Influence of PLL Parameters on Small-Signal Stability of Microgrids with Synchronous Generators

Hybrid microgrids (MGs) with both renewable energy sources (RESs) and diesel-generator sets are used to guarantee the continuity of power supply in remote areas with no access to electricity networks. RESs are commonly interfaced by using electronic power converters with their control system based on a current controller and phase-locked loop (PLL). When connected to MGs, these control loops interact with the control systems of diesel generators and there is almost no information in the literature assessing this interaction. Furthermore, small-signal stability studies of MGs including detailed models of diesel generators based on synchronous machines are scarce. In this paper, a small-signal model of a hybrid MG is developed. It includes a synchronous generator (SG) with damper windings that is driven by a diesel engine and a voltage source converter (VSC) that uses a PLL to synchronise with the SG. The impact of the PLL parameters on the MG eigenvalues is analysed. Transient responses obtained from theoretical models are verified in a laboratory set-up.