Optimal power control strategies for neutral point clamped (NPC) inverter topology

A programmed pulse-width modulation (PWM) technique for selectively eliminating several lower order harmonics at the output of a neutral point clamped (NPC) inverter topology is investigated. The switching function approach is utilized to derive relevant analytical expressions for input/output variables. An evaluation of the NPC inverter topology based on the switching function approach is described. Optimal power control strategies are proposed for an NPC inverter using programmed PWM patterns. For a constant-frequency variable-voltage NPC inverter power supply, the proposed strategy is to maintain a minimum specified total harmonic distortion using a low-impedance output filter. In the case of an NPC inverter powering an AC motor drive, the proposed strategy is to maintain a minimum specified harmonic current factor. The power control strategies are achieved without substantial increase in inverter switching frequency and are therefore suitable for high-power applications using gate turn-off (GTO)-type devices.<<ETX>>