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Ensuring service continuity in safety critical applications is crucial. In some of these applications, multilevel converters play a vital role. In this regard, this research work presents a self-healing fault-tolerant control approach to ensure the resiliency of a neutral-point clamped converter when a semiconductor component encounters an open circuit fault. The defective semiconductor can be a power switch or a clamping diode. By applying the proposed real-time fault-tolerance control, the rated output voltage and output current are restored during post-fault operation. Furthermore, the total harmonic distortion value of the output voltage during application of the real time self-healing control does not increase when compared with that during healthy operation. Since the realization of the proposed control strategy does not require any bidirectional switch, a fast transition between the healthy and fault-tolerant operation is accomplished. Moreover, the proposed structure can ensure service continuity in case of a fault event in the anti-parallel diodes, something which has been overlooked in previously conducted research works. [ABSTRACT FROM AUTHOR]

Therefore, Konstantinou et al. [[4]] intended to design a TEG system that produced the maximum power possible using the exhaust gases of a maritime internal combustion engine. Waste heat present in exhaust gas produced from various industrial processes or internal combustion engines in transport are a reservoir of untapped energy. According to Sousa et al. [[2]], to maximize the exploitation of the TEG, the operation should take place at a uniform temperature near the temperature limit of the TEG. [Extracted from the article]

As wind energy production increases, reliability and fault-tolerant operation capability of wind energy systems are becoming more important. Modern wind energy production systems use power electronic converters which are unfortunately proved to be one of their most fragile parts and responsible for most of the system downtime. Real-time fault monitoring, fault diagnosis and proper system reconfiguration in these converters are therefore mandatory for fault-tolerant operation of the converter and the whole system. In this paper, a comprehensive fault-tolerant power electronics interface for wind energy systems with doubly-fed induction generators is presented and validated. The same power production capability will be guaranteed. The proposed solution also includes a robust and very fast open-circuit switch fault diagnosis algorithm, which is not sensitive to the operation conditions and is therefore suitable for this application. Simulation, Hardware in the Loop validation and experimental tests are carried out to demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

The increased penetration of photovoltaic (PV) systems in different applications with critical loads such as in medical applications, industrial control systems, and telecommunications has highlighted pressing needs to address reliability and service continuity. Recently, distributed maximum power point tracking architectures, based on dc–dc converters, are being used increasingly in PV systems. Nevertheless, dc–dc converters are one of the important failure sources in a PV system. Since the semiconductor switches are one of the most critical elements in these converters, a fast switch fault detection method (FDM) is a mandatory step to guarantee the service continuity of these systems. This paper proposes a very fast FDM based on the shape of the inductor current associated to fault-tolerant (FT) operation for boost converter used in PV systems. By implementing fault diagnosis and reconfiguration strategies on a single field-programmable gate array target, both types of switch failure (open- and short-circuit faults) can be detected, identified and handled in real time. The FDM uses the signal provided by the current sensor dedicated to the control of the system. Consequently, no additional sensor is required. The proposed FT topology is based on a redundant switch. The results of hardware-in-the-loop and experimental tests, which all confirm the excellent performances of the proposed approach, are presented and discussed. The obtained results show that a switch fault can be detected in less than one switching period, typically around 100 ms in medium power applications, by the proposed FDM. [ABSTRACT FROM PUBLISHER]

This paper proposes fault-tolerant (FT) operation of a single-switch dc-dc converter under a switch failure. In order to improve the reliability in critical applications, FT operation is mandatory to guarantee service continuity. The FT operation of a power system can be performed in three steps: fault diagnosis (detection and identification) and remedial actions. In the case of a switch failure, suitable fault detection is essential to avoid its propagation to the whole system. This study is based on a fast and efficient open- and short-circuit switch fault diagnosis. Both types of switch failure can be detected, identified, and handled in real time by implementing fault diagnosis and reconfiguration strategies on a field-programmable gate array target. No additional sensor is required to perform the fault detection. A redundant switch and a bidirectional switch are needed for converter reconfiguration in postfault operation. The results of hardware-in-the-loop and experimental tests, which all confirm the good performances of the proposed approach, are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, an FPGA-based fault-tolerant back-to-back converter without redundancy is studied. Before fault occurrence, the fault-tolerant converter operates like a conventional back-to-back six-leg converter, and after the fault, it becomes a five-leg converter. Design, implementation, and experimental verification of an FPGA-based reconfigurable control strategy for this converter are discussed. This reconfigurable control strategy allows the continuous operation of the converter with minimum affection from a fault in one of the semiconductor switches. A very fast detection scheme is used to detect and locate the fault. Implementation of the fault detection and of the fully digital control schemes on a single FPGA is realized, based on a suited methodology for rapid prototyping. FPGA in loop and also experimental tests are carried out, and the results are presented. These results confirm the capability of the proposed reconfigurable control and fault-tolerant structure. [ABSTRACT FROM PUBLISHER]

Abstract: This paper deals with reconfigurable back-to-back converter topology and control orders in Wind Energy Conversion Systems (WECS). A typical WECS with Doubly Fed Induction Generator (DFIG) in balanced conditions is concerned. Based on the classical topology, a fault tolerant converter without any redundancy has been studied. The presented fault tolerant topology allows a “five-leg” structure with converters reconfiguration after switch failure detection. Furthermore, the control strategy for classical topology can no longer be applied after fault occurrence. Thus, a “five-leg” control strategy has also been proposed. The validation of the reconfigurable digital controller for the studied WECS with DFIG topology has been performed using a Hardware-in-the-Loop (HIL) reconfigurable platform including a Field Programmable Gate Array (FPGA) chip. HIL simulation results in both healthy and fault conditions have been presented to show simultaneously the viability of the studied converters topology and the reconfigurable control. [Copyright &y& Elsevier]

Fast fault detection and reconfiguration of power converters is necessary in electrical drives to prevent further damage and to make the continuity of service possible. On the other hand, component minimized converters may provide the benefits of higher reliability and less volume and cost. In this paper, a new fault-tolerant converter topology is studied. This converter has five legs before the fault occurrence, and after fault detection the converter continues to function with four legs. A very fast fault detection and reconfiguration scheme is presented and studied. Simulations and experimental tests are performed to evaluate the structure requirements, the digital reconfigurable controller, and fault detection scheme. For experimental tests, the control and the fault detection and reconfiguration schemes are implemented on a single field-programmable gate array (FPGA) chip. Experimental and simulation results show the effectiveness of the proposed fault-tolerant topology and its FPGA-based control. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, application of a five-leg converter in Doubly Fed Induction Generator (DFIG) for Wind Energy Conversion Systems (WECS) is investigated. The five-leg structure and its PWM control are studied and performances are compared with the classical six-leg topology. The main drawback of five-leg converter with respect to the six-leg back-to-back converter is the need to increase the dc-link voltage for the same operation point, i.e. the same powers in case of WECS. So, different methods for the reduction of the required dc-link voltage in the five-leg case are studied. The five-leg converter is used to replace the conventional six-leg one, with the same ability. For the performance evaluation of this structure and its fully digital controller in a more realistic and experimental manner, Hardware in the Loop experiments is carried out. It is shown that efficient control of active and reactive powers and dc-link voltage is performed. Hardware in the Loop results demonstrate the high performance of the proposed fully digital control which is implemented on an Altera FPGA target. [Copyright &y& Elsevier]

Abstract: Most of actual real time simulation platforms have practically about ten microseconds as minimum calculation time step, mainly due to computation limits such as processing speed, architecture adequacy and modeling complexities. Therefore, simulation of fast switching converters’ instantaneous models requires smaller computing time step. The approach presented in this paper proposes an answer to such limited modeling accuracies and computational bandwidth of the currently available digital simulators.As an example, the authors present a low cost, flexible and high performance FPGA-based real-time digital simulator for a complete complex power system with Neutral Point Piloted (NPP) three-level inverter. The proposed real-time simulator can model accurately and efficiently the complete power system, reducing costs, physical space and avoiding any damage to the actual equipment in the case of any dysfunction of the digital controller prototype. The converter model is computed at a small fixed time step as low as 100ns. Such a computation time step allows high precision account of the gating signals and thus avoids averaging methods and event compensations. Moreover, a novel high performance model of the NPP three-level inverter has also been proposed for FPGA implementation. The proposed FPGA-based simulator models the environment of the NPP converter: the dc link, the RLE load and the digital controller and gating signals. FPGA-based real time simulation results are presented and compared with offline results obtained using PLECS software. They validate the efficiency and accuracy of the modeling for the proposed high performance FPGA-based real-time simulation approach. This paper also introduces new potential FPGA-based applications such as low cost real time simulator for power systems by developing a library of flexible and portable models for power converters, electrical machines and drives. [ABSTRACT FROM AUTHOR]

This paper presents a top-down design flow for design, implementation, and verification of digital controllers associated with electrical systems. In the proposed design flow, the functional description of the studied system and the detailed electronic hardware design and validation of the digital controller are performed using a hardware-in-the-loop (HIL)-based reconfigurable platform in a unique design environment. The way of using this design flow and the reconfigurable HIL platform is analyzed through a fault-tolerant shunt active power filter application. The experimental results obtained with a laboratory prototype fault-tolerant active filter demonstrate the performances and the efficiency of the proposed design flow and HIL-based reconfigurable platform. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new reference current computation method suitable for shunt active power filter control under distorted voltage conditions is proposed. The active power filter control is based on the use of self-tuning filters (STF) for the reference current generation and on a modulated hysteresis current controller. This active filter is intended for harmonic compensation of a diode rectifier feeding a RL load under distorted voltage conditions. The study of the active filter control is divided in two parts. The first one deals with the harmonic isolator which generates the harmonic reference currents and is experimentally implemented in a DS1104 card of a DSPACE prototyping system. The second part focuses on the generation of the switching pattern of the inverter by using a modulated hysteresis current controller, implemented in an analogue card. The use of STF instead of classical extraction filters allows extracting directly the voltage and current fundamental components in the α–β axis without phase locked loop (PLL). The performances are good even under distorted voltage conditions. First, the effectiveness of the new proposed method is mathematically studied and verified by computer simulation. Then, experimental results are presented using a DSPACE system associated with the analogue current controller for a real shunt active power filter. [Copyright &y& Elsevier]

The performances of conventional shunt active power filters heavily depend on accurate active filter current sensing. A sudden failure in one of the active filter current sensors decreases the filter performances. Moreover, if the fault is not detected and compensated for quickly, its effect leads to disconnection or hard failure of the active filter. Hence, to reduce the failure rate and to prevent unscheduled shutdown, a real-time fault detection, isolation and compensation scheme could be adopted. This article introduces a new fast and robust current sensor fault detection and compensation method for three-phase shunt active power filters. The proposed current sensor fault detection is achieved with a predictive model associated with a logical decision. The satisfactory performances obtained by experimental 'FPGA in the loop' prototyping validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, the authors detail a top-down design methodology for a power electronic fully digital controller based on a field programmable gate array (FPGA). This design flow uses the very high speed hardware description languages-analogue mixed signal (VHDL-AMS) language. The case of a shunt three-phase active filter is studied. An optimised architecture is designed and each step is detailed. Each block of the architecture is modelled in the VHDL at several levels of abstraction, from real data format to specific binary format. To achieve closed-loop simulation, analogue and power elements are modelled in the VHDL-AMS. The whole closed-loop system is successfully validated at various levels of abstraction of the digital control, using the ADVanceMS computer-aided design tools. An experimental validation of the proposed architecture, implemented on the target Xilinx Virtex-II 2V4000bf95 FPGA is discussed. [ABSTRACT FROM AUTHOR]

In photovoltaic systems, dc–dc converters have been identified as one of the most critical and challenging subsystem in terms of failure rate. Thus, this paper proposes fault-tolerant operation of a two-stage buck/buck–boost converter under open-circuit switch failure. Remedial actions are efficient in any failure of one of the two switches of the converter. Here, a new unified approach is considered, for the overall fault-tolerant operation of the two stages of the converter. The fault-tolerant circuit we propose lies on performing redundancy by implementing the equivalent synchronous switch for the two main switches of the two stages, in offline mode. The fault-tolerant circuit results from the basic two-stage buck/buck-boost converter and its equivalent circuit with a synchronous switch, merged together to form the new dc–dc fault-tolerant circuit. Therefore, postfault operation at full power can also be performed. By using a switch fault management unit with reduced complexity, inserted between the control block and the switches, we have designed an unified, efficient, and optimized fault-tolerant control, suitable in both healthy and postfault operations. Some selected experimental tests, which all confirm the good performances of the proposed fault-tolerant approach, are presented and discussed. [ABSTRACT FROM AUTHOR]

Energy harvesting has become a promising and alternative solution to conventional energy generation patterns to overcome the problem of supplying autonomous electrical systems. More particularly, thermal energy harvesting technologies have drawn a major interest in both research and industry. Thermoelectric Generators (TEGs) can be used in two different operating conditions, under constant temperature gradient or constant heat flow. The commonly used TEG electrical model, based on a voltage source in series with an electrical resistance, shows its limitations especially under constant heat flow conditions. Here, the analytical electrical modeling, taking into consideration the internal and contact thermal resistances of a TEG under constant temperature gradient and constant heat flow conditions, is first given. To give further insight into the electrical behavior of a TEG module in different operating conditions, we propose a new and original way of emulating the above analytical expressions with usual electronics components (voltage source, resistors, diode), whose values are determined with the TEG's parameters. Note that such a TEG emulation is particularly suited when designing the electronic circuitry commonly associated to the TEG, to realize both Maximum Power Point Tracking and output voltage regulation. First, the proposed equivalent electrical circuits are validated through simulation with a SPICE environment in static operating conditions using only one value of either temperature gradient or heat flow. Then, they are also analyzed in dynamic operating conditions where both temperature gradient and heat flow are considered as time-varying functions. [ABSTRACT FROM AUTHOR]

In this paper, an FPGA-controlled fault tolerant back-to-back converter for DFIG-based wind energy conversion application is studied. Before an open-circuit failure in one of the semiconductors, the fault tolerant converter operates as a conventional back-to-back six-leg one. After the fault occurrence in one of the switches, the converter will continue its operation with the remaining five healthy legs. Design, implementation, simulation and experimental verification of a reconfigurable control strategy for the fault tolerant six/five leg converter used in wind energy conversion are discussed. The proposed reconfigurable control strategy allows the uninterrupted operation of the converter with minimum affection from an open-circuit switch failure in one of the semiconductors. Software reconfiguration is also necessary in PWM signal generation unit, to assure that proper gate signals are calculated and generated based on the actual five-leg structure Simulations and experimental tests are carried out and the results are presented and compared. They all confirm the capability of the studied reconfigurable control and proposed fault tolerant architecture in ensuring the system's service continuity. [ABSTRACT FROM AUTHOR]

Fault detection (FD) in power electronic converters is necessary in embedded and safety critical applications to prevent further damage. Fast FD is a mandatory step in order to make a suitable response to a fault in one of the semiconductor devices. The aim of this study is to present a fast yet robust method for fault diagnosis in nonisolated dc–dc converters. FD is based on time and current criteria which observe the slope of the inductor current over the time. It is realized by using a hybrid structure via coordinated operation of two FD subsystems that work in parallel. No additional sensors, which increase system cost and reduce reliability, are required for this detection method. For validation, computer simulations are first carried out. The proposed detection scheme is validated on a boost converter. Effects of input disturbances and the closed-loop control are also considered. In the experimental setup, a field programmable gate array digital target is used for the implementation of the proposed method, to perform a very fast switch FD. Results show that, with the presented method, FD is robust and can be done in a few microseconds. [ABSTRACT FROM PUBLISHER]

Power-electronics-based hybrid dc power systems (HDCPSs) are increasingly used in many industrial applications such as land, sea, and air vehicles. In these systems, small dc-link and LC filter capacitors are of great interest for weight saving. Usually, in HDCPSs, there are constant power loads and negative dynamic impedance of these loads may generate unstable oscillations. Besides, the risk of resonance may be increased under unbalanced load conditions. In this paper, a distributed active oscillation suppression approach is presented. It is based on the analytical study of the linearized model of the studied system around the operating point. The studied system consists of one main dc source and one storage element supplying two loads: a permanent magnet synchronous motor connected to the dc link by a voltage source inverter and a resistive load supplied by a dc/dc converter through the same dc bus. The proposed approach is particularly used to overcome the resonance under unbalanced load conditions and allows reducing dc link and LC filter capacitors for weight saving. Simulations and experimentations are carried out which confirm the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

The performances of wind energy conversion systems (WECS) heavily depend on the accurate current sensing. A sudden failure in one of the current sensors decreases the system performances. Moreover, if a fault is not detected and handled quickly, its effect leads to system disconnection. Hence, to reduce the failure rate and to prevent unscheduled shutdown, a real-time fault detection, isolation, and compensation scheme could be adopted. This paper introduces a new field-programmable-gatearray (FPGA)-based grid-side-converter current sensor fault-tolerant control for WECS with doubly fed induction generator. The proposed current sensor fault detection is achieved by a predictive model. "FPGA-in-the-loop" and experimental results validate the effectiveness and satisfactory performances of the proposed method. [ABSTRACT FROM AUTHOR]

This paper discusses the design, implementation, experimental validation, and performances of a field-programmable gate array (FPGA)-based real-time power converter failure diagnosis for three-leg fault tolerant converter topologies used in wind energy conversion systems (WECSs). The developed approach minimizes the time interval between the fault occurrence and its diagnosis. We demonstrated the possibility to detect a faulty switch in less than 10 μs by using a diagnosis simultaneously based on a "time criterion" and a "voltage criterion." To attain such a short detection time, an FPGA fully digital implementation is used. The performances of the proposed FPGA -based fault detection method are evaluated for a new fault tolerant back-to-back converter topology suited for WECS with doubly fed induction generator (DFIG). We examine the failure diagnosis method and the response of the WECS when one of the power switches of the fault tolerant back-to-back converter is faulty. The experimental failure diagnosis implementation based on "FPGA in the loop" hardware prototyping verifies the performances of the fault tolerant WECS with DFIG. [ABSTRACT FROM AUTHOR]

In this paper, a comparative analysis has been presented of two equivalent circuits of non-isolated buck/buck-boost converters under synchronous control, used in a stand-alone Photovoltaic-battery-load system. The first circuit consists of two cascaded buck and buck-boost classical converters with two controllable switches. The buck converter is used to extract the maximum power of the Photovoltaic source, and the buck-boost converter is applied for the output voltage level control. The second circuit consists of a proposed converter with a single controllable switch. In both cases, the switching frequency is used to track the maximum power point and the duty ratio controls the output voltage level. Selected simulation results and experimental tests confirm that the two conversion circuits have identical behavior under synchronous control. This study shows that the single switch converter has a lower size and cost, but it is limited in the possible control strategy. [ABSTRACT FROM AUTHOR]

Numerous advantages offered by Photovoltaic (PV) generation systems coupled with the increasing power demands for clean energy put PV systems in the front of many research works. For stand-alone applications powered with PV systems, the reliability of the power conversion stage is essential to ensure the continuous supply of energy. Therefore, in the case of any failure occurring in the power conversion stage, it is mandatory to provide remedial actions to guarantee the service continuity of the produced electrical power. This paper analyses the service continuity of a two-stage buck/buck-boost converter with energy storage, driven with synchronous control. The initial two-stage converter is made fault-tolerant and robust to failures of its two switches by adding only one additional switch associated with two diodes. In this study, only open-circuit switch faults are considered. The proposed fault-tolerant circuit and the initial one have the same electrical behavior when synchronous control is used. The applied synchronous control in both healthy conditions and post-fault operation ensures the same functionalities without degrading the system’s performances. The proposed two-stage synchronously-controlled circuit is validated through simulation in the cases of open circuit faults on the two switches of the initial converter. The obtained results show the feasibility of the proposed functional redundancy and the continuity of operation at full power after switch fault diagnosis. [ABSTRACT FROM AUTHOR]

As an industry consumer of electric power, an electric arc furnace (EAF) is a major voltage flicker source that causes significant power-quality (PQ) problems. The fast response of the static synchronous compensator (STATCOM) makes it an efficient solution for improving PQ in distribution systems facing this kind of very nonlinear load. In this study, for voltage flicker mitigation of a 100-MVA EAF installed in Europe, a voltage-source-converter (VSC)-based STATCOM with high bandwidth is designed. The STATCOM's current reference includes both active and reactive current components. The performance of the STATCOM in voltage flicker mitigation is highly improved by applying this control strategy which uses the dc voltage margin of the VSC to provide for an active compensating current without oversizing the STATCOM converters capacitor. In this paper, first, the proposed STATCOM is studied through a generalized steady-state analysis. Second, the STATCOM's control strategies for voltage flicker mitigation are introduced and simulation results are provided and compared. Finally the complete model is validated by field tests over a 60-MVAr industrial STATCOM. Static and dynamic performance of the STATCOM is evaluated and voltage fluctuation mitigation studies are performed and discussed. The voltage flicker mitigation is evaluated through onsite measurements respecting international standards. [ABSTRACT FROM PUBLISHER]