electric drives challenges and solutions for the future drives challenges and solutions for the...

Electric DrivesChallenges and solutions for the future

Robert Eriksson

Nikitas Sidiropoulos

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Swedish Hybrid Center WS – Challenges with electric drives for vehicles Lund 2014-04-04

Robert Eriksson, Nikitas Sidiropoulos – Volvo Car Group 2014-04-04

VCC Electrification plan/ World leading PHEV

VCC’s history and Future regarding Electrification

• Efficiency in focus for 40 years

• Hybrid and Plug-In Hybrid vehicles studied and implemented

• World first Diesel PHEV

• BEV ”Test Fleet” cars, C30 Electric

• We plan for massive renewal of our product program with

Electrification as a key ingredients

2Robert Eriksson, Nikitas Sidiropoulos – Volvo Car Group 2014-04-04

Strategies for VCC 2015

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Green Connected

Safe


CO2 fleet average - 95 g by 2020Finding optimum customer

benefit at lowest possible

added cost

New attributes added

ZEV mandate

Local/regional requirements

Increased electrical power

higher efficiency.

Efficiency & Electrification

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CO2 reduction

Plug-In Technology

Kinetic Energy Recovery

Implications from Feature growth

Robustness to dynamic load


Electric DrivesChallenges and solutions for the future

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Nikitas Sidiropoulos M.Sc.Electric Drives System LeaderVolvo Car GroupApril 4th, 2014


Electric Drives – Present solutions

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IEM eRAD EMCIDD ISG

Generator power / 270-420 V Front Electric Drive SystemInverter: IGBT power modules (bondless) gen IElectric Machine: PMSM

Traction power / 270-420 V Rear Electric Drive SystemInverter: IGBT power modules (bonded) gen IElectric Machine: PMSM

V60 PHEV

Future eAWD PHEV


Electric Drives – Challenges of the future

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Advantages

- Proven technology

- High performance and driveability

- Electric efficiency and range….

Technical and commercial challenges

- Double Inverter and Electric machine systems → high system cost

- Expensive HV components such as HVAC cables and connectors

- EMC / EMF

- Thermal performance and lifetime of IGBT modules

- Scaleability

- Battery energy still expensive → further efficiency improvements needed

- Switching noise

- PMSM rare earth element cost fluctuation

- Compactness…


Electric Drives – Future solutions

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How do we face the technical and commercial challenges ?

Technologies under investigation:

- Single Inverter and Electric Machine system → topology impact

- Maximisation of common parts of Inverter and Electric Machines in different platforms / topologies

- Integrated Inverter and Electric Machine

- Next generation power module (bondless, more efficient, scaleable)

- Increased switching frequency / reduced IGBT losses with new materials such as SiC / GaN

- Electric Machine with reduced REE content


Electric Drives – Future solutions – eFAD/HyFAD

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Single Electric Drive system

Maximisation of common parts with eRAD topology

Advantages

- Single Electric Drive system → reduced system cost

- Inverter parts commonality with ISG/eRAD topology

- Strategic partnership with Electric Drive system supplier

Challenges

- Increased complexity (Electric Machine – transmission interface)

- Engine bay package

C30 EV

Future EV

Future FWD PHEV


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Integrated Electric Drive

Advantages

- Elimination of HVAC cables, connectors, brackets ... → part numbers and cost reduced

- Significant weight reduction

- Free space can be used for spare wheel or increased luggage capacity

- Improved EMC

- Common parts with Front Electric Drive components

- C/o Electric Machine from present solution

- Could be used for both eRAD and eFAD topology

- Could be an enabler for high power charger

Challenges

- Vibration withstandability of power electronics

- Packageability in engine bay (HyFAD topology)

- Investment

- Scaleability

Inverter and Electric Machine as one unit

Integrated cooling and housing

Using next generation of power module

Package protected for all targeted platform variants

Close co-op with strategic partner

Decision for production pending

Electric Drives – Future solutions – IED


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Next generation power module (~2017)

Advantages

- Improved thermal performance and life time (~8 x higher for VCC customer profile)

- Reduced inverter losses and improved vehicle duty cycle efficiency (range & CO2)

- Package protected

Challenges

- IGBTs in <200 V region (Mosfet can be more efficient but no commonality with 400 V)

- High temperature operation

From bonded wires → bondless technology

Sintered – no solder joints

Reduced conduction and switching losses by use of more efficient chip

Improved scaleability (phase current rating 400 – 700 A, voltage rate 650 V)

Power cycling and life time studied with in-house developed software tool

(rainflow analysis of IGBT and Diode delta Tj)

Increased in-house SW control

Electric Drives – Future solutionsNext Gen power modules


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SiC / GaN power module (~2020)

Advantages

- Smaller chip size

→ compactness

→ lower switching losses

→ enabler for higher switch frequencies (16-20 kHz) & reduced switching noise

& lower DC link capacitance

Trade off versus

- Reduced conductive losses and improved vehicle duty cycle efficiency

- Thermal capability

Challenges

- Cost (SiC module today ~ same cost as complete inverter)

- Chip size, current capability & manufacturing (material imperfections, difficult to process)

- Tier 1 ability / willingness to shift to new power module technology

Improved material enables smaller chip for same current rating compared to Si

SiC Mosfet 600-1200 V (switch transient in VCC applications <750 V)

GaN Fet 70-600 V

SiC thermal conductivity ~3 x better than Si

Mosfet Ron @ 1 kV

Si 10000 mΩ•mm2 (3600)

SiC 35 mΩ•mm2 (13)

GaN 2.8 mΩ•mm2 (1)

→ much smaller conductive losses for same chip size

OR

→ same conductive losses but for much smaller chip size

Electric Drives – Future solutions – SiC / GaN


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EM with reduced REE content

Advantages

- Less Nd, Dy and thus lower component cost and sensitivity to market price

- Close co-operation with supplier to ensure feasiblity

- C/o Inverter and stator solution with conv. PMSM (tbd)

- Could be used for both eFAD (larger space available) and eRAD applications

- Could be an enabler for sensorless drive (if Ld/Lq distinction kept at saturation)

Challenges

- Performance with same active dimensions as conv. PMSM design

- Harmonics

Idea: MBPM – Multi Barrier Permanent Magnet Machine

Similar to conv. PMSM but higher utilisation of reluctance

Volvo Cars in-house study of different rotor designs

Maxwell used as software tool

Target is to reduce magnet content with ~20% and keep acceptable performance density

Other machine concepts such as IM, SyRM, SRM and EMSM benchmarked and studied

→ conclusion is that torque and power density is too inferior to meet VCC installation requirements

Electric Drives – Future solutions – MBPM


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