Reactive Power Sources Research Articles

Optimal Power Flow with Renewable Generation: A Modified NSGA-II-based Probabilistic Solution Approach

The rapid expansion of renewable generation has drastically increased the planning complexity of modern power systems as additional uncertainties, environmental concerns, and technical–economic issues should be accounted for. Within this context, the best operation performance of contemporary power system operators (SOs) depends not just on tractable realistic optimal power flow (OPF) formulations, but also on powerful optimization approaches. In this work, a tractable life-like multi-objective probabilistic OPF-based model for the SO’s medium-term operation considering high penetration of renewable resources is proposed. This model includes an explicit formulation of the operation of dispatchable and non-dispatchable generation, shunt reactive power sources, and under-load tap-changing (ULTC) transformers. The resulting model is a large-scale probabilistic multi-objective non-convex nonlinear mixed-integer programming (NLMIP) problem with continuous, discrete, and binary variables. To ensure tractability, uncertainties are modeled through a fast and efficient 2m probabilistic approach. To handle the nonlinearities and non-continuous variables that characterize the problem, a modified non-dominated sorting genetic algorithm (NSGA)-II solution approach is proposed and effectively tested.

Керування навантаженням асинхронного генератора з короткозамкненим ротором

The use of asynchronous generators as load devices for testing and running-in of power drives of new and refurbished equipment is the most efficient. Frequency converters with a direct current link are most often assumed to control the load. There are other methods of controlled loading of an asynchronous generator using a capacitor bank as a source of reactive power. Thyristor voltage regulators could become an alternative to the frequency converter with a link of a direct current. The purpose of the study is to study the possibility of increasing the reliability and efficiency of drive load systems and (or) generating systems when working on the network using asynchronous generators through the use of a three-phase choke in parallel with a thyristor voltage control module. A new way of the load control of an induction generator is being explored. The results of testing the physical model of the load stand of the asynchronous generator during its operation together with the thyristor voltage regulator and three-phase coil are given. The results of the study of the forms and magnitude of the stator current of an asynchronous generator at different modes and levels of its load are presented in the paper. A comparative analysis of the magnitude and phase of the sine wave offset with respect to the phase voltage of the network. The results show the increase of the active component of the stator current as the conduction angle of the thyristor modules of the voltage converter increases. The studies confirm the presence of recovery of part of the energy consumed from the network by the drive motor, when the opening angle of the thyristors exceeds about 1 rad. The oscillogram can be concluded that there is a significant distortion of the sinusoidal shape of the current, which can have a significant impact on the processes in the electric machine. Key words: induction generator, three-phase coil, voltage regulator, load control

MULTI-OBJECTIVE OPTIMAL REACTIVE POWER DISPATCH USING DIFFERENTIAL EVOLUTION

Reactive power optimization is a major concern in the operation and control of power systems. In this paper a new multi-objective differential evolution method is employed to optimize the reactive power dispatch problem. It is the mixed–integer non linear optimization problem with continuous and discrete control variables such as generator terminal voltages, tap position of transformers and reactive power sources. The optimal VAR dispatch problem is developed as a nonlinear constrained multi objective optimization problem where the real power loss and fuel cost are to be minimized at the same time. A conventional weighted sum method is inflicted to provide the decision maker with a example and accomplishable Pareto-optimal set. This method underlines non-dominated solutions and at the same time asserts diversity in the non-dominated solutions. Thus this technique treats the problem as a true multi-objective optimization problem. The performance of the suggested differential evolution approach has been tested on the standard test system IEEE 30-bus.

Optimal Placement, Sizing and Coordination of FACTS Devices in Transmission Network Using Whale Optimization Algorithm

Flexible AC Transmission Systems (FACTS) play an important role in minimizing power losses and voltage deviations while increasing the real power transfer capacity of transmission lines. The extent to which these devices can provide benefits to the transmission network depend on their optimal location and sizing. However, finding appropriate locations and sizes of these devices in an electrical network is difficult since it is a nonlinear problem. This paper proposes a technique for the optimal placement and sizing of FACTS, namely the Thyristor-Controlled Series Compensators (TCSCs), Shunt VARs Compensators (SVCs), and Unified Power Flows Controllers (UPFCs). To find the optimal locations of these devices in a network, weak buses and lines are determined by constructing PV curves of load buses, and through the line stability index. Then, the whale optimization algorithm (WOA) is employed not only to find an ideal ratings for these devices but also the optimal coordination of SVC, TCSC, and UPFC with the reactive power sources already present in the network (tap settings of transformers and reactive power from generators). The objective here is the minimization of the operating cost of the system that consists of active power losses and FACTS devices cost. The proposed method is applied to the IEEE 14 and 30 bus systems. The presented technique is also compared with Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). The findings showed that total system operating costs and transmission line losses were considerably reduced by WOA as compared to existing metaheuristic optimization techniques.

Reactive power sources control in railroad power supply systems

This article presents computer modeling results for AC railroads power supply system modes. It considers various methods of connection of controlled reactive power sources (RPS). It is shown that the various problems of stabilizing the voltage levels in the traction network and reducing electrical energy losses can be solved. The computer-aided modeling indicates that to install RPS into all phases of traction substations is the best way to stabilize voltage levels in traction networks and reduce electrical energy losses. When the reactive power sources are present in the free phase, traction network losses increase in comparison with the option when the RPS are not present. The installation of sources in the retarding or leading phase allows stabilizing voltage in the load utilizing equipment, reducing losses and non-symmetry in supply mains. The best option in terms of electrical energy losses is connecting the RPS to the leading phase. In terms of non-symmetry in supply mains, the best performance is produced when the RPS are installed in the retarding phase.

Moth Flame Optimization based Reactive Power Planning

Reactive power planning is one of the challenges facing an integrated power network to operate efficiently. It requires optimal coordination of all the reactive power sources in the network. In this work, Moth flame optimization (MFO) based algorithm used for optimal location of flexible alternating current transmission system (FACTS) devices. In standard IEEE 30 and IEEE 57 test systems the proposed approach is examined. The static Var compensator (SVC) and thyristor controlled series capacitor (TCSC) are the two FACTS devices used. The load ability of the power system is enhanced by installing FACTS controllers considering both active and reactive loading. The reactive sources are placed optimally which is chosen by considering position and size of FACTS devices. The proposed method with FACTS devices is compared with other recent techniques like Particle swarm optimization (PSO) and gravitational search algorithm (GSA). It is observed that the MFO based approach is better as compared to other methods in terms of loss and the running cost at various loading conditions.

A novel management scheme to reduce emission produced by power plants and plug-in hybrid electric vehicles in a smart microgrid

Recently, with the growth and development of distributed generation (DGs) and energy storage systems (ESSs), as well as smart control equipment, microgrids (MGs) have been developed. Microgrids are comprised of a limited number of constitutive parts, including loads, DGs, ESSs, and electric vehicles (EVs). This paper presents a novel scheme to manage active and reactive powers, based on DGs, ESSs, and EVs to reduce the total operation cost including power generation and emission costs. Simultaneous management of active and reactive power makes it possible to consider grid operation constraints together. In the proposed schedule, the vehicles are assumed to be plug-in hybrid electric vehicles. They are able to run both on gasoline and electricity. The proposed schedule incorporates the cost of the consumed fuel and generated pollution into the function of the MG. It is programmed using GAMS software as a mixed-integer second-order cone programming problem and is implemented on a test MG. Simultaneous management of active and reactive power sources can result in lower cost compared to separated scheduling.

Coordinated Optimal Control of Multiple Reactive Power Devices at Different Voltage Levels in UHVDC Near Zone

Affected by different steady-state reactive power output ratios among generators, capacitors and other reactive devices in the end-to-end power grid, voltage collapse may occur due to the failure of the receiving-end AC system, and the problem of voltage stabilization in multi-DC feed systems is particularly common. For suppressing voltage collapse, sufficient dynamic reactive power support is an effective measure, and there are some differences in the dynamic support effect of different reactive power sources. The dynamic reactive power response of the generator and its reactive power margin are two important factors affecting the coordination and optimization of the reactive power of the generator. The comprehensive evaluation index is adopted to optimize the sequencing of the reactive power output of the generator near the DC drop point. A coordinated control method of dynamic and static reactive power for DC near-point systems at different voltage levels is proposed. By controlling the steady-state reactive power output ratio between multiple reactive devices, the node voltage is maintained near the target value, and reactive power control schemes at different voltage levels can be given to meet load changes. Finally, taking the actual situation of Central China Power Grid as an example, the results of different reactive voltage control strategies are compared and analyzed, which proves that the coordinated control strategy of multiple reactive power devices can significantly improve the stability of the receiving grid voltage.

Оценка эффективности применения полуволновой линии электропередачи с тиристорным стабилизатором параметров

The article assesses the efficiency of half-wave power transmission with intermediate power take-off and its implementation. The transportation of AC electricity over extremely long distances is possible using two fundamentally different methods, i.e. compensated and half-wave power transmissions. The former method involves compensated power transmission with power take-offs, which include reactive power sources located at the terminal and intermediate points of the line. The latter method uses half-wave and half-wave power transmission. The task of power selection from a half-wave power transmission is carried out using a thyristor parameter stabilizer. To conduct a comparative assessment of efficiency the capital costs for the construction of overhead lines and substations are compared for both transmission options, while other parameters are equal. The calculation is made according to the aggregated cost indicators of power lines and substations with a voltage of 35-750 kV, approved and recommended by PJSC FGC UES. The above calculations show that the cost of constructing overhead lines and substations for half-wave power transmissions with a thyristor stabilizer parameters is 11 % cheaper than the construction of compensated power transmission.

Optimal Reactive Power Dispatch Using Chaotic Bat Algorithm

In this paper, the chaotic bat algorithm (CBA) is applied to solve the optimal reactive power dispatch (ORPD) problem taking into account small-scale, medium-scale and large-scale power systems. ORPD plays a key role in the power system operation and control. The ORPD problem is formulated as a mixed integer nonlinear programming problem, comprising both continuous and discrete control variables. The most outstanding benefit of the bat algorithm (BA) is its good convergence for optimal solutions. The BA, however, together with other metaheuristics, often gets stuck into local optima and in order to cope with this shortcoming, the use of the CBA is proposed in this paper. The CBA results from introducing the chaotic sequences into the standard BA to enhance its global search ability. The CBA is utilized to find the optimal settings of generator bus voltages, tap setting transformers and shunt reactive power sources. Three objective functions such as minimization of active power loss, total voltage deviations and voltage stability index are considered in this study. The effectiveness of the CBA technique is demonstrated for standard IEEE 14-bus, IEEE 39 New England bus, IEEE 57-bus, IEEE 118-bus and IEEE 300-bus test systems. The results yielded by the CBA are compared with other algorithms available in the literature. Simulation results reveal the effectiveness and robustness of the CBA for solving the ORPD problem.

Моделирование группового управления напряжением с источниками активной и реактивной мощности в электрических сетях

Моделирование группового управления напряжением с источниками активной и реактивной мощности в электрических сетях

An Induction Machine With Tapped Stator Windings for LCI-Fed Medium Voltage Drive Applications

The search for thyristor-based load commutated inverter (LCI) fed induction motor drives for medium voltage (MV) applications has been ongoing since the past few decades, and several new topologies have been proposed. Low cost, better efficiency, and greater ruggedness are the definite advantages of these drives. Since leading power factor is an absolute necessity for load commutation, most of these drives supply additional auxiliary reactive power at the motor terminals. However, in MV applications, this would require the auxiliary source of reactive power (typically a capacitor bank or voltage source inverter (VSI)), also to be rated for MV. To overcome this issue, a new topology using a tapped stator winding induction machine is proposed in this article. Here, a low voltage tapping on the stator winding is used to connect a low voltage VSI which supplies reactive power to the machine. The LCI is used to provide all the active power required from the main stator terminals rated for the MV operation. This article describes the proposed machine and drive configuration and the vector control method for the LCI fed drive. Experimental verification is done using a 75-kW, 3.3-kV prototype machine with a 350 V tapping on the stator winding.

A mutated salp swarm algorithm for optimum allocation of active and reactive power sources in radial distribution systems

The purpose of this paper is to get shunt capacitors (SCs) and distributed generations (DGs) such as photovoltaic (PV) allocated to compensate the reactive power of the distribution systems and enhance the system performance. Finding the optimal sizing and siting of mentioned devices needs a powerful optimization tool. Hence, this paper presents an efficient, simple, and accurate optimization algorithm based on modifying the standard version of salp swarm algorithm (SSA) named mutated salp swarm algorithm (MSSA). In other words, a mutation mechanism is applied on the standard version of SSA to escape from the local minima and enhancing the diversity in population. To validate the efficiency of proposed optimization algorithm, it is firstly applied on optimizing some well-known benchmark functions. Then, it is handled to cope with allocating SCs as the reactive source and PVs as the active power source in the distribution systems. The proposed method is accomplished on the IEEE 33 and 69-nod distribution systems and the obtained results are compared with some published papers. The results illustrate that MSSA has better performance for planning the distribution systems compared with existing methods.

Islanding Detection Scheme for Inverter-Based Distributed Generation Systems Using Cumulative Reactive Power Harmonics

In this paper, a new islanding detection scheme using cumulative reactive power harmonics (CRPH) for inverter-based distributed generation (DG) systems is presented. In the proposed method, first, any changes in the system are detected using a change detection index. Desired harmonic components of the voltage and current signals at DG terminals are extracted by a discrete Kalman filter (DKF). Then, a criterion based on CRPH is defined using the extracted harmonic signatures. The change detection index is based on the difference of measured current and its estimated fundamental component. At the initial moments of any events, reactive power controller of the inverter is disabled just for a short time interval. Since the main grid as the main source of reactive power loses in islanding condition, the reactive harmonic power of the system experiences significant variations. Then, islanding can be discriminated from other similar conditions by processing the captured signals of the mentioned time interval. Performance of the proposed method is assessed using plenty of simulations. Moreover, the superiority of the proposed method is confirmed by performing a comparison with other similar techniques.

Risk Assessment Method for Integrated Transmission–Distribution System Considering the Reactive Power Regulation Capability of DGs

High distributed generation (DG) penetration makes the traditional method of equalizing the distribution power system (DPS) to the PQ load bus in the risk assessment of the transmission power system (TPS) no longer applicable. This paper proposes a risk assessment method for an integrated transmission–distribution system that considers the reactive power regulation capability of the DGs. Based on the DG’s characteristics and network constraints, the regulation capacity is mapped to the boundary buses of the distribution networks. Coordinating the relationship between reactive power and active power, the utilization of the regulation capacity is maximized to reduce the load shedding in the fault analysis of the TPS. Simulation results in the integrated transmission–distribution system illustrate that the effective use of the regulation capacity of the DPS can reduce the risk of the TPS. The method can be applied to the reactive power sources planning and dispatching of power system.

Coordinated Voltage Control Strategy for Voltage Regulators and Voltage Source Converters Integrated Distribution System

This paper presents a situational-aware, data-driven, and agnostic-coordinated control methodology for voltage regulation in the active distribution systems (DS) considering voltage source converters (VSCs) as reactive power sources that work in conjunction with the existing legacy controllers. The approach uses time-scale coordination based on regulator warnings such that the voltage support from regulators is time separated from the reactive power support using VSCs. Two type of voltage changes are considered; a slow changing one based on the feeder load and a fast-changing one based on sudden changes in load or PV output. The reactive support for both these changes is then designed based on the voltage to reactive power sensitivities. The combined reactive support is then used as a set-point to dispatch reactive power from the VSCs. The proposed control technique has been tested in the field verified model of a real feeder and the scalability is verified on an 8500-node real feeder. Results show that the proposed coordination approach has major economic as well and power quality benefits in the operation of DS. It has also been shown that this can be achieved without major changes in the communication framework currently utilized by the utility.

Adaptive Dynamic Grid Partitioning for Reactive-Power/Voltage Control Based on Secondary Voltage Control

Reactive power voltage partition control is an important part of AVC secondary voltage control. Aiming at the current status of secondary voltage control, based on the voltage/reactive sensitivity and modularity function, an adaptive dynamic partitioning method is proposed, which changes with the operating conditions of the grid. With each reactive power source partition center, the load nodes are mapped to the corresponding reactive power sources according to the voltage/reactive sensitivity, and the regional merging automatically forms the optimal partition by using the modularity function as a measure. Finally, the proposed method is verified by the IEEE-39 system.

Power quality improvement of distribution system with photovoltaic and permanent magnet synchronous generator based renewable energy farm using static synchronous compensator

This paper presents power quality improvement for effective power transfer in a grid-integrated solar photovoltaic-wind energy hybrid system. The hybrid system constitutes a renewable energy farm, based on photovoltaic energy generation system and wind energy conversion system. The system experiences frequent disturbances in AC loads and power output from the renewable farm. This creates reactive power mismatch and raises voltage instability and power quality issues. This gap can be eliminated using an adjustable reactive power source i.e. static synchronous compensator. Three case scenarios of the hybrid system, i.e. hybrid system in (I) standalone mode, (II) grid-integrated mode and (III) grid-integrated mode with STATCOM, are tested to compare their dynamic and transient performances. Results show that scenario-III best fulfilled the dynamic compensation requirement among all cases. Under this scenario, load bus voltage is regulated at around 1.0 p.u. and total harmonic distortion in voltages/currents are maintained at around 1%. Furthermore, this scenario demonstrated superior transient response towards a step change in reactive power load, significantly reducing maximum peak deviation by 73.4% and settling time by 75% in load voltage compared to the worst case of scenario-I.

Coordination of Distributed Reactive Power Sources for Voltage Support of Transmission Networks

The provision of voltage support from distribution systems to transmission networks requires new cost-effective coordination schemes to drive thousands of non-centrally monitored distributed energy resources (DERs). In this paper, we demonstrate how small-scale photovoltaic systems in distribution systems can provide reactive power services to other networks. This is achieved by means of their local controllers that change their logic to respond to external requests. These controllers operate with local information and without direct knowledge of the full system performance. This facilitates scalability as new DERs can be added to participate in a plug-and-play fashion. The paper focuses on the voltage support concept for the Swiss transmission system. The coordination defines when DERs must participate in voltage support, which task to perform and how to fulfill it. It is demonstrated that dispersed units can engage in system objectives, and still be able to support local voltages when required. The proposed approach is tested in different systems with high penetration of PV systems.

Investigating the Regulation System of the Synchronous Motor Excitation Mode Serving as a Reactive Power Source

Investigating the Regulation System of the Synchronous Motor Excitation Mode Serving as a Reactive Power Source