High Power Permanent Magnet Synchronous Traction Motor Torque Close-Loop Control Based On Stator Flux Observation

Permanent Magnet Synchronous Motor (PMSM) needs to be controlled according to the torque command in traction drive system. Common PMSM torque control methods such as the look-up table method and the formula calculation torque closed-loop control method are affected by the changing motor inductance parameters. The torque is not accurate. High power traction driving system needs to keep low switching frequency because of switching devices limit, and needs to transit to six step mode because of the dc side voltage limit. The voltage asymmetry of traditional over modulation method is serious. Using voltage phase control in six step mode can expand the speed range even the voltage is saturated. According to the above problem, this thesis does the research of torque observation and PMSM torque control in full speed range.This thesis establishes the state observer based on PMSM expand flux mathematical model at first. Expand flux state observer observes the expand flux by PMSM voltage, current and speed. Then the stator flux is calculated according to the expand flux. The observed stator flux is not affected by PMSM inductance parameters. Then the poles assignment according to the demand of the permanent magnet synchronous traction drive system is carried out. Observer simulation model is built, which proves the observed stator flux convergence and parameter robustness.Electromagnetic torque is calculated by stator current and stator flux. The accuracy of the stator current and stator flux are not affected by the motor inductance parameters, so the estimate torque is not affected by inductance parameters, which assures the accuracy of the torque closed loop feedback. In order to reduce the loss of traction drive system, analyze the MTPA current control strategy. In order to increase the speed when the inverter voltage is saturated, adopt the method of voltage phase control. Based on the above analysis, the thesis proposes a permanent magnet synchronous traction system torque close loop control scheme in full speed range. Verifies the scheme by simulation. The case of torque control affecting by inductance parameters changing has been analyzed. In addition, to ensure the modulation transition from linear region to six step mode, a non-constant carrier frequency SVPWM is proposed. The method and the basic bus bar clamp modulation is analyzed and experimented.Set up A 300kW PMSM experiment platform based on the TMS320VC33 controller. At first verify the accuracy of the observation flux and torque based on extend flux observer. Then put the observation torque as a feedback, the experiment of constant torque closed loop control in steady state and dynamic state have been done. At last, the experiment of the motor torque closed loop control of steady state and dynamic state in full speed range have been done. The experiment results verify that the torque closed-loop control scheme proposed by this thesis control the torque well in full speed range.