Reactive Power Sources Research Articles

Reactive Power Optimization of Power System Based on Improved Differential Evolution Algorithm

This paper presents a novel differential evolution (DE) algorithm, with its improved version (IDE) for the benchmark functions and the optimal reactive power dispatch (ORPD) problem. Minimization of the total active power loss is usually considered as the objective function of the ORPD problem. The constraints involved are generators, transformers tapings, shunt reactors, and other reactive power sources. The aim of this study is to discover the best vector of control variables to minimize power loss, under the premise of considering the constraints system. In the proposed IDE, a new initialization strategy is developed to construct the initial population for guaranteeing its quality and simultaneously maintaining its diversity. In addition, to enhance the convergence characteristic of the original DE, two kinds of self-adaptive adjustment strategies are employed to update the scaling factor and the crossover factor, respectively, in which the detailed information about the two factors can be exchanged for each generation dynamically. Numerical applications of different cases are carried out on several benchmark functions and two standard IEEE systems, i.e., 14-bus and 30-bus test systems. The results achieved by using the proposed IDE, compared with other optimization algorithms, are discussed and analyzed in detail. The obtained results demonstrated that the proposed IDE can successfully be used to deal with the ORPD problem.

Reactive Power Planning in Distribution System Using Genetic Algorithm.(Dept.E)

This paper presents a solution for the Volt/VAR control (VVC) problem in distribution system using Genetic Algorithm (GA). The problem is divided into two parts. In the first part the candidate buses for reactive power insertion are determined. In the second part the locations, number and sizes of reactive power sources are determined in an optimal manner. The solution method has been implemented and tested with a 12-bus IEEE test system.

Design of fractional evolutionary processing for reactive power planning with FACTS devices

Reactive power dispatch is a vital problem in the operation, planning and control of power system for obtaining a fixed economic load expedition. An optimal dispatch reduces the grid congestion through the minimization of the active power loss. This strategy involves adjusting the transformer tap settings, generator voltages and reactive power sources, such as flexible alternating current transmission systems (FACTS). The optimal dispatch improves the system security, voltage profile, power transfer capability and overall network efficiency. In the present work, a fractional evolutionary approach achieves the desired objectives of reactive power planning by incorporating FACTS devices. Two compensation arrangements are possible: the shunt type compensation, through Static Var compensator (SVC) and the series compensation through the Thyristor controlled series compensator (TCSC). The fractional order Darwinian Particle Swarm Optimization (FO-DPSO) is implemented on the standard IEEE 30, IEEE 57 and IEEE 118 bus test systems. The power flow analysis is used for determining the location of TCSC, while the voltage collapse proximity indication (VCPI) method identifies the location of the SVC. The superiority of the FO-DPSO is demonstrated by comparing the results with those obtained by other techniques in terms of measure of central tendency, variation indices and time complexity.

Combined Firm and Renewable Distributed Generation and Reactive Power Planning

The benefits of integrating Distributed Generation (DG) into the distribution networks depend on the characteristics of different types of DG units, loads and Reactive Power Sources (RPS). These benefits can be optimized if the firm DG units such as biomass energy and renewable DG units such as photovoltaic (PV) and wind system are optimally sized, located and coordinated with reactive power sources. In this paper, by assuming that the Distribution System Operator (DSO) has got the ownership and operation of DG units and RPS, a new planning strategy is proposed for determining the optimal placement and rating of DG units and RPS. This strategy overcomes the challenge of intermittency of renewable production in order that this planning will assist the system operators in defining the better integration strategies of firm and intermittent energy systems and reactive power sources in distribution networks. The proposed planning is based on single objective optimization so that it optimizes one of the following objective functions every time: the system energy losses, voltage stability margin, self-adequacy of microgrids defined on the distribution system and exchange of active and reactive powers between the distribution system and upstream network. The proposed technique accounts for the uncertainties associated with solar irradiance, wind speed and demand through a probabilistic optimization. The formulation of each planning problem is presented and applied to the 69-bus distribution system. The results of different planning strategies are compared and analyzed. Furthermore, the impact of the planning with each objective function on other indices is evaluated.

Calculation of the payback period for the introduction of reactive power sources into power supply systems

At present, the sources of reactive power are widely used in telecommunication facilities that have windings (electric motors, transformers, etc.) in the design. To manage these sources, necessary to introduce new technical means and elements, including microprocessor blocks. Combined control of reactive power sources and voltage regulation with the help of a microprocessor-based unit of electric receivers of telecommunication objects turns out to be technical and economical not only for reactive power sources, but also for lowering transformers of the power supply system.

Modern Features of Price Formation on the Reactive Power Market

This article discusses the specific features of such a product as reactive power. The degree of reactive power compensation both in the domestic electric power industry and in most industrialized countries is clearly insufficient. The possibilities available in electric grids, at power plants and at consumers of electricity for coordinated regulation of reactive power and voltage levels are not fully used. The main factors influencing the formation of the reactive power market in the electric power industry are revealed. The proposed market is based on the organization and implementation of qualified selection of reactive power suppliers. The scheme of the price bid of reactive power suppliers, developed on the fundament of the cost structure of various types of reactive power suppliers is proposed. Rational regulation of reactive power is currently not considered as an economic problem, but it is one of the main tools for managing the efficiency of EPS. The proposed organizational mechanism of pricing for reactive power and the qualified selection of its suppliers is aimed at determining the range of suppliers of reactive power capable of meeting the demand for it with the least costs, as well as to stimulate investments in the construction of new sources of reactive power.

Features of autonomous and parallel operation of an asynchronous generator with a network of endless power in the current stage of EPS development

The article describes the use of asynchronous machines in generator mode to provide power to threephase consumers, as well as the features of autonomous and parallel operation of an asynchronous generator with an infinite power network. The use of static sources of reactive power allows widespread introduction of an asynchronous generator in the electric power system as a reliable source of active power.

A Common Capacitor Based Three Level STATCOM and Design of DFIG Converter for a Zero-Voltage Fault Ride-Through Capability

To meet the augmented load power demand, the doubly-fed induction generator (DFIG) based wind electrical power conversion system (WECS) is a better alternative. Further, to enhance the power flow capability and raise security margin in the power system, the STATCOM type FACTS devices can be adopted as an external reactive power source. In this paper, a three-level STATCOM coordinates the system with its dc terminal voltage is connected to the common back-to-back converters. Hence, a lookup table-based control scheme in the outer control loops is adopted in the Rotor Side Converter (RSC) and the grid side converter (GSC) of DFIG to improve power flow transfer and better dynamic as well as transient stability. Moreover, the DC capacitor bank of the STATCOM and DFIG converters connected to a common dc point. The main objectives of the work are to improve voltage mitigation, operation of DFIG during symmetrical and asymmetrical faults, and limit surge currents. The DFIG parameters like winding currents, torque, rotor speed are examined at 50%, 80% and 100% comparing with earlier works. Further, we studied the DFIG system performance at 30%, 60%, and 80% symmetrical voltage dip. Zero-voltage fault ride through is investigated with proposed technique under symmetrical and asymmetrical LG fault for super-synchronous (1.2 p.u.) speed and sub-synchronous (0.8 p.u.) rotor speed. Finally, the DFIG system performance is studied with different phases to ground faults with and without a three-level STATCOM.

Analysis of current conversion primary sensors dynamic characteristics of a reactive power source with renewable energy sources into secondary voltage

This paper presents the structure of a sensor for converting multiphase primary currents into a secondary voltage of reactive power networks with renewable energy sources, an algorithm for modeling processes in the sensor, which provides control over the primary current and a control device. The dynamic characteristics of the investigated sensor are given on the basis of the proposed analytical expressions. A graph model to study the conversion processes into secondary output voltages has been created. The sensor has been shown to be capable of generating a secondary signal at high speed.

Магнитно-вентильные управляемые реакторы трансформаторного типа с пофазным регулированием мощности

The article outlines the basic theory, operation principle, peculiarities of electromagnetic processes, and circuit and design solutions of a fundamentally new three-phase magnetic-valve controllable reactor, which combines increased response speed with high-precision stabilization of the current reactive power value. The advisability of a monoblock design with all power elements of the device placed in one transformer-type tank is substantiated. An example of the design of a magnetic-valve controllable transformer-type reactor for a capacity of 25 Mvar, and rated voltage of 35 kV is given along with an analysis of the effectiveness of its three-year operation as part of the Petrovsk-Zabaikalskaya 220/110/35 kV digital substation. It is shown that a reactive power source based on a new magnetic-valve controllable reactor is able---in addition to its main function of optimizing reactive power flows between power supply centers and load nodes---to normalize the voltage quality in a three-phase network with a nonlinear asymmetrical load in terms of such indicators as compensation of slow deviations of the three-phase voltage, symmetry of line-to-line voltages, and elimination of their waveform distortion.

სისტემაწარმომქმნელ ქსელში რეაქტიული სიმძლავრის დამატებითი წყაროს შერჩევის კრიტერიუმი და მათემატიკური მოდელი

In a backbone network (𝑈􀯡 ≥ 220 𝑘𝑣), when the high-voltage lines are loaded with power less than natural power, we have excess reactive power. Supplying this power into the lower-voltage networks (𝑈􀯡 ≤ 110 𝑘𝑣) would be technically and economically unfeasible and requires compensation on site. In the article, in accordance with the electricity quality criterion, and taking into account the principle of a systemic approach, and using the self- and mutually reactive impedances of the network junction points, a mathematical model for selecting a compensating device in a backbone network is adopted. The quality criterion of electricity involves enforcement of requirements for the operating voltages in the junction points of a backbone network. According to the obtained mathematical model, in the junction points nodes where the operating voltages exceed their permitted values, there will be installed the compensating devices for receiving excess reactive power. However if any junction point has a high reactive load and the voltage, in this context, is below its permitted value, then, according to a model, there is a need for installing the source of reactive power in this junction point. Herewith, according to economic criterion, the model envisages the optimal redistribution of mentioned source of reactive power between the junction points of a distribution network connected to backbone network junction point.

Комплексное использование технологий Smart Grid в тяговых сетях железных дорог

The purpose of the paper is to develop a methodology for modeling railway power supply systems equipped with a set of devices implemented on the base of smart grid technologies. The research is carried out using the Fazonord software package designed for modeling the modes of railway power supply systems in phase coordinates. The calculation model is implemented for the power supply system of a two-track section with five traction substations. The results obtained show that reliable and high-quality power supply of train traction and non-traction consumers can be ensured on the basis of the integrated use of active Smart Grid elements, such as a phase number converter, active harmonic conditioner, controlled reactive power source, and a distributed generation unit. Computer simulation allows to establish that in the absence of reactive power sources there are noticeable voltage fluctuations on 10 kV buses of non-traction consumers; the asymmetry is approaching the limit of normally acceptable values; disabling of the active filter results in the increase of the total harmonic coefficient of voltages up to 16%; if the entire complex of active devices is available, the high quality of electrical energy is achieved; the phase number converter is robust and features low sensitivity to the errors in parameter setting; voltage deviations caused by the limited variation range of reactive power in the reactive power source are short-term and do not exceed the values acceptable in practice. Thus, on the basis of Smart Grid technologies, distributed generation units can be connected directly to the traction network using a phase number conversion device formed according to the reciprocal Steinmetz circuit. Elimination of harmonic distortions created by rectifier electric locomotives is carried out by means of an active conditioner of higher harmonics. A controlled reactive power source can be used to maintain voltage levels.

Optimal Placement and Sizing of Reactive Power Sources in Active Distribution Networks: A Model Predictive Control Approach

Reactive power sources have the potential for active distribution network (ADN) loss reduction and voltage profile improvement. However, the effective operation of reactive power sources depends upon their proper placement and sizing. To address this issue, this paper presents an optimal reactive power source allocation strategy in ADN. The salient feature of this strategy is that, by incorporating the ADN control scheme into the allocation process, it achieves the optimal allocation in a dynamic context. Specifically, smart transformer is considered as a particular realization of reactive power source, and the allocation problem is formulated as linear programming, which aims to minimize the investment cost of smart transformers. Meanwhile, the ADN control scheme is designed via model predictive control (MPC), with objectives of voltage regulation and loss reduction. Subsequently, the MPC formulation is embedded into the allocation problem, thus forming an integrated optimization problem, which links the control domain with the planning domain. By using the generalized Benders decomposition, this integrated problem is decomposed into a master problem and a set of subproblems, which can be solved alternately and iteratively. Simulation results verify the effectiveness of the proposed strategy.

Assessment of voltage changeability with reactive power source allotment for real time network

In this research work investigation of reactive power necessity at standard voltage level is practiced. The 39-bus test network modeled in mipower application is a part of Rajasthan power system, attached with North Regional National Grid synchronized at 765 kV voltage level. State power utilities are unable to obtain the profoundness in providing, static or dynamic compensation at multiple voltage available within the grid. Reactive power drawl from the network end is judged and analysed by placing imaginary generator at available voltage level. In Rajasthan power system voltage level arrays from 765 kV to 33 kV and the utilities are puzzled in managing var penetration due to poor estimation. As a result, higher loading levels and abrupt line tripping raises losses and reduces system reliability. The simulation case studies presented herby from the database of financial year 2018-19 will be envisaged by the utilities after evaluation is over. Presently State Load Dispatch Centers deliver instruction to substations to utilize any compensation device available without prior calculation. But this paper underlines a way to access the effects on voltage profile, losses etc. in power system structure after planned var support at optimum voltage level. Case studies over real time network is detailed, to check the observability for a load of 370 MW. The impact of practices followed is observed for the designed network.

МОДЕЛИРОВАНИЕ РЕЖИМОВ ДАЛЬНИХ ЛЭП, ОСНАЩЕННЫХ УСТАНОВКАМИ ПРОДОЛЬНОЙ КОМПЕНСАЦИИ

The results of computer studies of long-distance transmission modes of 500 kV, equipped with a longitudinal compensation unit, shunt reactors and a controlled source of reactive power are presented. It is shown that in the presence of all of the above devices, the relative losses of active power at the main section of the power transmission line are reduced by half compared with situations of their absence.

Coordination of PV Inverters and Voltage Regulators Considering Generation Correlation and Voltage Quality Constraints for Loss Minimization

Distributed generation sources (DGs) are widely considered as important sources of power generation in distribution systems during the last few decades. Despite the substantial benefits of DGs, increasing the penetration level of the DGs can cause dramatic voltage magnitude fluctuations. Coordination of the use of dynamic reactive power sources such as photovoltaic (PV) inverters and voltage control equipment can mitigate rapid voltage magnitude fluctuations. A coordinated volt-var control method is proposed herein to achieve the optimal expected performance (e.g., system losses) while considering the spatial correlation among PV source powers and constraining the variability of voltage magnitudes throughout the distribution network within permissible ranges. The proposed strategy formulates chance constraints on the voltage magnitude and considers the uncertainty of PV power injections over the interval of interest to maintain voltage magnitudes within acceptable limits. The proposed method has been tested on the IEEE 123-node radial distribution system for validation. Moreover, the simulation results demonstrate that the proposed method can effectively mitigate the fast voltage magnitude deviations with an acceptable reduction in system losses in the presence of intermittent renewable resources.

Quantifying robustness of Type 4 wind power plant as reactive power source

The quantification of reactive power reserves can be essential for transmission system operators for the secure operation of large power systems with high share of renewables. Reactive power support from renewable energy sources needs to be included in reactive power reserve estimation. The reactive power capability of variable renewable energy sources like wind power plants depends on active power production. The stochastic nature of wind speed, and thereby active power production, makes reactive power reserve estimation quite complex. This article proposes a novel methodology to estimate reactive power reserve of wind power plants, taking the uncertainties such as the active power fluctuation, the technical availability of wind turbines as well as the on-load tap changer position of wind power plant transformers into account. The methodology incorporates the definition and determination of robustness index for wind power plant as a reactive power source. The proposed methodology is evaluated on a test system, by assessing the impact of the robustness index on long-term voltage stability. The results show that the choice of an appropriate time period for assessment of wind power plant as a reactive power source is critical to have a high degree of confidence in reactive power reserve estimation. Furthermore, the investigation reveals the importance of considering the power fluctuation and availability in the estimation of the reactive power reserve. The presented case study shows that ignoring fluctuation and availability can lead to overestimation of maximum power transfer, resulting in wrong assessment of the power system security. The proposed methodology can be used by the transmission system operators to quantify the reactive power reserve in real-time and allow better integration of wind power plants in voltage stability assessment studies.

Control Design of Automatic Voltage Regulator to Improve the Voltage Stability at Sengkang Power Plant, South Sulawesi Indonesia

The change in voltage at the generator terminal is highly correlated with the change in reactive power at the center load. There are several reactive power sources in the power system including those from field amplifiers that are controlled by equipment called Automatic Voltage Regulators (AVR). Changes in reactive power in the system will change the voltage profile including the voltage at the generator terminal. To maintain the voltage level on the generator terminal, the AVR must be adjusted properly. Determination of the value of the amplifier gain on the AVR largely determines the performance of the AVR in stabilizing the voltage. Wind Turbine penetration greatly affects the system voltage. This research is to see the impact of voltage changes due to wind turbine penetration in sulseltrabar interconnection systems. Determination of AVR gain is generated from the Routh-Hurwitz equation. Furthermore, in this study PID control will be applied to increase the AVR output response. Determination of the correct Kp, Ki and Kd constants is obtained with the help of a MATLAB simulation model. The simulation shows that using a PID controller, the overshoot and settling times obtained are better. The maximum exceeded voltage is 1 per unit and the settling time is 10.15 seconds.

A New Approach for PV Nodes Using an Efficient Backward/Forward Sweep Power Flow Technique

Most of the distribution networks may contain reactive power sources such as distributed generators with reactive support, static VARs compensators or even switching capacitors. In this sense, it is necessary to have an appropriate and convenient model for controlled-voltage (PV) nodes to be applied in power flow distribution networks. On the other hand, the conventional power flow analysis has been an important tool for all power systems engineers. The nonlinear methods based on the Newton- Raphson method and its decoupled forms and the Gauss-Seidel with Ybus factorized method have been popular to nowadays. However, these methods have presented some convergence problems when are applied to distribution networks analysis. The reasons are the inherent characteristics of distribution networks, such as high r/x ratios, very low branch impedances, radial feeder configurations, among others. In this sense, the techniques based on Backward/Forward Sweep (BFS) methods for power flows have been widely applied in distribution systems. However, as above mentioned for controlled-voltage (PV) nodes some challenges in BFS power flow algorithms are presented, some authors have proposed hybrid methods, iterative methods, sensitivities matrix- based methods, among others. Unfortunately, those methods usually require complex formulations and long execution times. In this paper a new approach and easily controlled-voltage (PV) formulation joint with a simple power flows methodology, called LRSV method, is presented. The results show that this no-complex methodology permits to obtain better execution times, responses in a better way for different load, generation and configurations and some tests cases to demonstrate the effectiveness of the proposed methodology.

A Coordinated Voltage and Reactive Power Control Architecture for Large PV Power Plants

The increasing presence of nonprogrammable renewable energy sources (RES) forces towards the development of new methods for voltage control. In the case of centralized generation, the hierarchical regulation or secondary voltage regulation (SVR) is guaranteed by coordinated voltage and reactive power controls in transmission systems. This type of regulation loses effectiveness when the generation becomes distributed and based on small and medium sized generators. To overcome this problem, it is important that also distributed generators, typically based on RES, participate in the voltage regulation. By starting from the methodologies already applied, this work wants to present a new method for involving distributed generators in SVR. The novelty is given by the application of an existing methodology to the new configuration of electrical grids characterized by a relevant distributed generation. The aim is to control the distributed generators (DGs) as coordinated sources of reactive power for conveniently supporting the voltage regulation. In this paper, a real large photovoltaic (PV) plant is considered. The power plant is composed of several PV generators connected through a distribution network. With the algorithm proposed, the set of generators can be treated as a single traditional power plant that can participate in the hierarchical voltage regulation. The reactive power of each single generator is coordinated in a way similar to the SVR used in several national systems.