(3) Magnetic elements

For inductors and transformers, it is necessary to take into consideration the high-temperature characteristics and insulation properties of windings and magnetic cores. High-temperature-resistant enameled wires and Kapton electrical tape are readily available above 200 ◦C. As for the magnetic cores, high-temperature characteristics are a ffected by Curie temperature, coating materials, and power losses. The optimal operating point for most magnetic material is approximately 100 ◦C for most magnetic materials, and the e fficiency will be reduced with the further rise of temperature.

The magnetic elements with rated operation temperature above 200 ◦C mainly involve three types of magnetic cores such as ferrite cores, power cores, tape wound, and cut cores, which are usually utilized for power supply, signal isolation and current detection in high-temperature converters. However, the operating temperature will a ffect their magnetic properties, and the B/H curve will drift with the temperature variation, which will lead to a significant detection error, especially for measurement sensors. Therefore, a compensation algorithm is needed to improve the detection precision. Reference [62] shows a strong correlation between the temperature variation and the magnetic characteristics of Mn–Zn Ferrite materials, the magnetic characteristics should be assessed when these components work in such thermal conditions. Ferrite cores with Curie temperature of 350 ◦C have been commercially available so far, and they can work reliably up to 250 ◦C.

#### **3. High-Temperature Converter and MEMS Devices**

With the commercialized development and mature application of SiC power electronic devices, high-temperature converters and MEMS devices have brought and will bring broad prospects in electric vehicles, more electric aircrafts, deep-earth oil explorations, and geothermal energy exploitations.

#### *3.1. SiC-based Motor Drive*

High-temperature motor drives are required for the flight control actuators and fuel pumps of the aviation system as well as for the control units of electric vehicles, which will face the challenge to meet the requirement of higher efficiency, higher power density, and higher reliability in harsh operation condition. Take an example of a new generation of high-power electric vehicles; the motor drive system will undergo a change from traditional industrial grade to automobile industrial grade. United States Department of Energy draws up the development goal for hybrid electric vehicle (HEV) by 2020, the dramatic advancement will be developed. The power density of power electronic equipment will be higher than 14.1 kW/kg, and volume will be less than 13.4 kW/L, efficiency will be higher than 98%, the price will be lower than 3.3 \$/kW [63]. SiC power electronic devices make motor drives have the ability of high-temperature operation, which plays an essential role in goal achievement.

Figure 8 shows the electrical connection diagram of a three-phase inverter and motor, where a selection of power electronic devices is full SiC-MOSFET, full SiC-JFET, full SiC-BJT, or SiC/Si (e.g., SiC-SBD/Si-IGBT) hybrid devices. As the anti-parallel diode, SiC-SBD is hardly any reverse recovery time and is not affected by temperature variation. The radiator volume of a 2.5 kW motor drive based on SiC-SBD hybrid devices is reduced by 2/3 when compared with the radiator of the motor drive based on Si diode [64]. In [65], a three-phase air-cooling inverter is designed by using full SiC-JFET devices, the motor drive can work in the high-temperature environment of 200 ◦C, and the output efficiency with 18 kW power rating reaches up to 98.2%.

**Figure 8.** Electrical connection diagram of three-phase inverter and motor.

APEI Company has developed a 4 kW high-temperature motor drive by using the SiC-JFET multichip power module (MCPM) and SOI-based integrated circuit technology. The core of control electronics is a high-temperature microcontroller (SOI-based MOS HT83C51) produced by Honeywell Inc., outputting low power signals. Thus, an amplifying circuit provides a connection between the microcontroller and the power module, and the amplifying circuit is constituted of the high-temperature operational amplifiers and high-temperature passive components. A high-temperature transformer is designed by APEI to isolate the digital controlled circuit from the power circuit. Figure 9 shows the mentioned MCPM with high-density power electronics designed by APEI [66]. The MCPM approach is one of the packing strategies for power electronics, and the main idea is that the control and power circuitry components are integrated together into a single compact power module. AlN DBC material for power substrate and AlSiC material for heat spreader connected to the DBC substrate are selectable due to their excellent thermal conduction capabilities and a close CTE match. Multilayer polyimide for PCB is available for high-temperature applications since the glass transition temperature (Tg) is as high as 260 ◦C. An implementation of MCPM in a 4 kW 3-phase motor drive shows the SiC-JFET can operate at a junction temperature of 250 ◦C, Figure 10 shows the prototype of the 3-phase motor drive and the 3-phase multichip power module. Based on these state-of-the-art technologies, the motor drive module can operate in a high-temperature environment. Meanwhile, the converter has a substantial increase in respect of efficiency and power density.

**Figure 9.** Multichip power module with high-density power electronics designed by Arkansas Power Electronics International.

(**a**) 3-phase motor drive prototype (**b**) 3-phase multichip power module
