A coordinated controlling strategy in current and power quality for grid-connected inverter under unbalanced grid voltage

When the grid is under the condition of unbalanced voltage, the problems such as the inverter output active and reactive power oscillation, output power quality degradation and overcurrent can be occurred. In order to overcome these problems, there are three different controlling targets: balancing current, suppressing active power as well as reactive power fluctuation. According to the instantaneous power theory, it is impossible to achieve all controlling targets simultaneously. This paper proposed a grid-connected inverter current quality/power coordinated controlling strategy. The method which uses the IPSO algorithm to set the weight coefficient considers the current balance, the active power and the reactive power fluctuation comprehensively. Simultaneously, the output current can be limited to the maximum output current of the inverter. On this basis, the grid-connected model predictive current controlling strategy based on the reference voltage is established to realize the fast and accurate tracking of the reference current. The simulation results show that the proposed method can coordinate the inverter output current balance, suppress the active power and the reactive power fluctuation oscillation, as well as effectively limit the current peak.