An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> This paper studies operation of the multipole single-phase switched reluctance generator (SRG) under faults, in particular an 8/8-pole switched reluctance machine. A new converter topology which connects coils two banks in parallel is proposed. The combination of multiple coils per phase and the converter circuit suggests improved operation under faults compared with conventional topologies. Output power per coil current under faults is studied by finite-element analysis and static torque measurement. Circuit equations under faults are derived and operation under faults is evaluated by simulation. An SRG controller is constructed and experiments are performed. The experimental results support the equations and simulation results. It is concluded that the SRG can continue generating operation, even when open- or short-circuited coil faults occur, with the proposed converter and proper fault detection circuits. <s> BIB001 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> A fuzzy inference system is used to characterize switched reluctance motor, SRM, drive systems under normal and fault operating conditions. The Fuzzy Logic (FL) is applied for its ability to be very suitable for problems with large uncertainty. Knowledge about the system is accumulated using coupled finite-element (FE) magnetic field and state space (SS) models. The validity of the FL based model is demonstrated by applying it to a prototype SRM drive system. <s> BIB002 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> The switched reluctance drive is known to be fault tolerant, but it is not fault free. The goals of this study are the systematic classification of all electrical faults, short-and open-circuits, in the switched reluctance drive (excluding the controller itself), and the investigation of fault patterns and possible remediation. Each situation is analyzed via finite element analysis, and/or experiments. The transient effects during the faults are described. Possible remediation schemes other than disabling the faulted phase are explored. There is a particular focus on switch short-circuit for which new results are presented. <s> BIB003 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> This paper presents a novel method for diagnosis of eccentricity in a switched reluctance motor (SRM). The method employs two-dimensional finite-element analysis to calculate mutual fluxes and mutually induced voltages in an 8/6 SRM. An investigation of the effect of static eccentricity on these quantities shows that eccentricity has a considerable effect on them. Since flux measurement is costly, the method introduces mutual voltage as a suitable criterion for diagnosis of eccentricity in SRMs. <s> BIB004 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> A concept of an integrated and distributed inverter for switched reluctance machines is introduced. The application at hand is an outer-rotor direct drive designed for railway traction applications. A five-phase switched reluctance machine (SRM) was developed and is used to demonstrate the function of the integrated and distributed inverter. The distribution is achieved by supplying each phase coil with its own modular inverter. Each inverter module is placed evenly around the end of the stator stack next to its dedicated coil. This increases the redundancy of the drive significantly. The likelihood of phase-to-phase faults is reduced, because no overlapping end-turns are necessary. Also, the integration of machine and inverter is simplified, because the semiconductors can be evenly distributed around the machine. The concept reduces the amount of terminals between drive and vehicle to communication, power supply and cooling, independent of the number of machine phases. With the integrated and distributed inverter new control strategies can be developed to influence machine vibration and radiated noise. In this paper the design of the prototype, the direct torque control of the five-phase machine and the behavior in case of a fault inside a module is analyzed. <s> BIB005 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> In safety-critical systems, faults can cause life losses, environmental degradation, or significant financial losses. In this paper, a segmental stator switched reluctance machine is proposed for such applications. A short overview of its design is given. Its fault tolerance is investigated by dynamic simulations and laboratory tests. It is demonstrated via both methods that the proposed machine is able to have a continuous operation despite five severe winding fault conditions. <s> BIB006 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> Power converter plays a very important role in switched reluctance motor (SRM) systems, and it is also the easiest one to experience failures. Power converter faults will cause the motor to run in non equilibrium states, and a long time fault operation will lead to motor and other modules damaged, and make the system completely lose working stability. This paper uses an asymmetric bridge converter as the research object with three-phase SRM, employs the wavelet packet decomposition for the phase currents. It analyzes and studies the short circuit fault condition of IGBT, uses an energy discrete degree of the wavelet packet nodes as the fault characteristic, and conducts the corresponding experimental and simulation analysis to verify the effectiveness and practicality of the proposed method. <s> BIB007 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> Accurate fault identification allows the adoption of procedures that minimize the fault impact on the machines operation. Switched reluctance motors (SRMs) have been recognized for their fault-tolerant capabilities and they present a very robust configuration, particularly due to the absence of windings or magnets in the rotor. All these attributes make the SRM a competitive solution for aircraft and automotive applications, where systems reliability is a crucial feature. Therefore, in this paper, a new algorithm for real-time diagnosis of power converter faults in SRM drives is proposed. In contrast to other methods that use additional sensors or devices, the presented technique uses the measured phase currents only, which are already available for the drive control. The proposed algorithm effectively detects the inverter faulty phase and is capable to localize the faulty power switch. Power switch open-and short-circuit fault occurrences in an asymmetric full-bridge converter are considered and analyzed. <s> BIB008 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> A modular stator switched reluctance motor (SRM) for fault tolerant drive systems is proposed. Owing to the particular construction of the stator there is no mutual coupling between adjacent phases. Hence, the motor can work also when a part of the coils is faulted and the faulted modules can be replaced without uncoupling the machine from the load or gearbox. The sizing particularities are presented and the mathematical model of the motor is developed. The results obtained via finite element analysis are compared with the analytical ones, and with that resulting after testing the constructed laboratory model. All these prove that the proposed SRM can be used in safety–critical drives. <s> BIB009 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> 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. <s> BIB010 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> 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. <s> BIB011 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> 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. <s> BIB012 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> Reliability of power converters is of crucial importance in switched reluctance motor drives used for safety-critical applications. Open-circuit faults in power converters will cause the motor to run in unbalanced states, and if left untreated, they will lead to damage to the motor and power modules, and even cause a catastrophic failure of the whole drive system. This study is focused on using a single current sensor to detect open-circuit faults accurately. An asymmetrical half-bridge converter is considered in this study and the faults of single-phase open and two-phase open are analysed. Three different bus positions are defined. On the basis of a fast Fourier transform algorithm with Blackman window interpolation, the bus current spectrums before and after open-circuit faults are analysed in details. Their fault characteristics are extracted accurately by the normalisations of the phase fundamental frequency component and double phase fundamental frequency component, and the fault characteristics of the three bus detection schemes are also compared. The open-circuit faults can be located by finding the relationship between the bus current and rotor position. The effectiveness of the proposed diagnosis method is validated by the simulation results and experimental tests. <s> BIB013 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> Power converters are a key, but vulnerable component in switched reluctance motor (SRM) drives. In this paper, a new fault diagnosis scheme for SRM converters is proposed based on the wavelet packet decomposition (WPD) with a dc-link current sensor. Open- and short-circuit faults of the power switches in an asymmetrical half-bridge converter are analyzed in details. In order to obtain the fault signature from the phase currents, two pulse-width modulation signals with phase shift are injected into the lower-switches of the converter to extract the excitation current, and the WPD algorithm is then applied to the detected currents for fault diagnosis. Moreover, a discrete degree of the wavelet packet node energy is chosen as the fault coefficient. The converter faults can be diagnosed and located directly by determining the changes in the discrete degree from the detected currents. The proposed scheme requires only one current sensor in the dc link, while conventional methods need one sensor for each phase or additional detection circuits. The experimental results on a 750-W three-phase SRM are presented to confirm the effectiveness of the proposed fault diagnosis scheme. <s> BIB014 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> Switched reluctance motor (SRM) drives are one competitive technology for traction motor drives. This paper proposes a novel and flexible SRM fault-tolerant topology with fault diagnosis, fault tolerance, and advanced control functions. The converter is composed of a single-phase bridge and a relay network, based on the traditional asymmetrical half-bridge driving topology. When the SRM-driving system is subjected to fault conditions including open-circuit and short-circuit faults, the proposed converter starts its fault-diagnosis procedure to locate the fault. Based on the relay network, the faulty part can be bypassed by the single-phase bridge arm, while the single-phase bridge arm and the healthy part of the converter can form a fault-tolerant topology to sustain the driving operation. A fault-tolerant control strategy is developed to decrease the influence of the fault. Furthermore, the proposed fault-tolerant strategy can be applied to three-phase 12/8 SRM and four-phase 8/6 SRM. Simulation results in MATLAB/Simulink and experiments on a three-phase 12/8 SRM and a four-phase 8/6 SRM validate the effectiveness of the proposed strategy, which may have significant economic implications in traction drive systems. <s> BIB015 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> 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. <s> BIB016 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> In this paper a new on-line fault diagnostics technique of the occurrence of stator faults in an 8/6 Switched Reluctance Motor is proposed. To validate the proposed approach a dynamic model was developed in Matlab/Simulink environment, based on the utilization of a specific lookup table for each phase, obtained with FEMM. <s> BIB017 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> Winding insulation degradation may lead to phase-to-phase fault in switched reluctance machines (SRMs). First, the fault modes are described considering the connected sequence of the coils and the fault behaviours are analysed in details. Second, the equivalent circuit of three-phase windings is represented and the faulty SRM is modelled based on the derived electromechanical equations. Third, the locations of three current sensors are optimised to calculate the incoming line current and outgoing line current of each phase without utilisation of any extra hardware. The phase-to-phase fault can be detected and located by monitoring the residuals between the two line currents during motor operation. Forth, to improve the post-fault operation performance of the motor, a triple closed-loop control scheme aiming at suppressing the short-circuit current is conducted by modifying the switching states of power transistors. Finally, simulations and comparative experiments on a three-phase 12/8 structure SRM validate the effectiveness of the proposed methods. <s> BIB018 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> 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. <s> BIB019 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> This study is focused on a new approach of current profile computation to minimise switched reluctance motor (SRM) torque ripple both in healthy and one open phase fault condition. The analysis of static parameters by means of finite element method is carried out and it is verified by measurements. The mathematical model of SRM is described to simulate all transients. The new current profiling method is applied and tested for normal and faulty operation of a real SRM. The torque ripple is measured at a 10 kHz switching frequency. Lower torque ripple is obtained when compared with standard control methods, both under normal and open phase conditions. The simulations of diverse dynamic states are carried out and compared with experimental results. <s> BIB020 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> 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. <s> BIB021 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> 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. <s> BIB022 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> This study presents a generalised fault diagnosis method for power transistors in the asymmetric half-bridge power converter of switched reluctance motor (SRM) drive. In order to extract the remarkable fault features, three current sensors are rearranged. Each phase current can be calculated by solving the equations associated with the detected values of three current sensors and three coefficients obtained based on different switching states. Different faults are preliminarily detected by monitoring the error between the estimated bus current and the actual bus current. After the identification of fault occurrence, the error will be calculated with all the combinations of three coefficients. The minimum error will be found and the corresponding coefficients are recorded. The fault types and fault power transistors are located by comparing the actual coefficients with the recorded coefficients. Being different from the existing methods, the developed diagnostic strategy can detect multiple fault types and can be used in different control modes, including voltage pulse width modulation, current chopping control and angular position control schemes. Moreover, the proposed technique is easy for online implementation without extra sensors and additional electric devices. The effectiveness of the proposed solution is validated on a three-phase 12/8 SRM drive. <s> BIB023 </s> An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems <s> D. SUMMARY <s> This paper presents the design, analysis, prototype, and testing of a new fault tolerant electrical drive topology. The segmented rotor switched reluctance machine (S-SRM) has been modified to include permanent magnet assist by placing magnets in the stator slot opening. This introduces a magnetic bias which extends the magnetic operating region of the machine and results in greater torque when compared to the conventional fault tolerant segmental rotor switched reluctance machine. This new torque dense, fault tolerant topology was investigated using 2-D (two-dimensional) and 3-DFE methods and a prototype machine built, tested and verified against the simulations. Experimental testing was carried out with and without the magnets to assess the effect of the PM assist on torque performance. Static tests were carried out to obtain the torque—flux linkage—angle waveforms and then this information used to tune a bespoke drive and test the system under dynamic conditions. The superior fault tolerant performance of this PMA S-SRM topology is highlighted by measurements taken under phase open and short circuit fault conditions. The tests show that this fault-tolerant topology not only meets the mass requirements of the aerospace application, set originally by a PMSM, but also, with the magnets now placed on the stator the rotational induced EMFs and associated short circuit currents during a fault are drastically reduced. Hence the fault tolerance of this topology is an improvement on the PMSM topology, and it will be of benefit to fault critical systems such as aerospace drives and actuators. <s> BIB024
The summary and comparison of fault diagnosis methods mentioned above are presented in Table 1 with regard to superiorities, disadvantages, target fault types, and fault location ability. The mathematical transformation and digitizing method are commonly used in fault detection and the TE method is suitable for fault location. The first four methods, including the spectrum analysis, wavelet packet analysis, extended Kalman filter, and coordinate transformation, are classified as mathematical transformation, which have excellent accuracy and simple implementation. These methods generally use analytical formulas such as FFT BIB021 , BIB013 , wavelet packet decomposition BIB014 , BIB007 , and coordinate transformation BIB017 . However, complex analytical formulas usually accompany with a long time to deal with sampled signals, reducing the real-time performance. The following three methods, including current profiling, voltage profiling, and gate signal auxiliary, directly handle the digital signals from sensors and compare them with reference values or preset thresholds to detect and locate faults. Current profiling, voltage profiling, and differential current methods have high reliability with short fault detection time, which TABLE 1. Summary and comparison of the fault diagnosis techniques. VOLUME 7, 2019 can minimize the fault impacts BIB004 , BIB018 . Gate signals and phase currents are important features in faulty conditions, which can be acquired without extra devices. Combining these two signals improves the fault diagnosis process BIB023 . The above methods are feasible and effective, which have great potential for high-performance fault diagnosis. However, their fault location ability is limited, and additional operations to identify faulty components are required. Hence, the TE method is employed to precisely locate the faulty element. The phenomena are expected to be observed under certain artificial conditions, such as turning on the upper switch or injecting HF pulse to possible faulty winding to verify the assumptions BIB008 . Whereas, the secondary fault may occur due to large peak current when locating the shortcircuit fault. The tendency of the fault diagnosis methods is to equip with more accurate and fast response, more precise fault location, and on-line implementation on the basis of new fault diagnosis technique, fast fault detection algorithms, and advanced hardware. In mathematical transformation, reducing fault diagnosis time is a crucial problem, requiring simpler calculation and implementation. Digitizing methods need improvement in terms of complex algorithm of reconstructing currents and extra sensors. TE method may lead to fault spreading in the motor drive compared to other methods, which demands further improvements. In order to optimize the performance of the SRM drives under faults, different kinds of fault tolerance techniques are listed and comprehensively compared in Table 2 . The position signal assistance strategies are useful in fault-tolerant control. The position sensors can compensate each other for position sensor displacement fault BIB019 . The sensorless methods are also adopted for faults in position sensors and circuits BIB010 , BIB011 , BIB022 . Nevertheless, the position sensor assistance method mainly focuses on position signals acquisition without repairing the open-and shortcircuit fault, which needs other strategies for fault resilience. The hardware auxiliary is the most effective way to handle faults by adding redundant switches, modifying power converter, double coil banks, and optimized motor design. The redundant switches and relay networks are employed as the safety backup BIB015 , BIB016 and dual three-phase power converters combined with DCSRM BIB012 are used for open-and short-circuit fault tolerance. The double coil banks method is specially designed for single-phase SRM, providing the ability to mitigate the faulty impacts BIB001 , BIB024 . In terms of the optimized motor design, assistant PM embedded in the stator reduces the EMFs and consequently suppresses the peak current in short-circuit fault BIB009 . Segmental stator motor structure is also a good option in fault-tolerance control. The spacers in the stator serve as obstacles in the flux path, reducing the coupling effect among phases and impeding the fault spreading BIB006 , BIB020 . The current profiling strategies can also be used to maintain a steady operation during faults. The current commands are regulated by TSF function for torque ripple minimization BIB005 and the mathematical model is proposed for levitation force compensation BIB003 . Additionally, fuzzy logic control smooths the output torque by adjusting the conduction time with its self-adaptive ability BIB002 , [81]. As mentioned above, the future trends of the fault tolerance methods are predicted as follows. In position signal assistance strategies, either multiple position sensors or sensorless techniques need to be adopted. A more economical and simple position signal assistance strategy with reduced sensors and reliable algorithm is expected. Hardware auxiliary is the most common strategy in fault tolerance accompanying with high cost. On one hand, the novel topology of the power converter is desired with fewer extra devices. On the other hand, special motor design is also important in compensating faults. The intelligent algorithm is supposed to be simpler and easier to implement, reducing the calculation requirement for the controller. Generally, simple, reliable, robustness, and powerful fault tolerance strategies with fast response are the future trends.