Control Of Electric Power Systems Research Articles

セメント粉砕閉回路の静特性に基づく制御系設計指針 粉砕閉回路のロバスト制御に関する研究（第２報）

It is known that the typical control system based on BE electric power, which has been applied in many cement grinding plants, has some problems. Other types of controls therefore have recently been proposed. They require both to stabilize the process and to improve the product quality against the changes in clinker grindabilty. The authors have already constructed the transfer function model from population balances of the process. The purpose of this paper is to present an optimal control strategy based on the steady-state characteristics. Firstly we criticized several conventional control methods. For instance, it was quantitatively confirmed that the BE electric power control system could not regulate the product property and the multivariable one by manipulating the classifier cut size could not keep the product quality as well as its quantity simultaneously against the feed change in grindabilty. Consequently we have proposed a hierarchy control system, consisting of the two stages. The higher one is to determine the product set-point values and the lower one is to control the stability and the product quality. In this system, when the grindability becomes low the decrease of the product quantity can be prevented by changing the set point of the product quality. This system has also an advantage of avoiding the mill choking. As to the detection of gindability it was suggested to estimate it by measuring the product quantity and quality (specific surface) simultaneously, or practically mill discharge quality only.

The Electric Power System in China: Rapid Development Calls for Advanced Technologies

Rapid growth of electric power systems in China and the prospects of future development up to year 2010 are briefly reviewed. The rapid growth brings about problems to be resolved by advanced technologies in the fields of electric power generation, power system and power plant control, power system technology, the socialistic, electricity market competition They are outlined in this paper.

A structure-based modeling and control of Electric power systems

This paper addresses the modeling and closed-loop control of large-scale electric power systems operating under normal conditions. A new structure-based modeling approach is introduced—an approach which reveals fundamental properties of power system dynamics, and offers physical insight into the interactions between its constituent subsystems. These properties and insights lead to the formulation of simple, higher level models which represent slow interactions among subsystems driven by slow load variations. The models which evolve from this structure-based approach enable hierarchical control design, without any a priori assumptions regarding the strength of the interactions among the subsystems. New control designs are thus proposed at both the subsystem and the interconnected system levels, a key element in their formulation being that both react to variables reflecting interactions between subsystems. Reactive power/voltage ( Q V ) control problems are used to illustrate the proposed modeling and control approach.

Use of UPFC for optimal power flow control

This paper deals with optimal power flow control in electric power systems by the use of a unified power flow controller (UPFC). Models suitable for incorporation in power flow programs are developed and analysed. The application of UPFC for optimal power flow control is demonstrated through numerical examples. It is shown that a UPFC has the capability of regulating the power flow and minimising the power losses simultaneously. An algorithm is proposed for determining the optimum size of UPFC for power flow applications. The performance of UPFC is compared with that of a phase shifting transformer (PST).

Discussion of "Harmonic analysis of industrial power systems" [and reply

The author argues that a good introduction to IEEE Standard 519-1992 (IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems) was made in the original paper (Ellis, see ibid., vol. 32, p. 417-21, 1996), in addition to the presentation of a study case related to an industrial power system. Here, comments are made on the above paper and the original author's reply is also included.

Model-based, real-time control of electrical power systems

Automated control of a large electrical power distribution network through a single controller can provide advantages in efficiency and reliability as well as reduction in maintenance costs. For control to be most effective, it is necessary that a global view of the entire network be had by the controller, so that it can reason as to the cause of the readings of the various sensing devices located throughout the network, Traditional approaches to power system control have involved a set of local devices (i.e., protective relays) that base their decision on the instantaneous reading of a single sensor. These single-parameter decisions can sometimes be incorrect due to sensor failures. Furthermore, a special type of fault called a soft fault, where a fault impedance limits the current to a value below the relay operating point, are nearly impossible to detect with decisions based on a single local parameter. By reasoning over an entire suit of sensing devices spread throughout the entire network, protection decisions based on a global view can become more reliable as well as comprehensive. Some previous approaches have implemented global control with varying degrees of success through the use of rule-based knowledge-based systems. This paper describes an alternative knowledge-based approach that makes use of so-called models of structure-and-behavior, to which model-based diagnosis is applied. The objective of this approach is to develop a system that can reliably diagnose faults in power distribution networks (especially soft faults), identify sensor failures, and carry out appropriate corrective action automatically. An intelligent power controller (IPC) which has these capabilities is described. This IPC was rigorously tested in an DC electrical power distribution system testbed and found to successfully carry out the required functions. This paper also describes in detail the tests and the conclusions drawn from their results.

Sensory Systems and Intelligent Control for Electric Power Plants

The power industry in the US and Europe is going through a major transition. The change that the telecommunication industry experienced in the early 80's as a result of government deregulation is analogous to what is now facing the utilities. Government deregulation, open transmission access, presence of independent power producers (IPPs), and increased attention to the global air pollution have introduced major challenges to the utility industry. Smart sensors and intelligent control are believed to play a very important role in the future operation and survival of the electric power industry. Development of real-time optimal load scheduling, on-line optimal power rate determination, signature analysis, and pattern recognition for major load identification, active control for increased power quality, optimal demand-side management, closed loop combustion process control for pollution reduction, etc., are examples of control system application areas that have potential for major economic impacts in the power industry. Development of new sensors and sensory systems, e.g., real-time SO2 measurement in generation control or gas density sensor for high power transformer, that would provide information about die state of the system can be used for preventative maintenance as needed rather than as scheduled. Thus, advanced control and sensory systems can provide the technological advancement required for power industry in this highly competitive era. In this regard, the Electric Power Research Institute (KPRI) along with major utilities and the National Science Foundation (NSF) have initiated several programs both in industry and in universities in the areas of smart sensory systems and intelligent control. The main objective of this panel is to bring together industry representatives as well as university researchers involved in these initiatives to discuss:•State-of-the-art in control of electric power systems;•Role of smart sensors and intelligent control in the new utility business environment;•Industry needs and identification of future research directions.

96/01620 Decentralized control of interconnected electric power systems in competitive markets

96/01620 Decentralized control of interconnected electric power systems in competitive markets

Nonlinear dynamics and switching time bifurcations of a thyristor controlled reactor circuit

We study a thyristor controlled reactor circuit used for static VAR control of utility electric power systems. The circuit exhibits switching times which jump or bifurcate as fold or transcritical bifurcations. We study the nonlinear dynamics of the circuit using a Poincare map and demonstrate that the Poincare map has discontinuities and is not invertible. The circuit has multiple attractors, moreover, the basin boundary separating the basins of attraction intersects with the Poincare map discontinuities. These novel properties illustrate some of the basic features of dynamical systems theory for thyristor switching circuits.

Decentralized control of interconnected electric power systems in competitive markets

This paper investigates the prospects of decentralized control in the emerging competitive electricity markets. The weaknesses of current control performance criteria for dealing with such markets are discussed and it is hypothesized that decentralized control, providing full control over economically independent electrically interconnected areas, is necessary in such markets. To study the feasibility of such a decentralization rigorously, a state space decomposition method is introduced and applied to the model of an interconnected system. As a result it is shown that, in electric power systems, regardless of the number and location of the tie lines and implemented control schemes, the frequency and phase of each area are in the controllable subspaces of all areas in the interconnection. This shows that, if decentralization is to be achieved, flexible links which decouple the phases of areas must be utilized. The side effects of such implementations are also discussed.

A modeling and control framework for operating large‐scale electric power systems under present and newly evolving competitive industry structures

This paper introduces a systematic, structure‐based modeling framework for analysis and control of electric power systems for processes evolving over the mid‐term and long‐term time horizons. Much simpler models than the detailed dynamics specifically for control design at different hierarchical levels are obtained by applying both temporal and spatial separation. These simple models, or the aggregate models, represent the net effect of interactions among interconnected regions on specific hierarchical levels. They are exact, since no assumptions on weak interconnections among the subsystems are made. Moreover they are easily understood in terms of power flows among the regions. The approach is essential for improving present performance of the system. It is also potentially useful in a competitive utility environment in which it is critical to study the interplay between technical and economic processes.

160 Real-time fuzzy control of electric power systems

160 Real-time fuzzy control of electric power systems

The Electromagnetic Transients Program (EMTP) as an effective tool to evaluate active power filters for harmonic compensation

The Institute of Electrical and Electronic Engineers (IEEE) ‘Recommended Practices and Requirements for Harmonic Control in Electric Power Systems’ sets limits for the current and voltage harmonic distortions at the point of common coupling in order to maintain an acceptable quality of electric power in the presence of nonlinear loads. Both the utility and its customers share a common responsibility since enforcement of the above practice by the utility would require that the affected customer use a suitable harmonic mitigating method. To this effect, this paper demonstrates how the Electromagnetic Transients Program (EMTP) may be used to investigate two harmonic mitigating methods, namely, the use of shunt passive power filters and the combination of a series active (APF) and shunt passive (PPF) power filters. Both methods reduce the harmonic currents injected into the distribution system; however, the combination of the series APF and shunt PPFs has a better compensation characteristic with a higher capital cost than only shunt PPFs. Before a final decision is reached, the cost of the higher harmonic losses throughout the distribution system when using only shunt PPFs must be taken into account.

A specification of neural network applications in the load forecasting problem

This paper investigates the effectiveness of the artificial neural network (ANN) approach to short term load forecasting in electrical power systems. Using examples, the learning process and capabilities of a neural network in the prediction of peak load of the day are demonstrated. Different data normalizing approaches and input patterns are employed to exploit the correlation between historical load and temperatures and expected load patterns. A number of ANN's are included with emphasis given to their practical implementation for electrical power system control and planning purposes. The networks have been trained on actual power utility load data using a backpropagation algorithm. The prospects for applying a combined solution using artificial neural networks and expert systems, called the expert network are also discussed. Consideration is given to expert networks as a more complete solution to the forecasting problem which neither system alone can provide.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of self‐commutated SVC for power system

AbstractA 50‐MVA self‐commutated Static Var Compernsator (SVC) using the worlds's largest GTO thyristors rated 6 kV‐2500 A has been developed for voltage control of electric power systems. The rated dc voltage is 16.8 kV which is four times higher than the highest one manufactured so far. To achieve the high dc voltage, eight GTO thyristors are connected in series. Voltage unbalance between GTOs during switching transient was investigated. A new overcurrent limiting method is proposed, since conventional fuse protection cannot be applied due to such high voltage. Newly developed technologies for this large and high‐voltage self‐commutated SVC are described.Although simple star‐delta connection transformers are used, harmonics generated from SVC are almost equivalent to the 24‐pulse converter by shifting the pulse timing appropriately. The PWM control based on 150 Hz is applied and the SVC is designed to continue operation during system faults. The performance of the controller is tested successfully by a simulator, and typical rest results are introduced.

Power flow control by use of controllable series components

Power flow control in electric power systems by use of controllable series power capacitors and phase shifters is discussed. Models suitable for incorporation in power flow programs are developed and analyzed. The power flow control problem is defined in a stringent way, and a method for solving the power flow control problem is proposed based on decomposition. This method is applied on test systems and the convergence rate of the algorithm is discussed. Simplified models of the components are also derived. These simplified models are shown to be quite accurate in most situations, and are used to construct regions of feasible power flows of the controlled lines.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New modelling, analysis and computation techniques needed for power system control centres

In this paper the new modelling, analysis and computation techniques needed in the coming generation of electric power system control centres are outlined. The motivation is to provide better utilization of the power system. This means better economy, which requires more elaborate optimization, with acceptable security, which requires more accurate analysis of the system behaviour. At present, the optimization available is advancing from not considering system limits (economic dispatch) to taking into account the steady-state constraints (optimal power flow), while analysing the system is limited to its steady-state behaviour (static security analysis). The addition of dynamic analysis (transient, small perturbation, and voltage stabilities) is desperately needed but remains a challenge. The calculation of these security limits and their reflection into the optimization are also significant challenges. The effects of the coming deregulatory operational environment further adds to the optimization complexity.

Digital input filters for measurement, control and protection in electric power systems

AbstractPower system control and protection equipment is subject to especially stringent sensitivity and operational reliability requirements.Projected digital signal processing systems suitable for electric power systems fulfill these requirements by means of fast sampling and digital filtering by a 32‐bit floating point DSP (Digital Signal Processor). The sampling rate of 3 kHz is carefully selected in order to separate the power spectra of the A‐D conversion output errors from the signal bandwidth. The new 12‐bit A‐D conversion unit equipped with a recursive‐type digital filter achieved a high resolution equivalent to 14‐bit conversion.This paper describes the design concept and the operating characteristics and illustrates applications to current differential relays, distance relays and power system controllers.

Preventive control in an autonomous decentralized system

For more rational operation and control of future electric power systems which would continue to expand in size and complexity, an autonomous decentralized control system is proposed as one of the new control architectures. In the autonomous decentralized control system, each generating station and substation behaves independently and cooperatively without being controlled by the central station. Besides the inherent fault-tolerant characteristics of the architecture, flexible and rapid control depending on the circumstances can be achieved. In this paper, the fundamental logic of preventive control in an autonomous decentralized system is developed. It is based on the bidding method in which each station proposes its own output taking into consideration its own situation and cooperation with others. The economic load dispatch including preventive control can be performed, based on the bidding rule adopting the equivalent incremental generating cost curve in which the security constraints are incorporated. Application of the logic to a model system revealed satisfactory control performance for preventing the overload of transmission lines and the undervoltage.

Digital input filters for measurement, control and protection of electric power systems

Power system control and protection equipment has required higher sensitivity and operational reliability than conventional one. Studies of digital signal processing suitable for electric power systems fulfill this objective using fast sampling and digital filtering by a 32-bit floating point DSP (Digital Signal Processor). The sampling rate of 3 kHz is carefully selected in order to separate the power spectrums of the A-D conversion output errors from the signal bandwidth. The new 12-bit A-D conversion unit equipped with a recursive-type digital filter achieved the equivalent high resolution of 14-bit conversion. This paper describes the design concept and the characteristics showing applications to current differential relays, distance relays and power system controllers.