Single Switch Open-circuit Faults Research Articles

An open circuit fault-tolerant seven-level inverter with symmetric sources and reduced switch count

In this study, a new structure of symmetrical multilevel inverter is proposed. The proposed structure offers fewer controlled switches, power diodes, DC sources voltage stress across switches and losses compared with classical and a few recently proposed topologies in the literature. This paper presents a fault-tolerant (FT) seven-level inverter to provide uninterrupted supply to the connected load under open circuit fault in any single switch of the presented configuration. This configuration uses only six unidirectional and one bidirectional switch for any switch fault-tolerant operation. The phase opposition disposition sinusoidal pulse width modulation (POD-SPWM) and phase disposition sinusoidal pulse-width modulation (PD-SPWM) scheme are used for proper DC link utilisation in seven-level output voltage. The proposed symmetrical 7-level topology requires fewer power components and offers reduced voltage total harmonic distortion (THD) compared to other multi-level inverter (MLI) topologies. This MLI is investigated in MATLAB and validated using hardware in the loop platform of OPAL-RT. The obtained results are presented to demonstrate the successful FT operation under any single switch open circuit fault.

Multiple Open-Circuit Fault Detection and Isolation Using Universal Low-Cost Diagnosis Circuits for Reconfigurable Dual-Active-Bridge Converters

Compared with single-switch open-circuit faults (SOCFs), multiple switches open-circuit faults (MOCFs) of power electronic devices (PEDs) due to high voltage or current stress, false triggering, and manufacturing tolerance have become more challenging. To address this issue, a reconfigurable dual-active-bridge (R-DAB) converter is presented with a fast, accurate, robust, and low-cost fault detection (FD) and fault isolation (FI) scheme to accommodate both SOCFs and MOCFs. Compared with the standard dual active bridge (DAB) topology, the proposed R-DAB will utilize a center-tapped high-frequency transformer and two symmetrical auxiliary inductors, where inherent half-bridge conduction branches are capable of maintaining uninterrupted operations. The proposed FD and FI scheme is straightforward and universal since only the center-tap current in the primary and secondary bridge is monitored as the universal fault signature. Moreover, a simple and low-cost fault diagnostic circuit was designed, which can detect and isolate various open circuit faults (OCFs) of PEDs under varying input and output conditions, without using expensive voltage and current sensors. This sensorless fault diagnosis technique can achieve the fastest fault detection and isolation speed reported so far, which is within a couple of \boldmath <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu s$</tex-math></inline-formula> for various OCFs. Experimental results were acquired from an R-DAB prototype under various OCFs to validate the effectiveness of the proposed technique.

Open Circuit Fault Mitigation in a Nine-Level Modified Packed E-Cell Inverter

Reliability of the multilevel inverters (MLIs) is one of the most important concerns in industrial applications, mainly due to the semiconductor devices. Whenever a fault occurs in one of the switches of the inverter, it leads to abnormal conditions and can also cause serious damage to the equipment connected to the multilevel inverter. In this paper, a recently proposed nine-level Packed-E-Cell (PEC) multilevel inverter topology is investigated for its fault-tolerant capability and improved reliability. The analysis is carried out for a reduced device multilevel inverter topology that, due to a lack of redundant states, cannot tolerate switch failures. The fault-tolerant (FT) topology provides additional redundant states in the switching sequence of the existing topology. The work in this paper presents Packed-E-Cell MLI modified for fault tolerance against single-switch open-circuit faults. The modified FT topology inherently achieves self-voltage balance in the DC-link capacitors. Nearest Level Control(NLC) is used as the modulation strategy for generating the desired switching pulses. Simulation results are obtained in MATLAB/Simulink for the conditions prior to the fault, during the fault and post fault, and results are discussed. Experimental verification of the modified FT topology is also performed, in order to validate its effectiveness.

A Study of Inverter Open-Circuit Fault in Grid Connected Photovoltaic Systems: Influence on Output Power and Detection Method

The paper presents an investigation of single switch open-circuit fault in the inverter of photovoltaic (PV) systems. An IGBT two-level three-phase inverter which is used to connect the photovoltaic system to the main grid is considered in this application. First, the fault is created by modifying the control gate signal sent to the inverter. Second, the operation of a PV system is simulated under various levels of the irradiation under both healthy state and the condition of single switch open-circuit fault. The output powers generated by the system are then compared to show the influence of fault occurrence. Based on the DC current of the inverter, fault detection method is recommended. Investigation results show that the fault strongly affects the output power and that can be detected by judging the amplitude of three first orders of the AC side fundamental frequency.

Single-Phase Voltage Source Multi-Level Inverter Hysteresis SVPWM Reconfigurable Fault-Tolerant Control Method

A hysteresis space vector pulse width modulation (SVPWM) reconfigurable fault-tolerant method for single-phase voltage source multi-level inverter with current tracking is proposed. Firstly, the influence of single switch open circuit fault and double switches open circuit fault on the voltage vector of the inverter is analyzed, and on this basis, the equivalent replacement of the voltage vector is obtained by using the topology reconstruction of the inverter, and the redundant voltage vectors with overlapping positions are preferred for equivalent replacement. If there are no coincident non-fault vectors, the other non-fault vectors with the closest position and effect are selected. The fault-tolerant method does not need the switching operation between the main power switching device and spare power switching device of the inverter, and can directly control the on–off process of the inverter reconfiguration unit through the driving signal of insulated gate bipolar translator (IGBT), which is simple and stable. Under the conditions of single switch open circuit and most double switches open circuit, the output current of the inverter can accurately track the reference current.

A Family of Asymmetrical SVPWM Schemes with Normal and Open-Circuit Fault-Tolerant Operation Capability for a Three-Phase Isolated AC-DC Matrix Converter

The three-phase isolated ac–dc matrix converter (3P-IMC) inherits all the merits of the conventional matrix converter. But it also suffers from a large number of bidirectional switches and cannot operate safely in an open-circuit fault condition. Hence, with a general space vector PWM (SVPWM) model presented in this article, three types of asymmetrical SVPWM (ASVPWM) schemes are first proposed for normal and open-circuit fault-tolerant operation. The ASVPWM schemes have more kinds of synthetic vectors with asymmetrical distribution, however, also feature a higher freedom and flexibility to further improve the system performance. Then by sectional combining the above ASVPWM schemes with the conventional one, the 3P-IMC could be continued to operate with a tight dc output voltage regulation under single-switch open-circuit fault condition, which has an inherent open-circuit fault-tolerant capability. Compared with the conventional two-phase fault-tolerant operation, the proposed strategy has a smaller output voltage ripple, lower current stress, lower current harmonic, higher maximum output power, etc. The safety and reliability of the converter are greatly improved. Finally, a 3P-IMC experimental prototype is built up to verify the performance of the proposed ASVPWM schemes.

A Dual-Loop Control to Ensure Fast and Stable Fault-Tolerant Operation of Series Resonant DAB Converters

When a single-switch open-circuit fault occurs in the series resonant dual-active bridge (SRDAB) converter, the output dc voltage will drop by a half or rise by twice. To maintain a continuous power supply, a fault-tolerant control method based on the voltage single-loop control is proposed in this article, where the rectifier-side output square voltage is regulated. Nevertheless, it may excite the resonance between the resonant inductors and dc capacitors, leading to severe low-frequency oscillations, (appearing as the envelope of the high-frequency current). This may trigger the overcurrent protection and the SRDAB fails to ride through the fault. To address this issue, low-frequency equivalent models are proposed first for the bidirectional power-flow of the SRDAB, enabling frequency-domain analysis of the single-loop voltage control. The analysis reveals that the oscillation depends on the duty-cycle and control parameters, and it is more likely to occur when the converter operates in the boost mode. However, it is not possible to suppress the oscillations by the voltage single-loop control. Thus, a dual-loop fault-tolerant control method is developed. The proposed control strategy includes an outer-loop voltage control, an inner-loop current envelope control, and a nonlinear correction unit. Experimental tests on a 1-kW SRDAB are performed, which validate the effectiveness of the proposal in terms of oscillation suppression.

Single-Switch Open-Circuit Diagnosis Method Based on Average Voltage Vector for Three-Level T-Type Inverter

Fault-tolerant control strategy plays a significant role in improving the reliability of three-level T-type inverter where fault diagnosis method is the key and a research hotspot. Load power factor variation and modulation index regulation have great effect on conventional load current based diagnosis methods. Therefore, this article proposes a novel voltage vector based method for single-switch open-circuit fault diagnosis in three-level T-type inverter. Average output voltage vector calculated by voltages between dc-link neutral-point and bridge output terminals is taken as the eigenvector in the procedure and failed switch can be located by three diagnosis variables including angle of eigenvector, normalized modulus of eigenvector, and neutral-point potential. These variables will be some certain values under circuit fault, which are defined as eigenvalues. The vector trajectory prediction technology is utilized for threshold setting, by which the diagnosis is suitable for different power factors and different modulation indices. The strategy of redundant vector replacement is applied to realize fault-tolerant operation and verifying the proposed scheme. Simulations and experiments are carried out to illustrate the superiorities of the proposal.

A Fast and Robust Diagnostic Method for Multiple Open-Circuit Faults of Voltage-Source Inverters Through Line Voltage Magnitudes Analysis

In this article, a fast and robust diagnostic method for multiple open-circuit (OC) faults is presented for voltage-source inverters. Only two line voltages are used as diagnosis variables, which is economic, simple, and can reduce the influence caused by the failure rate of information sources. Possible magnitudes of these line voltage vectors are characterized in detail both for the healthy and faulty operations. Then, several voltage features are extracted for diagnosis. Single-switch open-circuit faults and double-switch open-circuit faults can be accurately and quickly located through the proposed method. The fastest diagnostic process can be finished in 1/20 of the fundamental period. The diagnostic results of the proposed method are not affected by certain load OC faults, which may lead to false diagnosis of the existing methods. Moreover, the proposed method is robust to different control strategies, filter components, and carrier frequencies. Experiments are carried out on a dSPACE platform, and the effectiveness of the proposed method is verified.

Open-Switch Fault Tolerance Capabilities of Some Reduced Device Count Multilevel Inverter Topologies

In this paper, some of the recently proposed reduced device count multilevel inverter (RDC-MLI) topologies are considered and analyzed in the light of imparting “any switch” open circuit fault tolerance capability. In RDC-MLIs, the occurrence of faults would shut down the system due to the lack of redundant switching states. However, for the cases involving “any single switch open circuit fault,” the system can continue to operate uninterrupted. This is achieved by adding redundant states of switching combinations, obtained by addition of switching device(s). By the proposed solution, the complete system shutdown can be prevented, thereby attaining higher reliability in RDC-MLIs. Further, the modified systems under normal and faulty conditions have been simulated using MATLAB/Simulink environment and the results are experimentally validated to prove the feasibility of the strategy for imparting fault tolerance to RDC-MLIs.

Approach to synthesis of fault tolerant reduced device count multilevel inverters (FT RDC MLIs)

Multilevel inverters (MLIs) are rapidly acquiring techno-economic feasibility for both high-power and medium-power applications. Increased number of power switches has been cited as one of the most important limitations of MLIs; and to overcome it, a whole new class of MLI topologies has come up. These topologies are commonly called `reduced device count' MLIs (RDC-MLIs). As the number of controlled switches is significantly reduced in RDC-MLIs, the redundant states are also reduced. Hence, the possibility of fault tolerant operation is severely affected. This study looks at the possibility of imparting fault-tolerant characteristics to RDC-MLIs. In this study, some of the recently proposed RDC-MLI topologies are first analysed for the possibility of fault tolerant operation in the case of `any single switch open-circuit fault (ASSOF)'. Thereafter, an optimal addition of power switch is proposed which enables fault tolerant operation in the event of ASSOF. Furthermore, these modified RDC-MLIs are verified under normal and faulty conditions using software simulations and experimental set-ups and these results are presented.

A Nonintrusive Diagnostic Method for Open-Circuit Faults of Locomotive Inverters Based on Output Current Trajectory

Open-circuit (OC) fault diagnosis of voltage source inverters on trains still has two problems to be improved. First, it is usually forbidden to change the system structures of trains or to add any extra sensor. Therefore, diagnostic methods which need pulse width modulation control signals or extra output voltage sensors are no longer suitable for trains. Second, loads on the train vary in a wide range and have significant influence on output currents. In order to solve these problems and increase the maintenance efficiency, an online diagnostic method for single switch OC (SSOC) faults and double switches OC (DSOC) faults is proposed. Supposing that three phases are balanced, it is proved that the trajectory of two output currents is an ellipse in the Cartesian coordination, and each OC fault has a unique trajectory. SSOC faults and DSOC faults can be isolated by detecting abnormal slopes and directions of several consecutive points on the trajectory. The fastest diagnostic process takes less than half a period. Load variation has impact on the size and shape of the trajectory but does not affect the diagnostic method. Experimental tests are carried out on dSPACE platform. Results show the accuracy of the mathematical model and the effectiveness of the online diagnostic method proposed in this paper.

Post-Fault Operation Strategy for Single Switch Open-Circuit Faults in Electric Drives

Single switch open-circuit faults in three-phase ac drives lead to undesired effects and potentially to a total failure of the drive. This paper proposes a postfault operation strategy for such faults with a focus on the limitation of losses after the reconfiguration and thereby an extension of the possible range of operation. Furthermore, a method for the reduction of alternating torque components during the postfault operation of a squirrel cage induction machine drive is proposed. The performance of the postfault operation strategy and the alternating torque reduction method are shown both via simulations and experiments.

Performances Analysis of SPWM Inverter-Fed Three Phase Induction Motor during Fault Conditions

Induction motors are the most widely used electrical machines and the most popularly in the industrial applications, aerospace, and electrical vehicles or hybrid electrical vehicles. This celebrity of these machines because of some of their benefits such as: relatively low manufacturing cost, robust construction, moderate power factor, ability to operate in hostile environments, good reliability, and ease of control especially in the recent years. In fact, induction motors are the main component of many of these applications and they are used in the most of these applications with their power electronic drivers in order to control their speeds, torques, or control their starting conditions. However, these motors and their drivers may encounter several faults due to operating conditions. In fact, these faults are either due to the motor itself or due to its power electronic driver circuit. Therefore, this paper presents the performance analysis and simulation of a Sinusoidal pulse width Modulation (SPWM) inverter-fed three-phase induction motor under some fault conditions. Two different types of faults are studied and analyzed in detail. These faults were: driver single switch short circuit fault, and driver single switch open circuit fault. The motor currents and voltages at pre-fault and post-fault conditions are presented and investigated. In the two fault cases, the motor phase currents are changed and increased, but in different ratios, under same load conditions. Also, decreasing and oscillating in both motor speed and its developed torque are occurred due to these faults. The simulation and analysis results show that the single switch short circuit fault has the sever effect on the motor performance, therefore especial care should be taken under this fault conditions.

A Novel Diagnostic Technique for Open-Circuited Faults of Inverters Based on Output Line-to-Line Voltage Model

An output line-to-line voltage model-based fault diagnostic technique is presented in this paper. From the theoretical analysis of the output voltage under normal and faulty conditions, a preprocessing method is developed to extract fault features from diagnosis eigenvalue. A voltage envelope line is generated by the proposed voltage envelope function. By comparing the preprocessed diagnosis eigenvalue and the voltage envelope, single-switch open-circuit faults can be located precisely. Because the proposed method does not rely on the accurate amplitude of the output line-to-line voltage, the influence of the load changing is minimized and simple hardware is adopted, which has advantages of low cost, high reliability, and short diagnosis time. Moreover, as long as the inverter output voltages have the feature of periodic nonpositive and nonnegative, this method is valid no matter what control strategy is adopted by the inverter and no control signal is required for the diagnosis process. The prototype system is tested to validate the adaptability of the proposed method under different conditions, such as the diverse loads, various control strategies, and fault-occurrence time.

Adding Inverter Fault Detection to Model-Based Predictive Control for Flying-Capacitor Inverters

As inverters are often used in critical applications, reliability is an important issue. In particular, the power electronic switches and gate drivers, the most essential components of the inverter, are vulnerable parts in real live operation. Therefore, this paper focuses on open-switch fault detection for multilevel inverters. When a single-switch open-circuit fault occurs in one of the power electronic switches, the algorithm can detect the fault and the switch that is causing it. The detection is worked out for both a linear resistive inductive load and an induction motor. The proposed algorithm is an extension of an already available finite-set model-based predictive control algorithm. Therefore, no extra hardware or measurements are required. This paper also discusses a suggested method for reconfiguration after fault detection. Computer simulation and experimental verifications validate the proposed methods.

FAULT DETECTION AND DIAGNOSIS OF HIGH SPEED SWITCHING DEVICES IN POWER INVERTER

Power electronic based inverters are the major components in industry. A fault diagnostics framework composed of a pattern recognition system, having machine learning technology as its integral part is utilized for failure detection of different switches and tracing multiple types of faults in an inverter. Hardware point of view power electronics inverter can be considered to be the weakest link. Hence, this work is carried on detecting faults and classifies which switches in the inverter cause the fault. Diagnosis can help to avoid unplanned breakdown, to make possible to run an emergency operation in case of a fault. On the basis of theoretical foundations of electronic power inverter a simulation model has been developed to simulate the healthy condition and all single-switch open circuit faults. The generated signal is processed using Discrete Wavelet Transform (DWT) and Fuzzy Inference Logic (FIL). A smart and accurate classification of faults is obtained using simulation results, which are tested on a wide operation domain and various load conditions.

PARTICLE SWARM AND NEURAL NETWORK APPROACH FOR FAULT CLEARING OF MULTILEVEL INVERTERS

This study presents a machine learning technique for fault diagnostics in induction motor drives. A normal model and an extensive range of faulted models for the inverter-motor combination were developed and implemented using a generic commercial simulation tool to generate voltages and current signals at a broad range of operating points selected by a Particle Swarm Optimization (PSO) based machine learning algorithm. A structured Particle Swarm (PS)-neural network system has been designed, developed and trained to detect and isolate the most common types of faults: single switch open circuit faults, post-short circuits, short circuits and the unknown faults. Extensive simulation experiments were conducted to test the system with added noise and the results show that the structured neural network system which was trained by using the proposed machine learning approach gives high accuracy in detecting whether a faulty condition has occurred, thus isolating and pin-pointing to the type of faulty conditions occurring in power electronics inverter based electrical drives. Finally, the authors show that the proposed structured PS-neural network system has the capability of real-time detection of any of the faulty conditions mentioned above within 20 milliseconds or less.

Intelligent diagnosis of open and short circuit faults in electric drive inverters for real-time applications

This study presents a machine learning technique for fault diagnostics in induction motor drives. A normal model and an extensive range of faulted models for the inverter-motor combination were developed and implemented using a generic commercial simulation tool to generate voltages and current signals at a broad range of operating points selected by a machine learning algorithm. A structured neural network system has been designed, developed and trained to detect and isolate the most common types of faults: single switch open circuit faults, post short-circuits, short circuits and the unknown faults. Extensive simulation experiments were conducted to test the system with added noise, and the results show that the structured neural network system which was trained by using the proposed machine learning approach gives high accuracy in detecting whether a faulty condition has occurred, thus isolating and pin-pointing to the type of faulty conditions occurring in power electronics inverter-based electrical drives. Finally, the authors show that the proposed structured neural network system has the capability of real-time detection of any of the faulty conditions mentioned above within 20 ms or less.