AUTOMATIC GENERATION CONTROL OF A HYDROTHERMAL SYSTEM WITH NEW AREA CONTROL ERROR CONSIDERING GENERATION RATE CONSTRAINT

ABSTRACT

The paper presents an analysis of the automatic generation control based on a new area control error strategy for an interconnected hydrothermal system in the discrete-mode considering generation rate constraints (GRCs). The investigations reveal that the system dynamic performances following a step load perturbation in either of the areas with constrained optimum gain settings and unconstrained optimum gain settings are not much different, hence optimum controller settings can be achieved without considering GRCs in the mathematical model.     

SELECTION OF SAMPLING PERIOD FOR AUTOMATIC GENERATION CONTROL

ABSTRACT

The paper presents the analysis of automatic generation control (AGC) of a two-equal area reheat thermal system in the presence of generation rate constraints considering a discrete-continuous time mathematical model. The effect of variation of sampling period on optimum integral gain setting and system dynamic performance has been analyzed considering supplementary controllers based on conventional area control errors (ACEs) and new area control errors (ACENs). Investigations reveal that the optimum integral gain setting and system dynamic performance are hardly affected over a wide range of sampling period T for controllers based on conventional ACEs. Studies also reveal that the permissible sampling period is further enhanced with integral controllers based on new area control errors (ACENs).     

AUTOMATIC GENERATION CONTROL WITH SUPERCONDUCTING MAGNETIC ENERGY STORAGE IN POWER SYSTEM

ABSTRACT

This paper describes the development of a digital computer model for a two area interconnected power system which includes the governor deadband nonlinearity, steam reheat constraints and boiler dynamics. The improvement in automatic generation control (AGO with the addition of a small capacity Superconducting Magnetic Energy Storage (SMES) unit is studied. Time domain simulations are used to study the performance of the power system and the controller. Parameter optimization of the controller are carried out by the second method of Lyapunov, which ensures the stability of the system. Suitable methods for the control of SMES unit are also described.     

QUICK AND PRECISE POSITION CONTROL OF ULTRASONIC MOTORS WITH TWO CONTROL INPUTS

ABSTRACT

Ultrasonic motor (USM) has an excellent performance and many useful features. Since this motor is superior in holding torque and high response characteristic, it has been expected to use as position servomotor for small motors.

There have been reported some mathematical models of the ultrasonic motor. however, these models are too complex to apply for control of the motor. Therefore position controllers based on PI control or fuzzy control have been proposed in recent years. It is difficult to control the ultrasonic motor with high-performance using such controllers, thus simple and convenient mathematical model is necessary for precise control.

This paper presents a new position control scheme of ultrasonic motor, it consists of a PI controller and an adaptive controller which compensates the speed characteristic variations with online parameter identification. Moreover, this system controls both driving frequency and phase difference in order to achieve a quick and precise position control. The effectiveness of proposed control.scheme is demonstrated by experiments.     

WELDING TRANSFORMER CONTROL BY THE ELECTRONIC CONTROL OF LEAKAGE FLUX

ABSTRACT

In this paper, the triac is used to control the welding transformer leakage reactances and thus the welding currents. This new method keeps the input and output currents and voltages in sinusoidal wave forms.

The triac is connected across the terminals of a coil wound on a fixed limb magnetic shunt. A simple triggering circuit is used to control the current of the triac and thus the current of magnetic shunt coil. This leads to variation of welding transformer leakage flux, leakage reactances and thus a variation of welding current.

The distortion due to the triac is only affecting the leakage flux of the welding transformer. The leakage flux is very small (compared with main flux) and most of it passes in the transformer window. Then, no harmonic pollution in the bus–bar or in the welding transformer. Thus, high operating efficiency is obtained.

This new method can be used with single or three phase are welding transformer. In this work, a three phase multi–operator welding transformer is experimentally checked with the new system. The recorded wave forms support the system advantages. Performance characteristics are experimentally measured and give adequate results.     

APPLICATION OF STATIC VAR COMPENSATION FOR LOAD FREQUENCY CONTROL

ABSTRACT

In this paper the problem of designing load frequency control CLFO system which reduces frequency oscillation based on static Var compensation (SVC) has been investigated. A linear model of a power system area has been used, and a new feedback control signal sent from SVC to power houses is suggested. The new feedback controller includes the frequency deviation and the change of reactive power due to SVC. The dynamic response of the system is determined in the presence of the suggested control system and compared with the case of no control action to evaluate the capabilities of the proposed control system.     

POSITION CONTROL OF A TWO DEGREE-OF-FREEDOM ACTUATOR

Abstract

The paper describes control of a helical-motion induction motor (HMIM) which can be used in a tandem arrangement of two units to form a direct-acting, two degree-of-freedom actuator capable of producing pure rotary motion, pure linear motion, or helical motion. A microprocessor-based controller is designed to drive this closed-loop position control actuator. A proportional control with high gain about command position is implemented to give a desired stiffness coefficient. Using the microprocessor system, an artificial viscous damping is introduced to enhance the dynamic performance.     

AN MILP FORMULATION FOR LOAD-SIDE DEMAND CONTROL

ABSTRACT

This paper presents a mixed integer linear programming formulation for load-side control of electrical energy demand. The formulation utilizes demand prediction to determine if control actions are necessary, and it schedules both shedding and restoration times based on an optimization model that minimizes the net cost of load shedding. Operational constraints are satisfied through the use of minimum/maximum uptimes/downtimes, which depend upon the current state of the system. The algorithm is evaluated using a simulation model of an underground coal mining operation where, (i) its performance is compared with a traditional static, priority-based, load-shedding schedule, and, (ii) its potential is established for producing net savings through demand control.     

ACTIVE AND REACTIVE POWER FLOW FOR MULTIAREA SYSTEMS ON AUTOMATIC GENERATION CONTROL IN THE PRESENCE OF RAPIDLY CHANGING LOADS

ABSTRACT

In this paper, the control area dynamics of power systems on automatic generation control are revisited. The role of reactive power flow between regions under automatic generation control is studied by review of simulations in which the reactive power flow is modeled/not modelled. The effect of transmission line loading is also studied. Reactive power control is accomplished in part by automatic voltage regulation, and reactive power resides in a control “loop” much in the same way as active power resides in conventional automatic generation control. An important observation of the analysis is that short term phenomena (e.g., peaks in tie line flow after a load disturbance ΔP = j ΔQ) require the reactive loop in the model in order to obtain accurate response. Long term phenomena are less sensitive to reactive power modelling. Although these observations are well known qualitatively, examples in this paper help to quantify the role of reactive power in power flow dynamics. The main lesson learned is that there are cases in which reactive power flow must be modelled in order to accurately study active power control and flow. An emphasis in the paper is rapidly changing, heavy industrial loads. The multiarea case is considered.     

LQI-TYPE LOAD-FREQUENCY CONTROL WITH FIRST-ORDER SAMPLING HOLDER WHICH IMPROVES CONTROL PERFORMANCE AGAINST RAMPWISE LOAD DISTURBANCES

ABSTRACT

This paper presents a new method of designing discrete-type load-frequency regulator with a first-order sampling holder which improves control performance against rampwise load disturbances.An attractive feature of the proposed control scheme is that the first-order holder is used as the hold device and then, in addition to the accumulative quantity of the area control error (ACE), the accumulative quantity of time multiplied by ACE is used as feedback signal,to cancel the rampwise load disturbance effect on the frequency and the scheduled tie-line power.Another feature Is that it considers the time delay due to the computation time of the control law and the transmission time of the system data over the telemeter links to the controlling plant.The realization of such a regulator may be easy and of low cost because of its simple construction.     

A FULLY DIGITAL SENSORLESS DIRECT TORQUE CONTROL SYSTEM FOR SYNCHRONOUS MACHINE

ABSTRACT

A new sensorless controller based on direct torque control, for a synchronous machine is proposed. Using direct torque control, stator resistance is the only parameter of the machine which should be known. The use of reactive torque control simplifies the field current control loop. Initial stator induced currents are used to estimate the initial stator flux. The outputs of the control system are switching commands of stator inverter and rotor chopper.     

CHARACTERISTICS OF SUPERCONDUCTING SYNCHRONOUS GENERATOR WITH ELECTROMAGNETIC SHIELD COIL CONTROL

Abstract

A new type of control concept for the superconducting generator with electromagnetic shield coil instead of damper shells is proposed to avoid field current variations and improve the dynamic performance during transients

This concept comprises both a field forcing system and a controller on the electromagnetic shield coil, which should be adjusted according to a specific control principle

Comparisons are made, in the dynamic performance, when employing the field forcing alone and when the shield coil control is added to it.     

REDUCTION OF DC TRACTION MOTOR ARMATURE COPPER LOSSES THROUGH OPTIMAL CONTROL

ABSTRACT

An optimal control that minimizes energy dissipated as armature copper losses for a thyristor converter powered DC drive motor subjected to acceleration under conditions of constant field excitation is presented. Pontryagin's Maximum Principle is employed in the control derivation. A closed-form expression for the optimal control in terms of system parameters is found.

Effectiveness of the control to reduce losses is demonstrated through example. In addition, nature of armature current and motor speed resulting from application of the optimal control are examined. Design trade-offs and implementation techniques are explored.     

SOLID-STATE CONTROL OF A WIND-DRIVEN SELF-EXCITED INDUCTION GENERATOR

ABSTRACT

The paper analyses a system of autonomous induction generator directly feeding,without a d.c link, an induction motor. The generator is driven by a wind energy turbine and the motor is driving a water pump. The analysis is based upon a mathematical model that accounts for the various nonlinearities and mutual interactions of the system elements. Investigations of such a system revealed that it can be controlled to extract the maximum available wind energy by proper adjustment of the terminal voltage of the generator. The required control strategy is formulated, then it is implemented by a static VAR controller which supplies the induction generator with necessary reactive power.     

POWER FLOW CONTROL IN SYSTEMS WITH FACTS DEVICES

ABSTRACT

The modern trend for consolidating electric power companies, even though the participants in these mergers may be not well connected electrically, suggests that technologies that permit power flow control in AC power networks may be favored for some applications. In this paper, the analysis of steady state power flow control in the presence of flexible AC transmission system devices (FACTS devices) is discussed. Objectives such as wheeling, line loading and unloading, ‘electronic fence’ methods to block power transfer, prevention of loop flows, and steady state security enhancement using FACTS are discussed. Newton-Raphson power flow studies for systems with FACTS devices are discussed. An example based on a large American power system is presented.     

A STATIC VAR COMPENSATOR CONTROL STRATEGY TO MAXIMIZE POWER SYSTEM DAMPING

ABSTRACT

A study of power system transient stability enhancement through effective use of static VAR compensator is presented. Optimal theoretical control strategy is derived from direct Lyapunov method for multi-machine system model as a control which forces the fastest dissipation of energy released in the system by a given fault. Strategy of this theoretical optimal control uses signal based on the state variables not available at the compensator bus. It is shown in the paper that optimal control signal can be replaced by the time derivative of locally measurable electric quantities. Dynamic properties of two such quantities are compared using eigenvalue analysis. On the basis of this study a current-orientated control strategy is proposed. Its validity and robustness is confirmed by simulation results for nonlinear multi-machine model.     

VOLTAGE COLLAPSE AND CONTROL ACTIONS: EFFECTS AND LIMITATIONS

ABSTRACT

This paper focuses on control actions determination for voltage collapse prevention. Sensitivity matrices are proposed based on the knowledge of the critical bus. By critical bus one means that bus whose state variables vary at most at the voltage collapse point. A tangent vector is used to identify the critical bus, and its behavior as a function of load increase is also investigated and compared with other indices previously proposed. It is shown that generator control actions may not work to increase voltage collapse margin, whereas local control actions may produce better results. The tests are carried out in the IEEE-300 bus test system, with and without reactive power limits consideration.     

Optimal Automatic Generation Control of Asynchronous Power Systems Using Output Feedback Control Strategy with Dynamic Participation of Wind Turbines

Abstract—This article presents the design of optimal output feedback automatic generation control regulators for an interconnected power system with dynamic participation of doubly fed induction generator based wind turbines. The power systems consist of plants with hydro-thermal turbines and are interconnected via parallel AC/DC links. Efforts have been made to propose optimal automatic generation control regulators based on feedback of output state variables, which are easily accessible and available for the measurement. The designed optimal output feedback automatic generation control regulators are implemented, and the system dynamic responses for various system states are obtained considering 1% load perturbation in one of the areas. The dynamic performance is compared with that obtained with optimal automatic generation control regulators designed using full state vector feedback. The pattern of closed-loop eigenvalues is also determined to test the system stability.     

ADAPTIVE REAL-TIME KNOWLEDGE BASED APPROACH FOR BULK POWER SYSTEM RESTORATION

ABSTRACT

This paper presents the prototype of a real-time knowledge based restoration system developed for the generation and transmission system of Singapore. The multi-objective knowledge based restoration system is divided into urgent actions, predefined plans and feasible plans, and implemented through the generation of targets and the associated action plans. It is aimed to guide the system control engineer to identify the system state and generate effective and reliable restoration procedures which will restore power supply to the whole system within the shortest possible time.     

SPEED AND CURRENT CONTROL OF DC MOTOR IN CONTINUOUS CURRENT OPERATION

ABSTRACT

In this paper we present a non-linear rigurous model of a d.c. motor fed from single phase thyristor bridge. The current and speed control are realized by ; internal current loop with proportional controller and external speed loop with proportional-integral one without zero. This model has been linearised around a steady state operating point to study the behaviour of the system for small perturbations. Analytical formulas are given for the controller parameters for any desired response. A general method of simulation is presented to study the behaviour of the system, taking into account all the discontinuities which may be occur in such a system.