低载波比工况下永磁同步电机磁链矢量轨迹分析

Flux Linkage Vector Trajectory of Permanent Magnet Synchronous Machines Under Low Carrier Ratio Condition

永磁同步电机采用空间矢量脉宽调制控制时,每个PWM周期内施加适当的电压矢量(包括电压矢量的模值、相位及作用时间)。通常情况下电机的每个基波周期内包含多个PWM周期,因此电压矢量的积分会产生一个多边形的磁链矢量运行轨迹,接近于圆形轨迹。但是,当载波比(即PWM频率与电机基波频率之比)较低时,气隙磁链矢量的多边形运行轨迹的边数很少,远远偏离于圆形,导致电流矢量的运行轨迹也偏离圆形,从而使得相电流波形畸变、电机的矢量控制性能恶化。本文将对比分析常规三相永磁同步电机和双三相永磁同步电机的数学模型、电压矢量的合成以及磁链矢量的轨迹特性,为在低载波比工况下改善电机的控制性能提供理论依据。

When a permanent magnet synchronous machine(PMSM)runs under SVPWM-based vector control,during each PWM cycle,a voltage vector with proper magnitude,phase angle and time interval is determined and applied on the machine.Integration of the voltage vectors will make the flux linkage vector,of which the trajectory is a polygon.Usually,there are many PWM cycles within each fundamental cycle,hence,the polygon is close to a circle.However,when the carrier ratio which is the ratio of the PWM frequency to the machine fundamental frequency is low,the polygon has few edges thus is far away from a circle,and so is the trajectory of the current vector.Consequently,the phase current waveform is distorted,and the vector control performance is deteriorated.In this paper,the common three-phase PMSM and the dual-three-phase PMSM were comparatively studied,in aspects of their models,synthesis of voltage vectors,and the characteristics of the flux linkage vector trajectories,so that the PMSM control performance under low carrier ratio condition can be improved.