Fig. 8 shows the influence of the drive output power on
the dominant pair of eigenvalues when the current control
loop bandwidths for the converter and motor drive are set to
1.0 kHz and 800 Hz, respectively. The output power in this
case is varied by changing the load torque TL from 1Nm to
10Nm. It is seen that the system stability deteriorates with
the increase in the drive output power. It is also seen that the
857
system has a maximum power limit for stable operation. This
limit can be increased by increasing the filter capacitance Cf
or the damping resistance Rf, or reducing the filter inductance
Lf, all of which will affect the filter size, efficiency and cost,
as well as the harmonic attenuation characteristics. Optimal
selection of the converter and drive control bandwidth will
also improve the system stability. Nevertheless this result is
presented for comparison with the time domain simulation in
the subsequent section.