AUTOMOTIVE DESIGN
assembly process, results in an inverter package of around 7kg dry weight with a sub-four-litre active component volume. This is compatible with the US Department of Energy Vehicle Technologies Off ice 2025 power density target of 100kW per litre. Assembly of the core elements
of the new inverter has been simplifi ed. The largest component
is the bulk capacitor, its physical size dictated by system parameters such as operating voltage, peak phase current, voltage ripple and switching frequencies. Employing next generation capacitor technology enables those dimensions to be minimised while retaining the performance characteristics and self-healing properties of a conventional capacitor. Segmenting the bulk capacitor
into smaller blocks further improves scalability, increases power density, and improves thermal performance.
THE POWER MODULE BorgWarner’s SiC based Viper power module is used in a single switch confi guration with dual-sided cooling, to deliver higher power density and eff iciency for extended range and better performance. The same footprint is retained regardless of power class, allowing the number and type of SiC dies and the cooling module design to be confi gured to suit the customer’s application. A die-attach process
is used to assemble the high- temperature SiC devices, screw mounting or laser welding for the power connections, and soldering for auxiliary connections. The fi nished power module is encapsulated with a new type of epoxy overmould compound and can operate with junction temperatures at or beyond the typical 175°C to reduce
system losses and improve current handling. Dual-sided cooling for the Viper
power module employs top and bottom heat sinks with a novel fi n design that optimises thermal performance and reduces system pressure drop within the cooling channels. Simple stamping and brazing processes are employed in manufacturing the scalable cooling module, which allows eff icient handling at high temperatures while keeping costs reasonable. Aluminum is used as standard, but copper may be substituted if necessary to meet thermal performance demands. High voltages and currents,
combined with the potential for rapid accelerative and decelerative forces mean that priority must be given to the electrical and dynamic safety of the electric vehicle drivetrain. With this in mind, BorgWarner set out to achieve Automotive Safety Integrity Level (ASIL) D – the top safety tier defi ned in the ISO 26262 standard – for its next-generation traction inverter. The modifi cations needed to render the inverter ASIL D compliant would normally mean increased component count with their associated extra cost, leading to a larger inverter package.
A SAFE SOLUTION The Inverter Safety System ASIC (INSSA) provides a reliable feedback loop for sensing, control, and actuation functions, while allowing controller and gate driver circuitry to share a single reduced-footprint mainboard. Each INSSA enables an independent power supply for the gate drive circuitry on each side of the high voltage supply, so a single point electrical fault in the inverter causes the system to react independently of microprocessor intervention. This is a major advantage of the latest BorgWarner technology; using voltage and motor speed measurements plus the fault signature ensures that the high voltage bus is always maintained within a safe range. The innovative design techniques
implemented in BorgWarner’s next- generation traction inverter have created a cost-balanced package with industry-leading fault-tolerant control architecture that complies with ISO 26262 ASIL D and satisfi es the VTO 2025 goal of 100kW/l power density. ●
For more information visit
www.borgwarner.com
It features a patented, dual-
sided-cooled SiC-based power switch that is 40% lighter and 30% smaller compared to
previous generations of inverters
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