Analysis of AC-DC-AC converter with shared legs under unbalanced conditions

This work analyses a three-phase AC-DC-AC converter under unbalanced conditions of load power and grid voltages. The converter is composed of one three-leg AC-DC- AC converter per phase, with the three shared legs connected to the load neutral-point, in this way there is a three-wire grid and a four-wire load. A control strategy is proposed to perform the DC- link voltage control by injecting a negative sequence component in the grid currents. An additional control employs the commonmode voltage to redistribute power among phases and minimize the requirement of negative-sequence current. Converter model and pulse-width modulation were presented as well as steady- state power analysis. Experimental results validates the feasibility of the proposed strategy. Compared with the conventional control strategy, the proposed one increases the range of operation of the converter in unbalanced scenarios.