Advance Topic
The phase current method was used in [7],
[8] and [9].
This method is based on monitoring the phase current waveform with the aim of
detecting its rate of change. The rate of change of current is dictated by the
incremental inductance and the incremental inductance is in turn a function
of rotor position and phase current. Therefore, rotor position can be deduced
from a knowledge of phase current and its rate of change. By using the existing
power switching circuit to provide voltage pulses of short duration in an unenergised
phase, the phase current rises to a small fraction of the rated current. The
voltage drop across the winding resistance due to this small current is negligible
as compared to the DC supply voltage used in providing the voltage pulse. Furthermore,
the flux linkage with the winding is small if the current is small and the rate
of change of flux linkage with rotor position, and hence the back EMF, can be
neglected. This simplifies the calculation of the rate of change of current
to simply the ratio of the phase voltage and incremental inductance.
Sensorless Control of Switched
Reluctance Motor - Active Probing Methods
