Publications
496 results found
Hui SYR, Chung H, 1999, Paralleling power converters for AC-DC step-down power conversion with inherent power factor correction, IEE Proceedings: Electric Power Applications, Vol: 146, Pages: 247-252, ISSN: 1350-2352
The authors describe the modular development of a single-stage AC-DC step-down power converter. The converter offers advantages such as simple DC-DC type switching control, electrically isolated output and inherent power factor correction. It also provides single-stage power conversion without using power devices with excessively high voltage and current rating, the flexibility for expansion of power capability, and a simplification of design and production procedure for the manufacturing of power converter products. The operating modes of the converter are described and analyzed. Experiments have confirmed the validity of the modular converter operation.
Hui SY, Tang SC, Chung HSH, 1999, Optimal operation of coreless PCB transformer-isolated gate drive circuits with wide switching frequency range, IEEE Transactions on Power Electronics, Vol: 14, Pages: 506-514, ISSN: 0885-8993
Gate drive circuits for power MOSFET's and insulated gate bipolar transistors (IGBT's) often require electrical isolation. Coreless printed circuit board (PCB) transformers have been shown to have desirable characteristics from a few hundreds of hertz to a few megahertz and can be used for both power and signal transfer at low-power level. At low operating frequency, the magnetizing inductance has such low impedance that the driving power requirement could become excessive. This paper describes the use of a coreless PCB transformer for isolated gate drive circuits over a wide-frequency range. Based on a resonance concept, the optimal operating condition that minimizes the power consumption of the gate drive circuits is developed and verified with experiments. The coreless PCB transformer demonstrated here confirms a fundamental concept that the size and volume of a magnetic core could approach zero and become zero if the operating frequency is sufficiently high. Coreless PCB transformers do not require the manual winding procedure and thus simplify the manufacturing process of transformer-isolated gate drive circuits and low-power converters. Their sizes can be much smaller than those of typical core-based pulse transformers. The electrical isolation of a PCB is much higher than that of an optocoupler.
Hui SY, Chung HSH, Tang SC, 1999, Coreless printed circuit board (PCB) transformers for power MOSFET/IGBT gate drive circuits, IEEE Transactions on Power Electronics, Vol: 14, Pages: 422-430, ISSN: 0885-8993
Gate drive circuits for modern power electronic switches, such as MOSFET and insulated gate bipolar transistor (IGBT), often require electrical isolation. This paper describes the modeling and experimental results of some coreless printed circuit board (PCB)-based transformers that can be used for MOSFET and IGBT devices at high-frequency (500 kHz to 2 MHz) operation. PCB-based transformers do not require the manual winding procedure and thus simplify the manufacturing process of transformer-isolated gate drive circuits. With no core loss, coreless transformers are found to have favorable characteristics at high-frequency operations. This project demonstrates an important point that the size of the magnetic core can approach zero and become zero when the frequency is sufficiently high.
Hui SYR, Ho YKE, Chung H, 1999, Modular single-stage, three-phase full-bridge converter with inherent power factor correction and isolated output, IEE Proceedings: Electric Power Applications, Vol: 146, Pages: 407-414, ISSN: 1350-2352
The modular development of a three-phase, single-stage AC-DC power converter based on single-phase AC-DC full-bridge converters is described. Three-wired and four-wired modular converter systems are examined and compared. The three-wired system is found to have inherent power factor correction and is better than the four-wired system in terms of harmonic content. The fluctuation of the converter neutral voltage in the three-wired system and the voltage stress on the power switches are analysed. A simulation based on a PSPICE model is included. The modular converter does not have a minimum component count when compared with non-modular converters. But the modular converter offers attractive features such as simple DC-DC switching control, electrically isolated output, inherent power factor correction and single-stage power conversion without using power devices with excessively high voltages and current ratings. It also has flexible power expandability and the potential to simplify the design and production of high-power AC-DC power converter products. The operation of the modular full-bridge converter has been confirmed with a 1.5kW prototype. Both predictions and measurements show that the power quality of three-wired modular converter system is good and well above IEC-1000 standards.
Hui SY, Shrivastava Y, Sathiakumar S, et al., 1998, A comparison of nondeterministic and deterministic switching methods for DC-DC power converters, IEEE Transactions on Power Electronics, Vol: 13, Pages: 1046-1055, ISSN: 0885-8993
An analysis and experimental results of the random pulsewidth modulation (RPWM) and random pulse-position modulation (RPPM) methods for dc-dc converters are presented. The characteristics and performance of power converters under two randomized modulations are evaluated. The theoretical relationships of discrete harmonics, continuous noise, and output-voltage ripple of the RPWM and RPPM schemes are established and compared with those of a standard deterministic pulsewidth modulation (PWM) scheme in a buck converter. Limitations in the randomly switched dc-dc converters, which have not been addressed before, are highlighted. Randomized schemes generally have inherent problems in achieving low-output-voltage ripple due to the low-frequency continuous noise within the passband of the converter filter. The inherent low-frequency noise-induced voltage ripple problems of nondeterministic switching methods for dc converters are confirmed experimentally. The performance of the RPPM method is found to be closer to the standard PWM method than that of the RPWM method. For dc-dc power conversion, the RPPM method offers much better output-voltage performance than the RPWM method.
Chung H, Hui SYR, Tse KK, 1998, Reduction of power converter EMI emission using soft-switching technique, IEEE Transactions on Electromagnetic Compatibility, Vol: 40, Pages: 282-287, ISSN: 0018-9375
Measurements of conducted and radiated electromagnetic interference (EMI) emission from hard-switched and soft-switched buck, boost, and flyback converters of similar power ratings are presented. Results indicate that EMI emission can be substantially reduced by using soft-switching technique in power converters. Thus, soft-switching technique provides a practical and useful solution to reduce EMI emission from switched-mode power circuits. A comparison of EMI emission on the three classes of converters is also included. The flyback converter is found to be the least EMC friendly among the converters tested.
Hui SYR, Chung H, Ho YKE, et al., 1998, Modular development of single-stage 3-phase PFC using single-phase step-down converters, PESC Record - IEEE Annual Power Electronics Specialists Conference, Vol: 1, Pages: 776-782, ISSN: 0275-9306
This paper describes the modular development of a family of single-stage AC-DC power converters. The family of converters offers advantageous features such as simple switching control, electrically isolated output, inherent power factor correction, single stage power conversion without using power devices of excessively high voltage and current ratings, the flexibility for expansion of power capability and a simplification of design and production procedure of power converter products. Prototypes up to 1 kW are used to demonstrate the operating principle. © 1998 IEEE.
Chung H, Hui SYR, Wang WH, 1998, An isolated ZVS/ZCS flyback converter using the leakage inductance of the coupled inductor, IEEE Transactions on Industrial Electronics, Vol: 45, Pages: 679-682, ISSN: 0278-0046
This paper describes a simple and effective way to modify an existing hard-switched flyback converter into a circuit with zero-voltage switching (ZVS) and zero-current switching (ZCS). The key improvement is to turn the unattractive features of the coupled inductor leakage inductance and snubber capacitor into attractive ones. The coupled inductor leakage inductance and snubber are used to form a quasiresonant circuit to facilitate ZVS/ZCS of all power devices. The operating principles of the converter and experimental results are presented. Index Terms-Converter, power electronics, power supplies, resonant power conversion. © 1998 IEEE.
Shrivastava Y, Sathiakumar S, Hui SY, 1998, Improved spectral performance of random PWM schemes with weighted switching decision, IEEE Transactions on Power Electronics, Vol: 13, Pages: 1038-1045, ISSN: 0885-8993
The authors present a statistical approach to the analysis of random pulsewidth modulation (RPWM) methods which generate PWM signals by comparing a reference modulating function with random numbers or signals. Such an approach is used to analyze and optimize a new weighted RPWM (WRPWM) method and also a standard trapezoidal RPWM method. The WRPWM scheme combines the advantages of the nondeterministic and deterministic PWM methods by adding some deterministic nature into the nondeterministic RPWM method. Both theoretical and experimental results confirm that the optimized WRPWM method has better spectral performance over the standard RPWM schemes and has attractive features such as the potential of third-harmonic boosting, reduced acoustic noise, and minimal low-order harmonics under an over modulation condition for electronic drive applications.
Ho YKE, Hui SYR, Lee YS, 1998, Optimal operation of single-stage three-phase power factor correction circuit using modular PWM DC-to-DC converters, Electronics Letters, Vol: 34, Pages: 2300-2301, ISSN: 0013-5194
A critical conduction parameter A3Φ is derived for the three-phase modular system. This parameter optimises the output filter to achieve the highest power factor of the system. The voltage conversion ratio required to achieve a high power factor to fulfil the harmonic requirements is also derived. Both simulations and experimental results from a 1.5kW prototype using full-bridge converters have confirmed the analysis.
Hui SYR, Tang SC, Chung H, 1998, Coreless printed-circuit board transformers for signal and energy transfer, Electronics Letters, Vol: 34, Pages: 1052-1054, ISSN: 0013-5194
The authors describe the optimal use of a printed-circuit board transformer with minimum power consumption. The proposed transformer is much smaller than a standard pulse transformer and is suitable for both signal and energy transfer. It can be operated in the megaHertz frequency range. With the use of modulation/demodulation circuits, it can be used for digital signal transmission over a wide frequency range from DC to ∼300kHz. The proposal can replace core-based transformers in many low-power applications.
Zhu P, Hui SYR, 1998, Modelling of a high-frequency operated fluorescent lamp in an electronic ballast environment, IEE Proceedings: Science, Measurement and Technology, Vol: 145, Pages: 111-116, ISSN: 1350-2344
The authors describe the dynamic modelling of a high-frequency operated fluorescent lamp in an electronic ballast environment. The model inherently includes the negative resistive characteristic, allows the study of electronic ballast design using series resonant converters, and can provide useful information for the optimisation of the electronic ballast design. The fluorescent lamp model for high-frequency operation has been developed and implemented. Predictions for the lamp system operation generally agree very well with measurements obtained from a 33 kHz electronic ballast - fluorescent lamp system. The use of the model for the designing the ballast components is illustrated. This model is simple and can be employed in existing simulation packages for computer-aided electronic ballast designs. © IEE, 1998.
Lu HY, Zhu JG, Hui SYR, et al., 1998, A generalized dynamic transformer circuit model including all types of core losses, Pages: 978-983
This paper describes a generalized dynamic transformer circuit model that includes all types of core losses, nonlinear magnetic characteristics, skin effects of eddy currents in the core, and thermal effects on hysteresis of core materials. A TLM-based transform with variable time steps is employed in the simulation. This model can provide an accurate prediction of transformer performance and core losses and is suitable for simulation of high frequency switching mode converters using transformer isolated outputs. Some interesting issues such as stray capacitance, are discussed. Simulations of a 500 W transformer in a full bridge inverter operated at 15 kHz and 25 kHz have been confirmed by experiments.
Lee YS, Wang SJ, Hui SYR, 1997, Modeling, analysis, and application of buck converters in discontinuous-input-voltage mode operation, IEEE Transactions on Power Electronics, Vol: 12, Pages: 350-360, ISSN: 0885-8993
By adding a suitable LC filter to the input of a Buck converter, it is possible to force the converter into discontinuous-input-voltage mode operation. A Buck converter in this mode of operation has useful properties such as power factor correction and soft turn-off switching. The operation, modeling, low-frequency behavior, and application of the converter are studied. Experimental results verifying the theoretical predictions are also presented. © 1997 IEEE.
Hui SYR, Fung KK, 1997, Fast decoupled simulation of large power electronic systems using new two-port companion link models, IEEE Transactions on Power Electronics, Vol: 12, Pages: 462-473, ISSN: 0885-8993
Algorithms of novel two-port companion link models for fast decoupled simulation are presented. The link models enable a large circuit to be broken down into many small subcircuits for easy circuit formulation and fast simulation. The proposed link algorithms are demonstrated in a converter-fed dc transmission system with a transmission-line length equivalent to 1000 km. Simulation and experimental results from a laboratory setup have confirmed the validity of the link models. Proposed simulations are also found to be faster and more accurate than PSpice simulations in the example. © 1997 IEEE.
Hui SYR, Eric Cheng KW, Narayana Prakash SR, 1997, A fully soft-switched extended-period quasi-resonant power-factor-correction circuit, IEEE Transactions on Power Electronics, Vol: 12, Pages: 922-930, ISSN: 0885-8993
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EP-QR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method, supported with simulation and measurements, is included.
Hui SYR, Oppermann I, Sathiakumar S, 1997, Microprocessor-based random PWM schemes for DC-AC power conversion, IEEE Transactions on Power Electronics, Vol: 12, Pages: 253-260, ISSN: 0885-8993
Two classes of microprocessor-based random PWM (RPWM) real-time schemes for dc-ac power conversion are compared and evaluated. Performance of the RPWM schemes based on the mathematical and logical approaches is examined. The proposed schemes exhibit excellent harmonic content with all low and high-order harmonics suppressed and are suitable for both MOSFET and IGBT inverters. © 1997 IEEE.
Hui SYR, Sathiakumar S, Sung KK, 1997, Novel random PWM schemes with weighted switching decision, IEEE Transactions on Power Electronics, Vol: 12, Pages: 945-952, ISSN: 0885-8993
A new random pulse-width modulation (RPWM) scheme, which includes a weighted decision switching process, has been developed and tested. The switching strategy can be applied to the entire range of the modulation index. The scheme combines the advantages of the deterministic nature of the standard pulse-width modulation (PWM) schemes, and the nondeterministic spread-spectral characteristic of RPWM schemes. Test results have confirmed the improved spectral performance of the proposed schemes over a standard RPWM scheme at both low- and high-modulation indexes.
Hui SYR, Chung H, 1997, Parallellism of power converters for automatic power factor correction, Electronics Letters, Vol: 33, Pages: 1274-1276, ISSN: 0013-5194
The modular development of a single-stage AC-DC power converter is described. The converter offers several advantageous features.
Shrivastava Y, Hui SYR, Sathiakumar S, et al., 1997, Effects of continuous noise in randomised switching DC-DC converters, Electronics Letters, Vol: 33, Pages: 919-921, ISSN: 0013-5194
A randomly switched DC-DC converter reduces the magnitude of discrete harmonics but creates continuous noise in the output voltage. Continuous noise within the passband of the output filter is found to induce low-frequency voltage ripple in the converter output. This adverse effect is inherent in all randomised switching schemes and is confirmed by both theory and experiment.
Fung KK, Hui SYR, 1997, Duality of transmission line models for simulation of reactive circuit components, Mathematics and Computers in Simulation, Vol: 44, Pages: 143-154, ISSN: 0378-4754
This paper presents Norton transmission line (TL) models and equivalent circuits for the simulation of reactive circuit components. These models, not only retain the obvious physical concepts of Thevenin-TL models, but also allow the nodal analysis technique to be used, overcoming the inherent difficulties in system matrix formation using the Thevenin models. The Norton models are derived and then applied to simulate a high-frequency switched mode power supply circuit. Details of the simulation process are discussed in a tutorial style.
Hui SYR, Gogani ES, Zhang J, 1996, Analysis of a quasi-resonant circuit for soft-switched inverters, IEEE Transactions on Power Electronics, Vol: 11, Pages: 106-114, ISSN: 0885-8993
This paper presents an analysis of a quasi-resonant circuit for soft-switched inverters. The quasi-resonant circuit provides zero-voltage instants for zero-voltage inverter switching by pulling down the dc link voltage momentarily to zero without increasing the peak value of the nominal dc link voltage. Switches in the quasi-resonant circuit can also be turned off at zero current/voltage conditions. The proposed circuit allows creation of zero voltage conditions for inverter soft-switching under loaded and no-load conditions. The operating principle of this circuit is explained, and the analysis of each operating mode is described. Design criteria for achieving zero voltage switching are derived from the general mathematical analysis. Operation of the circuit has been verified by PSPICE simulation and experiments. © 1996 IEEE.
Hui SYR, Zhu JG, Ramsden VS, 1996, A generalized dynamic circuit model of magnetic cores for low- and high-frequency applications - Part II: Circuit model formulation and implementation, IEEE Transactions on Power Electronics, Vol: 11, Pages: 251-259, ISSN: 0885-8993
This paper describes the formulation and implementation of a generalized dynamic magnetic core circuit model suitable for both low- and high-frequency applications. The behavior of magnetic cores with any arbitrary flux waveforms is modeled by a simple ladder network consisting of nonlinear inductors and resistors. The nonlinear B-H loop and the hysteresis loss are incorporated in distributed nonideal inductors and calculated by the Preisach scalar model of magnetic hysteresis. The eddy current and anomalous losses are accounted for by the generalized nonlinear equivalent resistors reported in Part I of the paper. The transmission line modeling (TLM) method is employed to solve the nonlinear state equations. Numerical aspects and software implementation of the model are discussed. The generalized model has been verified by simulations and measurements at both lowand high-frequency operations. © 1996 IEEE.
Fung KK, Hui SYR, 1996, Fast simulation of multistage power electronic systems with widely separated operating frequencies, IEEE Transactions on Power Electronics, Vol: 11, Pages: 405-412, ISSN: 0885-8993
This paper presents a fast and efficient way of simulating multistage power electronic circuits with different stages operating at widely separated frequencies, using the transmission-line modeling (TLM) technique. A multistage circuit can be modeled as several smaller subcircuits, which can then be simulated individually with different time steps according to their circuit time constants. Energy exchange between linked subcircuits are made possible via the use of a new TLM stub link conversion technique and improved TLM link algorithms. The proposed technique has been tested successfully in a simulation of a switched-mode power supply. Simulation results confirm that the new approach can greatly reduce the computing time of the simulation when compared with conventional TLM simulation methods. A reduction of about two-thirds of the computing time has been achieved in the simulation of a three-stage switched-mode power supply. © 1996 IEEE.
Zhu JG, Hui SYR, Ramsden VS, 1996, A generalized dynamic circuit model of magnetic cores for low- and high-frequency applications - Part I: Theoretical calculation of the equivalent core loss resistance, IEEE Transactions on Power Electronics, Vol: 11, Pages: 246-250, ISSN: 0885-8993
This paper describes the theoretical calculation of the equivalent core loss resistance for a dynamic magnetic core loss model. The equivalent core loss resistance incorporates the effects of both the classical eddy current and anomalous losses. Derivation of a generalized nonlinear core loss resistance expression is presented. This new equivalent core loss resistance can be incorporated into a generalized dynamic magnetic core circuit model suitable for low and high frequency applications (Part II of this paper). © 1996 IEEE.
Shrivastva Y, Sathiakumar S, Hui SYR, 1996, Random discrete PWM method for DC-DC power converters, Electronics Letters, Vol: 32, Pages: 2105-2106, ISSN: 0013-5194
A random discrete pulse-width modulation (RDPWM) scheme is examined and compared with the randomised pulse-position modulation (RPPM) method for DC-DC power conversion. The RDPWM method has no switching harmonics while the RPPM method has significant switching harmonics. Power spectral characteristics of the two methods are presented and discussed.
Fung KK, Hui SYR, 1996, Transputer simulation of decoupled electrical circuits, Mathematics and Computers in Simulation, Vol: 42, Pages: 1-13, ISSN: 0378-4754
This paper describes a parallel simulation of an electrical circuit using the Transmission Line Modelling (TLM) method. The TLM method is used to decouple the circuit into sub-circuits which are then simulated concurrently in a parallel processing system. This approach not only simplifies the circuit formulation process but also reduces the overall computing time of the circuit simulation when compared with traditional sequential method. The techniques for decoupling the circuit and implementing the parallel algorithm are described. The method is demonstrated in an electrical circuit simulation. Comparison of the computing time and simulated results with the sequential approach confirms the computing efficiency and accuracy of the proposed method.
Woolfson MS, Hui SYR, 1996, Application of the transmission line method to the solution of the continuous Kalman filter equations of general order, Mathematics and Computers in Simulation, Vol: 42, Pages: 15-33, ISSN: 0378-4754
In this paper, the transmission line method (TLM) is applied to the solution of the general, nth order, continuous Kalman filter estimation equations. A comparison is made between this method, the first-order Gear algorithm and the fourth-order Runge-Kutta method, in the estimation of the voltage drop and its derivative across a capacitor in an LCR circuit. An analysis is made of the sensitivity of the algorithms to changing time step and measurement error variance. In most cases, the Runge- Kutta method has the best performance at the expense of computing time. However, in some cases, the new algorithm yields less biased and smoother estimates. The TLM algorithm performs consistently better than the Gear method for the particular problem analysed. The CPU time for the TLM algorithm has also been compared with that required by the Gear and Runge-Kutta methods; the TLM method is found to take approximately 25% of the time required by the Runge-Kutta method to process one measurement. The TLM algorithm appears to present a compromise between accuracy of estimation and computing time. Finally, suggestions are made for further work.
Fung KK, Hui SYR, Christopoulos C, 1996, Concurrent programming and simulation of decoupled power electronic circuits, IEE Proceedings: Science, Measurement and Technology, Vol: 143, Pages: 131-136, ISSN: 1350-2344
The authors describe the parallel simulation of a multistage power electronic circuit using the transmission line modelling (TLM) method. In this approach, a large stiff circuit can be decoupled into smaller subcircuits by TLM links. Each subcircuit is then formulated with a small system matrix and simulated in one program module. The overall simulation is done by running all the program modules in parallel. This parallel simulation allows significant speed improvements over normal sequential simulation, as shown by the results of numerical experimentation. © IEE, 1996.
Fung KK, Hui SYR, 1996, Improved TLM link model for reactive circuit components, IEE Proceedings: Science, Measurement and Technology, Vol: 143, Pages: 341-344, ISSN: 1350-2344
An improved transmission line modelling (TLM) link model for reactive circuit components is presented. This improved model reduces the propagation delay error in the conventional TLM link model. Consequently the improved model provides significant improvement in accuracy over the conventional link model. Simulation confirms that results obtained from the improved link model are much more accurate than those from the conventional link model. The simulation results also indicate that the improved link model is as accurate as the stub model. © IEE, 1996.
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