Frequency Division Compensation Method for Phase Margin of Grid Connected Converters in the Weak Grid
Under the condition of weak grid,aiming at the interaction between the control links of grid connected converter and the grid impedance,which is easy to cause system oscillation and instability,this paper proposes a frequency division phase compensation control strategy.First,the output admittance matrix model of grid connected converter in dq coordinate is established.In view of the negative damping characteristics of the output admittance of the converter caused by the phase-locked loop(PLL)in the low frequency band,the influence path of the PLL on the control system is analyzed without changing the dynamic characteristics of the PLL.The compensation matrix containing integral elements is added to offset the negative damping effects of the PLL,and the admittance model is simplified at the same time.Furthermore,the compensation matrix containing only constant elements is introduced to achieve advance correction,and phase compensation is carried out for the negative damping outside the current loop bandwidth,so that the admittance matrix elements are positive real parts in the full frequency band,providing positive damping for the grid connected control system,thus enhancing the stability of the grid connected converter.Finally,the proposed compensation scheme is verified by simulation and experiments under different short-circuit ratios,which proves the effectiveness of the proposed scheme.
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