Euihoon Chung

Design of single switch DC-DC converter with parasitic parameters

This paper proposes an isolated single switch dc-dc converter suited to a high frequency switching operation. The impedance seen at the drain to source node of the switch is mainly designed for achieving zero voltage switching (ZVS) operation and reducing the voltage stress across the switch device. In the proposed converter, leakage inductances of the transformer are integrated to the resonant network. By the proposed design procedure, the transformer is designed to have a proper coupling coefficient in order to satisfy the design requirement solely by the leakage and magnetizing inductances without extra inductors. Thus, it is possible to miniaturize the converter size and achieve high power density. In addition, the junction capacitance of the switch device is used for establishing the resonant network, so it is possible to mitigate the non-linear effect of the junction capacitance of the switch device. As a design example, a 10MHz-18W GaN-based prototype is presented, and the performance of the proposed converter is verified.

A Family of High-Frequency Single-Switch DC-DC Converters with Low Switch Voltage Stress Based on Impedance Networks

This paper presents a novel family of single-switch resonant dc–dc converters with low switch voltage stress. The single-switch resonant converter which has a ground-referenced switch is advantageous for implementing the gate drive circuit and operating at several-MHz switching frequency. However, the conventional ones mostly have high voltage stress on the switch, roughly 4–5 times the input voltage. In this paper, we propose the single-switch converter topologies derived from the drain-source impedance networks consisting of two inductors and two capacitors. The switch voltage of the proposed converters is shaped into a near trapezoid by designing the resonant networks to have the desired drain-source impedance. Furthermore, a simple and specific design scheme is presented here so that the peak switch voltage is lowered to 2.2–2.5 times the input voltage while zero voltage switching is achieved. Experimental results from a 20-W GaN-based prototype operating at 10 MHz demonstrate the feasibility of the proposed converter topologies and the design method.

Design and control of 10-MHz classs E DC-DC converter with reduced voltage stress

This paper presents a novel design method for class E dc-dc converter and a control scheme capable of operating in a wide load range. The class E converter is suitable for several-MHz switching frequency; however, the conventional design has two drawbacks: high voltage stress on the switch (theoretically about 3.6 times the input voltage), and a large input inductor. Here we propose the design scheme to reduce the peak switch voltage up to 2.2-2.5 times the input voltage without additional circuit element and to improve transient performance by a small input inductor. In addition, an on-off control is implemented to regulate the output voltage, allowing the fixed-frequency, fixed-duty-cycle operation and zero voltage switching (ZVS) at light load. Experimental results from a 20-W laboratory prototype operating at 10 MHz verify the feasibility and the effectiveness of the proposed method.

System conditions monitoring method for a wireless cellular phone charger

This paper presents a technique to be used for the cellular phone charger. The proposed technique identifies system conditions to control the output voltage, measuring only the primary side voltage and current. The method estimates the load and the coupling coefficient of the circuit by perturbing the operating frequency. The control method, designed in Primary-Series-Secondary-Series (SS) topology maximizes the efficiency by working at the resonant frequency, hence the output voltage is controlled by the switching duty cycle. The way to get the required duty cycle is proposed by this paper.

Output voltage control for series-series compensated wireless power transfer system without direct feedback from measurement or communication

This paper proposes a primary side control for series-series compensated wireless power transfer system. By eliminating the need for a communication link for signal feedback, the control method not only reduces volume and cost of the system, but also improves a dynamic response. This controller only requires the information of the primary side voltage and current to identify the load resistance and the mutual inductances which are essential parameters to estimate the output voltage. To regulate the output voltage, PI controller is used to adjust the switching duty cycle of a full-bridge inverter. The proposed control concept is verified by experimental results. For experiments, the laboratory prototype is designed to achieve 50-W and achieves 89% efficiency at the rated condition.

Variable time step control with synchronous PWM in low frequency modulation index for AC machine drive

This paper proposes a variable time step controller with synchronous PWM. Since a frequency modulation index is low in an ultra-high speed or high power drive system, the modulated voltage by a fixed time step control includes large harmonic components. The optimal PWM method is one of the solution to minimize the harmonic components, but it needs many offline calculations and its structure is complicated. The proposed variable time step control has small calculation burden and it does not need offline calculations. Furthermore, the harmonic components of the modulated voltage is small because the frequency modulation index is kept as integer value in all speed conditions. Also, the transition strategy between synchronous PWM methods is proposed and it is verified with simulation and experimental results.

Output impedance network based design in 10MHz isolated DC-DC converter of Class Φ 2

This paper proposes the design method of a high frequency dc-dc isolated Class Φ2 converter with a transformer and rectifiers. In the proposed design method, the relation between the Class Φ2 inverter, which has an AC load such as a resistor, and the dc-dc type one is derived and used for a certain degree accurate output power regulation. Also, the input impedance between the switch drain and source nodes is designed for the reduced switch voltage stress and a ZVS operation. Here, since the input impedance is determined while considering the output impedance network, the voltage waveform applied to the switch is almost uniform and not varied by the output impedance network design. In this paper, the isolated type of the dc-dc Class Φ2 converter is analyzed and the design procedure is specifically presented. To verify the feasibility of the proposed design method and analysis, simulation results are presented from a 10MHz isolated dc-dc converter of Class Φ2 at an input voltage of 50 V, an output voltage of 19V, and a power level up to 20W.

Loss Minimizing Vector Control of Interior Permanent Magnet Synchronous Motor

This paper presents a loss-minimizing vector control method for interior permanent magnet synchronous motor (IPMSM). Conventionally, maximum torque per ampere (MTPA) control, which minimizes copper loss, has been widely used in industry. Iron loss, however, is not considered in MTPA control. In this paper, the loss model, including iron loss and copper loss, is derived to further reduce drive loss. The loss-minimizing vector controller is implemented based on the loss model. The controller generates optimal current vectors according to the operating conditions. The performance and validity of the proposed method are proved by experimental results through comparison with conventional methods.