Parallel operation of photovoltaic inverters with autonomous voltage control strategies - comparison of Q(V)/P(V) and automatic voltage limitation

A major issue for distribution system operators is to maintain voltage quality in their networks. This holds especially for networks with high local PV penetration. In times of high solar irradiation, reverse power flows can lead to voltage rises and violations of voltage limits at critical nodes. Inverter-based autonomous voltage control strategies can be applied to mitigate voltage violations in distribution systems. In this study, two autonomous voltage control strategies for PV-inverters, Q(V)/P(V) and automatic voltage limitation, are investigated. The investigated control approaches are implemented in the control loop of real PV inverters from "Triphase". The stability, voltage support - and load-sharing capability of two parallel operated inverters with proposed local control strategies have been investigated in laboratory environment. As results, both control strategies could successfully mitigate voltage rises under parallel operation. The load-sharing capability of two inverters, however, can be significantly influenced by the grid impedance and voltage filter time constant of the inverter.