Wheel diameter measuring apparatus of an electric vehicle

Obtaining a wheel diameter measuring apparatus for measuring a wheel diameter of an electric car speed sensorless vector control according to the synchronous motor. A wheel diameter measuring apparatus of an electric vehicle equipped with a synchronous motor driven by the power converter for converting a DC voltage into an AC voltage, During coasting of the electric vehicle in which the power converter is stopped, a voltage detector for detecting an AC voltage generated by the field of the synchronous motor, From the detected AC voltage by the voltage detector and the electric vehicle speed information, it was decided and a calculator for calculating a wheel diameter of a wheel driven by the synchronous motor.