8
Power metering calibration
8.1
Background
The
provides to the host continuous power metering information about:
•
PFC integrated power in raw format (resulting from the PID integrator)
•
Input voltage
•
PFC operating mode and skipping area
•
PFC fault status
The instantaneous raw power estimation can be computed by:
PRaw W = PFClsb × 128 ×
FSRVin
256
2
×
tsmed
L
(1)
where
P
Raw
is the PFC power (not corrected)
PFC
lsb
is the PFC integrated power in raw format
FSR
Vin
is the full scale ADC voltage reading = 480 V
t
smed
is the smed event (PFC timer) minimal duration = 1/60 MHz = 16.67 ns
L
is the PFC inductor value (typically 250 µH on the evaluation board)
The raw power is almost proportional to the actual PFC power.
On the basis of the PFC mode and the input voltage, it is possible to correct the raw power to deduce the actual
power consumption.
As a lot of parameters have to be taken into account, a very simple approach is to use a calibration method for
each PFC operating mode.
The output power is also compensated with skipping area and input voltage, via the equation below:
Pout W = PRaw × CMode × CVin × CPAM × 1 + CTdel
(2)
where
P
Raw
is the raw power
C
Mode
is the PFC mode correction factor (typically between 0.7 and 1)
C
Vin
is the input voltage correction using a second order polynomial (a+b*Vin+c*Vin²). However since we typically
consider only two voltages (EU/US), the second order term is set to 0
C
PAM
is the skipping area correction factor (1 for no PAM, 0.26 for minimum PAM)
C
Tdel
is the DCM mode correction using a first order equation (a+b*Tdel)
8.2
Metering calibration
To display the power metering correction factors described in the previous section, go to
Application→Power
Metering Calibration
menu; the GUI highlights the current PFC operating mode in yellow.
UM2342
Power metering calibration
UM2342
-
Rev 1
page 19/57
