Diagnosis And Fault-tolerant Control Of Underwater Permanent Magnet Synchronous Motor

Due to the small size, high efficiency, small torque ripple and the low inertia, permanent magnet synchronous motor has been widely applied in various industry fields. The inverter, the core of the motor drive system, is closely relevant with the reliability of the driver. Therefore, the motor drive system with fault diagnosis and tolerance system has been brought to the forefront of the research. In this paper, as to the open fault of the inverter, several methods about fault detection and tolerance are elaborated.In the first place, the paper introduces and analyzes the switch mode method and the simple current mothed. Tested by the simulation and experiment, these two methods have the drawbacks — the extra sensors and mistaken diagnosis in mutation load. In order to overcome these shortcomings, this paper proposes a normalized current method based on current Park vector. The experimental result shows that this way can eliminate the influence of the changeable load. Nevertheless, since the offset of the current in the nonfault phase, the fault-locating may be mistaken. For this, a new fault detecttion method is needed.In the second place, multi-switch fault diagnosis method, which uses the average absolute value of the current to avoid the influence of the offset current, is put forward to overcome the mistaken diagnosis above. Besides, this technique can also diagnose the multi-switch open fault. Simulation and experiment demonstrates that this method is valid and dependable with the fault diagnosis.Next, in order to detect the intermittent fault, this paper contributes the fuzzy theory to the multi-switch fault diagnosis method. Accroding to the open time, the method gives the fault degree of the inverter. However, the multi-switch intermittent fault cannot detect by this technique.Then, when the system detects the open fault, this paper makes use of the threephase four-switch topology to do the fault-tolerance control. The paper expounds the method to generate the 4-sector SVPWM and compares the torque ripple in 4-dual SVPWM and 7-dual SVPWM using Simulink. Also, some experiments show that this three-phase four-switch topology is effective in fault-tolerance control, but this method need higher bus voltage in big load compared with the normal three-phase six-switch topology.Finally, for the motor with neutral point extraction, this paper proposes a three-phase four-bridge topology and two-phase four-switch topology. Through the analyze, the SVPWM methods are respectively similar to three-phase six-switch topology and threephase four-switch, so the additional algorithm is not needed. When using the control method 4)(9= 0, the phase between the two phase current is 60°. However, there is inherent defect due to the larger current amplitude. The simulation result shows this topology is valid to fault-tolerance control.