Load Flow Control Research Articles

Hierarchical-power-flow-based energy management for alternative/direct current hybrid microgrids

Modern microgrids are systems comprising both Alternative Current (AC) and Direct Current (DC) subgrids, integrated with Distributed Generations (DGs), storage systems, and Electric Vehicles (EVs) parking facilities. Achieving stable and reliable load flow control amidst varying load, generation, and charging/discharging strategies requires a hierarchical control scheme. This paper proposes an hourly power flow (PF) analysis within an Energy Management System (EMS) for AC/DC Hybrid Microgrids interconnected via an Interlinking Converter (IC) in both grid-connected and islanded modes. The framework operates within a two-level hierarchically controlled platform. Tertiary control at the top level optimizes DGs' reference power for generation and consumption, minimizing power purchase costs and load shedding in grid-connected and islanded modes, respectively. DG converters employ current control mode to share their power references as the primary controller. While no secondary controller is adopted in this scheme, the Battery Energy Storage System (BESS) in islanded mode utilizes P/Q droop control to maintain voltage and frequency in the AC subsystem. Power sharing between AC and DC subgrids through IC is determined by the difference between AC grid frequency and DC link voltage. Integration of controlled converters’ buses into PF equations enables solving the unified system using the traditional Newton-Raphson (NR) method. A segment of a real distribution grid planned for installation in Italy under the HYPERRIDE project serves as a case study. Comparison with MATLAB/Simulink results confirms the effectiveness, precision, and convergence speed of the proposed model and control schemes, demonstrating efficient load distribution and voltage/frequency restoration in islanded mode.

Active power management of grid-connected PV-PEV using a Hybrid GRFO-ITSA technique

In this manuscript proposed a hybrid Garra Rufa Fish Optimization (GRFO) and Improved Tunicate Swarm Algorithm (ITSA) for improving the power quality of the integrated Photovoltaic (PV) and Plug-in Electric Vehicle (PEV) in Smart Grid (SG) system. The GRFO-ITSA approach is hybrid wrapper of GRFO and ITSA. Commonly it is named as GRFO-ITSA approach. The grid-connected PV-PEV, active power management is performed by the proposed approach. The proposed GRFO approach is used to determine the individual harmonic components and to reduce the recompense currents applied to PVs via PEV converters. The load flow control is performed by ITSA approach, which controls the power among the PVs, and PEVs. Additionally, it satisfies the power demand, and voltage variation. The proposed approach is also to analyze the mutual properties of PVs as well as PEVs on the feeder and transmitting loads, voltage outlines, harmonic alterations of an urban electric power distribution system. Also, the performance of the GRFO-ITSA is implemented on MATLAB site as well as associated with several existing approaches. The GRFO-ITSA have improved the power quality and compensate the harmonics and reactive power of the system. The optimal outcome is obtained by GRFO-ITSA with less computation time.

An improved Grey Wolf algorithm for optimal placement of unified power flow controller

Most crucial techniques for power system operation as well as control is Optimal Power Flow (OPF) that establishes the lowest operating costs and keeps the control variables within safe ranges. Furthermore, bus voltage and power flow across a power system are controlled by a device called a Unified Power Flow Controller (UPFC) and it is one of the most promising Flexible AC Transmission Systems (FACTS) devices for load flow control. Due to the necessary adjustments to take into account the UPFC characteristics, solving optimal power flow (OPF) problems with UPFC is a crucial and challenging task. Hence, this work intends to introduce a new Grey Wolf with Populace-based Update Evaluation (GW-PUE) algorithm for optimal placement of UPFC to achieve OPF.Different objective functions like minimization of power loss, voltage profile deviation and UPFC cost are consideredfor solving the placement problem. Moreover, the adoptedapproach is an improved form of the traditional Grey Wolf Optimization (GWO).At last, the adopted model is tested on the standard IEEE 5, IEEE 14 as well as IEEE 30 bus system. The performance of the suggested work is contrasted with extant methods in terms ofvarious measures. Especially, thecomputation time of the adopted GW-PUE method in IEEE 5 bus system is 59.61%, 14.85%, 1.33%, and 16.29% higher than the existing FF-CS, BBO, FF, and MSSA methods, respectively.

The problem of combined optimal load flow control of main conveyor line

The problem of combined optimal load flow control of main conveyor line

The Problem of Combined Optimal Load Flow Control of Main Conveyor Line

The Problem of Combined Optimal Load Flow Control of Main Conveyor Line

Intelligent Network Traffic Control Based on Deep Reinforcement Learning

This paper studies the problems of load balancing and flow control in data center network, and analyzes several common flow control schemes in data center intelligent network and their existing problems. On this basis, the network traffic control problem is modeled with the goal of deep reinforcement learning strategy optimization, and an intelligent network traffic control method based on deep reinforcement learning is proposed. At the same time, for the flow control order problem in deep reinforcement learning algorithm, a flow scheduling priority algorithm is proposed innovatively. According to the decision output, the corresponding flow control and control are carried out, so as to realize the load balance of the network. Finally, experiments show, the network traffic bandwidth loss rate of the proposed intelligent network traffic control method is low. Under the condition of random 60 traffic density, the average bisection bandwidth obtained by the proposed intelligent network traffic control method is 4.0mbps and the control error rate is 2.25%. The intelligent network traffic control method based on deep reinforcement learning has high practicability in the practical application process, and fully meets the research requirements.

Power flow control capability analysis of unified power flow controller

In the field of power system restructuring, Flexible Alternating Current Transmission System (FACTS) technology has become indispensable for alleviating the challenges of load flow control, voltage control, transient stability, and dynamic stability. The Unified Power Flow Controller (UPFC) is the fastest, most flexible, and most capable FACTS device because it has the full advantage of providing simultaneous and independent real-time control of voltage, impedance, and phase angle, which are the main power system parameters that affect system performance. This paper uses a Newton-Raphson load flow that includes UPFC to analyze how UPFC can control the flow of power.

Distributionally Robust CVaR Constraints for Power Flow Optimization

Recent research on optimal power flow (OPF) in networks with renewable power involves optimizing both first and second stage variables that adjust the decision once the uncertainty is revealed. In general, only partial information on the underlying probability distribution of renewable power production is available. This paper considers a distributionally robust framework for solving the OPF problem. The formulation stipulates a probability mass function of wind power production, whose probabilities and scenario locations vary in a box of ambiguity with bounds that can be tuned based on historical data. Distributionally robust optimization (DRO) is used to derive new conditional value-at-risk (CVaR) constraints that limit the frequency and severity of branch flow limit violations whenever the renewable power generation deviates from its forecast. Numerical results are reported on networks with up to 2736 nodes and contrasted with classical robust optimization (RO) and stochastic optimization (SO) solutions. The results show an advantage to adopting the proposed DRO for load flow control. In particular, the solution benefits from the observed correlation amongst the uncertain parameters to mitigate branch flow limit violations, and yet maintain an acceptable worst-case expected operational cost as compared to RO and SO solutions.

Metodología para Modelación Estacionaria y Dinámica del S.N.I en HYPERsim, Aplicación del Modelo en Análisis de Transitorios Electromagnéticos para Sistemas de 500 kV

Este artículo presenta un modelamiento detallado del Sistema Nacional Interconectado (S.N.I) ecuatoriano en el software de simulación en tiempo real HYPERsim, que incluye líneas de transmisión, transformadores, reactores, capacitores y el grupo generador – AVR – PSS de las centrales hidroeléctricas Coca Codo Sinclair (CCS) y Sopladora. Adicionalmente, se presentan dos metodologías para la validación del sistema construido, tanto en estado estacionario como estado dinámico sustentadas en análisis de flujo de potencia y la respuesta de los sistemas de control de CCS y Sopladora, respectivamente. La importancia de este trabajo radica en el potencial del modelo construido para desarrollar estudios especializados, inclusive incluyendo o integrando equipos físicos (PMUs, IEDS) y/o sistemas reales (SCADA, WAMS) con el simulador digital en tiempo real del Operador Nacional de Electricidad CENACE. Por ejemplo, se prevé una integración entre el simulador con PMUs y con el sistema WAMS de CENACE, a mediano plazo, para el entrenamiento en tiempo real de operadores bajo escenarios de inestabilidad oscilatoria. Mientras tanto, y como una de las primeras aplicaciones del modelo desarrollado, se muestra un análisis de transitorios electromagnéticos durante la energización del corredor de transmisión El Inga-Tisaleo-Chorrillos 500 kV del S.N.I.

Load Compensator with an Energy Storage for a Grid Connected PV Based Active Generator

At present, in order to build a sustainable economy with less greenhouse emission, the attention has been drawn towards the smart grid concept. In this context, grid connected photovoltaic (PV) systems play a major role. When it comes to grid connected PV systems, the intermittent nature of PV generation and the uncontrolled power injection may cause excess variations in the grid voltage, frequency and the power quality. Therefore, the concept of active generator with innovative energy management strategies is a good alternative with which the PV generated power can be injected to the grid in a controlled manner while achieving the output power quality, instantaneous power, balance, frequency control and voltage control. This work proposes an innovative architecture for a grid connected PV based active generator with multi sources; a PV array, battery and the grid supply which are connected to a common AC bus as well as it analyses the innovative load flow control strategy associated with the proposed architecture. To make sure an uninterruptable power supply to the load, PV arrays inject the generated power in maximum power point tracking mode and the battery compensates the power requirement in coordination with the grid while maintaining the frequency stability within the system. Therefore, this paper analyses the performance of the energy controller and the load management capability of the proposed system while achieving the frequency control.

The flow refueling location problem with load flow control

Battery electric vehicles as well as renewable energy are two key factors that can contribute significantly to sustainable development within the transportation and the energy sector. However, the market introduction of these technologies results in new challenges, especially with regard to the interaction between both sectors. So far, neither location models for charging stations nor load flow models for the electrical grid consider these interactions sufficiently. Thus, an integration of planning problems from both sectors is needed in order to exploit potential synergies and to avoid negative impacts.In this paper, we present such an integrated planning approach to locate charging infrastructure for battery electric vehicles considering interactions with the electrical grid. Herein, we combine a charging station location model and a power flow model with integrated energy stores. We aim at determining a network configuration that satisfies the charging demand of battery electric vehicles, herein maximizing the benefits and minimizing the negative impacts resulting from the interactions of the two sectors. To demonstrate the benefit of our integrated planning approach, we apply it to an illustrative case and present results of a sensitivity analysis. We derive managerial insights regarding the interdependencies of the number of sited charging stations and the installed storage capacity based on renewable energy generation and charging demand.

UPFC based transmission line power load flow control under different operating methods

In this paper the methods to control operation of shunt and series inverters using power flow controller (UPFC) is analyzed with real power flow in power system transmission line. These operation mode using UPFC are executed to reduce Swaying in the control framework transport. The execution about every system may be resolved toward the predefined administrative control. Those arrangement What's more shunt converter working under four separate blending from claiming working modes may be used to ponder An example force framework organize. The line flow in MW oscillation damping is predicated with various modes of operations and verified same with MATLAB/ SIMULINK.

Solvability and solutions for bus-type extended load flow

In traditional load flow calculation, only three types of buses, PQ, PV, and Vθ, are generally specified. To accommodate the integration of new kinds of power equipment and flexible load flow control facilities, extra bus types are needed in load flow model. The load flow model incorporated with all possible bus types is named as bus-type extended load flow (BELF) for short in this paper. Both Newton–Raphson and decoupled BELF solutions are developed. An important problem for BELF is its solvability, which is carefully studied and topology-based criteria are proposed to ascertain BELF’s solvability. Numerical tests are carried out to verify the convergence of the BELF solution and the correctness of the proposed solvability criteria.

New approach for optimal UPFC placement using hybrid immune algorithm in electric power systems

The unified power flow controller (UPFC) is one of the most promising flexible AC transmission systems (FACTS) devices for the load flow control. Simultaneous optimization of location and parameters for UPFCs is an important issue when a given number of UPFCs is applied to the power system with the purpose of increasing system loadability. This paper presents the application of hybrid immune algorithm (HIA) such as immune genetic algorithm (IGA) and immune particle swarm algorithm (IPSO) to find optimal location of UPFC to achieve optimal power flow (OPF). The overall cost function, the objective function in the OPF, includes the total active and reactive production cost function of the generators and installation cost of UPFCs and hence, should be minimized. The OPF constraints are generators, transmission lines and UPFCs limits. In power system, it may not always be possible to dispatch the contracted power transactions completely due to congestion of the corresponding transmission corridors. In this study simulations were performed on IEEE 14-bus and IEEE 30-bus test systems for different methods. Under all equality and inequality constraints, the HIA proposed approach minimized the objective function better than other methods such as GA, PSO, and IA; and as far as HIA methods were concerned, the IPSO algorithm gave better minimum cost than IGA method. Results of simulations are encouraging and could efficiently be employed for power system operations.

Optimal control of UPFC for load flow control and voltage flicker elimination and current harmonics elimination

Recent advances in the power system handling capabilities of static switches have made the use of the voltage source inverter (VSI) feasible at both transmission and distribution levels. Most of the control schemes introduced were designed either for eliminating current harmonics or eliminating voltage flickers or for load flow control. They are mostly based on the PI controller. None of these control schemes were based on a systematic optimal control law that can control the converters to achieve all purposes at the same time, load flow control, voltage flicker elimination and also current harmonics elimination. This paper presents three novel control strategies: optimal control with tracking according to desired steady-state behaviour, optimal control with linear quadratic tracker design, and optimal control with tracking with PI controllers. The strategies were tested using a power system distribution model. The presented results show that all three control strategies improve the performance of the load flow and eliminate the current harmonics and voltage flicker. The controller design based on the desired steady-state behaviour is superior compared to other way of designs as the low value of the weighting matrix Q is satisfactory to obtain the desired tracking.

Load-flow conditions for hvdc transmission in synchronous networks

The basic purpose for HVDC (high-voltage direct current) transmission is to transmit a determined value of electrical power from one electrical node to another. If there is an AC system in parallel to an HVDC transmission, the load flow via this parallel AC system can be controlled directly. Since HVDC systems offer possibilities to perform fast load-flow control, they can also be used for improving stability. In this paper load-flow calculations of a simplified network are presented. First a comparison between HVDC transmission operating in asynchronous resp. synchronous networks is shown. Synchronous network means that the HVDC transmission works in parallel to an AC system at the same voltage level. It is shown how voltage at the point of installation and how the load angle are influenced due to the synchronous operation. A special regard is drawn to the losses of the transmission. Conditions for minimum total losses are presented. Informer calculations loads are involved. It is shown how they influence the minimum total losses.

The economies of power quality

The subject of power quality embraces a very wide and diverse field of both system and customer problems. There are many requirements for appropriate solutions, from simple power factor corrections of a load to sophisticated load flow control in a high-voltage transmission system. It can be simply defined as the quality of power supplied to the end user. The evaluation of power quality improvement alternatives is an exercise in economics. Utility engineers must evaluate the economic impacts of the power quality variations against the costs of improving performance for the different available alternatives. The best choice will depend on the costs of the solution and its total operating costs. Improving facility performance during power quality variations can result in significant savings and can be a competitive advantage. Therefore, it is important for customers and suppliers to work together in identifying the best alternative for achieving the required level of performance.

Two Separate Continually Online-Trained Neurocontrollers for a Unified Power Flow Controller

The crucial factor affecting the modern power systems today is load flow control. The Unified Power Flow Controller (UPFC) provides an effective means for controlling the power flow and improving the transient stability in a power network. The UPFC has fast complex dynamics and its conventional control is based on a linearized model of the power system. This paper presents the design of neurocontrollers to provide better damping during transient and dynamic control. Two separate neurocontrollers are used for controlling the UPFC, one neurocontroller for the shunt inverter and the other for the series inverter. Simulation studies carried out in the PSCAD/EMTDC environment is described and results show the successful control of the UPFC and the power system with two neurocontrollers. Performances of the neurocontrollers are compared with the conventional proportional plus integral controllers for system oscillation damping under different operating conditions for large disturbances.

Compensation Strategy of Autotransformers and Parallel Lines Performance, Assisted by the UPFC

In this paper, reactive power compensation through the tertiary winding of an autotransformer, is proposed. Such an approach emerges as an alternative to support the significant voltage variation present over two parallel connected autotransformers, in the South Eastern Brazilian system. The above proposal will also help in controlling the line voltage variation due to the UPFC series converter action. A detailed steady-state analysis of the series voltage and the shunt reactive current when supporting line voltage, is realized. Such analysis is based upon the d-q coordinates. The UPFC effect over an uncompensated parallel line, is also studied. The waveform simulations performed to control each transformer terminal voltage, were obtained utilising the ATP/EMTP program. Results concerning the effectiveness of the autotransformer tertiary winding reactive power injection by the UPFC shunt converter, as well as the load flow control over the referred transformers, are also presented.

High voltage series reactors for load flow control

Liberalization efforts are continuing in electricity markets all over the world. The change from monopolistic to free market structures leads to a significant increase in the trading of electrical energy. Since current power plant operation is driven by price aspects, the load flows in the networks are mainly determined by the economic situation and are no longer driven by the technical design of the networks. However, as the networks were built according to the former monopolistic market conditions and requirements, the desired load flows resulting from energy trading in the free market might cause problems when forced into the physical limitations of the actual networks, such as overloading, loop flows or stability/security limit violations. Also within the Austrian transmission grid, the effects of liberalization have led to bottlenecks caused by changes in the load flow due to the new power plant regime. To ensure a safe grid operation Verbund-Austrian Power Grid (APG), the Austrian transmission system operator, must apply cost-intensive measures for congestion management (CM). APG plans to build new 380 kV overhead lines to overcome the bottleneck situations, but the erection of new lines is delayed by extensive authorisation procedures and strong opposition by the public. In general, there are a number of approaches to overcome or mitigate load flow problems, including the instaliation of high voltage (HV) dry-type series reactors. The paper describes in some detail the design and construction of HV series reactors. It focuses on dry-type air core reactors which have become the technology of choice for many applications because of their design features and their cost effectiveness. Based on the actual situation in the Austrian transmission grid, the relevance for load flow control in the APG network is analyzed. The result shows that the present high loading of the 220 kV north to south lines within Austria can be reduced by installation of HV series reactors on condition that operational limits (e.g. node voltages and voltage angles) are kept within a certain range. Especially in combination with other measures, like the usage of phase shifting transformers and special switching conditions within the grid, the installation of (switchable) series reactors becomes an attractive option for power flow control. The comparison of cost for power plant re-dispatch versus the investment cost for series reactors provides a good reason to consider the installation of series reactors if the intended extension of the 380 kV grid cannot be realized in the short term.