(1990). ENERGY FUNCTION ANALYSIS FOR POWER SYSTEM STABILITY. Electric Machines & Power Systems: Vol. 18, No. 2, pp. 209-210.

Energy function analysis for power system stability

A unified PID tuning method for load frequency control (LFC) of power systems is discussed in this paper. The tuning method is based on the two-degree-of-freedom (TDF) internal model control (IMC) design method and a PID approximation procedure. The time-domain performance and robustness of the resulting PID controller is related to two tuning parameters, and robust tuning of the two parameters is discussed. The method is applicable to power systems with non-reheated, reheated, and hydro turbines. Simulation results show that it can indeed improve the damping of the power systems. It is shown that the method can also be used in decentralized PID tuning for multi-area power systems.

Unified Tuning of PID Load Frequency Controller for Power Systems via IMC

A new PID controller for resistant differential control against load disturbance is introduced that can be used for load frequency control (LFC) application. Parameters of the controller have been specified by using imperialist competitive algorithm (ICA). Load disturbance, which is due to continuous and rapid changes of small loads, is always a problem for load frequency control of power systems. This paper introduces a new method to overcome this problem that is based on filtering technique which eliminates the effect of this kind of disturbance. The object is frequency regulation in each area of the power system and decreasing of power transfer between control areas, so the parameters of the proposed controller have been specified in a wide range of load changes by means of ICA to achieve the best dynamic response of frequency. To evaluate the effectiveness of the proposed controller, a three-area power system is simulated in MATLAB/SIMULINK. Each area has different generation units, so utilizes controllers with different parameters. Finally a comparison between the proposed controller and two other prevalent PI controllers, optimized by GA and Neural Networks, has been done which represents advantages of this controller over others.

A robust PID controller based on imperialist competitive algorithm for load-frequency control of power systems.

The large-scale power systems are liable to performance deterioration due to the presence of sudden small load perturbations, parameter uncertainties, structural variations, etc. Due to this, modern control aspects are extremely important in load frequency control (LFC) design of power systems. In this paper, the LFC problem is illustrated as a typical disturbance rejection as well as large-scale system control problem. For this purpose, simple approach to LFC design for the power systems having parameter uncertainty and load disturbance is proposed. The approach is based on two-degree-of-freedom, internal model control (IMC) scheme, which unifies the concept of model-order reduction like Routh and Pade approximations, and modified IMC filter design, recently developed by Liu and Gao [24]. The beauty of this paper is that in place of taking the full-order system for internal-model of IMC, a lower-order, i.e., second-order reduced system model, has been considered. This scheme achieves improved closed-loop system performance to counteract load disturbances. The proposed approach is simulated in MATLAB environment for a single-area power system consisting of single generating unit with a non-reheated turbine to highlight the efficiency and efficacy in terms of robustness and optimality.

Load Frequency Control in Power Systems via Internal Model Control Scheme and Model-Order Reduction

This paper discusses the pricing of marginal transmission network losses in the locational marginal pricing approach recently deployed in the ISO New England (ISO-NE) standard market design (SMD) project implemented by ALSTOM's T&D Energy Automation and Information (EAI) Business. The traditional loss model is studied and a new model is proposed. The new model achieves more defendable and predictable market-clearing results by introducing loss distribution factors to explicitly balance the consumed losses in the lossless dc power system model. The distributed market slack reference is also introduced and discussed. The LMP components produced by the two models are studied and compared under changes in slack reference. Numerical examples are presented to further compare the two models.

Marginal loss modeling in LMP calculation

Extended integral control for load frequency control with the consideration of generation-rate constraints

This paper presents a new PID (proportional, integral and differential) control scheme based on the feedback of averaged derivatives to realize a noise-tolerable differential control with its application to the load frequency control in the power system. It is well known that the LFC (load frequency control) is exposed to the quite noisy environment. The noisy environment has made it difficult to adopt the differential feedback loop since the derivatives of the signals deteriorated by high frequency noise causes the system instability. This paper proposed a new PID control scheme adopting averaged derivative of the signal as the differential feedback signal in order to remove the effects of high frequency noise. This study deals with an application of the average differential feedback to the LFC problem in the power systems. The proposed control scheme has been tested for the load frequency control of power systems.

Power system load frequency control using noise-tolerable PID feedback

This paper presents an extended integral control to LFC (load frequency control) scheme with the presence of GRC (generation rate constraints) in order to get rid of the overshoot of conventional PI control. The conventional LFC scheme does not yield adequate control performance with consideration of the singularities of speed-governor such as rate limits on valve position and GRC. In order to overcome this drawback, an extended integral control is developed for the PI control of the speed governor under the presence of GRC. The key idea of the extended integral control is using a decaying factor to reduce the effects of the error in the past. The decaying factor greatly affects the control performance, and should be carefully selected. This study determines the decaying factor in proportion to the degree of deviation in several levels. The computer simulation has been conducted for the single machine system with various load changes. The simulation results show that the proposed controller based on extended integral control yields much improved control performance, compared to the conventional PI controller.

The power system stability mostly depends on the surplus kinetic energy which is stored in the generator during the fault period. The steam valve control is the most direct method to control the surplus kinetic energy. This paper proposes a new LFC scheme with a modified PID controller which improves the system damping. The proposed frequency controller is designed to guarantee the stability of frequency control for any change in the feedback gain of frequency deviation. The proposed LFC scheme adopts the nonwindup cutoff model for the steam valve position. It has been shown that the steam valve control is the most direct method to control the surplus kinetic energy stored in the generator during the fault period and control performance significantly depends on steam valve modeling. The proposed LFC scheme has been applied for two sample systems, 4-machine 10-bus and New England 39-bus systems.

Improvement of system damping by using the differential feedback in the load frequency control

This paper proposes a new load frequency control (LFC) scheme with a modified PID controller which guarantees the stability of the LFC loop for the wide control ranges of PID feedback gains. By observing the fact that the ratios between PID gains have more information than the individual gains, we proposed a modified PID controller by implementing feedback circuits by differentiating and integrating the output of the flyball speed governor. The proposed control scheme guarantees wide-range stability boundary of the PID gain controls, which can be easily checked by observing the root locus diagram. This paper shows that the valve position limits can be modeled in several ways, and that the control performance significantly depends on steam valve modeling in the case of large disturbances. The proposed LFC scheme has been tested for a sample 4-machine 10-bus system.

Modified PID load-frequency control with the consideration of valve position limits

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Extended integral control for load frequency control with the consideration of generation-rate constraints

Power system load frequency control using noise-tolerable PID feedback

Extended integral control for load frequency control with the consideration of generation-rate constraints

Improvement of system damping by using the differential feedback in the load frequency control

Modified PID load-frequency control with the consideration of valve position limits