Current control techniques for three-phase power converters

As a result of continuous developments in power electronics, applications of power electronics systems directly connected to the power grid have been increasing significantly. An increasing number of modern adjustable speed drives and other high power electrical or electromechanical energy conversion devices are presently interfaced with the three phase utility through Voltage Source Converters (VSC). Space-vector Pulse-Width Modulation (PWM) current regulators are gaining acceptance as an important control technique for the VSC. Despite its conceptual simplicity, space vector PWM current regulator implementation is generally computationally complex and incompatible with the desire for high switching frequencies.; This thesis presents a new approach to regulate currents of voltage source converters based on fuzzy logic control. The thesis goal is to develop an appropriate fuzzy logic controller as a current regulator which can simplify the implementation but maintain comparable performance. Since fuzzy logic control requires less complex mathematical operations than classical controllers, its implementation does not require very high-speed processors. Fuzzy logic control is represented by if-then rules and thus can provide a user-friendly and understandable knowledge representation. We also examine space vector PWM techniques for current regulation of VSC operated as a rectifier.; This thesis also presents a simplified controller for soft switching based on the auxiliary resonant commutated pole (ARCP). The ARCP converter provides zero-voltage switching transition without increasing the voltage and current stress of main power devices. Elimination of switching losses and reduction of electromagnetic interference (EMI) through implementation of this form of soft switching enable an increase of the converter switching frequency, without a reduction in power converter efficiency.; We present the experimental setup which can be divided into hardware and software development. In hardware development, a main power circuit for a 20 kW VSC, a soft switching circuit, a sensing signal circuit, a blanking time circuit, an over-current protection circuit and an IGBT gate drive is designed and built in the Power Electronics Research Laboratory at Rensselaer Polytechnic Institute. In software development, a space vector PWM program and a fuzzy logic control program are written in the C and assembly of 68HC16 microcontroller programming language to control the voltage source converter. Finally, the experimental data for closed-loop operation for both current control techniques under different loads are presented. These data show comparable performance both waveform distortion and system efficiency between the fuzzy logic and space vector PWM techniques, with an approximately 30% reduction in computation time.