Voltage Control System Research Articles

Study on Control Strategy of Hydropower Asynchronous Integration Coupling with DC Emergency Power Support

The hydropower group is a kind of weak AC system while hydropower asynchronous interconnected with main network through VSC-HVDC (Voltage Source Converter based High Voltage Direct Current). Thus, VSC-HVDC should be taken part into the system voltage and frequency control, which can enhance the transient stability of power grid while reduce the conventional control costs at the same time. The transfer function of turbine governor is introduced to expound the principle of hydraulic turbine unit participating in DC power support. Different kinds of DC power modulation have been compared which show the difference of power angle recovery after fault between VSC-HVDC and LCC-HVDC (Line Commutated Converter based High Voltage Direct Current) power support, thus the modulation priority of different kinds of DC in the emergency control should be taken into consideration. The DC power support quantity calculation method after fault is proposed in this paper. The emergency coordination control strategy can be formulated by considering with both priority and DC power support quantity under different fault.

A virtual energy storage system for voltage control of distribution networks

—Increasing amount of Distributed Generation (DG) connected to distribution networks may lead to the voltage and thermal limits violation. This paper proposes a Virtual Energy Storage System (VESS) to provide voltage control in distribution networks in order to accommodate more DG. A VESS control scheme coordinating the demand response and the energy storage system was developed. The demand response control measures the voltage of the connected bus and changes the power consumption of the demand to eliminate voltage violations. The response of energy storage systems was used to compensate for the uncertainty of demand response. The voltage control of energy storage system is a droop control with droop gain values determined by voltage sensitivity factors. The control strategy of the VESS was applied to a medium-voltage network and results show that the control of VESS not only facilitates the accommodation of higher DG capacity in the distribution network without voltage violations or network reinforcements but also prolongs the lifetime of transformer on-load tap changer.

Harmonic Impact in Induction Generator Voltage Using Thyristor Control Reactor

As commonly known that theload fluctuations that have been performed on an induction motor operated as an induction generator (IG) triggers unstable induced voltage and frequency. Asthe result, the load that receiving the power quality is not running properly and the efficiency is low. The problems that have beenmitigated in this research in such way is the stability of the voltage that generated by IG due to fluctuating loading, and the harmonics can be damped by single tuned due to the work of thyristors and non-linear loads. The used method is the Ziegler-Nichols method by measuring and testing the design of prototype to get the best performance in stabilizing the voltage by using thyristor control reactor (TCR). The results showed that the induced generator with single tuned filter and TCR to nonlinear load variation at 1618 RPM is maintained stably for the voltage and frequency. Although, 3rd order harmonics of voltage and current that has been tuned can be dampedby using THDI 8.36%. Furthermore, it can be said that the response that generated by voltage control system using proportionalintegral (PI) control in 1kW-4 poles three-phase IG with additional and reductionalload generated a stable response.

Baseband simulation model of the vector rf voltage control system for the J-PARC RCS

Baseband simulation model of the vector rf voltage control system for the J-PARC RCS

Experimental Validation of Peer-to-Peer Distributed Voltage Control System

This paper presents experimental validation of a distributed optimization-based voltage control system. The dual-decomposition method is used in this paper to solve the voltage optimization problem in a fully distributed way. Device-to-device communication is implemented to enable peer-to-peer data exchange between agents of the proposed voltage control system. The paper presents the design, development and hardware setup of a laboratory-based testbed used to validate the performance of the proposed dual-decomposition-based peer-to-peer voltage control. The architecture of the setup consists of four layers: microgrid, control, communication, and monitoring. The key question motivating this research was whether distributed voltage control systems are a technically effective alternative to centralized ones. The results discussed in this paper show that distributed voltage control systems can indeed provide satisfactory regulation of the voltage profiles.

Secondary voltage regulation based on average voltage control

This paper compares a conventional Secondary Voltage Regulation (SVR) scheme based on pilot nodes with a proposed SVR that takes into account average voltages of control zones. Voltage control significance for the operation of power systems has promoted several strategies in order to deal with this problem. However, the Hierarchical Voltage Control System (HVCS) is the only scheme effectively implemented with some relevant applications into real power systems.The HVCS divides the voltage control problem into three recognized stages. Among them, the SVR is responsible for managing reactive power resources to improve network voltage profile. Conventional SVR is based on dividing the system into some electrically distant zones and controlling the voltage levels of some specific nodes in the system named pilot nodes, whose voltage levels are accepted as appropriate indicators of network voltage profile.The SVR approach proposed in this work does not only consider the voltage on pilot nodes, but it also takes the average voltages of the defined zones to carry out their respective control actions. Additionally, this innovative approach allows to integrate more reactive power resources into each zone according to some previously defined participation factors.The comparison between these strategies shows that the proposed SVR achieves a better allocation of reactive power in the system than conventional SVR, and it is able to keep the desired voltage profile, which has been expressed in terms of network average voltage.

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.

Development of hardware and software for calculation and monitoring of the unbalance factor in three­phase voltage system

Hardware and software for measuring and monitoring the unbalance factor of the three-phase voltage system is developed. The shortcomings of the existing technical and software solutions for calculating the unbalance factor, as well as problems of applying the methods used for analog control systems to digital systems are described. The block diagram of the microprocessor system for measuring the voltage unbalance factor in the ship three-phase network with the effective values of phase voltages is used. The analysis of the analytical expressions to calculate the unbalance factor allowed minimizing the utilization of system hardware necessary for the formation of all necessary signals. The optimized structure of the digital filter to calculate the effective value of the deterministic periodic signal at the optimum speed of a discrete system is proposed. An increase in the sampling rate in the optimized filter structure does not lead to an increase in the number of arithmetic operations of addition and multiplication, which is an advantage of the proposed system in comparison with similar ones. This allows monitoring of instantaneous changes in the unbalance factor of three-phase voltage and enables the system to operate in real time. The developed hardware and software can be integrated into the automated control system of the power plant and used in voltage control systems, as well as for the timely detection of voltage unbalance to protect equipment and prevent violation of normal operation.

Power System Security Under False Data Injection Attacks With Exploitation and Exploration Based on Reinforcement Learning

The false data injection (FDI) attack is a potential threat to the security of smart grids, and therefore, such threats should be assessed carefully. This paper proposes a self-governing FDI attack method with exploitation and exploration mechanisms and then evaluates its threat to power systems. The attack is executed by viruses embedded in monitoring systems in substations. First, the FDI attack is formulated as a partially observable Markov decision process. Then, an improved online reinforcement learning method called nearest sequence memory Q-learning is adopted to make the attack more effective. Finally, propagation, an inherent property of viruses, is described using a propagation-evolution model that serves as the exploration mechanism for the proposed FDI attack. To validate the proposed attack method, cosimulations of daily operations of the IEEE 39-bus system are performed in which both the automatic voltage control system and the proposed FDI attack are modeled. Test results show that the proposed FDI method can cause voltage collapse even if only a few substations are infected.

Stability Analysis of AC–DC Full-Bridge Converters With Reduced DC-Link Capacitance

Voltage ripple in single-phase ac–dc converters is usually disregarded to design the dc-link voltage control system, since large dc-link electrolytic capacitors are typically employed. However, replacement of electrolytic capacitors by film capacitors has been widely considered for increasing reliability. Consequently, due to cost constraints, such replacement usually employ low capacitance and may be combined with fast dc-bus voltage controllers. This paper shows that the conventional linear time-invariant (LTI) model may not represent the real converter behavior for reduced capacitance and/or faster controllers, leading to poor system performance or even instability. In this way, for any of these cases, the linear time-periodic (LTP) model is highly encouraged for stability and transient analysis as a tool for the controller design. Experimental results confirm that stability margins are precisely obtained from the LTP model but may not from the LTI model. Finally, this paper also compares both LTI and LTP models while considering the control gain and the dc-bus capacitance size. It is graphically revealed that the phase margin of the LTI model diverges from the LTP model for low dc-bus capacitances and high control gains.

Design and Implementation of Power Plant High-Side Voltage Controller for Coordinated Voltage Control

This paper describes the design and implementation of the Power Plant Voltage Controller (PPVC) with an adaptive control which equips at the power plant level with the local high side voltage control. The Power Plant Voltage Controller is part of the hierarchical voltage control system which consists of Tertiary Voltage Control (TVC) at the higher control level and then followed by Secondary Voltage Control (SVC) as a regional controller and Primary Voltage Control (PVC) at the lowest control level to perform the control command. In this control approach, PPVC participates in the lowest control level in the Coordinated Voltage Control (CVC) system. The Power Plant Voltage Control regulators are autonomous controllers that regulate the high-side bus of the power plant while maintaining balanced VAR generation of the individual units and avoiding the dynamic interaction among multiple controlled generators. This paper presents a method of controlling the terminal voltage of the generators at the power plant by utilizing a quasi-steady-state sensitivity to get a control parameter for the PPVC. Using a simple control strategy, an adaptive control can be achieved by periodically calculating the quasi-steady-state sensitivity to update the control parameter, in such a way the PPVC control parameter not only can adapt to the variation of the interconnected network but also with the fluctuation of the load demands.

A new method to point of common coupling voltage control in distribution grid-connected photovoltaic systems

A new method to point of common coupling voltage control in distribution grid-connected photovoltaic systems

Automatic voltage control system with market price employing large wind farms

The automatic voltage control (AVC) system is typically to minimize the grid loss while maintaining the voltage magnitude in an acceptable operational band. Being a market-driven power system, the power loss is normally purchased based on the market price. This paper proposes an approach for the Danish AVC system to couple the automatic voltage control (AVC) system to the market price in order to accurately assess the operational cost, where the objective is to minimize the total operational cost including the grid loss, the shunt switching cost, the transformer tap change cost and the cost of the voltage control service provided by the power plant owners. The benefit of employing the large offshore wind farms in this AVC system is investigated. The simulation based on the measurement data from the Danish electricity control center demonstrates the superiority of the proposed approach in terms of the cost minimization. The gained profit by employing the wind farms can be an argument to purchase the voltage control service provided by these wind farms.

Distribution voltage monitoring and control utilising smart meters

The conventional distribution voltage control system does not monitor and control wide area of low voltage (LV). In the case that LV near the end of the distribution line is deeply dropped due to heavy load, there is the potential that LV surpasses the upper or lower limit of distribution voltage. To regulate LV within the limits, the voltage control is required to improve its performance. On the other hand, smart meter, a device that reports the voltage and energy consumption at each customer, is installed in various regions. To regulate LV within the voltage limits, the control which utilises LV measured by smart meters is proposed in this study. As a problem about the proposed control, the control requires to select meters for monitoring and controlling the voltages in all LV networks. Therefore, the selection method of smart meters and voltage control utilising smart meters is studied, and the performance of the voltage control is evaluated.

Real-time, centralised voltage control in 33 and 11 kV electricity distribution networks

This study describes a real-time, centralised voltage control system for 33 and 11 kV electricity distribution networks, aiming to optimise the network voltages and release network capacity by dynamically adjusting the previously static target voltage settings of substations' voltage control relays. This study is based on learning to date from Western Power Distribution's (WPD) Tier-2 Low Carbon Networks (LCN) Fund project, Network Equilibrium.

Field demonstration and evaluation of centralised voltage control system for distribution network

With the expansion of introduction of renewable energy sources such as photovoltaics (PV), voltage fluctuations (fluctuated voltage by PV output ups and downs depending on sunshine changing) in distribution network can be increasing. As a method of suppressing voltage fluctuations, intensive control of voltage control equipment by the introduction of a centralised voltage control system (CVCS) should be mentioned. In this study, through a field demonstration, the effect of suppressing voltage fluctuations by introducing the CVCS was evaluated and confirmed.

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.

Comparative study of MPC based coordinated voltage control in LV distribution systems with photovoltaics and battery storage

This paper compares traditional local voltage control strategy with coordinated, optimization-based ones in low voltage (LV) distribution systems with photovoltaics and battery energy storage systems. Optimization-based strategies are formulated within a model predictive control (MPC) framework. Three strategies based on MPC are proposed and implemented, namely, centralized, decentralized and distributed MPC. The formulated strategies for voltage control are compared in a case study using a modified CIGRÉ European 3-area low-voltage network. Results indicate that decentralized MPC gives a better voltage profile in the network when compared to local voltage control strategy, since the latter inherently fails to maintain voltages of buses in the network not connected to photovoltaics or battery storage system within limits. Centralized MPC strategy is able to provide the optimal voltage profile across the network but utilizes 13% higher reactive power from the control devices to achieve this when compared to decentralized MPC. The latter performs well as long as the reactive power reserves within an area is sufficient but faces drawbacks similar to that of local voltage control strategy when the reactive reserves are completely exhausted. Distributed MPC utilizes 1.3% higher amount of reactive power reserves compared to centralized MPC in order to provide a network voltage profile similar to that of the latter while also yielding architectural advantages of decentralized MPC.

Wide‐area voltage control system of flexible AC transmission system devices to prevent voltage collapse

Hydro-Québec has identified wide-area control system as a key initiative able to significantly increase the voltage stability of its grid. In this context, an innovative project for wide-area and local voltage control of shunt compensators was initiated. Its main objective is to implement a closed-loop control system on Hydro-Québec's network to optimise the reactive power support from the dynamic shunt compensators. The outcome of this project is the ‘global and local control of compensators’ (GLCCs) system which is based on synchrophasor technology and intelligent electronics devices. Applied to each shunt compensator of Hydro-Québec's network, this robust voltage control system measures voltage variations in the load area and adjusts the operation set point of each shunt compensator accordingly, thus avoiding voltage collapse resulting from extreme contingencies. The GLCC control solution was intensively tested in simulation using PSSE software. Moreover, a pilot project was commissioned on a test bench replica of the system and also tested in real time using Hydro-Québec's Hypersim digital simulator. Field tests of the GLCC were conducted on a −230/ + 660 MVars static vars compensator. The results of this pilot project were deemed conclusive and the deployment of the new voltage control system has been initiated by Hydro-Québec.

Fuzzy-Based Reactive Power Control for Smart PV Inverters in LV Distribution Systems

Future society entails new paradigms in how the world will work; new ideas as Smart Grid, Smart Cities, Smart Homes, and their interactions have been established and studied. With the inclusion of Information and Communication Technology (ICT) components into the low-voltage (LV) distribution grid, some measurement signals from smart meters are available for distribution network control with high penetration of photovoltaic systems (PV). This paper takes a local voltage-control strategy for smart LV distribution networks, by using a fuzzy based methodology using local information collected from smart meters as status information source of the grid. Comparative studies are presented for a smart home LV distribution system to validate the method, showing the robustness of proposed method compared with the traditional local approaches. To illustrate the applicability of the proposed method, a real-time digital simulator for smart distribution power grids with a the developed voltage-control system are used. The results show the proposed method can simultaneously mitigate the PV reactive power injection, as well as minimize the voltage rise and power losses.