ADE7759ARS datasheet(20/32 Pages) AD

20 / 32 page

REV. 0

ADE7759

–20–

PGA1

V1P

V1N

ADC 1

HPF

PGA2

V2P

V2N

ADC 2

DELAY BLOCK

1.12 s/LSB

LPF2

60Hz

0.1

CHANNEL 2 DELAY

REDUCED BY 4.48 s

(0.1 LEAD AT 60Hz)

FCH IN PHCAL [7:0]

PHCAL [7:0]

–110 s TO +103 s

60Hz

Figure 28. Phase Calibration

FREQUENCY – Hz

0.30

100

0.25

0.20

0.15

0.10

0.05

0.00

–0.05

–0.10

200

300

400

500

600

700

800

900

1000

Figure 29. Combined Phase Response of the HPF and

Phase Compensation (10 Hz to 1 kHz)

FREQUENCY – Hz

0.30

0.25

0.20

0.15

0.10

0.05

0.00

–0.05

–0.10

Figure 30. Combined Phase Response of the HPF and

Phase Compensation (40 Hz to 70 Hz)

FREQUENCY – Hz

0.4

0.3

0.2

0.1

0.0

–0.1

–0.2

–0.3

–0.4

Figure 31. Combined Gain Response of the HPF and Phase

Compensation (Deviation of Gain in % from Gain at 60 Hz)

ACTIVE POWER CALCULATION

Electrical power is defined as the rate of energy flow from

source to load. It is given by the product of the voltage and current

waveforms. The resulting waveform is called 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/second

Equation 3 gives an expression for the instantaneous power signal

in an ac system.

()

(

)

= 2

(1)

( )

sin(

)

= 2

(2)

where

V = rms voltage,

I = rms current.

i t

p t

()

( )

–

cos(

)

=×

(3)

The average power over an integral number of line cycles (n) is

given by the expression in Equation 4.

pt dt

∫

()

(4)

where T is the line cycle period. P is referred to as the Active or

Real Power. Note that the active power is equal to the dc com-

ponent of the instantaneous power signal p(t) in Equation 3, i.e.,

VI. This is the relationship used to calculate active power in the

ADE7759. The instantaneous power signal p(t) is generated by

multiplying the current and voltage signals. The dc component of

the instantaneous power signal is then extracted by LPF2

(Low-Pass Filter) to obtain the active power information. This

process is illustrated graphically in Figure 32. Since LPF2 does not

have an ideal “brick wall” frequency response (see Figure 33),

the Active Power signal will have some ripple due to the instanta-

neous power signal. This ripple is sinusoidal and has a frequency

equal to twice the line frequency. Since the ripple is sinusoidal

in nature it will be removed when the Active Power signal is

integrated to calculate Energy—see Energy Calculation section.

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