Multiple Unified Power Flow Controllers Research Articles

Mathematical modelling and application of generalized unified power flow controller (GUPFC) steady state model for power system network

Unified power flow controller (UPFC) is a unique kind of flexible alternating current transmission system device which can adjust power system parameters like active power, reactive power, and voltage magnitude as well as phase angle. Power transmission network is going to be more and more complex because of increase in multi-machine systems. In multi-machine systems, there is a need to adjust the power system parameters of two or more bus. In such cases, power system requirements are achieved by multiple UPFC. A reformed form of unified power flow controller which is defined as generalized UPFC comprises of one shunt converter and one then one series converter. Generalized UPFC is able to adjust the power system parameters for two or more bus or a subsystem. This paper provides the mathematical modeling of generalized UPFC in details. A novel approach based on a controlled current source employed for the scheming of phasor model of generalized UPFC in MATLAB. A comprehensive assessment is done between a phasor generalized UPFC model and multiple UPFC for congestion management of power system. The results establish the supremacy of generalized UPFC over multiple UPFC. This is the only work that brings forth for the first time, the time scheming of the phasor model of GUPFC in MATLAB/ Simulink.

Sensitivity-based coordination to controllable ranges of UPFCs to avoid active power loop flows

With its power setting decided by power system conditions, the unified power flow controller (UPFC) changes the direction of the power flow of the transmission branches, possibly yielding or intensifying the active power loop flows (APLFs). This paper studies the controllable range of the active power setting of the UPFC to avoid the APLF. The sensitivity between the active power setting of the UPFC and the active power flow of the critical branch is proposed, and iteratively solved to find the marginal power setting yielding zero active power flow of the critical branch. The controllable range of the active power setting to avoid the APLFs is decided by the max/min marginal power settings. The coordinated model between the series and shunt converters is newly proposed to determine corresponding controllable ranges with the change of the voltage setting, and the coordinated model of multiple UPFCs is proposed to decide active power settings of multiple UPFCs. The Floyd-Warshall algorithm is improved to satisfy the rule of rectangular algorithm, thus to find the APLFs and the critical branches. The numerical results on the New England 39-bus system show the feasibility and effectiveness of the proposed models.

Development of generalized unified power flow controller (GUPFC) detailed model with a comparison with multi-UPFC

Unified power flow controller (UPFC) is a unique type FACTS device which is able to regulate power system parameters such as active and reactive power along with voltage magnitude and phase angle. In restructured power system, use of multi-machine systems increasing exponentially. In such systems, there is a need of control of parameters of more than one line. In such situation, multiple Unified power flow controllers (M-UPFCs) is used to achieve these power system requirements. A modified form of UPFC which is known as generalized unified power flow controller (GUPFC) is also used to control the power system parameters for more than one bus or even a subsystem. This paper envelops a innovative approach based on voltage source converter is used for the designing of detailed model of GUPFC in MATLAB/Simulink. A detailed comparison is done between a detailed GUPFC model and M-UPFC for power flow control (active power, reactive power and voltage). The simulation results the superiority of GUPFC over M-UPFC. This paper states first time designing of the detailed model of GUPFC in MATLAB/Simulink.

Krill herd algorithm for optimal UPFC placement in transmission system

Evolutionary algorithms (EAs) are well-known optimisation approaches to deal with nonlinear and complex problems. However, most of these population-based algorithms are computationally expensive due to the slow nature of the evolutionary process. This paper presents a fast, efficient and relatively new krill herd algorithm (KHA) to find optimal location of unified power flow controller (UPFC) for solving the optimal power flow (OPF) problem taking nonlinearities of valve-point effects into consideration. The proposed algorithm is tested on standard IEEE 30-bus system incorporating single and multiple UPFC devices for two different load conditions. The simulation results of the proposed KHA method are compared with other well popular artificial intelligent techniques namely, particle swarm optimisation (PSO), differential evolution (DE), genetic algorithm (GA) and biogeography-based optimisation (BBO). The solutions obtained by the proposed KHA algorithm are quite encouraging and it is found that the proposed KHA-based approach is able to provide better solution than other evolutionary optimisation techniques in terms of cost, computation time and convergence.

Solution of multiple UPFC placement problems using Gravitational Search Algorithm

Optimal power flow is one of the key tasks to be performed in the complicated operation and planning of a power system. The Unified Power Flow Controller (UPFC) is a powerful power electronics device capable of providing complex control of power systems. In this paper, Gravitational Search Algorithm (GSA) is applied to solve optimal power flow problem in the presence of multiple UPFC devices. The performance of GSA is compared for accuracy and convergence characteristics with heuristic search techniques like Biogeography-Based Optimization (BBO), Stud Genetic Algorithm (StudGA), Genetic Algorithm (GA), Ant Colony Optimization (ACO), Probability-Based Incremental Learning (PBIL), on the different cases of standard test systems and real life power system. The tabulated results reveal that GSA has a great capability in handling power system planning and operational problems and to provide good quality solution quickly. The effort of optimal placement of multiple UPFC devices in power system cannot be commonly found in technical literature.

Efficient and optimal approach for location and parameter setting of multiple unified power flow controllers for a deregulated power sector

This study presents an efficient approach to optimal allocation of unified power flow controller (UPFC) in a pool and bilateral power market. The optimisation technique has been used with an objective to maximising social welfare (SW) by suitable location, number and rating of the UPFC in power system working under a deregulated environment. The proposed method accurately evaluates SW by determining locational marginal pricing based on the marginal cost theory. The impact of the UPFC on system real power losses has also been investigated. The effectiveness of the proposed optimal technique has been tested on the 39-bus New England system with addition of four bilateral transactions.

Coordinated Control of Multiple Unified Power Flow Controllers for Stability Enhancement of the Multi-Machine Power System

AbstractThis paper presents an application of UPFC (unified power flow controller), a kind of FACTS (flexible AC transmission systems) devices, to stability enhancement in a multi-machine power system. A novel control scheme using wide-area information from generators in the system is proposed for two parts of UPFC, shunt and series connected components, which mainly affect bus voltage and line active power flow around the installation site respectively. The proposed control scheme is based on a control law for shifting a time derivative value of the kinetic energy function in the negative direction. Numerical simulations are carried out on a 27-machine meshed test system where several UPFCs are installed, and the impacts of the two controlled components of UPFC and number of UPFCs on stability enhancement are investigated. The results show that both of the UPFC components controlled by the proposed method are effective for damping enhancement and the shunt connected component is particularly effective fo...

A Novel Real-Time Approach to Unified Power Flow Controller Validation

This paper presents the development of a real-time hardware/software laboratory to interface a soft real-time power system simulator with multiple unified power flow controllers (UPFC) via hardware-in-the-loop (HIL) to study their dynamic responses and validate control and placement approaches. This paper describes a unique laboratory facility that enables large-scale, soft real-time power system simulation coupled with the true physical behavior of a UPFC as opposed to the controller response captured by many other real-time simulators. The HIL line includes a synchronous machine, a UPFC, and a programmable load to reproduce the physical dynamics of the UPFC sub-network.

A Novel Approach to Interarea Oscillation Damping by Unified Power Flow Controllers Utilizing Ultracapacitors

This paper discusses a novel approach for damping interarea oscillations in a bulk power network using multiple unified power flow controllers (UPFCs) utilizing ultracapacitors, also known more generally as electrochemical capacitors (ECs). In this paper, a new control is introduced to mitigate interarea oscillations by directly controlling the UPFCs' sending and receiving bus voltages that better utilizes the stored energy in the ECs. The results of this controller are compared with and without ECs. The proposed control provides better interarea oscillation mitigation when applied to multiple UPFCs in the 118-bus IEEE test system.

Multiple UPFC damping control scheme using ANN coordinated adaptive controllers

AbstractThis paper presents a novel design of an adaptive damping control scheme using artificial neural network (ANN) coordinated multiple unified power flow controllers (UPFCs). In this study, a centralized global control scheme is proposed in which three UPFCs are first assumed to be strategically installed in the system to achieve a steady state power flow control objective, then utilized to demonstrate the proposed control scheme in enhancing the damping of low frequency electromechanical oscillations exhibited by a three‐area, six‐machine power system. The coordination of controllers is accomplished by a genetic algorithm based tuning process that is based on considering various system operating conditions and minimizing a set of predefined coordinated damping performance indices (CDPI). The task of real‐time adaptation of system uncertainties is carried out using a trained ANN as an adaptive coordinator to achieve the robust control objectives. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Minimization of Interrupted Power by Optimal Power Flow Control with Multiple UPFCs

Our study aims at minimization of power not supplied (PNS) under the severe fault condition such as tripping of double circuits of transmission lines. In this paper, we propose a new static control method which can minimize PNS by coordinately controlling multiple unified power flow controllers (UPFCs), generators and loads. The proposed method is based on multiple optimal power flow (OPF) calculations, and determines not only control variables of UPFCs but also which and how much generators and loads should be shed after the fault. Digital simulations are carried out with the IEEE RTS-24 system. Three simulation cases, with and without UPFCs, and with uncontrollable UPFCs, are compared and the results shows that reduction of PNS can be accomplished by UPFCs with the proposed control method. Furthermore, it is made clear that the multiple OPFs, which consider the priority loads to be shed, are very effective on reduction of total PNS.

The Line Flow Control of Multiple UPFCs for Enhancing Power System Security

This article presents a method to determine operating points of Unified Power Flow Controllers (UPFC), the line flow control of which can enhance system security level. The decoupledmodel has been employed as a mathematical model of UPFC for power flow analysis so as to analyze the effect of these devices on the power system. The security index that indicates the congestion level of transmission line has been proposed and minimized by iterative method. The sensitivity of objective function for control variables of an UPFC has been derived, and it represents the change in the security index for a given set of changes in real power outputs of UPFC. The proposedalgorithmwithsensitivity analysis gives the optimalset of operatingpoints of multiple UPFCs that reduces the index or increases the security margin, and Marquart method has been adoptedas an optimization methodbecause of stable convergence. The algorithm is verified by the 10-unit, 39-bus New England system that includes multiple UPFCs. The simulation results show that the power flow congestion can be relieved in the normal state and the security margin can be guaranteed even in a fault condition by the cooperative operation of multiple UPFCs.

Investigation into the dynamic interactions of multiple multifunctional unified power flow controllers

This letter investigates the dynamic interactions among different control functions of a single unified power flow controller (UPFC) and between multiple UPFCs installed in power systems. Study cases presented in this letter demonstrate that the existence of the dynamic interactions can lead to the instability of whole closed-loop control systems when all UPFC control functions are in joint operation even though each UPFC controller has been designed satisfactorily.