Voltage support strategies in a rural low voltage network with high photovoltaic penetration

Abstract

The rapidly increasing penetration of rooftop PV systems in rural LV distribution networks calls for the attention of DNOs in order to secure end-user voltage range. In times of high photovoltaic generation and low load consumption, voltage at PCCs may exceed the specified upper limit and make PV inverters trip. This phenomenon hinders further PV integration in the network although MV/LV transformer and conductors are by far not used up to their full capacity yet. In this thesis, voltage rise problem is analysed through load flows and simulations on a suitably designed rural test network model implemented in PowerFactory software. The suggested local voltage support strategies by the German directive VDE-AR-N 4105 and the recent European standard EN 50438, namely PF(P) and Q(V), which require reactive power control capability of photovoltaic inverters, are implemented, tested and analysed in order to check their effectiveness and compare their behaviour. As active power curtailment capability is also already required by some DNOs, a dynamic active power curtailment control algorithm is designed and tested as well, taking into account the local load demand and the network’s feed-in limitations. Afterwards, local battery storage is also incorporated in every PV system model and all the three aforementioned strategies are tested and analysed again. All studied strategies manage to mitigate the voltage rise problem up to a PV-integration level of 10 kW/household. However, their effectiveness is compared in terms of a set of evaluation criteria for a range of PV-integration levels. Subsequently, the best candidate strategy, among the ones studied, emerges through the help of experts’ opinion and a suitably designed overall evaluation score number, for both the perspectives of a DNO and a PV system owner. It is revealed that the overall preference of a DNO is for a solution which involves active power curtailment and local storage, in contrast to the overall preference of a PV system owner for a reactive power based strategy without storage.