Parallel Operation of Transformers With on Load Tap Changer and Photovoltaic Systems With Reactive Power Control

In recent years, the number of active grid components for voltage regulation in distribution grids has increased significantly. Besides voltage regulators, such as transformers with on load tap changers (OLTCs), distributed generators can provide a certain voltage support by means of reactive power control (RPC). The different control entities, OLTC, and RPC by photovoltaic (PV) systems, usually operate based on local measurements and control characteristics. Hence, unintended interactions between the control entities cannot be excluded in general. This paper analyzes the parallel operation of OLTC transformers with a voltage-based control and PV systems with different RPC strategies (e.g., Watt/power factor control PF(P), volt/var control (Q(V)) in a distribution system environment. The focus is on unintended interactions, such as an increase of OLTC switching operations by PV RPC. The contribution and novelty of this paper is to raise awareness for the likelihood of these unintended interactions and to provide a first methodology to assess the parallel operation of OLTC control and PV RPC in detail. The results show that the impact of PV RPC on the number of OLTC switching operations and the effectiveness in parallel operation can differ considerably between the applied PV RPC strategies.