TABLE OF CONTENTS As well as accurate modelling of the power components, effective transient simulation requires detailed representation of their control and protection processes.
A variety of network signals need to be generated as inputs to the control system, such as active and reactive powers, r.m.s. voltages and currents, phase angles, harmonic frequencies, etc. The output of the control functions are then used to control voltage and current sources as well as provide switching signals and firing pulses to the power electronic devices. These signals can also be used to dynamically control the values of resistors, inductors and capacitors.
A concise description of the control functions attached to the state variable solution has been made in Chapter 3. The purpose of this chapter is to discuss the implementation of control and protection systems in electromagnetic transient programs.
The control blocks, such as integrators, multipliers, etc. need to be translated into a discrete form for digital computer simulation. Thus the controller itself must also be represented by difference equations. Although the control equations could be solved simultaneously with the main circuit in one large set of linear equations [1], [2], considering the large size of the main circuit, such an approach would result in loss of symmetry and increased computation. Therefore electromagnetic transient programs solve the control equations separately, even though this introduces time-step delays in the algorithm. For analogue controls a combined electrical/control solution is also possible, but laborious, by modelling in detail the analogue components (e.g. op-amps, ...) as electrical...
