An efficient method for small-signal stability assessment of P − ƒ/Q − V̇ droop control in an isolated micro-grid

Abstract

An efficient method for small-signal stability assessment of P − ƒ/Q − V droop control methods for multiple converters in an isolated micro-grid (MG) is proposed in this paper. A MG model described with arbitrary number of converters is explored first. If there are more number of converters in a chosen MG, only dominant eigenvalues related to droop control are of primary interest. Therefore, constructing a reduced-order model to speed up the small-signal stability assessment becomes necessary. By extending the previous work of MG with P − ƒ/Q − V droop control, a reduced-order model of MG with P − ƒ/Q − V droop control is investigated under mild assumptions. Such a simplified model will facilitate to compute the poles and zeros of the closed-loop systems and provide more physical insight to examine the relationship between dominant eigenvalues and each droop control gain. As the mathematical analysis of conventional P − ƒ/Q − V droop control provides the characteristic polynomials contributed by P − ƒ and Q − V droop controls, the P − ƒ/Q − V droop control also provides a similar characteristic polynomials contributed by P − ƒ and Q − V droop controls. These characteristic polynomials of the system helps MG operators for better tuning of each droop gain for stable operation of MG. A detailed study of actual plant model and the reduced-order plant model are investigated. Both simulation and experimental results are presented to validate the proposed method.