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TRCDRIVE Pack with SiC Module Helps Shrink EV Inverters

July 2, 2024
SiC power devices continue to gain popularity in electric powertrain system development, but achieving low loss in a small size has been difficult. ROHM confronts that challenge in powertrains with its TRCDRIVE pack.

For the electrification of cars to assist in achieving a decarbonized society, the development of more efficient, compact, and lightweight electric powertrain systems must continue to progress. And while silicon-carbide (SiC) power devices are attracting attention as key components, achieving low loss in a small size has been a difficult challenge. 

ROHM addresses those issues in powertrains with its TRCDRIVE pack. The TRCDRIVE pack supports up to 300 kW and features high power density and a unique terminal configuration, helping solve key challenges of traction inverters in terms of miniaturization, higher efficiency, and fewer man-hours needed in design.

TRCDRIVE’s Optimized Internal Layout

The TRCDRIVE pack reduces switching losses by optimizing the internal layout to achieve a small inductance of 5.7 nH. What’s more, incorporating low on-resistance, 4th-generation SiC MOSFETs results in a current density of 19.1 A rms/cm2 (BST780D12P4A163), with an output current greater than 600 A rms for both 750-V-rated (e.g., BST740D08P4A154) and 1,200-V-rated (e.g., BST780D12P4A163) models.

The TRCDRIVE pack will have a lineup of 12 models in different package sizes (small/large) and mounting patterns (TIM: heat dissipation sheet/Ag sinter). In addition, ROHM is developing a 6-in-1 product with built-in heatsink that’s expected to facilitate rapid traction-inverter design and model rollout tailored to a variety of design specifications.

The company has four new models as part of the TRCDRIVE pack series with 2-in-1 SiC molded modules (two 750-V-rated, BSTxxxD08P4A1x4 and two 1,200-V-rated, BSTxxxD12P4A1x1) optimized for electric-vehicle traction inverters. Traction motors in electric cars are driven by three-phase AC power with a phase shift of 120 degrees. 

Traction inverters convert direct current supplied from the battery into three-phase alternating current. To convert DC into three-phase AC, one high-side and one low-side MOSFET are required per phase for switching. A 2-in-1 configuration combines both of these MOSFETs into a single module (note that the x-in-1 configuration of the drive unit in the main body of the xEV differs from the x-in-1 configuration in the traction inverter).

SiC Molded Modules Target Traction Inverters

A trademarked brand for ROHM, SiC molded-type modules were developed specifically for traction-inverter drive applications. The TRCDRIVE pack reduces size by utilizing a unique structure that maximizes heat dissipation area. The pack is said to deliver equivalent heat dissipation performance to that of competitor's products in a smaller single-sided heat dissipation design through a proprietary molded module structure. 

In addition, ROHM’s 4th-generation SiC MOSFETs are built in. That results in what’s claimed to be a power density 1.5X higher than that of general SiC molded modules, while greatly contributing to the miniaturization of xEV inverters.

The modules are equipped with control signal terminals using press-fit pins, enabling easy connection by simply pushing the gate-driver board from the top, considerably reducing installation time. In addition, low inductance (5.7 nH) is achieved by maximizing the current path and utilizing a two-layer busbar structure for the main wiring, contributing to lower losses during switching.

Despite developing modules, ROHM has established a mass-production system similar to discrete products, making it possible to increase production capacity by 30X compared to conventional SiC case-type modules, according to the company.

Supporting TRCDRIVE Materials

ROHM states its commitment to providing application-level support, including the use of in-house motor testing equipment. A variety of supporting materials are also offered, such as simulations and thermal designs that enable quick evaluation and adoption of TRCDRIVE pack products.

Two evaluation kits (EVKs) are available, one for double-pulse testing and the other for three-phase full bridge applications, enabling evaluation in similar conditions as practical inverter circuits. In the EVK for Double-pulse Test, for example, pre-connected, screw-fastened external terminals eliminate the need for additional terminal welding. No dedicated capacitors are required, enabling evaluation in standard various environments.

ROHM independently develops SiC technologies ranging from wafer fabrication and production processes to packaging and quality-control methods. At the same time, to solidify its position as a SiC supplier, ROHM notes that it has established an integrated production system throughout the manufacturing process.

Read more articles in the TechXchange: Silicon Carbide (SiC).

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