Next Generation
Traction Inverter
Safe, Efficient and Compact
Version: November 2023

borgwarner.com
Next Generation
Traction Inverter

1/5BorgWarner has improved the performance, integration and reliability of its inverter technology by redesigning the power, cooling and control systems and simplifying production.

Background and Design targets
As electric propulsion continues to gain market

being the high voltage and current values, andshare against the internal combustion engine, it is

the potential for strong acceleration/deceleration.

vital to maintain this momentum by refining tech-BorgWarner set out to achieve Automotive Safety

nologies in preparation for the next generation ofIntegrity Level (ASIL) D, the top safety level de-electric drives. Major components such as batter-

fined in the ISO 26262 standard. The company’sies, inverters and electric motors must become

newly-developed Inverter System Safety ASIC

more compact while offering improved safety and(INSSA) would play an important role in reachingefficiency. This paper explores the measuresthis design target.

taken by BorgWarner to redesign the traction inverter to meet the latest market demands.

It was considered desirable to meet or exceed theUS Department of Energy (DOE) Vehicle Tech-

Taking into account the requirements of both pas-

nologies Office (VTO) 2025 goal of 100kW/liter

senger cars and medium power commercial vehi-

power density at a cost of USD2.7/kW or less. To

cles, an 800VDC system was indicated with RMS

assist in achieving this, BorgWarner limited thephase currents of 650A peak/400A continuous todesign size of the complete inverter package tocater for power ratings of up to 400kVA. The

four liters in volume.

power output could be scaled down by modifying
the number or size of certain components; for example reducing the silicon carbide (SiC) die countor capacitor footprint. Inverter performance andWith the basic system parameters determined,
BorgWarner identified a number of areas where
further innovation could improve existing inverter
designs; these are described below.

efficiency should be stable in an environment of 40 to +85°C and at altitudes of up to 5,000m. An
IP67 rated enclosure would protect against ingress of dust and water.
The electrical and dynamic safety of a traction inverter are dominant concerns, notable hazards

Next Generation
Traction Inverter

2/5Implementing design improvements
Power and cooling modules
Power scalability relies on BorgWarner’s estab-

Cooling for the power module is designed for opti-

lished Viper switch module. Starting with a single

mum performance but uses simple manufacturingswitch module of identical footprint for eachprocesses, a combination that yields a scalable

power class, the type and quantity of SiC diescooling module to efficiently handle high tempera-

and the cooling layout can then be varied totures at reasonable cost. Aluminum is the stand-reach the ideal solution for each application.

ard construction material, with copper substituted

The improved power device is a single switch
package with dual-sided cooling. Uniquely, it accepts various arrangements of different manufacturers’ bare SiC dies on the same substrate. The
high-temperature SiC devices are assembled using a die-attach process; power connections arescrew mounted or laser welded, and auxiliary
connections are soldered. A new type of epoxy
overmold compound encapsulates the package.
The finished module can operate with junction
temperatures at or beyond the typical 175°C, reducing system losses and improving current handling without increasing the SiC active materialarea.

where the highest thermal performance isneeded, depending on the power devices used in
the package. Dual-sided cooling is provided by
top and bottom heat sinks featuring a novel heatsink fin design. The fins optimize thermal performance and reduce system pressure drop within
the cooling channels, by modifying flow near thefin wall area to improve heat transfer from wall tocoolant. Dual-sided cooling also enables different
thermal interface materials (TIM) and various joining methods to be used on the top and bottom of
the power module. Each heat sink is manufactured by stamping the cover, base and coolingfins from high thermal conductivity copper alloy
then brazing the components together.

Controller design with INSSA
BorgWarner's newly developed Inverter System

Inverter modifications required to achieve ASIL D

Safety ASICs (INSSA) have been added to thecompliance inevitably lead to increased package

inverter’s electrical control architecture. Thesesize, component count and cost, but these areenable controller and gate driver circuitry to sharesignificantly offset by the addition of INSSA to thea single main board with a reduced footprint, anddesign. Each INSSA helps provide a fully inde-provide a high reliability feedback loop for sens-

pendent power supply to the gate drive circuitry

ing, control and actuation. Figure 1 shows a sin-on each side of the high voltage supply, so if agle control/gate driver board with the INSSA out-

single point electrical fault occurs in the inverter,lined in red.

the system can react independently of micro-Next GenerationTraction Inverter

3/5Figure 1: Next generation architecture with INSSA

processor intervention. It continues monitoring

the high voltage bus is always maintained within

the high voltage supply and motor speed, anda safe range.

uses those measurements and the current fault
signature to maintain a safe operational state.
This is a significant advantage of the latest
BorgWarner inverter technology; the INSSA’s
ability to monitor system diagnostic informationand command proper system usage ensures thatINSSA can also save additional space and costby eliminating the need for large dissipation resistors. Its active discharge feature can instead harness losses across the high voltage power modules to release energy from the high voltage buslines.

Component integration and assembly
System characteristics such as operating voltage

BorgWarner settled on the use of next generationand peak phase current of the electrical machine

capacitor technology to achieve a significant size

have a bearing on the design of the inverter com-

reduction but retain the performance and self-ponents, including power modules and bus bars.

healing abilities of conventional capacitors. A fur-

These characteristics, plus acceptable voltage

ther improvement in scalability was gained byripple and circuit couplings indirectly controlled bysegmenting the bulk capacitor into several

inverter switching frequencies and slew rates,

smaller blocks arranged in parallel, which brings

also define the physical size of the bulk capacitor,

the additional benefits of easier thermal manage-

the largest of the inverter components. For easement and reduced equivalent series resistanceof inverter scalability and to increase thermal per-(ESR). Laser welding the individual blocks to aformance and power density, methods of minimiz-

fully laminated DC bus bar sub-assembly gives

ing bulk capacitor size were investigated as partthe lowest equivalent series inductance (ESL)of the design process.

and maximizes performance. The segmentationof a bulk capacitor into six blocks can be seen inFigure 2.

Next Generation
Traction Inverter

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Figure 2: Segmented capacitors and modular bulk construction

The next generation inverter can now be built inand simplification of the construction process re-fewer stages; the bulk capacitor, HVAC bus bars,

sults in an inverter package with a dry weight ofHVDC unit, power module and main circuit board

approximately 7kg and a sub-four liter active

are assembled within the main housing, then thecomponent volume. Figure 3 shows the basic in-cover is mounted. Greater component integration

verter design.

SummaryBorgWarner innovations and design techniquesthat achieves ISO 26262 ASIL D compliance andhave successfully delivered a safe, efficient andthe VTO 2025 goal of 100kW/liter power density,

compact next generation traction inverter with in-all in a cost-balanced package.

dustry-leading, fault tolerant control architecture

Figure 3: Exploded view of next generation inverter design

Next GenerationTraction Inverter

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