Usama Anwar, Hyeokjin Kim, Hua Chen, Robert Erickson, Dragan Maksimović and Khurram K. AfridiColorado Power Electronics Center, ECEE Department

University of Colorado Boulder

Compact On-board Drivetrain-Integrated Level II Electric Vehicle Charger

SELECT Annual Meeting and Technology Showcase – Logan, Utah – September 27-28, 2016

INTRODUCTION On-board electric vehicle (EV) charger size and weight reduction helps:

Incorporate higher power (Level II) on-board chargers

Minimize vehicle styling constraints

Reduce range anxiety

Accelerate EV adoption

Existing approaches to incorporate on-board Level II chargers: On-board charger separate from drivetrain power electronics – adds excessive size and weight

On-board charger integrated with drivetrain using traction motor windings – adds complexity, cost and reliability issues

Recently proposed composite boost converter provides opportunity for new approaches for charger integration Composite boost converter has superior performance than conventional boost converter

Comprises buck, boost and DCX modules

Utilizes lower voltage devices due to stacked nature

Modular nature allows multiple options for on-board charger integration

ALTERNATIVE DRIVETRAIN INTEGRATED CHARGER ARCHITECTURES

Architecture A

Bridgeless Boost + PSFB converter

Achieves low level of integration

Only utilizes composite converter filter

SELECTION OF DRIVETRAIN INTEGRATED CHARGER ARCHITECTURE

SUMMARY AND CONCLUSIONS

OPPORTUNITY Goal of research is to identify and develop optimal way to integrate on-board charger with EV drivetrains utilizing

composite boost converter: Achieve on-board Level II charging functionality with minimal additional size and weight, while maintaining high efficiency

Maximize reuse of existing drivetrain parts

Minimize additional switches and passive components

Architecture A

Architecture B

Architecture B

Rectifier + PFC Boost Isolated DC/DC converter + Buck converter

Achieves high level of integration

Reduced efficiency due to hard switching in Isolated PFC Boost converter

Architecture C

Architecture D

Architecture C

Bridgeless Boost + DAB + Buck converter

Achieves high level of integration

Energy buffering at two places

Architecture D

Bridgeless Boost + DAB + Buck converter

Three winding transformer reduces weight

Achieves high level of integration

Energy buffering at two places

Architecture D selected as it offers best tradeoff between weight and losses

Designed using Silicon super-junction FETs

Interfaced with existing drivetrain by adding third winding to DCX transformer

Energy buffering at two places reduces capacitor weight

Added Module:

PFC bridgeless boost converter + H-bridge + one transformer winding

Proposed architectures compared in terms of added weight and losses

Factors considered for comparison: Weight of added charger module components:

capacitors, inductors, heat sink

Losses introduced by added components

Architecture Added Weight [kg] Losses [W]

A 2.67 238

B 1.97 322

C 2.07 268

D 1.90 265

Recently proposed drivetrain composite boost converter well suited for on-board charger integration

Four alternative approaches for achieving charger integration explored and quantitatively compared Selected charger architecture only adds bridgeless boost converter, one

H-bridge and one extra winding to the existing converter

PFC stage of the selected charger architecture uses a bridgeless boost converter The converter is operated in DCM at 20 kHz

Hybrid feedforward control architecture is used to achieve PFC functionality

Effective zero crossing mitigation techniques employed to achieve natural commutation of input current between the half bridge legs

Second stage DAB is controlled by introducing phase shift between primary and secondary H-bridges

Third stage boost converter regulates battery power by controlling input current. Current reference is generated by sensing input voltage of the converter

POWER FACTOR CORRECTION STAGE

Measured zero crossing

Hybrid feedforward control eliminates high bandwidth current sensor

Control objective: 𝑖𝑖𝑛 𝑇𝑠 =𝑣𝑖𝑛

𝑅𝑒

Inductor current

𝑖𝑖𝑛 𝑇𝑠 =𝑇𝑠2𝐿

.𝑑2

1 −𝑣𝑖𝑛𝑣𝑜𝑢𝑡

𝑣𝑖𝑛

Duty cycle modulation equation:

𝑑 =2𝐿

𝑅𝑒𝑇𝑠1 −

𝑣𝑖𝑛𝑣𝑜𝑢𝑡

Zero crossing distortion mitigated by switching both switches with same duty cycle command around input voltage zero crossing

Efficiency

Switching Waveforms

Low Power

6.6kW Results

Input voltage and current and output voltage waveforms

REFERENCES U. Anwar, D. Maksimovic and K.K. Afridi,

“Generalized Hybrid Feedforward Control of Pulse Width Modulated Switching Converters,” IEEE Workshop on Control and Modeling for Power Converter (COMPEL), Trondheim, Norway, June 2016.

B. Whitaker, A. Barkley, Z. Cole, B. Passmore, D. Martin, T. McNutt, A. Lostetter, J. S. Lee, K. Shiozaki, “A High-Density, High-Efficiency, Isolated On-Board Vehicle Battery Charger Utilizing Silicon Carbide Power Devices,” IEEE Transactions on Power Electronics, vol. 29, no. 5, May 2014.

J. Sun, “On the Zero-Crossing Distortion in Single-Phase PFC Converters,” IEEE Transactions on Power Electronics, vol. 19, no. 3, May 2004.

R.W. Erickson and D. Maksimović, Fundamentals of Power Electronics, Second Ed., Kluwer Academic Publishers, 2001

ISOLATION AND REGULATION STAGESDual Active Bridge Isolation Stage

Each half bridge switches at ~50% duty cycle

Output voltage regulated by control of primary and secondary phase shifts

ZVS can be achieved on both primary and secondary H-bridges

DAB output capacitor performs energy buffering

Input and output voltage waveform

Boost Power Regulation Stage

Regulates power flowing into the battery

Controls input current and generates current reference by sensing input voltage

Simulation Results

Inductor current waveform

Boost converter topology, model and control architecture

Converter simulation waveforms