An Improved Virtual Synchronous Generator Control Strategy Considering Unbalanced Load and Line Parameters

Unbalanced load connected to the microgrid will cause the three-phase output voltage of the VSG to lose symmetry. In addition, the mismatch of parameters in multi-machine parallel lines will create circulating currents between parallel VSGs, which will also increase voltage fluctuations in the microgrid. This will reduce the stability of the operation. To address the issues of circulating current and voltage fluctuations caused by imbalanced load and line parameters, an improved VSG control strategy considering imbalanced load and line parameters is proposed. By using a second-order generalized integrator to decompose the three-phase voltage into the positive sequence, negative sequence, and zero sequence components, the positive sequence voltage component is introduced into the excitation voltage control loop to eliminate low-frequency fluctuations caused by asymmetric loads. At the same time, negative sequence voltage is introduced into the voltage and current control loop, and voltage compensation is introduced in the voltage control process. The three-phase voltage asymmetry caused by load asymmetry and mismatched line parameters is reduced by adjusting the voltage compensation amount according to the changes in load and correcting reactive power. The circulating current between parallel VSGs is also suppressed. Simulation and experimental results have confirmed that the proposed strategy solves the virtual VSG voltage imbalance and multi-machine circulating current problems caused by load and line parameter imbalance and improves the stability of microgrid operation.