Page 230 - Mathematical Models and Algorithms for Power System Optimization

222 Chapter 7

7.8 Implementation 265
7.8.1 Parameters From Figs. 7.4 and 7.7 265
266
7.8.2 Simulation Results of Identification for Load Disturbance Model ΔP L
7.8.3 Simulation Results of Local Estimator and Central Estimator 267
7.8.4 Simulation Results of Compensation Controller 271
7.8.5 Simulation Results of Tracking Control for Five-Unit Test System 274
7.8.6 Verifications of Transformation Methods among Mathematical Models 276
7.9 Conclusion 282

7.1 Introduction

7.1.1 Descriptions of the Problem

The objectives for load frequency control are to provide a mechanism to track the
desired generation allocation specified by an economic dispatching program, and to
regulate the system frequency and tie line interchanges in specified values. The most
widely used load frequency controller in the power system is the integral feedback type. In
recent years, many applications of optimal linear quadratic control theory have also
been examined to improve power system control performance. However, in the optimal linear
load frequency controller, much information between various plants or areas is not accessible
due to communication and economic difficulties. Furthermore, optimal linear quadratic control
is optimal only for a particular type of load disturbances, whose mathematical model is not
clearly known.

This chapter studies the issues of load frequency control in the power system under normal
operating conditions. Due to the stochastic characteristics of load, the power system is subject
to different types of load disturbances even under normal operating conditions. Therefore, it is
necessary to study the model and algorithm, which is applicable to small disturbances (second-
level power load changes) and to maintain the system frequency in the given range by
controlling the power angular acceleration of the generator. Maintaining stable frequency of the
power system is an important part of power system control. The changes of frequency will
affect the production targets of industrial enterprises, such as to change the speed of rotation of
the machine, to make the power of the working machine insufficient or overloaded, and to
damage production in severe cases. Hence, the frequency control of the power system must
be fast, stable, and accurate.

The most basic operation requirements of synchronous operation of power systems are to
maintain system frequency, voltage distribution, active and reactive powers of generators, and
active and reactive powers of transmission lines within specified steady-state values. The
stochastic variations of system load and different disturbances make the system deviate from its