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:  A. POSITION SIGNAL ASSISTANCE 
1. Abstract of Cited Paper (BIB001):  Existing position sensorless methods rely on (1) one-one correspondence between magnetic characteristics of SRM and rotor position and (2) access to terminal quantities (i.e. voltage and current) for all phases. The occurrence of a fault in one or more phases will prohibit the necessary access to the phase/s and as such introduces a challenge to successful implementation of existing position sensing technique. This paper introduces a generalized strategy for sensorless operation of SRM under single and multi-phase faults using existing sensorless method. Experimental results of a four phase SRM drive with different numbers of faulty phases are presented to validate the proposed methods. 
2. Abstract of Cited Paper (BIB002):  An accurate rotor position signal is quite necessary for high-performance control of switched reluctance motor (SRM). In general, the position signal faults may lead to abnormal operation, which deteriorates the reliability of the switched reluctance drive system. Thus, it is quite vital but still a challenge to develop a control strategy that can diagnose and control the position signal faults in an autonomous way. In this paper, a square-wave position signal edge prediction-based control strategy is proposed for position signal faults diagnosis and position faults recovery. Integrated with the rotor position fault-tolerant control method, the SRM drive system can maintain reliable operation under different position signal fault conditions. In addition, a phase inductance slope-based sensorless control method is proposed for position fault-tolerant control under the extreme case with failure of all position signals. To verify the validation of the proposed methods, the experiments have been implemented in a 12/8 structure SRM prototype. The results show that the proposed control methods can further improve the fault-tolerant capability of the SRM system. 
3. Abstract of Cited Paper (BIB003):  Existing position sensorless methods rely on: 1) one-to-one correspondence between magnetic characteristics of switched reluctance motor (SRM) and rotor position; and 2) access to terminal quantities (i.e., voltage and current) for all phases. The occurrence of a fault in one or more phases will prohibit the necessary access to the phase/s and as such introduces a challenge to successful implementation of the existing position sensing techniques. This paper investigates the existing sensorless methods with the occurrence of phase faults and introduces a family of generalized strategies for sensorless operation of SRM under single and multiphase faults. The experimental results of a four-phase SRM drive with different numbers of faulty phases are presented to validate the proposed strategy. 
4. Abstract of Cited Paper (BIB004):  A fault tolerant position estimation for Switched Reluctance Motor (SRM) is proposed in the paper based on relationship between inductance and rotor position. First, the particular position signal is obtained by comparing the real-time flux linkage with the particular position flux linkage, the position is estimated by the particular position signal. Second, the delay method is used based on inter-phase independence under the phase fault, the fault phase position is estimated by the normal phase the particular position signal. Finally, the experimental have been implemented in a 12/8 structure SRM prototype. The results show that the proposed methods are verified the correctness and feasibility. 
5. Abstract of Cited Paper (BIB005):  Accurate and continuous rotor position information is essential for switched reluctance motor (SRM) drives operating in variable speed drive applications. To increase the SRM drives reliability regarding position sensor failures, an active position sensor fault-tolerant controller is presented in this paper. The proposed approach uses two sensorless methods and a position sensor with a maximum-likelihood voting algorithm. The rotor position is estimated from the sensorless method in case of position sensor fault, by an improved pulse injection method in the current-chopping-control mode in a low-speed operation and a current-gradient method in the single-pulse-control mode in a high-speed operation. Through the analysis of the fault position signals of SRM, a new fault diagnosis method of position signals based on the predictions of the edges is adopted in this paper. Experimental results on a three-phase 12/8 SRM demonstrate the effectiveness of both the fault diagnosis algorithm and the fault-tolerant control scheme. 
6. Abstract of Cited Paper (BIB006):  Winding short-circuit is one of the more common faults in switched reluctance motors (SRM). This paper takes an in-depth look at winding short-circuit. The characteristic of non-sinusoidal intermittent single phase current, fundamental components are extracted to reconstruct four phase symmetrical currents based on spectrum analysis of phase currents. The method of symmetrical component is used to calculate positive and negative sequence components of reconstructed currents, where then the ratio between positive and negative sequence component is seen as a fault feature and the diagnostic criterion is proposed. The simulation and experimental results are presented to confirm the implementation of the proposed method. 
7. Abstract of Cited Paper (BIB007):  A sensorless control strategy with one-phase lacking fault-tolerant capability is proposed in this paper for the switched reluctance motors (SRM). This strategy consists of a phase inductance slope zero-crossing detection scheme and a series of phase inductance partition logic algorithms, which is capable of capturing at least one-phase aligned position under both normal operation and one-phase lacking fault operation. With the recorded index position in each electric period, the rotor position can be estimated for sensorless driving accordingly. To ensure stable calculation of the phase inductance in this method, the SRM should be started and operated under single pulse control mode. Thus, for sensorless starting, an idle phase inductance double thresholds based sensorless synthetic starting scheme is also developed. The proposed strategy is easy for implementation and can ensure stable sensorless operation in full speed range. Moreover, it does not need any prior measuring process, complicated logic algorithm, or complex mathematical calculation. The theoretical analysis is conducted, and experimental results are provided to verify the feasibility of the proposed control strategy.

Literature Review:
The position sensor with sampled deviation delivers inaccurate angular signals to the controller, resulting in phase commutation issues. Conversely, open-and short-circuit faults also lead to the failure of sensorless techniques BIB002 . In order to handle these two problems, several fault-tolerant control strategies are put forward, accordingly. In BIB005 , a position estimator is invented based on the realtime flux linkage calculation. The inter-phase independence feature is fully utilized for position estimation when the phase fault happens. The rising edge impulse of the faulty phase is acquired by detecting 15 • position of foregoing phase in a 12/8 SRM and the falling edge impulse is generated 22.5 • after its own rising edge. The real-time flux linkage is calculated by   where ψ k is the phase flux linkage, U k is the phase voltage, R k is the phase resistor, i k is the phase current, and T is the computation period. For position signal tolerant control, a maximum-likelihood voting (MLV) strategy based on an active position sensor method is proposed in BIB006 . One position sensor and two sensorless techniques are adopted and their outputs are regarded as the inputs of the MLV algorithm. The main idea of MLV is to choose, based on how reliable each input is and how faithful its output is, the output that is most likely correct. The possibility X j is expressed in mathematical form as formula BIB007 and (23), which are analyzed in details in BIB006 . Rotor position still can be estimated when the position sensor is disabled by the proposed method. where j represents the input, R is the winding resistance, and N is the number of the input. Another effective position fault-tolerant strategy is investigated in BIB003 . Three optical position sensors are installed on the motor for rotor position detection. Position signal edge prediction (PSEP) method is adopted for the fault detection of the position sensor. When one or two position sensors are in the fault state, they are disabled immediately and the rotor mechanical angle AR is acquired by averaging the healthy position signals denoted in BIB001 . In the worst case, three sensors are damaged simultaneously during operation. The position index pulse is generated by means of inductance slope and phase currents. This position index pulse achieves the position estimation without extra devices. BIB001 where S i = 1 represents for healthy sensors, while S i = 0 is for faulty sensors. AR_i denotes rotor mechanical angle detected by sensor i, and i = 1, 2, 3. In sensorless control, the rotor position is always estimated with the utilization of phase voltages, phase currents, and phase inductances. However, they are distorted in open-and short-circuit faults, resulting in position estimation failure and system broken down. To ensure reliable sensorless operation, these faults are supposed to be considered in position fault-tolerance strategies. The sensorless control strategy comprising a slope zero crossing comparison scheme and maximum inductance partition strategy is investigated in BIB008 . This technique can effectively estimate the rotor position and motor speed, even with one phase open-circuit fault. Even if the estimated phase inductance value is zero due to the lacking phase operation, the rotor position can still be calculated from other estimated phase inductance profile, as presented in Fig. 14. A robust sensorless control scheme with high reliability achieving rotor position estimation under single and multiphase fault is put forward in BIB004 . For single-phase fault, the position signal is absent due to the phase-deficiency operation. To compensation the position signal, a conducting time estimator of the healthy phase is adopted. Besides, aiming at rotor position evaluation in multiphase fault, a combination of inactive and active sensorless method with and without pulse injection, known as multiphase hybrid method is developed. HF pulses injection in idle phase and the flux linkage calculation with look up table in active phase are associated to constitute the global position estimation method depicted in Fig. 15 . This method can acquire accurate position information as long as one phase is in a healthy state.