An analysis of constant R.M.S. current ripple PWM control for permanent magnet AC drives

This paper presents a method to predict and control current ripple in permanent magnet AC drives. First, analytical expressions for the switching-period current ripple are determined in the synchronous reference frame. These are then used to determine closed form expressions for fundamental-cycle averaged current ripple. The technique described is applicable to salient and non-salient pole permanent magnet machines under PWM inverter control using conventional space vector or sinusoidal carrier-based modulation. The use of the analytical expressions developed is then investigated to control inverter current ripple by variable switching frequency modulation. An electric vehicle simulation case study is used to demonstrate potential benefits in terms of reduced inverter switching loss while motor current ripple is controlled at near a desired value. It is also shown that inverter semi-conductor device junction temperature-cycling can be reduced using the proposed method.