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

2. Contents Introduction PFC unit LLC resonant converter01
Introduction
PFC unit 02
LLC resonant converter 03
Proposed topology 04
Magnetic control 05
Conclusions and future work 06

3. 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

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

5. 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

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

7. 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

8. 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

9. 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

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

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

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

13. 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.