Research on control strategy of off-grid three-phase four-leg inverter under unbalanced load
In view of the fluctuations caused by unbalanced load under off-grid conditions,the advantages of three-phase four-leg topology in the application of unbalanced system are applied,combined with the control strategy of virtual synchronous machine,and the positive and negative sequence separation method based on all-pass filter is adopted to control.Aiming at the problems that the real output of active power will fluctuate the power frequency regulator and the power equalization and circulating current suppression effect is poor when multiple inverters are connected in parallel,a virtual impedance is introduced,improved parallel pre synchroniza-tion control strategy for virtual synchronous machines based on positive and negative sequence separation.The results show that the proposed control controller can maintain the balance of output voltage under unbalanced load,improve the power equalization accura-cy,suppress the circulation current,and enhance the operating performance under off-grid conditions.
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