Changing an EV’s power output

With internal-combustion engines, power is often related to displacement. What about electric vehicles (EVs)? Are their motors built for a specific output and hence a larger motor is necessary for more power? As such, would a vehicle with Category B certificate of entitlement (COE) have a different motor from the Category A version of the same model?

While the electric motor is a relatively simple assembly, the control of energy supply from the battery is immensely complex.

The battery management system leads this effort, monitoring the charge and health of every single battery cell. Meanwhile, a power inverter controls the motor speed and power. These are in addition to the thermal management system, on-board charger and DC-DC converter.

Many EV-makers differentiate their sporty models by adding a second motor, making them all-wheel-drive machines with sharper acceleration. Twin motors also boost the car’s overall power output.

However, there are also cases where two single-motor EVs of the same model are offered with different outputs.

Generally, the motors are capable of producing a range of power outputs, although maximum torque may remain the same. An electric motor that produces 100kW can be “tuned” to produce 150kW, for instance. At the same time, a 140kW EV can be tuned down to make 110kW – the maximum allowed for Category A COE.

While hardware such as a reduction gearbox, brakes and even power-inverter may be upsized for the more powerful variant, the motors in both cases are often identical.

EV manufacturers use a different software for the power-inverter control system to achieve different power characteristics.

The motor with a higher peak motor speed (measured in revolutions per minute, or rpm) will produce more power. Conversely, restricting the rpm will limit peak power. And since peak torque arrives at a much lower rpm, it is rarely affected by such changes.