Deyan Lin

Current source ballast for high power lighting emitting diodes without electrolytic capacitor

An LED driver requiring no electrolytic capacitor in the whole power conversion process is presented. It consists of two power conversion stages. The first stage is a buck converter operating in discontinuous capacitor voltage mode, so that the input current is continuous. It is used to deliver a regulated current for the second stage. The second stage is a current-fed inverter, in which the semiconductor switches are operated at constant switching frequency and constant duty cycle of 0.5. The power supplying to the LED string is regulated by controlling the duty cycle of the main switch in the front-stage buck converter. The two stages are interconnected by an LC filter, which is designed to attenuate harmonics at double of the line frequency. Instead of using an electrolytic capacitor for the filter, a polyester capacitor of better lifetime expectancy is used. An 18 W experimental prototype has been built and tested.

Two- and Three-Dimensional Omnidirectional Wireless Power Transfer

Nonidentical current control methods for 2- and 3-D omnidirectional wireless power systems are described. The omnidirectional power transmitter enables ac magnetic flux to flow in all directions and coil receivers to pick up energy in any position in the proximity of the transmitter. It can be applied to wireless charging systems for low-power devices such as radio-frequency identification devices and sensors. Practical results on 2-D and 3-D systems have confirmed the omnidirectional power transfer capability.

A Simple Method for Comparative Study on the Thermal Performance of LEDs and Fluorescent Lamps

A simple method is proposed to measure the heat dissipation of LEDs and fluorescent lamps in an open system that allows light energy to escape. Based on this method, a comparative study on the thermal and luminous performance of high-brightness LEDs and fluorescent lamps is presented. At rated power, T5 and T8 fluorescent lamps generate about 73%-77% of their total power as heat, while three types of high-brightness LEDs dissipate about 87%-90% of input power as heat. Heat dissipation is an important factor particularly for air-conditioned buildings when overall energy efficiency is considered. T5 fluorescent lamps perform better than some existing LEDs in terms of luminous efficacy and heat generation in this study.

A Simple Method for Comparative Study on the Thermal Performance of Light Emitting Diodes (LED) and Fluorescent Lamps

A simple method is proposed to measure the heat dissipation of LEDs and fluorescent lamps in an open system which allows light energy to escape. Based on this method, a comparative study on the thermal and luminous performance of high-brightness LEDs and fluorescent lamps is presented. At rated power, T5 & T8 fluorescent lamps generate about 73% - 77% of their total power as heat, whilst three types of high-brightness LEDs dissipate about 87% to 90% of input power as heat. Heat dissipation is an important factor particularly for air-conditioned buildings when overall energy efficiency is considered. T5 fluorescent lamps perform better than some existing LEDs in terms of luminous efficacy and heat generation in this study.

A Systematic Approach for Load Monitoring and Power Control in Wireless Power Transfer Systems Without Any Direct Output Measurement

A systematic method is presented in this paper to show that, based only on the measurements of the input voltage and current, the load impedance of a wireless power transfer system can be instantaneously monitored and load power controlled without using any direct measurement from the load. A new mathematic procedure for deriving the output load information based on input voltage and current is explained. This systematic method, which can be applied to wireless power systems with two or more coils, eliminates the need for sensors and communication devices on the load side, thereby greatly simplifying the power control circuitry. The principle of the load estimation method, the power loss optimization and control scheme are described and favorably verified with measurements obtained from an eight-coil wireless power transfer system.

Gas Discharge Lamps Are Volatile Memristors

Discharge lamps can be classified as high-pressure and low-pressure lamps, which operate under different scientific principles. They have exhibited the well-known fingerprints of memristors. This paper describes the mathematical models of both of high- and low-pressure discharge lamps based on their respective physical nature and behaviors, and then explains how these models can be unified into a generalized mathematical framework that confirms their memristor characteristics. Practical and theoretical results from high-pressure and low-pressure lamps are included to illustrate their 3 fingerprints of the memristor characteristics. The results indicate that gas discharge lamps are not ideal but volatile memristors.

Chromatic, Photometric and Thermal Modeling of LED Systems With Nonidentical LED Devices

With the emergence of new color-mixing LED systems based on LED devices of different color temperatures, the need for a new modeling technique for LED systems with nonidentical LED devices becomes imminent. This paper presents a modeling technique for LED systems with LED arrays comprising nonidentical LED devices that have nonidentical optical-thermal-electrical properties. Based on a general 3-D photo-electro-thermal LED node model, LED devices of different kinds can be arranged in various array forms according to their system construction and design. By linking the system matrix to the correlated-color-temperature prediction, the proposed modeling technique provides an accurate prediction of the temperature distribution, luminous flux, and correlated color temperature of the LED systems. The temperature distribution and light output of the LED systems have been measured using an infrared imaging system and a spectrophoto-colorimeter with an integrating sphere. The modeling technique has been successfully demonstrated and experimentally verified on several LED systems comprising nonidentical LED devices. It is particularly useful as a modeling tool to study new color-mixing LED systems based on different types of LED devices.

Basic Control Principles of Omnidirectional Wireless Power Transfer

This paper presents the basic control principles of omnidirectional wireless power transfer (WPT) based on the current amplitude control. The principles involve 1) an “omnidirectional” scanning process for detecting the power requirements in a 3-D space and 2) a “directional” power flow control for focusing the wireless power toward the targeted areas. Such principles apply to any WPT system comprising three orthogonal transmitter coils and multiple receivers with coil resonators. A current amplitude control method capable of generating a magnetic vector at a set of points evenly distributed on a spherical surface is explained. Based on the voltage and the current information in the transmitter circuit, the power involved in each vector over the spherical surface can be obtained. By scanning the vector over the spherical surface, the collective power flow requirements for the targeted loads can be determined. Based on the power requirements for the vectors over the spherical surface, a weighted time-sharing scheme is adopted to focus the wireless power toward the targeted areas. This method has been successfully applied to a hardware prototype. Both theoretical and experimental results are included to confirm these principles.

Front-End Monitoring of Multiple Loads in Wireless Power Transfer Systems Without Wireless Communication Systems

This paper describes a method for monitoring multiple loads from the front end of a wireless power transfer system without using any wireless communication systems. A mathematical approach based on scanning the frequency around the resonant frequency has been developed for deriving the load conditions. The proposal requires only information of the input voltage and current, thereby eliminating the requirements of using wireless communication systems for feedback control. The proposal has been practically confirmed in hardware prototype with good results.

Design of a Single Ultra-Low-Loss Magnetic Ballast for a Wide Range of T5 High-Efficiency Fluorescent Lamps

A patent-pending single design of an ultralow-loss (ULL) magnetic ballast for T5 high-efficient (T5-HE) fluorescent lamps rated from 14 to 35 W is presented. Based on the use of a nonlinear physical low-pressure discharge lamp model, it is discovered that the same set of ballast parameters can be chosen for operating T5-HE 14-, 21-, 28-, and 35-W lamps at their respective rated power at a mains voltage in the range of 220-240 V. With energy efficiency higher than and lifetime much longer than their electronic counterparts and being recyclable, the ULL ballasts offer a more environmentally friendly solution to T5-HE lamps than electronic ballasts. This single-ballast design offers great convenience to both ballast manufacturers and users, because only one product design can cover a range of the most popular T5-HE lamps. Both theoretical analysis and experimental results are included to confirm the validity of the proposal.