Power System Voltage Control Research Articles

Optimal coordinated voltage control of power systems

An immune algorithm solution is proposed in this paper to deal with the problem of optimal coordination of local physically based controllers in order to preserve or retain mid and long term voltage stability. This problem is in fact a global coordination control problem which involves not only sequencing and timing different control devices but also tuning the parameters of controllers. A multi-stage coordinated control scheme is presented, aiming at retaining good voltage levels with minimal control efforts and costs after severe disturbances in power systems. A self-pattern-recognized vaccination procedure is developed to transfer effective heuristic information into the new generation of solution candidates to speed up the convergence of the search procedure to global optima. An example of four bus power system case study is investigated to show the effectiveness and efficiency of the proposed algorithm, compared with several existing approaches such as differential dynamic programming and tree-search.

Ant colony search algorithm for optimal reactive power optimization

The paper presents an (ACSA) Ant colony search Algorithm for Optimal Reactive Power Optimization and voltage control of power systems. ACSA is a new co-operative agents? approach, which is inspired by the observation of the behavior of real ant colonies on the topic of ant trial formation and foraging methods. Hence, in the ACSA a set of co-operative agents called "Ants" co-operates to find good solution for Reactive Power Optimization problem. The ACSA is applied for optimal reactive power optimization is evaluated on standard IEEE, 30, 57, 191 (practical) test bus system. The proposed approach is tested and compared to genetic algorithm (GA), Adaptive Genetic Algorithm (AGA).

Coordinated AVR and tap changing control for an autonomous industrial power system

A strategy for voltage and reactive power control of an autonomous industrial power system including distributed generators and loads is presented. The investigation is based on time-domain simulations and aims to define the main functions for the power management system (PMS) that will govern the operation of the power system. Inter-bus transformers (IBTs) are used to limit the fault level but will affect the sharing of the total load reactive power between distributed generators. Generator AVR and on-load tap changing of the IBTs, both supervised by the PMS, are used together to regulate the local load voltages and at the same time to allow reactive power flow through the IBTs for the purpose of equalised sharing. A coordinated strategy is obtained. The knowledge gained from this study can be useful in future cases.

NODAL VOLTAGE CONTROL IN POWER SYSTEMS BASED ON THE MODEL-REFERENCE ADAPTIVE APPROACH

The paper illustrates the design of a power system voltage control scheme based on the model reference adaptive approach. Firstly, for an assigned operating condition, a power system approximated linear model is build-up which represents the system dynamics as seen from the busbar at which the controller is connected. Then, by imposing a desired reference model, the controller parameters are obtained by solving the model-following problem which ensures that the controlled voltage tracks the voltage reference. In presence of unknown operating conditions changes, the regulator parameters are varied according to an adjustment laws designed on the basis of the gradient rule. The task of the adaptation mechanism is to counteract the effects of such changes. Referring to a Static VAR System (SVS) controllable compensator device the adopted model-reference adaptive control scheme has been designed and its performance analyzed by accurate numerical time simulation studies in the case of both unknown load variations and changes in the power system structure, in particular line opening.

Control and Performance of a Self-Commutated GTO Converter Operating in Parallel With Line-Commutated Thyristor Converters

Recently, static var generators (SVGs) or static synchronous compensators based on self-commutated converters have been put into practical use for the purpose of compensation for reactive power, power swings damping, and/or voltage control in power systems. The SVGs have also been applied to reduce voltage fluctuations appearing at high-speed train substations. When parallel resonance occurs between passive filters installed at a point of common coupling (PCC) and the power-system impedance existing upstream of the PCC, voltage/current harmonics are significantly amplified in the power system. This paper describes the control and performance for a self-commutated gate-turn-off (GTO) converter operating in parallel with conventional line-commutated thyristor converters. This hybrid power conversion system rated at more than dozens of MVA has an inductive load at the dc side. A bank of passive filters is connected not only for harmonic compensation of the line-commutated converters, but also as a constant leading reactive-power source. The GTO converter can control either leading or lagging reactive power so as to achieve unity power factor operation. In addition, it has the capability of damping out parallel resonance between the passive filters and the power-system impedance. This paper confirms the viability and effectiveness of the hybrid system by means of theory and computer simulation.

Voltage Control of Demand Area Power System by Autonomous Decentralized Method

Voltage Control of Demand Area Power System by Autonomous Decentralized Method

Control of electric power systems

The increase in size and complexity of interconnected electric power systems, coupled with the industrial commitment to maximize security at a minimum cost, has led to the development of many special control devices. These control devices ensure that the electric power system is able to operate, without instability, under a wide range of system conditions. This article presents a tutorial overview of the basic concepts and techniques of control for stability in electric power systems. Emphasis is placed on the robustness of the overall electric power system along with modifications to the basic control necessary to achieve this robustness. Different stability concepts are illustrated and the associated stabilizing mechanisms and equipment are described. To facilitate the implementation of the stability criteria, models of power system components are described. Special considerations are then given to the tuning of the automatic voltage regulators and the associated analytical tools for steady-state regulation as well as small- and large-signal performance. Next, the issue of automatic generation control is critically examined before an efficient system-wide control scheme is presented. This scheme gurantees power system stability against any disturbance occuring anywhere in the power network. Some important topics like control during restoration, overvoltage control, new concepts in interconnected power system control, coordinated voltage control and artificial neural networks in power systems are discussed.

DC bus voltage control for a distributed power system

This paper addresses voltage control of distributed DC power systems. DC power systems have been discussed as a result of the introduction of renewable, small-scale power generation units. Also, telecommunication power systems featuring UPS properties might benefit from a broader introduction of DC power systems. Droop control is utilized to distribute the load between the source converters. In order to make the loading of the source converters equal, in per unit, the voltage control algorithm for each converter has to be designed to act similar. The DC side capacitor of each converter, needed for filtering, is also determined as a consequence. The root locus is investigated for varying DC bus impedance. It is found that the risk of entering converter over-modulation is a stronger limitation than stability, at least for reasonable DC bus cable parameters. The stationary and dynamic properties during load variations are also investigated.

Voltage and reactive power control in power systems by genetic algorithm considering system decomposition and control process

AbstractThis paper presents a new approach to optimal voltage and reactive power control based on a genetic algorithm (GA), and attempts to shorten the time of the GA, which calculates the control process. For this purpose, a network is decomposed into subsystems by means of region/area information, and the control counts of the controller are considered in the voltage and reactive power control. Therefore, some methods that give the control procedure are proposed in the GA algorithm. The effectiveness of the proposed method is demonstrated by practical 15‐ and 118‐bus systems. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(3): 1–16, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10242

A novel modelling approach for decentralized voltage and speed control of multi-machine power systems

This paper proposes a novel modelling approach of multi-machine power systems for the design of decentralized multi-variable voltage and speed regulators. In this approach, each generator views the rest of the network as effective instantaneous impedance. The new model contains time-varying parameters representing the interactions among the system generators. The time-varying parameters depend only on the operating conditions of the power system and are independent of the structure of the latter. The advantages of this model are its simplicity, the fact that each generator's terminal voltage and rotor speed are expressed only in terms of local measurable variables and its capability to model inter-machines interactions. A decentralized multi-input multi-output (MIMO) non-linear voltage and speed regulator based on the new model is then used to dampen oscillations in a four-machine power system and to illustrate the advantages of the proposed modelling approach. Simulation results show that voltage, rotor and inter-area oscillations are well damped.

Application of cell immune response modelling to power system voltage control by STATCOM

Just like neural networks and genetic systems, immune systems are sophisticated, biologically motivated information processing systems of human beings. A mathematical model for the cell immune response is proposed, aiming at an application in power system voltage control. This application is based on the idea that the violations of a power system voltage profile are antigens to the healthy operation of a power system, and they can be killed through the cell immune response implemented by voltage control. An example of STATCOM control via the cell immune response is demonstrated in the New England 10-machine 39-node power system. The STATCOM control based on the cell immune response can not only maintain the voltage level at the STATCOM busbar at the setting reference value for normal operation mode, but also eliminate voltage violations at the STATCOM's adjacent busbars in system contingencies.

Power system voltage control by multiple STATCOMs based on learning humoral immune response

An approach for power system voltage control is proposed based on the learning humoral immune response which can not only fulfil the conventional task of a voltage controller in a power system to keep the voltage at the controller's busbar to a setting reference value at the normal operation mode, but also minimise or eliminate voltage violations at its adjacent busbars in power system contingencies. This dual voltage control function is the major advantage of the approach proposed and is achieved by the capability of the humoral immune voltage control to identify self and nonself antigen intrusion (voltage variations and violations) to the power system. It is proposed that the parameters of a humoral immune voltage controller are trained by learning algorithms via offline simulation. The training is assisted by the injections of artificial reactive loads at relevant busbars in the power system and by the provision of a learning reference signal. An example 10-machine 39-node power system installed with two STATCOMs (static synchronous compensators) is presented. The success of applying the proposed humoral immune voltage control and associated learning algorithms to the design of STATCOMs is demonstrated.

系統分割と制御手順を考慮したGAによる電圧無効電力制御

系統分割と制御手順を考慮したGAによる電圧無効電力制御

Enhancement of voltage stability by an optimal selection of load following units

In this paper we examine how the voltage stability and control of power systems can be enhanced by an appropriate choice of load following units. An algorithm is proposed to optimize this choice using the relationship between reactive power limits in the system and voltage instability. A variety of experiments are presented for the IEEE 118 bus system, with seventh order two axis generator models.

Fuzzy-based voltage/reactive power scheduling for voltage security improvement and loss reduction

This paper presents a new approach using fuzzy set theory for voltage and reactive power control of power systems. The purpose is to find a solution which takes both voltage security enhancement and loss reduction into account for an electric power system. The approach translates violation level of buses voltage and controlling ability of controlling devices into fuzzy set notations using a linearized model. A feasible solution set which achieves voltage improvement is first attained using the max-min operation of fuzzy sets, the final solution which takes power loss reduction into account is then determined employing the min-operation on the feasible solution set previously obtained. A modified IEEE 30-bus test system is used to demonstrate the application of the proposed approach. Simulation results show that the approach is efficient, simple, and straightforward.

Fuzzy-Based Voltage/Reactive Power Scheduling for Voltage Security Improvement and Loss Reduction

This paper presents a new approach using fuzzy set theory for voltage and reactive power control of power systems. The purpose is to find a solution that takes both voltage security enhancement and loss reduction into account for an electric power system. The approach translates violation levels of buses voltage and controlling ability of controlling devices into fuzzy set notations using a linearized model. A feasible solution set that achieves voltage improvement is first attained using the max-min operation of fuzzy sets. The final solution, which takes power loss reduction into account, is then determined employing the min-operation on the feasible solution set previously obtained. A modified IEEE 30-bus test system is used to demonstrate the application of the proposed approach. Simulation results show that the approach is efficient, simple, and straightforward.

Multi-agent co-ordination for the secondary voltage control in power-system contingencies

The secondary voltage control of power systems initiated by EDF has been developed successfully and applied mainly for the generator AVRs to improve power system voltage stability. Work on secondary voltage control is presented involving various types of power system voltage controllers, AVRs, SVCs and STATCOMs, for a new application: power system voltage management in system contingencies. The secondary voltage control is proposed, to be implemented based on the principles of multi-agent system theory, an active branch of applications in distributed artificial intelligence. An example power system is presented to demonstrate the necessity of the secondary voltage control among an AVR, an SVC and a STATCOM installed in the power system, and also to illustrate the success of applying the multi-agent co-ordination for their secondary voltage control in system contingencies.

STATCOM control for power system voltage control applications

A static compensator (STATCOM) is a device that can provide reactive support to a bus. It consists of voltage sourced converters connected to an energy storage device on one side and to the power system on the other. In this paper the conventional method of PI control is compared and contrasted with various feedback control strategies. A linear optimal control based on LQR control is shown to be superior in terms of response profile and control effort required. These methodologies are applied to an example power system.

An accurate autotransformer model for load flow studies effect on the steady-state analysis of the Hellenic transmission system

This paper gives a closed formula which expresses the variation of the leakage reactance of power autotransformer, with tertiary winding, as a function of the autotransformer tap position. The derivation of the formula is based on the analysis of the distortion of the leakage field as portions of the winding are cut out by means of tappings. The case which is examined is the most common when the tap changers on the parallel winding are cut out symmetrically at the end of the winding. The validity of the derived model is tested by comparison with existing autotransformer impedance correction data. The importance of implementing such a model is shown by tap-changing voltage control of the Hellenic power system. The voltage control at the remote buses of the region of East Macedonia and Thrace, is achieved within the specified range, by the implementation of the derived formula on the tap-changing voltage control on load flow calculations.

Robust predictive control for the flexible coordinated secondary voltage control of large-scale power systems

A robust predictive control strategy is proposed for the secondary voltage control of large-scale power systems. It is based on the decoupling between control and prediction. The asynchronous part of the input delay is taken into account in the controller synthesis, while the output delay plus the synchronous part of the input delay is handled using an original minimal state Kalman predictor.