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UBC Theses and Dissertations

EMTP modelling of control and power electronic devices Bonatto, Benedito Donizeti

Abstract

The quality of the electric power delivered to customers by utilities may not be acceptable for some types of sensitive loads, which are typically power, electronics- and computer-based loads, particularly in the control of industrial processes. There are cases where the increasing use of power electronics to enhance process efficiency and controllability creates power quality problems. The growing application of shunt capacitors for voltage support, power factor correction, and system loss reduction, as well as the use of series capacitors (fixed or controlled, for line reactance compensation) will increase the potential risk of transient disturbance amplifications and potential electrical and mechanical resonances in the presence of more and more power electronic devices, and of steam, and gas turbines in distributed and co-generation power plants. As the natural order of the system grows, so does its ability to oscillate more! At the same time, new power electronic devices also offer the means for adequate "power conditioning", to meet the special requirements of electric power quality in a system. To evaluate the promising solutions offered with the introduction of more and more power electronic devices in transmission and distribution systems, such as FACTS (Flexible AC Transmission Systems) Controllers and Custom, Power Controllers, as well as to analyze their interaction and, impact on either the load, or the network side, computer programs based on the EMTP (Electromagnetic Transients Program) are becoming more useful. The development of new EMTP-based models for representation of controls and power electronic devices has been the main subject of this Ph.D. thesis project. Its main contributions are summarized as follows: • development of a "simultaneous solution for linear and nonlinear control and electric power system equations" (SSCPS) in EMTP-based programs, through the compensation method and the Newton-Raphson iterative algorithm. This solution method eliminates not only the one time step delay problem at the interface between the solution of power and control circuits, but also all the internal delays, which may exist in methods based on the transient analysis of control systems (TACS) since 1977. A "circuit approach" was proposed in this thesis, as an innovative alternative to the solution presented by A. E. A. Araujo in 1993; • experimental implementation in MicroTran® (the UBC version of the EMTP), based on SSCPS, of a "simultaneous solution" for: linear and, nonlinear current and voltage dependent sources; independent current and voltage sources, which can also be connected between two ungrounded nodes; hard and soft limiters; transfer functions; mathematical and transcendental FORTRAN functions; special control devices and some digital logic gates; transformation of variables (such as the abc to αβ0 transformation and its inverse); voltage-controlled switches; nonlinear model of a diode semiconductor; • development of the subroutine "GATE" in MicroTran, allowing the dynamic control of the turn-on and turn-off times of semiconductor devices (e.g., thyristors, GTO's, IGBT's, etc.), which are modeled as EMTP-based voltage-controlled switches; • development of power electronics simulation cases in MicroTran, using the simultaneous solution approach (SSCPS) for the dynamic control of semiconductor switching devices (as in a three-phase six-pulse thyristor-controlled bridge rectifier, and a three-phase PWM voltage source inverter (VSI)) and evaluation of current and voltage waveforms; • interaction with a Brazilian utility company and industries for the realization and analysis of field measurements of electromagnetic phenomena affecting the quality of power, such as voltage sags and voltage swells; harmonic current and voltage distortions; transients, etc., with determination of causes, consequences and investigation of possible solutions for power quality problems, as for example, the application of Custom. Power Controllers; • synthesis of simulation guidelines for the evaluation of the impact of power electronic devices on the quality of power, based on realistic field measurements and EMTP time and frequency domain simulations. The assessment of electric power quality, with the use of EMTP-based programs, and the evaluation of the technical impact of power electronic devices on the quality of power, can hopefully be performed with the models developed in this Ph.D. thesis project.

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