Wide-bandgap (WBG) switch and powertrain integration are among the key technologies supporting high-power-density inverter design. WBG technology such as silicon carbide (SiC) allows engineers to design higher-power systems in the same footprint with weight and gain efficiency across temperature, speed, and torque to increase the vehicle’s driving range.
Advancing Performance
Traction inverters have traditionally used insulated-gate bipolar transistors (IGBTs). But with the advancement of semiconductor technologies, SiC metal-oxide semiconductor field-effect transistors (MOSFETs) offer the ability to switch at higher frequencies than IGBTs. Thus, they improve efficiency through resistive- and switching-loss reductions while increasing power and current density. Moreover, SiC MOSFETs have lower switching losses, are smaller than IGBTs and run cooler, reducing weight, size and energy waste in the drive system.
The very fast switching capability of SiC transistors is part of their efficiency advantage. Moving to SiC switching, however, presents challenges. This high switching speed also creates the potential for high levels of electrical noise that could mistakenly activate a motor. And a SiC switch is more susceptible to damage from short circuits than IGBT technology.
To combat these shortcomings, the EV needs the right driver technology to accompany the move to SiCs. Gate drivers can control these risks with safety features that reduce the impact of noise in the drive system.
Although most EVs today use 400-V batteries, there’s a notable transition to 800-V architectures. A higher-voltage system makes it possible to use a lower current when charging the battery, which reduces overheating and allows for better power retention in the system. This power can be applied toward achieving a longer driving range.
An 800-V system also has the added advantage of reducing mass. Since the higher voltage enables the motors to run at speeds of 20,000 rpm, well over double that of a 400-V system, it improves power density.
MCUs and Fast Control Loops
Advances in traction inverters, enabled by microcontrollers with real-time control capabilities and isolated gate drivers, is another element pushing EV performance. An MCU with a fast control loop allows for the use of a high-speed, lighter motor as well as powertrain integration such as an inverter integrated with dc-dc converters. A fast control loop also helps to minimize torque ripple and provides smooth speed and torque current profiles to the traction motor.
Texas Instruments has a deep roster of MCUs and gate drivers featuring fast current loop control that can adjust the motor switching algorithm every one-millionth of a second when detecting a short to protect the switch from damage. A low-latency control loop also enables engineers to run the motor at a higher rpm, which can reduce both the size and weight of the motor.
TI MCUs have traction inverter control-loop latency as low as 2.5 µs, with the new automotive quad-core Arm Cortex-R5F AM2634-Q1 demonstrating latency <4 µs (Fig. 2). These high-performance real-time control MCUs can help solve most common design challenges to achieve higher efficiency and greater performance in 800-V traction-inverter systems.
