Research On Multirate Sampling Digital Control System Of Permanent Magnet Motor

With the advantages of high efficiency and high power density, Permanent Magnet Synchronous Motor (PMSM) has been widely applied in rail transit. That high power traction driving system requires low switch frequency in order to reduce switching losses, which makes digital control inherent delay problem become more prominent. Delay problem had a bad influence on the system’s characteristics. When the motor is running in the high-speed domain, it may lead to system instability. In other hand, In order to improve the utilization ratio of DC voltage, high power traction driving system usually worked in Six-step operation. However, during the six-step operation, there is only one degree of freedom for the inverter output:the phase angle of the voltage. Conventional vector control strategy is incompatible with the six-step operation, which also bring difficulty to flux weakening control.In this paper, mathematical model of permanent magnet synchronous motor was established first, and then, gave an outline of the vector control. In order to Smoothed transition to six-step operation, a synchronous over-modulation algorithm based on the Basic Bus Clamping Strategy (BBCS) was applied.Digital delay problems are analyzed theoretically. Then, the modeling analysis of the multirate sampling digital control system is carried out. At last, put forward a delay compensation method based on state observer, the system response speed and decoupling performance under lower switching frequency are improved effectively.Aimed at conventional vector control strategy is incompatible with the six-step operation, used a voltage phase control method. Avoiding conflict between the two PI controllers, ensure the control of at full speed range.A simulation model and a 300kW PMSM traction drive system experimental platform based on TMS320VC33 is built. The experiment results show that the proposed scheme is feasible.