SiC devices deliver higher power efficiency in aircraft

By Maurizio Di Paolo Emilio, contributing writer

Silicon carbide (SiC) is a next-generation material that plans to significantly reduce power losses and enable higher power density, voltages, temperatures, and frequencies while reducing heat dissipation. High-temperature operability reduces the complexity of cooling systems and therefore, the overall architecture of the power supply system.

The aviation industry has experienced rapid growth recently compared to the last few decades, and by 2020, it is estimated that air traffic will grow by 5% per year. The new aerospace world has found new power management solutions in SiC devices for power supply and motor control.

SiC promises low-weight components to reduce fuel consumption and emissions in the aeronautics industry, and the stable operability of the SiC MOSFET at higher operating temperatures, for example, has attracted researchers’ interest for high-power-density power converters.

SiC devices for aircraft
More Electric Aircraft (MEA) has been a research and development topic focused on the aeronautics industry for more than 10 years, and it has represented a revolution in the design and production of electronic systems. The result has led to the expansion of new power solutions from a predominantly auxiliary support network toward a significantly higher energy requirement to power not only flight entertainment systems (rear flat screens) but also environmental control devices, electric motors, and a myriad of safety systems and sensors throughout the aircraft.

The development of new semiconductor devices capable of tolerating high voltages and currents using materials such as SiC and gallium nitride (GaN) has provided a decisive and positive change for power electronics. SiC has a wide bandgap, high thermal conductivity, and high resistance to electric field breakage, which helps reduce power losses. A particular area of application is electric vehicles, in addition to the aerospace sector, wherein the demand for greater compactness, high power density, and high-temperature operation are of critical importance.

Silicon has been the primary technology in many applications, but with the emergence of these new broadband power semiconductors — in particular, SiC MOSFETs and SiC diodes — designers of power electronics can leverage new higher switching speeds and reduce losses compared to traditional silicon-based technology.

Furthermore, SiC MOSFET technology promises to significantly reduce the size and weight of avionic power switches, with significant reductions in fuel consumption and emissions, in line with the objectives of various national governments. The aviation industry has recognized the potential benefits of SiC with an evident impact on all areas of the power supply system.

In an aircraft, we can identify various electronic systems that use power components. The AC/DC and DC/DC power converters are used for various solutions both for high voltage and low voltage (28 V).

One of the critical design problems for power electronics and motor drive circuits using SiC devices is the management of the gate drive conditioning circuit. Managing gate timing is a serious challenge. One approach is to balance the speed of the SiC device to ensure that losses are kept to a minimum, and this can be done with an accurate gate driver design.

In the last few years, 1,200-V SiC MOSFETs available on the market from multiple suppliers have reached an outstanding quality level in terms of high channel mobility, oxide lifetime, and threshold voltage stability.

Solutions for aircraft
The new generation 1,200-V SiC MOSFETs and 1,200-V SiC Schottky barrier diodes (SBDs) from Microchip Technology Inc., via its Microsemi subsidiary, as an example, are suitable for use in power supply and control applications of the switching mode in commercial aviation but also in the automotive sector. One example is the 40-mΩ MSC040SMA120B MOSFET that offers high short-circuit resistance for reliable operation.

SiC MOSFETs and SiC SBDs are designed with a high repetitive capacity of unclamped inductive switching (UIS) at rated current, without degradation or failure. The integration of SiC devices in the on-board recharge and the DC-to-DC power supply conversion systems allows a higher switching frequency and lower losses (Fig. 1 ).

An important parameter in evaluating SiC MOSFETs is the avalanche ruggedness, which is assessed through the UIS test. Avalanche energy shows the ability of the MOSFET to survive transients sometimes incurred when driving inductive loads.

Fig. 1: Dynamic characteristics of Microsemi’s MSC040SMA120B MOSFET. (Image: Microsemi)

SiC MOSFETs offer 10× less failure-in-time (FIT) speed than IGBTs. They offer similar nominal voltages, while SBDs complete the robustness of the SiC MOSFET with UIS values 20% higher than other typical solutions. They also offer better efficiency at higher switching frequencies than IGBTs, a reduced system size and weight, high temperature operating stability (175°C), and significant savings on cooling costs.

Because silicon carbide has a higher critical rupture field than silicon, SiC MOSFETs can achieve the same rated voltage in a smaller package than silicon MOSFETs. The SFC35N120 from Solid State Devices Inc. (SSDI) is one example. The 1,200-V SiC power MOSFETs offer a typical fast switching speed of less than 30 ns. With a resistance of 190 mΩ max at 150°C, this device facilitates parallel configurations and reduces the need for thermal management hardware such as fans and heat sinks (Fig. 2 ).

Fig. 2: Package styles available for the SSDI’s SFC35N120. (Image: Solid State Devices)

The collaboration between Analog Devices Inc. and Microsemi brought to market the first high-power evaluation board for SiC half-bridge power modules  with a switching frequency up to 1,200 V and 50 A @ 200 kHz. The card was designed to improve the reliability of the design while reducing the need to create additional prototypes to save time, as well as to reduce costs and time to market. The high-power evaluation board is suitable for applications such as electric vehicle (EV) charging, onboard EV/HEV charging, DC/DC converters, switched-mode power supplies, high-power motor control and actuation systems aviation, magnetic resonance, and X-rays.

The 1,200-V CAS325M12HM2  SiC power supply module, configured in a SiC half-bridge topology, from Wolfspeed, a Cree company, represents a new generation of all SiC power modules housed in a high-performance 62-mm package. This module uses 1,200-V C2M SiC MOSFETs and 1,200-V Schottky diodes. The superior thermal characteristics of SiC devices, together with the design and packaging materials, allow this module to operate at 175°C, which is a crucial advantage for many industrial, aerospace, and automotive applications (Fig. 3 ).

Fig. 3: The Wolfspeed CAS325M12HM2 module. (Image: Wolfspeed/Cree)

Conclusion
The SiC MOSFET and SiC SBD product lines increase the efficiency of power systems compared to silicon MOSFET and IGBT solutions while reducing the total cost of ownership, allowing scaled systems as well as smaller and cheaper cooling.

One of the main advantages of SiC-based switching devices is operation in hostile environments (600°C) in which conventional silicon-based electronics cannot work. The ability of silicon carbide to operate at high-temperature, high-power, and high-radiation conditions will improve the performance of a wide variety of systems and applications, including aircraft, vehicles, communications equipment, and spacecraft.

Today, SiC MOSFETs are long-term reliable power devices. In the future, expect to see multi-chip power or hybrid modules play a more important role in the SiC world.

This article was originally published on EE Times .