An enhancement method ensuring robust passive impedance of LCL-type grid connected converter

Voltage source converters are essential in renewable energy power systems. For LCL-type voltage source converters, the stable operation of itself can be ensured through proper active damping control. However, the impedance interaction with a weak grid can further threaten the stability. To overcome this, shaping a passive output impedance of a converter is an effective and promising solution for power system to integrate more renewables energies. Traditional ideal passivity shaping methods have limited margins and can be sensitive to time delays or parameter fluctuations, posing instability risks in practical operation. To this end, a passivity enhancement method is proposed to ensure a robust passive output impedance of the converter in this article. It can be used to compensate for the vulnerable region of the passive output impedance. First, the risk of ideal passivity control is analyzed. Next, the principle and structure of the passivity enhancement method are presented. Furthermore, the parameter design methods and procedure are studied, followed by a practical design example. Finally, the effectiveness of the proposed method is verified by experimental results.