Compatible Selective Harmonic Elimination for Three-Phase Four-Wire NPC Inverter with DC-Link Capacitor Voltage Balancing

In this article, a compatible selective harmonic elimination pulsewidth modulation (CSHE-PWM) is designed for the three-leg four-wire (3L/4W) neutral-point-clamped (NPC) inverter. The proposed CSHE-PWM is capable of eliminating both triplen and nontriplen harmonics from phase voltages and empowers the 3L/4W NPC to handle both single-/three-phase and linear/nonlinear loads. It has been mathematically proven that dc capacitors self-voltage balancing is achieved thanks to the direct control of the phase voltage waveform symmetry. Moreover, the cancellation of specified triplen and nontriplen orders has the advantage of having low capacitor voltage ripple. Therefore, the applied technique not only helps removing one leg of the inverter that reduces associate complex calculations and switching losses, but also directly controls phase voltage harmonic profile compared with SHE-PWM for the four-leg four-wire NPC. CSHE-PWM is practically tested on an NPC inverter prototype to validate the efficient harmonic elimination from the phase voltage waveforms along with capacitor voltages balancing under symmetrical/asymmetrical loads.