Control Strategy of Three-phase Four-Leg Inverter under Unbalanced Load

In order to simplify the space vector pulse width modulation (SVPWM) of three-phase four-leg inverters under unbalanced loads, this paper presents a single carrier modulation method based on SVPWM, which can modulate the first three legs and the N-th leg separately. If SVPWM is used for the front three axle arms, trigonometric function calculation and sector determination are required.This means that the modulation become very difficult. The single carrier modulation strategy uses the action law of the switch to derive the corresponding modulation wave, and then compares the modulation wave with the carrier wave to obtain the corresponding switching signal. This process avoids a large number of trigonometric function calculations, greatly reduces the modulation difficulty. At the same time, the neutral voltage under unbalanced load is analyzed and derived, and the neutral voltage is controlled to the corresponding zero sequence voltage, so that the N-th bridge arm can be independently controlled. The final realization is to output three-phase symmetrical sinusoidal voltage under both balanced and unbalanced loads. Finally, the feasibility of the modulation technology is verified by simulation.