Dr. Chris R. Gould

The University of Sheffield

United Kingdom

Design and Implementation Of A 4kW High-Frequency Resonant On-Board Bidirectional

Charger (OBBC) for EVs

“ecoCity eMotion” 24-25th September 2014, Erlangen, Germany

European Conference on Nanoelectronics and Embedded Systems for Electric Mobility

Presentation Outline

Introduction

OBBC Review & Comparison Results

Specification of 4kW HFT OBBC

Optimised CLL resonant tank design

Ideal Component Parameters

Full AC-DC System

Results

Summary

Introduction

In the Internet of Energy project (IoE), the UK demonstrator

at Haslar demonstrated a residential system comprising of

solar array, Li-ion battery storage system, 3-phase inverter

and Electric Vehicle (EV)

Introduction

In order to provide stabilization of the utility power supply

during peak-load times, the use of an EV traction battery

for energy buffering has been proposed

An On-Board Bidirectional Charger (OBBC) allows efficient

battery charging (Grid-to-Vehicle or G2V), whilst enabling

power to be fed back to the grid (Vehicle-to-Grid operation

or V2G)

Investigation into the weight, cost and efficiency trade-offs

between 50Hz grid-tied OBBC and high-frequency

resonant OBBC technologies has previously been

undertaken for 2.2kW µ-Class EV (NESEM 2013)

OBBC Variants

HighHigh--frequency Dual frequency Dual

Active Bridge (DAB) Active Bridge (DAB)

AC/DCAC/DC

GridGrid--tied 50Hz AC/DCtied 50Hz AC/DC

Making “ReMaking “Re--Use” of Use” of

EV InverterEV Inverter

2.2kW OBBC Comparison Results

??? Do charger malfunctions affect the drive system of the EV ???

Specification of 4kW OBBC

Single-phase UK residential utility supply currently runs at

230Vrms at a fused level of 13A (3kW)

Most solar installations are installed with a 4kW, 230Vrms

capability

The comparison matrix identified the HFT system as being

better suited to OBBC, and the idea is now extended to

4kW charging of an A-Class EV (Nissan Leaf specification)

Specification of 4kW OBBC

4kW On-Board Bidirectional Charger: features Efficiency under full load > 90% (4kW input power)

Input voltage 50Hz, 230Vrms +/- 10% (giving 380V DC-link)

Input current AC < 20 A

DC Output power 3.6kW @ 90% eff. during full charge of battery

DC Output voltage 240V (depleted) – 403V (fully charged) - Nissan Leaf

Control PWM for AC-DC, Frequency control for DC-DC

EMC standard IEC61000-1-1 and < 5% THD

Protection class Galvanic isolation

Cooling Air-cooled

Optimised resonant tank design

HFT turns ratio of N = 1.66:1 is selected to allow the

converter to develop a DC-link voltage of 380V+5% near

the series-resonant frequency (fsr) from a fully discharged

battery (240V)

Series-resonant frequency of 130kHz selected as a control

bandwidth limit – G2V mode operates below fsr and V2G

mode has to operate above fsr

Control Bandwidth of 100kHz – 170kHz is selected for

initial investigation (SiC will allow higher frequencies)

Normalised bandwidth-limited design procedure previously

investigated and published by USFD allows optimised CLL

resonant components to be selected

Component-based simulations validate operation points

Ideal component parameters

HFT system specification/metrics Primary turns 15 turns 20/84/0.071 Litz

Secondary turns 9 turns 20/84/0.071 Litz

Parallel inductance Lp 137µH (Gapped HFT)

Total series inductance Ls 97µH (Leakage + Discrete)

Series capacitance Cs 15.5nF polypropylene (Discrete)

Operating frequency 100kHz – 170kHz

Power rating 4kW (input)

Core material / type 3C95 / ETD59 cores

HFT + CLL DAB weight ~10Kg incl. fans

HFT + CLL DAB efficiency >90%

HFT + CLL DAB cost £539.70

N.b. MOSFETS are SiC

Full AC-DC System Flow-Diagram

Front-end AC-DC Resonant DC-DC

Full AC-DC OBBC System - Built

System volume ~ 450mm x 200mm x 110mm System weight ~10kg

Results – DAB - Charging

0 0.5 1 1.5 2 2.5

x 10-5

-500

-400

-300

-200

-100

0

100

200

300

400

500380V 45R 99kHz 10.04Ain 406Vout

Time (s)

Vo

lta

ge

(V

) /

Cu

rre

nt

(A)

Vchop

Isec x 10

VGS1

x 10

VGS2

x 10

0 0.5 1 1.5 2 2.5

x 10-5

-500

-400

-300

-200

-100

0

100

200

300

400

500380V 25R7 121kHz 625Ain 240Vout

Time (s)

Vo

lta

ge

(V

) /

Cu

rre

nt

(A)

Vchop

Isec x 10

VGS1

x 10

VGS2

x 10

(a) (b)

Resonant transformer current (secondary) with respect to switched bridge voltage

in charging mode for (a) fully charged battery, and (b) fully depleted battery

100kHz – 403V/9A DC out 125kHz –240V/9A DC out

Results – DAB - Discharging

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x 10-5

-600

-400

-200

0

200

400

600

Time (s)

Vo

lta

ge

(V

) /

Cu

rre

nt

(A)

Vchop

Isec x 10

VGS1 x 10

VGS1 x 10

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x 10-5

-600

-400

-200

0

200

400

600

Time (s)

Vo

lta

ge

(V

) /

Cu

rre

nt

(A)

Vchop

Isec x 10

VGS1 x 10

VGS1 x 10

403V in - 173kHz – 380V DC-link 240V in - 141kHz –380V DC-link

(a) (b)

Resonant transformer current (secondary) with respect to switched bridge voltage

in discharging mode for (a) fully charged battery, and (b) fully depleted battery

Results: Integrated and Front-End

(a) (b)

(a) 230V rms grid voltage providing 380V DC-link in charging mode for

a 380V battery voltage (maximum 3kW input power for UK 13A

utility)

(b) 380V battery providing 360V DC-link (threshold limit of 2.2kW

power back to grid before RCD trip limit = 210Vrms)

Integrated 3kW (380V/7.5A DC out) Front-End V2G (2.2kW into grid)

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05-400

-300

-200

-100

0

100

200

300

400

Time (s)

Vo

lta

ge

(V

) /

Cu

rre

nt

(A)

V

Grid

IGrid

x 10

VDClink

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05-400

-300

-200

-100

0

100

200

300

400

Time (s)

Vo

lta

ge

(V

) /

Cu

rre

nt

(A)

V

DClink

IGrid

x 10

VGrid

Summary

A 4kW HFT DAB OBBC has been designed and

constructed to validate its capability to bidirectionally

charge/discharge an EV battery of Nissan Leaf

specification with a CC-CV charging scenario (9A CC,

403V CV)

Practical validation of the DC-DC converter has been

achieved at the minimum and maximum operating points

Integrated testing of the complete AC-DC system in G2V

mode has been completed at a 3kW power rating

Integrated testing of the system in V2G mode has been

achieved at low power, but further research into the noise

and ringing on the SiC devices needs to be undertaken for

full system validation and control implementation

Internet of Energy

Thank you for your attention!

Questions ???

Contact: Dr. Chris R. Gould - c.gould@shef.ac.uk