Small-Signal Analysis of a Hybrid Microgrid with High PV Penetration

Abstract

This paper presents small signal stability analysis of a hybrid microgrid from three different aspects. First, a generalized droop control of interlinking converter (ILC) is proposed which defines voltage and frequency droops at its terminals to achieve a bidirectional, autonomous power flow between grids. The impact of the droop gains on the stability is discussed and an operational range is defined for a stable system operation. Second, contrary to previous literature which have modeled the ac and dc grids by ideal sources and converters, the ac grid in this scheme is represented as a second-order synchronous generator and the dc grid is modeled as a PV system so as to analyze the dc grid dynamics in detail. It is observed that the dc link capacitor and inductor filter can lead to large system oscillations which can compromise stability. Third, the stability of the hybrid grid is analyzed from the aspect of short circuit ratio (SCR). Both rectifier and inverter mode of operation are used to understand how stability is affected with strength of ac grid. The time-domain simulations in PSCAD are used to confirm the validity of results obtained in frequency domain.