Distributed Generation Inverter: New control Strategies to Supply Local Load with Standard Voltage under Distorted Grid Voltage

In this paper, two control strategies are proposed for distributed generation inverter (DGI) to control 1) active power exchange with the grid, 2) load voltage and 3) grid current. The main goal in these strategies is supplying local load with a standard sinusoidal voltage in the presence of grid voltage distortions and load current nonlinearity. In conventional DGIs, the load is directly and without intermediate impedance connected to the grid; thus, the possibility of load feeding with appropriate voltage quality is hindered in the grid connected mode. In order to overcome this deficiency, DGI with an LC-L filter topology and two control strategies are presented in this paper to supply the local load with standard voltage and to exchang power with the grid, simultaneously. In the first control strategy, the local load is supplied with pure sinusoidal voltage and grid current quality is not important. In the second control strategy, load voltage waveform and grid current waveform are controlled by adding appropriate harmonics to load voltage. For the implementation of the mentioned control strategies, a cascade power-voltage-current control structure has been proposed. A new controller has been introduced in the stationary reference frame for the voltage loop which gives the opportunity for compensation and tracking of harmonics without the need for complex and vast calculations. Test results under nonlinear load and non-ideal grid conditions validate that the proposed method can supply the local load with a standard voltage, inject power to the grid, and also control the grid current.