Dusan Povh

Basic control of unified power flow controller

A unified power flow controller (UPFC) is a typical FACTS device capable of instantaneous control of three power system parameters. This paper presents a basic control system which enables the UPFC to follow the changes in reference values of the active and reactive power supplied from the outer system controller. The analysis is based on the transformation of the three-phase power system to the rotating reference frame. As a step closer to a practical application of the UPFC, a modified control structure with a predictive control loop and precontrol signal for a DC-voltage control was designed. The new control system offers better stability and transient performance in comparison with the classical decoupled strategy, especially considering the harmonic distortion of the current being controlled. The derived basic control of the UPFC was tested with the NETOMAC program system.

Improvement of transient stability using unified power flow controller

The aim of the paper is to analyze the effect of a unified power flow controller (UPFC) on transient stability margin enhancement of a longitudinal power system. To utilize the UPFC possibilities fully, the three controllable UPFC parameters were determined during the digital simulation process performed by the NETOMAC simulation program. The basis for determination of the suitable damping strategy and for determination of the optimal UPFC parameters is a mathematical model, which describes the interdependence between longitudinal transmission system parameters, operating conditions and UPFC parameters in the form of analytical equations. On the basis of the mathematical model, the theoretical UPFC limits were also detected, and their appearance explained.

Optimization and Coordination of Damping Controls for Improving System Dynamic Performance

This paper presents a global tuning procedure for FACTS device stabilizers (FDS) and power system stabilizers (PSS) in a multimachine power system using a parameter-constrained nonlinear optimization algorithm implemented in a simulation program. This algorithm deals with such an optimization problem by solving a sequential quadratic programming using the dual algorithm. The main objective of this procedure is to simultaneously optimize preselected parameters of the FDSs and PSSs having fixed parameters in coping with the complex nonlinear nature of the power system. By minimizing a nonexplicit target function in which the oscillatory rotor modes of the generators involved and swing characteristics between areas are included, interactions among the FACTS controls under transient conditions in the multimachine system are improved. A multimachine power system equipped with a TCSC and an SVC, as well as three PSSs, is applied to demonstrate the efficiency and robustness of the tuning procedure presented. The results obtained from simulations validate the improvement in damping of overall power oscillations in the system in an optimal and globally coordinated manner. The simulations also show that the stabilizers tuned are robust in providing adequate damping for a range of conditions in the system.

Advanced SVC control for damping power system oscillations

A new SVC (static VAR compensation) control for damping of power system oscillations has been developed. To increase system damping an SVC uses a phase angle signal estimated from the measurement of voltage and power at the SVC location. By means of an optimization and identification procedure, optimized design of the damping control with various control concepts can be determined, taking into account nonlinear power systems. As a result of this method it is possible to increase power system damping considerably, in particular in critical situations close to the stability limit, using only locally measured state variables at the SVC, thus leading to an increase in the transmission capability of the power system. >

The energy function of a general multimachine system with a unified power flow controller

In order to be able to successfully apply direct methods or other energy-function-based calculations in power systems, which include flexible AC transmission systems (FACTS) devices, the influence of those devices should be properly considered. This is currently not always possible in power systems incorporating unified power flow controllers (UPFCs) because the present energy functions for electric power systems do not involve proper UPFC actions. This paper presents a way of incorporating the transient-stability augmentation action of the most versatile FACTS device, i.e., the UPFC, into an energy function for multimachine systems. After making some assumptions, a new term of the structure-preserving energy function (SPEF) that represents a UPFCs energy function was constructed. This term can simply be added to any existing SPEF. The extended SPEF was tested for one UPFC in a longitudinal test system and for one and two UPFCs in an IEEE nine-bus machine test system. A comparison between the critical clearing times (CCTs) acquired directly with the use of the newly constructed SPEF and those obtained with time-simulation results shows that the proposed UPFCs energy function is suitable because the correct CCTs were obtained.

Use of HVDC and FACTS

The fast development of power electronics based on new and powerful semiconductor devices has led to innovative technologies, such as high voltage DC transmission (HVDC) and flexible AC transmission system (FACTS), which can be applied in transmission and distribution systems. The technical and economical benefits of these technologies represent an alternative to the application in AC systems. Deregulation in the power industry and opening of the market for delivery of cheaper energy to the customers is creating additional requirements for the operation of power systems. HVDC and FACTS offer major advantages in meeting these requirements.

A large integrated power system software package-NETOMAC

The simulation system NETOMAC/sup (R)/ (Network Torsion Machine Control) offers a wide range of modern methods of analyzing and synthesizing electric power systems. In order to design individual elements of transmission systems or to perform stability calculations on large systems, it is possible to simulate electrical networks in the time domain and also, with the aid of eigenvalue calculations, to study the frequency domain too. These methods find general application in the design of control systems add in analyzing the behavior of large networks. User support is provided in the form of a graphical interface to facilitate the inputting of the electrical systems and control structures, One uniform database is being used for all calculations regardless of whether time domain or frequency domain is being investigated. Workstations, PCs or notebooks provide the platform from which NETOMAC can provide the user with the flexibility, mobility and speed that he needs.

Improvement Of Transient Stability By Insertion Of Facts Devices

The aim of the paper is to analyze the effect of Series Compensation (SC) and FACTS devices (Static Var Compensator (SVC), Advanced Static Var Compensator (ASVC), Thyristor Controlled Phase Shifting Transformer (TCPS) and Unified Power Flow Controller (UPFC) ) on transient stability. The basic operating principles of each device are described. Each FACTS device mentioned, except the UPFC, has only one controllable parameter. UPFC has three controllable parameters which are determined to maximize damping. They can be expressed as the function of network parameters, machine parameters and voltage angles between terminal busses. With damping strategy we wanted to achieve the following goals: to maintain the system in synchronism during the lSt swing, to damp as effectively as possible the following swings, and to prevent the system from persevering near the maximum of 1st swing. To fulfill the above three requirements appropriate damping strategies for UPFC and TCPS are developed. The efficiency tests of damping control strategies and the comparison of the damping effectiveness of particular devices are carried out on the test AC system, using NETOMAC simulation program. Therefore appropriate models of damping devices and control are developed according to theoretical considerations.

Optimization and coordination of damping controls for improving system dynamic performance

Summary form only given as follows. This paper presents a global tuning procedure for FACTS device stabilizers (FDS) and power system stabilizers (PSS) in a multimachine power system using a parameter-constrained nonlinear optimization algorithm implemented in a simulation program. This algorithm deals with such an optimization problem by solving a sequential quadratic programming using the dual algorithm. The main objective of this procedure is to simultaneously optimize preselected parameters of the FDSs and PSSs having fixed parameters in coping with the complex nonlinear nature of the power system. By minimizing a nonexplicit target function in which the oscillatory rotor modes of the generators involved and swing characteristics between areas are included, interactions among the FACTS controls under transient conditions in the multi-machine system are improved. A multi-machine power system equipped with a TCSC and an SVC as well as three PSSs is applied to demonstrate the efficiency and robustness of the tuning procedure presented. The results obtained from simulations validate the improvement in damping of overall power oscillations in the system in an optimal and globally coordinated manner. The simulations also show that the stabilizers tuned are robust in providing adequate damping for a range of conditions in the system.

300 kW battery energy storage system using an IGBT converter

Increasing automation in modern industry and deregulation have changed the requirements on power quality. Computer and process control equipment as well as drive converters are sensitive to deviations of the line voltage from the ideal sinusoidal. Voltage sags, harmonic distortion, flicker and interruption of power supply are the most common problems. In an increasing number of cases, where conventional equipment cannot solve these problems, PWM converter-based shunt- and series connected power conditioners named DSTATCOM (distribution static synchronous compensator) and DVR (dynamic voltage restorer) have been introduced. With energy storage added to the power conditioner even more flexibility in system operation and planning is provided for utilities and industry. This paper describes such a 300 kW power conditioner with a chemical battery and its benefits to an industrial plant. If, for example, load demand exceeds the power rating of the supplying transformer or the negotiated power with the utility only at certain times of day, the excessive active power demand can be provided by the power conditioner. In addition, the power conditioner can be used for reactive power compensation or other tasks, if it is not fully used for charging or discharging. The new technology can therefore be used to postpone or avoid major investments and to optimize energy consumption costs.