Power

SiC IPMs scupper range anxiety in electric vehicles

12th April 2021
Caroline Hayes

 

Shifting focus from the battery to the drivetrain in electric vehicles allows design engineers to optimise the use of SiC in intelligent power modules

 

The migration of transportation to the next generation of advanced core technologies has been a disruptive, but necessary, evolution. Since the car took a dominant role in human society in the 1930s, it has had a huge impact on every aspect of society. The role of the vehicle is so important to today’s way of life that any changes, however useful and/or necessary, impact us all in multiple ways.

Even vehicles using a fossil-fuelled powertrain will have an extensive suite of vehicle to everything (V2X), IoT, and infotainment/navigation/social software and hardware systems.

Range anxiety and power electronics

The fear of running out of fuel and being stranded in an electric vehicle (EV) without sufficient operational range to go any further has caused many people to reject EVs as a viable transport option. Range anxiety tends to focus on battery capacity, when it is actually equally important that the drivetrain and automotive system electronics are highly efficient and capable of high power optimal performance under demanding conditions.

That is why the EV industry is embracing wide-bandgap semiconductors, especially silicon carbide (SiC), to address the advanced demands of next generation automotive power electronics. SiC power transistors are displacing silicon counterparts because of their low on-resistance at high blocking voltages, high switching speed, and next-level thermal performance.

These attributes enable design engineers to create power systems with significant reductions in size and weight, while also significantly increasing efficiency; this is required for motor drives and battery chargers. An EV using SiC-based power systems helps to address range anxiety and can even allow automotive engineers to reduce battery size to bring weight and form factor advantages to the vehicle design for aereodynamic and performance improvements.

Adoption and integration

Wide-bandgap solutions have long been accepted, so now the pressure has shifted to the need to optimise that integration of SiC devices into the automotive drivetrain. This has created some concern from those without the depth of resources needed for the design and development effort required to create those solutions.

Recent advances in convergence and device integration have resulted in the creation of intelligent power modules (IPMs). These address development challenges by offering highly integrated, drop-in building blocks. Being able to build on an established foundation accelerates time to market while saving engineering resources. The potential problems involved in the migration to SiC can be shrunk drastically by adopting devices such as SiC IPMs (Figure 1) from manufacturers with expertise from developing SiC power modules and gate drivers.


Figure 1: Cissoid’s SiC intelligent power module (IPM)

For example, the CXT-PLA3SA12450 is a three-phase 1200V/450A SiC MOSFET IPM integrating power switches and a gate driver based on the CISSOID HADES2 chipset. The module serves high density power converters at high junction temperatures of up to 175°C. The IPM gives designers access to all of the benefits of SiC technology to achieve high power density, thanks to low switching losses and high temperature operation.

The integration of a SiC power module with a gate driver optimised to drive it not only shortens design cycles, it increases confidence in system performance. Mechanical, electrical and thermal modelling of the power module is also easier and using a base module supports the creation of families of power inverters or active rectifiers.

Dynamic and flexible IPMs

The SiC IPM can rapidly adapt to dynamically changing voltage/current requirements. The integration of the gate driver, together with the power module, gives direct access to a fully validated and optimised solution in terms of switching speed and losses, robustness against high dI/dt and dV/dt, and protection of the power stages.

The three-phase SiC MOSFET IPM has low conduction losses, 3.25mΩ on resistance, and low switching losses, with 8.3mJ turn-on and 11.2mJ turn-off at 600V/300A.

The IPM is water-cooled through a lightweight aluminium SiC (AlSiC) pin-fin baseplate for a junction-to-fluid thermal resistance of 0.15°C/W. The power module is rated for junction temperature up to 175°C and withstands isolation voltages up to 3600V (50Hz, 60s).

The high level of integration of the power module with gate driver and ALSiC baseplate allows rapid mechanical integration with the other elements of the power converter, such as the DC bus capacitor and the reference cooler.

The built-in gate driver includes three on-board isolated power supplies (one per phase) delivering each up to 5W per phase allowing to easily drive the power module up to 25KHz and at ambient temperatures up to 125°C. Peak gate current up to 10A and immunity to high dV/dt (>50KV/µs) enable fast switching of the power module and low switching losses.

The IPM also has under-voltage lockout (UVLO), active miller clamping (AMC), desaturation detection and soft-shutdown (SSD).

The system designer may also save a lot of time having access to an accurate 3D model of the IPM, including the gate driver, from the very start of development. Power converter design is also supported with an LTSpice model of the IPM. Figure 2 shows an IPM 3D model which enables virtual mechanical integration together with other elements of the power converter, for example the DC Bus companion capacitor or the liquid cooler.

Figure 2: The IPM 3D model showing integration with a DC bus companion capacitor or the liquid cooler

Driving forward

The next generation of advanced EVs will have SiC-based power systems, as they can provide the performance levels needed to address issues such as user range anxiety, system energy density, and overall thermal management. Using an IPM like the CXT-PLA3SA12450 can ensure design goals are met cost-effectively. Co-integration of the power module and gate driver enables it to be directly used as a foundation in power conversion designs.

About the author:

Pierre Delatte is chief technology officer, CISSOID

 

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