Department of Electrical Engineeering
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Item Development of Insulators in Tanzania(ANSTI EE, 1987) Mwinyiwiwa, Bakari M. M.; Kadete, H.Item Construction and Test of a Delta Modulated Buck Type 3 Phase Converter(McGill University, 1989) Mwinyiwiwa, Bakari M. M.A Delta Modulated, Buck Type, Three Phase PWM Converter was constructed and tested. The converter is of the current source type and can be used in conjunction with current source inverters. The d.c. current is regulated by proportional feedback control loop. By delta modulation of the voltages across the a.c. terminaIs of the converter, the a.c. source currents are "indirectly" controlled so that the fundamental components remain in a predefined phase with respect to the source voltages. Test results have shown that the converter draws near sinusoidal a.c. currents at unit y power factor, with leading power factor a possibility.Item Modelling of a Three Phase BUPC for Stability Analysis(Uhandisi Journal, 1990-12) Mwinyiwiwa, Bakari M. M.; Kadete, H.Item Operating Limits of the Current Regulated Delta Modulated Current Source PWM Rectifier(IEEE Transactions on Industrial Electronics, 1991) Ooi, B. T.; Mwinyiwiwa, Bakari M. M.; Wang, X.; Joos, G.A stand alone, three-phase, delta-modulated, current-source PWM rectifier has been built and has been shown to be capable of operating with near sinusoidal current waveforms, unity power factor. and good DC current regulation. A mathematical model that has been justified against experimental measurements and results from digital simulations is presented. The current waveform distortion limit and the asymptotic stability limit are established. It is shown that the rectifier can operate safely within these limits in the entire range of its power ratingsItem On the Switching Behaviour of a Single Phase CS PWM Converter(Uhandisi Journal, 1991) Mwinyiwiwa, Bakari M. M.Item DC Drive System Using Delta Modulated CS Delta Modulated PWM Converter(ANSTI EE, 1991-11) Mwinyiwiwa, Bakari M. M.Item A Set up for Investigation of Dynamic Relationship Between Tension and Length in the Tissue(ANSTI EE, 1991-11) Mwinyiwiwa, Bakari M. M.Item Delta Modulated Buck Type PWM Converter(IEEE Transactions on Industry Applications, 1992) Mwinyiwiwa, Bakari M. M.; Birks, P. M.; Ooi, B. T.A delta-modulated, current-source, three-phase pulsewidth modulation (PWM) rectifier is described. The rectifier is intended to be used in conjunction with controlled current inverters. An outer proportional feedback loop regulates the unidirectional output current flowing through the DC link. An inner feedback loop maintains near sinusoidal waveform currents at unity or leading power factor from the utility power supply. The inner loop controls the current indirectly by delta modulation of the voltage across the AC terminals of the converter. The converter has been conceived as the circuit dual of the hysteresis current-controlled boost-type rectifier. Experimental results from a laboratory model are presentedItem High Power Switch Mode Linear Amplifiers for Flexible AC Transmission System(IEEE Transactions on Power Delivery, 1996) Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.The pulse width modulation (PWM) technique has been proposed for the force-commutated shunt and series VAr controllers and unified power flow controllers in flexible AC transmission systems. The PWM converters can be operated as linear amplifiers of constant gain so that linear control system theory can be brought to bear more easily when applying feedback controls. For example, pole-placement and active filtering have been successfully applied in laboratory models. This paper is written as a tutorial describing the stages of signal processing: modulation, amplification and demodulation, without reference to power electronics since the solid-state switches are modelled as ON-OFF switchesItem Some Methodologies for FACTS Controllers(McGill University, 1997) Mwinyiwiwa, Bakari M. M.Flexible AC Transmission Systems (FACTS) have been conceived to increase the transmissibility of electric power without the necessity of building new transmission iines. An important family of controllers proposed for FACTS are based on high power solidstate switches, such as the gate-tuni-off thyristor (GTO), which is presently rated at 6kV, 6kA. The FACTS controlier operates at the transmission voltage, in the order of 5ûûkV, and it rnust be mted at hundreds of MVA. The research of this thesis contributes in developing the rnethodologies necessary for the integration of the sotid-state switches so that the FACTS controllers have the voltage withstand and the cwent carrying capacity. The rnethodologies followed in the thesis are based on organizing the solid-state switches firstly in the forrns of: (a) 2-level, voltage-source converter modules or (b) multilevel, voltage-source, converter modules. Thereafter, the modules are connectai in series and/or in parallel. Switching strategies such as: (i) the phase-shifted triangle can-ier technique and (5) the fundamental fiequency switching, are show to be proniising. The thesis addresses the methodologies of unithg the modules: (i) in parallel, (ii) in series and (Üi) in @el groups of series-comected modules. Senes connecti011~ require magnetic transformers. Transforrners also enable 6-phase and 12-phase ac systems to be produced from the standard 3-phase ac utility supply. The thesis has initiated research in incorporating the multi-phase ac syst ems to the multi-rnodular , dti-level convert ers. The thesis has also developed the interface methodology for digital (digital signal ,orocessor, DSP) control of the amy of modules in rd-the. The methodologies of the thesis have ken proven in digital simu1ations and experimentally in laboratory models.Item Regulating and Equalizing dc Capacitance Voltages in Multilevel STATCOM(IEEE Transactions on Power Delivery, 1997) Chen, Y.; Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.Because of the high MVA ratings, it would be expensive to provide independent, equal, regulated DC voltage sources to power the multilevel converters which are proposed for STATCOMs. DC voltage sources can be derived from the DC link capacitances which are charged by the rectified AC power. This paper addresses two control issues: (1) regulation of the DC capacitance voltages and (2) their equalization. Equalization is necessary (i) to ensure the even sharing of voltage stresses in the gate-turn-off thyristors (GTOs), and (ii) to prevent the degradation of total harmonic distortion (THD) factors, as all harmonic elimination strategies depend on equal voltages in their assumptions. The strategies considered are: (a) the fundamental frequency method, and (b) the sinusoidal pulse width modulation method. Digital simulations are used to confirm the feasibility of the control methodsItem Multimodular Multilevel Converters with Input/Output Linearity(IEEE Transactions on Industry Applications, 1997) Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.Multilevel converters constitute the key technology of power electronics to reach the high power ratings required by controllers of flexible AC transmission systems (FACTS). This paper shows that the sinusoidal pulsewidth modulation (SPWM) technique, as applied to multilevel converters, inherently requires a high switching rate. The paper then presents a strategy based on multiple modules of multilevel converters which operate with the lowest possible switching loss (each gate-turn-off thyristor (GTO) switches ON and OFF only once during the modulation period), while maintaining the high gain-bandwidth product of linear amplifiers to handle fast feedbacks, which FACTS controllers must be capable of, in order to carry out dynamic performance enhancementItem Multilevel STATCOM with Third Harmonic Elimination on the DC Link Capacitor Voltages(IEEE, 1997-06) Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.Simulation studies, confirmed by laboratory experiments, show that the undesirable third harmonic inherently present on the DC link capacitor voltages of multilevel converters can be eliminated by a 6-phase configuration in a shunt multilevel STATCOM. The principle can be extended to eliminate the residual sixth harmonic by configuring a 12-phase STATCOMItem Multilevel Converters as Series VAR Compensators(IEEE, 1997-06) Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.; Chen, Y.This paper presents experimental results of a multilevel converter applied as a series static VAr compensator (SVS or STATCOM). An outer feedback loop maintains the VAr operating condition and inner feedback loops equalize the DC capacitor voltages. The delta connection of the transformer secondaries provide paths for zero sequence currents to flow. The tests show its capability for operation under normal balanced condition and under faulted conditions of single line and double line outagesItem Microprocessor Implemented SPWM for Multiconverters with Phase-Shifted Triangle Carriers(IEEE, 1997-10) Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.The paper reports on research aimed at achieving the computer-control of power electronic converters for high power applications. Hitherto, in motor drive applications, the four-timer method has been adequate in approximating the sinusoidal pulse width modulation (SPWM) strategy for microprocessor control. This paper shows that the ideas of the four-timer method can be extended, with modifications, to the multi-module arrays of power converters which will be required to meet high MVA ratings. Simulation and experimental results have shown that the resultant seven-timer method can implement the linear SPWM strategy for multi-convertersItem Multimodular UPFC Operated by Phase-Shifted Carrier SPWM Strategy(IEEE, 1997-10) Mwinyiwiwa, Bakari M. M.; Ooi, B. T.; Wolanski, Z.The acronym UPFC covers L. Ggugyi's unified power flow controller and Akagi and Fujita's unified power flow conditioner. The paper describes one method of meeting high MVA specifications by using multiple modules of 2-level, 3-phase power converter modules controlled by the phase-shifted triangle carrier technique of the sinusoidal pulse width modulation (SPWM) strategy. Two conceptual designs are presented: (1) the GTO-SPWM-UPFC at the lowest switching rate, fc/fm=3, to minimize GTO switching loss. The design is based on applying the fundamentals of SPWM theory to overcome unbalances arising from sideband harmonic interferences; and (2) the IGBT-SPWM-UPFC, at fc/fm=12 or higher, which SPWM theory assures that direct paralleling of the modules is free of current unbalance. A laboratory UPFC based on 6 modules of 3-phase, 5 kVA size, IGBT power converters operating at the baseline condition of dual unity displacement factor at the sending-end and the receiving end, has been implementedItem "Microprocessor Implemented SPWM for Multiconverters with Phase-Shifted Triangle Carriers(IEEE Transactions on Power Electronics, 1998) Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.This paper reports on research aimed at achieving computer control of power electronic converters for high-power applications. Hitherto, in motor-drives applications, the 4-Timer Method has been adequate in approximating the sinusoidal pulsewidth modulation (SPWM) strategy for microprocessor control. This paper shows that the ideas of the 4-Timer Method can be extended, with modifications, to the multimodule arrays of converters which will be required to meet high megavoltampere ratings. Simulation and experimental results have shown that the resultant 7-Timer Method can implement the linear SPWM strategy for multiconvertersItem Multi-Terminal Unified Power Flow Controller(IEEE, 1998-05) Mwinyiwiwa, Bakari M. M.; Lu, B.; Ooi, B. T.This paper describes a multi-terminal unified power flow controller (UPFC) for the management of the real and reactive powers of several transmission lines emanating from a single bus. The example of the paper consists of the bus of a generator station. The multi-terminal UPFC (M-UPFC) is based on synthesizing several of L. Gyugyi's UPFCs so that they share a single pair of DC buses. The realizability of the M-UPFC has been demonstrated experimentally in a laboratory-size model constructed from three IGBT, voltage-source, SPWM convertersItem UPFC Using Multi-Converters Operated by Phase-Shifted Triangle Carrier SPWM Strategy(IEEE Transactions on Industry Applications, 1998-06) Mwinyiwiwa, Bakari M. M.; Ooi, B. T.; Wolanski, Z.The acronym UPFC covers Ggugyi's unified power flow controller and Akagi and Fujita's unified power flow conditioner. This paper describes one method of meeting high MVA specifications by using multiple modules of two-level three-phase power converter modules controlled by the phase-shifted triangle carrier technique of the sinusoidal pulsewidth modulation (SPWM) strategy. Two conceptual designs are presented. The first is the gate-turn-off (GTO)-SPWM-UPFC at the lowest switching rate, fc/fm=3, to minimize GTO switching loss. The design is based on applying the fundamentals of SPWM theory to overcome unbalances arising from sideband harmonic interferences. The second is the insulated gate bipolar transistor (IGBT)-SPWM-UPFC, at fc/fm=12 or higher, in which SPWM theory assures that direct paralleling of the modules is free of current unbalance. A laboratory UPFC based on six modules of three-phase 5-kVA size IGBT power converters operating at the baseline condition of dual unity displacement factor at the sending end and the receiving end has been implementedItem Current Equalization in SPWM FACTS Controllers at Lowest Switching Rates(IEEE Transactions on Power Electronics, 1999) Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.This paper shows that sinusoidal pulse width modulation (SPWM) FACTS controllers can be synthesized by employing “phase shifted triangle carrier technique” to multiconverters at a switching rate of only 3 pulses. The options of parallel, series and series/parallel module connections are examined for current equalization. The paper presents simulation and experimental results