Discussions of parallel-connected five-level PWM inverters

Multi-level PWM inverters have significant advantages such as the ability to operate the motor with nearly sinusoidal current waveforms and higher output voltages. In order to increase the inverter size, the parallel connection method would be effective for the present. In high-power applications, for instance, the carriers should be synchronized to modulating sinusoidal waves. Moreover, for the interphase reactor, lower order harmonic application is prohibited. In practice, to improve the harmonic characteristic of the parallel-connected five-level inverters, various modulation strategies are devised and designed in this paper. It is found that the DC current flow of DC power supplies can be controlled by means of phase shifting of the injected third order harmonics or modifications of them. In the case of the SVC (static VAr compensator), by means of this technique, the output capacitor voltages could be controlled individually.