Abstract-There are more large-scale PV plants being established in rural areas due to availability of low priced land. However, distribution grids in such areas traditionally have feeders with low X/R ratios, which makes the independent reactive power compensation method less effective on voltage regulation. Consequently, upstream Step Voltage Regulator (SVR) may suffer from excessive tap operations with PV induced fast voltage fluctuations. Although a battery energy storage system (BESS) can successfully smooth PV generation, frequent charge/discharge will substantially affect its cost effectiveness. In this paper, a real-time method is designed to coordinate PV inverters and BESS for voltage regulation. To keep up with fast fluctuations of PV power, this method will be executed in each 5s control cycle. In addition, charging/discharging power of BESS is adaptively retuned by an active adjustment method in order to avoid BESS premature energy exhaustion in a long run. Finally, through a voltage margin control scheme, the upstream SVR and downstream PV inverters and BESS are coordinated for voltage regulation without any communication. This research is validated via an RTDS-MatLab co-simulation platform, and it will provide valuable insights and applicable strategies to both utilities and PV owners for large-scale PV farm integration into rural networks.Index Terms--Coordinated voltage control, photovoltaic (PV), battery energy storage system (BESS), real-time control, state of charge (SOC) regulation.

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Most traditional Var compensation-based voltage regulation methods are developed following the single-phase Volt-Var response rule. These methods typically have competent voltage regulation performance with balanced photovoltaic (PV) integration. However, certain randomness of single-phase rooftop PV installation may lead to significant PV power imbalance across three phases, especially in low voltage (LV) distribution systems. In such unbalanced situations, unintended inter-phase Volt-Var response which is ignored in the single-phase Volt-Var response rule will become significant and greatly challenge the effectiveness of the traditional methods on voltage regulation. This can further cause inverter saturation and consequently makes distribution systems vulnerable to overvoltage problems. In this paper, the mathematical equations of unbalanced three-phase Volt-Var response are first derived and analyzed to identify the strong MVE (mutual Var compensation effect) and the weak MVE. This analysis provides the theoretical foundation for the development of the proposed interphase coordinated consensus algorithm, which can successfully overcome PV imbalance-induced voltage regulation challenges (e.g. inverter saturation and network overvoltage), while does not need exact system parameters. The effectiveness of this method has been validated by time-series simulations with a real LV distribution system and recorded data.

Understanding power system dynamics is essential for online stability assessment and control applications. Global positioning system-synchronised phasor measurement units and frequency disturbance recorders (FDRs) make power system dynamics visible and deliver an accurate picture of the overall operation condition to system operators. However, in the actual field implementations, some measurement data can be inaccessible for various reasons, for example, most notably failure of communication. In this study, a measurement-based approach is proposed to estimate the missing power system dynamics. Specifically, a correlation coefficient index is proposed to describe the correlation relationship between different measurements. Then, the auto-regressive with exogenous input identification model is employed to estimate the missing system dynamic response. The US Eastern Interconnection is utilised in this study as a case study. The robustness of the correlation approach is verified by a wide variety of case studies as well. Finally, the proposed correlation approach is applied to the real FDR data for power system dynamic response estimation. The results indicate that the correlation approach could help select better input locations and thus improve the response estimation accuracy.

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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.