Inverter Fault Tolerant Study Of PMSM DTC System

Permanent Magnetic Synchronous Motor (PMSM) is well known due to its high power density, high efficiency and high power factor. Direct Torque Control (DTC) is widely used in the areas such as industry, business machine and transportation for its simplicity and quick torque response. The safety and reliability of the system is highly required as the expansion of its application, especially in some important areas.Permanent Magnetic Synchronous Motor Direct Torque Control (PMSM DTC) system is fed by an inverter, which reduces the possibility of motor faults but the inverter faults still happen frequently. The direct torque control system controls the motor and the inverter as a whole, which means the whole system can lose its operation capability when inverter faults happen. For this reason, the investigation of fault tolerant operation with inverter faults is very necessary.The inverter faults, which happen the most, is analyzed in the dissertation firstly, then the three phase four switch inverter (TPFSI) topology, which has a good performance while saving the cost, is chosen as system topology after fault tolerant operation. The performance of TPFSI PMSM DTC system is investigated and the scheme of space vector modulation (SVM) is used to improve its operation performance. At last, in fault condition, the switching process from six switches to four switches of an inverter and uninterrupted operation are achievedMain work in the dissertation is presented as follows:1. Redefine the voltage vectors. The DTC is based on the choosing of the proper voltage vectors. The crucial difference between a six switch inverter system and a four switch inverter system is the different voltage vectors provided by the inverters. Base on the detailed analysis of the topology of TPFSI feds system, the voltage vectors are redefined after the analysis of motor phase voltage under different switch conditions.2. Establish a new voltage switching table, and based on which, simulation and experiment study of TPFSI fed PMSM DTC system are performed. The control scheme of flux linkage and torque is analyzed to establish the new voltage switching table based on the redefinition of voltage vectors; the system is modeled for the purpose of simulation analysis. Finally the hardware system is built up for the experiment study. The experiment results verified the feasibility of using TPFSI system as the system topology in the post-fault operation.3. Performance improvement. Zero vector composition technique is adopted for a four switch inverter to provide the equivalent zero vector. Then SVM scheme is adopted to solve the high torque ripple problem. Simulation analysis is used to study the performance of various SVM schemes; and a improved scheme is chosen to apply for the fault tolerant system. Experiment results show that this improved SVM scheme can reduce the torque ripple and improve the performance greatly.4. Experiment study of switching process from three phase six switch inverter system to a three phase four switch inverter system is performed, which verified the feasibility of PMSM DTC inverter fault tolerant operation.