Robust placement and tuning of UPFC via a new multiobjective scheme‐based fuzzy theory

The selection of positions for unified power flow controller (UPFC) placement in transmission network is an essential factor, which aids in operating the system in a more reliable and secured manner. This paper focuses on strengthening the power system performance through UPFC placement employing self‐adaptive firefly algorithm (SAFA), which selects the best positions along with parameters for UPFC placement. Three single objectives of real power loss reduction, voltage profile improvement, and voltage stability enhancement are considered in this work. IEEE 14, 30, and 57 test systems are selected to accomplish the simulations and to reveal the efficacy of the proposed SAFA approach; besides, solutions are compared with two other algorithms solutions of honey bee algorithm (HBA) and bacterial foraging algorithm (BFA). The proposed SAFA contributes real power loss reduction, voltage profile improvement, and voltage stability enhancement by optimally choosing the placement for UPFC.

In a large scale power network, maintaining the magnitude of bus voltages within nominal operating level at all buses is a vital requirement. With such condition, the system will have an optimal transmission line performance with minimum power losses and no overloading issue. To achieve this, the power flow along transmission line ought to be properly controlled using special devices like the Unified Power Flow Controller (UPFC) - a multipurpose device which can control power flow by modifying the voltage magnitude, phase angle and impedance of transmission lines. Hence, this paper proposes a technique for mitigating voltage level and real power losses in transmission system using optimal placement of UPFC and Evolutionary Programming (EP). The implementation of the proposed technique involved IEEE 14-bus reliability test system. Experiment and analysis has justified the capability of EP-based UPFC placement for voltage stability improvement and power loss minimization as well.

The Unified Power Flow Controller (UPFC) is the most complex and powerful FACTS device, which can provide full or independent control of line transmission parameters, such as voltage, line impedance and phase angle. In this paper, steady-state model of unified power flow controller (UPFC) and power flow algorithm of power system with UPFC were studied. The parallel and series sides of UPFC were equivalent to separate power injections, and an alternating iteration algorithm of power flow for power system with UPFC was presented. In order to improve the convergence of the algorithm, this paper analyzes the impact of UPFC’s various control strategies on the convergence of power flow calculations, and proroses a control strategy for converting constant power control to constant variable control during the iterative process. Based on the actual project of Nanjing Western UPFC, the correctness and effectiveness of the model and algorithm are verified.

This paper presents a screening technique for greatly reducing the computation involved in determining the optimal location of a unified power flow controller (UPFC) in a power system. The first-order sensitivities of the generation cost with respect to UPFC control parameters are derived. This technique requires running only one optimal power flow (OPF) to obtain UPFC sensitivities for all possible transmission lines. To implement a sensitivity-based screening technique for guidance in optimally locating a single UPFC in a power system, we propose a new UPFC model, which consists of an ideal transformer with a complex turns ratio and a variable shunt admittance. In this model, the UPFC control variables do not depend explicitly on UPFC input and output currents and voltages. Accordingly, this model does not require adding extra buses for UPFC input and output terminals. IEEE five-, 14- and 30-bus systems were used to illustrate the technique

UPFC (Unified power flow controller) is one of the most powerful and complex FACTS (Flexible AC transmission system) devices in a power system today. It is primarily used for simultaneous or independent control of real and reactive power in transmission lines for flexible, reliable and economic operation and loading of power systems. In this paper, the effectiveness of UPFC has been explored in transmission system network when subjected to three phase to ground fault condition. The comparison has been made between VSI (Voltage Source Inverter) based UPFC and ZSI (Z-Source Inverter) based UPFC. From the results so obtained, it has been established that the performance of ZSI based UPFC is superior as compared to that of VSI based UPFC.

Optimization of system capacity electric power transmission systems requires a reliable power flow controller. The power flow controllers must be able to control the level of electrical voltage and active and reactive power flow without reducing the level of stability and security of the transmission system. Latest technology in the control of power flow is a Unified Power Flow Controller (UPFC). The entire transmission line parameters are impedance, voltage, and phase angle can be controlled simultaneously by the UPFC. The method used in the conventional algorithms based UPFC is still firmly with logic. These algorithms have difficulties to electric power transmission systems multimachine very dynamic, i.e. systems that are experiencing rapid changes in the electrical load from time to time. Therefore, in this study was developed based on neuro-fuzzy method is applied to the adaptive UPFC for adaptively controlling the power flow in electric power transmission systems multimachine very dynamic. In this study, three phase fault is applied to the multimachine system. The results are taken to be consideration of PI and neuro-fuzzy controllers. The PI and neuro-fuzzy controllers show nearly same results but there is a low overshoot occurred during the fault in the neuro-fuzzy controllers results. According to results that UPFC improves the system performance under the transient and the normal conditions. However, it can control the power flow in the transmission line, effectively.

This paper deals with an alternative proposition for the steady state modeling of unified power flow controller (UPFC). Since current limitations are determinant to FACTS apparatus design, the proposed current based model (CBM) assumes the current as variable, allowing easy manipulation of current restrictions in optimal power flow evaluations. The performance of the proposed model and of the power injection model (PIM) are compared through a Quasi-Newton optimization approach. Two operating situations of a medium size network with 39 busbars were studied from the point of view of optimization and current limits, observing the performance of the UPFC modeling.

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

This paper addresses two issues in operation of a unified power flow controller (UPFC), enhancement of fault recovery and controller design accounting for filter dynamics. Performance of a UPFC is improved by a temporary modification of the UPFC into double static synchronous series compensator (SSSC) in order to double its capability in fault recovery mode. A battery is required as an energy source in the DC link of the double SSSC. The size of the battery for the SSSC has been be investigated. It was found that the double SSSC in fault recovery mode has almost twice the performance of the UPFC and the size of battery for the UPFC is reasonable for grid scale use. With the double SSSC in fault recovery mode, a combination control mode is suggested for the UPFC. One of the important parts of the UPFC is the filter at the output of the inverter. The function of the UPFC filter is to attenuate the harmonics generated by the inverter. In this paper a harmonic trap filter together with a low-pass filter are applied to the UPFC and investigated. Single-phase models are used to design cut-off frequencies whilst the d-q model is included in the UPFC controller design. It was found that if the filter dynamics are neglected in the control design, then the controllers response will be different. The test system used is a one-machine, two transmissions lines and an infinite busbar. All of the simulations were implemented using the EMTP. Additionally Matlab and Simulink programming environment were used to provide transfer function simulation for the controller design. The simulation results from both programs are compared.

Due to ever-increasing power demand, the power system is facing issues such as congestion, line outages, system reliability, and stability challenges. The impetus to revise the traditional power transmission theory and practice, and to introduce new concepts for improving the performance of the existing AC transmission system caused the development of flexible AC transmission system controllers (FACTs). Due to their capability of controlling transmission system parameters, the utilization of FACTs controllers has become essential to enhance the power system capability. To investigate the performance of FACTs controllers, this study incorporates the Unified Power Flow Controller (UPFC) in the power system. UPFC is used to mitigate transmission line congestion by controlling the transmission line power flow. In this paper, a modified control circuit for UPFC is implemented. Moreover, the selection of a suitable location for UPFC is necessary because of its techno-economic impacts. Therefore, this work uses a sensitivity-based approach for the selection of a suitable place of UPFC. To decide the suitable location, control parameters of UPFC along with system loss sensitivity indices are used. The model of UPFC along with the control circuit is simulated in PSCAD/EMTDC. To investigate the performance of UPFC, a five bus seven-line transmission system is used. After installing the UPFC at an appropriate location, the power flow results of transmission lines are compared with and without the usage of UPFC.

A unified power flow controller (UPFC) locating and sizing method is proposed to solve problems of uneven distribution of power flow in the transmission ring network and unsatisfactory of N-1 contingency standard for some lines. UPFC adjusts the active and reactive power flow of the line, so as to fully utilize the capacity of each transmission channel in the grid and improve the transmission capacity of the grid. By establishing the UPFC locating and sizing evaluation index system, and by evaluating and sorting the UPFC planning scheme, the UPFC installation location and configuration capacity are optimized. Finally, the feasibility and effectiveness of the method are verified by an actual case of South Hebei Province Power Grid.

Application of the injection modeling approach to power flow analysis for systems with unified power flow controller

SUMMARY The task of modelling and locating steady-state unified power-flow controllers (UPFCs) for static voltage stability enhancements in power system planning is addressed. A hybrid UPFC model for power flow studied is proposed. The series side of the UPFC is represented by an ideal voltage source, while the shunt side is represented by an idea current source model. Equivalent relationships among our new models and existing models will also be investigated. Integrations of this hybrid UPFC model into existing Newton-type power-flow solvers are presented. Extensions of continuation methods for locating the voltage collapse point of power systems embedded with UPFCs are studied. Strategies of determining the UPFC rating and locations for voltage stability enhancements will also be discussed. Numerical demonstrations of IEEE 300-bus test system and Taiwan power system are performed to verify the correctness of the proposed UPFC model and the computational tool. Copyright © 2012 John Wiley & Sons, Ltd.

The Unified Power Flow Controller (UPFC) integrates properties of shunt and series compensations and can effectively alters power system parameters in a way that increases power transfer capability and stabilizes system. Simple Proportional-Integral (PI) controllers are applied to UPFC as usual controllers, but parameters of PI controllers are usually tuned based on the trial-and-error approaches and they are incapable to obtain a good dynamic performance under a wide range of operating conditions. To solve this problem, robust control methods are proposed to design UPFC controllers. Also a supplementary damping controller to increase damping of power system oscillations is developed. A Single-Machine Infinite Bus (SMIB) power system installed with a UPFC with system parametric uncertainties is considered as case study. The system parametric uncertainties are obtained by 40% changing parameters from their typical values. Proposed methods are compared with each other to show their effectiveness and robustness. The objectives are to study and comparison robust control methods performance for UPFC control problem.

Unified Power Flow Controller (UPFC) combines function of voltage control, power flow control and oscillation damping. Before installation to a system, analysis for interactions between UPFC and system are needed. Building up steady, transient and dynamic models by present software to realize accurate simulations of UPFC under different system situation is a key step. In this paper, an UPFC model under dq axis including dynamic characteristics on DC side is built by switching function method. After control scheme analysis, effects of different damping strategies are compared. Simulation results show the correctness of the model and the validity of UPFC in controlling power flow and damping system oscillation.