A Generalized-Impedance Based Stability Criterion for Three-Phase Grid-Connected Voltage Source Converters

TL;DR

This paper introduces a generalized-impedance based stability criterion for three-phase grid-connected VSCs that effectively accounts for coupling terms, improving stability analysis accuracy and considering PLL effects, validated through HIL simulation.

Contribution

It proposes a new stability criterion using generalized-impedances to handle coupling in three-phase VSCs, enhancing analysis accuracy over traditional methods.

Findings

The new criterion effectively handles coupling terms in impedance matrices.

PLL parameters significantly influence system stability.

Validation confirms the criterion's effectiveness through HIL simulation.

Abstract

The output impedance matrices of three-phase grid-connected voltage source converters (VSCs) are widely used in power system stability analysis. Regardless of how the impedance is modeled, there always exist coupling terms in the impedance matrix, which makes the system a multi-input- multi-output (MIMO) system. Some approximation approaches omit the coupling terms so that a three-phase system can be treated like a single-phase one, and the impedance-based stability criterion for a single-input-single-output (SISO) system is applicable. However, such handling may result in analytical errors or even incorrect conclusions in a mirror frequency coupled system. By introducing the concept of generalized- impedances, this letter proposes a new stability criterion based on a virtual SISO system, which can effectively handle the coupling terms. Further, the effects of the phase-locked-loop (PLL) parameters on system stability are studied based on the proposed criterion. The effectiveness of the proposed criterion is verified by a hardware-in-the-loop (HIL) simulation based on RT-LAB.