Fault-Tolerant Operation Of Four Switch Three Phase Inverter Fed PMSM DTC System

Permanent Magnet Synchronous Motor (PMSM) features high power density and high power factor, direct torque control (DTC) is famous for its simplicity and fast torque response, therefore, PMSM DTC systems, with the advantages of both, are widely applied in electric vehicles, military, home appliances and many other fields, and their reliabilities have been paid more and more attention. PMSM DTC system usually use voltage source inverter, due to the frangibility of the power electronic devices, various faults could occur in the inverter. Because DTC considers motor and inverter as a whole for control, inverter faults could result in lossing the operation ability for drive system. So it's necessary to conduct a in-depth study of fault-tolerant operation for inverter faults. Compared to other inverter fault-tolerant schemes, three-phase four-switch inverter costs less and has better performance, so in this thesis three-phase four-switch inverter is selected for fault-tolerant operation. Deterioration of power supply added to the inherent large torque ripple of DTC makes the ripple of torque even more prominent. So it is urgent to solve the contradiction of dynamic and static characteristics under the new condition of power supply, namely suppressing of torque ripple while basically maintaining the fast dynamic response. This thesis's main work include:1. Three-phase four-switch inverter fed PMSM conventional DTC. based on the operation of three-phase six-switch inverter fed PMSM conventional DTC, the voltage space vector and the corresponding switch table is redefined for three-phase four-switch inverter by analyzing its topology. Finally three-phase four-switch inverter fed PMSM conventional DTC is realized.2. Three-phase four-switch inverter fed PMSM SVPWM-DTC. By the inspiration of the fact that the technique of Space Vector Pulse Width Modulation (SVPWM) is able to reduce the torque ripple significantly in the three-phase six-switch inverter system, SVWPM is introduced in the three-phase four-switch inverter to optimize the performance of drive system.3. Three-phase four-switch inverter fed PMSM SMC-DTC. Sliding mode control features outstanding merits of good interference rejection, good robustness, and it's applicable for nonlinear control, and it is introduced for the three-phase four-switch inverter to realize the SMC-DTC strategy. The control results are compared with theSVPWM-DTC.4. Suppression of DC bus capacitor voltage imbalance and the calculation under theunbalance condition. The motor winding corresponding to the fault phase of theinverter is connected to the midpoint of the two dc-link capacitors in series, and alongwith capacitor charging and discharging, the voltage will change. Simulation analysisand experimental study are performed under the unbalance condition in this thesis.