Current Measurement Gain Tuning Using High Frequency Signal Injection

Accurate measurement of the phase currents in electric machines is a requirement for most high performance drives. Incorrect current measurement gain estimates, caused by device tolerances, temperature drifts, age and noise, reduce the accuracy of the current measurements and degrade the drive's performance. This paper presents a method for compensating current measurement gain errors using a periodically injected, high frequency voltage. The positive and negative sequence components of the resulting high frequency current are measured and used for balancing and scaling the phase current measurement gains. The method can be used either as part of an initial commissioning, or start-up sequence, or periodically during the regular operation of the machine.