An improved modulation strategy is proposed to reduce the switching loss and balance the NP voltage simultaneously. Firstly, a novel zero sequence injection method is presented to generate P-type and N-type switching sequence based on the carrier based PWM (CB-PWM). With this method, the switch status of one leg is fixed during half of grid voltage fundamental period, so the switching loss is reduced. Then, to further reduce the switching loss, a new switching function is proposed to realize only one switching status changing in a switching sequence. In addition, the NP voltage balance is maintained by selecting P-type or N-type switching sequence.