Unified Framework for the Analysis of the Effect of Control Policies on Automatic Voltage Regulators

With the advent of smart grids, voltage fluctuation has increased, especially in active distribution networks with a high penetration of distributed energy resources and a large deployment of electric vehicles. In this context, on-load tap-changer (OLTC) distribution transformers have become a key component, mainly because they provide automatic voltage regulation capability. In order to maximise the lifetime of OLTC devices, the number of tap operations should be minimised, avoiding unnecessary changes, but ensuring the main requirement: to keep the voltage within the limits permitted. Therefore, when the automatic mode is active, the control policy followed by the automatic voltage regulator is decisive. This paper presents a novel form of functional approximation of these policies. Furthermore, by means of a unified framework, a methodology for the simulation of policies based on control theory is proposed. The unified framework has been validated using real data. The results confirm the ability of the introduced framework to simulate different scenarios, optimising and validating both existing and new policies by observing their effect on transformer behavior. In addition, it allows the determination of the best fit policies depending on characteristics such as the pre-selected voltage set point or the voltage variation between transformer taps.