An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> Recently, research has picked up a fervent pace in the area of fault diagnosis of electrical machines. The manufacturers and users of these drives are now keen to include diagnostic features in the software to improve salability and reliability. Apart from locating specific harmonic components in the line current (popularly known as motor current signature analysis), other signals, such as speed, torque, noise, vibration etc., are also explored for their frequency contents. Sometimes, altogether different techniques, such as thermal measurements, chemical analysis, etc., are also employed to find out the nature and the degree of the fault. In addition, human involvement in the actual fault detection decision making is slowly being replaced by automated tools, such as expert systems, neural networks, fuzzy-logic-based systems; to name a few. It is indeed evident that this area is vast in scope. Hence, keeping in mind the need for future research, a review paper describing different types of faults and the signatures they generate and their diagnostics' schemes will not be entirely out of place. In particular, such a review helps to avoid repetition of past work and gives a bird's eye view to a new researcher in this area. <s> BIB001 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> This paper introduces a new index for noninvasive diagnosis of static eccentricity in permanent magnet synchronous motors (PMSM). Use of this index makes it also possible to precisely determine the eccentricity degree. The index is the amplitude of the harmonic components with a particular frequency pattern. Occurrence and increase of the fault degree cause the rise of amplitude of the harmonic components which can be used to diagnose the fault and determine its degree. To evaluate the ability of the proposed index for static eccentricity detection and estimation of its severity, the correlation between index and eccentricity degree is calculated. Then a three-layer artificial neural network is employed to classify the current and torque profiles to one of the four possible classes of eccentricities. After all, a white Gaussian noise is added to the both measured current and torque and robustness of the proposed index is analyzed with respect to the noise variance. A PMSM under static eccentricity fault is modeled using time stepping finite element method. This modeling includes all geometrical and physical characteristics of the machine components, non-uniform permeance of the air gap and non-uniform characteristics of the PM material. Use of this precise modeling makes it possible to access the demanded signals for a very high precision processing. <s> BIB002 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> Mixed-eccentricity (ME) fault diagnosis has not been so far documented for permanent-magnet (PM) synchronous motors (PMSMs). This paper investigates how the static eccentricity (SE), dynamic eccentricity (DE), and ME in three-phase PMSMs can be detected. A novel index for noninvasive diagnosis of these eccentricities is introduced for a faulty PMSM. The nominated index is the amplitude of sideband components with a particular frequency pattern which is extracted from the spectrum of stator current. Using this index makes it possible to determine the occurrence, as well as the type and percentage, of eccentricity precisely. Meanwhile, the current spectrum of the faulty PMSM during a large span is inspected, and the ability of the proposed index is exhibited to detect eccentricity in faulty PMSMs with different loads. A novel theoretical scrutiny based on a magnetic field analysis is presented to prove the introduced index and generalize the illustrated fault recognition method. To show the merit of this index in the eccentricity detection and estimation of its severity, first, the correlation between the index and the SE and DE degrees is determined. Then, the type of the eccentricity is determined by a k-nearest neighbor classifier. At the next step, a three-layer artificial neural network is employed to estimate the eccentricity degree and its type. After all, a white Gaussian noise is added to the simulated current, and the robustness of the proposed index is analyzed with respect to the noise variance. In this paper, the PMSM under magnetic fault (demagnetization) and electrical faults (short and open circuits) is modeled, and the current spectrum of the faulty PMSM under demagnetization, short circuit, and open circuit faults is analyzed. It is demonstrated that the proposed index, due to eccentricity fault, is not generated in the current spectrum due to magnetic and electrical faults. Indeed, it is exposed that the introduced index is only created due to eccentricity fault and it is not sensitive to other faults. To model the PMSM eccentricities, a time-stepping finite-element method, which takes into account all geometrical and physical characteristics of the machine components, nonuniform permeance of the air gap, and nonuniform characteristics of the PM material, is employed. This model facilitates the access to the demanded signals in order to have accurate processing. A comparison of simulation and experimental results validate the proposed index. <s> BIB003 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> The permanent-magnet hybrid brushless (PMHB) motor adopts both DC field windings and PMs for excitation. It not only offers effective online flux control, but also flexible brushless DC (BLDC) or brushless AC (BLAC) operations. The key of this paper is to investigate two remedial strategies for fault-tolerant operations of the PMHB motor drive under open-circuit faults. First, by utilizing field excitation boosting, the reduced torque due to one phase loss can be remedied, the so-called remedial BLDC operation mode. Second, by reconstructing armature fields due to the healthy phase currents, the reduced torque can also be remedied, the so-called remedial BLAC operation mode. Finally, these two remedial operation modes are compared and verified by experimentation, hence confirming the validity of the proposed fault-tolerant PMHB motor drive. <s> BIB004 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> A sensor fault detection and isolation unit is considered for induction-motor drives based on an adaptive observer with rotor-resistance estimation. Generally, closed-loop induction-motor drives with voltage-source inverters use a speed or position, a dc-link voltage, and two or three phase-current sensors. In the proposed fault-detection and isolation unit, the estimated phase currents and rotor resistance are sent to a decision-making unit, which identifies the faulty sensor type based on a deterministic rule base. In the case of a current-sensor failure, it also detects the phase with erroneous sensor output. It is shown that, unlike the other proposed model-based fault-tolerant systems, using a bank of observers is not necessary, and only one current observer with rotor-resistance estimation is sufficient for isolation of all sensors' faults. The accuracy of the proposed approach is analytically proved. Furthermore, extensive simulation and experimental tests verify the effectiveness of the proposed method at different operating conditions. <s> BIB005 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> A new index is introduced for eccentricity fault diagnosis in three-phase squirrel-cage induction motors. Basically, some physical quantities of the motors structure such as air gap length influence this index, while other operational factors including motor supply, control type, load level, and its fluctuation cannot affect the proposed index. The influence of various eccentricity faults upon this index is investigated and shows the segregation ability of different eccentricity types by the index. It is indicated that the change of load, speed, and saturation level can slightly change the index value. Experimental results confirm the simulation results. <s> BIB006 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> The aim of this paper is to study the fault-tolerant control strategies when faults occur in paralleled-inverter-fed permanent-magnet-synchronous-motor drives. Different from removing the faulty inverter channels completely, this paper proposes and compares three fault-tolerant control strategies, which fully use all the healthy phase legs, including those in faulty inverters. The three schemes are called “normal channel direct compensation,” “normal channel asymmetric currents,” and “equivalent current value compensation,” respectively. The proposed control schemes not only provide smooth torque but also have smaller copper loss under open-circuit faults. The corresponding principles and design criteria of control are given. Moreover, the proportional-resonant current controller is designed to track the asymmetrical current references of fault-tolerant control and avoid the possible circulating currents among paralleled inverter channels. The experiments are given to verify and compare the performance of the proposed fault-tolerant control schemes. <s> BIB007 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> Brushless dc (BLDC) motors are commonly used in space application for its simplicity and high reliability. The fault-tolerant control (FTC) of the motor is important for its continuous operating capacity even under the faulty situation. The fault diagnosis should be achieved in advance in order to implement the FTC strategy. This paper proposes an online model-based inverter fault diagnosis method for three-phase full bridge inverter with buck dc-dc converter based on the high-speed BLDC motor with low inductance and nonideal back electromotive force in a magnetically suspended control moment gyro. The method can detect and identify both open-circuit and short-circuit damages of single switch in buck converter or three-phase full bridge. Also, protective measures are proposed to isolate the fault and avoid the secondary fault. Both simulation and experimental results are taken out to prove the validity and effectiveness of the proposed fault diagnosis method. <s> BIB008 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> Linear induction motors (LIMs) are being gradually applied in the urban rail transit due to their simplified mechanical structure and feasibility for both low-speed and high-speed operations. Direct-torque control (DTC) is a classical control scheme that can be readily extended to LIMs. However, due to the high thrust ripple and poor dynamic performance for the low-speed operation, control performance of DTC is not satisfactory. This paper is to propose an explicit model predictive control to be combined with the DTC scheme. First, the LIM model is presented and discretized. Then, the LIM drive and its operating principle are discussed. Thirdly, the controller design, including control variables, and the objective function are depicted. Finally, both the simulation and the experiment are engaged for verifying the proposed control algorithm. <s> BIB009 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> Due to the simplicity and high reliability, brushless dc (BLDC) motors are widely used in space application. High-reliability levels are the vital aspect for ensuring the long-term stable operation of the BLDC motor system, which is used in aerospace applications. The fault-tolerant control of the BLDC motor is of great importance for its continuous operating capacity even under the faulty situation. This paper proposes a fault-tolerant topology composed of an additional phase leg and a fault-protective circuit for the high-speed low-inductance BLDC motor. Based on the analysis of the overcurrent and overvoltage phenomenon after the switch faults, a novel fault isolation and system reconfiguration method is presented. The method can achieve safe isolation and reconfiguration to avoid the secondary fault caused by direct switch of the redundant switch and the faulty switch after the fault-diagnosis process. Both simulation and experimental results confirm the feasibility and effectiveness of the proposed method. <s> BIB010 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> This paper introduces new schemes for detection, isolation, and compensation of speed and current sensor (CS) faults in field oriented induction motor (IM) drives. These schemes do not use any kind of machine model and motor parameters. This is a prominent feature of the proposed approaches, which only rely on main concepts of field-oriented control (FOC)-based IM drives. Moreover, the proposed fault detection and isolation (FDI) schemes can take partial sensor failures into account. These kinds of faults that might be caused by mechanical or electrical failures, or intentional sensor tampering, are difficult to be dealt with since embedded speed and current control loops react swiftly, and inherently try to camouflage partial sensor failures. CS faults result in imbalance current flow in the motor stator phases, and speed sensor fault repudiates the orthogonally alignment of field and torque current components in field oriented IM drives. These features are cornerstones of introduced FDI methodology. Furthermore, model and parameter free compensators are proposed to recover normal operation of the machine before fault incident. After in-depth analysis, extensive simulation and experimental tests validate the proposed schemes. <s> BIB011 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> Thermal analysis is an important issue in machine design which allows to have a knowledge of the machine temperature rise. This paper presents the thermal analysis, modeling, and experiments of a linear-switched reluctance machine (LSRM) with toroidally wound mover and segmental structure. First, a 3-D heat flow model with the homogenized region for the presented LSRM is established using the thermal equivalent circuit. The equivalent thermal resistance of the model is developed together with the nodes forming of the thermal resistance network. The thermal identification to each component such as windings and core steel is performed. Then both the numerical 2-D and 3-D heat flow model for the presented LSRM are established by finite-element analysis which can give the detailed temperature distribution of the entire machine. At last, the actual experiment on a prototype is carried out, validating the accuracy, and feasibility of the thermal equivalent model above. <s> BIB012 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> This letter presents an open-phase fault detection method for delta-connected permanent magnet synchronous machine (PMSM) drive systems. This method is based on zero sequence current component (ZSCC) and stator currents. First, the model of the delta-connected PMSM is established under healthy and fault conditions. Then, the expression of the ZSCC is presented, and fault indicators are defined based on the ZSCC and stator currents, which are used for the open-phase fault detection and location. Finally, both the simulation and experimental results validate the effectiveness of the proposed method. <s> BIB013 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> As interturn short fault (ISF) in a permanent-magnet synchronous machine (PMSM) degrades its energy efficiency and may cause other problems, accurate fault diagnosis for the PMSMs is necessary. In this paper, we present a method that uses voltage and current residual components to diagnose the phase and the severity of the ISF in PMSMs. A faulty-winding model (FWM) is introduced to analyze the fault; the model describes a relationship between the voltage decrease of the faulty winding to the characteristics of the fault such as a fault resistance and a fault turn ratio. Based on the model, we suggest a fault index (FI) that shows the severity of the ISF. As the ISF induces residual components to both voltage and current, the proposed method utilized those components with the FWM. A least squares (LS) method is used to estimate the FI and to diagnose the ISF of PMSMs. Experimental results demonstrate that the proposed method diagnose the ISF effectively. <s> BIB014 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> With the development of electric vehicles (EVs), the reliability and security of the motor drive system have been in high demand in recent years. EVs can still work reliably even when the motor drive system encounters some failures. Therefore, fault-tolerant motors have become the focus of research all over the world. The hybrid excitation axial field flux-switching permanent magnet machine (HEAFFSPMM) is a novel stator excitation brushless PM machine. It combines the advantages of AFFSPMM and hybrid excitation PM machine. Based on a 600 W prototype of three-phase 12/10 stator/rotor pole AFFSPMM, these parameters of HEAFFSPMM are optimized by 3-D finite element method in order to obtain the high self-inductance and low ratio of mutual and self-inductances, including the number of rotor poles, the split ratio, the width of permanent magnet, and the width of stator middle teeth. Then, the fault-tolerant control method of the space vector pulse width modulation based on minimum copper loss is proposed in this paper with the combination of adjusting the field current. The control methods of the HEAFFSPMM are simulated and investigated at healthy and one-phase open-circuit operation. Finally, the experiments are done to validate the proposed fault-tolerant control method. The results indicate that the HEAFFSPMM has good fault tolerance under the proposed control method. <s> BIB015 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> With the increasing proliferation of variable speed drive, the demand for the more reliable drive is also on the rise. Despite the growing interest on more advanced motors like permanent magnet and flux switching motors, three-phase induction motors (3ph-IMs) are still the main workhorse in the industry and hence the fault-tolerant control of these motor drives remains an interesting and important topic. In this paper, a simple fault-tolerant field-oriented control technique for 3ph-IMs is presented. It is shown that by injecting zero-sequence compensation voltage in a feedforward manner, open-circuit faults can be effectively tolerated. Compared to the previous feedforward fault-tolerant control methods, the proposed approach does not require the knowledge of the magnetizing inductance, which is tricky to be obtained in induction motors. Furthermore, the unified feedforward approach allows the same control structure to be used for different fault-tolerant 3ph-IMs drive topologies, with minor modifications to the feedforward terms. In addition, the effect of inverter non-idealities on the performance of the proposed control method is also highlighted and addressed. The effectiveness of the proposed controller is verified using MATLAB simulation and further validated using experimental tests. This paper is accompanied by a video demonstrating the experimental results. <s> BIB016 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> In this paper, a universal two-sensor current detection scheme is proposed for the current control of different multiphase switched reluctance motors (SRMs) under multiphase excitation. In the proposed scheme, only two current sensors are utilized to separate the phase currents by selecting the currents flowing through each sensor, and detect the excitation current flowing through the lower switch of each phase. The current overlapping states are analyzed for SRM drives with different phase numbers. Compared to existing schemes, the proposed method is applicable for all three-phase, four-phase, five-phase, and six-phase drives, without external circuits and any changes in converter topologies, which is much easier to implement. For three-phase and four-phase SRM drives, the phase currents can be simply calculated from the two sensor currents, without pulse injection and voltage penalty, which improves the sampling accuracy and system performance. Furthermore, with the proposed scheme, the five-phase and six-phase systems both can be made equivalent to two independent single-sensor systems, where all the phase currents can also be obtained by employing pulse injection. Therefore, it provides a promising solution to phase current detection for different SRMs with multiphase excitation by using only two current sensors. Simulation and experimental results are provided to verify the proposed schemes. <s> BIB017 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> This paper proposes a modular multilevel converter (MMC) based switched reluctance motor (SRM) drive with decentralized battery energy storage system for hybrid electric vehicle applications. In the proposed drive, a battery cell and a half-bridge converter is connected as a submodule (SM), and multiple SMs are connected together for the MMC. The modular full-bridge converter is employed to drive the motor. Flexible charging and discharging functions for each SM are obtained by controlling switches in SMs. Multiple working modes and functions are achieved. Compared to conventional and existing SRM drives, there are several advantages for the proposed topology. A lower dc-bus voltage can be flexibly achieved by selecting SM operation states, which can dramatically reduce the voltage stress on the switches. Multilevel phase voltage is obtained to improve the torque capability. Battery state-of-charge balance can be achieved by independently controlling each SM. Flexible fault-tolerance ability for battery cells is equipped. The battery can be flexibly charged under both running and standstill conditions. Furthermore, a completely modular structure is achieved by using standard half-bridge modules, which is beneficial for market mass production. Experiments carried out on a three-phase 12/8 SRM confirm the effectiveness of the proposed SRM drive. <s> BIB018 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> The current reconstruction strategies using single current sensor in the motor drives are widely researched. However, the sampled currents do not represent the average values within the modulation period, especially for the asymmetric modulation or asymmetric sampling solutions. This is due to the following two reasons: 1) The detected current values obtained at different sampling points are utilized to calculate the three-phase currents; and 2) the detected instantaneous currents are applied to estimate the average current values. In this letter, the current change rates under different action vectors are estimated to compensate these errors in a three-phase four-switch interior permanent magnet synchronous motor (IPMSM) drive with single current sensor. The effectiveness of the proposed strategy is verified by experimental results on a 5-kW IPMSM motor prototype, which shows that the current reconstruction errors are reduced after compensation. <s> BIB019 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> I. INTRODUCTION <s> Detection of winding faults in permanent magnet synchronous machines (PMSMs) with stranded winding designs remains a challenging task for conventional diagnostic techniques. This paper proposes a new sensing approach to this problem by investigating the application of dedicated electrically non-conductive and electromagnetic interference immune fiber Bragg grating (FBG) temperature sensors embedded in PMSM windings to enable winding open-circuit fault diagnosis based on observing the fault thermal signature. The final element analysis thermal and electromagnetic models of the examined practical PMSM design are first developed and used to enable the understanding of open-circuit winding fault-induced signature that can be used for effective diagnostic purposes, indicating in situ thermal excitation as an optimal diagnostic measurand. A purpose build test rig with an inverter-driven commercial PMSM instrumented with in situ FBG sensors monitoring phase winding hot spots is then used to evaluate the efficacy of the proposed diagnostic scheme. It is shown that unambiguous diagnosis and severity trending of winding open-circuit faults is enabled by the use of in situ FBG sensors. A comparison with conventional fault diagnostic technique utilizing current signal sensing and analysis is also reported, indicating the considerable advantages of the proposed monitoring scheme employing FBG sensors. <s> BIB020
The electric motors have been wildly used in industrial manufacturing and traffic transportation since they were invented a long time ago BIB009 , BIB016 . At that time, the protection of the machine only contains some simple components, such as fuse cutout, to ensure the safety BIB001 . With the development of the human society, stable and reliable operation becomes a common sense in motor control BIB016 , BIB010 , and BIB007 . However, electric motors are often used in high-temperature and harsh The associate editor coordinating the review of this manuscript and approving it for publication was Mohsin Jamil . environments, which may lead to various faults in motor drives BIB017 , BIB012 . These faults are usually unrecoverable, and may lead to fault spreading to motor drives, causing further damage to other healthy components. Without handling these faults, the electric motors will not be available for safetycritical applications, where even a small mistake may cause heavy financial losses. The electric motors should continue to work and keep stable operation in fault conditions. Hence, the fault ridethrough capability is crucial in motor control system BIB018 . To achieve this purpose, fault diagnosis methods should be first employed to accurately detect the motor faults when happening. Then, further fault tolerance strategies ought to be implemented by the controller to maintain stable operation, avoiding uncontrollable broken-down and heavy financial losses. The combination of fault diagnosis and fault tolerance strategies are of great significance for motor fault ride-through capability. For the electric motor drive system, different faults can occur in different parts. Typical faults of the electric motor drive can be categorized as follows : 1) open-and short-circuit faults of power transistors and diodes in the power converter; 2) unexpected connection or disconnection in phase windings, such as open-and short-circuit faults BIB013 , BIB014 ; 3) abnormal operation of the position sensors BIB005 ; 4) static and dynamic eccentricity of the rotor BIB003 , BIB002 ; 5) current sensor faults such as scaling and dc bias errors lead to inaccurate current sampling BIB019 . When the above faults happen during normal motor operation without any remedial arrangements, it could bring about serious consequences as follows: 1) overvoltage and overcurrent in SRM drives; 2) distortion in current and voltage waveforms; 3) short-circuit currents leading to permanent insulation damage and faults, and spreading to healthy elements; 4) large circulating current bring on cooling issue; 5) high loss, high torque ripple, and low efficiency; 6) unexpected phase conduction and commutation; 7) non-uniform air gap and unbalanced phase currents. To avoid these consequences, the faults are required to be handled instantly. Fault diagnosis and fault tolerance methods have been developed for permanent magnetic synchronize motor (PMSM), brushless dc motor (BLDC), and induction motor (IM). In terms of fault diagnosis, a novel thermal sensing approach by utilization of fiber Bragging grating (FBG) is proposed for open-circuit fault detection in PMSM in BIB020 . In BIB008 , an online fault detection method for open-and shortcircuit faults is developed in BLDC motor drive. Induction motor eccentricity fault is detected by the analysis of the spectrum information of inductance in BIB006 . For fault-tolerant control, the position sensor and current sensor faults are detected, isolated, and compensated without prior knowledge of the machine model and parameters BIB011 . In hybrid brushless motor drives, two fault-tolerant strategies are investigated for open-circuit faults BIB004 , where field excitation boosting and reconstructing armature fields are adopted to compensate the torque drop due to phase-deficiency operation. The space vector regulation method used for minimizing the copper loss is proposed under open-circuit fault in flux-switching permanent magnet motor BIB015 . The available methods of fault diagnosis and fault tolerance for electric motors are illustrated in Fig. 1 , making it possible to achieve fault ride-through in reliability-critical applications. Switched reluctance motors (SRMs) with doubly salient structure take the advantage of high reliability, large starting torque, large speed range, and rare-earth free, receiving widely concerns for industry and research  . Nevertheless, the SRM drives are still vulnerable in some fault conditions. As a consequence, it is very important to develop intelligent fault diagnosis and reliable fault tolerance strategies. The open-circuit faults in power converter or winding lead to phase-deficient operation, where the output torque is decreased and large torque ripple is generated in SRM. The winding short-circuit fault will produce the over-current issue, leading to overheating, which may damage the SRM if not handled. Sensor faults also affect the SRM normal operation. Failures in current sensors cause failure in closedloop current control, making the chopping current control (CCC) become invalid. Phase commutation will fail when the position sensor cannot reflect an accurate position signal to the controller. Rotor eccentricity and bearing fault worsen the motor robustness. In order to maintain the reliable and stable operation for SRM systems, fault diagnosis and fault tolerance strategies are essential, which will be discussed in details in followings.