Efficiency Improvement of Flyback Converter Using Stepped-Airgap Inductor 계단형 공극 인덕터를 이용한 Flyback Converter의 효율 개선 Yong-Hwan Shin - Department of Electrical Engineering - Gyeongsang National University-South Korea

Efficiency Improvement of Flyback Converter
Using Stepped-Airgap Inductor

계단형 공극 인덕터를 이용한 Flyback Converter의 효율 개선
Yong-Hwan Shin
Department of Electrical Engineering
Graduate School
Gyeongsang National University

Abstract
This thesis deals with the efficiency improvement of flyback converter using stepped-airgap transformer, in order to improve the efficiency and/or power density of power electronic systems. The stepped-airgap inductor has been proposed for the flyback converter in order to improve the efficiency over the entire load range, especially light load. The design procedure is also presented. The center leg has typical air gap while the outer gap has a step-shape core. The inductance of the flyback transformer is increased at light load, so that CCM operation can be extended to lighter load. In addition, both the air gaps in the center and outer legs operate at heavy load, so that the AC winding loss can be reduced. The usefulness of the proposed flyback transformer is experimentally verified and compared with the conventional flyback transformer with one inductance value. The experimental results show that the proposed stepped-airgap transformer has higher efficiency at not only light load but also heavy load. Especially, light load efficiency can be much improved. The first part of the thesis introduced method improving flyback converter at light load. Improving efficiency is introduced by many other methods at the entire load. Efficiency is also compared with switching frequency and variable inductance at the entire load. To improve efficiency at light load, stepped-airgap core was suggested. The second part of the thesis introduces how to model stepped-airgap for reluctance circuit. Stepped-airgap is calculated by stepped air gap length and stepped core area. Inductance is analyzed by relative permeability. According to current, stepped-airgap inductor have linear, saturated and hard saturated region. To analyze stepped-airgap is also calculated by flux intensity. Finally, stepped-airgap inductor is summarized by the inductance and relative permeability according to inductor current. The third part of the thesis deals with design of stepped-airgap inductor and flyback transformer. Stepped-airgap is simulated by Maxwell 3D and PSIM simulation tools according to inductor current. To improve efficiency of flyback converter can extend the CCM range with changeable inductance value. Before experiment of flyback converter, simulation is preceded using Maxwell 3D program to confirm permeance, relative permeability value and flux density at stepped core. The operation of flyback converter with varying load current is also simulated by PSIM program. The fourth part of the thesis deals with measurement of inductance about stepped-airgap inductor. Inductance is measured by circuit that can measure the inductance according to current. When input current is changed, inductance is measured by LCR Meter using DC power supply. Inductance is also measured to change part of stepped core area. Until now, there is no relative permeability data of PC95 according to current. Relative permeability of PC95 is gathered by measurement in lab. Stepped-airgap inductor is analyzed and modeling about length of air gap and core area by PC95 relative permeability data. Relative permeability of PC95 is also described that inductance curve about change of current and compared with normal air gap inductor. The fifth part of the thesis deals with experiment of flyback converter with stepped-airgap transformer. Efficiency of converter is measured when the load is changed from high to low or low to high. The waveform is measured when the converter is entered the CCM, CRM and DCM. To verify theory the experimental results is confirmed by measured ring of vds voltage for extended CCM range over the entire load. The sixth part of the thesis deals with conclusion of flyback converter with stepped-airgap transformer. Stepped-airgap inductor advantage to improve the efficiency of flyback converter over the entire load range. The thesis researches the pros and cons of the stepped-airgap transformer. Stepped-airgap transformer using variable inductance will improve efficiency of other many converters, especially efficiency of magnetics components.