Automatic Voltage Control System Research Articles

Study on the influence of automatic voltage control system with dead zone on the stability of hydropower unit

The existing research on automatic voltage control of hydropower station is mostly simplified as linear control model, ignoring the dead time and delay effect. Based on the existing automatic voltage control model, this paper considers the dead zone of automatic voltage control, establishes the corresponding theoretical equivalent model of dead zone, and analyzes the influence of dead zone on the stability of hydropower grid connection. In this method, the dead zone is simplified as a smooth nonlinear function, which makes the small signal analysis method suitable for the nonlinear system with dead zone. This method has good guidance for the actual operation. The effectiveness of the method is verified by the analysis of an actual hydropower plant.

Influence of automatic voltage control on small signal stability of photovoltaic system

In order to solve the problem of large delay and uncertain impact on the system when traditional automatic voltage control is used in photovoltaic power station system control, a small signal analysis model of photovoltaic grid connected system including automatic voltage control is established. Firstly, considering that the actual automatic voltage control system contains dead time and delay link, the continuous dead time model of photovoltaic system is defined; Then, considering the nonlinear part of automatic voltage control, the small disturbance model of photovoltaic grid connected system with dead time and delay part is derived. The small disturbance model of photovoltaic system is formed by using the linearization principle, which is used to describe the expressions of damping torque and synchronous torque of photovoltaic system; Then, the expressions of PV active power increment, power angle increment and speed increment are obtained by small signal model; Finally, the validity of the model is verified by the comparison of theoretical calculation and simulation results. The results show that the proposed model can describe the damping component and synchronous component effect of photovoltaic system under disturbance, and provide a reference for the study of photovoltaic stability.

Research on Intelligent Substation Based on Automatic Voltage Control System (AVC) in Power Plant

Research on Intelligent Substation Based on Automatic Voltage Control System (AVC) in Power Plant

Hybrid planning of distributed generation and distribution automation to improve reliability and operation indices

This paper intends to give an effective hybrid planning of distributed generation and distribution automation in distribution networks aiming to improve the reliability and operation indices. The distribution automation platform consists of automatic voltage and VAR control and automatic fault management systems. The objective function minimizes the sum of the expected daily investment, operation, energy loss and reliability costs. The scheme is constrained by linearized AC optimal power flow equations and planning model of sources and distribution automation. A stochastic programming approach is also implemented in this paper based on a hybrid method of Monte Carlo simulation and simultaneous backward method to model uncertainty parameters of the understudy model including load, energy price and availability of network equipment. Finally, the proposed strategy is implemented on an IEEE 69-bus radial distribution network and different case studies are presented to demonstrate the economic and technical benefits of the investigated model. By allocating the optimal places for sources and distribution automation across the distribution network and extracting the optimal performance, the proposed scheme can simultaneously enhance economic, operation, and reliability indices in the distribution system compared to power flow studies.

Optimization Analysis of AVC Adjustment Strategy for Power System with Large-scale Wind Power

As a kind of economical and clean renewable energy, wind power generation is more and more widely used. Wind power plants are far away from the load center and the output power is highly random. Therefore, the control of reactive power, voltage and network loss at public connection points are more difficult. The automatic voltage control system uses the real-time operating data of the power grid to select the best reactive voltage control scheme from the perspective of the entire system. It takes the voltage safety and quality as the conditional limit, takes the economy of the system as the goal, and optimizes the voltage in real-time control. This article gives a control strategy for the problem of inability to smooth transition and repeated oscillations in the signal processing of the abnormal state of the AVC system. The upper and lower limit planes of voltage and reactive power are divided into 27 areas, and each area corresponds to different control strategies. This method can be used to achieve smooth transition of control strategy, real-time voltage optimization control.

Automatic Voltage Control of Large-scale Synchronous Condensers in UHV-DC Converter Station

Large-scale synchronous condenser can provide a powerful dynamic reactive power for the Ultra high-voltage (UHV) Direct Current (DC) transmission system. The dynamic characteristics of synchronous condenser ensure the reactive power support capability in the case of grid fault. In this paper, the control strategy and deployment of the synchronous condensers in East China Power Grid are presented. Taking converter station as an example, this paper introduces the main architecture of automatic voltage control (AVC) system, and the relationship between host computers and slave computers. In the substation, it describes the mechanism of several control modes, and designs the on-site test scheme of the control modes. After on-site testing, the correct operation of the large-scale synchronous condensers can be guaranteed.

Improvement of the system of contactless automatic regulation of voltage of converter traction units of traction substations

The article discusses the problem of increasing the energy efficiency of the 3 kV DC traction power supply system on the railways of the Russian Federation. As one of the ways to amplify it, the authors consider a system of contactless automatic voltage regulation under load of converting units of traction substations, where reactor controlled devices serve as the regulatory body. As one of the directions for improving the system, the use of thyristors in the design of a controlled device is proposed. The article presents the functional diagrams of contactless automatic voltage control systems with thyristor-reactor and thyristor controlled devices, shows the external characteristics of the converter unit with these systems. To calculate the economic efficiency when introducing contactless automatic voltage control systems with reactor, thyristor-reactor and thyristor controlled devices, a methodology has been developed based on calculating the savings in reduced costs, as well as the payback period when replacing a contactless automatic voltage control system under load with a reactor controlled device by a system with thyristor-reactor and system with thyristor.

Hardware-in-loop test platform design for AVC sub-station of the new energy station based on RT-LAB

In order to ensure the safe and stable operation of the large power grid with high proportion of renewable energy access, the automatic voltage control (AVC) system of the new energy power station is very important. The control strategy of the AVC and the response characteristics of the voltage and reactive power regulating equipment will affect the AVC regulation effect directly. However, the pure digital simulation software cannot simulate its actual response characteristic. This paper established a hardware in loop (HIL) testing platform based on RT-LAB real-time simulation system. The real AVC controller and the real static var generator (SVG) controller hardware are connected to RT-LAB testing platform via I/O physical interface and MODBUS communication, and the HIL coordinated simulation testing scheme is studied based on FPGA of RT-LAB. With established testing platform, the voltage regulating characteristic and reactive power replacement capacity of AVC control strategy is verified.

Robust Voltage Control Strategy for Hybrid AC/DC Sending-Side Systems to Prevent Cascading Trip Failures

Line-commutated-converter-based high-voltage direct current (LCC-HVDC) is an important and attractive method of transmitting large-scale integrated wind power. However, the contingencies induced by LCC-HVDCs and nearby areas usually lead to an overvoltage problem in hybrid AC/DC sending-side systems, which may result in severe cascading trip problems. Therefore, a robust voltage control strategy for hybrid AC/DC sending-side systems is proposed in this paper to prevent cascading trip failures and accommodate more wind power. The proposed strategies address the voltage control complexity of LCC-HVDCs and converter stations, appropriately formulate the different locally fast-response switching strategies of filter banks and different control modes of the LCC-HVDCs in the automatic voltage control system. To compute the formulated problem efficiently and quickly for online application, a method of transforming the robust optimization problem and the Benders decomposition method are introduced. Based on case studies, the computational efficiency and accuracy of the proposed method are determined using operational data for the TianShan District in the Northwest China Power Grid.

Detection of the ratio error drift in CVT considering AVC

With the wide use of the capacitor voltage transformer (CVT), ensuring its accuracy is important. The conventional method is periodical on-site calibration, which is time-consuming and needs the power cut. This paper proposed an on-line method detecting the ratio error (RE) drift based on the correlation between three phase voltages. Considering the widely used automatic voltage control (AVC) system, the independent component analysis (ICA) rather than principal component analysis (PCA) is more suitable to separate the ratio error drift from the load fluctuation. The simulation on field data shows that ICA can detect the drift under AVC whereas the PCA cannot. The laboratory experiment shows the ICA is more sensitive than the PCA.

Continuation Power Flow Model for Interconnected Systems Considering the Electricity Market Influence and Its Corresponding Distributed Algorithm

The existing continuation power flow (CPF) methods, which mainly focus on regional independent systems, are not suitable for multi-area interconnected bulk systems in the electricity market environment. These existing CPF models cannot simulate the control behaviors of active/reactive power exchange among subsystems, and the corresponding CPF algorithms cannot satisfy the requirements of data sharing. This study presents a novel CPF model and its corresponding distributed algorithm for interconnected systems in which the influence of the electricity market is considered. This CPF method has the following unique features: 1) Regarding the bilateral power trading contracts (BPTCs) among regional subsystems, the nonlinear constraint equations of the directional trading active power via the interface are derived, and a multi-balancing machine strategy is introduced for realizing the active power balance of each subsystem. 2) Based on the simulation of the constant-voltage control behavior of the pilot buses in the regional automatic voltage control (AVC) system, the constant-voltage control behavior of the boundary buses of the tie-lines is further simulated to realize the reactive power balance among the regional subsystems. 3) According to the characteristics of the proposed CPF model, a novel distributed CPF algorithm based on block matrix computations is presented for realizing the decomposition and coordination calculation of multiple regional subsystems. This distributed algorithm preserves the precision and convergence of integrated CPF algorithms and has an advantage in terms of the calculation speed. The performance of the proposed CPF model and distributed algorithm is demonstrated via case studies and comparative analyses.

Key Technologies Research of Urban Power Grid AVC System with High Load Density Based on Big Data

In recent years, with the rapid expansion of urban power grids, the automatic voltage control (AVC) system develops some new characteristics. Based on the technology of big data analysis and mining, this paper expounds an AVC system for urban power network with high load density based on the integrated dispatch and operation mode. This paper introduces several different application modes, and shows the operation characteristics of the multi-point distribution mode and the integrated control mode. The big data mining technology is used to discovering the hidden troubles and defects in AVC system. This paper also presents some other AVC key technologies such as security check of remote control, self-adaption analysis method and so on.

Suppression Methods for Low Frequency Oscillation of Wind Farm Considering SVG Minimum Output Dead Zone

At present, the research of Static Var Generator (SVG) mainly focuses on the main circuit topology, the optimization of control strategy, the method of selection, and lack of research on the low frequency oscillation of the wind farm caused by SVG minimum reactive output dead zone in practical engineering applications. For this reason, this paper first studies the mechanism of the low frequency oscillation of the wind electric field induced by the SVG minimum output dead zone of the wind farm, and discusses the conditions of this type of oscillation. On this basis, the automatic voltage control system (AVC) optimization model of wind farm is established with the minimum reactive variation of SVG output near the zero point as the optimization goal, and an optimization control strategy of wind farm with SVG minimum output reactive dead zone is proposed. Finally, the correctness of the result is verified by simulation. The results show that, due to the existence of the minimum output dead zone in the wind farm, the large reactive step may occur near the zero point of the SVG output, which causes the voltage low frequency oscillation of the wind farm. The optimization strategy proposed in this paper can significantly suppress the low frequency oscillation by coordinating and optimizing reactive power output near the zero point of multiple SVGs in wind farm.

A Cost-Effective Redundant Digital Excitation Control System and Test Bed Experiment for Safe Power Supply for Process Industry 4.0

Recently, the energy demand and supply situation in the Republic of Korea (ROK) has been largely affected by the fluctuations in the energy markets around the world. Such a situation has provided a basis for requiring improvements to power plant facilities. The automatic generator voltage control systems in large-scale power plants are adopting a rapid-response static excitation method to improve the transient stability. A domestic commercially developed large-scale triple-redundant excitation system is currently operated by the 1000 MW-class nuclear power plant and its efficiency has been verified at the same site. However, such a system is too costly for smaller power plants so that a reliable and low-cost redundant digital excitation control system was developed and introduced in this study to resolve the cost problem. The system has improved its stability and reliability at the same time through double (redundant) configuration. Additionally, the system’s performance was put to the test by conducting a series of control function tests after applying it to the gas turbine used in a thermal power station. This study includes the development of system hardware, simulations as well as on-site experiments and each element was validated as a result. Also, the study discusses and validates the method used for replacing the protective relays at the Kanudi power plant operating in Papua New Guinea. The replacement of 27 and 81 protective relays at the existing power plant was carried out as they did not function properly. New relays were installed after removing the power supply in the existing panel. The individual power output sections of new relays were connected in parallel with the existing properly functioning relays, as previous protective relays had only allowed monitoring without outputting the contents. Thus, the new protective system was designed to enable both existing and new relays to carry out the detection function. It was validated that the replacement was successful. The new system with the new relays is performing properly by protecting its power generator and preventing further accidents.

An adaptive zone-division approach for voltage control of power grid with distributed wind farms: A case study of a regional power grid in central south China

With the increasing penetration level of wind power generation, it is essential to coordinate the dispersed wind farms with the automatic voltage control (AVC) system to take part in the voltage regulation of the power grid. In this paper, an adaptive zone-division approach is proposed to identify the optimal controllable zone for each wind farm. The reactive power generation capability of wind farms with inverters is adequately exploited. A multidimensional V-Q sensitivity analysis is implemented to evaluate the ability of reactive power regulations, based on which an online zone-division method is adopted to determine the control clusters for wind farms. The proposed approach can be applied in the AVC system of power grid to alleviate the regulation burden for voltage stability. Moreover, the reactive power generations from wind farms can be effectively utilized to improve the penetration of wind power. A case study on a regional power grid from central south China is carried out, which indicates that, with the proposed approach the capability to maintain the voltage stability for power system operations can be enhanced with more wind power penetration.

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.

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.

Multivariate statistical analysis‐based power‐grid‐partitioning method

A multivariate statistical analysis (MSA)-based power-grid-partitioning method is proposed. Considering the effectiveness of automatic voltage regulation of generators, network modelling is based on the quasi-steady-state sensitivity of voltage with respect to reactive power. The MSA-based power-grid-partitioning method contains two stages: a quantitative method for determining the appropriate number of zones and allocation of nodes into a number of zones. The proposed method is applied to an automatic voltage control system and an N − 1 robust pilot node selection method is presented. Simulation studies on IEEE 14-bus, 39-bus systems and a real provincial power system in China are described to illustrate the effectiveness of the proposed method.

Multi-Stage Optimization Based Automatic Voltage Control Systems Considering Wind Power Forecasting Errors

This paper proposes an automatic voltage control (AVC) system for power systems with limited continuous voltage control capability. The objective is to minimize the operational cost over a period, which consists of the power loss in the grid, the shunt switching cost, the transformer tap change cost, and the generator reactive power output cost. The problem is formulated in a multi-stage optimal reactive power flow (MORPF) framework, solved by the nonlinear programming techniques via a rolling process. The voltage uncertainty caused by wind power forecasting errors is considered in the optimal voltage/var dispatch by including a security margin in the voltage magnitude constraints. The robustness of the MORPF solution considering the voltage security margin is therefore improved. A platform is built for the offline investigations, employing the measurement data from the Danish national electricity control center, where study cases based on the western Danish power system demonstrate the superiority of the proposed AVC system in term of the cost minimization. Monte Carlo simulations are carried out to verify the proposed method on the robustness improvements.

Adaptive and Automatic Closed-Loop Coordinated Voltage Control Based Model for Optimal Voltage Control: a Case Study

Effective and efficient management of voltage control devices and reactive power resources is one of the most challenging tasks in power system operation. The need for proper voltage control is mainly to fulfill the following requirements: system security, economic operation and voltage quality. In Malaysian Transmission System (MTS), most of the voltage control devices and reactive power resources are manually control. Since the guidelines for controlling the primary and secondary voltage control are broad in nature, control actions could vary from one operator to another depending on experience, system information and knowledge. Tenaga Nasional Berhad (TNB) as system operator for MTS System believes that improvement in the approach and methods for voltage controls are desirable. This paper presents the newly developed hierarchical voltage control system called Adaptive and Automatic Closed-Loop Coordinated Voltage Control (A2CLCVC) based system model as a possible solution for better voltage control within Malaysia Transmission System. The A2CLCVC system model is basically a hierarchical voltage control approach that operates at three different voltage control levels which consists of Tertiary, Secondary and Primary voltage control modules. The A2CLCVC based system model will be used to coordinate and optimize the voltage control operation in order to improve security, quality and economic of Malaysian Transmission System. To verify the A2CLCVC model system performance, two new simulation methodologies based on PSS/E simulation software has been developed: 24-hours Load Flow Python-programming (24LFP-PSS/EM) and 24-hours dynamic simulation based method (24DS-PSS/EM). The two simulation methodologies results has shown that the proposed A2CLCVC system can provide great benefits to TNB especially for better voltage control and power system operational. The comparative studies with the commercial automatic voltage control system have shown that the performance of A2CLCVC system is much similar.