Control device of the neutral point clamp type inverter

摘要

PURPOSE:To control the fluctuation of the potential at a neutral point even in a low-frequency region without complicated control systems and without increasing capacity. CONSTITUTION:In a control device for a three-phase neutral-point-clamp type inverter, which outputs a voltage corresponding to a voltage reference in every phase by using PWM control, a mode determining part 2 and a voltage-reference converting part 3 are provided. The mode determining part 2 switches a positive- polarity mode and a negative-polarity mode at every constant polarity switching period. When the mode is switched to the positive-polarity mode, the voltage reference is converted into the voltage reference so that the polarity of the voltage reference becomes positive for all three phases or becomes zero for only one phase and becomes positive for the other two phases. When the mode is switched to the negative polarity mode, the voltage reference is converted into the voltage reference so that the polarity is negative for a 11 three phases or becomes zero for only one phase and becomes negative for the other two phases. The voltage reference converting part 3 alternately outputs the respective voltage references. Thus, the fluctuation of the potential at the neutral point can be suppressed.