Control-Oriented Model of a Generating Set Comprising a Diesel Engine and a Synchronous Generator

Mutaz Tuffaha,Jan T Gravdahl

doi:10.4173/mic.2015.4.1

Abstract

A generating set (Genset) comprises a prime mover such as a Diesel Engine, and a synchronous generator. The most important controllers of such systems are the speed governor to regulate the engine or shaft speed and the automatic voltage regulator (AVR) to regulate the terminal voltage. The speed governor is a PID controller that uses the dierence between the speed and its desired value as a feedback signal to change the fuel mass input by changing the fuel rack position. AVR is also a PID that uses the dierence between the terminal voltage of the generator and its desired value, and changes it by manipulating the voltage of the eld excitation circuit. Thus, the two controllers act separately. That is to say, if the speed varies from the desired value, the speed governor will react, while the AVR will not react as long as the voltage is stable, and vice versa. In this work, a control-oriented model is suggested for a Genset, and then a controller, that regulates the shaft speed and the terminal voltage, is designed by feedback linearisation. The proposed controller has two inputs: the fuel mass and the eld circuit voltage. Simulations show that the proposed controller makes the two inputs act, simultaneously. Thus, any change of the speed e.g., forces the two input controls to react, in contrast to the ordinary PID controllers. Further, we discuss the robustness of the proposed controller to uncertainties and time delay.

Highlights

The most important control objectives in power systems stability studies are the voltage control, which leads to reactive power control, and frequency control, which leads to active power control
The automatic voltage regulator (AVR) is a PID controller that uses the error between the terminal voltage and its desired value as a feedback signal to control the terminal voltage by controlling the magnetic field of the rotor, which can be produced by an excitation circuit or a permanent magnet, as will be explained later
Because the flux linkages are hard to measure in practice, it is common in the literature on power system stability to use the following transformations, see Kundur (1994) and Machowski et al (2008): Remark 1 The rate of change of the terminal voltage is much less than the rate of change of the stator currents

Summary

Introduction

The most important control objectives in power systems stability studies are the voltage control, which leads to reactive power control, and frequency control, which leads to active power control. Both controllers will react by increasing the fuel input to the engine, and the field circuit excitation This may cause the terminal voltage to increase above the steady-state value, and increasing the load on the engine, which in turn drives the governor to increase the fuel, and stability may be lost or retarded, McCowan et al (2003). Tuffaha and Gravdahl (2014) used the flux linkage as a state variable which is usually difficult to be measured They used the first-order model of the Diesel engine in Fossen (1994) that uses the fuel rack input to manipulate the torque, without taking in consideration the air dynamics. Our simulations show that the proposed controller can be considered robust to the uncertainty of the air/fuel ratio

Synchronous Machine

Diesel Engine

Simplified Model and Control Design

Simulation Results

Time Delay

Conclusion