Open-loop-based Island-mode Voltage Control Method for Single-phase Grid-tied Inverter with Minimized LC Filter

This paper proposes an island-mode voltage control method by using an open-loop control applying a high-gain disturbance observer (DOB) for a single-phase inverter with a low capacitance output filter. The output voltage is distorted with the low capacitance by the conventional method which consists of a PID regulator for an automatic voltage regulator (AVR) and a PI regulator for an automatic current regulator (ACR). In order to compensate the output voltage distortion, the high-gain DOB for the output voltage is applied in the open-loop-based voltage control. DOB is implemented into a field-programmable gate array (FPGA) with high-speed sampling. In the LC filter of a 1-kW prototype, the impedance of the inductor is minimized to 1.0% of the normalized inverter impedance, whereas the admittance of the capacitor is reduced to 0.25% of the normalized inverter admittance. By the proposed method, the inverter output voltage total harmonic distortion (THD) is reduced by 82.4% even with the diode rectifier load compared to the conventional voltage control, whereas the constant output voltage is achieved regardless of any conditions of load.