Objectives In view of the problems that the capacity of the independent microgrid system of wind- Photovoltaic(PV) -battery on the offshore platform is small, and the intermittent power generation of new energy and load surge (bilateral randomness) have a significant impact on the stable operation of the weak-grid microgrid system, the equivalent impedance analysis method on the grid-interface converter is adopted. It is proposed to add capacitor voltage feedforward control in the wind or PV inverter for changing its output equivalent impedance to eliminate the influence of the bilateral randomness on the stability of the independent microgrid system on the offshore platform.

Methods Firstly, the circuit structure of the wind-PV-battery microgrid system on the offshore platform is constructed. A mixed operation mode of master-slave and peer-to-peer is adopted: the energy storage unit is used as the main power source to stabilize the grid voltage; the inverters of each energy storage sub-unit adopt power droop control to achieve the peer-to-peer operation mode, and the wind and PV power generation units are used as slave power sources. Then, for the influence of the bilateral randomness of the system on the system stability, the microgrid system equivalent model and the inverter model are established, and the stability characteristics of the system are analyzed from the inverter device level and the microgrid system level. Finally, the implementation method of the capacitor voltage feedforward control of the new energy inverter is determined, and the related mechanism of weakening the LCL resonance, improving the phase angle stability margin and reducing the influence of the inductive current on the stability of the bus voltage in the weak grid is analyzed.

Results The results show that the capacitor voltage feedforward adopted in the control of the wind-PV inverter has the capacitor characteristic, and its leading phase angle characteristic can increase the phase angle margin of the inverter by 13.8°, effectively improving the stability of the new energy power generation device connected to the weak grid.

Conclusions This method has important theoretical significance and application prospects for improving the stability of the independent microgrid system of wind-PV-battery on the offshore platform.