Capacitor voltage controls of novel five-level inverter having only double DC power supplies

The five-level PWM inverter has many advantages such as ability to operate the AC motors or the power compensator with very large capacity in nearly sinusoidal current waveforms. For these reasons, these applications have just begun to study. However, this circuit must provide four DC power supplies for supplying the active power. In this paper, we propose a novel double power supply method, in which both power supplies are inter-connected by DC capacitors. The voltages of the inter-connected DC capacitor are controlled by a novel third order harmonic injection method, where the phase of modified third order harmonic signal having positive or negative polarity is controlled individually