S.Y.R. Hui

A new generation of universal contactless battery charging platform for portable consumer electronic equipment

This invention is related to a new planar inductive battery charger for portable electronic equipment such as mobile phones, palm pilots and CD players. New multilayer printed-circuit-board winding matrices of hexagonal structures that can generate magnetic flux of almost even magnitude over the surface of the winding arrays have been developed. The new concept forms the basis for a new generation of universal charging platform for a wide range of portable electronic equipment. Different types of portable electronic equipment can be placed and charged simultaneously on the charging platform, regardless of their positions and orientation. The principle and structure of the charging platform are explained and the feasibility has been confirmed with practical measurements. The proposed universal charging platform has been successfully used for mobile phones, MP3 players and electronic dictionaries.

A novel maximum power point tracking technique for solar panels using a SEPIC or Cuk converter

A novel technique for efficiently extracting the maximum output power from a solar panel under varying meteorological conditions is presented. The methodology is based on connecting a pulse-width-modulated (PWM) DC/DC SEPIC or Cuk converter between a solar panel and a load or battery bus. The converter operates in discontinuous capacitor voltage mode whilst its input current is continuous. By modulating a small-signal sinusoidal perturbation into the duty cycle of the main switch and comparing the maximum variation in the input voltage and the voltage stress of the main switch, the maximum power point (MPP) of the panel can be located. The nominal duty cycle of the main switch in the converter is adjusted to a value, so that the input resistance of the converter is equal to the equivalent output resistance of the solar panel at the MPP. This approach ensures maximum power transfer under all conditions without using microprocessors for calculation. Detailed mathematical derivations of the MPP tracking technique are included. The tracking capability of the proposed technique has been verified experimentally with a 10-W solar panel at different insolation (incident solar radiation) levels and under large-signal insolation level changes.

A General Photo-Electro-Thermal Theory for Light Emitting Diode (LED) Systems

The photometric, electrical, and thermal features of LED systems are highly dependent on one another. By considering all these factors together, it is possible to optimize the design of LED systems. This paper presents a general theory that links the photometric, electrical, and thermal behaviors of an LED system together. The theory shows that the thermal design is an indispensable part of the electrical circuit design and will strongly influence the peak luminous output of LED systems. It can be used to explain why the optimal operating power, at which maximum luminous flux is generated, may not occur at the rated power of the LEDs. This theory can be used to determine the optimal operating point for an LED system so that the maximum luminous flux can be achieved for a given thermal design. The general theory has been verified favorably by experiments using high-brightness LEDs.

A novel maximum power point tracker for PV panels using switching frequency modulation

A novel technique for efficiently extracting maximum power from photovoltaic (PV) panels is presented. The power conversion stage, which is connected between a PV panel and a load or bus, is a SEPIC or Cuk converter or their derived circuits operating in discontinuous inductor-current or capacitor-voltage mode. A method of locating the maximum power point (MPP) is based on injecting a small-signal sinusoidal perturbation into the switching frequency and comparing the AC component and the average value of the panel terminal voltage. Apart from not requiring any sophisticated digital computation of the panel power, the proposed technique does not approximate the panel characteristics and can globally locate the MPP under wide insolation conditions. The tracking capability has been verified experimentally with a 10 W solar panel under a controlled experimental setup. Performances under the steady state and in the large-signal change of the insolation level will are given.

A Novel Single-Layer Winding Array and Receiver Coil Structure for Contactless Battery Charging Systems With Free-Positioning and Localized Charging Features

The planar contactless battery charging system is an emerging technology that can be applied to a wide range of portable consumer electronic products. Beginning with a brief historical background, this paper presents a new single-layer winding array and receiver coil structure with cylindrical ferrite cores for planar contactless battery charging systems. Complying with the “Qi” standard, this design enables multiple devices to be placed and charged simultaneously on the wireless charging pad in a free-positioning manner. The charging flux is totally localized within the covered area between the selected primary winding and the secondary winding inside the load. The electromagnetic characteristics of such winding design are studied in finite-element analysis and confirmed by practical implementation.

A Novel Passive Offline LED Driver With Long Lifetime

This paper describes a patent-pending passive offline light-emitting diode (LED) driver that has no controlled semiconductor switches, electrolytic capacitors, auxiliary power supply, and control board. It can provide a fairly smooth current from the ac mains to drive LED strings. The new circuit has the advantages of high input power factor, high energy efficiency and luminous efficacy, long lifetime, stable luminous output, and high robustness against extreme weather conditions. In addition, over 90% of the driver material is recyclable, leading to reduction of electronic waste. It is particularly suitable public LED lighting systems, such as road lighting systems. Experimental results based on a 50-W system are included in the paper to confirm the validity of the proposal. Due to the circuit simplicity, an energy efficiency exceeding 93.6% has been achieved.

Circuit-level comparison of STATCOM technologies

This paper performs a comprehensive circuit-level evaluation of four modern STATCOM systems, namely true-48-pulse and quasi-48-pulse STATCOMs, cascade multilevel and binary multilevel inverters. The comparison is based on a number of factors including circuit topology, harmonic distortion, system losses, GTO quantities, their specific applications, and other considerations. The theoretical results are verified by simulation with the use of MATLAB-Simulink Power System Blockset.

A novel electrode power profiler for dimmable ballasts using DC link voltage and switching frequency controls

A novel electrode power profiler for dimmable ballasts using series-resonant parallel-loaded inverter is presented. Dimming of the fluorescent lamp is primarily based on reducing the dc link voltage. Variations of the electrode power (due to the decrease in the lamp current) during dimming is compensated by changing the switching frequency of the inverter, so that the resonant tank circuit current is also varied. The current gradient along the electrode, which is due to the distributed lamp current property on the electrode, is deliberated in formulating the power and voltage models of the electrode. As the electrode heating relies on two near-orthogonal current components including the lamp current and the resonant tank circuit current, a simple feedback control is developed to derive the electrode power and program the electrode power. Experimental results of a T8 36 W prototype are verified with theoretical predictions.

Reduction of power converter EMI emission using soft-switching technique

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 a soft-switching technique in power converters. Thus, the 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.

Mutual inductance calculation of movable planar coils on parallel surfaces

Recent developments of wireless battery charging platform have prompted the requirements to investigate the mutual inductance between a movable planar coil and the fixed planar coil on the charging platform. The wireless battery charging platform must allow the load to be placed anywhere on the charging surface. Therefore the relative position between the movable energy-receiving coil and the energy-transmitting coils on the charging platform must be flexible. In this paper, an extended formula is proposed for the mutual inductance calculation for two coaxial or non-coaxial planar spiral windings sandwiched between two double-layer substrates. It can quickly determine the mutual coupling of two planar windings that can have different relative positions and distance between them. This new calculation method provides a new and useful tool for determining the mutual inductance of a movable planar coil and the fixed planar coil on the wireless battery charging platform. The theory has been favorably tested and compared with practical measurements and also finite-element analysis.