1 PRIMARY CONTROL SYSTEM AND STABILITY ANALYSIS OF A HYDROPOWER PLANT Maria Regina Gomes Zoby, Jurandir Itizo Yanagihara Department of Mechanical Engineering – Polytechnic School of the University of São Paulo Abstract: The objective of this work is to study the primary control system of a hydropower plant operating isolated. The plant is modeled by differential equations and the results are compared with field data from an actual hydropower plant, with deviations lower than 1.0%. The study of the primary control system is conducted in order to define optimal parameters for the controllers. Four controllers are studied: traditional, PI, PID and PI- PD. The controllers’ performances are evaluated by stability criteria and a performance index. For the hydropower plant studied, the PI controller has the best performance. Copyright © 2006 IFAC Key words: modeling, hydroelectric systems, primary regulation, optimal control, stability 1. INTRODUCTION This work deals with the operation and control of hydropower plants and its basic equipments and presents an analysis of the dynamic behavior of an actual hydropower plant. The main objectives are to model an actual plant using a nonlinear model based on differential equations with parameters that can be easily estimated or obtained from field tests and to study the primary control system for the plant in isolated operation in order to define the optimal parameters for the chosen controllers. The power plants have particular control systems to ensure stable operation. The satisfactory operation of a power system requires a frequency control that keeps it to acceptable limits when the system is submitted to significant load variation. As the frequency is common to all the system, a change on the active power at one point will be reflected on the net as a frequency variation (KUNDUR, 1994). 1.1. Primary Control System The primary control system is composed of the speed sensor, the controller, the actuator and the hydraulic supply system. Its main functions are to maintain the angular speed constant and equal to its nominal value and to change the distributor position when the load varies or the operation conditions (as head) changes. Each operation condition has its requirements so the controller parameters that are adequate to one condition may not be adequate to another one. The use of adaptive control is an option to satisfy different operating conditions. Otherwise, the usual procedure to define the controller parameters is to consider the isolated condition that imposes the most severe operation requirements and guarantees that the stability will be sustained in this case (SILVA, 2000). This procedure is adopted in the stability study of this work. 2. MODEL EQUATIONS 2.1. Hydraulic Circuit The model is based on the assumption that water is as an incompressible fluid and that the penstocks are rigid. Two kinds of plants are presented: single penstock and multiple penstocks with a common conduit. IFAC Symposium on Power Plants and Power Systems Control, Kananaskis, Canada, 2006 165