Volt-ampere Reactive Compensator Research Articles

Voltage stability improvement of wind farms by self-correcting static volt-ampere reactive compensator and energy storage

Maintaining synchronism and voltage stability, especially in the presence of wind farms, has a crucial role in confirming the reliability requirements of the power grid, as the natural fluctuations of wind speed result in intermittency and uncontrollability of power generation. To this end, an optimized Battery Energy Storage System (BESS) was suggested to make an equilibrium between the generation and consumption in wind farms under harsh conditions. Additionally, the instability of wind farms is very likely after transmission line faults occur. To overcome this problem, in this paper, the impact of a constant capacitor bank, connected in parallel with the wind generators, is investigated. Also, a novel self-corrective Static Volt-ampere reactive Compensator (SVC) is proposed to overcome the variations of voltage and damp the reactive power oscillations after occurring the faults. The proposed SVC compares the network voltage profile as the reference voltage with the voltage deviations in a control block diagram. For this purpose, three similar wind farms of Permanent Magnet Synchronous Generator (PMSG) type are considered in a wind park. The simulation case studies are performed in Matlab/Simulink under different conditions of transient and steady-state voltage stabilities in the presence of proposed BESS including, only capacitor bank (without self-corrective SVC), and with self-corrective SVC. The results authenticate the ability of the proposed SVC strategy to correct the voltage deviations, and voltage stability improvement of the under study system.

Optimization of synchronized frequency and voltage control for a distributed generation system using the Black Widow Optimization algorithm

Abstract A distributed generation network could be a hybrid power system that includes wind–diesel power generation based on induction generators (IGs) and synchronous generators (SGs). The main advantage of these systems is the possibility of using renewable energy in their structures. The most important challenge is to design the voltage-control loop with the frequency-control loop to obtain optimal responses for voltage and frequency deviations. In this work, the voltage-control loop is designed by an automatic voltage regulator. A linear model of the hybrid system has also been developed with coordinated voltage and frequency control. Dynamic frequency response and voltage deviations are compared for different load disturbances and different reactive loads. The gains of the SG and the static volt-ampere reactive compensator (SVC) controllers in the IG terminal are calculated using the Black Widow Optimization (BWO) algorithm to insure low frequency and voltage deviations. The BWO optimization algorithm is one of the newest and most powerful optimization methods to have been introduced so far. The results showed that the BWO algorithm has a good speed in solving the proposed objective function. A 22% improvement in time adjustment was observed in the use of an optimal SVC. Also, an 18% improvement was observed in the transitory values.

Scheduling of Generation Stations, OLTC Substation Transformers and VAR Sources for Sustainable Power System Operation Using SNS Optimizer

Typically, the main control on alternating current (AC) power systems is performed by the scheduling of rotary machines of synchronous generators and static machines of on-load tap changer (OLTC) transformers and volt-ampere reactive (VAR) sources. Large machines of synchronous generators can be managed by utilizing terminal voltage control when synchronized in parallel to the power system. These machines are typically terminal voltage regulated. In addition, substation on-load tap changer (OLTC) transformers improve system voltage management by controlling variable turn ratios that are adjusted in different levels known as taps along either the primary or secondary winding. Moreover, volt-ampere reactive (VAR) sources of static VAR compensators (SVCs), which are automated impedance devices connected to the AC power network, are designed for voltage regulation and system stabilization. In this paper, scheduling of these machines is coordinated for optimal power system operation (OPSO) using a recent algorithm of social network search optimizer (SNSO). The OPSO is performed by achieving many optimization targets of cost of fuel, power losses, and polluting emissions. The SNS is a recent optimizer that is inspired from users in social networks throughout the different moods of users such as imitation, conversation, disputation, and innovation mood. The SNSO is developed for handling the OPSO problem and applied on an IEEE standardized 57-bus power system and real Egyptian power system of the West Delta area. The developed SNSO is used in various assessments and quantitative analyses with various contemporary techniques. The simulated findings prove the developed SNSO’s solution accuracy and resilience when compared to other relevant techniques in the literature.

Transient Stability Analysis of a Transmission Network Using Eigenvalue Principles with Automated VAR Compensation: A Case Study of the Nigerian Eastern Grid

Power systems may encounter disturbances during operation as a result of switching of various components, etc. Such perturbations include transformer tap-changing action, load variations, and line outages due to various types of faults of which an earth fault is the most common. Stability analysis of a transmission system is necessary for us to determine the stability state of the system so that appropriate control measures can be implemented to guarantee system stability. This article presents the use of eigenvalue obtained from the system-linearized eigenvectors to analyze the stability state of the system. The choice of the eigenvalue principle is based on the strength of accuracy of the method to determine the actual state of the system providing adequate data for easy solution to the problem. The node admittance parameters computed from the line parameters is applied to the eigenvalue–eigenvector model to determine the system stability state. The state of the eigenvalue is used as an input to a control system, which utilized static volt-ampere reactive (VAR) compensators (SVC) to automatically stabilize the non-stable buses in the transmission network. The 6 × 6 nodal admittance matrix is formed and fed to the developed eigenvalue–eigenvector model via MATLAB in order to compute the right and left eigenvectors and the diagonal or eigenvalue of the network under steady-state and contingency condition. After this, the system stability state is determined, and necessary control actions by the SVC are implemented to guarantee system security. The developed model was tested on the 6 bus Eastern Grid Nigerian Transmission Network and validated using a 41 bus network of the same country. The compensated model showed considerable efficiency in improving the transient stability state of the transmission networks in terms of ease of operation, seamless integration into existing control system, and efficient utilization of SVS to compensate for reactive power imbalances. The results from the step response graph of the compensated model shows performance accuracy as the system regained stability in less than 0.5 s, which is a significant improvement over the uncompensated model.

Secure Power Distribution Against Reactive Power Control Malfunction in DER Units

Penetration of distributed energy resources (DERs) such as wind, solar and battery units are rapidly increasing in distribution power system (DPS). In view of power grid reliability and efficiency, cyber and physical secure of these units are highly important since it can directly impact power system operations. This paper investigates the dynamic behavior of power distribution during cyber, physical and natural strikes on reactive power control in DER units. Various fault scenarios including modifications in voltage-reactive power (Volt-Var) curve pattern such as slope of the curve, dead band; and changes in capacitive or/and inductive reactive power delivery to the power grid are presented. Further, fault scenarios are investigated with the presence of dynamic VAR (volt-ampere reactive) compensation (DVC) units in the system. A southern California 140-bus commercial distribution power system is selected as a test system and faults are analyzed in both Matlab/Simulink and ETAP simulation platforms. The results evidence that the modifications in reactive power control values at DER units significantly affects the voltage quality/security of the system and affect the number of switching actions of voltage regulators (VRs). In contrast, DPS connected with DVCs improves voltage quality and reduces the number of switching actions of VRs, also voltage quality/security is maintained during the faults.

An SVC controller for Power Quality Improvement of a Heavily Loaded Grid

Pakistan is faced with energy crises from the last two decades. Generation cannot balance the load demands of the electricity consumers. Power delivery systems are generally old-fashioned and overloaded. They are unable to provide consistent and uninterrupted supply to commercial, industrial, and domestic loads. Generally speaking, the Power Systems consist of loads that are inductive and resistive in nature. Heavy machinery, induction motors, and arc furnaces are heavily inductive in nature. Inductive loads when operated in a weak power system results in lagging VARs (Volt Ampere Reactive) and poor voltage regulation, which must be balanced by the same number of leading VARs in order to ensure unity power factor and thus helps in improving the voltage profile. At times the reactive VARs injected may not be sufficient to balance the VARs requires by the system, but still the power factor is improved up to some extent. In hot and humid climatic conditions, air-cooling system and chillers greatly burdens the grids. Such loads require excessive reactive VARs, and if not offered with ample reactive power, causes severe voltage drops in distribution system. To manage low voltages and power-factor, household users use automatic voltage regulators while industries connect capacitor banks. Voltage regulators control output voltage within the required limits at the expense of excessive line current from transformer, which may overburden it. Moreover, with each operation of tap changer, current rises which further intensifies line losses. Static capacitors provide stable voltage but repeated variations in load demands reliable and vigorous voltage regulation. This investigation aims to come up with a power quality improvement scheme which would deliver instantaneous control of power (reactive) with SVC (Static VAR Compensator) thus overcoming the shortcomings of step-wise banks of capacitors and or voltage regulators. Simulation work is carried out in MATLAB/SIMULINK and the results are compliance with IEEE Standards for SVCs. The device can offer steady state as well as dynamic VAR compensation under changing load conditions. Result showed considerable improvement both in terms of response time and power factor. Switching time has been improved to less than 1/10th fraction of a second which in previous simulations was 0.7 seconds approximately. Initial power factor without disturbance and without compensation was recorded to be 0.6 lagging, which after compensation was improved to 0.95 lagging. Similarly, in presence of disturbance without compensation the power factor fluctuated between 0.55 and 0.9 lagging, which after compensation was improved to 0.95 lagging and above throughout the course of operation.

An SVC controller for Power Quality Improvement of a Heavily Loaded Grid

Pakistan is faced with energy crises from the last two decades. Generation cannot balance the load demands of the electricity consumers. Power delivery systems are generally old-fashioned and overloaded. They are unable to provide consistent and uninterrupted supply to commercial, industrial, and domestic loads. Generally speaking, the Power Systems consist of loads that are inductive and resistive in nature. Heavy machinery, induction motors, and arc furnaces are heavily inductive in nature. Inductive loads when operated in a weak power system results in lagging VARs (Volt Ampere Reactive) and poor voltage regulation, which must be balanced by the same number of leading VARs in order to ensure unity power factor and thus helps in improving the voltage profile. At times the reactive VARs injected may not be sufficient to balance the VARs requires by the system, but still the power factor is improved up to some extent. In hot and humid climatic conditions, air-cooling system and chillers greatly burdens the grids. Such loads require excessive reactive VARs, and if not offered with ample reactive power, causes severe voltage drops in distribution system. To manage low voltages and power-factor, household users use automatic voltage regulators while industries connect capacitor banks. Voltage regulators control output voltage within the required limits at the expense of excessive line current from transformer, which may overburden it. Moreover, with each operation of tap changer, current rises which further intensifies line losses. Static capacitors provide stable voltage but repeated variations in load demands reliable and vigorous voltage regulation. This investigation aims to come up with a power quality improvement scheme which would deliver instantaneous control of power (reactive) with SVC (Static VAR Compensator) thus overcoming the shortcomings of step-wise banks of capacitors and or voltage regulators. Simulation work is carried out in MATLAB/SIMULINK and the results are compliance with IEEE Standards for SVCs. The device can offer steady state as well as dynamic VAR compensation under changing load conditions. Result showed considerable improvement both in terms of response time and power factor. Switching time has been improved to less than 1/10th fraction of a second which in previous simulations was 0.7 seconds approximately. Initial power factor without disturbance and without compensation was recorded to be 0.6 lagging, which after compensation was improved to 0.95 lagging. Similarly, in presence of disturbance without compensation the power factor fluctuated between 0.55 and 0.9 lagging, which after compensation was improved to 0.95 lagging and above throughout the course of operation.

An SVC based Power Quality Improvement Model for Consumers Connected to Weak Busses in Distribution Systems

Power quality is a major concern considering weak bus systems. In order to improve power quality, residential consumers go with voltage stabilizers as a cheap solution consequently overstressing weak busses. Industrial consumers use other alternatives like switched capacitor banks to cope with low power factor but the limitation is step-wise reactive power injection which does not meet the changing load requirements. Real time improvement requires constant monitoring and real-time injection of Volt-Ampere-Reactive (VAR) which is possible with the help of a Static VAR Compensator (SVC). An SVC based Power Quality Improvement (PQI) is proposed in this paper which addresses the real time varying reactive VAR requirement with reduced harmonic content.

Integrating multilevel converters application on renewable energy sources—A survey

Multilevel inverters emerged as the solution for overcoming the limitations of two level inverters, such as total harmonic distortion, high magnetic interference, and high dv/dt in high power voltage applications. The ability to generate sinusoidal output voltage is another speciality of multilevel inverters. The wide range of applications in fields such as power grids, motor drives, and Volt-Ampere Reactive compensation enhances the visibility of multilevel inverters. This paper identifies the conventional multilevel inverter topologies such as diode clamped multilevel inverters, flying capacitor multilevel inverters, and cascaded H bridges and presents a literature review on the topologies considering the facts of structural and functional diversities over the ages which have been adapted right from the beginning of its emergence. It also details the various optimization technologies that are used in multilevel inverters to obtain the optimal switching angle for harmonic elimination. This paper also explains the modulation techniques that are in effect for a specific purpose in different applications to get the best possible result.

A novel dynamic reactive power planning methodology to enhance transient voltage stability

Summary Transient voltage stability (TVS) is an important issue for security operation with the development of power system topology and loads. Lots of research on reactive power planning mainly focus on static voltage stability. But the research on the dynamic reactive power planning considering TVS is very lacking so far. And most of them are only analyzed on some serious buses without covering all the weak faults. And some research considering TVS are limited under some conditions and not general enough for large-scale applications. Therefore, it is an urgent task to propose a feasible dynamic reactive power planning methodology to enhance TVS. So a novel dynamic reactive power planning methodology is proposed in this paper. In addition, although some TVS assessment indices have been proposed, they may not be suitable to be used in dynamic reactive power planning in the iteration calculation. To evaluate voltage stability after contingencies, a TVS assessment index is presented. Then an approach based on compensation sensitivity analysis is discussed for the best dynamic volt ampere reactive planning candidate locations. And a dynamic reactive power planning optimization methodology based on the memetic immune algorithm for multiobjective optimization is proposed to enhance TVS with the least static volt ampere reactive compensator investment cost and power loss cost. The methodology can cover all faults through random faults selection in the optimization. Afterwards, IEEE 39 power system and Zhejiang power grid in China are illustrated and analyzed for the improvement of TVS. It is proved that the proposed dynamic reactive power planning methodology is effective and beneficial to the security operation for power system.

Fault ride-through capability improvement of doubly fed induction generator-based wind turbine using static volt ampere reactive compensator

The use of wind energy is increasing due to rapid increase in energy consumption and rapid deployment of wind energy. Among different types of wind turbine generators, doubly fed induction generators are most widely used because of their low cost and capability to work in different wind speeds. On the other hand, doubly fed induction generators (DFIGs) are very sensitive to voltage drop. If a fault occurs in the network the voltage of DFIG terminal drops. So the rotor current increases and this may lead to damage DFIG converters. So, a protection system must be used to protect DFIG converters. One of the common schemes used to protect DFIGs is crowbar protection. In this paper, the effects of static volt ampere reactive compensator (SVC) on DFIG operation during voltage drop and crowbar protection are investigated in detail. Results show that by using SVC the voltage drop of DFIG terminal during grid faults decreases. Therefore, the operation time of crowbar decreases and the fault ride through capability of DFIG increases.

A new hybrid technique for power systems multi-facts optimization design

SUMMARY The purpose of this paper is to develop a new tool to the dispatching and optimization of reactive power resources using two kinds of the flexible alternating current transmission system devices, namely the static volt ampere reactive compensator and the Thyristor controlled series compensator. The fast voltage stability index and line stability index (Lmn) are used to identify the critical buses and lines, which will receive the flexible alternating current transmission system devices. The methodology carried out in this work is deployed in two phases. In the first one, we consider that the power system network is secure and operates within its stability limits and the balance between consumption and generation is satisfied. Thus, the solution of optimization program of the fuel cost minimization problem using the interior point method gives a feasible solution where the reactive power compensation is not considered. In the second phase, the power system network is unsecure and operates close to its secure limits. Although the optimization program of the fuel cost minimization problem gives a non-feasible solution, the reactive power compensation is, in this case, introduced to solve the problem. The power transmission line factor minimization problem is applied after each phase to improve the solution of the problem by minimizing the power flow in the transmissions lines. The reactive power planning and the power transmission line factor minimization problems are solved with a new hybrid technique combining particle swarm optimization with a nonlinear interior point method. Furthermore, the fuel cost minimization problem is solved with the interior point method. The methodology has been tested with the IEEE 57-bus system, and the simulation results show the effectiveness of the proposed approach for improving the reactive power planning problem. Copyright © 2014 John Wiley & Sons, Ltd.

Modeling and Experimental Analysis for Modernization of 100-t EAF

This paper presents an experimental investigation and modeling solutions of an electric arc furnace (EAF) with 100-t capacity used for steel melting in order to evaluate the best option for improvement. Experimental results show that EAFs represent a substantial source of electric disturbances such as voltage fluctuations, flicker, harmonics, and imbalance between phases. Improvement of the energetic performances of an EAF imposes a careful technical and economical analysis. The static voltampere reactive compensator solution is the best one for compensating the reactive energy and increasing the power factor but has the highest costs. Also, we evaluate existing processes' equipment performance, the point of improvement opportunities for the best operating efficiency. Substantial reductions in the energy consumption and in the defects of mechanical nature are obtained by the proposed automation solution of the auxiliary installations.

FACTS Controllers for Grid Connected Wind Energy Conversion Systems

In this paper, the dynamic performance of grid connected wind energy conversion system (WECS) is analyzed in terms of rotor speed stability. The WECS considered is a fixed-speed system that is equipped with a squirrel-cage induction generator. The drive-train is represented as a two-mass model. Results show that for a particular fault simulated, the voltage at the point of common coupling drops below 80% immediately after fault application and exhibits sustained oscillations. The rotor speed of induction generators becomes unstable. In order to improve the low voltage ride-through of WECS under fault conditions and to damp the rotor speed oscillations of induction generator, various flexible ac transmission system (FACTS) controllers such as static VAR (volt ampere reactive) compensator, static synchronous compensator, and unified power flow controller (UPFC) are employed. The gains of these FACTS controllers are tuned with a simple genetic algorithm. It is observed that among the FACTS controllers considered, UPFC is superior not only in regulating the voltage but also in mitigating the rotor speed instability.

Static Volt Ampere Reactive Compensator for Self-excited Induction Generator Feeding Dynamic Load

This article presents the modeling and transient analysis of a 3-φ self-excited induction generator (SEIG) feeding an induction motor and a rectifier-controlled DC motor as dynamic loads with a static volt ampere reactive (VAR) compensator. It also deals with the necessary steps and guidelines to decide the parameters of a static VAR compensator (STATCOM) for a SEIG feeding an induction motor and controlled rectifier-fed DC motor loads. The STATCOM (an insulated gate bipolar transistor-based current-controlled voltage source inverter) provides the additional VAR required by the load and, thus, results in good voltage regulation. With consideration of the designed STATCOM parameters, the system is studied for switching of the static compensator and startup and loading of both an induction motor and a rectifier-fed DC motor. With the STATCOM, the performance of a SEIG feeding an induction motor and a controlled rectifier-fed DC motor is found commendable, as far as startup, voltage dip, and total harmonic distortion are concerned.

A current regulated switched capacitor static volt ampere reactive compensator

This paper introduces a current regulated switched capacitor static VAr compensator (SVC). The physical mechanisms governing the performance of the switched capacitor SVC are explained in detail. A relevant equivalent circuit is presented which helps prove that the oscillation of reactive power takes place in two different loops; between the main 60 Hz source and the AC input of the converter bridge; and between the energy storing device (in this case, a capacitor) and a set of fictitious voltage sources used for modeling the solid-state switches. The paper discusses the performance of such a device and presents the basic analytical expressions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Control strategies for multiple static VAr compensators in long distance voltage supported transmission systems

The authors address the small-signal stability and control problems associated with a long distance voltage supported AC transmission system. Linear techniques are used for the control design of multiple static volt-ampere reactive (VAr) compensators along the transmission system. Different voltage control strategies are investigated and additional stabilizing signals are designed using frequency response techniques. A new centralized control strategy is proposed and its performance is shown to be superior to the traditional individual bus voltage control. Linear time responses to step disturbances are included to illustrate the performance of the different control strategies investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Co-ordinated control of synchronous generator excitation and static VAR compensator

The application of multivariable control to a synchronous generator excitation and static volt-ampere reactive (VAR) compensator system is described to design a coordinated excitation and firing angle discrete controller. It is based on a reduced-order linearized model, obtained by system identification, which represents the nonlinear dynamics around a specified operating point. The model structure was investigated by simulation studies indicating that a third-order representation was suitable. Direct comparisons of identified model responses with corresponding results from the nonlinear model show that accurate modeling can be achieved by this approach. Quantitative assessments also established that the models are satisfactory. The controller was evaluated by simulation of a nonlinear generator model, involving comparisons between the coordinated controller with several different controllers, over a wide range of operating conditions and disturbances. It is shown that the coordinated control arrangement can provide better stability, voltage control, and damping than the other schemes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Small signal stability program analysis of SVC and HVDC in AC power systems

High-voltage DC transmission links and static VAr (voltampere reactive) compensators (SVCs) have controllable characteristics with potential for affecting system stability. To study these effects and to design their controllers for improving system stability, there is a need for their representation in small-signal stability programs as well as time simulation programs. The formulation of DC link and SVC models and their controllers for small-signal stability are addressed. Several examples are studied to show the capability and application of the small-signal DC link and SVC models. The small-signal results are verified by time-domain simulation results of the same study cases. Modes obtained by spectral analysis of the time simulation results are very close to those obtained by small-signal stability analysis. >

Application of compact static VAR compensators to distribution systems

The application of SVCs (static volt-ampere reactive compensators) to distribution systems to solve voltage fluctuation problems is discussed. Fast and repetitive voltage fluctuations can exist on an electric utility's distribution system. These voltage fluctuations, which are usually caused by motor-starting or other pulsating or irregular loads such as welders, can be objectionable and can pose problems to the utility. Conventional equipment such as voltage regulators or breaker-switched capacitors are not effective in controlling fast and repetitive voltage fluctuations. Static volt-ampere reactive compensators provide an excellent solution to control voltage fluctuation problems. It is more common to apply SVCs to transmission systems and very large industrial loads because of size and cost constraints. A class of compact SVCs which offers ratings as low as 1 Mvar capacitive and small physical size is described. With the advent of compact SVCs, distribution engineers have another viable option available to solve many of the voltage fluctuation problems in their systems. Information and field experience concerning the compact SVC installed on the Kansas Gas and Electric distribution system are provided. >