가변 스위칭 방식을 적용한 마일드 하이브리드 차량용 양방향 DC-DC 컨버터의 디지털 제어
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Digital Variable Switching Frequency Control of the Bi-directional DC-DC Converter for Mild-Hybrid Electric Vehicle
Advisor : Prof. Seongjun Lee, Ph.D.
Department of Automotive Engineering
Graduate School of Industrial Technology
Recently, the research and development of the 48V mild hybrid electric vehicle have been progressed to achieve the fuel economy and to reduce the exhaust gas due to a low cost solution compared to the full hybrid and battery electric vehicle. In the mild hybrid electric vehicle, the 48V electrical system which is composed of the starter-generator, the lithium battery and the DC-DC converter is newly added to the conventional 12V electrical system. Because the conventional generator in the 12V electrical system is substituted to the 48V starter-generator for charging the 48V lithium battery, the DC-DC converter is utilized as an energy conversion device for charging the lead acid battery of the conventional 12V electrical system.
The bi-directional power-flow control method using the 2 analog integrated circuit(IC) chips is conventionally studied. One IC is utilized to stabilize the 12V lead acid battery using the 48V lithium battery source during the step down operation mode. On the other hand, the other IC is utilized to stabilize the 48V lithium battery using the 12V battery source during the step-up operation mode. However, there is a problem to raise the device cost due to increasing the component counts, and also to reduce the power density of the converter due to increase the size of the printed control board (PCB). Also, although EMI noise mitigation method using the dedicated IC was studied, this causes a problem of increasing the cost and size.
Therefore, this paper proposes the digital variable switching frequency control method using the micro-controller. Because the functions of the step-up, step-down control operation and variable switching frequency using the linear congruential generator (LCG) are integrated for achieving the low cost and increasing the power density of the DC-DC converter. The proposed method is verified through the simulation software testbed using MATLAB/SIMULINK.
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