Abstract:

In response to the inherent neutral point voltage imbalance problem in type-I three-level power conversion system (PCS),the principle of neutral point voltage imbalance is analyzed based on space vector modulation,and a hybrid modulation strategy is proposed combining seven segment space vector pulse width modulation (SVPWM) with five segment SVPWM.When the neutral point voltage offset is large,the seven segment SVPWM with balance factor is used to quickly adjust the neutral point voltage.When the neutral point voltage offset is small,the five segment SVPWM without switching at high current is adopted to effectively reduce the switching times of the switch and reduce the loss.A 12 kW PCS prototype is built.The experiments show that compared with the traditional seven segment SVPWM,the neutral point voltage offset and fluctuation of the hybrid modulation strategy is reduced,and the efficiency of the prototype is improved by about 0.3%.The correctness and effectiveness of the proposed hybrid modulation strategy are verified.

Key words: three-level power conversion system, neutral point voltage imbalance, space vector modulation, hybrid modulation strategy