Derivative current sensor for inverter fed ac machines

In modem inverter fed ac drives, the transient current change can advantageously be exploited for condition monitoring, as well as estimation of the flux or rotor position without a mechanical sensor. For this, it is necessary to measure the transient current change due to voltage pulses applied to the machine. The proposed ferrite core sensor with airgap is modelled and the results are compared to di/dt measurements. Finally, the deviations and material selection criteria are discussed. The benefits of the sensor turn out as reduced sample time by a factor of 3, reduced calculation power and higher signal to noise ratio up to +10dB. The derivation sensitivity is defined and given for the proposed sensors. (C) 2003 Elsevier B.V. All rights reserved.