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The multiphase machine is a competitive candidate for applications where uninterrupted operation is demanded under postfault conditions. In this paper, the decoupling vector control for a surface mounted five-phase permanent-magnet synchronous machine (PMSM) under single-phase open-circuit fault is investigated. The decoupled mathematical model of the five-phase PMSM under single-phase open-circuit fault is derived. Then, two postfault control strategies are obtained, which are based on the principles of minimum copper loss and equal amplitudes of currents, respectively. The postfault control strategy based on the feed-forward compensation is proposed in order to eliminate the influences of certain factors and decrease the current ripple. The validity of the postfault control strategies is proved by experiments. [ABSTRACT FROM AUTHOR]

For the purpose of reducing cost and volume, as well as to increase reliability in hostile environments, techniques of reconstructing three-phase current through a single current sensor have been reported for a three-phase alternating current motor vector control system. Based on the phase current reconstruction method, this paper proposes a novel open-circuit fault diagnosis method for the low-power voltage source inverter in the three-phase permanent-magnet synchronous motor drive. Other than sampling the single dc-link current sensor, the zero voltage vector sampling method (ZVVSM) is adopted to implement the fault diagnosis. By placing the single current sensor at a special position, ZVVSM is able to sample current during the two zero voltage vectors and reconstruct the three-phase currents. The reconstructed three-phase currents are used to generate the diagnostic variables that can detect and locate the faulty power switches. The PWM modulation strategy remains unchanged in this method and the reconstructed phase currents are with less waveform distortion and less harmonic contents, which are suitable for the fault diagnosis. The effectiveness of the proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]

The cascaded H-bridge multilevel inverter (CMI) is one of the most popular converters, especially in renewabale energy applications. Beyond offering some significant benefits, this inverter suffers from the drawback of employing great number of components which reduces the reliability of the inverter. Thus, designing a scheme to enhance reliability in this kind of inverter is of crucial importance. In this paper, a fault-tolerant structure for the cascaded H-bridge multilevel inverter is designed. Failure rates of the switches and diodes are calculated. Then, by using the Markov method, reliability and mean time to failure (MTTF) of the mentioned inverter, before and after employing the suggested scheme, are evaluated. In order to prove proper performance of the suggested scheme, a laboratory built prototype is employed. The results show that employing the suggested scheme significantly enhances reliability and MTTF of the inverter. [ABSTRACT FROM AUTHOR]

Direct torque control (DTC) has been recently used for the development of high-performance five-phase induction motor (IM) drives, where normal operation of the system has been usually considered and the ability of DTC to manage the situation has been analyzed in comparison with different rotor-field-oriented control (RFOC) strategies. The exploitation of fault-tolerant capabilities is also an interesting issue in multiphase machines, where the utility of RFOC controllers has been stated when the open-phase fault operation is considered. In this paper, the performance of DTC and RFOC controllers based on proportional resonant regulators and predictive control techniques is compared when an open-phase fault appears in a five-phase IM drive. Experimental tests are provided to compare the performance of the system using these control alternatives. [ABSTRACT FROM PUBLISHER]

A widely adopted multilevel converter topology is the cascaded H-bridge (CHB), as it can provide voltage and power scalability. However, since the CHB converter can be composed by cells with different remaining lifetime, it could be useful to delay a fault of higher aged cells in order to prolong the entire converter's lifetime. In this paper, a thermally compensated discontinuous pulse width modulation (DPWM) strategy is proposed in order to reduce the thermal stress for power semiconductors in power modules of higher aged cells. Considering the thermal cycles as the most influencing cause of wear out of power modules, the proposed method compensates the thermal cycles under a varying power profile by manipulating the clamping angle of the DPWM. Moreover, the proposed method obtains a comparable total harmonic distortion performance to the phase-shifted carrier modulation. [ABSTRACT FROM PUBLISHER]

This paper presents a model-based open-circuit fault diagnosis approach for single-phase three-level neutral-point-clamped (3LNPC) converters in electric railway application. The diagnosis algorithm, which only requires the signals existing in the control system, not only detects open-circuit faults but also identifies the faulty device among the transistors and clamping diodes. The mixed logical dynamic (MLD) model of the converter is built to estimate the grid current. The residual generated from the measured current subtracting the estimated one is analyzed under different open-circuit faults. According to the characteristics of the residual changing rate, the proposed approach allows fault localization. The proposed method is effective both in traction and regenerative braking operation and has fast diagnosis speed. Hardware-in-the-loop (HIL) experiments are carried out to verify the effectiveness of the proposed fault diagnosis algorithm. [ABSTRACT FROM PUBLISHER]

Fault tolerance is much appreciated at industry in applications with high-reliability requirements. Due to their inherent fault-tolerant capability against open-phase faults (OPFs), drives with multiple three-phase windings are ideal candidates in such applications and for this reason many efforts have been devoted to the development of different fault-tolerant control strategies. Fault detection is, however, a previous and mandatory stage in the creation of fault-tolerant drives, and the study of specific OPF detection methods for six-phase drives is still scarce. Taking advantage of the secondary currents (so called x-y currents) that are unique in multiphase machines, this study proposes new fault indices that detect and locate the OPFs without additional hardware. The method proves to be simple and independent of the operating point, control technique, and drive parameters. Comparative experimental results confirm the capability of the proposed method to achieve fast detection times with good robustness. [ABSTRACT FROM PUBLISHER]

The nonredundant voltage-source inverter, which exploits the possibility of minimum additional components for reconfiguration and operation, is a promising solution to manage faults in one inverter leg. However, control schemes at prefault and postfault conditions are always designed, separately making it hard for control scheme adaptation from normal to fault tolerant. In order to achieve smooth transitions from prefault to postfault, an embeddable fault-tolerant method based on predictive torque control (PTC) is proposed. A generalized voltage vectors, switching command, and cost function accounting for both healthy and faulty conditions are introduced to carry out a general control scheme. A novel fault-diagnosis method based on probability density analysis of the sampling currents is presented for open-circuit fault isolation under PTC scheme. Seamless likely and rapid transient processes from fault occurrence to postfault operation are achieved. Experimental results have demonstrated that the proposed scheme can make power switch fault easily managed by the controller itself. [ABSTRACT FROM AUTHOR]

The Z-source dc circuit breaker has been introduced as a new circuit for quickly and automatically switching off in response to faults. A modified Z-source breaker design is introduced for the operation at medium-voltage dc with future applications in naval ship power systems. Compared to existing designs, the respective design will allow for greater control of step changes in load. This new design also limits capacitor current in the circuit and can be easily modified for fault detection. Analysis of the breaker operation is presented during both the fault and step changes in load. Low-voltage laboratory validation of the breaker was carried out on two different versions of the proposed circuit. [ABSTRACT FROM AUTHOR]

This paper proposes a new fault-tolerant strategy for the purpose of revamping the performance of three-phase multilevel (ML) converters with faulty switches. The proposed fault-tolerant strategy is based on an adaptation of the modified space vector modulation (SVM) technique to the fundamental phase-shift compensation method. The proposed fault-tolerant strategy generates balanced line-to-line voltages with increased voltage levels in the faulty condition. In this paper, first a brief background about cascaded H-bridge (CHB) ML converters and SVM technique is provided. Then the proposed fault-tolerant strategy and the modified SVM technique are presented. Finally, several experimental results are provided to validate operation of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper is a continuation of part I, which presented interturn fault (ITF) models for interior permanent magnet synchronous motors (IPMSMs). ITFs are defined by two ITF parameters: the healthy turn ratio and the fault contact resistance. First, this paper presents a proof that the two fault parameters defining a given ITF condition cannot be individually estimated from motor information and drive information (applied voltage, phase current, rotor speed, etc.) because they have multiple solutions. However, it is also shown that the additional Ohmic loss, which is the most important factor in heat generation and deterioration due to ITFs, is not dependent on these solutions. Thus, after arbitrarily setting one fault parameter, the other can be estimated for a given ITF condition; this model can be used to represent the effect of an ITF, particularly its Ohmic power loss. In this paper, an online fault parameter estimation method for IPMSMs is proposed after presenting one of the two fault parameters. The proposed method utilizes a searching algorithm that finds the fault parameter that has the minimum negative-sequence voltage error between the applied voltage and the ITF models (presented in part I). An experiment was performed to verify the proposed fault parameter estimation method. [ABSTRACT FROM AUTHOR]

New grid codes demand the wind turbine systems to ride through recurring grid faults. In this paper, the performance of the doubly Ffed induction generator (DFIG) wind turbine system under recurring symmetrical grid faults is analyzed. The mathematical model of the DFIG under recurring symmetrical grid faults is established. The analysis is based on the DFIG wind turbine system with the typical low-voltage ride-through strategy—with rotor-side crowbar. The stator natural flux produced by the voltage recovery after the first grid fault may be superposed on the stator natural flux produced by the second grid fault, so that the transient rotor and stator current and torque fluctuations under the second grid fault may be influenced by the characteristic of the first grid fault, including the voltage dips level and the grid fault angle, as well as the duration between two faults. The mathematical model of the DFIG under recurring grid faults is verified by simulations on a 1.5-MW DFIG wind turbine system model and experiments on a 30-kW reduced scale DFIG test system. [ABSTRACT FROM AUTHOR]

Multilevel inverters, for their distinctive performance, have been widely used in high voltage and high-power applications in recent years. As power electronics equipment reliability is very important and to ensure multilevel inverter systems stable operation, it is important to detect and locate faults as quickly as possible. In this context and to improve fault diagnosis accuracy and efficiency of a cascaded H-bridge multilevel inverter system (CHMLIS), a fault diagnosis strategy based on the principle component analysis and the multiclass relevance vector machine (PCA-mRVM), is elaborated and proposed in this paper. First, CHMLIS output voltage signals are selected as input fault classification characteristic signals. Then, a fast Fourier transform is used to preprocess these signals. PCA is used to extract fault signals features and to reduce samples dimensions. Finally, an mRVM model is used to classify faulty samples. Compared to traditional approaches, the proposed PCA-mRVM strategy not only achieves higher model sparsity and shorter diagnosis time, but also provides probabilistic outputs for every class membership. Experimental tests are carried out to highlight the proposed PCA-mRVM diagnosis performances. [ABSTRACT FROM AUTHOR]

The mutually coupled dual three-phase switched reluctance motor (DTPSRM) is a new type of special 12/8 SRMs, which possesses high-reliability and fault-tolerant feature. In the past researches, the model, analysis, and fault-tolerant operation were mainly focused on the classical single three- and four-phase SRMs. This paper is mainly to analyze and investigate the fault-tolerant performances of a 12/8-pole mutually coupled DTPSRM drive under various open-circuit operations. First, the static magnetic characteristics of DTPSRM with single- and two-phase excitations are calculated by finite-element analysis. Then, the mathematic model of the DTPSRM drive under open-circuit condition is developed with a combination of state and fault functions. The simulation model of the DTPSRM drive system with a fault-tolerant control strategy is established for dynamic analysis. The faulty characteristics and fault-tolerant performances of the DTPSRM with diverse open circuits are predicted. Finally, a 12/8 DTPSRM is prototyped and an experimental setup is built for verification. The experimental normal results and diverse open-circuit operations and self-starting capability under lack of phases are presented, validating the accuracy of the analysis and simulation as well as fault-tolerant characteristics of the DTPSRM drive system. [ABSTRACT FROM AUTHOR]

This paper develops an online interturn fault diagnosis method for permanent magnet synchronous machine (PMSM). The mathematical model of the PMSM with interturn fault is established. The zero-sequence voltage component and zero-sequence current component are analyzed in the PMSM, respectively. Then, the new fault indicators are defined to remove the influence of the variation of the rotor speed and an effective frequency tracking algorithm is presented to extract fault indicators. In this proposed method, not only the interturn fault can be effectively detected, but also the phase in which this fault occurs can be accurately identified. The experiments are carried out and the experiment results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Doubly-fed induction generators are one of the most popular machines for variable-speed wind turbine. However, they are very sensitive to grid fault since the stator is directly connected to the grid. This paper analyzes the low-voltage ride-through performance of a doubly-fed induction generator-based wind turbine under balanced grid fault. An improved demagnetization control, immune to system parameter variation, is proposed to shorten the dynamic process. The investigation shows that the proposed method increases the probability of a successful ride-through at the recovery moment of balanced grid fault. Feasibility region for a representatively sized system is also investigated for balanced grid fault. In order to verify the proposed control method, laboratory experiments are carried out and the results demonstrate the analysis. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is attractive for medium- or high-power applications because of the advantages of its high modularity, availability, and high power quality. However, reliability is one of the most important issues for MMCs which are made of large number of power electronic submodules (SMs). This paper proposed an effective fault detection and localization method for MMCs. An MMC fault can be detected by comparing the measured state variables and the estimated state variables with a Kalman filter. The fault localization is based on the failure characteristics of the SM in the MMC. The proposed method can be implemented with less computational intensity and complexity, even in case that multiple SM faults occur in a short time interval. The proposed method is not only implemented in simulations with professional tool PSCAD/EMTDC, but also verified with a down-scale MMC prototype controlled by a real-time digital signal controller in the laboratory. The results confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a new thermography-based maximum power point tracking (MPPT) scheme to address photovoltaic (PV) partial shading faults. Solar power generation utilizes a large number of PV cells connected in series and in parallel in an array, and that are physically distributed across a large field. When a PV module is faulted or partial shading occurs, the PV system sees a nonuniform distribution of generated electrical power and thermal profile, and the generation of multiple maximum power points (MPPs). If left untreated, this reduces the overall power generation and severe faults may propagate, resulting in damage to the system. In this paper, a thermal camera is employed for fault detection and a new MPPT scheme is developed to alter the operating point to match an optimized MPP. Extensive data mining is conducted on the images from the thermal camera in order to locate global MPPs. Based on this, a virtual MPPT is set out to find the global MPP. This can reduce MPPT time and be used to calculate the MPP reference voltage. Finally, the proposed methodology is experimentally implemented and validated by tests on a 600-W PV array. [ABSTRACT FROM AUTHOR]

This paper proposes a simple method for single switch and double switches open-circuit fault diagnosis in pulsewidth-modulated voltage-source inverters (PWM VSIs) for vector-controlled induction motor drives, which also applies to secondary open-circuit fault diagnosis. According to the phase angle of one phase current, the repetitive operation process of VSI is evenly divided into six operating stages by certain rules. At each stage, only three of the six power switches exert a vital influence on this operation and the others make a negligible influence. An open-circuit fault of power switches introduces the repetitive current distortions, whose period is identical to that of the three-phase currents. The current distortions appear at faulty stages and disappear at healthy stages. The stage is determined by recalculating the current vector rotating angle. The d - and q-axis current repetitive distortions are applied to the detection of faulty switches due to its simplicity and fair robustness, while the faulty stages are used for the identification of faulty switches. The simulations and experiments are carried out and the results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Voltage-sourced converter (VSC)-based static synchronous compensators (STATCOMs) are used for voltage regulation in transmission and distribution systems. Unlike PWM-controlled STATCOMs, angle-controlled STATCOMs are switched at line frequency to limit the system losses. In recent years, angle-controlled STATCOMs have been deployed by utilities for the purpose of transmission system voltage regulation, voltage stability improvement, and increasing operational functionality. Despite the superior feature on voltage waveform quality and efficiency, the practical angle-controlled STATCOMs suffer from the over-current (and trips) and possible saturation of the interfacing transformers caused by negative sequence current during unbalanced conditions and faults in the utility. This paper specifically proposes a control structure to improve the angle-controlled STATCOMs performance under unbalanced conditions and faults. The main improvement is a substantial decrease in the negative sequence current and dc-link voltage oscillations under power system faults by the proposed control. This eliminates the need to redesign the STACOM power components to operate under fault current and dc-link voltage oscillations. The proposed control structure is designed based on adding appropriate oscillations to the conventional angle-controller output that is the control angle by which the VSC voltage vector leads/lags the line voltage vector. Since this control structure uses two angles for controlling the VSC output voltage, it is called dual angle control (DAC). PSCAD/EMTDC and experimental results verify the validity of the proposed control structure under unbalanced system conditions and faults. The experiments were conducted on a transient network analyzer, a unique hardware-based flexible ac transmission system simulator which was designed to study system faults and transients for a 2 × 100 MVA STATCOM field installation. [ABSTRACT FROM AUTHOR]

In this study, interturn short fault models of permanent magnet synchronous motors (PMSMs) employing series and parallel winding connections are developed using deformed flux models based on both fault winding flux information and inductance variations caused by cross flux linkages that depend on the distribution of same phase windings. As these models take into account fault winding within a three-phase winding dynamics analysis, they constitute fourth-order assessments. In the parallel-winding model, an additional dynamical analysis is used to describe variations in current distribution caused by the parallel connection between fault and healthy windings. Based on deformed flux modeling and positive sequence current assumptions, the proposed model is derived in both positive and negative sequence synchronous reference frames. A finite-element method-based simulation is applied to validate the proposed PMSM model. [ABSTRACT FROM AUTHOR]