Datasheet

78M6610+PSU Data Sheet
2.3 Power Calculations and Power Factor
The 78M6610+PSU computes the active, reactive, and apparent power. In addition, the 78M6610+PSU
computes the fundamental power, determined only by the fundamental components of the voltage and
current and the harmonic power, determined by the harmonic components of the voltage and current.
2.3.1 Active Power Calculation
Active power is calculated as the product of the voltage and current waveforms. The resulting waveform
is the instantaneous power signal, and it is equal to the rate of energy flow at every instant of time. The
unit of power is the watt or joules/sec. The instantaneous power is then averaged over N samples
(accumulation time) for the computation of the active power available at register WATT.
=








2.3.2 Apparent Power
The apparent power (S) is the product of RMS voltage (V
RMS
) and current (I
RMS
). The apparent power
results, also referred as Volt-Amps, are available at the register VA.
S = I
RMS
* V
RMS
2.3.3 Power Factor
The power factor (PF) is calculated as active power (WATT) divided by the apparent power (S). The sign
of the power factor is determined by the active power sign.
=
WATT
S
2.3.4 Reactive Power
The reactive power is calculated as multiplication of instantaneous samples of current (i) and the
instantaneous quadrature voltage (Vq). The quadrature voltage is obtained through a 90° phase shift
(quadrature delay) of the voltage samples. The samples are then averaged over the accumulation time
interval and updated in the VAR register.
=

 



× 

Figure 2-4: Power (Active, Reactive, and Apparent) and Power Factor Calculation
WATT
÷N
X
i
v
Σ
WATT
X
Irms
Vrms
S
VA
PF
P
Quadrature
Delay
X
Vq
VAR
i
v
N=0
N-1
÷N
X
÷
Σ
N=0
N-1
+
POff
12 Rev 3