Measurement of electric motor currents in a speed varying inverter, uses shunt current sensors in lower branches of inverter

摘要

Shunt sensors (Rs) are mounted in lower branches of inverter. Means are provided for measuring currents delivered by the sensors at instants (Tmes) determined by a control signal (Tsample). Sensor currents include fundamental value of motor phase currents. Means are provided to determine best instant for measurement so as to obtain validity range for direct measurements as extensive as possible, and to find limits where measure of current is not directly exploitable.. System for measuring motor currents in a speed varying inverter. Has in arms of bridge current measuring sensors (Rs) delivering signals from samplers (EB) designed to measure currents which can be sent to a micro-controller ( mu C) after conversion by an analogue-digital converter. System includes means to control switches (T1 to T6) whose switching instants are determined by the comparison between a reference wave and a triangular carrier (P). Means are provided to calculate the duration (Tref) of control commands (CT) and means to cause the micro-controller to deliver a control signal (Tsample) to the samplers (EB). The signal (Tsample) is synchronized with the summits of the triangular carrier (P) to measure the voltage at the sensor terminals and to utilize the current measure if the duration of the command is greater than a preset value or to calculate the phase current (Ip) if the command duration is less than the preset value.