Electric Motor Thermal Optimization for Hybrid Vehicle Application

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Demand for electric motor capable of running at Higher-power duty cycles will continue to rise As Over-sizing the electric machine is getting costly, thermal efficiency improvement has much more important role to play Customer wants most efficient motor with higher

o Cost ($/kW) o Weight (kW/kg) o Volume (kW/L)

Efficient thermal management can improve power capability within cost/efficiency constraints as well as improve performance of an electric motor

Introduction

Source: http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2011/adv_power_electronics/ape030_bennion_2011_o.pdf

Left side of the triangle is the

specification

Right Side is the performance

At the top is the application,

middle is component and at

bottom is the thermal

Thermal Design Optimizationn Hierarchy

Source: http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2011/adv_power_electronics/ape030_bennion_2011_o.pdf

Motor Thermal Optimization Paths

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Motor Thermal Optimization Strategy

Motor Thermal

Optimization

Specification/Application Driving Profile Optimization Points Transient & Continuous Thermal Operating Points Full Load Curve Efficiency Max allowable losses at optimization points Temperature limits Geometry Restriction Cost

Packaging /Mechanical Constraints Machine Type Geometry Materials Thermal Resistance Circuits

Cooling Optimization Cooling Fluid Cooling Mechanism ( Jacket, Fin, Jet) Flow optimization Area Enhancement Thermal transport

Design Selection Flowpaths: Hybrid, Spray nozzle, Oil Flow rate (Cooling) Operating Points (Customer) Cost

Cooling Performance

(UA)

Thermal Resistance

(Rth )

Loss Calculation

Thermal Load Distribution

Thermal Modeling

Thermal Optimization

Source: http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2011/adv_power_electronics/ape030_bennion_2011_o.pdf

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Motor Thermal Optimization Strategy

Motor Thermal

Optimization

CTS

o Develop Heat Generation Model o Review Past Motor Thermal Test Data

Thermal Model

o Develop Thermal Model o Debug and Correlate Thermal model

Cooling Technology

Selection

o Identify Cooling limitations o Identify Areas of Improvement

o Pugh Matrix for multiple New Concepts o Customer Collaboration for Optimum Design

Design Selection

Source: http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2011/adv_power_electronics/ape030_bennion_2011_o.pdf

Motor Thermal Optimization Strategy

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Electro-Magnetic FEA Thermal Resistance Circuit

Thermal Equivalent Motor Circuit

Motor Node Temperature Prediction

Motor Losses

Resistance Value

Source: http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2011/adv_power_electronics/ape030_bennion_2011_o.pdf

Customer Driving Profile

Motor Thermal Optimization Strategy

Source: www.fueleconomymy.gov http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

Source: http://techno-fandom.org/~hobbit/cars/heatgames/results-03.html

Source: www.fueleconomymy.gov http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

As electric motor efficiency varies based on load points, motor must operate at most efficient points Thermal optimization should be based on customer specific performance points Typical such points usually defined by following:

Speed (RPM) Torque (Nm) Energy Loss (Kj) Duration (Sec)

Motor Thermal Optimization: Typical Driving Profile

Motor Thermal Optimization: Typical E-mag Results

Motor Thermal Optimization: Typical Motor Nodal Circuit

−

−

−

−+=

−−f

ff

TR

TR

TR

TRRRcmdt

dT 11111116

162

1_21

161_211

1

Conductive Resistance

Motor Nodal Thermal : Governing Equations

g

nj

j ji

ijipi Q

RTT

dtdTcm

i+

−=∑

=

=1 _

Governing Equation

∆=

LTKAqconduction

KAL

TTq ji )( −=

KALRcond =

Convective Resistance

ThAqconvection ∆=hA

TTq ji

1)( −

=hA

Rcond1

=

Typical Nodal Solution for Temperature

Get Coolant Property Inputs

(Flowrate & Temperature)

Get Motor Load Inputs (Speed, Current, Voltage)

Check if Inputs are Valid

No Take Default Action

Define Thermal Resistance Network at

Time = T

Yes

Calculate Change in Temperature Between Time =T and

Time = T-TaskRate

Add Change in Temperature To

Temperature from Previous TimeStep

Motor Thermal Nodal Model: Solution Tree