Adjustable harmonic mitigation for grid-connected photovoltaic system utilizing surplus capacity of utility interactive inverter

Increasing nonlinear loads result in a voltage distortion on an electric power distribution line. Installation of an active filter can be one of the solutions to mitigate the line voltage distortion, but it requires additional costs. On the other hand, many photovoltaic (PV) systems become interconnected to the distribution system in Japan. There is some surplus capacity of the inverter in accordance with variations of the PV array output. Therefore, it is useful to apply some additional functions such as power quality enhancement to the inverter. This paper deals with a new harmonic mitigation method by the inverter of the PV system based on an adjustable harmonics compensation method. First, the inverter decides a sinusoidal current output in order to inject the solar energy into the power system as the active power. Then, by the surplus of the inverter capacity, it also outputs a compensating current in order to mitigate a voltage distortion at a load terminal. Therefore, the inverter can realize effective harmonic voltage mitigation within its rated capacity. Following discussions explain the control system, and confirms its compensation and operation characteristics under various situations.