低开关频率下异步电机电流环的数字控制

Discrete-time Current Controller for Induction Motors at Low Switching Frequency

电流环数字控制在异步电机矢量控制系统中占有非常重要的地位,其性能的优劣直接影响电机转矩与磁链解耦控制效果、输出转矩响应速度,甚至牵引变流器–异步电机系统稳定性。而在大功率传动系统中,为降低开关器件损耗,牵引变流器开关频率通常较低,从而产生较大数字控制延时,加剧电机定子电流励磁分量与转矩分量之间的耦合程度。为解决上述问题,文章全面分析异步电机耦合因素,结合零极点对消原理提出一种改进型离散电流控制器,在离散时间域下,不仅确保电流环系统具有良好的动态响应,而且可以实现定子电流转矩分量与励磁分量的有效解耦。模型仿真与实验验证了改进型离散电流控制器的有效性与可行性。

Discrete-time current controller plays an important role in vector control of induction motors, which affects the decoupling effect of motor torque and flux, output torque response and even the stability of converter-motor system. However, in high power AC drive system, the traction converter often operates at low switching frequency to reduce the dynamic losses of the power devices, which leads to large digital control delay, enhancing the induction motor dq axis current cross coupling. In order to overcome the problem, this paper provided a comprehensive analysis of the induction motor coupling factors. Then using the principle of zero-pole cancellation, an improved discrete current controller was proposed, which not only ensures excellent dynamic performance but also cancels cross coupling between the torque component and flux component of stator current in the discrete-time domain. The results of model simulation and experiment prove the validity and feasibility of improved discrete current controller.