Comparitive Analysis of Frequency Support Provided by Grid-Forming and Grid-Following PVs

Abstract

Widespread Photovoltaics (PVs), which are seen by a distribution network (or an isolated microgrid) as a constant power injecting source, can be detrimental to the frequency stability of the network. To assist in frequency regulation and response, the constant current control for a Distributed Energy Resource is substantially modified to provide inertial response within the low voltage network. PVs that deploy inertial control require an additional storage in order to cater to the demand supply balance. This approach is feasible for large scale PVs, however, rooftop PVs possess limited flexibility for additional storage. This paper studies case of a low-voltage networked microgrid with an appreciable PV penetration, in the presence of a diesel generator (DG) as a separate bus. A coordinated control for PV is designed in this paper, which can help in the transition in between the grid-forming mode to the grid-following modes (with the inertial control loop acting as the Phase locked loop), with the help of an auxiliary DC link voltage based control which is designed in a way that does not require any switching action.