Control technology for grid-forming energy storage under unbalanced working conditions of weak current networks
The impedance inside weak current network is large,and when unbalanced loads are connected,it is unable to maintain the stability of its own voltage,resulting in three-phase voltage imbalance and output power fluctuations.Virtual synchronous generator(VSG)technology,as a grid-forming control,can provide support for voltage of the weak current network.However,under the connection of unbalanced loads,the VSG technology cannot maintain output voltage balance.To solve this problem,an improved VSG sequence decoupling control strategy is proposed.Firstly,the principle of three-phase imbalance and power fluctuation in VSG output voltage caused by unbalanced load connection is investigated.Secondly,a dual synchronous coordinate system decoupling(DDSRF)is adopted to separate the positive and negative sequence voltages of the power grid,and a positive and negative sequence control strategy is employed to control the negative sequence voltage component in dq rotating coordinate system.Finally,a VSG simulation model is built and the simulation results indicate that the proposed improved VSG sequential decoupling control strategy can suppress the unbalanced voltage output of the VSGs.
grid-forming controlenergy storageVSGunbalanced control
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