Bohwan Choi

Dynamics Characterization of the Inductive Power Transfer System for Online Electric Vehicles by Laplace Phasor Transform

A large-signal dynamic model of the inductive power transfer system (IPTS) for the online electric vehicle (OLEV) is developed using the recently proposed Laplace phasor transform. With the help of this dynamic model, the effect of the output capacitor and load resistance variation on the transient response of the IPTS is analyzed. The maximum pickup current and output voltage for an abrupt in-rush of the OLEV are examined by both the proposed analysis and simulations, and verified by experiments with good agreement. Thus, it is found that the voltage and current ratings of the pickup remain relatively constant regardless of the load resistance.

A Novel Single-SiC-Switch-Based ZVZCS Tapped Boost Converter

A new single-active-switch-based zero voltage and zero current switching (ZVZCS) tapped boost converter is proposed. For the ZVZCS operation of the converter, three diodes and two capacitors were added to an ordinary tapped boost converter. When turned ON, the active switch is in zero current switching with the help of leakage inductance of a tapped inductor. When turned OFF, the energy of the leakage inductance is transferred to a snubber capacitor through a diode, which results in zero voltage switching of the active switch. Then the energy of the snubber capacitor is retrieved by a recovery capacitor connected to the tapped inductor. Different from most conventional soft switching converters that need at least two active switches, the proposed converter requires only one active switch such as JFET and MOSFET to guarantee ZVZCS operation for wide operating ranges of duty cycle, load current, and input voltage. The voltage stress of the active switch is always less than the load voltage, and soft switching turn-on and off is achieved without cumbersome current or voltage sensing, which could not be obtained from quasi-resonant converters that also have an active switch. Furthermore, the dc voltage gain of the proposed converter is quite robust against load change and is determined only by duty cycle like a canonical boost converter; hence, it can be even open-loop controlled. All the diodes are in ZVZCS as well, and all the components except an output diode have the voltage stress less than the load voltage. In this paper, the voltage stress of the output diode was selected to have two times the load voltage. A detailed analysis for the continuous conduction mode and the design procedures of the proposed converter is fully established, and experimentally verified for a 450-W prototype over the input voltage of 100-250 V, achieving 98.1% of maximum efficiency at the switching frequency of 100 kHz with a SiC JFET. Due to its versatile soft switching characteristics, the proposed scheme can be generally applied to high-frequency and high-efficiency dc-dc converters as well as power factor correctors.

Robust Active LED Driver with High Power Factor and Low Total Harmonic Distortion Compatible with a Rapid-Start Ballast

A new active LED driver with high power factor (PF) and low total harmonic distortion (THD) compatible with a rapid-start ballast is proposed. An LC input filter is attached to the ballast to increase PF and reduce THD. A boost converter is then installed to regulate the LED current, where an unstable operating region has been newly identified. The unstable region is successfully stabilized by feedback control with two zeroes. The extremely high overall system of the 10th order is completely analyzed by the newly introduced phasor transformed circuits in static and dynamic analyses. Although a small DC capacitor is utilized, the flicker percentage of the LED is drastically mitigated to 1% by the fast controller. The proposed LED driver that employs a simple controller with a start-up circuit is verified by extensive experiments whose results are in good agreement with the design.

Fast and reliable phasor detectors for single phase AC systems by derivative quadrature generation

The detection of amplitude and phase information in a single phase AC system is quite challenging due to the lack of quadrature component available in multi-phase AC systems. To produce the reliable quadrature component of the single phase AC system with harmonic noises, a derivative quadrature generator with appropriate filters is proposed. A low pass filter (LPF) optimizing the reductions of total harmonic distortion (THD) and response time of sensed signals was found, surveying generalized n-th order filters. To nullify phase shift of the LPF, an all pass filter was adopted. By simulations and experiments for the proposed phasor detector at 60 Hz, a fast time response of less than 8 ms was achieved under severe THD of 9.3 %.

Development of 2W-Level Wireless Powered Energy Harvesting Receiver using 60Hz power line in Electricity Cable Tunnel

Using high magnetic flux from a 60 Hz high-current cable, a 2 W wireless-powered energy harvesting receiver for sensor operation, internet of things (IoT) devices, and LED lights inside electrical cable tunnels is proposed. The proposed receiver comprises a copper coil with a high number of turns, a ring-shaped ferromagnetic core, a capacitor for compensating for the impedance of the coil in series, and a rectifier with various types of loads, such as sensors, IoT devices, and LEDs. To achieve safe and easy installation around the power cable, the proposed ring-shaped receiver is designed to easily open or close using a clothespin-shaped handle, which is made of highly-insulated plastic. Laminated silicon steel plates are assembled and used as the core because of their mechanical robustness and high saturation flux density characteristic, in which the thickness of each isolated plate is 0.3 mm. The series-connected resonant capacitor, which is appropriate for low-voltage applications, is used together with the proposed receiver coil. The concept of the figure of merit, which is the product weight and cost of both the silicon steel plate and the copper wire, is used for an optimized design; therefore, the weight of the fabricated receiver and the price of raw material is 750 gf and USD

Long-Lasting and Highly Efficient TRIAC Dimming LED Driver with a Variable Switched Capacitor

2 each, respectively. The 2.2 W powering capability of the fabricated receiver was experimentally verified with a power cable current of 100Arms at 60Hz.

Compact and low cost magnetic bearing with saturated coil for gas turbine generators

A triode for alternating current (TRIAC) dimming light emitting diode (LED) driver, which adopts a variable switched capacitor for LED dimming and LED power regulation, is proposed in this paper. The proposed LED driver is power efficient, reliable, and long lasting because of the TRIAC switch that serves as its main switch. Similar to previous TRIAC dimmers for lamps, turn-on timing of a TRIAC switch can be controlled by a volume resistor, which modulates the equivalent capacitance of the proposed variable switched capacitor. Thus, LED power regulation against source voltage variation and LED dimming control can be achieved by the proposed LED driver while meeting the global standards for power factor (PF) and total harmonic distortion (THD). The long life and high power efficiency of the proposed LED driver make it appropriate for industrial lighting applications, such as those for streets, factories, parking garages, and emergency stairs. The detailed analysis of the proposed LED driver and its design procedure are presented in this paper. A prototype of 80 W was fabricated and verified by experiments, which showed that the efficiency, PF, and THD at V s = 220 V are 93.8%, 0.95, and 22.5%, respectively; 65 W of LED dimming control was achieved with the volume resistor, and the LED power variation was well mitigated below 3.75% for 190 V s < 250 V.

The Design of Long-life and High-efficiency Passive LED Drivers using LC Parallel Resonance

A novel magnetic bearing system for gas turbine generators of next generation nuclear power plant is proposed. This system newly adopts saturated coils for generating main bias force and small size linear auxiliary coils for stabilizing the suspension. The saturated coils operate in the region of magnetic saturation in order to maximize the magnetic flux density and reduce the bias current. This results in compact size of core, significant reduction of copper loss; hence, a low cost and high efficiency magnetic bearing is achieved. The proposed system is under development for the goal of 50 ton rotor mass and 300MWe project.

Active LED driver of high PF and low THD compatible with rapid-start ballast

This paper proposes a new passive type LED driver which satisfies the standard of power factor (PF) and total harmonic distortion (THD). The proposed passive LED driver also has high-efficiency and long-life time characteristics compared to active LED driver which is composed of op-amp, switches and so on. By using just passive components such as inductor, capacitor, and diode, it has resolved extremely short-life time and low-efficiency problems of previous LED drivers. It has achieved PF of 0.99, THD of 16.4 %, and the total efficiency of 95 %. The proposed passive LED driver is fully analyzed and verified by simulations and experiments, which results are in good agreement each other.

Novel Dummy Load for 40W Fluorescent Lamps

A new active LED driver with high power factor (PF) and low total harmonic distortion (THD) compatible with a conventional rapid-start ballast is proposed. A dedicated LC compensation circuit is attached to the ballast to increase the PF and lower the THD of the source current. A boost converter is used for regulating the LED current, however its duty cycle is bounded to avoid the unstable operating region, which is analyzed and characterized in this paper. A small DC input capacitor is used to prevent the ballast from an excessive transient voltage and current. The design of the active LED driver for the highly non-linear ballast is verified by extensive experiments.