Voltage Control In Distribution Systems Research Articles

Evaluation of Voltage Unbalance Definitions for Voltage Control in Distribution Systems with Photovoltaic Penetration

AbstractThis paper examines the impact of different voltage unbalance definitions on voltage control in unbalanced distribution systems. Traditional voltage regulation methods for unbalanced systems rely on a single voltage unbalance definition with inconsistent adoptions. In such a situation, voltage control performance can vary between definitions, and improper choice leads to control failures. In this study, we perform numerical analysis and simulations to investigate the impact of different definitions. In the numerical analysis, two definitions quantifying negative and zero sequence components are used as reference definitions, and the theoretical error range of the remaining definitions is identified. The results are further verified by the simulations on the IEEE 123 node test system with phase‐by‐phase controlled three‐phase step voltage regulators and smart photovoltaic inverters. The control of the devices is optimized to minimize or limit a specific definition. The results show that the values of each definition at the same voltage condition can differ significantly, and inappropriate definitions may lead to significant uncertainty in the voltage control. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Fuzzy Multi-Agent Based Voltage and Reactive Power Control

. Variations in load and generation profiles cause overvoltages leading to equipment insulation failure and undervoltages, which impact voltage stability margin. Voltage and reactive power control aims to keep the voltage profiles within desired limits and reduce power losses. In this paper multi-agent system based on Java technology and adaptive fuzzy logics algorithms are implemented to control voltage and reactive power. Agents communicate with each other using Foundation for Intelligent Physical Agents (FIPA) to be able to achieve their objectives. A fuzzy agent controls the voltage at the busbars. Multi-agent systems make it possible to do three hierarchal voltage control in distribution systems.

Microgrids-Based Approach for Voltage Control in Distribution Systems by an Efficient Sensitivity Analysis Method

High levels of renewable energy sources (RESs) in distribution networks have led to complex operational needs. The management of the network in microgrids (MGs) allows the implementation of effective and innovative management strategies. We propose a hybrid control strategy to maintain voltage levels within the operational limits using the RESs reactive and active power outputs. The proposed regulation strategy considers different MGs that are managed by different owners, who contribute to regulating the voltage on the distribution systems. In order to obtain an effective regulation, each MG can collaborate with the others. In the first instance, voltage is regulated inside MG using available distributed generation resources in correspondence of the bus of over/undervoltage is detected (stage 1). Next, more MGs can contribute to alleviating the problem involving other distributed generation resources (stage 2). The control method is based on sensitivity analysis, which allows selecting the appropriate distributed resources: we propose also a new method of calculating the sensitivity coefficients for radial and meshed networks. We demonstrate the effectiveness and the robustness of the proposed voltage control scheme using comparisons and representative studies by extensive simulations on two test networks performed by the proposed methodology. The results demonstrate the effectiveness of the control actions and the used algorithm.

Application of Model Predictive Control to Voltage Control in Distribution System for Coordination of SVR and SVC

With increase in the number of photovoltaic system installations, the prospect of voltage deviation from the acceptable range in a distribution system is increasing. Voltage distribution can be controlled using step voltage regulators (SVRs) and static var compensators (SVCs); however, for their coordination, it is necessary to stringently adjust the set value for each distribution line. In this study, a method of applying model predictive control to the coordination between an SVR and an SVC is investigated. In this paper, we first describe the proposed method and subsequently present the results of the performance comparison of the proposed and conventional methods to validate the effectiveness of the proposed method. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Data-Driven Multi-Agent Deep Reinforcement Learning for Distribution System Decentralized Voltage Control With High Penetration of PVs

This paper proposes a novel model-free/data-driven centralized training and decentralized execution multi-agent deep reinforcement learning (MADRL) framework for distribution system voltage control with high penetration of PVs. The proposed MADRL can coordinate both the real and reactive power control of PVs with existing static var compensators and battery storage systems. Unlike the existing DRL-based voltage control methods, our proposed method does not rely on a system model during both the training and execution stages. This is achieved by developing a new interaction scheme between the surrogate modeling of the original system and the multi-agent soft actor critic (MASAC) MADRL algorithm. In particular, the sparse pseudo-Gaussian process with a few-shots of measurements is utilized to construct the surrogate model of the original environment, i.e., power flow model. This is a data-driven process and no model parameters are needed. Furthermore, the MASAC enabled MADRL allows to achieve better scalability by dividing the original system into different voltage control regions with the aid of real and reactive power sensitivities to voltage, where each region is treated as an agent. This also serves as the foundation for the centralized training and decentralized execution, thus significantly reducing the communication requirements as only local measurements are required for control. Comparative results with other alternatives on the IEEE 123-nodes and 342-nodes systems demonstrate the superiority of the proposed method.

Voltage Control in Distribution System with Reactive Power Dispatch

Voltage Control in Distribution System with Reactive Power Dispatch

Fast Resource Scheduling for Distribution Systems Enabled With Discrete Control Devices

This article proposes a framework for fast short-term scheduling and steady-state voltage control in distribution systems enabled with both continuous control devices, e.g., inverter interfaced distributed generators (DGs) and discrete control devices (DCDs), e.g., on-load tap changers. The voltage-dependent nature of loads is taken into account to further reduce the operating cost by managing the voltage levels. Branch and cut method is applied to handle the integrality constraints associated with the operation of DCDs. A globally convergent trust region algorithm (TRA) is applied to solve the integer-relaxed problems at each node during the branching process. The TRA subproblems are solved using interior point method. To reduce the branching burden of branch and cut algorithm, before applying TRA at each node, a simplified optimization problem is first solved. Using the convergence status and value of objective function of this problem, a faster decision is made on stopping the regarding branch. Solving the simplified problem obviates the application of TRA at most nodes. It is shown that the method converges to the optimal solution with a considerable saving in computation time according to the numerical studies.

신재생에너지 수용량 증대를 위한 머신러닝을 활용한 예측 기반 배전계통 전압제어

신재생에너지 수용량 증대를 위한 머신러닝을 활용한 예측 기반 배전계통 전압제어

Two-level centralized and local voltage control in distribution systems mitigating effects of highly intermittent renewable generation

This paper describes a method for voltage control towards optimal power flow (OPF) operation of radial distribution systems through reactive power (Q) control of distributed energy resources (DERs). A two-level control system consisting of an upper-level centralized controller and lower-level local controllers is proposed. First, a stable local control scheme and a criteria for its voltage stability via a discrete-time state-space model are presented. Second, the local control scheme is combined with a centralized AC OPF optimization to minimize delivery losses in the distribution system while maintaining bus voltages at optimal levels. The control system is modeled and simulated in Matlab/OpenDSS considering real world input data. In a simulation study of the IEEE 123-bus test system with historical load and solar generation data for a 24-h period, the proposed method is compared to other Q modes of DERs, specifically the volt-var droop control mode and a centralized OPF control mode. Furthermore, the control system is used in a scenario with an on-load tap changer and in unbalanced loading conditions. Overall, the proposed control method enhances existing local controllers with faster convergence and reduced voltage variations while ensuring stability, particularly in cases with highly intermittent renewable generation. In addition, it can reduce system voltage unbalance and transformer tap changer operations.

구간 선형 P-Q 드룹 기반 배전계통 연계 재생에너지 전압 제어

구간 선형 P-Q 드룹 기반 배전계통 연계 재생에너지 전압 제어

Innovative Volt/VAr Control Philosophy for Future Distribution Systems Embedded With Voltage-Regulating Devices and Distributed Renewable Energy Resources

Conventional voltage-regulating devices such as load tap changers, voltage regulators, and local capacitor banks are commonly used for voltage-regulation purposes in medium-voltage distribution systems. Although such devices exhibit excellent capability for Volt/VAr control (VVC) support, fine-tuning of their controller parameters and enactment of Volt/VAr support by renewable distributed generation (DG) units is essential for effective and efficient operation of future distribution systems embedded with wind and solar-Photo-voltaic (PV) units. In this paper, an innovative algorithm is conceptualized for control set-point re-adjustment of different VVC devices for coordinated voltage control in distribution systems. The intended VVC strategy is able to minimize the voltage variations including voltage drop and rise cases mainly caused by power output of renewable DG units that cannot be solved by voltage regulating devices due to their time-delayed operation. Moreover, the control algorithm is proposed to be implemented online using advanced distribution management system for effective voltage control. The simulation studies are carried out using the test distribution system derived from an electricity network in New South Wales, Australia. The simulation results show that voltage regulation can effectively be achieved in renewable rich future distribution systems by applying the proposed tuning algorithm, which has been designed based on a new VVC philosophy.

Efficient Distribution System Optimal Power Flow With Discrete Control of Load Tap Changers

Load tap changers (LTCs) are commonly used for voltage control in distribution systems. The mechanical relays on LTCs are controlled in discrete steps; hence, distribution optimal power flow (DOPF) formulations require LTCs to be modeled with integer variables. Integer variables are generally ignored or relaxed and rounded off to reduce the computational burden in DOPF models. However, in this paper, we highlight and overcome complex infeasibility issues caused by rounding methods. Moreover, recent advances in convex optimization have improved the computational tractability of the DOPF problem. In this paper, we develop and analyze numerical efficiency of different but exact formulations for incorporating LTCs as integer control assets in a relaxed second-order cone program (SOCP) version of the DOPF model. The resulting formulation becomes a mixed-integer SOCP (MISOCP), which is computationally tractable compared to mixed-integer non-linear program (MINLP). To recover the exact optimal solution in the proposed MISOCP-DOPF model, a McCormick relaxation is employed within a sequential bound-tightening algorithm. We show that solutions obtained from MISOCP-DOPF are always ac feasible. Thus, the MISOCP-DOPF yields optimal and realistic ac solutions, and is validated in large distribution feeders and is compared to MINLP counterpart.

Signal-Anticipation in Local Voltage Control in Distribution Systems

We consider the signal-anticipating behavior in local Volt/Var control for distribution systems. Such a behavior makes interaction among the nodes a game. We characterize Nash equilibrium of the game as the optimum of a global optimization problem and establish its asymptotic global stability. We also show that the signal-anticipating voltage control has less restrictive convergence condition than the signal-taking control. We then introduce the notion of Price of Signal-Anticipation (PoSA) to characterize the impact of signal-anticipating control, and use the gap in cost between network equilibrium in the signal-taking control and Nash equilibrium in the signal-anticipating control as the metric for PoSA. We characterize how the PoSA scales with the size, topology, and heterogeneity of the distribution network for a few network settings. Our results show that the PoSA is upper bounded by a constant and the average PoSA per node will go to zero as the size of the network increases. This is desirable as it means that the PoSA will not be arbitrarily large, no matter what the size of the network is, and no mechanism is needed to mitigate the signal-anticipating behavior. We further carry out numerical experiments with a real-world distribution circuit to complement the theoretical analysis.

Impact of Grid Voltage Feed-Forward Filters on Coupling Between DC-Link Voltage and AC Voltage Controllers in Smart PV Solar Systems

This paper presents a novel study of impact of filters of grid voltage feed-forward signals on the coupling between dc-link voltage and ac voltage controllers in smart photovoltaic (PV) solar systems which are used for voltage control in distribution systems. A comprehensive linearized state space model of a PV system including the dynamics of grid voltage feed-forward filters, dc-link voltage and ac voltage controllers is developed for the first time. This model is validated by electromagnetic transients software PSCAD/EMTDC. This model is used to identify the coupling between dc-link voltage and ac voltage controllers by eigenvalue and participation factor analyses. The impact of time constant of feed-forward filters on this coupling is studied by eigenvalue sensitivity analysis for PV systems with proportional and proportional integral type ac voltage controllers. The range of time constants over which the filters interact with controllers and create instability for systems with different strengths and X/R ratios is identified. Insights are provided on the choice of time constants of grid voltage feed-forward filters for the stable system design. The developed state-space model can also be used for impact studies of various other parameters, e.g., system strength, X/R ratios, types and gains of controllers, on system stability.

Optimal voltage controls of distribution systems with OLTC and shunt capacitors by modified particle swarm optimization: A case study

This paper presents a new framework to determine the optimal voltage control of distribution systems based on modified particle swarm optimization. The problem is to determine the set-points of the existing regulation devices such as on-load tap changers, shunt capacitors, etc. which minimizes the multi-objective function including power losses, voltage deviations, switching operations while subject to the constraint of allowable voltage levels, switching stresses, line capacity, etc. The problem is formulated and solved by modified particle swarm optimization methods with the trial, test and analysis techniques due to its large-scale and high nonlinearity property. In each iteration, a Newton-Raphson-based simulation is run to evaluate the performance of the regulation devices and the distribution system as well. The convergence is guaranteed by defining neighborhood boundaries for each trial. The proposed method is applied in a practical case study of 15-MVA, 22-kV, 48-bus distribution systems in Vietnam. The result of simulations shows that the voltage profile can be improved significantly with no bus voltage out of the boundaries while the voltage deviations is reduced as much as 56.5% compared to the conventional nominal setting. In the case study, the power loss is not improved much (1.21%).

Research on Effective Use of Photovoltaic Power Generation by Voltage Control of Distribution System in Railway Distribution Line

Research on Effective Use of Photovoltaic Power Generation by Voltage Control of Distribution System in Railway Distribution Line

Adjustable VAr compensator with losses reduction in the electric system

Among the existing power quality problems, the reactive power compensation plays a key role once it helps to maintain the system stability and increases the efficiency. Currently, there are many solutions for reactive power compensation, which unfortunately present a wide variety of problems as large inrush currents, non-continuous compensation and harmonics injection in the system. The application of devices like static VAr compensator, static synchronous compensator or unified power flow controller has demonstrated to be an effective solution for reactive power compensation. However, it is important to note that these options are rarely used in distribution systems by companies that prefer to assimilate the drawbacks of switched capacitor banks instead of investing in more expensive, sophisticated and complex solutions. Despite the large number of proposed devices in distribution systems, there is a lack of solutions with emphasis on cost reduction. Therefore, this paper presents a new topology for reactive power compensation and voltage control in distribution systems. The proposed topology has several interesting features as reduced switching losses, small capacitors and simple control scheme. In addition, the proposed solution uses already existing capacitor banks which makes possible its usage in distribution companies with minimum modifications. Experimental results have been obtained on a 6-kVA prototype to demonstrate the feasibility of the proposed solution.

An event-trigger two-stage architecture for voltage control in distribution systems

With the increasing penetration of distributed generations (DGs) in distribution systems, new challenges are introduced into voltage control of distribution systems, such as the frequent switching operations of traditional voltage control devices, resulted from rapid voltage fluctuations, and coordination between traditional voltage control devices and fast controllers such as inverters in DGs. In order to solve the challenges above, an event-trigger based two-stage architecture is presented, taking the characteristics of inverters and conventional devices, such as on-load tap-changers (OLTCs) and shunt capacitor banks (CBs), into account. An event-trigger mechanism is designed to make a fast response to large voltage deviations and reduce unnecessary switching operations of traditional devices, compared with periodic methods. The integration of inverter-based voltage control, in the proposed two-stage architecture, can provide a fast and continuous response to voltage deviation. Moreover, as reactive capacities in DGs, determined by inverters, are reserved in global voltage optimization, it can further reduce the switching operations of traditional devices in the following voltage control process. Simulations in a IEEE 33-bus distribution system show that the proposed architecture can ensure a higher voltage quality and reduce the number of switching operations of OLTCs and CBs by the event-trigger mechanism, the integration of inverter-based local voltage control, and the inverter’s reserved reactive power capacity in global voltage optimization.

Examining the Interactions between DG Units and Voltage Regulating Devices for Effective Voltage Control in Distribution Systems

Voltage regulation by means of coordinated voltage control is one of the challenging aspects in an active distribution system operation. Integration of distributed generation (DG), which can also be operated in Volt/VAr control mode, may introduce adverse effects including control interactions, operational conflicts, steady-state voltage variations, and oscillations. Therefore, examining and analyzing the phenomenon (both steady state and dynamic) of the control interactions among multiple Volt/VAr support DG units and voltage regulating devices such as tap changers and capacitor banks would be essential for effective voltage control in active distribution systems. In this paper, the interactions among DG units and voltage regulating devices are identified using their simultaneous and nonsimultaneous responses through time-domain simulations. For this task, an analytical technique is proposed and small signal modeling studies have been conducted. The proposed methodology could be beneficial to distribution network planners and operators to ensure seamless network operation from voltage control perspective with increasing penetration of DG units.

Online Coordinated Voltage Control in Distribution Systems Subjected to Structural Changes and DG Availability

The responses of multiple distributed generation (DG) units and voltage regulating devices, such as tap changers and capacitor banks, for correcting the voltage may lead to operational conflicts and oscillatory transients, where distribution systems are subjected to network reconfiguration and availability of the DG units. Therefore, coordinated voltage control is required to minimize control interactions, while accounting for the impact of structural changes associated with the network. This paper proposes a strategy for coordinating the operation of multiple voltage regulating devices and DG units in medium voltage (MV) distribution systems, under structural changes and DG availability, for effective voltage control. The proposed strategy aids to minimize the operational conflicts by allowing voltage regulating devices to operate in accordance with the priority scheme designed based on the electrical-distance between voltage regulating devices and DG units, while maximizing the voltage support by the DG units. The proposed coordination scheme is designed to enact with an aid of a substation centered distribution management system for online voltage control. The control actions of proposed coordination strategy are tested on a MV distribution system, derived from the state of New South Wales, Australia, through simulations, and results are reported.