Reducing the Size of xEV Inverters

­Mobility is a key part of our daily life. The rapid move to carbon-neutral and energy-efficient means of transport is making an important contribution to a greener future. Development of electric drives that are more compact, efficient and also lighter has a key part to play here - not only in promoting greater interest and use of the next generation of electric vehicles (xEVs) but also hitting environmental targets such as carbon neutrality. Improved drive inverter efficiency is extremely important in this regard, particularly for electric vehicles, as this allows the range to be extended and the size of the on-board battery to be reduced.

The importance of silicon carbide in the automotive industry is undisputed. Sales figures from the last few years confirm that the transformation towards electric mobility is continuing to drive growth, particularly in the European and Asian automotive industry. ROHM supports this transformation on a sustainable basis through multiple confirmed cooperations with manufacturers of vehicles and traction inverters.

Two-Year Development Cycle Promotes Innovation

To support the progress of innovation in the automotive industry, ROHM has announced that it will be reducing the development cycle of its SiC generations to two years. However, components will definitely not be phased out because of this. Thanks to ROHM’s production capacities, older generations can continue to be produced. Depending on the life cycle of the products, this means that the requirements can still be met with regard to component availability for long-term industrial applications.

ROHM adopts the “brownfield” approach to ensure success when producing newly developed products. Thanks to retrofitting and modernisation of existing factories, such as the Miyazaki facility, production of 8-inch substrates is plannedto begin this year. This reduces the construction time of production sites by two years over a new building, since the infrastructure already in place can be used. ROHM will then able to increase production of modules by a factor of 30 over conventional SiC housing modules. Production of 5th generation SiC MOSFETs on 8-inch substrates would be expected to significantly increase production capacity.

In addition to this, ROHM and Toshiba have announced a cooperation for the manufacture of power semiconductors. The Japanese Ministry of Economy, Trade and Industry (METI) is supporting this plan, the aim of which is to ensure a stable and secure supply of semiconductors. Both companies are investing intensively in the production of silicon carbide (SiC) and silicone (Si) power semiconductors in order to improve their supply capacities, as well as make optimum use of one another’s production capacities.

SiC as a Key Component in the Field of Electric Mobility

However, ensuring low losses while maintaining a compact size represents a major challenge for SiC power components. ROHM is attempting to solve this dilemma with the company’s TRCDRIVE pack.

TRCDRIVE pack is a trademark for SiC modules from ROHM that have been developed specifically for traction inverter applications and feature a reduced size thanks to a unique structure for maximising the heat dissipation surface. Integration of ROHM’s 4th generation SiC-MOSFETs with low ON resistance offers industry-leading power density, which is 1.5 times higher than with conventional SiC modules. At the same time, it makes a significant contribution to the miniaturisation of inverters for xEVs.

The TRCDRIVE pack modules from ROHM are half-bridge modules that are equipped with 4th generation SiC FETs. These modules are designed in such a way that they offer high current density and low switching losses. Modules such as these support the automotive industry in driving forward the technological change and supplying highly efficient drives.

The TRCDRIVE pack excels through its performance. A one-sided, highly thermally conductive housing ensures easy installation and a high current density. An optimised internal arrangement allows a very low inductance of just 5.7 nH to be achieved. This is made possible by a two-layer busbar structure, which maximises the current path. Thanks to a very low ON resistance (R_DS(on)), an industry leading current density of 19.1 Ampere/cm² can be achieved. The modules are available for voltages of 750 V and 1,200 V.

Offering power of up to 300 kW and outstanding power density, the module contributes to satisfying the most important requirements of traction inverters in terms of miniaturisation, greater efficiency and lower development costs. The modules have control signal terminals with press-fit pins, which facilitate easy connection by simply being plugged into the gate driver board from above.

TRCDRIVE pack will be integrated in a series of twelve models in various housing sizes (small / large) and mounting patterns (TIM: heat deflection plate / Ag sintering) by March 2025. In addition to this, ROHM is developing a 6-in-1 product with integrated heat sink. This facilitates a fast design process for drive inverters, as well as early market launch of models that are tailored to handle a large number of design specifications.

Click image to enlarge

Figure 2: TRCDRIVE pack product range

User support

ROHM offers extensive support at application level, including use of its in-house motor testing equipment. In addition to this, the company makes a large number of auxiliary materials available. These include simulations and thermal designs that facilitate rapid evaluation and introduction of TRCDRIVE pack products. Two evaluation kits are also available: one for double pulse tests and the other for 3-phase full bridge applications. These facilitate evaluation under similar conditions as practical inverter circuits.

Click image to enlarge

Figure 3: Two evaluation kits facilitate quick evaluation and introduction of TRCDRIVE pack products

The evaluation kit for double pulse tests comes with pre-welded, screw-retained external connections. This eliminates any need for additional welding of the terminals. No special capacitors are required, which in turn allows evaluations to be performed in various standard environments. The device driver board is supplied with 24 V as standard, while the maximum switching frequency is 20 kHz. The operating voltage is also independent of the withstand voltage of the respective capacitor/component.

The evaluation kit for 3-phase full bridge applications also comes with pre-welded, screw-retained external terminals, as well as pre-welded capacitors and an integrated cooling system. Further specifications include a gate driver board power supply (typically 24 V), a switching frequency of up to 20 kHz and an operating voltage of up to 900 V.

Greater efficiency and reliability

Although electric vehicles are generally considered sustainable, it is still important to ensure that the components used in the vehicles are also designed on a sustainable basis. As the world's first provider, starting mass production of SiC MOSFETs back in 2010, ROHM continues to enjoy a leading role in the development of SiC component technology. These components are marketed under the EcoSiC brand and cover an extensive range, including bare chips, as well as discreet components and modules.

EcoSiC stands for silicon carbide products with enhanced efficiency and reliability, particularly those used in high-performance applications such as electric vehicles, industrial equipment and systems for renewable energies. With the introduction of EcoSiC, ROHM is positioning itself as a provider of advanced and sustainable technologies that target higher switching frequencies, lower losses and environmentally friendly properties. The EcoSiC logo symbolises the connection between the ecosystem and technological excellence. It is part of the superordinate “Power Eco Family” concept, which aims to maximise the efficiency and compactness of electronic applications. Production of the EcoSiC modules is already being performed on a Co₂-neutral basis.

Summary

With its TRCDRIVE pack range, ROHM has developed compact modules with heat dissipation on one side that offer a high current density. These modules have been optimised for xEV traction inverters and are based on ROHM’s proprietary module technology. The modules make a valuable contribution to overcoming the most important challenges in terms of miniaturisation, greater efficiency and lower development costs. ROHM will also continue to expand its range of SiC MOSFETs in various housings and with even lower ON resistances. The objective here is to reduce power consumption in various devices and thereby make a contribution to achieving societal objectives such as environmental protection.

ROHM