Impedance shaping of grid-connected three-phase PV systems

The growing demand for clean energy sources has driven the insertion of photovoltaics (PV) in low-voltage networks. However, the non-dispatchable nature of these units can produce instability issues like voltage fluctuations or frequency deviation. It can be worse if these units are connected to a weak network. One way to overcome this problem is to impose suitable impedance values on PV inverter. However, it is hard to shape the PV output impedance by simply adjusting its control loop gains. For that reason, this paper proposes a method for shaping the PV output impedance by using a virtual impedance scheme, which can be designed independently of the PV control system. With the proposed method, the stability margin of grid-connected system can be increased by imposing desirable PV output impedance. Experimental results validate the proposed impedance shaping strategy.