Eun S. Lee

General Unified Analyses of Two-Capacitor Inductive Power Transfer Systems: Equivalence of Current-Source SS and SP Compensations

A general and systematic comparison of eight compensation schemes in the inductive power transfer system (IPTS) of single magnetic coupling and two capacitors is proposed in this paper. The characteristics of series-series (SS), series-parallel (SP), parallel-series (PS), and parallel-parallel (PP) compensation schemes for a voltage source or a current source are widely explored in terms of maximum efficiency, maximum power transfer, load-independent output voltage or current, magnetic coupling coefficient (k) independency, and allowance of no magnetic coupling (k = 0). Through comparative analyses using a general unified IPTS model, the current-source-type SS and SP are found to be superior to other compensation schemes in terms of the five criteria mentioned above, and they are found to have nearly the same efficiency, load power, and component stress characteristics for the same load quality factor. A design guideline for the current-source-type SS and SP is suggested and experimentally verified by a 200-W prototype of air coils at 100 kHz.

Generalized Models on Self-Decoupled Dual Pick-up Coils for Large Lateral Tolerance

Self-decoupled dual pick-up coils for large lateral tolerance and low electromagnetic field for pedestrians are proposed. Analytical models are developed that are applicable to any self-decoupled coils, regardless the coil types such as single/dual pick-ups and core/coreless coils. An optimum decoupling distance between adjacent pick-up coils is determined and found to be independent of the existence of a core plate. Maximum load power over a large lateral tolerance is obtained for the optimum decoupling distance. The proposed models are so general that they can be applied to any self-decoupled pick-up coils for stationary charging and dynamic charging systems. Moreover, the self-decoupled coils are compatible with any compensation method such as serial, parallel, and serial-parallel. A prototype system of 1.5 kW and Q = 60 for roadway powered electrical vehicles was implemented and showed fairly good agreements with the theoretical models and simulations. The measured lateral tolerance was 90 cm, which is about 1.5 times of the coil width.

Dipole-Coil-Based Wide-Range Inductive Power Transfer Systems for Wireless Sensors

A dipole-coil-based extremely loosely coupled inductive power transfer system (IPTS) for wireless sensors over a wide range is proposed. The overall superiority of dipole coils for a long-distance power delivery over loop coils with an identical configuration of a square core is verified by comparing the magnetizing inductance between primary and secondary coils. Series-parallel resonant circuits were used to achieve a higher load voltage than that of the series-series scheme. Contrary to conventional IPTSs or coupled magnetic resonance systems, the quality factor Q was set as low as 100, guaranteeing a frequency tolerance of 1%, where a prototype of narrow dipole coils with a length of 2 m was used to deliver 10.3 W of power up to 7 m away at a low frequency of 20 kHz. The powering capabilities of the proposed IPTS were experimentally compared inside and outside of a metal container 8 m × 4 m × 2.5 m in size at different frequencies ranging from 20 to 150 kHz, where the proposed IPTS is highly likely to be surrounded by arbitrary distributed conductors in most wireless sensor usage environments. The coupling coefficient κ between the primary and secondary coils was measured over a long distance from 2 to 12 m for different secondary coil positions, where κ is mostly much less than 0.01. A comparative analysis of the maximum amounts of load power among different core materials, i.e., two ferrite cores and an amorphous core, was conducted in relation to the design of a secondary coil. The results were verified by experiments at a given switching frequency of 20 kHz.

7m-off-long-distance extremely loosely coupled inductive power transfer systems using dipole coils

An extremely loosely coupled inductive power transfer system (IPTS) for 7m-off-long-distance wireless power transfer using dipole coils is proposed. The superiority of dipole coils for a-long-distance power delivery over loop coils with same configuration of square core, in general, is verified by comparing magnetizing inductance between primary and secondary coils. Series-parallel resonant circuits are used to achieve higher load voltage than the series-series scheme. Contrary to conventional IPTSs or coupled magnetic resonance systems, quality factor Q is set as low as 100, which is, moreover, fixed for guaranteeing frequency tolerance. An optimum number of turns of the secondary coil is derived theoretically and verified by experiments, where a prototype of narrow dipole coils with 2m-length were used to deliver 11.1 W power up to 7m-distance at a very low frequency of 20 kHz.

Temperature-Robust LC 3 Passive LED Drivers With Low THD, High Efficiency and PF, and Long Life

New passive LED drivers that can reduce the total harmonic distortion (THD) significantly by LC parallel resonance are proposed. Using an inductor and three capacitors, called LC3, novel characteristics, such as high power efficiency and power factor (PF) with extremely long life time are achieved. The proposed LED drivers have a temperature-robust characteristic, because their power is hardly changed by temperature. By selecting the number of LEDs in series ns appropriately, the LED power variation caused by temperature change in LED can be zero. For the universal use of the proposed LED drivers in various countries with different frequencies, circuit configurations applicable to 50/60 Hz are proposed. To analyze the LED power and PF of the proposed LED driver, the phasor transformation was, for the first time, applied to nonlinear diode rectifier modeling. Although the proposed LED driver is a nonlinear switching circuit, the proposed analyses matched well with simulation and experimental results. A prototype LED driver showed a very high power efficiency of 95.2% at 70 W, meeting PF and THD regulations for source voltage variation of ±6% of 220 V, even when a reasonably small number of filters were used.

Lumped Impedance Transformers for Compact and Robust Coupled Magnetic Resonance Systems

An innovative coupled magnetic resonance system (CMRS), introducing two lumped impedance transformers, is proposed. There are three major magnetic couplings between coils in CMRS: source-transmitter (Tx), Tx-receiver (Rx), and Rx-load couplings. Except for Tx-Rx coupling, other couplings do not directly contribute to wireless power transfer. Hence, in this paper, this miscellaneous coupling is replaced with a lumped transformer with ferrite core. Because there is only a Tx-Rx coupling, the CMRS becomes compact in size and robust to ambient changes. Moreover, the design of CMRS is drastically simplified without complicated multiresonance tunings due to little magnetic flux linkage from the source coil or load coil. Coreless coils are used for Tx and Rx coils to examine the characteristics of CMRS with lumped transformers. A detailed static analysis on the explicit circuit model of the proposed CMRS and design procedures are fully established. Experiments for 1- and 10-W prototype CMRSs with a class-E inverter at the switching frequency of 500 kHz, where the quality factors are less than 100, verified the usefulness of the proposed model, achieving 80% of the maximum Tx coil-to-load efficiency. It is concluded in this paper that the conventional CMRS, in general, is just a special form of an inductive power transfer system where the quality factor is extremely high.

Temperature-robust LC 3 LED driver with low THD, high efficiency, and long life

A new type of passive LED driver that can reduce total harmonic distortion (THD) significantly by LC parallel resonance is proposed in this paper. Using an inductor and three capacitors, called LC3, novel characteristics such as high efficiency and power factor (PF) with extremely long life time are achieved. The proposed LED driver has a temperature-robust characteristic because its power is hardly changed by temperature, selecting the number of LED in series ns appropriately so that the LED power variation due to temperature change in LED can be zero. For analyzing LED power of the proposed LED driver, the phasor transformation technique is applied, which is firstly applied to a non-linear diode rectifier modeling. Nevertheless this non-linear switching, the proposed analyses agreed well with simulation and experiment results. A prototype LED driver showed very high power efficiency of 96.7 % at 60 W, meeting high PF of 0.95 and low THD of 10.1 %, though a reasonably small filter was used.

Versatile LED Drivers for Various Electronic Ballasts by Variable Switched Capacitor

An LED driver compatible with various electronic ballasts that are currently commercially used is newly proposed, which adopts a variable switched capacitor by controlling the switching duty cycle for LED power regulation. The resonant frequency of an LC resonant tank of electronic ballasts can be changed, which makes the proposed LED driver versatile for electronic ballasts for various switching frequencies. In this way, the fluorescent lamp is replaced with an LED lamp, where the electronic ballast in the lighting infrastructure remains unchanged. The zero voltage switching is applied for the variable switched capacitor in the electronic ballast, operating at a frequency of 30-60 kHz. Neither an inductor nor a transformer is introduced in the proposed LED driver, which leads to compact size and high efficiency. Furthermore, no electrolytic capacitor is used, which is beneficial for the long lifetime of LED drivers. A prototype LED driver of 16 W was implemented and verified for the three types of electronic ballasts that are most popular in markets. The LED power was well regulated for a wide range of the source voltage variations between 180 and 270 V, and the power efficiencies of the proposed LED driver were 95.8%, 96.1%, and 94.1% for the instant start, rapid start, and programmed start types of the electronic ballasts, respectively.

A novel TRIAC dimming LED driver by variable switched capacitance for power regulation

A novel TRIAC dimming LED driver that can control the brightness of LED arrays for a wide range of source voltage variation is proposed. Contrary to conventional PWM LED drivers, proposed LED driver uses TRIAC as a main switch, which inherently guarantees zero current switching and proven to be quite reliable. These characteristics can significantly improve switching loss and provide a long lifetime, which is requisite for LED drivers. The power of the proposed LED is regulated by variable switched capacitance, which is modulated by the TRIAC turn-on timing. Moreover, dimming control is obtained, in the same way of conventional TRIAC dimmers of lamps, by a volume resistor, which changes the current slope of a controlled current mirror of the proposed feedback control circuit. A prototype LED driver of 80 W was implemented with a TRIAC and DIAC, and verified by experiments, where the power factor and total harmonic distortion are 0.94 and 18.9 %, respectively. The maximum LED power variation was well mitigated below 2.5 W for 190 V <; Vs <; 250 V by using the proposed simple control circuit.

Optimal shaped dipole-coil design and experimental verification of inductive power transfer system for home applications

1m-off long distance and high efficiency inductive power transfer system (IPTS) with optimal shaped dipole-coil structure is proposed for home appliance charging applications. Conductive reflectors for transmitter (Tx) and receiver (Rx) dipole coils are investigated to improve power efficiency and to mitigate electromagnetic field for human safety. By adopting the Tx reflector behind the Tx core, the exposure level of magnetic flux density can be reduced by 94% in average verified by a finite-element method simulation. The optimal switching frequency of 200 kHz was experimentally found for maximum power efficiency, meeting an international guideline of Power Matters Alliance (PMA). It was experimentally verified that 4.2% of power efficiency reduction for the Rx reflector and 7.8% of the power efficiency improvement for the Tx reflector were observed. A prototype of the proposed IPTS for home appliances has achieved 83.1% of high efficiency with 150W of output power transfer.