Voltage Control and Power-Shortage Mode Switch of PV Inverter in the Islanded Microgrid Without Other Energy Sources

The growing installation capacity of distributed photovoltaic inverter needs change of the operation method in the modern power grid. Recently, to better integrate into the grid, the active power control is investigated in photovoltaic inverter. Meanwhile, without energy storage, the photovoltaic inverter can use voltage control method to further support the grid voltage and frequency. Due to the stochastic photovoltaic power, the mode switch is needed when the maximum power still cannot meet the grid demands. The operation of PV inverter in this power shortage mode has not been sufficiently studied. Therefore, this paper investigates the mode switch method for voltage-controlled two-stage photovoltaic inverter. The power conversion principle of synchronous generator is realized in the inverter and the dc/dc converter maintains the dc-side voltage. The mode switch method between normal operation and power-shortage state is proposed. With this method, the PV inverter can real-time adjust the output power of photovoltaic battery and match the load demand without support from other energy source even under PV output power's intense change.