改善直接转矩控制性能的SVPWM方法

针对异步电动机直接转矩控制系统存在转矩和磁链脉动、器件开关频率不定等缺点,提出一种直接转矩空间矢量脉宽调制(SVPWM)预测控制方法。根据转矩和定子磁链的误差,通过驱使误差为零的原则确定参考电压矢量,然后利用SVPWM合成该矢量。由于采样时刻的电压和磁链误差,可在下一个控制周期内得到补偿,因此转矩和磁链的误差始终很小,二者的脉动很小。SVPWM算法保证了逆变器的开关频率恒定。仿真和实验的结果表明,利用这种方法在低于3kHz的恒定开关频率下,可以实现定子磁链近似为圆、异步电机电磁转矩脉动不明显的性能。

SVPWM method for performance improvement of direct torque control

A SVPWM (space vector pulse width modulation) predictive control method was developed to solve the problems of direct torque control (DTC) for induction motors related to the uncertainty of the switching frequency, the flux ripple, and the torque ripple. A u-n model is used to determine the actual stator flux and the torque and flux errors so that the method can then calculate the reference voltage space vector that can compensate for the errors. Finally the reference vector is then synthesized by a SVPWM algorithm. The voltage and flux errors at the sampling instant can then be compensated for in the next control period, so the errors are always kept small, which leads to small fluxes and torque ripple. The SVPWM algorithm keeps the switching frequency constant. Simulations and experiments show that torque and flux ripples are small with a constant switching frequency of less than 3 kHz.