Miniaturization of power electronics systems
Based on the application scenarios of an electric vehicle, various requirements are imposed by the automobile manufacturers on the power electronics systems. These are e.g. resistance to temperature changes, vibration resistance, operational reliability at different temperatures as well as a long lifetime. In addition, a requirement like high power density of the integrated systems is now considered self-evident by the automobile manufacturers. However, all these requirements are a major challenge for power electronics.
The range of the high-voltage battery is one of the biggest hurdles for the spread of hybrid and electric vehicles. In order to convince the end customer (i.e. the car owner) of the electric mobility, a number of car manufacturers currently rely on charging systems with fast charging times. This is to simplify the usage of electric cars. But a fast charge means for the technical implementation that a higher charging performance is required within a short time frame in order to charge the battery. Since the volume of available space within the vehicle is always limited, the battery charger system must feature a high-power density. This is the only way that such systems can be integrated into the vehicle in order to meet the market requirement.
Onboard Chargers are complicated systems consisting of different components for the power conversion. Several components are integrated in such systems. Examples include: semiconductors (such as diodes, MOSFETs), passive components (e.g., inductors and capacitors), and transformer with adapted translation ratios to charge the battery with the required voltage. In addition, the transformer is used to galvanically decouple the high-voltage battery during charging.
One of the options to miniaturize power electronics is the more compact design of passive components such as inductors and transformers. This is usually only possible if the deployed semiconductors in the same circuit can be controlled at a high switching frequency. In the case of Si semiconductors, the thermal load at a high switching frequency will limit this approach. Due to its excellent switching characteristics, the SiC-MOSFET is ideally suited for these cases.
Figure 3 shows the following example: For a DC / DC converter system with Si semiconductors, the switching frequency is limited to 25 kHz. If a SiC MOSFET is used, a switching frequency of 160 kHz is possible. This led to a major miniaturization of the winding quality in the entire system. High power density and significant overall weight reduction can be achieved.
The advantages of SiC semiconductors have finally been recognized by automotive manufacturers. The first products consisting of Rohm SiC diodes are used for onboard charging in various vehicles in mass production worldwide. The worldwide first SiC MOSFET qualified for Automotive will soon be available from Rohm. In addition to battery charging devices, the SiC semiconductor promises great potential for applications such as DC / DC converters as well as drive inverters. Concrete solutions from Rohm are available for this kind of applications.
Rohm's second-generation of SiC SBD currently includes products for 650V from 5 to 100A as well as for 1200V and 1700V with current carrying capacities up to 50A. Rohm's range of SiC MOSFETs is even more comprehensive. Rohm offers two different technologies: planar technology and double trench technology. The planar technology already offers discrete products and modules in the voltage range of 650V, 1200V and 1700V with a current carrying capacity of up to 300A.
ROHM is launching mass production of Third Gen SiC MOS for discrete components as well as full SiC modules featuring proprietary double trench technology, which extends the existing MOSFET product family and contributes to the further development of highly efficient and reliable power electronics.
About the author:
Aly Mashaly is Manager Power Systems Department, ROHM Semiconductor GmbH, Willich, Germany.