The Relationship Of Crest Factor And Power Factor - Chroma 63800 Series Operation & Programming Manual

Programmable AC/DC Electronic Load 63800 Series Operation & Programming Manual

3.4.6 The Relationship of Crest Factor and Power Factor

Crest Factor is the peak current divided by RMS current. When a crest factor is set as 1.414, it
means that the DSP creates a sinusoidal current waveform.
Power factor is defined as the true power divided by the apparent power. If the PF is not the
same as the setting value, the position of the current waveform will be modified to meet the
PF value by the DSP. For a resistive load, the power factor is one. If values of V and I are
rms rms
constant, the power factor decrease by the increasing of the crest factor because the effective
multiplication of voltage and current is down.
The following relationship of PF and CF is valid for the sinusoidal waveform of the input
voltage, because the estimated algorithm is established on that the input voltage waveform
and the sunk current waveform are sinusoidal or modified sinusoidal waveforms. The
maximum power factor of a determinate crest factor occurs at the maximum overlap of input
voltage waveform and sunk current waveform. That is, the peaks value of the voltage and
current are at the same time. The minimum power factor occurs at the minimum overlap of
input voltage waveform and sunk current waveform. That is, the zero-crossings of the voltage
waveform and current waveform are the same.
These two situations are illustrated in Figure 3-4 and Figure 3-5.
Figure 3-4 Maximum PF through Figure 3-5 Minimum PF through
a Determinate CF a Determinate CF
According to the algorithm, Figure 3-6 shows the relationship of PF and CF. However, for the
minimum operating voltage of the electronic load, the minimum PF through a determinate
crest factor will be varied. We have to adjust to appropriate value. The modified value is
illustrated on Table 3-1.
3-8