Investigation Of Inverter Fault-Tolerant Direct Torque Control For Permanent Magnet Synchronous Motor

Permanent Magnetic Synchronous Motor (PMSM) is well known as the most potential electrical drive element in the industries due to its high power density, high efficiency and high power factor, which tends to lower the life cycle cost even thought this type of motor drive is generally more expensive than induction motors. In the last few decades, the PMSM drives have been used in many applications where the high-performance motion control is very important and essential. Most of the past research on variable speed PMSM drives mainly concentrated on the development of the efficient control algorithms for high performance drives. However, the costs, simplicity, flexibility, especially the reliability of the overall drive system, are the most important aspects that did not get much concern to the researchers.One of the most important high performance control strategy for PMSM motors is the Direct Torque Control (DTC), which is widely used in some important control system, such as industry, business machine and transportation for its simplicity and quick torque response. The safety and reliability of the system are highly required as the expansion of its application, especially in some important fields.Permanent Magnetic Synchronous Motor Direct Torque Control (PMSM DTC) system is normally fed by a Six-Switch Three-Phase Inverter (SSTPI), which is one of the most important and fragile parts in the AC drive system where faults could easily occur. If the inverter faults happened, the whole system will lose its normal operation capability which is not allowed in the very important applications such as electric vehicle and some military equipment driven by a PMSM DTC system. For this reason, the investigation of inverter faults detection and diagnosis, the enhanced performance" operation of post-fault PMSM DTC system are quite essential and necessary to be investigated, which forms the main objective of this dissertation.The dissertation is divided into 7 chapters, which is organized as follows. ●Chapter 1 is the introduction, where the high performance control scheme of PMSM, direct torque control of PM Motor, inverter fault diagnosis schemes, fault-tolerant operation of PMSM DTC System and enhanced high performance operation of fault-tolerant PMSM drive system are all discussed and analyzed through literature review. And the dissertation is finally outlined.●Chapter 2 presents the basic theory of direct torque control strategy and its implementation on the permanent magnet synchronous motors, explained and verified by experiment study. Some inverter faults are analyzed and simulated successively.●Chapter 3 has reviewed some inverter faults diagnosis schemes presented in the literature firstly and the Adaptive Neural-Fuzzy System (ANFTS) method is discussed with the measured current as the only signal directly adopted for fault diagnosis. The single inverter fault, such as open-switch, short-switch, open-phase and short-phase faults can be effectively, directly detected and diagnosed by the proposed intelligent approach ANFIS.●Chapter 4 reviews different inverter fault-tolerant topologies that had been proposed in the literature and finally the Switch-Redundant topology is considered as the most appropriate fault-tolerant topology to be applied in PMSM DTC. Also, the operation principle of the potential fault-tolerant PMSM DTC is investigated in detail and verified successfully by both simulation and experiment.●Chapter 5 discusses the operation performance and some problems associated with the post faulted PMSM DTC system supplied by a Four-Switch Three-Phase Inverter (FSTPI), such as relatively large ripples in electromagnetic torque and stator flux linkage. Detailed simulation and experimental test verify that with the proposed fault-tolerant scheme, the PMSM DTC drive system is able to maintain its stable steady state operation with a slightly degraded performance. ●Chapter 6 introduces some high performance operation techniques to enhance the performance of the PMSM DTC fed by FSTPI, such as Perpendicular Flux Observer, Space Voltage Modulation (SVM) and Sliding Mode Control (SMC). Among them, the SMC is the most important measure of high performance operation for a FSTPI fed PMSM DTC system. Furthermore, some improvements on the SVM and the SMC techniques are proposed.●Chapter 7 is the conclusions for the present work and some suggestions for future work.