Research on paralleled three-phase four-leg voltage source inverters based on dual-loop control in αβo coordinate

This paper presents a dual-loop control scheme in αβo coordinates for paralleled three-phase four-leg voltage source inverters. Using α-β-o coordinate, output voltages of the inverter can be controlled in each channel (αβo) independently as the voltage component in relating to the inductor in the fourth leg only exists in o-channel. The use of interleaving for paralleled three-phase four-leg inverter would contribute to harmonic cancellation. For control loop, a proportional-resonant regulator in the outer loop and a proportional regulator in the inner loop are incorporated. Meanwhile a state observer for estimating the output voltage and inductor current in each channel is introduced to compensate one time-step delay of the system. The performance of proposed control scheme is verified by experimental results.