Improved Quasi-PCI Control Strategy of Inverter with Unbalanced Load

Since there is no grid supply, the microgrid inverters have to provide high-quality power for various load. However, the output characteristics of the inverter are easily affected by the load, especially under unbalanced load conditions, the three-phase output voltages will be asymmetrical without a good control strategy. In order to solve the influence of unbalanced load on the inverter, this paper proposes an improved quasi proportional complex integral (IQPCI) control strategy, which can not only reduce the steady-state error of tracking ac signals, but also effectively suppress voltage unbalance components. On the one hand, the mathematical model of the four-leg inverter is established. The double closed-loop control method is used in αβ0 stationary frame, and the working characteristics of the IQPCI controller are analyzed. On the other hand, the influences of controller parameters on the system performance are analyzed by the bode diagrams, and the design and verification of the parameters are also carried out. Finally, simulation of the inverter with unbalanced load is carried out, moreover, the correctness of the proposed control strategy and the selected controllers parameters are verified.