Reactive Power Reserve Research Articles

The Impact of Large Scale Wind Power Integration on a Regional Power Grid - A Case Study

Renewable Energy especially wind energy integration has attained profound growth across the worldwide power system. Wind energy integration at large scale comes up with the challenge on voltages and reactive power management at power system level. The research work presented in this paper has analyzed the impact of wind energy on reactive power reserve with special reference to Hebei Southern Power System. The maximum wind power integration capacity is calculated, and the effect of increasing wind power integration on voltage profiles is studied. Possible controls from system sides and its effects on wind power integration are explored. Study shows that with the increase of the wind power integration capacity, the intermittency and variation will bring more serious problems to the system frequency regulation, reserve service and voltage control. These problems also become the limiting factors for further increase of large-scale wind power integration. In order to make a better use of wind power resources in Heibei province and maintain system safety at the same time, further research should be performed on exploring the reactive and active power regulation and control of the wind farm and the methods to decrease the variability of wind farm outputs.

Adaptive Power Control Method Considering Reactive Power Reserve for Wave-Offshore Hybrid Power Generator System

The combined generator system with the wind and wave power can share the off-shore platform and therefore have the advantage of constructing the transmission system as well as the power conversion system. The established wind power generator systems do output determination by following the transmission system operator's directions and control the turbine by focusing at PCC, but when connected with the wave-power generator; it is needed to do the complex control. Especially, since the method and impact of active power control are different, it is required to distribute demanding power and responsibility to each turbine by considering the grid condition. In this paper, the control system is formed to do output determination of the combined generator system by paying attention to reactive power reserve of utility grid with the analysis of the controllable elements of the wind and wave power generator. And the comparison with the existing system is carried out based on the real system information. Through using the PSCAD/EMTDC simulation, the suitability of the new control technique of the combined system is estimated by proposing the active power control according to the reference signal of TSO and the reactive power capability followed by it.

An approach for real time voltage stability margin control via reactive power reserve sensitivities

This study proposes a man-in-loop control method to boost reactive power reserves (RPRs) while maintaining a minimum amount of voltage stability margin (VSM) bus voltage limits. The objective is to determine the most effective control actions in order to reestablish critical RPRs across the system. Initially, the concept of reactive power reserve sensitivity with respect to control actions is introduced. In the sequel, a control approach based on convex quadratic optimization is used to find the minimal amount of control necessary to increase RPRs above their pre-specified (offline) levels. Voltage stability margin constraints are incorporated using a linear approximation of critical RPRs.

Reactive power procurement model in electricity markets based on normalized effective reactive power reserve

SUMMARY As one of the important security criteria, power system operators closely monitor reactive power reserve in voltage control areas (VCAs) of their system to ensure voltage security and to prevent voltage collapse. Therefore, from a system/market operator perspective, proper management of reactive power reserve must be considered in reactive power procurement stage. This paper proposes a long-term procurement model to meet reactive power reserve requirements in competitive electricity markets considering both economical and technical issues. The model would be of interest to system/market operators since it is based on a new indicator referred to as normalized effective reactive power reserve (NERPR) as a more meaningful signal compared to other physical/economical indicators. The proposed framework for reactive power procurement determines accepted bids by minimizing the associated procurement cost while maximizing NERPR in each VCA of the system. Physical constraints such as generator capability curves and voltage security are taken into account in the formulation. Also, a population-based algorithm is introduced here to solve the mixed integer non-linear programming (MINLP) problem resulted from the procurement model. An algorithm is proposed to change the MINLP problem to series of NLP sub-problems. The CIGRE 32-bus test system is used to test the feasibility of the proposed procurement model. Copyright © 2013 John Wiley & Sons, Ltd.

A New Framework for Reactive Power Dispatch in Electricity Markets

This study proposes a reactive power dispatch model within the context of electricity markets considering both technical and economical issues. The model utilizes a new metric introduced here for reactive power reserve management in voltage control areas. Besides minimizing total reactive power payments, the objective function manages for an optimum reserve in each voltage control area. The proposed reactive power dispatch model is decoupled from active power dispatch and the generators' active power is assumed fixed during the procedure. The relation between active power and reactive power of a synchronous generator is also included in the model by considering the generators’ capability curves. The CIGRE 32-bus test system is used to demonstrate the feasibility and aspects of the proposed model.

A novel methodology for maximization of Reactive Reserve using Teaching-Learning-Based Algorithm

This paper presents a new algorithm to optimize the reactive reserve. As the amount of reactive reserves at generating station is a measure of voltage stability. A new approach for scheduling of reactive power control variables for voltage stability enhancement using teaching-learning-based optimization (TLBO) has been developed. An objective function selected for maximization of reactive reserve for maintaining the voltage stability. A Sensitivity inequality relation analysis based proximity indicator has been selected for obtaining desired stability margin whose value along with reactive power reserve maximization assures desired static voltage stability margin. TLBO has been selected because this is an efficient optimization method for large scale non linear optimization problems for finding global solutions. It is basically based on the influence of a teacher on an output of learners in a class. Developed algorithm has been implemented on 6-bus standard test systems. The problem of reactive power optimization has played an important role in the reliable and optimum operation of power system. Reactive power reserve optimization (RPRO) has complex and non-linear characteristic with large number of equality and inequality constraints (1). The reactive power optimization problem is a nonlinear combinational and computational optimization problem and during last two decades there are many efforts has been devoted to the development are done by using different mathematical methods known as optimization techniques for solving the reactive power optimization problems. Primarily the conventional optimization techniques such as linear programming and non linear programming are in practice with the advantage of computational speed and convergence with the objective function of continuous and differentiable value. These are so named as conventional optimization techniques because they cannot handle the large and discrete-continuous problems such as reactive power optimization. So recently, computational intelligence based optimization techniques are in practice and have been proposed in the application of reactive power optimization such as genetic algorithm (GA), Tabu search, simulation annealing, particle swarm optimization(PSO), differential evolution(DE) and most recent one is teaching- learning-based-optimization (TLBO).these all are consider as most practical, user friendly and powerful scheme to obtain the global optimum solution for different optimization problems(2).

Reactive Power Reserve Improvement Using Power Systems Inherent Structural Characteristics

This paper considers the use of the inherent structural characteristics of power system networks for improving the reactive power reserve margins for both topologically weak and strong networks. The inherent structural characteristics of the network are derived from the Schur complement of the partitioned Y-admittance matrix using circuit theory representations. Results show that topologically strong networks, operating close to the upper voltage limit could be made to increase their loadability margin by locating reactive power compensators close to generator sources, whereas topologically weak (ill conditioned) networks could be made to operate within the feasible operating limits by locating reactive power compensators on buses farther from generator sources.

OPF based reactive power planning and voltage stability limit improvement under single line outage contingency condition through evolutionary algorithms

Reactive power planning is vital for maintaining the voltage stability of power systems and evolutionary algorithms are highly useful for achieving this task. This paper compares the effectiveness of the differential evolution (DE) and evolutionary programming (EP) algorithms in optimizing the reactive power planning of power systems under line outage contingency conditions. DE is efficient in exploration through the search space of the problem, while EP is simple and easy to implement. The low cost but fast response thyristor-controlled series capacitor (TCSC) flexible alternating current transmission system (FACTS) device is incorporated to control the power flows. The optimal settings of the control variables of the generator voltages, transformer tap settings, and location and parameter settings of the TCSC are considered for reactive power planning and the resultant reactive power reserves. The effectiveness of the proposed work is tested on the IEEE-30 Bus test system under the most critical line outage condition.

Preventive reactive power management for improving voltage stability margin

Voltage stability imposes important limitations on the power systems operation. Adequate voltage stability margin needs to be obtained through the appropriate scheduling of the reactive power resources. The main countermeasures against voltage instability could be distinctly classified into preventive and corrective control actions. This paper proposes a preventive countermeasure to improve the voltage stability margin through the management of the reactive power and its reserve. The voltage and reactive power management is studied from the generator's point of view to maximize effective generator reactive power reserve (EGRPR). Detailed model of the generators including the armature and field current limits, as well as the switch mode between the voltage control and the reactive power limitations are considered to maximize the reactive power capability of the generators in emergency states. One-stage and two-stage optimization approaches are utilized to find the optimum solution. The proposed optimization procedure is applied on a 6-bus system and the New England 39-bus system to illustrate the effectiveness of the method.

Coordinated Optimization and Control Technology between Active and Reactive Power

As the coupling between active and reactive power is enhanced along with the expansion of the grid scale and the AC-DC hybrid operation, voltage stability is not only closely related to reactive power, but also related to active power. By the constraints of generator power circle and its operating limits, the mechanism of interaction between the active and reactive power is clarified. Also, the hierarchy structure of coordinated optimization and control technology between them is established, and an improved AGC control strategy consideration to static voltage stability is proposed. By optimizing the active power output of the AGC unit, the dynamic reactive power reserve capacity of each unit is improved and the system voltage is supported. The strategy is verified through a variety of experiments on the IEEE-39 bus system.

계통 안전성을 고려한 원자력발전의 부하추종 요건연구

Nuclear power generation is increasing domestic power supply ratio by lower CO2 emission and fuel prices. Currently, nuclear power generator has been operated with maximum power output. Therefore, nuclear power generator could be no effect to managing the reactive power reserve on power system. The reactive power reserve is calculated to the difference between maximum facility and operation generation capacity of the power system. This paper was proposed that load following of nuclear power is control by using 15-bus power system model. In the simulation result, power system is shown to safety state by operating load following of nuclear power generator. This method has be improved the supplied reliability through economic and efficient operation.

Coordination Control of Voltage Between STATCOM and Reactive Power Compensation Devices in Steady-State

This paper proposes a new coordinated voltage control scheme between STATCOM (Static Synchronous Compensator) and reactive power compensation devices, such as shunt elements(shunt capacitor and shunt reactor) and ULTC(Under-Load Tap Changer) transformer in a local substation. If STATCOM and reactive power compensators are cooperatively used with well designed control algorithm, the target of the voltage control can be achieved in a suddenly changed power system. Also, keeping reactive power reserve in a STATCOM during steady-state operation is always needed to provide reactive power requirements during emergencies. This paper describes the coordinative voltage control method to keep or control the voltage of power system in an allowable range of steady-state and securing method of momentary reactive power reserve using PSS/E with Python. In the proposed method of this paper, the voltage reference of STATCOM is adjusted to keep the voltage of the most sensitive bus to the change of loads and other reactive power compensators also are settled to supply the reactive power shortage in out range of STATCOM to cope with the change of loads. As the result of simulation, it is possible to keep the load bus voltage in limited range and secure the momentary reactive power reserve in spite of broad load range condition.

Optimal stochastic reactive power scheduling in a microgrid considering voltage droop scheme of DGs and uncertainty of wind farms

Distributed Generators (DGs) in a microgrid may operate in three different reactive power control strategies, including PV, PQ and voltage droop schemes. This paper proposes a new stochastic programming approach for reactive power scheduling of a microgrid, considering the uncertainty of wind farms. The proposed algorithm firstly finds the expected optimal operating point of each DG in V-Q plane while the wind speed is a probabilistic variable. A multi-objective function with goals of loss minimization, reactive power reserve maximization and voltage security margin maximization is optimized using a four-stage multi-objective nonlinear programming. Then, using Monte Carlo simulation enhanced by scenario reduction technique, the proposed algorithm simulates actual condition and finds optimal operating strategy of DGs. Also, if any DGs are scheduled to operate in voltage droop scheme, the optimum droop is determined. Also, in the second part of the research, to enhance the optimality of the results, PSO algorithm is used for the multi-objective optimization problem. Numerical examples on IEEE 34-bus test system including two wind turbines are studied. The results show the benefits of voltage droop scheme for mitigating the impacts of the uncertainty of wind. Also, the results show preference of PSO method in the proposed approach.

Systematic Design of Coordination Control between Damping Controller and SVC via Digital Simulator

AbstractThis paper describes a method to design an external controller for secondary voltage controller (SVC) and tune both controllers in order to improve transient stability with real-time simulation. Recently, Korea Electric Power Corporation (KEPCO) has developed a novel voltage management system (VMS), a kind of SVCs, and installed in Jeju Island. It has been operated successfully to balance reactive power reserve of the controlled generators and enhance the voltage stability. However, the VMS has an inherent demerit in short-term recovery after a disturbance such as load change and tripping transmission line occurs. In this paper, after having a discussion related to the demerit in detail, an external controller is proposed. Also, a method to tune the external controller for reducing the bad reaction of the VMS is implemented with real-time digital simulator (RTDS) which is a fully digital power system simulator in real-time. The performance is evaluated by time-domain simulation.

A Multilevel Approach for Optimal Participating of Wind Farms at Reactive Power Balancing in Transmission Power System

According to the different grid codes, wind farms which are connected to transmission network have to supply not only the active power, but also the reactive power to the grid. The aim of the proposed work is to present an optimal multilevel control system which allows the doubly fed synchronous generator based wind farms to participate at reactive power balancing in transmission network. In this method, we use a multilevel control system, consisting of two levels to regularly calculate the references of all wind turbines. First, the algorithm calculates the optimal reference values of reactive power for each wind farm at its point of common coupling with the grid. Second, it calculates the references of the wind turbines in each wind farm to consider the optimal reactive power references obtained at the first level. The proposed multilevel control system re-calculates the available reserve of the reactive power to determine the optimal references. A probabilistic method based on auto regressive integrated moving average is used to predict the available reactive power reserve which is strongly related to uncertain nature of wind speed. This control system is developed particularly to control the wind farm reactive power injected into the grid. It is well adapted to fluctuating nature of the wind speed. It is also faster than other methods with a global single level optimal control system.

A multi-objective fuzzy-based procedure for maximal preventive reactive power dispatch problem

This paper presents a proposed procedure depends on the multi-objective fuzzy linear programming (MFLP) technique to obtain the optimal reactive power reserve for generators and static switchable VAr sources, as a preventive control action to overcome any emergency condition. The proposed procedure is very significant to eliminate violation constraints and give an optimal reactive power reserve for multioperating conditions. The proposed multi-objective functions are: minimizing the real transmission losses, maximizing the reactive power reserve at certain generator, maximizing the reactive power reserve at all generation system and/or switchable VAr devices. The proposed MFLP is applied to a 5-bus test system and the West Delta region system as a part of the Egyptian Unified network. The numerical results showthat the proposed MFLP technique achieves a feasible real power loss with maximal reactive reserve for power systems.

Voltage Collapse Enhancement and Loss Reduction by Reactive Power Reserve

Voltage Collapse Enhancement and Loss Reduction by Reactive Power Reserve

Anticipatory reactive power reserve maximization using differential evolution

This paper presents an algorithm for anticipatory control of load bus voltages. The algorithm optimizes a set of reactive power control variables and maximizes reactive reserve available at generating buses. Voltage dependent reactive power limits have been accounted. The optimal settings of reactive power control variables have been obtained for next interval predicted loading condition. These optimized settings satisfy the operating inequality constraints in predicted load condition as well as in present base case loading conditions. A population based differential evolution strategy has been used for optimization. Results obtained have been compared with those obtained using another population based technique known as PSO.

Justification of Effective Reactive Power Reserves With Respect to a Particular Bus Using Linear Sensitivity

A constant reactive power (Q) reserve (CQR) is measured by the difference between the maximum reactive power generation and its current. However, all reactive power sources must not affect the entire power system when severe contingencies occur. Thus, generators must be evaluated as to whether or not they will have an impact on the maximum permissible loading of buses. This definition considers some generators to still have reactive power reserves when the system faces voltage collapse. This remaining reactive power reserve, although available, cannot be used in an arbitrary manner. This paper proposes the concept of an effective reactive power reserve and it is calculated on the basis of a sensitivity analysis. The computed reactive power reserve is analyzed using static and dynamic simulations in bulk power systems.

Assessing Reactive Power Reserves With Respect to Operating Constraints and Voltage Stability

This paper proposes a two-step approach to evaluate reactive power reserves with respect to operating constraints and voltage stability for a set of postulated operating scenarios. The first step determines the minimum overall needed reactive power reserves of generators such that the system withstands, from a static viewpoint, any postulated scenario. This problem is formulated as a security constrained optimal power flow (SCOPF) which includes operating constraints relative to all postulated scenarios. Particular attention is paid to the techniques aimed to reduce the large size of the SCOPF problem. The second step determines additional reserves to ensure voltage stability of scenarios for which, when modeling dynamic system behavior, the reserves obtained by SCOPF are insufficient. These reserves are computed using a heuristic technique which relies on dynamic simulation. Numerical results on four test systems of 60, 118, 618, and 1203 buses support the interest of the approach.