Browsing by Author "Wolanski, Z."
Now showing 1 - 11 of 11
Results Per Page
Sort Options
Item 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 resultsItem 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 "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 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 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 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 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 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 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 Unified Power Flow Controller (UPFC) Based on Chopper Stabilized Multilevel Converter(IEEE Transactions on Power Electronics, 2000) Chen, Y.; Mwinyiwiwa, Bakari M. M.; Wolanski, Z.; Ooi, B. T.As the diode-clamped, multilevel converter has been found to have attractive features for STATCOM application, there is interest in extending it to UPFC application by using multilevel converters as the series and the shunt converters. Unfortunately, as is demonstrated in this paper, the DC voltages at their DC links, are inherently unstable. Faced with this impasse, a solution is sought in a system of local feedback controlled Class B choppers to equalize the DC. A laboratory experimental model establishes the feasibility of the proposal. Digital simulations show that current ratings in the choppers need be only 10% of the current ratings in the converters. The chopper cost is estimated as 1% of the cost of the multilevel 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 implemented