Current ripple reduction of aircraft start generators in the starting mode with variable switching frequency method

This paper proposes a method of variable switching frequency pulse-width-modulation (PWM) to suppress current ripple when aircraft start generator (SG) operates in the starting mode. Compared with the widely used constant switching frequency PWM, the method can work evidently, especially in the range of low speed. Based on analysis of dead-time effects in the two-level voltage source inverter, relationship between the three-phase voltage error and dead time is acquired. Through adjusting switching frequency of switching devices with the SG speed, the dead-time effects can be weakened in order to reduce voltage distortion and current ripple. The proposed method is applied to a 75kVA SG drive system and implemented in a digital signal processor (DSP). Simulation and experimental results demonstrate the effectiveness of the proposed method.