EV Traction Inverter Design Trends: April 2025

Traction inverters play a critical role in the continuing adoption of EVs, as they are responsible for transforming DC power from the battery into AC power to operate the electric motor. This process is essential for enabling electric propulsion and also allows for regenerative braking, where the motor acts as a generator, converting kinetic energy back into AC power.  

The careful design of traction inverters for hybrid electric vehicles (HEVs) and electric vehicles (EVs) can help enable faster motor speeds, higher efficiency and a smaller system size while maintaining power density. The heightened efficiency leads to reduced power loss during the conversion procedure, hence improving the overall performance and driving distance of EVs.

With EV traction inverters approaching 300kW power levels, the need for higher reliability and higher efficiency is imperative. To build the next generation of these systems, power silicon carbide (SiC) MOSFETs are gradually replacing silicon-based power devices in production due to their higher switching speed, lower switching loss and higher operating temperature capabilities. Moreover, SiC devices have lower on-state resistance (Rds(on)) and switching losses compared to silicon devices. This results in higher overall efficiency in the power conversion processes within traction inverters.

Silicon carbide, as the name suggests, is a compound composed of silicon and carbon, The distinctive attributes of this material encompass elevated thermal conductivity, superior breakdown voltage and exceptional chemical resistance. SiC, unlike conventional silicon-based semiconductors, can function at elevated temperatures and voltages, rendering it a very suitable option for power electronics applications.

Because of these qualities, traction inverters with higher voltage capabilities can be designed, which can lead to a reduction in the number of powertrain components required. Traction inverters made of silicon carbide also need less cooling than inverters made of silicon because of SiC’s better thermal properties.

While most of the batteries and power-conversion systems in today's EVs operate at 400V, another emerging trend is the development of 800V EV bus drive systems. These systems enable faster charging and since doubling the operating voltage cuts the current flowing through the EV's wiring harness by roughly half. This reduces its weight, making it possible for automakers to produce vehicles with longer driving ranges.

SiC devices can turn on and off at significantly greater frequencies in comparison to conventional silicon devices. The inverter’s fast switching capabilities minimize the energy losses during switching, leading to enhanced overall efficiency and smoother operation. SiC-based inverters can achieve efficiencies above 98%, surpassing the capabilities of silicon inverters.

The higher switching speed brings about issues such as voltage and current overshoots and electromagnetic interference (EMI). These issues are amplified by fast di/dt (change in current with time) and dv/dt (change in voltage with time), which can cause unwanted transients and can potentially damage devices.

As traction inverters migrate to SiC-based designs, SiC power devices need to be paired with high-voltage isolated gate drivers to enable higher switching frequency, lower conduction losses, better thermal characteristics and higher robustness at high voltages.

The gate-driver IC has to turn on the SiC FETs as efficiently as possible, while minimizing switching and conduction losses that include both turn-on and turn-off energy. The ability to control and vary the gate-drive current strength reduces switching losses at the expense of increasing transient overshoot at the switch node during switching. Varying the gate-drive current controls the slew rate of the SiC FET,

A battery with a state of charge from 100% to 80% should use low gate-drive strength to maintain SiC voltage overshoot within given limits. As the battery charge drops from 80% to 20%, employing high gate-drive strength reduces switching losses and increases traction inverter efficiency. These scenarios are possible during 75% of the charging cycle, so the efficiency gains can be significant.

An isolated gate-driver integrated circuit provides low- to high-voltage (input-to-output) galvanic isolation, drives the high- and low-side power stages of each phase of a SiC-based inverter and monitors and protects the inverter against various fault conditions. The isolated gate driver coupled with an isolated bias supply solution significantly reduces the PCB size and eliminating numerous discrete components improving system power density.

Real-time variable gate drive strength enables improvement in system efficiency. Compared to PCB-level active gate drivers, the on-chip integrated active gate driver has advantages in terms of reducing size, decreasing delay and lowering application complexity.

A standard way to evaluate a traction inverter’s power-stage switching performance is the double pulse test (DPT), which turns the SiC power switch on and off at different currents. Varying the switching times makes it possible to control and measure the SiC turn-on and turn-off waveforms over operating conditions, thus facilitating an evaluation of efficiency and SiC overshoot, which affects reliability.

Finally, In order to extend driving range and reduce motor size and weight without compromising the power level, a traction motor needs to be able to run at higher speeds (>30,000 rpm). This requires fast sensing and processing, as well as the efficient conversion of DC to AC voltages. To achieve these goals, in addition to employing SiC MOSFETs for the switching transistors in the power stage and using high-voltage 800V batteries, traction inverter design trends include using advanced control algorithms. These algorithms include techniques such as direct torque control (DTC), field-oriented control (FOC), and adaptive fuzzy logic. They also incorporate online road condition estimates and anti-slip control to optimize traction in various scenarios.