For the most part, electric vehicles use an invertor to change the direct current coming from the battery pack to alternating current to power the electric motor.
Direct current [DC] motors are more efficient than alternating current [AC] motors, but aren’t found very much in electric vehicle application because they waste energy starting up and aren’t easy to control at low speed.
They can be fitted with a sensor to determine position to maximize torque during startup without wasting a lot of energy, but the technology isn’t very reliable. Because of this, DC electric motors have been relegated to applications which don’t require startup very often, such as fans and pumps.
Hitachi’s new DC motor control system could revolutionize the way we think about AC and DC motors, especially in electric vehicles. Instead of measuring the voltage of the coil, which is non-existent at zero rpm and almost undetectable at low speeds, Hitachi’s new motor management system measures the inductance.
The inductance of the DC motor coil, which varies by position and not by speed, which enables the new motor to balance energy and torque output very efficiently at any speed. Because DC electric motors are more efficient than AC motors, application in an electric vehicle could result in much further range than currently.