Method and apparatus for measuring electricity in a frequency converter control type motor

PURPOSE: To provide a rather low price method and an apparatus for measuring a current and cos ϕ of a simplified motor by utilizing a frequency converter. CONSTITUTION: A current can be measured within the power supply of a frequency converter 1 and within a conduction converter branch 7 of the inverter 6 of this frequency converter 1 using measuring resistors Ru, Rv, Rw in a 3-phase asynchronous motor 2 controlled by the frequency converter 1. Thereby, an instantaneous motor current is defined. The information when each branch 7 becomes conductive can be obtained from a closed loop control circuit of the frequency converter 1.