Capacitor Voltage Balancing Pulsewidth Modulation Method for a Single DC Source Driven Cascaded Three-level Inverter Drive

Cascaded retrofit of two, two-level inverters can generate three-level output voltage space vector alike the neutral-point clamped (NPC) three-level inverter. This topology however demands two isolated DC power sources to power the inverter drive system. The, input DC-link capacitor voltages of the cascaded three-level inverter drive are theoretically analysed to determine the neutral-point voltage fluctuations. Based on the study, a new carrier based pulsewidth modulation (CBPWM) method is proposed for this cascaded three-level inverter that is thoughtfully devised to balance the DC-link capacitor voltages. Sensing one of the DC-link capacitor voltages, suitable offset-voltage to be injected with the sinusoidal modulating signals are identified that manage to balance the capacitor voltages of the inverter drive obviating the need of two isolated DC power sources. Hence, the envisaged offset injected CBPWM enables the cascaded three-level inverter drive to be driven from a single DC power source. The proposed CBPWM for the single DC source drive is simulated and is also validated experimentally. Furthermore, superior computational performance of the proposed CBPWM is also demonstrated.