Abstract:

Based on the popular 125 kW power conversion system (PCS) module in the current market,considering the grid impedance factor,the mathematical modeling and the impedance analysis of a single energy storage PCS and a multi-machine parallel PCS system in the grid-connected operation mode are implemented.The suppression method of multi-machine parallel resonance in the grid-connected operation mode is studied.The system side impedance of multiple PCS parallel systems is analyzed from the point of common connection,and the change of grid-connected current is analyzed by superposition principle.It is found that the coupling between the line impedance of the power grid and PCS is the key to the resonance problem of the system.The harmonic peak suppression of passive damping is analyzed,and an active damping control strategy is proposed to provide virtual damping by optimizing the capacitor current sampling feedback link.Finally,the simulation is carried out by Simulink.The results show that the THD is reduced from 9.67 % to 2.02 % under the grid-connected operation mode of 125 kW PCS multi-machine parallel system with active damping control strategy,and the resonance peak of grid-connected current is well suppressed.

Key words: power conversion system (PCS), grid-connected operation, multi-machine parallel connection, resonance, active damping