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In the background of the global commitment to low-carbon renewable energy transformation, new energy sources such as distributed wind–solar storage and charging and single-phase loads, such as electric vehicles, are connected to the distribution network. Due to the asymmetric access of load and the randomness of load power consumption, the problem of three-phase imbalance is becoming more and more prominent, and the uncertainty is increasing. In this paper, by analyzing the three-phase load imbalance problem of the distribution network, starting from the cause of three-phase load imbalance, the three-phase imbalance calculation method of the distribution network is deduced. The access mode of a distributed power flow controller in the distribution network and the three-phase imbalance compensation method are studied. The control strategy of the distributed power flow controller for the three-phase imbalance control of the distribution network is proposed. The simulation results show that the proposed method can effectively control the three-phase asymmetry problem of the distribution network, the configuration is more flexible, and the capacity utilization rate is higher. [ABSTRACT FROM AUTHOR]

With large-scale access to distributed new energy, the power flow form of the distribution network tends to be complex. The distribution loop network rate increases, resulting in serious circulation of the distribution network, which places significant pressure on the loss of the distribution network. The problem of network loss change caused by distributed new energy grid connection, coupled with the inconsistency between load fluctuation and output power change of distributed new energy, will have a significant impact on the safety, reliability, and economic operation of the distribution network. Therefore, it is urgent to have good economic and technical means of power flow control. This paper proposes a minimum network loss optimization control strategy for active distribution networks based on a distributed power flow controller. First, according to the characteristics of the distribution network load and the new energy power supply along the distribution line, the multiple sub-modules of the distributed power flow controller are arranged in sections in the distribution loop network line. The regulation effect of the distributed power flow controller on the voltage and power flow of the distribution loop network is analyzed. The loop network current equation and power loss equation after the distributed power flow controller are constructed, and the power equation with the minimum active loss of the active distribution loop network is derived. Second, the control strategy for minimum network loss of the active distribution network based on the distributed power flow controller is proposed. Finally, the simulation model of the active distribution loop network is constructed by PSCAD/ EMTDC. The loss of the loop network before and after the distributed power flow controller is simulated and analyzed, and the effectiveness of the proposed strategy is verified. [ABSTRACT FROM AUTHOR]

At present, the usage of various energy sources in the electricity grid has formed new challenges like power quality effectiveness, energy utilization, and voltage stabilization. With the recognition of smart grid, the maintenance of power quality (PQ) has been regarded as the challenging one. Primarily, APF are employed in an attempt to recompense the issues associated with power quality, as they can filter out promptly and responds vibrantly. Here, in this work, an IEEE 9 Bus System based on WSCC is introduced along with UPQC combined DPFC system. To accommodate a renewable energy source, one of the generators test system. MGWO approach-based PID device is combined with DC Source as a converter for 3-phase inverter. This arrangement is studied using Simulation in both cases with and without DPFC. In addition, the performance estimation is done in terms of parameters like load voltage and current, shunt voltage and series current, and grid current along with their THD values. Based on the outcome, it is found that the proposed UPQC–DPFC combination helps in effective harmonic elimination and increased power storage at the output side. [ABSTRACT FROM AUTHOR]

In the background of the global commitment to low-carbon renewable energy transformation, new energy sources such as distributed wind–solar storage and charging and single-phase loads, such as electric vehicles, are connected to the distribution network. Due to the asymmetric access of load and the randomness of load power consumption, the problem of three-phase imbalance is becoming more and more prominent, and the uncertainty is increasing. In this paper, by analyzing the three-phase load imbalance problem of the distribution network, starting from the cause of three-phase load imbalance, the three-phase imbalance calculation method of the distribution network is deduced. The access mode of a distributed power flow controller in the distribution network and the three-phase imbalance compensation method are studied. The control strategy of the distributed power flow controller for the three-phase imbalance control of the distribution network is proposed. The simulation results show that the proposed method can effectively control the three-phase asymmetry problem of the distribution network, the configuration is more flexible, and the capacity utilization rate is higher.

New energy and multiple loads, such as distributed wind-solar storage and charging, are connected to the distribution network through power electronic converters, which increases the harmonic content in the distribution network and causes operational safety risks. In this paper, the mathematical model of harmonic current and harmonic power content in a distribution network is constructed by an equivalent circuit and vector diagram. The distributed power flow controller is proposed for harmonic control of the distribution network. The mathematical expressions of the harmonic current and harmonic power based on a distributed power flow controller are constructed, and the control strategy of the distributed power flow controller for harmonic control is proposed. The simulation results show that the proposed method can effectively suppress the fifth and seventh harmonics of the distribution network. [ABSTRACT FROM AUTHOR]

The demand for electricity globally has led to the search for renewable energy resources for power generation and attaining it in an eco-friendly manner. The solar photovoltaic systems and wind-based generators of power are regarded as primary resources of renewable energy and are called Distributed Generation units as they are scattered in nature. These are operated with bidirectional converters by providing auxiliary services at grid side and load side in either mode of microgrid operation. Besides, the DC power generation units’ integration gets converted into AC system by means of inverters. These types of systems not only increase voltage and current harmonics and power frequency deviations but also drive the distribution system to risky operating zone. This emphasizes the stipulation of advanced control schemes for microgrid architecture. Consequently, power electronic converters introduce harmonics in the system and affect system performance. To report these expanded issues, the authors recognized an advanced custom power device entitled Distributed Power Flow Controller (DPFC). In this study, the proposed system on solar–wind-based hybrid energy approach has been examined primarily through the strategy of DPFC mechanism. Later, the system has been examined with Genetic Algorithm (GA)-based fuzzy logic controller and GA-based adaptive neuro fuzzy inference system controller for shunt control of context built with DPFC mechanism. Furthermore, the validated results are verified using MATLAB/Simulink software.

The distributed power flow controller (DPFC) realizes large-scale power flow control through the series connection of sub-modules. The larger the DPFC capacity and the level of sub-modules connected to the system, the greater the impact that may be caused. Starting from the DPFC structure and operating principles, the paper proposes graded start strategy of DPFC based on the world’s first 220kV DPFC demonstration project. The strategy coordinates each sub-module to start step by step and unlock under lower DC voltage through the centralized control system, reduces system power fluctuation, and reduces the overall start-up time through the information interaction between the centralized control and the multi-series valve control systems in sub-modules. The test results of the HUZHOU DPFC demonstration project show that the strategy proposed can reduce the active power fluctuation amplitude of the 4 sub-modules DPFC by 75% which have good prospect of engineering application.

Among the FACTS device, the distributed power flow controller (DPFC) is a superior device. This can be evaluated after eliminating the dc capacitor between shunt and series convertors of the unified power flow controller (UPFC) and placing a number of low rating single phase type distributed series convertors in the line instant of using single large rating three phase series convertors as in the UPFC. The power flow through this dc capacitor as in the UPFC now takes place through the transmission line at a third harmonic frequency in the DPFC. The DPFC uses the D-FACTS that allows the replacement of a large three-phase converter as in the UPFC by several small-size series convertors present in the DPFC. The redundancy of several series convertors increases the system’s reliability of the power system. Also, there is no requirement for high voltage isolation as series convertors of the DPFC are hanging as well as single-phase types. Consequently, the DPFC system has a lower cost than the UPFC system. In this paper, the equivalent ABCD parameters of the latest FACTSdeviceDPFChave been formulated with the help of an equivalent circuit model of the DPFC at the fundamental frequency component. Further, the optimal location in the transmission line and maximum efficiency of the DPFC along with Thyristor Controlled Series Compensator (TCSC), Static Synchronous Shunt Compensator (STATCOM) and UPFC FACTS devices have been investigated using an iteration program developed in MATLAB under steady-state conditions. The results obtained depict that the DPFC when placed slightly off-center at 0.33 fraction distance from the sending end comes up with higher performance. Whereas, when the TCSC, STATCOM and UPFC are placed at 0.16, 0.2815, 0.32 fraction distances from sending end respectively give their best performance.

The main aim of this paper is to introduce a framework for the design and modelling of a photovoltaic (PV)-wind hybrid system and its control strategies. The purpose of these control techniques is to regulate continuous changes in the operational requirements of the hybrid system;currently, in power system networks, the distribution of energy plays a major role in maintaining power reliability in distribution systems. In this study, the proposed hybrid system was incorporated with a combined PV and wind energy system. Maximum power point tracking (MPPT) methods have been proposed to achieve maximum efficiency from the designed system. In addition, this study focused on improving the stability of the hybrid system. To improve the power quality and transient stability of the proposed system, we introduce a novel control strategy called the distributed power flow controller (DPFC) implementation with an optimization technique called the lion optimization algorithm(LOA)technique. This LOA control technique was developed for the first time in the application of a DPFC controller in a grid-connected system. The control technique was developed using signals from the system parameters, that is, voltage and current. To tune these parameters, this study used fuzzy logic and lion optimization techniques. The proposed system with controllers was tested in MATLAB/Simulink and the results were compared.

A distributed power flow controller (DPFC) can control the line power flow in a flexible and fast way to meet the requirements of a new power system. However, the output of DPFC sub-units is generally distributed by the even distribution method or proportional distribution method at present. The internal health status and output capacity of the device are not taken into account, which affects the efficiency and service life of the device. In this article, a reliability description method of DPFC based on fault probability is proposed. The coordination strategy of output voltage capability and the number of input sub-units is proposed, and the process of the proposed coordinated strategy for device output is presented. The simulation results show that the proposed coordinated output strategy can address the issue of rapid reliability decline caused by the long-term work of some sub-units and improve the overall reliability of the DPFC.

The distributed power flow controller (DPFC) has a positive effect of UC problem on the network side based on its ability to manage capacity of power flow. This study presents a novel two-stage robust model to optimize the status of the generator and location–allocation of the DPFC, while simultaneously considering wind and load uncertainties. The column-and-constraint generation (CCG) method is utilized to solve the two-stage problem into the master problem and the subproblem iteratively. The optimal status of the generator and location of the DPFC can be easily obtained with the master problem, and the dispatch solution and compensation level of the DPFC are solved in the subproblem. We conduct the IEEE 24 bus system to verify the performance of the proposed procedure. There are effects on wind spillage/load shedding and generator dispatch scheduling planning once the DPFC is injected. Detailed simulation results illustrate the effect of the proposed approach.

Distributed power flow controller (DPFC) has a considerable potential to regulate the power flow and generator rescheduling continuously. This study presents a novel two-stage stochastic model for optimal location allocations of the DPFC coupled with the interactions of DPFC to search for the optimal solutions. The Benders decomposition is utilized to reformulate the two-stage problem into the master problem and the subproblem. The optimal solution can be easily obtained with the master problem and subproblem iteratively. The relaxed DC power flow with a DPFC in the master problem accelerates the efficiency of optimal locations under a base condition. Slack variables are incorporated in the subproblem to check the feasibility of relaxed AC power flow. The optimal compensation levels of DPFC at different load/wind scenarios are optimized in the subproblem. The IEEE 118 bus system is conducted to verify the performance of the proposed procedure. The DPFC has positive impacts on unit costs, voltage performance, wind absorption, and power losses. Detailed simulation results illustrate the effect of the proposed approach.

Among the FACTS device, the distributed power flow controller (DPFC) is a superior device. This can be evaluated after eliminating the dc capacitor between shunt and series convertors of the unified power flow controller (UPFC) and placing a number of low rating single phase type distributed series convertors in the line instant of using single large rating three phase series convertors as in the UPFC. The power flow through this dc capacitor as in the UPFC now takes place through the transmission line at a third harmonic frequency in the DPFC. The DPFC uses the D-FACTS that allows the replacement of a large three-phase converter as in the UPFC by several small-size series convertors present in the DPFC. The redundancy of several series convertors increases the system's reliability of the power system. Also, there is no requirement for high voltage isolation as series convertors of the DPFC are hanging as well as single-phase types. Consequently, the DPFC system has a lower cost than the UPFC system. In this paper, the equivalent ABCD parameters of the latest FACTSdeviceDPFChave been formulated with the help of an equivalent circuit model of the DPFC at the fundamental frequency component. Further, the optimal location in the transmission line and maximum efficiency of the DPFC along with Thyristor Controlled Series Compensator (TCSC), Static Synchronous Shunt Compensator (STATCOM) and UPFC FACTS devices have been investigated using an iteration program developed in MATLAB under steady-state conditions. The results obtained depict that the DPFC when placed slightly off-center at 0.33 fraction distance from the sending end comes up with higher performance. Whereas, when the TCSC, STATCOM and UPFC are placed at 0.16, 0.2815, 0.32 fraction distances from sending end respectively give their best performance. [ABSTRACT FROM AUTHOR]

In this paper, distributed power flow controller (DPFC) constraints are analyzed. The energy balance relationship between fundamental wave and third harmonic in series and shunt-side converter is deduced. A proportional integral (PI) controller of the DPFC is constructed. The PI controller uses the voltage amplitude and phase angle injected into the system in the series side, along with the modulation ratio of the three-phase converter on the shunt side as the control variables. A multi-objective coordinated control equation is proposed, which factors the constraints of the energy balance between series and shunt side, device capacity limit, safe operation limit, fundamental component, as well as third harmonic component of the injection voltage at the series side. The equation minimizes the variance between the actual value of the control target and its given value to ensure that the DC capacitor voltage, both in the series and shunt side, is stable at target value. Simulations are conducted to verify correctness and effectiveness of the proposed control method.

Based on the topology and working principle of a distributed power flow controller (DPFC) and using the principle of linear superposition, in this article, an equivalent circuit of DPFC is constructed, and a mathematical model for the dynamic energy exchange of the third harmonic between DPFC series and shunt converters is derived, considering the energy constraint relationship between series and shunt converters. Based on this accurate model, the nonlinear models of the DPFC converters both in the shunt and series side are constructed, and their feedback linearization equations are deduced, consequently, the decoupling control strategy of the DPFC is proposed. The DPFC based on the proposed control method can well respond to the systems control requirements whether the systems are in normal operation or in fault. The achievements of this study will provide the theoretical basis for further research and engineering applications of DPFC with powerful functions, low investment cost and small operation and maintenance cost, and small footprint. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

In this paper, the modular multilevel converter (MMC) is introduced into the shunt side of the distributed power flow controller (DPFC), and a new topology of distributed power flow controller is constructed. The mathematical models are developed, in these models the internal energy relationship between the MMC module and the single-phase converter in the shunt side, as well as between the shunt-side single-phase converter and series-side single-phase converter are considered, and the corresponding control strategies are proposed based on the mathematical models. The internal electromagnetic transient characteristics of the MMC based DPFC are studied in PSCAD/EMTDC. The simulation results show that the MMC based DPFC is able to adjust the control variables such as voltage amplitude, phase angle and line reactance of the power system individually or simultaneously, and also the DPFC is able to respond to the power flow regulation demand effectively. [ABSTRACT FROM AUTHOR]

Power flow is limited by the control of active power in current power systems using different controlling techniques and power flow controlling devices. Flexible AC Transmission Systems (FACTS) are a revolutionary innovation in the area. Distributed Power flow Controllers (DPFC) are novel variants of Unified Power flow Controllers (UPFC) and a class of FACTS devices which control various parameters like voltage of the buses, impedance of the transmission line, phase angle adjustment between sending and receiving end voltages. The operation of the shunt converter does not relate or depend on the operation or working of series converter due to the absence of dc link in case of DPFC. The design of series converter is based on distributed concept of modeling of FACTS controllers. The reliability of the transmission system and minimization n of the overall cost is achieved by the use of individual single phase converters in contrast to the traditional three phase converter. The DPFC configuration is based on the transmission line enabled exchange of active power in the system which predominantly occurs in at 3rd harmonic frequency order. Single phase to ground voltage applied to the converter of the DPFC, eliminates the need for isolation of high voltage components. Therefore, the reduced cost of economics is an added advantage for DPFC unlike UPFC. The various control strategies are advocated for the control of novel FACTS technology devices. Among them, we have considered proportional integral controller and artificial neural network based soft computing technique and the preferred control technique is determined in this paper. [ABSTRACT FROM AUTHOR]

The inherent variability and randomness of large-scale wind power integration have brought great challenges to power flow control and dispatch. The distributed power flow controller (DPFC) has the higher flexibility and capacity in power flow control in the system with wind generation. This paper proposes a multi-time scale coordinated scheduling model with DPFC to minimize wind power spillage. Configuration of DPFCs is initially determined by stochastic method. Afterward, two sequential procedures containing day-head and real-time scales are applied for determining maximum schedulable wind sources, optimal outputs of generating units and operation setting of DPFCs. The generating plan is obtained initially in day-ahead scheduling stage and modified in real-time scheduling model, while considering the uncertainty of wind power and fast operation of DPFC. Numerical simulation results in IEEE-RTS79 system illustrate that wind power is maximum scheduled with the optimal deployment and operation of DPFC, which confirms the applicability and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

To control multiple series units of distributed power flow controller (DPFC), a hierarchical control method is proposed. This coordination control system consists of a coordination controller and multiple series unit controllers. According to the demand of power flow ordered by a dispatch center, the corresponding series-compensated voltage is calculated by a high-level controller and transferred to each series unit controller. Comparing the targeted compensated voltage with actual injected voltage, the modulation signal of the converter will be modified to change the power flow accurately. The DPFC system model is built in Power Systems Computer Aided Design/ Electromagnetic Transients including DC (PSCAD/EMTDC). The simulation result indicates that the proposed hierarchical control method is effective and can be considered as an option for practical engineering applications in the future.

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• The operating loss of its sub-units and analyzes the output of the DPFC device based on the topology of DPFC is investigated. • An optimal output power coordinated control strategy of DPFC multi-sub-unit is proposed. • Simulation analysis based on PSCAD/EMTDC is carried out to verify the effectiveness of the proposed coordinated control strategy. Distributed power flow controller (DPFC) is composed of multiple sub-units distributed on the line, which improves the power flow transmission capacity and ensures high reliability of the line. The overall performance and power losses of DPFC are the major concern, which is largely determined by the output power assigned to each sub-unit. This paper investigates the operating loss of its sub-units and analyzes the output of the DPFC device based on the topology of DPFC. Considering the total loss of the DPFC device, the capacity utilization rate of the sub-units and relative constraints, an optimal output power coordinated control strategy of DPFC multi-sub-unit is proposed. The simulation platform of PSCAD/EMTDC is used to develop the simulation model of a typical 110 kV system consisting of 10 groups of sub-units with different capacities. The simulation results show that the optimal output power coordinated control strategy proposed in this paper can greatly reduce the total loss of the device compared with the traditional methods, such as equipartition method and the capacity proportion method. And the capacity utilization rate of the operated sub-units can reach over 87.5%. [ABSTRACT FROM AUTHOR]

• Transient stability enhancement in two-area multi-machine system at uncertainties. • FACTS devices such as DPFC and UPFC are used to enhance the transient stability. • Resistive SFCL is suggested for mitigating the fault currents at diverse faults. • Compared the performance of DPFC and SFCL with UPFC and SFCL at uncertainties. This paper presents a novel approach in two-area interconnected power system for enriching the transient stability at perturbations. The challenging task in the interconnected system is to equalize the power production and load demand without changing the system parameters. Therefore, a sophisticated controller of flexible alternating current transmission system (FACTS) called distributed power flow controller (DPFC) is suggested to the two-area power system for enhancing the system stability. Furthermore, the resistive type superconducting fault current limiter (SFCL) is also suggested to employ with DPFC for alleviating the fault current, and power quality issues. In this work, three cases are investigated by using without auxiliary, SFCL, unified power flow controller (UPFC), SFCL-UPFC, and SFCL-DPFC on two-area multi-machine system. The objectives of the paper are to determine and evaluate the fault current, variations in voltage and inter-area oscillations, ascertain the performance of suggested techniques at diverse fault-clearance times, and find out the finest control method for different kinds of faults. The simulation outcomes disclose that the coordination of SFCL and DPFC yielded finer outcomes over other control approaches. [ABSTRACT FROM AUTHOR]

To control multiple series units of distributed power flow controller (DPFC), a hierarchical control method is proposed. This coordination control system consists of a coordination controller and multiple series unit controllers. According to the demand of power flow ordered by a dispatch center, the corresponding series-compensated voltage is calculated by a high-level controller and transferred to each series unit controller. Comparing the targeted compensated voltage with actual injected voltage, the modulation signal of the converter will be modified to change the power flow accurately. The DPFC system model is built in Power Systems Computer Aided Design/ Electromagnetic Transients including DC (PSCAD/EMTDC). The simulation result indicates that the proposed hierarchical control method is effective and can be considered as an option for practical engineering applications in the future. [ABSTRACT FROM AUTHOR]