Browsing by Author "Ooi, B. T."
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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 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 Design of a Robust Speed and Position Sensorless Decoupled P-Q Controlled Doubly-Fed Induction Generator for Variable- Speed Wind Energy Applications(IEEE, 2007-10) Gogas, K.; Joos, G.; Ooi, B. T.; Mwinyiwiwa, Bakari M. M.; Zhang, Y.This paper proposes an implementation of a decoupled P-Q control of a DFIG that does not rely on mechanical sensors and a speed and position sensorless algorithm that is robust to variations of the values of the machine parameters. In this paper, the sensorless control is based on a modified phase-locked loop with an improved positioning algorithm. This eliminates the need to estimate the speed based on the machine parameters, which results in a significant improvement in speed control robustness to parameter variations. In addition, the algorithm avoids using differentiation which can lead to significant inaccuracy due to the noise inherent in measured signals. Theoretical and simulation results were validated on an experimental setup, using a laboratory 5 hp DFIG.Item 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 Multi- Terminal UPFC for Power System Deregulation(IEEE, 2000-01) Mwinyiwiwa, Bakari M. M.; Lu, B.; Ooi, B. T.; Galiana, F. D.; McGillis, D.; Marceau, R.; Joos, G.One original purpose of FACTS controllers is to increase the transmission capacity of existing lines thus deferring the necessity of building new lines. FACTS, such as the unified power flow controller (UPFC), have also been regarded as controllers for routing power in the market-driven, deregulated power systems. Hitherto, the UPFC has been conceived to control the complex powers through a radial line. This paper presents the concept of a multi-terminal UPFC (M-UPFC), which serves to control the complex powers of several transmission lines converging towards (or radiating from) a transmission node. In order to show that a M-UPFC can be built, that it has stable operation and that it has all the control degrees of freedom of UPFCs, a laboratory model based on 3 units of 3-phase, voltage-source converters has been assembled and testedItem Multi-Terminal Unified Power Flow Controller(IEEE Transactions on Power Electronics, 2000) Mwinyiwiwa, Bakari M. M.; Lu, B.; Ooi, B. T.This paper describes a multiterminal unified power flow controller (M-UPFC) for the management of 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 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 insulated gate bipolar transistor (IGBT), voltage-source, sinusoidal pulse width modulation (SPWM) converters. An example is given where it is shown that the M-UPFC is more economical than single UPFCs Published in:Item 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 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 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 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 Rotor-Position Phase Lock Loop for Decoupled P-Q Control of DFIG for Wind Power Generation(IEEE Transactions on Power Electronics, 2009) Mwinyiwiwa, Bakari M. M.; Shein, B.; Zhang, Y.; Ooi, B. T.Implementation of decoupled P-Q control of doubly fed induction generators requires the positions of the rotors to be known. The rotor position phase-lock loop (PLL) is an invention that extracts rotor position and speed simultaneously by ¿sensorless¿ means. The rotor position PLL is parameter-insensitive because, apart from an approximate value of the magnetization reactance, knowledge of the other parameters is not required for it to function. Experimental results obtained under noisy conditions demonstrate that it is also insensitive to noise.Item Sensorless Maximum Power Point Tracking of Wind by DFIG Using Rotor Position Phase Lock Loop (PLL)(IEEE Transactions on Power Electronics, 2009) Shein, B.; Mwinyiwiwa, Bakari M. M.; Zhang, Y.; Ooi, B. T.This paper presents an invention, the rotor position phase lock loop (PLL), which enables maximum power point (MPPT) tracking of wind by doubly-fed induction generators without needing a tachometer, an absolute position encoder, or an anemometer. The rotor position PLL is parameter variation insensitive, requiring only an estimate of the magnetization inductance for it to operate. It is also insensitive to noise in the electrical measurements. Proof of concept is by: (1) digital simulations and (2) experimental testing of a laboratory prototype.Item 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