Dynamic VAR Compensation Research Articles

Optimal configuration of dynamic VAR compensators considering uncertainty and correlation

AbstractThe transient voltage stability of modern power systems is challenged by the increasing uncertainty on source‐load dual sides. To cope with it, a robust optimal configuration method for dynamic VAR compensators (DVCs) is proposed. First, a series of power‐flow scenarios are generated with uncertainty and correlation considered, where nonparametric kernel density estimation is used to predict the marginal distribution of wind speeds and combined Copula function is employed to characterize correlations between nearby wind farms. Then, the variation‐of‐information indicator is introduced to assess the similarity among power‐flow (PF) scenarios, and representative PF (RPF) scenarios are screened with the help of Spectral clustering algorithm. Finally, locating and sizing of DVCs for RPF scenarios are achieved. By synthesizing the compensation schemes for RPF scenarios, the robust configuration scheme is suggested. Simulation studies in the modified New England 10‐machine 39‐bus system show the proposed method can ensure transient voltage security of the studied power system under source‐load uncertainty.

Dynamic Reactive Power Optimization Configuration of New Energy Power Station Based on Fault Limit Removal Time

The large-scale construction of long-distance, high voltage level transmission projects and sustained load demand increase negatively influence transient voltage stability. A certain amount of dynamic Var compensation at the receiving end of the power grid can significantly improve the stability. Most new energy power plants, such as wind power, and photovoltaic generation, have installed dynamic Var compensation devices. The potential for safety and stability control should be fully exploited. In this paper, it is concluded that the critical fault clearing time is the main index to measure the transient voltage stability of the system, and the critical fault clearing time has been extended by allocating dynamic Var compensation. According to these conclusions, a method for optimal allocation of dynamic Var compensation to improve critical fault clearing time is proposed. The method has determined the optimal capacity and the installation point. The effectiveness of the proposed method is illustrated through simulations on the actual power grid.

Adopting Dynamic VAR Compensators to Mitigate PV Impacts on Unbalanced Distribution Systems

Adopting Dynamic VAR Compensators to Mitigate PV Impacts on Unbalanced Distribution Systems

Reactive power compensation using STATCOM in a PV grid connected system with a modified MPPT method

Commonly Static Synchronous Compensators (STATCOMs) are employed extensively as voltage regulators and VAR compensators in transmission networks in power systems. This research proposes the integration of STATCOMs in distribution networks, particularly in PV grid-connected systems that use distributed energy resources to reduce active and reactive power demand from the grid by supplying variable reactive power from an alternative supply which adapts to the load demand. This decreases the dependence on the utility power supply and promotes the integration of STATCOMs with renewables. Complete case studies between the differences in application of a fixed reactive power compensating condenser and STATCOM for dynamic VAR compensation to loads connected at the point of common coupling in a grid connected Photo-Voltaic (PV) system is presented. The scope of this research is to examine the behavior of dynamic loads, such as an induction motor, at steady state operation when the reactive power demand from the supply increases, as well as the effect of this demand variation on the network that supplies such loads. Complete system modeling and analysis for both scenarios, the fixed reactive power compensator and the STATCOM, supplying various load demands, have been developed. The simulation is based on a 100-kW rated PV grid-connected system to simulate behavior and performance of such study. Adaptive Neuro Fuzzy Inference System with Particle Swarm Optimization was used to extract the maximum power point of the PV array proceeded by a sliding mode controller. MATLAB/ Simulink was developed for modelling and analysis. Various load dynamics with varying solar irradiance and increasing reactive power demand of the associated load were simulated to evaluate various challenges and disturbances on the power supply.

Coordination of D-STATCOM & SVC for Dynamic VAR Compensation and Voltage Stabilization of an AC Grid Interconnected to a DC Microgrid

This article presents a new collaborative control method based on expert decision, proposed for the combined system of an ac grid with a low THD thyristorized static var compensator (SVC), interconnected to a dc microgrid through a distribution static compensator (D-STATCOM) that also works as a bidirectional power converter. The combination of large rating SVC and a low rating D-STATCOM functions as a hybrid compensator for the ac distribution grid. In the combined mode of operation, the D-STATCOM mitigates voltage fluctuations and compensates initial var demands, while the SVC caters to the base var requirements. The D-STATCOM has also been used for integration of a dc microgrid to the utility grid, permitting exchange of power between the grids and thereby reducing voltage fluctuations of both the systems. The proposed collaborative control method based on expert decision can extract the full advantages of the respective subsystems as per demand of the operating condition. This combined system complies with the relevant harmonic standards and can effectively correct system power factor, stabilize bus voltage, and mitigate voltage flicker under fluctuating load conditions. Theoretical analyses with simulation results as well as experimental results show that the proposed system can meet the requirement of continuous dynamic reactive power compensation and voltage stabilization with low cost, high reliability, and large capacity.

Control of Buck-Type Dynamic Capacitor (DCAP) Using Model Predictive Control Method with PSO optimization algorithm for Dynamic Var and Harmonic Compensation

This paper presents a control method based on model predictive control (MPC) to control the buck-type dynamic capacitor (DCAP) to improve power quality. In this method, the reference current consists of two distinct parts, i.e., reactive power compensator (RPC), and harmonic current eliminator (HCE) and based on the load current and dynamically, it adapts itself to load changes. The proposed prediction model (PM) was extracted from the linearized differential equations of the DCAP. In the proposed method, vector decision variables in each cycle converter switching are updated only once during the prediction horizon, and the optimization problem related to predictive control is solved based on the particle swarm optimization (PSO) algorithm. This reduces the volume of calculations significantly. By considering the total harmonic distribution (THD) value and the power factor (PF) value, the prediction horizon is proposed. The proposed method, unlike the EHM method, has fewer control parameters and can be implemented more easily. The simulation results in MATLAB software showed the superiority of the proposed method in comparison with the EHM method on a single phase DCAP.

Reactive Power Compensation Device Performance Analysis in Fault Recovery of Weak AC System

With the large-scale and large-capacity operation of HVDC transmission, the operating characteristics of the receiving-side power grid have changed significantly. In order to improve the dynamic recovery performance of HVDC transmission system, it is urgent to configure dynamic VAR compensation device in the system inverter Station. In this paper, the PSCAD/EMTDC electromagnetic transient simulation software is used to study the dynamic recovery performance of HVDC system for several different var compensating devices in HVDC inverter. In the case of HVDC inverter station commutation bus short-circuit fault, the effect of static var compensator (SVC), fixed capacitor (FC) and synchronous compensator (SC) on system power recovery is studied. The research results show that fixed capacitors have a certain effect on system fault recovery; SVC can effectively improve the voltage level after the fault but its effect and response speed are not as good as SC, At the same time, a large number of TSC will weaken the strength of the AC system; Synchronous compensator can quickly provide emergency reactive support for the system, accelerate system recovery, and enhance system strength, with obvious advantages.

Integer quadratic programming model for dynamic VAR compensation considering short‐term voltage stability

Dynamic VAR compensation (DVC) planning is important in power system planning to enhance short-term voltage stability. However, since its optimisations models include differential algebraic equations (DAEs), existing methods cannot directly solve the problem as that in the optimal power flow problem. In this study, the authors design an integer quadratic programming (IQP) model for the DVC planning problem which can simultaneously optimise the sites and size of DVCs. On the basis of the defined dynamic correlation indices, a quadratic programming objective function is defined to minimise the total investment of DVCs as well as to avoid redundant installation of DVCs on adjacent buses. Subsequently, sensitivity coefficients about the control effect of DVCs are introduced to form the linear inequations as the substitute for DAEs in constraints. Then, an iterative process is applied to solve the IQP. The proposed method is applied on a modified NE 39-bus system and a real power grid. Comparisons to the existing methods are carried out to show its superiority in model complexity and solving efficiency.

Multi‐objective robust dynamic VAR planning in power transmission girds for improving short‐term voltage stability under uncertainties

Modern power transmission grids are facing more and more critical short-term voltage stability problems. This study proposes a novel robust dynamic VAR planning approach for improving the short-term voltage stability level under uncertainties including the peak load level, the maximum proportion of dynamic load, fault clearing time and deviation of the actual capacity of dynamic VAR compensators from rated capacity when contingencies occur. The robust dynamic VAR planning problem is formulated as a multi-objective optimisation model with objectives including the investment cost, the expectation and robustness of the short-term voltage stability level. The complexity of the planning model is firstly reduced by selecting severe contingencies and potential buses, leading to a simplified multi-objective optimisation model. Latin hypercube sampling is then used for the uncertainty quantification. The simplified multi-objective optimisation model is then solved by the combination of a multi-objective evolutionary algorithm called ${\rm \epsilon }$e-NSGAII and extreme learning machine-based surrogate modelling with adaptive training data sampling. This combination significantly reduces the unaffordable computing burden. Simulations are carried on the IEEE 39-bus system, illustrating that the authors proposed methodology is reliable with high computational efficiency, and offering decision-makers planning solutions with high mean performance and strong robustness with respect to the short-term voltage stability level.

A Modular Isolated Topology for Instantaneous Reactive Power Compensation

This paper presents a novel topology for instantaneous reactive power compensation. The topology is derived from the Dynamic-Current or Dyna-C, which is a patented power converter capable of transferring energy for two or multiterminal dc, single- and/or multiphase ac systems. The proposed topology, named dynamic VAr compensator (DVC), has a current source power conversion stage and can provide instantaneous leading or lagging reactive power. The proposed DVC has three individual bridges coupled through a three-winding high-frequency transformer. It has a modular structure that allows it to be series stacked for medium-voltage applications. In addition, the high-frequency Galvanic isolation link provides interphase fault isolation among the three phases. The circuit eliminates the use of electrolytic capacitors for bulk energy storage, which usually lowers life and reliability. Operating principles, theoretical analysis, and design of the proposed topology are described. The converter functionality is validated through simulation as well as experimental results.

Heuristic planning for dynamic VAR compensation using zoning approach

Heuristic planning for dynamic VAR compensation using zoning approach

Pareto-efficient double auction power transactions for economic reactive power dispatch

Pareto-efficient 12-h variable double auction bilateral power transactions have been considered here. Effect of such on the economic welfare is observed while solving the reactive power dispatch (RPD) by differential evolution with random localization technique. This has been accomplished by a combination of static and dynamic var compensators like capacitor and superconducting magnetic energy storage (SMES) considering the IEEE 57-bus network. Out of these 12-h variable power transactions, the Pareto efficient transactions which were reconciled by planed biding, have provided the maximum global welfare. The economics were ascertained by cumulating the net benefits of the market players and the reduced merchandising surplus caused by the var compensators. The combined capacitor–SMES based Pareto efficient observations on economic RPD were able to reduce 7.41% more power loss and 2.5 times improved economic benefit over the singular capacitor placement. This further achieved 0.069% profit enhancement in connection to the fundamental global welfare.

A Multi-Mode Control Strategy for VAr Support by Solar PV Inverters in Distribution Networks

This paper proposes a multi-purpose VAr control strategy for solar PV inverters for voltage support in distribution networks. The proposed strategy can be applied under various PV power generation conditions. The inverters will normally operate in a dynamic VAr compensation mode for voltage support (including low PV and no PV periods). During mid-day when PV has surplus power, the proposed strategy will control the PV inverters to absorb VAr for voltage rise mitigation using a droop characteristic approach. During passing clouds, the strategy will mitigate voltage fluctuations by ramp-rate control of inverter VAr output. A dynamic model of the proposed PV inverter control has been developed to analyze its performance in terms of fast VAr control and voltage support under various PV generation conditions. The results of the analysis performed on an Australian distribution system show that the proposed VAr control strategy can mitigate voltage rise, and improve the voltage profile despite potential vast changes in the sun irradiation during passing cloud and also in the absence of PV output during the evening.

Simulation Research on Starting Resistor Parameter Selection of 10kV Chain Static Var Generator

Before commissioning, SVG first requires a separated excitation process: network voltage charges the capacitor on DC side in each H-bridge power module via the starting resistor (IGBT in all modules shall lock impulse). After charging, SVG has enough power for dynamic var compensation of the system. This paper introduces fundamental functions of the starting resistor in SVG, analyzes the influence of starting resistor selection on safe operation of the device, raises the principle of selection and conducts simulation verification by using of PSCAD.

Stability Study of Grid Connected to Multiple Speed Wind Farms with and without FACTS Integration

Integration of wind power into power grid has developed several problems like lack of reactive power at point of common coupling which leads to voltage stability problems for the utility owner. Due to the weakness of shunt capacitor banks in maintaining voltage stability as well as reactive power improvement at point of common coupling and wind turbine generator bus, STATCOM and SVC as dynamic var compensators have been attached at the transmission network to support the stability of the proposed system. In this paper, three wind farms of different wind speed connected to grid with and without flexible AC transmission systems have been proposed. Simulations are carried out using Matlab/Simulink to investigate the performance of the proposed system under normal and abnormal conditions. 

Research on Supporting Effect of Dynamic Var Compensation to the Security of Large-Scale Wind Power Integration

There are security and stability problems happened in northwest china power grid connected with jiuquan large-scale wind farms in practice, such as voltage rising and low-frequency oscillation. Analyzing data is the high load mode of Northwest Power Grid in the winter of 2012 in this paper. On this basis, simulation was implemented by using BPA simulation software to analyze the support and improvement of dynamic reactive power compensation equipment on security problems happened in jiuquan. Analysis results show that: dynamic reactive power compensation equipment has characteristics as automatic, fast regulation of reactive power. The security and stability of power grid connected with jiuquan large-scale wind farms can be enhanced effectively when these characteristics are full used.

Research of SVC Control System Based on Real-Time Operation System for Wind Farm

Wind power generation was developed rapidly in China. And many wind farms are configured Dynamic Static Var Compensators (SVCs) as reactive power compensator, which can meet the dynamic demands of the reactive power compensation for the wind farm. The paper put forward a coordination control strategy of reactive power for wind farm based on embedded real-time operation system in DSP, and by using LabVIEW to realize PC management and network communication management, and provides the research foundation for coordination and the optimal control of reactive power in large wind farm.

The Study on a New Type of Full-Voltage Starting Method of Asynchronous Motors

For various problems in the procedure of high-power induction motor’s starting and disadvantages of traditional starting methods, this paper proposed a new type of full-voltage starting method of high-power induction motor—a full-voltage starting method with dynamic reactive power compensation, introduced its principle, studied the control strategy of full-voltage starting with dynamic var compensation emphatically, and established the simulation model for direct starting, soft starting and full-voltage starting with dynamic var compensation based on the Matlab/Simulink simulation software to do digital simulation and compared three methods. The simulation results indicated that the method proposed in this paper can make the high-power induction motor start fast and smoothly with both high-torque and low starting current, and it has a better starting performance than traditional starting methods and the advantage of not affecting power quality.

Design and Application of Var Compensation Method for Traction Power Supply Systems of Electrified Railway

The application of electric power, which acts as a pillar energy and economic artery in modern society, is one of the most important symbols of the level of development and comprehensive national power of a country. Var is a crucial factor for the design and operation of AC power systems, and is closely bound up with the safety, stabilization, and economical operation of power systems. With the development of electrified railway, the importance of the dynamic var compensation for traction power supply systems of electrified railway becomes more and more distinct. Developing the var compensation strategy vigorously has important senses in theory and practice. In this article, synthetically considering technique and economic leval of power systems in our country, parameters modeling and design and verification and specific engineering application of a var compensation method are presented. This method is a preferable one for resolving undesirable effect on power systems from traction power supply systems of electrified railway, especially having dynamic and real time characteristics of var compensation.

Optimal Siting and Sizing of UPFC Control Settings in Grid Integrated Wind Energy Conversion Systems

The depletion of fossil fuel reserves, emission of greenhouse gases and the uneven distribution of existing reserves led the countries to look for sustainable alternatives, especially wind power. In India mostly Squirrel cage induction generators (SCIG) are used for extracting energy from the wind. Induction generators inject real power to the grid and absorb reactive power from grid. Normally, fixed capacitors of rating equal to no-load compensation are installed at the wind-turbine. Reactive power absorbed by the SCIG over and above the no-lad compensation is dependent on the operating condition. To compensate for the reactive power (over and above the no-load compensation) dynamic VAR compensator can be installed at the point of common coupling. When the wind-farm is connected to a weak grid there may be a problem with wind penetration into the grid. UPFC (a versatile FACTS controller) will be able to alleviate the problems associated with fixed speed wind-farms that are connected to a weak grid. In this paper finding the location and capacity of the UPFC for minimisation of power generation cost is posed as a non-linear optimization problem. An efficient Primal-Dual Interior Point algorithm in conjunction with second order sensitivity analysis is made use for solving the above problem. The optimal line placement for wind penetration in terms of marginal values of UPFC variables are identified using first order sensitivity analysis. Second order sensitivity analysis has been employed to identify the optimal line placement for highest cost savings. Further actual cost savings and optimal control settings of UPFC are evaluated by actually placing UPFC in each line. The proposed approach is tested on a sample 9-bus system using the program developed in Matlab and the results are encouraging. The results indicate that the estimation of optimal placement of UPFC for a large system is possible reducing the computation time involved.