Research on Customer-Side Microgrid Inverters for Grid-Connected Non-Export Operation

To address two key issues caused by the disorderly connection of high-penetration photovoltaic (PV) grid-connected devices to low-voltage distribution networks, power quality deterioration and bidirectional active power flow, the latter of which may cause voltage violations, protection mis-operation, and metering errors, existing conventional control strategies for grid-connected inverters, such as droop control, active and reactive Power control, Virtual Synchronous Generator control, and Voltage and Frequency control, cannot simultaneously solve these two problems. To address this issue, this study proposes a customer-side microgrid grid-connected inverter device and its command signal calculation method. The method compares the load active current with the active current calculated based on PV output, load demand, and energy storage state of charge (SOC) to generate per-phase command currents, strictly limiting active power to flow from the grid to local loads, thereby achieving grid-connected non-export operation. The device has four operating modes: power quality compensation, bidirectional power supply, unidirectional power supply, and nighttime charging. MATLAB/Simulink simulations show that the proposed device can suppress the grid-side current total harmonic distortion (THD) below 5%, with a mode-switching response time of only 10–30 ms. Under load step changes, the grid active current remains zero, and reverse power flow is completely eliminated in all operating modes.