Parallel-connected five-level PWM inverters

Multilevel PWM inverters have significant advantages over the conventional one because of the capability of operating the motor with nearly sinusoidal current waveforms and higher output voltages. In order to increase the power rating of the inverter, connection in parallel would be effective in the present case. In high-power applications, for instance, the carriers should be synchronized to the modulating sinusoidal waves. Moreover, for the interphase reactor, lower order harmonic application is prohibited. In practice, to improve the harmonic characteristics of the parallel-connected five-level inverter, two modulation strategies have been devised and designed in this paper. It is found that the DC current flow through the DC power supplies can be controlled by means of phase shifting of the injected third order harmonics. In the case of a static VAr compensator (SVC), the output capacitor voltages can be controlled by means of this technique.