Hyun-Jun Choi

Design and implementation of high switching frequency LLC resonant converter for high power density

To improve the power density of switch-mode power supplies, high switching frequency operation is an effective method to make the size of passive components small. The new design methodology of magnetizing inductance for zero voltage switching condition, and the size reduction of passive components should be proposed for 500 kHz high switching frequency operation. To verify the proposed methodology, the simulation and experimental results which include power conversion efficiency, and temperature of each passive and active component will be presented. Using those results, dominant power losses will be investigated according to the comparison of 100 kHz and 500 kHz operations. In addition, the small-sized output capacitor which has small output capacitance, and small effective series resistance induces the unstable operation problem. To analyze these control issue, the frequency response of small signal will be discussed to design the optimal feedback loop compensator for high switching frequency LLC resonant converter.

Enhanced Power Line Communication Strategy for DC Microgrids Using Switching Frequency Modulation of Power Converters

To improve the reliability of dc microgrids operation, an enhanced power line communication (PLC) strategy is proposed using switching frequency modulation (SFM) of a power converter. The proposed PLC strategy uses the voltage ripple on the dc bus voltage, which is inherently generated by converters switching activities as an information signal. By using the SFM, all microgrid components sharing the dc bus as communication channel can obtain power flow information with fast Fourier transform analysis of dc bus line frequency. In addition, the operating performance of the dc bus voltage regulator is enhanced over a range of light load conditions. The proposed PLC strategy and design of modulated frequency range are verified through experimental results using a 3.3 kW prototype dual active bridge converter.

A novel DC bus control signal using pulse frequency modulation for DC microgrids

In order to improve the reliability and the stability of DC microgrids (MG) and performance of DC bus voltage regulator, at the same time, a new concept of DC bus control signal (DBCS) algorithm based on pulse frequency variation is proposed. In conventional power management algorithms such as centralized control, power line signaling (PLS), and DC bus signaling (DBS), the reliability of DC MGs could be degraded. In this paper, the switching ripple carried on the dc-bus voltage is presented as the operating information for communication between interfaced converters in DC MG. By varying the switching frequency of a grid-connected DC-DC converter according to the load conditions, all DC MG components connected to the DC bus can be aware of the operating status. Experimental results verify the practical feasibility and the effectiveness of the proposed strategy through the 3.3 kW prototype dual active bridge converter.

Practical Design of Dual Active Bridge Converter as Isolated Bi-directional Power Interface for Solid State Transformer Applications

As a bi-directional isolated interface for solid state transformer applications, practical design considerations of a dual active bridge (DAB) converter are proposed by means of a detailed mathematical model based on the converter’s steady state operations. The DAB converter is useful in isolated bi-directional power conversion applications due to high performance, high efficiency, and bi-directional control manner. However, design considerations should be taken into account to overcome the disadvantages of DAB converter, such as low efficiency caused by restricted soft switching capability at light load conditions and high circulating current at heavy load conditions. The practical design considerations of the converter’s power stage will be discussed to maximize soft switching capability and to minimize the conduction losses. In addition, to reduce the current stress of the power devices during a cold start sequence, an effective soft start algorithm will be proposed. Experimental results with a 3.3 kW prototype DAB converter will be given in order to validate the effectiveness of the proposed design considerations.

Design methodology of dual active bridge converter for solid state transformer application in smart grid

A design methodology of a dual active bridge (DAB) converter for solid state transformer applications is proposed using an elaborate mathematical model of the converter. The DAB converter is popular in bi-directional power conversion applications because of soft switching capability and seamless control in bi-directional power flows. However, several design considerations should be considered to overcome its demerits such as high RMS current at heavy load condition and limited soft switching capability at light load condition. Design methodology of the power stage will be discussed to minimize the conduction loss and to enlarge the soft switching region. In addition, the algorithm for soft start will be discussed to reduce overcurrent stress of the power switches during a start-up sequence. Experimental results of a 3.3 kW prototype DAB converter demonstrate the validity and effectiveness of the proposed methods.