Determination of an ideal ripple injection technique for high performance multi-pulse rectifiers

The derivation of an optimal ripple injection technique for multi-pulse rectifiers operating on variable frequency aerospace supplies is presented. This is determined by analysing the multi-level PWM operating mode of a 12-pulse rectifier that uses a bidirectional switch to modify its behaviour. The resultant line currents are almost sinusoidal, the THD being 1.06%. The injector current is 2.5% of the load current. The principle of the multi-level PWM injection mode, idealised waveforms and the determination of the ideal ripple injection are explained and experimental results obtained with a 4 kW prototype are presented.