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Overall Team Goal: create a smaller, lighter and more efficient traction inverter (motor controller for EVs) than industry.

 

  • Completed for fourth year design project

  • Team of four:

    • Me: mech for HV thermal components (design, analysis, manufacturing, validation)

    • 1 software

    • 1 electrical + controls

    • 1 mechanical for exterior + mounting

  • Timeline: September 2023 – March 2024

Results

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Assembly Level Design
Thermal Requirements
Thermal Solution Overview
Thermal Design Summary

Why Liquid Cooling?

  • Air cooling assy was too large – the team decided that the size was the most impressive part of the inverter

  • Decided using heat sink specs:

    • 1 large heat sink: 𝑅_𝑡ℎ = ∆𝑇/𝑄 = ((60−25)℃)/200𝑊

    • 18 small heat sinks: 𝑅_𝑡ℎ = ∆𝑇/𝑄 = ((60−25)℃)/11.11𝑊

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Cold Plate Overview
Material Selection

Coolant

  • Water:

    • Low viscosity

    • Good thermal properties

Cold plate

  • Al 6061:

    • Will not corrode

    • Good thermal properties

Fasteners

  • Zinc plated steel:

    • Will not corrode

Gasket

  • Silicone rubber, 60A hardness:

    • High melting point and low freezing point

Fittings

  • PVC:

    • Low pressure and moderate temperature application

    • Will not corrode

Considerations for hotter/colder operating temperatures

  • Consider if coolant will boil/melt

  • Consider if gasket material will melt/freeze or become brittle

Thermal Validation Summary

Using ASTM D5470:

  • Copper block simulates heat from MOSFETs.

Thermal Validation Results

  • Maximum simulation temperature is 34C (25C coolant temp)

  • Maximum real-life temperature will be less that 36C (25C coolant temp)

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Manufacturing Processes

Cold plate

  • Base: CNC mill

  • Lid: water jet

Gasket

  • Cut with scissors

  • Could also be laser cut or purchased

Busbars

  • Water jet then hand bent

Busbar Design
Manufacturing Improvements

  • Cold plate base can be created with a 3 axis CNC

    • Fittings moved

    • Thicker lid allows for counterbores

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  • High volume manufacturing

    • Cold plate can be cast

    • Use fittings with a quicker assembly

    • Busbars can be stamped

    • Gasket can be punched

Shape:

  • Busbars kept as short as possible to decrease losses, mass and EMI generation

Material:

  • Copper 110 (good electrical conductivity and workability)

Sizing:

  • Ampacity is dependent on cross sectional area

  • Current: 𝐼=𝑃/𝑉 𝑥 𝑆𝐹=(30 000𝑊)/600𝑉 𝑥 1.5=75𝐴

  • Dimensions are decided using standards found in literature for the given current: 12.7mm x 1.5875mm

Improvements:

  • Laminate the bus bars to decrease risk of EMI interference

(busbars were created by another group member)

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Bolted Joint Design

Goals:

  • Ensure the gasket is compressed enough to seal

  • Ensure the assembly can withstand the internal force due to the coolant pressure

Cold Plate Improvements
Gasket Design
Exterior Improvements
Traction Inverter + Cold Plate

2023 - 2024

Traction Inverter
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