Identification of the synchronous machine inductances by using switching power converters applied in sensorless and current control

This paper deals with the identification of a synchronous machine parameter usefull for the purpose of sensorless and current control. Deviations from the steady-state voltage are generated by the current controller in order to drive the current to its desired value. In sensorless drives, voltage deviations from steady state are used in the case the back-EMF is too low to obtain an accurate rotor position estimation. The voltage deviation applied, generates a measurable current ripple from which an estimation of the rotor position can be made. To study the dynamic behaviour of the current controller as well as the accuracy of the position estimator, the current response on voltage deviations from steady state is of importance. Furthermore, it can be of interest for the controller performance to take into account the influence of magnetic saturation and magnetic interaction. This paper discusses a strategy to measure the current dependence of the machine impedance. It uses the small voltage deviations generated during current control or sensorless control and consequently avoids interference with the normal operation of the drive. To verify the method, experimental identification of the machine impedance is conducted on a permanent-magnet machine of 3.7 kW supplied by using a voltage-source inverter (VSI) with IGBTs. A second set of experiments is performed on a synchronous machine of 150 kVA with rotor field winding for which the stator is supplied by using a full-bridge thyristor rectifier (FBR). The generation of voltage signals is discussed here for the VSI as well as the FBR as these converters are often used for the power convertion in synchronous drives.