Symmetrical Phase-Locked Loop and Power Control Loop for Grid-Connected Inverters

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Abstract
The stability of a grid-connected inverter (GCI) under weak grid can be assessed by checking whether the return ratio matrix satisfies the generalized Nyquist criterion. Due to the inherent asymmetry of the phase-locked loop (PLL) and power control loop (PCL), the eigenvalues of the return ratio matrix are complex, imposing challenges in stability analysis and parameter design of the PLL and PCL. In this article, the symmetrical PLL and PCL structures are proposed, and then a complex-vector-based model of the system is obtained, simplifying the loop-gain-based stability analysis. After that, a step-by-step parameter design method for the symmetrical PLL and PCL is presented. Experimental validation is finally conducted on a 10-kVA three-phase LCL-type GCI prototype in the lab. The results demonstrate the effectiveness of the proposed symmetrical PLL and PCL as well as the parameter design method.
Funding Information
  • National Natural Science Foundation of China (52077101)
  • Jiangsu Province 333 Program for Excellent Talents (BRA2020039)
  • Science and Technology Project of China Southern Power Grid (SEPRI-K23B081)

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