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This article proposes a simple multivector predictive direct power control (P-DPC) using geometric modulation. Different from the conventional counterpart using two active and one zero vector, the proposed multivector P-DPC uses a primary and a secondary equivalent vector having the opposite angular position to synthesise the voltage reference acquired from the deadbeat calculation. The generic equation of the rectifier voltage is established to calculate the primary and the secondary equivalent vectors as the weighted sum of two active vectors. The duty cycle optimization is achieved by combining the coefficients of the two equivalent vectors and the length ratio of the reference amplitude compared with the maximum rectifier voltage. The proposed multivector P-DPC offers a simple solution of duty cycle optimization that circumvents the calculation of instantaneous power rates and complex differential equations prevalent in conventional multivector approaches. This significant reduction of control complexity makes the proposed approach suitable to be implemented in low-cost microcontroller units. Experimental and simulation results have demonstrated the effectiveness of the new method. [ABSTRACT FROM AUTHOR]

Optimum energy efficiency in a wireless power transfer (WPT) system usually occurs only at a specific load value while the load such as a battery is normally not constant. A major challenge in WPT is, therefore, to achieve high energy efficiency over a wide load range. Previously, impedance transformation methods such as dc–dc converters and use of a relay coil have been used to transform the practical load resistance to the optimum (or near-optimum) value. In this paper, a new approach based on reconfigurable magnetic resonant structures is proposed to achieve high energy efficiency and low volt-amp ratings. This basic principle is to create more than one efficiency–load curve. The WPT system is controlled to be operated within the top regions of the energy efficiency curves of the reconfigurable circuits so that high energy efficiency can be achieved over a very wide load range. The principle of this new approach is explained with an analysis and verified with practical measurements. [ABSTRACT FROM PUBLISHER]

Maximum energy efficiency in wireless power transfer (WPT) systems can be achieved through the use of magnetic resonance technique at a certain load resistance value. However, practical load resistance is not constant. Previously, a switched mode dc–dc converter was used in the receiver circuit to emulate an equivalent load resistance for maximum energy efficiency. In this paper, a new approach based on the On–Off Keying is proposed to achieve the high energy efficiency operation over a wide range of load power without using an impedance-matching dc–dc power converter. This simple and effective method has reduced average switching frequency and switching losses. It can be applied to any series-series resonant WPT system designed to operate at a constant output voltage. Practical measurements have confirmed the validity of the proposal. [ABSTRACT FROM PUBLISHER]

Ultralow-loss passive ballasts for T5 fluorescent lamps have previously been proven to be more energy efficient than their electronic counterparts at room temperature operation. The absence of electrolytic capacitor, switched-mode circuit, and control integrated circuit makes them particularly suitable for extreme temperature conditions. This paper first describes the challenges required for low-temperature operation and frequent ignition of T5 high-efficiency lamps. Then, the design of passive inductive–capacitive (LC) ballast for T5 28-W lamps based on a physical discharge lamp model is illustrated. To reduce the blackening effects of the filaments, a bypass resistor is incorporated to each filament to avoid local hot spot formation. Frequent ignition tests have been conducted for the proposed ballast and electronic ballast to confirm the effectiveness of the bypass resistors in protecting the filaments. [ABSTRACT FROM AUTHOR]

This paper describes a technique for multifrequency wireless power transfer systems in which the wireless power can be transmitted through the wireless power transfer channel or channels from the transmitter to the targeted loads with receiver coils specifically tuned for energy reception. Auxiliary circuits comprising bandpass and/or bandstop circuits are proposed for incorporation into the receiver circuits and optional relay circuits so as to facilitate the selection and enhancement of the wireless power transfer to the designated load without causing significant cross interference due to the use of multifrequency wireless power flow control. A unique feature of this technique is that the nontargeted receiver will automatically act as a relay resonator to enhance 1) magnetic coupling, and thus, 2) the power transfer between the power transmitter and the targeted receiver. A second novel feature is that the chosen operating frequencies for the tuned receivers need not be widely apart because the auxiliary circuits consist of bandpass and/or bandstop filters to reduce any cross interference from the nontargeted frequency. The proposed technique has been practically verified in experimental prototype. [ABSTRACT FROM AUTHOR]

A method for automatic "maximum energy efficiency tracking" operation for wireless power transfer (WPT) systems is presented in this paper. Using the switched-mode converter in the receiver module to emulate the optimal load value, the proposed method follows the maximum energy efficiency operating points of a WPT system by searching for the minimum input power operating point for a given output power. Because the searching process is carried out on the transmitter side, the proposal does not require any wireless communication feedback from the receiver side. The control scheme has been successfully demonstrated in a two-coil system under both weak and strong magnetic coupling conditions. Experimental results are included to confirm its feasibility. [ABSTRACT FROM AUTHOR]

Current imbalance among parallel light-emitting diode (LED) strings could put excessive current and thermal stress on some of the LEDs in the systems, resulting in reduction in system lifetime. For LED road lighting systems, reliability is the paramount factor. This paper first explains how existing current-mirror (CM) circuits cannot cope with LED open-circuit faults and then describes a self-configurable CM circuit that can withstand open-circuit faults in LED systems with parallel LED strings. The ability to withstand open-circuit faults means that the LED systems can still function with reduced luminous output even if one LED string is cut off. The proposed circuit, which retains the feature of not requiring an auxiliary dc power supply, has been practically implemented and successfully tested in a 70-W LED system with three parallel strings. [ABSTRACT FROM AUTHOR]

Starting from Tesla's principles of wireless power transfer a century ago, this critical review outlines recent magneto-inductive research activities on wireless power transfer with the transmission distance greater than the transmitter coil dimension. It summarizes the operating principles of a range of wireless power research into 1) the maximum power transfer and 2) the maximum energy efficiency principles. The differences and the implications of these two approaches are explained in terms of their energy efficiency and transmission distance capabilities. The differences between the system energy efficiency and the transmission efficiency are also highlighted. The review covers the two-coil systems, the four-coil systems, the systems with relay resonators and the wireless domino-resonator systems. Related issues including human exposure issues and reduction of winding resistance are also addressed. The review suggests that the use of the maximum energy efficiency principle in the two-coil systems is suitable for short-range rather than mid-range applications, the use of the maximum power transfer principle in the four-coil systems is good for maximizing the transmission distance, but is under a restricted system energy efficiency (<;50%); the use of the maximum energy efficiency principle in relay or domino systems may offer a good compromise for good system energy efficiency and transmission distance on the condition that relay resonators can be placed between the power source and the load. [ABSTRACT FROM AUTHOR]

While LEDs enjoy relatively long lifetime up to 10 years, the lifetime of traditional LED drivers using electrolytic capacitor as storage element is limited to typically less than 5 years. In this paper, an ac/dc LED driver without electrolytic capacitor is studied. Compared with other methods to eliminate electrolytic capacitor, the proposed driver has the advantages of almost unity input power factor and constant output current for LEDs. The operation principle, detailed design procedure of the main circuit, and control strategy are presented. The feasibility of the proposed converter has been successfully verified by experiments. [ABSTRACT FROM AUTHOR]

Current imbalance should be avoided when multiple LED strings are connected in parallel. In this paper, a dimmable LED driver with magnetic-amplifier postregulators for multistring applications is presented. Powered by a common master source, parallel LED strings are individually regulated by their corresponding adaptive slave sources for current balancing in this proposal. Without linear current regulators, the proposed driver offers relatively high efficiency. Its structure is simpler than multiconverter structures for red, blue, and green LED applications, and is particularly suitable for LEDs with wide parameter variations. The performance of the proposed driver is experimentally verified by a 16.5-W prototype with a load of three 5.5-W LED strings. [ABSTRACT FROM AUTHOR]

The high-voltage and low-current features of T5 lamps imply that the copper and core losses of the magnetic ballast can be greatly reduced. This paper shows that magnetic ballasts for high-voltage T5 lamps are not only feasible but their luminous and ballast-loss performance can be better than those of the electronic ballasts. Contrary to common belief, high frequency operation of T5 28 W lamps increases the luminous efficacy by an average of 3.6% only (less than 5%). Practical implementation of an ultra-low-loss magnetic ballast system for T5 28 W lamps is presented. Its total system power is less than the 32 W upper limit specified for Class A2 of energy-efficient electronic ballast for T5 28 W lamps. High-luminous efficacy of 75.63–77.66 lm/W can be achieved. This important breakthrough has the potential of reversing the existing trend of using electronic ballasts as the energy-saving technology in lighting industry. With a better luminous efficacy, lower product and maintenance costs, much longer lifetime, and the use of recyclable metallic materials over its electronic counterparts, this patent-pending proposal provides a truly sustainable lighting solution to the lighting industry. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

An investigation into the effects of the structures of both LED devices and systems on the luminous performance is presented. Single-chip and multichip LED structures and concentrated and distributed LED systems are studied and compared. Practical tests on both of the device and system levels have confirmed the theoretical predictions that parallel LED structures can lead to much lower thermal resistance and thus higher luminous output. The results of this paper contribute to new information for both LED device manufacturers and system designers toward the optimization of the LED technology. [ABSTRACT FROM AUTHOR]

The availability of T5 high-efficiency (HE) and T5 high-output (HO) fluorescent lamp families not only increases the number of commonly used tubular fluorescent lamps from 9 to 18, but more importantly, increases the chance of ballast-lamp mismatch because T5 HO and T5 HE lamps have similar physical outlooks and dimensions but vastly different lamp characteristics. The large number of lamp types increases the number of specific ballast designs and users have the new inconvenience of ensuring the correct matching of the lamps and ballasts. In this paper, a survey and analysis of lamp characteristics of all commonly used T5, T8, and T12 tubular fluorescent lamps is presented. Based on the heated lamp electrodes, lamp voltage, and lamp current, a classification system that maps the lamp characteristics into various groups for automatic lamp detection is proposed. The successful implementation of this method is explained and demonstrated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Planar contactless battery charging platform is an emerging technology that has the potential of unifying the charging protocols of portable consumer electronic products. In this paper, a new hybrid structure which consists of a coil and a spiral winding is proposed for improving the uniform magnetic field distribution over the charging surface. An analysis into an optimal design of the number of turns and the dimension of the spiral winding is presented for a given concentrated coil. The uniform magnetic field distribution of the designed prototype is measured by an electromagnetic compatibility scanner and by an energy-receiving coil. Based on circuit modeling and analysis, the inverter circuit topology and particularly the resonant compensation tank is designed for maximizing power transfer for multiload applications. A design procedure is proposed and verified by the experiments. An efficiency of about 80% has been achieved for the coupled structures when four loads are charged on the platform simultaneously. [ABSTRACT FROM AUTHOR]

This paper presents a finite-element (FE) simulation study of a planar contactiess battery charging platform for portable consumer electronic equipment. Magnetic field plots of the charging platform are generated under no-load and loaded conditions so that the field distribution of the planar charging platform can be visualized. Three working modes of the platform have been investigated and compared, including full excitation and two forms of selective excitation. With new results arising from this FE simulation study and practical experiments, the theory of the magnetomotive force (mmf) generation of the multilayer planar printed-circuit-board winding array structure can be further understood. The results obtained in this paper provide a foundation of understanding for future design and optimization of planar contactless charging platforms. In addition, it has been confirmed that an electromagnetic shield structure that has been applied to coreless planar transformer applications, can work equally well for the planar charging platform. [ABSTRACT FROM AUTHOR]

In this paper, the authors present the results of an investigation into the starting process of a small wattage metal halide lamp and address the influence of the starting process, at extra-high frequency (>350 kHz), upon the performance of two most commonly used electronic ballast circuit topologies, namely the LCC resonant inverter and LCL resonant inverter. The starting transient processes driven by both ballast systems are captured, analyzed and explained. It has been found that the starting process could affect the operating performance of an LCL ballast and may destroy its power switches in the worst case while a LCC ballast gets the advantage over the LCL ballast for the stability during the transient starting process. [ABSTRACT FROM AUTHOR]

In this paper, an equivalent circuit model of a multilayer planar winding array structure that can be used as a universal contactless battery charging platform is presented. This model includes the mutual-inductive effects of partial overlaps of planar windings in the multilayer structure. It has been successfully simulated with PSpice and practically verified with measurements obtained from three prototypes. This circuit model forms the basis of an overall system model of the planar charging platform. It is demonstrated that model parameters can be derived from the geometry of the winding structure. Errors between the calculated and the measured results are found to be within a tolerance of 5%. [ABSTRACT FROM AUTHOR]

An auxiliary resonant tank-protected high-frequency electronic ballast and a pseudo-inductive soft-switching concept are proposed in this paper. Based on the steady state analysis of the series resonant converter, the operational characteristics of the ballast circuit for metal-halide (MH) lamps under different conditions are examined, and then potential hazards to the ballast circuit are addressed. To avoid those dangers, an auxiliary resonant tank is used for protecting the ballast circuit under all operations. With this auxiliary resonant tank operating in either inductive or pseudo-inductive modes, soft-switching can be ensured in the electronic ballasts. Feasibility of the proposal for the ballast circuit is verified by analytical and experimental results obtained from the 150-W prototype ballast for a MH lamp. [ABSTRACT FROM AUTHOR]

This paper provides some qualitative insights into, and a quantitative analysis of, the interrelationship between the ballast circuit parameters and the physical processes inside the lamp arc under dimming conditions. Qualitative explanation is supported by experimental observations on the dimming characteristics of fluorescent and high-intensity-discharge (HID) lamps. This understanding enables engineers to choose the right combination of dimming technique and electronic ballast topology for different types of discharge lamps. Verified by experiments, the fundamental approximation technique is used to characterize the frequency-control and voltage-control dimming technique for series-loaded and parallel-load resonant circuits. [ABSTRACT FROM AUTHOR]

Discharge lamps require high ignition voltage from typically one to several kilovolts for cold-start, but have low on- state voltage of typically 100 V. For discharge arc monitoring purposes, it is difficult or uneconomical to implement voltage sensor to cover such a wide range of voltage. In this paper, a nonintrusive and electrically isolated method, based on the single-sensor principle, is used to derive the system parameters and variables for system monitoring and control purposes. Unlike the traditional resistive potential divider for voltage feedback, the proposed method is nondissipative. Only one coupled winding is used to derive the converter inductor voltage, from which the lamp power, lamp arc resistance and inverter dc link voltage can be accurately derived. The proposal is verified with good agreement between derived values and measurements in an electronic ballast-fluorescent lamp system. The proposal can be useful in applications in which sensing the voltage across the load is either difficult or costly. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An improved physical high-intensity discharge lamp model that combines the concept of acoustic resonance prediction based on the geometric structure of the lamp, energy balance equations, and lamp arc resistance modeling is proposed. It can be incorporated into a PSpice model for prediction of lamp voltage and current under both low and high frequency operations. In particular, variation of lamp arc resistance due to acoustic resonance at high-frequency operation is incorporated into the model. The validity of the model has been confirmed with measurements. [ABSTRACT FROM AUTHOR]

Presents information on a study that discussed an operation and performance of a thyristor-based alternating current-direct current (ac-dc) current-controlled boost-type converter with power factor correction. Details on the principles of operation; Design example of the induction motor; Advantages of the converter switching operation of a bidirectional ac-dc power converter.

Presents information on a study that discussed a fundamental concept of using coreless printed-circuit-board (PCB) transformers. Significance of using magnetic cores; Structure, modeling and analysis of coreless PCB transformers; Characteristics of coreless PCB transformers; Experimental verification of the study.

Presents information on a study which analyzed the noise spectrum of various digital signal processor-implemented random pulsewidth modulation (RPWM) techniques using a statistical approach. Spectral analysis of RPWM scheme; Analysis of noise characteristics; Conclusions.

Presents information on a study that examined a simple and effective approach of turning an isolated hard-switched converter design into a soft-switched one. Description of a zero-current-switching (ZCS) direct current (DC)/DC flyback converter with an auxiliary switch; Theoretical analysis of the study; Experimental results of the study.

Presents algorithms of novel two-part companion link models for fast decoupled simulation. Summary of companion switch models with constant impedance.

Starting from the principle of instantaneous power theory, this article explores various direct power control (DPC) strategies for three-phase two-level pulsewidth modulation (PWM) converters. After summarizing the fundamental power formula of PWM rectifiers, this article studies the operating principle of the conventional table-based approach and its related improvements. It further looks into the advanced counterparts employing space vector modulation and different nonlinear control strategies. The emphasis is put on the prevailing predictive DPC. Besides, the voltage-sensorless and robust DPC methods based on the virtual flux concept and the state observer or estimator are investigated. Critical issues, including the sample delay, constant switching frequency, duty cycle optimization, objective function, and unbalanced operation are examined. [ABSTRACT FROM AUTHOR]

The energy efficiency of an inductive wireless power transfer (WPT) system will deviate from the possible peak value if the magnetic coupling of the transmitter and receiver coils or the load resistance changes. To achieve maximum-efficiency tracking regardless of coupling or load changes, on–off keying (OOK) modulation is used. However it has the issue of large surge current in the circuits during OOK modulation. The current overshoots of a series–series (SS) compensated WPT system at the startup stage might be much higher than the rated current. The current overshoots not only increase the stress on the power switch devices but also cause high voltage spikes across the windings and the resonant capacitors which is a challenge for insulation design. A soft-start scheme is proposed to address the current overshoot problem. The principle of the soft-start scheme can be essentially applied to WPT systems with different compensation topologies. The experimental results of a 3.3-kW prototype verify that the proposed soft-start scheme effectively suppress the current overshoots. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are solid-state devices with specific $v$ – $i$ characteristics. In this paper, we study the basic requirement of the driving circuits and discuss the proper approach to drive LEDs in view of their characteristics. We compare voltage source driving and current source driving, and discuss their relative advantages and constraints. We specifically introduce the use of circuit duality principle for developing new current-source-mode (CSM) drivers that are less known but are theoretically more versatile compared to their conventional voltage-source-mode counterparts. The study highlights the effects of the choice of driving circuits in terms of the number and size of circuit components used, duty cycle variation, sensitivity of control, nonlinearity and control complexity of LED drivers. We propose a CSM single-inductor multiple-output (SIMO) converter, which demonstrates the advantage of having inductorless and easily controlled current-source drivers, and present a comparison of the CSM SIMO converter with the existing SIMO converters. We further illustrate that a high-voltage-step-down ratio can be naturally achieved by the CSM high-voltage-step-down converter without the use of transformers. This paper presents a systematic and comparative exposition of the circuit theory of driving LEDs, with experimental evidence supporting the major conclusions. [ABSTRACT FROM AUTHOR]

A new wireless power transfer (WPT) system based on ball-joint structure is presented in this paper. A ball-joint WPT system consists of a ball structure with a mechanical rod attached to the ball and a ball socket that accommodates the ball structure. This ball-joint structure comprises at least one winding in the ball structure and at least one winding in the ball socket structure. The ball structure can be flexibly rotated over a wide range of angle inside the ball socket, while wireless power can still be transferred from the transmitter winding to the receiver winding through magnetic resonance. The magnetic coupling coefficient between the transmitter and receiver coil over a wide rotating angular range has been analyzed and experimentally checked. Experimental results confirm that an energy efficiency of up to 81% can be achieved. [ABSTRACT FROM PUBLISHER]

This two-part paper aims at providing the basic mathematical theory of omnidirectional wireless power transfer (WPT). Based on current vector control, the magnetic field vector can be generated and pointed at any direction, thus achieving genuine omnidirectional wireless power flow. Part-I of this paper contains the mathematical analysis of the two-dimensional (2-D) system. The 2-D analysis shows that the total input power and the system energy efficiency of the WPT system can be expressed as functions of the angle of the input magnetic field vector. These functions follow the Lemniscates of Bernoulli on the 2-D plane. The directional nature of such curves provides the crucial information of the locations of the receivers so that the wireless power can theoretically be directed to the loads efficiently. The 2-D theory is presented here with the support of experimental verification. Understanding the 2-D omnidirectional WPT theory would make it relatively easy to appreciate the three dimensional one reported in Part II. [ABSTRACT FROM AUTHOR]

Part-II of this paper focuses on the mathematical analysis of the 3-D omnidirectional wireless power transfer (WPT) and also addresses the general principle of load detection. It provides the mathematical forms of distributions of the input power vector and output power vector, and demonstrates that the geometry of such 3-D distributed space follows the revolution of the Lemniscate of Bernoulli along its longitudinal axis. It provides the mathematical proof that the direction of energy transfer for the maximum energy efficiency is always in line with that of the maximum load power path in the 3-D space. Experimental verification is included to confirm the 3-D omnidirectional WPT theory. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, a radial-chordal decomposition (RCD) technique is proposed to decouple the power angle and voltage control of a smart load based on the use of electric springs (ES). This RCD method is mathematically presented. A detailed comparison between the existing ES control schemes and the proposed RCD approach highlights its decoupling feature and merit on achieving multiple functionalities with a single ES. This RCD control method has been tested on a 2-kW small-scale power system. Simulation and experimental results confirmed that the power factor of the ES-integrated smart load can be improved by the chordal control while the mains voltage can be regulated by the radial control. It has also been demonstrated that the radial and chordal control can work simultaneously and independently. [ABSTRACT FROM PUBLISHER]

This paper demonstrates that organic light-emitting diodes (OLEDs) of different structures can be characterized and modeled using a combination of the photo–electro–thermal (PET) theory and spectral power distribution modeling. The photometric, electrical, thermal, and chromatic properties of OLED devices are incorporated into a model framework so that the performance of the OLED of different structures can be compared. A concept of luminance uniformity over the OLED surfaces is also introduced for comparing OLED with large surface areas. Experimental results are included to verify the OLED models and compare the characteristics of two different OLED samples. Based on the same PET framework, some differences of OLEDs and inorganic LEDs are addressed and discussed. [ABSTRACT FROM AUTHOR]

This paper proposes a nonlinear approach of controlling the luminous intensity and correlated color temperature (CCT) of white light-emitting diode (LED) systems with dual color temperatures. This LED system is made up of a warm color LED source (2700 K) and a cool color LED source (5000 K). The luminous intensity of each of these LED sources is individually controlled by pulsewidth modulation. The overall intensity of the LED system is due to the combined emitted flux of both LED sources. Its overall CCT is the mixed average CCT of both LED sources. This proposed method is based on the nonlinear empirical luminous and CCT models of the LEDs, which take into consideration the thermal effect of LEDs on its luminance and CCT properties. With reasonable approximation, the theoretical models are simplified into practical solutions, which are translatable into real-life applications. It is experimentally validated that the proposed approach is considerably more accurate than the existing linear approaches that do not consider color variations of LED sources. The idea is applicable to LED systems with multiple color temperatures and is not limited to white LEDs. [ABSTRACT FROM AUTHOR]

Modern high-power white light-emitting diodes (LEDs) composed of multiple blue LED chips and yellow phosphor coatings have been successfully commercialized because of their high-luminous efficacy. The multiple-chip LED packages usually come with flat structures that have large surface areas for considerable heat loss. Starting from the analysis and modeling of the blue LED chip, this paper introduces the thermal path through the phosphor layer to form the white phosphor-coated (PC) white LED device model for photometric, electric, and thermal performance analysis. The power distribution of the blue LED chip and that of the PC white LED device are compared. Based on this new analysis, the increase in the heat dissipation coefficient, equivalent thermal resistance, and power loss caused by the phosphor coating can be quantified. New equations suitable for device manufacturers to qualify their devices and design engineers to optimize LED system designs are derived. The analytical results are in good agreement with the practical mesurements. [ABSTRACT FROM AUTHOR]

A generic red, green, and blue (RGB) LED system encompasses complex interactions of power, heat, light, and color, which pose a major challenge for achieving precise control over luminance and color-mixing in high-quality lighting applications. In this article, new nonlinear empirical models of a practical RGB LED system with closed-loop control are formulated. They enable precise prediction of luminous flux and color coordinates by using the three distinct reference voltages as the control variables for independent current regulation across the RGB LED strings. The proposed empirical models are experimentally verified by using a hardware prototype of a dc–dc single-inductor three-output LED driver with proportional–integral compensators and time-interleaving control scheme. The measured values of luminous flux and color coordinates agree closely with the predicted values from the models. [ABSTRACT FROM AUTHOR]

The color, electrical, and thermal properties of LED devices are highly dependent on one another. The peak wavelength of GaN-based white LED shifts in opposite directions under the influences of current and junction temperature change. This affects the correlated color temperature (CCT). Importantly, duty cycle control for LED dimming does not provide constant color (against conventional wisdom). An analysis model that links the peak wavelength, electrical, and thermal properties of LED devices is proposed. The color-shift trend of the LED with respect to the changes in its thermal and electrical operating conditions is described. The stabilized CCT performance of a dc or a bilevel-driven LED over a dimming range is found to be a result of the complex interactions between the selected current levels, duty cycle, thermal resistances of the heatsink and device, heat dissipation conversion ratio, and the physical parameters of the LED device. The predicted color variation is verified by experimental results, which demonstrate that the CCT stabilization of an LED with a dc drive requires less thermal energy than that with a bilevel drive. For a given thermal design, the reduction in CCT variation during light intensity change is possible via the combined adjustment of the current level and its duty cycle over the dimming operation. [ABSTRACT FROM AUTHOR]

This paper provides a general analysis on the steady-state behavior and control principles of a recently proposed concept of “electric springs” that can be integrated into electrical appliances to become a new generation of smart loads. The discussion here is focused on how different real and/or reactive load powers can be canceled or altered using the electric springs. Mathematical derivations supporting the theoretical framework of the concept are detailed in the paper. Experimental results validate the theoretical discussions and solutions proposed. It is demonstrated that the electric spring is capable of providing different types of power/voltage compensations to the load and the source. [ABSTRACT FROM AUTHOR]

In this paper, the effects of the magnetic coupling of nonadjacent resonators on the optimal frequency of wireless power transfer are addressed. A power analysis has been carried out to identify the adjacent and nonadjacent power flow components. It is found that such cross-coupling effects of nonadjacent resonators would cause the maximum efficiency operation to slightly shift away from the resonance frequency of the resonators. Theoretical reasons for such phenomena are provided and experimentally confirmed with practical measurements in a wireless power transfer system comprising several magnetically coupled resonators arranged in a straight domino form. [ABSTRACT FROM AUTHOR]

Winding parasitic capacitance is a major factor limiting the bandwidth of an inductor. In this paper, 1) the traditional, 2) the alternating, and 3) the partial alternating winding methods are evaluated for the multilayer printed spiral winding inductors for megahertz operations. The self-capacitances of various winding structures are estimated by the summation of parasitic capacitance among the turns of a winding. The electric field energy distributions in the inductors are derived from the voltage profiles to illustrate the relative magnitudes of winding parasitic capacitances. The results show that parasitic capacitance reduction can be achieved by reducing stored electric field energy. The partial alternating winding method is found to have the widest frequency bandwidth with reduced number of through-hole vias for multilayer printed spiral winding design. The theoretical analysis has been confirmed with practical measurements. The results provide useful information for the optimal design of coreless or core-based high-frequency planar magnetics. [ABSTRACT FROM AUTHOR]

An extension of the use of the boundary control method using second-order switching functions for controlling single-phase multilevel inverters is presented in this paper. The time instant of switching the output voltage of the inverter bridge from one voltage level to another voltage level is governed by two second-order switching functions. The input variables of the switching functions are the input and output voltages of the inverter, reference output voltage, and output filter capacitor current. The switching functions are derived by first estimating the respective trajectories of the output voltage of the inverter with the two possible voltage levels from the inverter bridge supplying to the input of the output filter, and then formulating mathematical functions to approximate the two trajectories (one for each voltage level) that pass through the target operating point. The distinct feature of this method is that the output voltage of the inverter can reach the target operating point in two switching actions in the inverter bridge after the inverter is subjected to an external disturbance. Derivation of the switching functions and implementation of the controller will be given. Three single-phase inverter topologies, including cascaded five-level inverter, hybrid seven-level inverter, and three-level diode-clamped inverter, with the proposed control method have been built and tested. The steady-state and large- signal dynamic responses of the three inverters supplying to three different load types, including resistive, inductive, and nonlinear diode-capacitor circuits, will be discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recent developments of the wireless battery charging platform have prompted 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 noncoaxial 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 with finite-element analysis. [ABSTRACT FROM AUTHOR]

A new behavioral model for analyzing the current- source charge-pump-based ballast with a self-oscillatory gate drive circuit is proposed in this paper. A detailed model derivation is presented and the model is applied to analyze a ballast system of a 16-W compact fluorescent lamp (CFL) as an illustration. The ballast of the CFL consists of a self-oscillatory driven inverter stage and charge pump circuitry. The iterative modeling technique links together the three mutual dependent parts of the system, namely: 1) the charge pump circuit; 2) the self-oscillatory gate drive; and 3) the lamp model, so that they can be designed and studied as an integrated system. It is shown that the model can give a comprehensive interpretation of the whole system and provide a reasonable prediction of the ballast behavior. [ABSTRACT FROM AUTHOR]

Low-pressure discharge lamps obey a set of physical laws that are different from those of high-pressure discharge lamps. In this paper, these differences are addressed. Based on a recently developed HID lamp model frame, a semi-theoretical fluorescent lamp model that can be determined by genetic algorithms and simple electrical measurements is presented. This model does not require any lamp data from lamp manufacturers. Its parameters can be determined from electrical voltage and current measurements of the lamps under ac operation at mains frequency. With the same set of parameters, the model can predict the lamp terminal characteristics accurately under low, medium and high frequency operations. Good simulation results were achieved when the lamp power was reduced to 60% of rated power and when the lamp was operated under step-up and step-down transient processes. Simulation results for different sizes of tubular and compact fluorescent lamps agree well with their experimental results. Particularly, the differences between simulation results and experimental results under rated power are less than 10%. Hence, the proposed model shows a good degree of accuracy: 1) for different types of fluorescent lamps; 2) at different operating frequencies; 3) under different dimming levels; and 4) during step-up and step-down transient processes. [ABSTRACT FROM AUTHOR]