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CHAPTER 6: SIMULATIONS OF INPUT AND OUTPUT SYSTEM EMI
V[dBµV]
120
100
80
60
40
20
0
−20
Simulation
Measurement
1 10
Frequency [MHz]
Figure 6.3: Output Vab simulation/measurement comparison
voltage and current have been measured (Fig. 6.4 shows the measurements on phase
a). Applying the FFT operator to the sampled values measured with a scope (WavePro
715Zi sampling 500ms at 500kHz), the amplitude of the fundamental frequency with
its phase has been obtained. The model’s R/L parameters can be obtained from the
measured amplitudes:
RL = |V|
|I| · cos(φV − φI) (6.4.1)
XL = |V|
|I| · sin(φV − φI) (6.4.2)
In order to double check the phase offset between the two current and voltage signals,
the cross-correlation operator has been used. This operator is proportional to the over-
lapping between the two signals and, for real values, it is expressed by the formula
6.4.3.
c(m) =
N−m−1
∑ xn+myn,
n=0
m = −2N+ 1 . . . 2N− 1 (6.4.3)
The output is a vector as long as the sum of the lengths of the two input signals, voltage
and current in this case, and its peaks are located when the two signal match the most.
Since both voltage and current are sine waves, the peaks will be periodic, and peak
when the two signals are exactly in phase; this can be seen in Fig. 6.5. At the positive
peak the overlapping is at the maximum, so to obtain the phase offset the time shift
m must simply be divided by the periodicity of the signal and multiplied by 2π. The
values obtained with both methods are compared and contrasted in Table 6.1, where
we can observe the reliability of the measurements.
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