Boost Composite Converter Design Based on Drive Cycle Weighted Losses in Electric Vehicle Powertrain Applications

Hyeokjin Kim, Hua Chen, Dragan Maksimović, and Robert EricksonDepartment of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, Colorado, 80309

30 kW composite converter prototype experimental results

Driving Cycle

ConventionalBoost converter

CompositeBoost converter

US06 93.3 % , Q=13.9 98.4 % , Q=61.5UDDS 97.1 % , Q=33.5 99.0 % , Q=99.0

HWFET 91.8 % , Q=11.2 98.1 % , Q=51.6CAFE 94.7 % , Q=17.9 98.6 % , Q=70.4

DCX Pri. Sw. node voltage

DCX Sec. Sw. node voltage

Buck Sw. node voltage

Boost Sw. node voltage

DCX Pri. Tx. current

Buck inductor current rippleBoost inductor current ripple

Conclusions

Weighted loss method for converter optimization

EV powertrain simulation model

EV power conversion unit

Vehicle simulation parameterVehicle weight (Curb + occupants) 1493 + 250 Kg

Maximum speed 95 mphGear ratio 7.15

Motor poles 6Nominal battery voltage 250 V

Maximum inverter DC voltage 800 V

Number ofdata

Computation Time

[Normalized value]

US06average

efficiencyN = Full data 1

96.0 %N = 128 0.0011N = 64 0.0007N=16 0.0003N = 4 0.0002

94.9 %N = 1(most used op.) > 0.0001

𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 = �𝑛𝑛=1

𝑁𝑁

𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑜𝑜𝑜𝑜 𝑛𝑛 × 𝑝𝑝𝑝𝑝𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑙𝑙𝑝𝑝𝑝𝑝𝑦𝑦𝑜𝑜𝑜𝑜 𝑛𝑛

30 kW composite converter prototype

Buck / BoostMOSFET IPW65R041CFDSwitching frequency 20 kHzInductance 60 µH / 48 µHInductor core METGLAS

DCXMOSFET IPW65R041CFDSwitching frequency 33 kHzTank inductance 4.5 µHTransformer ratio 8 : 12Transformer core Ferrite

Design summary

• Decouples battery and machine optimization

• Inverter, motor, and system efficiencies can be higher, compared to the a battery-inverter architecture.

• Boost converter design significantly contributes to the system efficiency.

Power conversion unit consisting of a motor inverter and a boost converter

AbstractA weighted design optimization is introduced to minimize total loss of electric vehicle drivetrain power electronics over EPA standard drive cycles. It is shown that the net loss of the conventional boost converter can be reduced by a factor of 1.5 with this approach, while computational effort is reduced by three orders of magnitude. Even larger efficiency improvements are achieved by optimized boost composite converters: losses are reduced by factors of 4.5, 2.9, and 4.3 for US06, UDDS, and HWFET driving cycles, respectively. These design optimizationresults are experimentally verified with a 30 kW laboratory prototype boost composite converter, which demonstrates 98.4% average efficiency over the US06 driving cycle.

• Vehicle parameters are imported from Nissan LEAF vehicle.• Motor parameters are estimated based on Parker PMAC motor.• Variable DC bus voltage control scheme is employed for inverter DC bus

voltage control.

US06 driving cycle simulation

Speed schedule of US06, required inverter bus voltage, and magnitude of motor power

Density plot on power vs. bus volt.Darker shadings represent higher frequency counts.

• Brute-force, point-by-point loss evaluation over a drive cycle requires a prohibitively large computational effort.

• Weighted loss method is proposed to reduce computational effort without loss of accuracy.

Most frequently encountered power vs. bus voltage over US06

Probability of most frequent power at corresponding bus voltage

Computation time and projected average efficiency as function of N

• Based on the weighted loss, composite boost converter is optimized and designed.

• Required bus voltage and power are distributed over a wide operating range which necessitates boost converter optimization.

• Finding optimum set of design parameters to minimize weighted loss.• N is number of operating points considered for optimization.• For larger N, a more accurate optimization result is obtained, but the

computation time increases proportionally.• Compared to the brute-force approach (N= Full data), the weighted loss

model with N=16 reduces the computation time by more than 3 orders of magnitude, with essentially no loss in accuracy.

Measured waveforms at 250 Vin, 650 Vbus, 15kW

Average efficiency and converter quality factor Q = Pout/Plossover US06, UDDS, or HWFET driving cycle of conventional boost or composite boost converter

• Weighted loss method is further applied to the composite boost converter[1].

• Composite converter achieves loss reduction by a factor of 4.5, 2.9, and 4.3 over US06, UDDS, and HWFET driving cycles, compared to the conventional boost converter.

References

• Composite boost converter achieves 98.6 % peak efficiency at 250Vin, 650Vbus, 15 kW and maintains high efficiency over a remarkably wide operating range.

1. H. Chen, K. Sabi, H. Kim, T. Harada, R. Erickson, and D. Maksimovic, “A 98.7% efficient composite converter architecture with applicationtailored efficiency characteristic,” Power Electronics, IEEE Transactions on, vol. 31, no. 1, pp. 101–110, 2016.

Comparison of measured efficiency,loss model efficiency, and conventional DC-DC converter efficiency at 250 Vin, 650 Vbus vs. power

Efficiency contour plot at 250 Vin in the bus voltage vs. power plane, and operating points over US06

• Required operating points over EPA standard driving cycles are distributed over wide operating range which necessitates boost converter optimization.

• Weighted loss method is introduced to reduce the number of operating points to be considered, resulting in substantially reduced computing effort without loss of accuracy.

• 30kW laboratory composite boost converter projects 98.6% CAFE efficiency and 70.4 of converter quality factor.

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