Stability Analysis of Phase Locked Loop Controllers for Grid Tied Inverters in Weak Microgrids

Abstract

This paper analyses, the effect of the phase locked loop (PLL) controller in the stability of the voltage source converter(VSC) in a microgrid or when connected to a weak AC grid. While designing the controller for PLL, it may not be possible to consider the effect of the load and line impedance as they are not readily known. In a microgrid or in a weak grid, the dynamics of the PLL are affected due to the high impedance nature of the network. A small signal model is built to show how the PLL controller affects the stability of the VSC. A comparison is made between proportional (P) and proportionalintegral (PI) controller, using detailed time domain simulation in PSCAD/EMTDC to demonstrate this problem.

Remote Micro-Grid Synchronization Without Measurements at the Point of Common Coupling

“…The analysis in this paper was done with the application of a conventional SRF PLL algorithm. In the proposed grid synchronization application, this PLL is suitable for stable symmetric states in the MG and the UG, a case mentioned in [27] and [28]. If severe asymmetrical disturbances, such as ground faults or two phase short circuits occur in the UG or the MG, then such an algorithm may not be suitable for the proposed synchronization, cf.…”