Ilhem Slama-Belkhodja

FPGA-Based Current Controllers for AC Machine Drives—A Review

The aim of this paper is to present the interest of implementing digital controllers using field-programmable gate array (FPGA) components. To this purpose, a variety of current control techniques, which is applied to alternating current machine drives, is designed and implemented. They consist of on-off current controllers, proportional-integral current controller, and predictive current controller. The quality of the regulated current is significantly improved. It is mainly due to a very important reduction of the execution time delay. Indeed, in all described techniques, the execution time of the designed hardware architectures is only a few microseconds. This time reduction derives directly from the possibility offered by FPGAs to design very powerful dedicated architectures. Numerous experimental results are given in order to illustrate the efficiency of FPGA-based solutions to achieve high-performance control of electrical systems.

Direct Virtual Torque Control for Doubly Fed Induction Generator Grid Connection

This paper presents a grid-connection control strategy of doubly fed induction generator wind system based on the direct control of both a virtual torque and rotor flux of the generator. This control is achieved with no proportional-integral regulator and requires the measurement of only grid voltages, rotor currents, and rotor position. The same switching table is used for grid synchronization and for running process. A field-programmable-gate-array-based design of the proposed control is developed and tested on a 4-kW experimental prototype. Experimental results are provided to show the effectiveness of the fast and soft grid-connection method developed.

Easy and Fast Sensor Fault Detection and Isolation Algorithm for Electrical Drives

This paper focuses on sensor fault detection and isolation (FDI) for electrical systems. A new, easy and fast FDI algorithm is proposed, keeping system performances unchanged under certain faulty sensor conditions when reconfigurations are available. The proposed FDI algorithm is derived from a parity space approach and is based on temporal redundancies. It is insensitive to parameter variations since no model knowledge is required. Also, it is available for a large class of electrical systems such as single- or three-phase power converters, dc or ac electrical drives, etc. Moreover, the residual threshold used for FDI is accurately defined and is suitable for the whole operating range. Simulations results are presented to illustrate the good functionality of theoretical developments. Numerous experimental results are also shown to validate the effectiveness of the proposed FDI algorithm and to highlight its advantages for the control of electrical systems.

FPGA-Based Dynamic Reconfiguration of Sliding Mode Current Controllers for Synchronous Machines

This paper presents the concept of dynamic reconfiguration between two sliding mode current controllers for synchronous motor drives. The first one is a Direct Sliding Mode (DSM) current controller, which is based on a switching table synthesized via sliding mode theory. The second one is an Indirect Sliding Mode (ISM) current controller that computes a reference voltage vector via sliding mode theory. The computed reference voltage is then applied to the terminals of the synchronous machine through a Pulse Width Modulation (PWM) process. This item studies and discusses the reconfiguration criteria and presents the main interest of using FPGA digital solutions for dynamic reconfiguration process implementation between the two sliding mode current controllers. Numerous experimental results are presented in order to confirm the interest and performances of the proposed reconfigurable sliding mode current controller.

FPGA-Based Speed Control of Synchronous Machine using a P-PI Controller

In this paper, a P-PI speed controller for synchronous machine is developed. It is made up of both an internal and external speed control feedback loop. The internal one allows modifying the poles placement of the controlled system at the desired locations and the external one allows imposing the shape and the dynamic of the speed response. In order to ensure an efficient speed control operation, an accurate speed estimator that estimates the rotation speed from the mechanical rotor position provided via an absolute encoder is also developed. Experimental results carried on a prototyping platform are given to illustrate the efficiency of the developed synchronous machine speed controller.

Fault-Tolerant Control Using the GA Optimization Considering the Reluctance Torque of a Five-Phase Flux Switching Machine

This paper deals with the fault tolerance of a five-phase flux switching machine. Short-circuit currents calculation considering inductances variation is developed. Machine behavior (torque quality, copper losses, and homopolar current) under a single short-circuit phase fault, two consecutive and nonconsecutive phases short-circuited, is simulated with a two-dimensional finite elements (2-D FE) model and validated experimentally. Then, a new method is developed to improve its performances in faulty mode, by reconfiguring reference currents. In fact, an accurate torque model is established and then used in a genetic algorithm to optimize reference currents in faulty mode. In this approach of reference currents computation, the used algorithm has multiobjectives and multiconstraints, thereby allowing choosing the appropriate fault-tolerant current solution according to our application. The torque model is considered to be more accurate and closer to the 2-D FE results in both healthy and faulty modes. Then, a comparison of machine performances in healthy, degraded, and reconfigured modes is presented. Experimental results corroborate the analysis.

FPGA-Based Fault-Tolerant Space Vector-Hysteresis Current Control for Three-Phase Grid-Connected Converter

This paper investigates the field-programmable gate array (FPGA) implementation of a fault-tolerant space vector-hysteresis current control (SV-HCC) for three-phase grid-connected converter. The proposed control ensures continuous operation despite of an open-circuit fault in one grid current measurement circuit (caused by defected cables, lines or connectors at the output of the current measurement circuit). It is based on hardware redundancy of current measurement circuits for fault detection and isolation. The faulty measured current is identified through the computation of residuals with well-defined thresholds. Thanks to the high computation capabilities of FPGAs, the implemented fault-tolerant SV-HCC is executed with a very high sampling frequency and very low execution time. As a consequence, the defined theoretical thresholds remain available for the experimental tests. Several experimental results, carried out on FPGA-based prototyping platform, are given in order to illustrate effectiveness and reliability of the proposed fault-tolerant SV-HCC.

FPGA-based real-time simulation of fault tolerant current controllers for power electronics

This paper investigates a FPGA-based Real-Time Simulation of Fault Tolerant Current Controllers (FTCC) algorithm for three phase inverter fed electrical systems. The focus of the proposed method is on the identification of the faulty current sensor in AC machines drives and the actual reconfiguration between two control-sampling times which ensures a safety continuous working of the faulty system. For performances verification, the method is analyzed within a FPGA-based Real-Time Simulator (RTS) of the studied electrical system, based on criteria such as accuracy, execution speed and implementation complexity. For the RTS modeling process, a multi-sampling approach is adopted allowing a real-time functioning with different time-steps. ModelSim simulations and experimental results are presented to emphasize the effectiveness of the proposed method.

A novel grid impedance estimation technique based on adaptive virtual resistance control loop applied to distributed generation inverters

The penetration of the distributed power generation systems (DPGSs) based on renewable sources (PV, WT) is strongly dependent on the quality of the power injected to the utility grid. However, the grid impedance variation, mainly caused by grid faults somewhere in the electric network, can degrade the power quality and even damage some sensitive loads connected at the point of the common coupling (PCC). This paper presents detection-estimation method of the grid impedance variation. This estimation tehnique aims to improve the dynamic of the distributed generation (DG) interfacing inverter control and to take the decision of either keep the DG connected, or disconnect it from the utility grid. The proposed method is based on a fast and easy grid fault detection method. A virtual damping resistance is used to drive the system to the resonance in order to extract the grid impedance parameters, both resistive and inductive parts, using resonant filter frequency determination. Theoretical analysis and simulation results are presented to validate the proposed method.

Parity space approach for current sensor fault detection and isolation in electrical systems

The paper deals with faulty current sensor detection and isolation (FDI) in electrical systems. Current sensors are widespread in electrical drives and power converters control. They are used for monitoring or closed loop regulation and performances and robustness of the whole systems depend strongly on their outputs. Thus, a fault occurs on a sensor, fast FDI is required for fast reconfiguration control and then continuous operating. In this paper, a new and fast faulty current sensor detection and isolation is presented. It is derived from space parity approach. Theoretical developments highlights simplifications derived from choosing measurement sampling period much lower than control sampling time. The developed algorithm does not depend on system parameters but only on previous measures, so it can be easily added to any control. Simulation and experimental results demonstrates the effectiveness of the method for a 1kW induction motor.