A HIGH FREQUENCY, HIGH EFFICIENCY, HIGH POWER FACTORISOLATED ON-BOARD BATTERY CHARGER FOR ELECTRIC VEHICLE Yuqi Wei Professor Adel Nasiri

Contents Introduction PFC unit LLC resonant converter 01 Introduction PFC unit 02 LLC resonant converter 03 Proposed topology 04 Magnetic control 05 Conclusions and future work 06

Switching frequency fs Design Considerations Inductor: Current ripple requirement Capacitor: Voltage ripple requirement Input voltage Uin 90V-264V Output power Po 330W-3.3kW Switching frequency fs 100kHz Output voltage Vo 400V Diodes: Current and voltage stress MOSFETS: Current and voltage stress Interleaved technology: Current is evenly shared

Simulation Verification Input voltage 90V 220V 264V Power factor and THD

Summary Topology Traditional Boost PFC Totem-pole bridgeless PFC SiC based Totem-pole interleaved bridgeless PFC Slow Diode 4 2 MOSFET 1(Si) 2(Si) 4(SiC) Fast Diode 1 Input Inductor Output Capacitor Semiconductors in Path 3 Efficiency Low High Best Operation Mode CCM DCM CRM CCM CRM CCM CRM DCM

Operation Analysis t2-t3 Operation waveforms t0-t1 t1-t2

Voltage Gain Region 1: At the right hand of both curves. In this region, the voltage gain is lower than 1, the input impedance is inductive and the switches can achieve ZVS, the diodes at the secondary side are hard switching; Region 2: At the right hand of the resistive curve and the left hand of line fs*=1. In this region, the voltage gain is higher than 1, the input impedance is inductive and the switches can achieve ZVS, the rectifier diodes can achieve ZCS; Region 3: At the left hand of both curves. In this region, the voltage gain can be higher or lower than 1, the input impedance is capacitive and the switches can achieve ZCS, the rectifier diodes can achieve ZCS. Voltage gain curve with different Q value

Why two LLC resonant converters and magnetic control? Battery charging profile Why two LLC resonant converters and magnetic control? System efficiency is improved; Power handling ability is improved; The EMI design is simplified; The complexity of control circuit is reduced. Proposed topology

Simulation Verification Operation point a b c d e f Charge mode CC CC/CV CV Output power/W 2070 2333 3319 2002 1140 362 Output voltage of LLC1/V 210.5 210.6 211.1 212.2 214.3 Output voltage of LLC2/V 58.5 113.3 211.2 208.6 214.4 226.4 Output current/A 7.69 7.20 7.84 4.77 2.67 0.82 Equivalent load resistance/ohm 35 45 54 88 160 538

Simulation Verification Output voltage of LLC1 and LLC2 Output power of the system

Introduction Inductance value versus dc bias current Typical structure of a variable inductor Operation principle for the variable inductor

Spice Modeling and Simulation Simulation result for the inductance value versus dc bias current Variable inductor model implemented in LTspice

Conclusions and Future Work In this paper, a high frequency, high efficiency and high power factor isolated on-board battery charger is proposed. The topology includes two parts, AC/DC power factor correction (PFC) circuit unit and DC/DC converter unit. The following characteristics are achieved.​ 1) For AC/DC part, the efficiency is improved by using SiC devices; the inductor volume and input current ripple are reduced due to interleaved technology; and the measured power factor is greater than 0.98 during the whole operation range, the THD of the input current is less than 5% under different operating conditions;​ 2) For DC/DC part, by carefully designing the resonant tanks for two LLC resonant converters, ZVS operation for the primary switches and ZCS operation for the secondary diodes are achieved during the whole operation range.​ 3) The EMI design is much easier and system control is simplified due to the magnetic control; therefore, a constant frequency can be implemented. The simulation verifies the operation of variable inductor. Future Work​ Hardware implementation and experimental validation are the focus of the future work.