multiniveaux (MMC) sont les plus favorisés étant donné leurs avantages technologiques par rapport aux autres topologies de convertisseurs. Du fait de leur maturité industrielle, ils se sont imposés maintenant pour tous les convertisseurs AC/DC à transistors de forte puissance. Jusqu'ici, ils ont toujours été étudiés avec une source de tension côté DC. Or, lorsqu'ils sont équipés de DC breaker, on associe une inductance en série pour limiter les variations de courant. Ceci a des conséquences en terme de modélisation puis de détermination de la commande. Cet article a pour objectif de proposer une modification de commande afin de prendre en compte cette inductance.

Le Convertisseur Modulaire Multiniveaux (MMC) est une structure d’électronique de puissance utilisée dans des applications de variation de vitesse des machines électrique haute tension mais aussi des applications de transport de l’électricité à très haute tension et courant continu. La structure MMC présente beaucoup d’avantages tels que sa modularité, l’absence de bus DC haute tension et une fréquence de commutation très faible étant donnée le grand nombre de SM. Elle présente aussi des inconvénients comme la complexité de modélisation [2] et de contrôle [3] dû au grand nombre de semi-conducteurs à contrôler. Cet article a pour objectifs de présenter le dimensionnement d’un convertisseur MMC de laboratoire ainsi que son système de contrôle, le plus réaliste possible d’une structure échelle une, avec un grand nombre de SM. Le dimensionnement de ce dernier prendra en compte les contraintes et les caractéristiques son fonctionnement dans un réseau HVDC 640kV 1GW. Une architecture de contrôle, contraintes par le nombre de de sous module, sera présentée. Les protocoles de validation des sous modules, d’un demi-bras puis du convertisseur seront présentés.

Le système étudié dans cet article est un convertisseur Modulaires Multi-Niveaux. Dans une première partie, l’utilisation de la Représentation Energétique Macroscopique (REM) permet de mettre en évidence les couplages importants qui existent au sein de ce système. L’inversion du modèle conduit à une architecture générale de la commande amenant à avoir autant de correcteurs que les variables d’état. Avec la solution proposée, il est possible de contrôler chaque tension de condensateur équivalent. Dans une seconde partie, la méthodologie permettant de déterminer le diagramme PQ du convertisseur MMC est présentée. Quelques points de fonctionnement aux limites de ce diagramme sont validés par simulation. La maitrise des dynamiques ainsi que la connaissance du diagramme PQ sont des étapes nécessaires pour l’intégration de ce type de convertisseur dans un réseau alternatif.

This paper deals with small signal stability analysis of Voltage Source Converter based Multitermial HVDC grids (VSC-MTDC). First, a simplified model is used to predict the voltage dynamic behavior. Next, a modular method to build the state space model of the overall MTDC system is described. Model validation is achieved in time domain by a comparison with an electromagnetic simulation in EMTP-rv. As concrete example of effective application, a parametric study on the droop value is carried on a 3-terminal meshed HVDC grid. This example attests to the effect of the droop parameter on the stability of the overall system.

Résumé : L’augmentation des performances d’une machine passe obligatoirement par une augmentation de ses sollicitations. Il est alors nécessaire d’améliorer soit sa structure mécanique, soit sa structure de commande. Dans ce dernier cas, le choix d’une structure de commande adaptée peut améliorer les performances et réduire les vibrations venant des modes propres d’un système. Cet article propose une étude comparative de l’influence de différentes commandes sur le compromis temps/vibration. Cette analyse a été réalisée sur un robot cartésien. La liste des commandes retenues est loin d’être exhaustive cependant celles qui font l’objet de cette étude sont utilisables sur les systèmes actuels. Après avoir présenté le système sur lequel repose cette étude, chaque commande retenue est analysée et les résultats expérimentaux obtenus sont tous résumés à la fin du papier.

In the context of increasing demand for green energy, offshore wind plants, particularly in the North Sea, are a good means to meet the challenge and reach 20 % of renewable energies by 2020 in Europe. Since these wind turbines will be located quite far from the shore; DC links may be needed to transfer the power to the main grid. Instead of building several independent DC links in the same region, for economic reasons, it seems more advantageous to con- nect these DC links together and create a meshed DC grid among different countries. This idea is attractive but a lot of technical challenges have to be overcome. Some solutions may be found in the latest technological development, especially with the evolution of power electronics. However, all the solutions are not found yet. In this paper, we are presenting the state of the art of Voltage Source Converter (VSC) based HVDC grid technology. The generic structure of Modular Multilevel Converter (MMC) is presented. The basis of the control methods for a point- to-point link is first analyzed and then extended to a meshed DC grid. We are also presenting the major breakthroughs still to be done in terms of management and protection of the DC grid.