| Abstract |
Nowadays, current-controlled methods (CCM) are widely used to improve the performance of DC-AC converters in distributed generation (DG) units connected to the power distribution system. However, serious stability problems can occur when this unit switches to an operation mode off-grid. In this situation, it is preferred to change the control mode of DG units to a voltage-controlled method (VCM). This paper proposes an improved method to control, in a coordinated way, the voltage and current supplied by a single-phase inverter. When the inverter operates in tied-grid mode, an LCL filter is used to reduce the harmonic content of the current. On the other hand, when the inverter operates in islanding mode, an LCLC filter reduces the harmonic content of the voltage. For each operation mode, a Proportional-Integral (PI) controller is designed using the Robust Loop Shaping (RLS) method. The DG unit using the proposed method can be switched between tied-grid and islanding modes at any time, maintaining the quality of the supplied electrical power. Simulated results are provided to verify the feasibility of the proposed approach. |
