Input “C” to the reference current calculator is derived
from the voltage feed-forward signal. “C” causes power input
to the PFC regulator to remain constant at a specified level
(determined by the load) regardless of line voltage changes. In
order to obtain “C”, a voltage proportional to rms value of the
input voltage must be derived from the normalized voltage
feed-forward input to the processor. The average value of the
voltage feed-forward input satisfies this requirement. The
average value can be obtained either by analog low-passfiltering,
or better by averaging the signal over a period of the
input waveform. The averaging method is more easily
implemented by the digital processor, as described in [5]. The
same algorithm that synchronizes the processor-generated sine
shape to the voltage feed-forward signal also enables
averaging of the voltage feed-forward signal over a period.