This article presents a new device named flexible step-voltage regulator (FSVR) based on a multiwinding transformer for unbalanced distribution networks. While the traditional step-voltage regulator ...(SVR) can be used to control the voltage magnitude only, the proposed device can be used to control both voltage magnitude and phase angle for each phase independently. This allows greater flexibility during voltage control in unbalanced distribution networks. A mathematical model of the FSVR is derived for implementation in unbalanced power flow analysis. Simulation studies for IEEE 13 bus and IEEE 34 bus test networks demonstrate the effectiveness of the FSVR over the traditional SVR in reducing real power losses and voltage imbalance in the distribution network. A scaled-down model of the FSVR is designed in the lab to demonstrate the proof of concept.
This paper presents industrial insights into on-line robust local tap changer runaway inhibition issues in renewable distributed energy resources (DERs)-rich reconfigurable distribution networks with ...step-voltage regulators (SVRs). Based on the industrial insights, an algorithm is proposed for on-line robust local bi-directional inhibition of runaway events from only one tap change with robustness guarantees and without the need for coordinated test tap changes in cascade SVRs. The main contributions of the paper are the innovative application of the algorithm on on-line robust local bi-directional inhibition of tap changer runaway and the introduction to the industrial insights. The accuracy and robustness of the proposed algorithm are verified by time-series flow power simulation tests conducted on two test networks, with noise and gross errors in measurements, using extensive Monte Carlo simulations. Uncoordinated operation of test tap changes in cascade SVRs is examined through case studies on an actual long rural distribution network. Finally, the effect of photovoltaic (PV) power output variability on the proposed algorithm performance is assessed.
This paper develops a branch-flow-based optimal power flow (OPF) problem for multi-phase distribution networks that allows for tap selection of wye, closed delta, and open delta step-voltage ...regulators (SVRs). SVRs are assumed ideal and their taps are represented by continuous decision variables. To tackle the non-linearity, the branch-flow semidefinite programming framework of traditional OPF is expanded to accommodate SVR edges. Three types of non-convexity are addressed: (a) rank-1 constraints on non-SVR edges, (b) nonlinear equality constraints on SVR power flows and taps, and (c) trilinear equalities on SVR voltages and taps. Leveraging a practical phase-separation assumption on the SVR secondary voltage, novel McCormick relaxations are provided for (c) and certain rank-1 constraints of (a), while dropping the rest. A linear relaxation based on conservation of power is used in place of (b). Numerical simulations on standard distribution test feeders corroborate the merits of the proposed convex formulation.
The grounding system is one of the security systems in substations to channel excess voltage caused by lightning strikes that occur at substations, as well as electrical equipment. To design a ...grounding system, there are several factors that must be considered, including the type of soil, the configuration of the grounding system, the resistivity of the soil, and the condition of the surrounding environment. The aim of this research is to determine the safe limits in the substation grid grounding system which is influenced by the type of soil and influences the touch voltage and step voltage, which can be dangerous to humans. The method used is simulation with the Finite Element Method (FEM) in the ETAP application. Finite Element Method (FEM) is a method that uses image mediation by assuming that the grounding system is an equipotential structure. The test results were deliberately carried out with larger substation area parameters and different soil types, so that the differences between the influence and appearance of touch voltage and step voltage can be seen clearly.
Reverse power tap changerrunaway has become a challenging voltage issue with the increasing integration of distributed generation (DG) to reconfigurable distribution networks having step voltage ...regulators (SVRs). Local measurement-based runaway online inhibitor is important for correct tap changer operation when reverse power flow emerges on SVRs. However, gross errors of measurements available in SVR control can be quite significant, which further complicate the issue. This paper proposes a robust inhibitor of reverse power tap changer runaway events in reconfigurable and active distribution networks using local measurements and modes of operation available in SVR controls. 1 A recursive least squares (RLS) estimation is proposed to mitigate the effect of gross SVR load-side voltage measurement errors on identifying the SVR weak side used for triggering SVR control modes in reverse power flow scenarios. A threshold range to assist in the SVR weak side identification is determined through a sensibility analysis. Simulation results on a real reconfigurable and active distribution network with cascade SVRs validate the effectiveness and robustness of the proposed algorithm.
Voltage regulation in distribution systems is typically performed with the aid of multiple voltage regulating devices, such as on-load tap changer and step voltage regulators. These devices are ...conventionally tuned and locally coordinated using Volt/VAR optimization strategies in accordance with the time-graded operation. However, in case of distribution systems with distributed generation (DG), there could be a possibility of simultaneous responses of DG and multiple voltage regulators for correcting the target bus voltage, thereby resulting in operational conflicts. This paper proposes an online voltage control strategy for a realistic distribution system containing a synchronous machine-based renewable DG unit and other voltage regulating devices. The proposed strategy minimizes the operational conflicts by prioritizing the operations of different regulating devices while maximizing the voltage regulation support by the DG. It is tested on an interconnected medium voltage distribution system, present in New South Wales, Australia, through time-domain simulation studies. The results have demonstrated that voltage control for a distribution feeder can effectively be achieved on a real-time basis through the application of the proposed control strategy.
•Comprehensive step voltage regulator model.•Introduction of fictitious impedances overcomes divergence issues of power flow.•Generic applicability in all configurations of step voltage ...regulators.•Step voltage regulator taps are modelled as equivalent current sources.•Computation time of power flow is reduced.
This paper presents a comprehensive three-bus equivalent circuit model of three-phase step voltage regulators. The proposed model can be efficiently integrated in the Z-bus power flow method and can accurately simulate any configuration of step voltage regulators. In contrast to the conventional step voltage regulator models that include the tap variables inside the YBUS matrix of the network, the proposed model simulates them in the form of current sources, outside the YBUS matrix. As a result, the re-factorization of the YBUS matrix is avoided after every tap change reducing significantly the computational burden of the power flow. Furthermore, possible convergence issues caused by the low impedance of step voltage regulators are addressed by introducing fictitious impedances, without, however, affecting the accuracy of the model. The results of the proposed step voltage regulator model are compared against well-known commercial softwares such as Simulink and OpenDSS using the IEEE 4-Bus and an 8-Bus network. According to the simulations, the proposed model outputs almost identical results with Simulink and OpenDSS confirming its high accuracy. Furthermore, the proposed 3-bus equivalent model is compared against a recently published conventional step voltage regulator model in the IEEE 8500-Node test feeder. Simulation results indicate that the proposed step voltage regulator model produces as accurate results as the conventional one, while its computation time is significantly lower. More specifically, in the large IEEE 8500-node network consisting of four SVRs, the proposed model can reduce the computation time of power flow around one minute for every tap variation. Therefore, the proposed step voltage regulator model can constitute an efficient simulation tool in applications where subsequent tap variations are required.
There are more large-scale photovoltaic (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 5 s 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 a real-time digital simulator MatLab cosimulation 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.
In this paper, a new nonisolated interleaved boost topology with ultralarge step voltage ratio based on coupled inductors (CIs) and switched capacitors is proposed. CI applied in the low voltage side ...along with the interleaved structure and utilizing new topology provide ripple cancelation and considerably reduce the input current ripple and current stress through power switches and magnetic elements. In addition, utilizing CIs in the high voltage side provides a high-voltage gain with an appropriate duty ratio. Voltage lift capacitors used in this structure not only alleviate the voltage spikes across the power switches but also increase the voltage gain. Zero current switching (ZCS) turn-on condition for switches and ZCS turn-off condition for diodes are achieved by employing CIs without any auxiliary circuit. This feature degrades the reverse recovery losses and improves the efficiency of the converter. The voltage stress of the power switches is noticeably lower than the output voltage, especially at high output voltages. Therefore, the low-voltage rated switches can be adopted. This topology provides autocurrent sharing without any controller. Finally, a 600-W, 24-V/480-V laboratory prototype has been built to verify the performance.
Step voltage regulator (SVR) has been utilized in power distribution systems for decades as the voltage regulation device. Due to the increasing integration of distributed energy resources (DERs), ...the conventional SVR is severely challenged by the modern power distribution pattern with high renewable energy penetration. The induced arc from the conventional SVR tap change and more frequent tap changes due to voltage instability from the renewable energy impose constraints on the conventional SVR's lifetime. Meanwhile, the conventional SVR device cannot regulate the voltage accurately since the SVR regulates the voltage step by step. This paper proposed a hybrid voltage regulator with high efficiency and low contact wearing, which can achieve arcless tap change and stepless voltage regulation by using a fractionally rated back-to-back power converter. Accurate load voltage regulation is guaranteed while the tap changer mechanism remains in the system, which helps to promote the upgrade to the existing power distribution systems. The power converter capacity in the proposed topology is only 0.31% of the distribution transformer rating to achieve a stepless voltage regulation range of ±10%, significantly reducing the system cost compared with the full power electronics solutions and projects high total system efficiency. The proposed hybrid voltage regulator was simulated and experimentally validated. The experimental results demonstrate arcless tap change operation and stepless voltage regulation. Collaborative operation between the conventional mechanical tap change and the power converter operation is also demonstrated to acquire large voltage regulation with fast-acting voltage control.
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