Random Load Disturbances Research Articles

Feature extraction of AR as a performance index for load frequency controls of interconnected power systems

AbstractRecently, the evaluation of control performances of interconnected power systems has become an important issue with respect to individual load frequency controls. Several performance measures are in practical use such as Area Control Error (ACE), Mutual Aid Criterion (MAC), and Control Performance Standard (CPS). Area Requirement (AR) is an alternative expression for ACE, where AR=−ACE. However, the characteristics of these indices have not been sufficiently studied as far as the authors know. In particular, this is the case for their dynamic behavior against random load disturbances. This paper investigates the performance index, AR, through analysis of two‐area systems. Major dynamic elements of interconnected systems affecting the frequency are taken into account to investigate responses of the system against load disturbances. The analysis shows that, when new systems are interconnected, the smaller system tends to require more effort of control against load disturbances to keep the same value of the performance indices. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(1): 20–28, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20233

負荷周波数制御の性能指標ARの特徴抽出

Recently, the evaluation of control performances of interconnected power systems has become an important issue with respect to individual load frequency controls. Several performance measures are in practical use such as Area Control Error (ACE), Mutual Aid Criterion (MAC), and Control Performance Standard (CPS). Area Requirement (AR) is an alternative expression for ACE, where AR=−ACE. However, the characteristics of these indices have not been sufficiently studied as far as the authors know. In particular, this is the case for their dynamic behavior against random load disturbances. This paper investigates the performance index, AR, through analysis of two-area systems. Major dynamic elements of interconnected systems affecting the frequency are taken into account to investigate responses of the system against load disturbances. The analysis shows that, when new systems are interconnected, the smaller system tends to require more effort of control against load disturbances to keep the same value of the performance indices. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(1): 20–28, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20233

Optimal Robot Speed Trajectory by Minimization of the Actuator Motor Electromechanical Losses

This paper considers the control problem of a robotic manipulator with separately excited dc motor drives as actuators. An innovative method is proposed which achieves robot speed-control requirements, with simultaneous minimization of total electromechanical losses, while the drives follow the desired speed profiles of the robot joints under various loads and random load disturbances. If there is no demand for a specific speed profile, the optimal speed trajectory is determined by minimizing an electromechanical losses criterion. Controllable energy losses, such as armature copper losses, armature iron losses, field copper losses, stray load losses, brush load losses, friction and windage losses, can be expressed proportionally to the squares of the armature and the field (exciting) currents, the angular velocity and the magnetic field flux. The controllable energy loss term is also included in the optimal control integral quadratic performance index, defined for the whole operation period. Thus the appropriate control signals required for following the desired trajectory by simultaneous energy loss minimization for the whole operation interval are achieved. Two case studies of optimal robot control with and without minimization of actuator energy losses are presented and compared, showing the energy savings that can be achieved by the proposed methodology.

A security measure for random load disturbances in nonlinear power system models

This paper proposes a security measure to indicate vulnerability to voltage collapse in electric power systems. The voltage-collapse phenomenon is modeled as a large deviation in the nonlinear dynamics of the system, driven by small magnitude, broad spectrum disturbances in load. This model relates the collapse to shrinking of the region of attraction for the operating point. The security measure indicating vulnerability to voltage collapse is based on expected exit time from the region of attraction for the stable operating point. It is shown that expected exit time can be related to a natural Lyapunov function for the power system, and that a security measure based on this expected exit time can be calculated simply by evaluating an exponential function of the Lyapunov "energy" at a neighboring load flow solution.

Sampled Data Automatic Generation Control Analysis with Reheat Steam Turbines and Governor Dead-Band Effects

In this paper a systematic method of choosing the frequency bias parameter and the integrator gain of the sampled data supplementary control is presented by using the discrete version of the Lyapunov technique. The reheat effect of the steam turbines is considered in the state space model. The effect of governor dead-band nonlinearity is considered by using the describing function approach and including the linearized equations in the state space model. It is shown that the governor dead-band nonlinearity has a destabilizing effect on the transient response with deterministic and random load disturbances for purely integral ACE control. However, this destabilizing effect is reduced by proportional feedback of ACE.

A Comparative Assessment of Electronic and Pneumatic Controllers When Controlling Fast Processes Subject to Rapid Load Disturbance

Experimental and analytical methods have been developed for measuring the performance, in an integral-square-error sense, of process control systems subject to random load disturbances. Results are given for the relative performance of pneumatic and electronic controllers when controlling a fast process (process time constant 1.3 s) subject to rapid load disturbances. It is shown that the performance of both types of controller is essentially the same when short lengths of pneumatic transmission line are used, but the performance of the pneumatic controller considerably deteriorates when longer transmission lines are used. The analytical method of performance assessment can give accurate information on controllability at the process design stage, provided that the process is linear about its operating point and that the transfer function is known.

Evaluation of a quadratic performance criterion for 3-term control loops

A general procedure for evaluating a weighted mean-square-error criterion for multivariable systems is presented. By incorporating pure time delays as Padé approximations, the method may be applied to interacting computer control loops which are subjected to random load disturbances, thus leading to optimal-control-algorithm settings. A matrix solution of the integral criterion using Gaussian elimination obviates the need for standard-integral tables.

Study of the Effect of the DC Link on Frequency Control in Interconnected AC Systems

This paper presents a control effect of automatic frequency ratio control (AFRC) on an HVDC transmission to the AFC on ac systems when AFRC is applied to a random load disturbance in a steady state. The analysis of dynamic response of an ac-dc transmission system has been made by an analog computer. The frequency-improving and reduction effects of the output power of regulating power stations by AFRC are statistically analyzed by a digital computer.