The traction inverter is the heart of an
electric vehicle (EV) drivetrain system. As such, the inverter plays a vital role in
increasing the adoption of EVs worldwide. The traction motor provides excellent torque and
acceleration by converting DC power from the batteries or generator to AC power to power
traction drive motors such as permanent magnetic machines (PMSM), induction motors (IM),
externally excited synchronous motors (EESM), and switched reluctance motors (SRM). A traction
inverter also converts recuperation energy from the motor and recharges the battery while the
vehicle is coasting or braking.
There are several key design priorities and
trade-offs to consider when measuring the performance of the traction inverter:
- Functional safety and security – Functional
safety design usually follows ISO 26262 or an e-safety vehicle intrusion-protected
applications process that includes safety diagnostics; system-level failure mode and effects
analysis; failure modes, effects, and diagnostic analysis; and a hardware security module
(HSM).
- Weight and power density – The wide
band-gap switch and powertrain integration are the key technologies enabling high-power
density inverter design. The inverter power density target of OEMs continues to, for
example, 100 kW/L in the US market by 2025. The use of SiC enables 800-V DC bus voltage,
reduce the current rating and wiring harness. An MCU with fast control loop enables the use
of high-speed, lighter motor, and powertrain integration such as an inverter integrated with
DC-DC converters.
- Efficiency – System efficiency includes
traction inverter efficiency, motor efficiency, and inverter efficiency in regenerative
braking mode.
- Performance and reliability – Performance
of the inverter system is measured through motor torque control, a current-sensing loop, and
the motor torque transient response. Reliability includes power module reliability, motor
reliability, and isolation, and so forth.
- System cost – Apart from the electric
machine and wiring harness, the main components include:
- EMI filter
- DC link capacitor
- Busbar
- MCU and control electronics
- Power modules and drive stage
electronics
- Current sensor
- Inverter housing and cooling