Abstract
The increase proportion of power converters causes stability problems in the radial grid. To address these issues, this paper firstly proposes a unified modeling procedure and applies it to two types of converters. Secondly, the impedance models are used to analyze the stability of a radial grid with converters under four cases. The influence of the short circuit ratio (SCR) and line impedance on system stability are investigated. Then, a comprehensive sensitivity analysis is performed in order to investigate the effects of parameters variations on the closed-loop poles of the system under different conditions. Finally, the accuracy of the model and theoretical analysis are verified by simulations and Hardware-in-the-Loop (HiL) tests.
Highlights
The increase proportion of power converters causes stability problems in the radial grid
The existing research mainly uses small signal modeling method to model converters. This method can be divided into two categories: time domain modeling method based on the state space model and frequency domain modeling method based on the impedance model [2]
The above research investigates the influence of short circuit ratio (SCR) and line impedance under four cases and analyzes parameter sensitivity, which provides a guideline for system design to avoid instability problems: 1) Grid-following converters are preferred to strong grid while grid-forming converters can be connected to weak grid
Summary
With the development of renewable energy generation system, the penetration of power converters in a radial grid increases significantly, which causes modeling and stability issues [1]. In [9], the unified modeling method of grid-following converter under threephase balance and three-phase unbalance condition was studied. Based on the impedance model of converters, many researchers study the stability of the distribution grid with converters. In [13], the stability indices and margins of two grid-following converters with different parameters, with different PLL bandwidths and power injections were studied and it provided a general design guideline of PLL bandwidths of two converters. The sensitivity analysis of impedance of power converters in a radial grid is still missing. In this respect, this paper aims to study the stability of a radial grid on considering the influence of different types of converters and line impedance.
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