PDF (Thesis) - Nottingham eTheses - University of Nottingham

CHAPTER 4: MOTOR AND MATRIX CONVERTER MODEL
Impedance [kΩ]
2
1
0
−1
−2
−3
−4
−5
−6
Impedance [kΩ]
1
0
−1
−2
−3
−4
−5
−6
0.1 1
Frequency [MHz]
10
Real
Imag
Figure 4.2: Motor: parasitic impedance measurement
0.1 1
Frequency [MHz]
10
Real
Imag
Impedance [kΩ]
20
15
10
5
0
−5
−10
0.1 1
Frequency [MHz]
10
Figure 4.3: Motor: common and differential mode impedance measurement
supposed to characterize it, simply can not have a resonance as it appears at about
100kHz (Fig. 4.4). Therefore a new model has been proposed in this work that is able
to replicate with more accuracy the impedance behaviour of the actual measurement.
4.3 Suggested HF Motor model
To overcome the aforementioned mismatching a new model has been proposed. This
model has been developed on the reasonable assumption that the current, before cou-
pling to the motor’s case by means of the stray capacitance, will flow through some
part of the winding. Thus, in the proposed model, there is a coil like network be-
fore the stray capacitance components, and assuming input-output symmetry the new
model is represented in 4.5. Now the parasitic measurement can be easily fitted, as it is
possible to see in Fig. 4.6. For this fitting only the outer components in the model have
been identified during the optimization, the central part of the model will not carry any
current during the parasitic measurement, hence it will not be possible to characterize
it. The final optimized values for the components are listed in Table 4.1.
41
Real
Imag