A new SVPWM method for single-phase three-level NPC inverter and the control method of neutral point voltage balance

A space vector PWM (SVPWM) algorithm is proposed for the single-phase three-level NPC inverter, and the cause of the imbalance of the capacitor voltage in DC-side is analyzed. In order to lower the switching loss and avoid the abrupt change of output voltage vectors, an optimal SVPWM algorithm is proposed, it makes use of five-vectors modulation in which the positive (or negative) small vectors are used as the first output vector. The strategy of changing the voltage adjusting coefficient to adjust the effective time of the positive and the negative small vectors to control the neutral point potential balance is proposed, which is based on the detection of the direction of the load current and the capacitor voltage. The control of DC link neutral-point potential is easy to implement. The validity of the new SVPWM method is verified by simulation and experiment with a three-level MOSFET inverter.