| The Hybrid Electric Vehicle(HEV), which is considered as a new energy-saving product of automotive industry to solve the problem of energy and environment, becomes the research hot spot of the world automobile industry. The Permanent Magnet Synchronous Motor(PMSM), which has high power density and good timing performance, becomes the first choice for the HEV drive motor. So, the research on control strategy for PMSM has high theoretical and practical significance. At present, the Field Oriented Control(FOC) and Direct Torque Control(DTC) are two typical control schemes in the field of AC drive.FOC system has complex structure and high control precision, runs smooth in steady state. The common current control strategies have id=0 control and MTPA control. Establish system models of the two strategies by applying the MATLAB/Simulink simulation software. Analysis finds that the MTPA control more complicated than id=0 control, but has the advantage of making full use of the magnetic resistance torque. Because of the limitation of inverter performance, the torque will decline rapidly if the motor continues to speed up after reaching base speed. In order to broaden the motor speed range, put forward the use of field weakening method to optimize system when motor above the base speed. Establish system model of field weakening control. In result, the thesis gets the simulation waveforms of torque, rotating speed and three phase current. Analysis shows that the path of motor current vector reaches the pre-designed field weakening locus.DTC system has simple structure, fast dynamic response and good robustness to parameters. But the conventional pure integral flux observer has cumulative error caused by integral initial value and DC component, lead to the large ripple of the motor torque and flux linkage. In order to improve the stability of the system, put forward two improved flux observers: the first-order low-pass filter and the amplitude limited compensation integrator, present the algorithm designs. According to the results of Simulink simulation model, analysis shows that first-order low-pass filter exist flux observation distortion when motor runs in low speed, and DTC system based on the amplitude limited compensation flux observation observes more accurate flux value, reduces the ripple of torque and flux linkage effectively, is helpful for the stable running of the control system.Finally, based on dSPACE semi-physical simulation platform, build the algorithm control models of FOC and DTC, and analyze the results. Through physical motor control experiment, verify the feasibility and effectiveness of the improved schemes proposed in this paper. |
