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This paper presents and compares control strategies for three-phase open-end winding drives operating in the flux-weakening region. A six-leg inverter with a single dc-link is associated with the machine in order to use a single energy source. With this topology, the zero-sequence circuit has to be considered since the zero-sequence current can circulate in the windings. Therefore, conventional over-modulation strategies are not appropriate when the machine enters in the flux-weakening region. A few solutions dealing with the zero-sequence circuit have been proposed in literature. They use a modified space vector modulation or a conventional modulation with additional voltage limitations. The paper describes the aforementioned strategies and then a new strategy is proposed. This new strategy takes into account the magnitudes and phase angles of the voltage harmonic components. This yields better voltage utilization in the dq frame. Furthermore, inverter saturation is avoided in the zero-sequence frame and therefore zero-sequence current control is maintained. Three methods are implemented on a test bed composed of a three-phase permanent-magnet synchronous machine, a six-leg inverter and a hybrid DSP/FPGA controller. Experimental results are presented and compared for all strategies. A performance analysis is conducted as regards the region of operation and the machine parameters.

In this study, a three-phase drive with a six-leg voltage source inverter and an open-end winding interior permanent magnet synchronous machine designed for traction of an electric vehicle is studied in a flux-weakening operation. The topology allows the functionality of a high-power charger to be obtained, without adding any other supplementary power devices. On the other hand, since there are three independent currents, the control structure has to handle not only the two dq-current components but also a zero-sequence current. If neglected, in comparison with a wye-coupled three-phase drive, this zero-sequence component can cause a higher maximum peak value of the phase currents, additional stator Joule losses, torque ripple, inverter voltage saturation and insulated gate bipolar transistor (IGBT) oversizing. The proposed control strategy consists in adapting a conventional method used for wye-connected machines particularly in flux-weakening operation. This strategy allows the closed-loop control of the zero-sequence current to be maintained in the whole speed range and therefore inverter saturation is avoided. Simulations and experimental results are presented and analysed.

This communication deals with a comparison between two methods of discretisation: the well known Finite Element Method and the Natural Element Method that is a meshless method. An error estimator, based on the non-verification of the constitutive law, is used. This estimation has been applied to two examples: a device with permanent magnets and a variable reluctance machine.

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.

Given the widespread use of electric vehicles, they can be used in their idle state to provide services when connected to the grid or supply power in islanded operation using the bidirectional charger. Today, when connected to the grid, reversible chargers employ grid-following control, and when operating in islanded conditions, they use constant voltage constant frequency control. However, limitations exist for both control strategies. In this context, grid-forming control can be used to operate in all cases. This paper showcases the potential of grid-forming control when applied to a reversible charger for different operation modes of electric vehicles.

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.

As distributed generation increases, it is essential to study its impact on the grid dynamics. This paper focuses on understanding the influence of the emergent technology of Grid-Forming converters on the electromechanical oscillations of the power system. Interactions among synchronous generators and gridforming converters are analyzed thanks to simplified models. These highlight the similarities of both sources, and thus, explain the participation of the converter in the oscillation. They also revealed the differences that justify the damping effect of Grid-Forming converter. This conclusion, obtained with simplified models, is validated with a small-signal stability analysis of a detailed model in the dq0-frame

High-Frequency (HF) transformer is a central part of isolated HF power converters. Its parameters, in particular leakage inductance and losses, have a significant impact on the overall converter performances. With the increase of switching frequencies linked to the use of SiC and GaN based active devices, the control of the HF transformer parameters becomes essential. A HF transformer is usually designed without considering its surrounding. However, the latter can have a significant impact on the transformer's performance. In this paper, the effect of an aluminum casing surrounding the transformer is studied and quantified for two parameters: The transformer leakage inductance and the supplementary losses. The goal is to consider the casing effect in the early design stage of power converters.

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 presents a comparative analysis of the dynamic behavior of a Modular Multi-level Converter (MMC) with grid-forming control either with or without controlling the MMC internal energy. It has been demonstrated that the internal energy of the MMC in low-level control interacts with the high-level control, which is performed by a grid-forming scheme. In case of controlling the internal energy of the MMC, this interaction is mitigated. Moreover, it has been shown that the dynamic behavior of a grid-forming controlled MMC with internal energy control is identical to an equivalent 2-level Voltage Source Converter (VSC).

This paper investigates the effect of using phaselocked loop (PLL) on the performance of a grid-forming controlled converter. Usually, a grid-forming controlled converter operates without dedicated PLL. It is shown that in this case, the active power dominant dynamics are highly dependent to the grid short circuit ratio (SCR). In case of using PLL, the obtained results illustrate that the SCR has a negligible effect on the dynamic behavior of the system. Moreover, the power converter will not participate to the frequency regulation anymore; therefore, the converter response time can be adjusted independently to the choice of the droop control gain, which is not possible without PLL. A simple equivalent model is presented which gives a physical explanation of these features.

For Electric Vehicles (EV), the charger is one of the main technical and economical weaknesses. This paper focuses on an original electric drive [1]-[3] dedicated to the vehicle traction and configurable as a battery charger without need of additional components. This cheap solution can outfit either electric or plug-in hybrid automotive vehicles, without needing additional mass and volume dedicated to the charger. Moreover, it allows a high charging power, for short duration charge cycles. However, this solution needs specific cares concerning the electrical machine control. This paper deals with the control of this drive [1], focusing on traction mode. In introduction, a review is done about topologies of combined on-board chargers. Then, the studied topology is introduced; using a 3-phase brushless machine supplied with a 6-leg Voltage Source Inverter (VSI). A model for its control is defined in the generalized Concordia frame, considering the traction mode. Then, an analysis of this model is established using a multimachine theory and a graphical formalism (the Energetic Macroscopic Representation denoted EMR). Using EMR, a description of energy flows shows specific control constraints. Indeed, numerical simulations illustrate the perturbations on the currents and the torque when controlling the machine with standard control methodologies. An improved control, deduced from the previous analysis, shows good performances, strongly reducing currents and torque ripples. Keywords- Electric Vehicle, Plug-in Hybrid Vehicle, On-board Battery Charger, H-bridge Voltage Source Inverter, Multiphase Drive, Control

This paper deals with the identification of a new high power starter-alternator system, using both: a Finite Element Method (FEM) modeling and an elementary experimental vector control. The drive is composed of a synchronous 7-phase claw-pole machine supplied with a low voltage / high current Voltage Source Inverter (VSI). This structure needs specific approaches to plan its electrical and mechanical behaviors and to identify the parameters needed for control purpose. At first, a Finite Element Method (FEM) modeling of the machine is presented. It is used for the predetermination of the electromotive forces and of the torque. Experimental results are in good accordance with numerical results. In a second part, resistive and inductive parameters of the drive are determined by an original experimental approach that takes into account each component of the drive: the battery, the VSI and the machine.

This paper deals with the modeling and the control of a new high power 12V starter-alternator system. The drive is composed of a 7-phase synchronous claw-pole machine with separate excitation, supplied with a 7-leg Voltage Source Inverter (VSI) designed for low voltage and high current. The system is modeled in a generalized Concordia frame and a graphical description is used to highlight energetic properties of such a complex system. A control scheme is then deduced from this graphical description. Two controls are achieved in generator mode: one is using the VSI in a square-wave mode, the other in a Pulse Width Modulation (PWM) mode. Experimental results are provided.

This paper focuses on an experimental method to determine the electric parameters of a seven-phase low-voltage multiphase drive. The drive is a belt driven starter-alternator for powerful cars with Hybrid Electrical Vehicles (HEV) functions. The resistive and inductive parameters are necessary to obtain the six characteristic time constants of the control modeling. Classical direct measurements lead to imprecise results because of very low values for the windings electric resistance and inductance. Effects of the imprecision on the measurements are all the more important that time constants are obtained by a ratio of cyclic inductances by resistance, with cyclic inductances being a linear combination of seven measured inductances. The methodology for identification detailed in this paper is based on a stator current vector control, in a multi-reference frame. This methodology allows us to get directly these time constants. Numerous measurements allow the robustness of the method to be evaluated.

The Energetic Macroscopic Representation (EMR) has been developed in 2000 to develop control of systems with several drives. Since 2002 this graphical tool has been introduced to teach drive control in France, then Canada and Switzerland. The University of Lille proposes two drive control units for students in electrical engineering: initiation level and expert level unit. This first paper deals with the content of the initiation level unit and describes the simulation project of an electrical vehicle using EMR.

This communication deals with a comparison between two methods of discretisation: the well known Finite Element Method and the Natural Element Method that is a meshless method. An error estimator, based on the non-verification of the constitutive law, is used. This estimation has been applied to two examples: a device with permanent magnets and a variable reluctance machine.

In the context of high power low-voltage applications as starter-generator for automotive, multi-phase drives present the attractive characteristic of reducing the current per phase and per leg. A 5- or 7-phase machine is also more suitable for using concentrated windings, attractive for their short end-windings and subsequently for a higher expected torque-to-volume density. In this perspective, the 5- and 7-leg Voltage Source Inverters (VSI) are compared with the 3-leg VSI. In the first part, for the same set of resistances and inductances coupled in different wye-coupling configurations, we examined the DC-bus currents and the power recovered by the load for a square-wave VSI control: the 7-leg VSI is the more efficient because it makes best use of the harmonics. In the second part, the torque ripples of 3-, 5- and 7-phase drives are compared: the 7-phase drive torque ripples are the lowest ones because of the less sensitivity to the harmonics of the currents. In the last part, a Pulse Width Modulation control is studied, with almost the same voltage harmonics amount as this one obtained with the square-wave mode control. Experimental results are given for the 7-leg VSI either with a passive load or with a 7-phase permanent magnet synchronous motor.

On se propose ici d’utiliser l’estimateur basé sur la non-vérification de la loi de comportement pour évaluer l’erreur numérique lorsque la Méthode des Eléments Naturels (MEN) est utilisée pour résoudre un problème magnétostatique. La MEN est une méthode dite « sans maillage ». Cet estimateur est testé sur un exemple de deux aimants en mouvement.

The rotary drive system comprises: - a DC voltage source (102) - An electric motor (104) having an axis of rotation (A), and having independent phases (a, b, c) having directions around the axis of rotation (A) - An inverter (106) for connecting each phase (a, b, c) to the DC voltage source (102) and - a control device (110) for providing a command to the inverter (106). The control device (110) comprises: - means (118) for selecting the formula, for selecting a formula from predetermined formulas, each predetermined formula being adapted to calculate an homopolar voltage set point or a zero sequence current setpoint - Means (124) set point determination, for applying the selected formula to determine, according to the selected formula, a zero sequence voltage set point or a zero sequence current setpoint, and - the means (126) for controlling the determining , for determining the order of the inverter (106) from the determined set.