You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems 
Chapter Title:  1) REDUNDANT SWITCHES AUXILIARY 
1. Abstract of Cited Paper (BIB001):  Electric vehicles (EVs) and hybrid electric vehicles (HEVs) can reduce greenhouse gas emissions while switched reluctance motor (SRM) is one of the promising motor for such applications. This paper presents a novel SRM fault-diagnosis and fault-tolerance operation solution. Based on the traditional asymmetric half-bridge topology for the SRM driving, the central tapped winding of the SRM in modular half-bridge configuration are introduced to provide fault-diagnosis and fault-tolerance functions, which are set idle in normal conditions. The fault diagnosis can be achieved by detecting the characteristic of the excitation and demagnetization currents. An SRM fault-tolerance operation strategy is also realized by the proposed topology, which compensates for the missing phase torque under the open-circuit fault, and reduces the unbalanced phase current under the short-circuit fault due to the uncontrolled faulty phase. Furthermore, the current sensor placement strategy is also discussed to give two placement methods for low cost or modular structure. Simulation results in MATLAB/Simulink and experiments on a 750-W SRM validate the effectiveness of the proposed strategy, which may have significant implications and improve the reliability of EVs/HEVs. 
2. Abstract of Cited Paper (BIB002):  This paper introduces a new fault-tolerant strategy for the asymmetrical half-bridge converter used in switched reluctance machine drives. The proposed method can work under multiple open-switch faults by bypassing the faulty part with the minimum number of switches. Matlab/Simulink package is used to verify the proposed method. Simulation results for 3-phase 12/8 SRM under multiple open-switch faults are provided at low and high speeds when current chopping control (CCC) and voltage modulation control is used, respectively. The proposed method also characterizes by providing a complete tolerance at low speeds up to four open-switch faults, so that system dynamics is similar to healthy conditions. 
3. Abstract of Cited Paper (BIB003):  Switched reluctance motors (SRMs) are considered a competitive technology for more electric aircraft and automotive applications due to their excellent fault-tolerant capabilities and robust configuration. In such applications, system reliability is a crucial feature. Therefore, here, a new fault-tolerant control strategy with real-time fault diagnosis for power transistor faults in SRM drives is proposed. The developed fault-tolerant topology is composed of four additional power switches and a relay network based on the conventional asymmetric converter. Moreover, an online fault diagnostic algorithm based on high-frequency (HF) signal injection is proposed. In contrast to the existing strategies that use additional sensors, this diagnostic algorithm extracts the fault signatures from the fundamental current by injecting an HF voltage signal into the upper switches of the asymmetric converter. Open- and short-circuit faults of the power switches are analysed by monitoring the variation in frequency and amplitude of the resulting HF current along with the amplitude variation in fundamental current with the occurrence of fault. Simulations performed on a three-phase 12/8 SRM drive and results are presented to validate the effectiveness of the proposed strategy. 
4. Abstract of Cited Paper (BIB004):  Switched reluctance motor power converters are prone to open-circuit faults because it need to withstand large voltages and currents. Due to the small number of traditional asymmetrical half bridge topology switches, it is difficult to carry out fault tolerant control when power converters has an open-circuit fault, resulting in larger output torque ripple. This paper presents a five-level power converter based on the traditional asymmetric half-bridge power converter. The five-level topology has more switching states and can work in multi-level mode. Based on the topology, different excitation and demagnetization voltages can be choose at different speeds. A fault-tolerance strategy is developed to decrease the influence of the open-circuit fault. The five-level power converter has four switches per phase, and two of them will be used in one of the operating mode. So the remaining two of the switches can be used for safe backup, enabling fault-tolerant control when an open-circuit occur. Since each phase of the five-level power converter proposed in this paper is independent of each other, a reasonable control strategy can be used to avoid the unbalance of the midpoint potential. Finally, the topology and fault-tolerant strategy proposed in this paper are verified by simulation and experiment.

Literature Review:
Power switches are the key components to control phase currents. When they are open or short circuited, the power converter is out of control and the SRM drive cannot operate normally. To settle the problem, redundant switches which are idle during normal operation serve as a backup in abnormal conditions. For instance, a new power converter topology with the minimal number of backup switches is researched in BIB003 . Detailed investigations by using hardwire auxiliary to achieve fault tolerance control are presented in BIB005 -  , where redundant switches are selected and controlled to substitute for the open-or short-circuit one. A five-level power converter topology with two extra switches in each phase is presented in Fig. 16 for multiphase open-and short-circuit fault tolerance BIB005 . Six fault-tolerant schemes are presented for six kinds of switch open-circuit faults, correspondingly. This strategy improves the reliability of the SRM drive and offers multilevel voltage output ability, making it more applicable in safety-critical applications. To reduce the cost of the tolerance circuity, relay networks are added to cut down the quantities of redundant switches in BIB004 . Two upper switches and upper relay networks are used to replace faulty upper switches, while two lower switches and lower relay networks are used to take the place of the faulty lower switches. In BIB001 , two redundant half-bridge inverters are regarded as the safety backup for faulty components. Two center-tap nodes in each phase winding are extracted and connected to relay networks. This topology provides powerful open-and short-circuit fault tolerance capability by insulating the faulty components to sustain a stable operation. The simplified schematic for this strategy is exhibited in Fig. 17 . In BIB002 , the redundant half-bridge switch modules are adopted to bypass the faulty part in the SRM drive. The outputs of the backup half-bridge inverters are connected to the center-tapped nodes in phase windings. This method blocks the faulty part in SRM drive without much change to the converter circuit. Hence, the open-and shortcircuit fault problem can be easily solved. Instant power outage fault deteriorates the performance of the SRM drive and makes the drive system broken-down for a worse situation. An auxiliary switch cascaded into the converter known as the chopper switch undertakes the function of maintaining the supply voltage during power outage fault. The inductance and double-layer supercapacitor are also employed in the modified power converter. In the process of power outage fault, the chopper is turned off and the supercapacitor plays the role of supplying energy to the motor and controller. Then the chopper is regulated to charge the capacitor when the dc-link voltage is back to normal  .