A New Remote Tap Position Estimation Approach for Open-Delta Step-Voltage Regulator in a Photovoltaic Integrated Distribution Network

Abstract

With the saturation of rooftop PV installations in urban regions, an increasing tendency of mega-watt scale PV applications in rural areas has emerged, which makes voltage regulation in these areas more complicated. Presently, in distribution networks, step-voltage regulators (SVRs) and onload tap-changers (OLTCs) are the main voltage control devices for effective mitigation of voltage variations [6]. In long rural feeders, open-delta SVRs are commonly installed into distribution networks to maintain line voltage when dealing with slowly changing loads [7][8]. However, due to cloud transients, PV power can fluctuate more quickly and frequently than customer loads [9]. As a result, SVRs may suffer from excessive tap changes.Currently, there are two main categories of research on tap operations in the solar PV integration area: 1) interaction between solar PV systems and tap operations (PV-Tap) [10][11][12]; 2) coordinated voltage control of PV inverters and voltage regulators (e.g., SVR, OLTC) to mitigate excessive tap operations caused by PV power fluctuations [13][14][15]. However, these researches mostly involve theoretical studies based on simulation, and the use of actual tap positions is rare since tap positions are usually not accessible to customers. As for utilities, although they do have access to actual tap positions for relevant research, it is still difficult to obtain reliable and high-resolution tap information since SVRs are normally situated in rural networks with poor communication [16]. This situation can be improved by installing dedicated communication and data storage systems to SVR monitoring, however this will be a very expensive modification for SVRs in remote areas. Hence, it is hard to economically investigate PV-Tap interactions, let alone to develop and implement new PV-SVR coordination strategies for more effective voltage regulation. Further, in rural feeders with high PV penetration the variability of PV generation has already put a tremendous pressure for the remote open-delta SVRs, therefore, there is a genuine need on visibility of SVR taps from both utilities (monitoring and researching excessive tap changes) and PV owners (fulfilling connection agreement on the voltage regulation aspect):i. The actual tap record can assist utilities to schedule maintenance service according to the amount of tap changes instead of the traditional fixed period asset management based on empirical estimation. Timely maintenance can help to avoid unnecessary SVR downtime, which ultimately improves reliability.

An Average Voltage Approach to Control Energy Storage Device and Tap Changing Transformers Under High Distributed Generation

“…However, when distribution feeders being supplied are long, there will be no appropriate fixed reference voltage that can keep the voltage at the furthest points above the minimum prescribed voltage limit, hence SVRs are introduced. The operation of an SVR is similar to that of an OLTC, where they change tap position to keep a local voltage or a remote voltage, estimated through LDC, within defined margins based on a pre-set and fixed reference voltage [31]. However, the OLTC is located at the substation where distribution feeders emanate, and SVRs are installed along a feeder where voltage magnitudes start to drop below the minimum prescribed voltage.…”

An Excessive Tap Operation Evaluation Approach for Unbalanced Distribution Networks With High PV Penetration

“…load changes [8][9][10]. However, with more PV integrated into rural areas, PV power fluctuations can lead to considerable voltage variations due to high R/X ratio in distribution networks [11], which further result in excessive tap operations.…”

Coordinated Strategy for Controlling Multiple SVRs in Distribution Systems with Photovoltaics Using Moving Average Filters

“…[5] modeled open‐delta SVRs, while OPF‐based optimal control strategies were discussed from the viewpoint of optimization techniques in Refs [17, 18]. As a dedicated communication system is normally necessary for advanced centralized control, state estimation techniques that do not depend on direct communication [6,19,20] and distributed control schemes [21] have been proposed.…”