A Smarter Approach to Protecting Electric Vehicles: Enhanced Active Short Circuit

What is ASC and How Does It Work?

At the heart of every electric vehicle drivetrain are the electric motor, which converts electrical energy into motion, and the inverter, which manages the flow of energy to the motor. If a fault occurs, such as an inverter failure or electrical malfunction, excessive currents or overvoltage conditions can threaten system integrity.

ASC is a carefully engineered protection function that helps mitigate these risks. It does not prevent faults from occurring but increases the system’s robustness under fault conditions. In the event of a fault, ASC drives the electric drive system into a safe state by shorting the motor phases and dissipating excess energy in a controlled manner.

The Challenges of Conventional ASC Approaches

Implementing an effective ASC strategy is far from straightforward. Our research identified several major challenges that existing approaches struggle to address.

When ASC is activated, the sudden short circuit can generate current peaks reaching up to twice normal operating levels while creating significant thermal stress in the power semiconductors. These extreme conditions can exceed safe electrical and thermal limits, placing considerable stress on critical components such as silicon carbide devices, the DC-link capacitor, and the permanent magnets used in Permanent Magnet Synchronous Motors.

If not carefully managed, these effects can lead to permanent damage, including magnet demagnetization, accelerated semiconductor aging, and voltage overshoot that threatens system stability.

Conventional ASC approaches transition directly into a short-circuit state. As a result, high current peaks, DC-link overvoltage, and increased thermal stress can occur, reducing overall system robustness.

Enhanced ASC: An Advanced Protection Approach

SEG Automotive’s Enhanced ASC builds on conventional methods through an intelligent, stepwise control strategy.

Instead of immediately shorting all motor phases, the system first stabilizes the DC-link voltage using controlled charge and discharge cycles, maintaining the voltage within a safe range of 920 to 950 V in an 800 V system. To ensure smooth energy transitions, space vector modulation with six predefined voltage vectors is applied, selected in real time based on measured phase currents.

Once stable operating conditions have been established, two motor phases are shorted at the optimal rotor position of 90°. The protection sequence concludes with symmetrical three-phase shorting, ensuring balanced energy dissipation while minimizing torque ripple.

Rather than applying an immediate hard short-circuit, the enhanced ASC strategy first controls the energy transfer within the drive system before transitioning into the final ASC state.

The entire process takes less than 15 ms and reduces current peaks by approximately 30% compared with conventional approaches.