Multivariable design of a multiple-functional unified power flow controller

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.

Recently it has been shown that it is possible to design a power system stabilizer (PSS) as well as an unified power flow controller (UPFC) controller using a non-linear multi-machine system model in conjunction with Lyapunov's direct method. In this paper the features of two controllers implementing the proposed control laws have been compared: the PSS constitutes a supplementary loop to the main automatic voltage regulator (AVR) and UPFC controller. Theoretical analysis is supported by the results of eigenvalues analysis and simulations tests, which highlighted the differences between the actions of compared controllers. The tests performed on a multi-machine system model have shown a good performance of both proposed controllers.

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

Unified power flow controller (UPFC) consists two converters. There are three purposes of this paper, firstly to illustrate the UPFC device based VSC designs, then to describe a decoupling method the UPFC's controller into two separate control systems of the shunt and the series converters respectively in realizing an appropriate coordination between them. Finally, using the Matlab tool to build a discrete simulator for the UPFC with 12 pulse converters. The simulation results show that the developed UPFC model is reflected the static and dynamic characteristics of the UPFC. The harmonics of the output of the model were analyzed. Using the simple power system with UPFC as an example, the dynamics characteristics were studied. The fault status of the system with UPFC was analyzed too.

The Unified Power Flow Controller (UPFC) can inject voltage with controllable magnitude and phase angle in series with a transmission line. It can also generate or absorb controllable reactive power. UPFC is expected to be able to damp power system oscillations more effectively than power electronics devices such as SVG and TCSC. In this paper, a control system design of a UPFC for power system damping enhancement based on the eigenvalue control method is proposed. It is made clear that the best design method for the power system damping enhancement is to determine steady-state values of the UPFC control variables and the control parameters of the UPFC such as gains and time constants simultaneously, because the controllability of UPFC depends on the steady-state values of UPFC and the power flow condition. The effectiveness of the proposed control system taking into account UPFC inverter ratings is verified by digital time simulation. Furthermore the effects of the input signals to the UPFC controller on small-signal stability and transient stability enhancement are studied, and it is made clear that UPFC controllers using global information are more effective for power system damping enhancement than those using local information because global information has stronger observability for power system oscillations than local information. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 35–47, 2000

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.

This paper addresses two issues: enhancement of fault recovery and controller design accounting for filter dynamics. Performance of the unified power flow controller (UPFC) is improved by a proposed modification of the UPFC into a 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 during the recovery. The battery will be charged during normal operation of the UPFC. The size of the battery for the SSSC has been 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. 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, as is often seen in simulation studies, then the controller's response will be different. The test system used in this work is a one-machine, infinite bus bar system. All of the simulations were implemented using the Electromagnetic Transients Program (EMTP) which is a powerful simulation tool for power system simulation. In additional, the Matlab and Simulink programming environment were used to provide transfer function simulation for the controller design. The simulation results from both programs are compared.

Combining particle swarm optimization (PSO) with deep learning (DL), the present work provides a new method for the hybrid optimization of the best placement and real-time control of unified power flow controllers (UPFCs) in power systems. The suggested technique combines the global search capacities of PSO to identify the ideal position for UPFCs with the adaptive control power of DL to dynamically update UPFC settings in response to system changes, hence overcoming the limits of current approaches. This method is special in that it considers transient and voltage stability margins, hitherto neglected in earlier research. This element of the advised approach reduces UPFC costs, fuel, and power loss. The efficacy of the hybrid DL-PSO approach is confirmed by means of the IEEE-26 bus test system; the obtained results are compared with those of conventional algorithms like Genetic Algorithm (GA), PSO, and GSA. The advantages of the suggested technique in terms of speed and accuracy for UPFC deployment and control are shown by the simulation results, thereby stressing its possibility of raising power system stability and efficiency. This creative technique opens the path for further advancements in AI-driven power system management by providing a consistent answer for challenging power system optimization.

This paper proposes a new real and reactive power coordination controller for a unified power flow controller (UPFC). The basic control for the UPFC is such that the series converter of the UPFC controls the transmission line real/reactive power flow and the shunt converter of the UPFC controls the UPFC bus voltage/shunt reactive power and the DC link capacitor voltage. In steady state, the real power demand of the series converter is supplied by the shunt converter of the UPFC. To avoid instability/loss of DC link capacitor voltage during transient conditions, a new real power coordination controller has been designed. The need for reactive power coordination controller for UPFC arises from the fact that excessive bus voltage (the bus to which the shunt converter is connected) excursions occur during reactive power transfers. A new reactive power coordination controller has been designed to limit excessive voltage excursions during reactive power transfers. PSCAD-EMTDC simulation results have been presented to show the improvement in the performance of the UPFC control with the proposed real power and reactive power coordination controller.

The role of power transmission line is to transmit power of high quality without interruption. The flow of power basically depends on the line impedance, sending and receiving end voltage magnitudes. The most preferable Flexible AC Transmission System (FACTS) device is UPFC (Unified Power Flow Controller) which can provide the control of all these parameters simultaneously or independently. The control parameters of UPFC are traditionally set in parameter space. This spacial feature based controller cannot consider the spectral features of the system during dynamic fault conditions. In order to optimize the efficiency of the computational process, wavelet based neuro controller is proposed which speed up the process besides providing more flexibility to identify the dynamic changes. The results show that the rotor angle oscillations have been damped out quickly with wavelet based neuro controller for UPFC.

Design of output feedback UPFC controller for damping of electromechanical oscillations using PSO

The application of unified power flow controller (UPFC) has become an inevitable trend to deal with challenges faced by modern power system such as optimization of power supply and system operation. However, review researches on UPFC are less while the researches on specific technologies mostly focus on theoretical fields, which are difficult to guide actual engineering. To this end, this paper discusses several key issues of UPFC in its actual application. First of all, technical process of UPFC in actual application was proposed and its six key issues were pointed out. Then, for three issues in the process of “scheme-obtaining of UPFC application”, the principles of necessity to configure UPFC, the method of determining UPFC location and capacity, the method of determining UPFC control strategy are discussed. Finally, for three issues in the process of “influence analysis and optimization for UPFC”, simulation calculation method of power system with UPFC, influences of UPFC on power system operation, changes strategy of operating parameter for UPFC are discussed. The work done in this article aims to provide a reference for the actual application of UPFC.

The two converters are the basic parts of a unified power flow controller (UPFC). Based on the widely used MATLAB, a digital simulator for the UPFC with 12-pulse converters is developed. Simulation results show that the developed UPFC model is precise in reflecting the static and dynamic characteristics of the UPFC. The harmonics of the output of the model is also analyzed. Using a simple power system with the UPFC as an example, the dynamic characteristics of the UPFC is studied based on the model which has been developed. The simulation results show that the normal operating condition of UPFC could no longer be maintained following a severe disturbance. Furthermore, the fault status of the system could be aggravated by the UPFC if it is used only for power flow control.

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.

The wind power generation is rapidly growing and the use of wind farms and other distributed power generation systems have drastically increased. According to IEC standard, the power quality is determined from the performance of wind generators. In this paper using a FACTS controller device the power quality enhanced when the wind generators are connected to the grid system. The power quality becomes an issue when wind generators are connected to the grid, due to the interaction between the grid and the wind turbines. The main impact on the grid by the wind generators, regarding power quality, is related to voltage sag, reactive power, harmonics, power peaks and flickers. The power quality problem arises when the wind generators are equipped with the grid, can be improved by connecting a FACTS controller at a point of common coupling. In this paper, UPFC (UNIFIED POWER FLOW CONTROLLER) control scheme for the wind generators connected grid is used to improve the power quality using MATLAB/SIMULINK in power system block set. Also this UPFC control system that includes both the shunt converter and the series converter has been simulated. In this proposed model, the real and reactive power compensation is the main concern.