Space-vector PWM voltage control with optimized switching strategy

Since space vector modulation offers superior performance with respect to other modulation techniques, it is important to establish the sequencing strategy which is best suited for variable-frequency AC drives. The characteristics of regular direct-direct (DD) and inverted direct-inverse (DI) sequencing strategies are investigated both analytically and experimentally. The two strategies are compared with respect to the current ripple, the current spectrum, and the commutation losses. It was found that DD sequence offers superior performance for the majority of loads, such as induction motor drives. For other types of inverter loads, with small or leading power factors, the optimal modulation strategy consists in using the DI sequence when the output voltage is low and the DD sequence if the modulation index is between m(M) and 1. For best results, the switch-over point M has to be evaluated as a function of load and inverter design