Automotive Applications of Wide Bandgap Devices

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Switched-mode power supplies (SMPS) are well-known for their ability to regulate voltage or current by combining switches with energy storage elements. This technology first appeared in the twentieth century, first with mechanical switches, then with vacuum tubes, and finally with semiconductor-based switches.

The size of the storage elements is proportional to the amount of energy required, which is determined by the converter power and operating frequency. As a result, increasing the operating frequency of the converter allows it to reduce the size of the energy storage elements, which directly affects the converter volume, power density, and cost. This is possible through the use of WBG Semiconductors and  devices.

Figure 1 depicts the major power devices that can be found in any electric or hybrid vehicle. The main inverter is an important component in the car because it controls the electric motor while capturing the energy released by regenerative braking and returning it to the battery. The electric motor used can be synchronous, asynchronous, or brushless direct current (DC).

Figure 1. An electric vehicle outfitted with a variety of high-powered devices. Hyundai Motor Group provided this image.

The DC-DC converters in EVs are responsible for converting a high voltage battery into a low voltage for the power system bus. The auxiliary inverter or converter distributes power from the high voltage battery to a variety of auxiliary systems such as air conditioning, electronic power steering, oil pumps, and cooling pumps.

During charging and discharging, the battery management system regulates the battery’s state. This can be done intelligently to extend the battery’s life. Cell usage must be optimized as the battery ages by balancing performance during charging and discharging cycles.

In this case, the on-board battery charger is critical because it allows the battery to be charged from a standard power outlet. Because different voltage and current levels must be supported by the same circuit, this is considered an additional requirement for designers. Future capabilities, such as bidirectional power transfer, must also be included. The best part is that silicon carbide, SiC-based devices can effectively replace silicon-based devices in implementing all of these functions.

Traction inverters, DC boost converters, and on-board battery chargers are critical components in hybrid and electric vehicles (EVs). The energy efficiency of a vehicle can be affected in two ways: directly through switching and other losses, and indirectly by adding volume and weight. By operating at higher switching frequencies, efficiencies, and temperatures, WBG Semiconductors are known to reduce both direct and indirect losses.

The use of silicon carbide, SiC-based traction inverters is expected to improve energy efficiency in representative hybrid EVs. Increased drivetrain electrification has the potential to save even more energy. 

WBG semiconductors converters will also improve the commercial viability and adoption rate of EVs by enabling efficient, lightweight, and low-cost DC fast charging infrastructure. When combined with a cleaner electricity generation portfolio, this has the potential to significantly reduce the transportation sector’s one-quarter contribution to total US greenhouse gas emissions.

Electric motors with ever-increasingly compact sizes and ever-increasing performance are required for automotive applications. Motor driver circuits have traditionally been silicon semiconductor based, and meeting these kinds of stringent requirements is becoming increasingly difficult. In fact, silicon technology is approaching its theoretical limits in terms of power density, breakdown voltage, and switching frequency, all of which have an impact on power losses. The main consequences of these constraints are manifested primarily in a suboptimal level of efficiency. There are additional potential issues, particularly when operating at high temperatures and switching rates.

When silicon-based power devices are operated at high frequency, switching losses exceed conduction losses, with cascading effects on overall power losses. It is necessary to use a suitable heat sink to dissipate the excess heat produced. This comes with the drawbacks of increased cost, increased overall device weight, and an excessive footprint. 

In contrast, gallium nitride, GaN-based devices are thought to have superior electrical properties and can be used in high voltage and high switching frequency motor control applications as an alternative to conventional MOSFET and IGBT transistors.

The switching losses of a gallium nitride, GaN-based transistor decrease significantly as the switching frequency increases, compared to a silicon-based conventional semiconductor device.

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