ADE7880 datasheet(44/104 Pages) AD

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ADE7880

Data Sheet

Rev. A | Page 44 of 104

INSTANTANEOUS

PHASE A

ACTIVE POWER

HPFEN BIT

CONFIG3[0]

HPF

DIGITAL SIGNAL PROCESSOR

AIGAIN

AVGAIN

HPFEN BIT

CONFIG3[0]

INTEN BIT

CONFIG[0]

LPSEL BIT

CONFIG3[1]

HPF

LPF

APGAIN AWATTOS

APHCAL

AWATT

Figure 70. Total Active Power Data Path

INSTANTANEOUS

POWER SIGNAL

INSTANTANEOUS

ACTIVE POWER

SIGNAL: V rms × I rms

p(t)= V rms × I rms – V rms × I rms × cos(2ωt)

0x339CBBC =

54,119,356

V rms × I rms

0x19CE5DE =

27,059,678

0x000 0000

i(t) = √2× I rms × sin(ωt)

v(t) = √2× V rms × sin(ωt)

Figure 71. Active Power Calculation

Because LPF2 does not have an ideal brick wall frequency

response, the active power signal has some ripple due to the

instantaneous power signal. This ripple is sinusoidal and has a

frequency equal to twice the line frequency. Because the ripple

is sinusoidal in nature, it is removed when the active power

signal is integrated over time to calculate the energy. Bit 1

(LPFSEL) of CONFIG3 register selects the LPF2 strength. If

LPFSEL is 0 (default), the settling time is 650 ms and the ripple

attenuation is 65 dB. If LPFSEL is 1, the settling time is 1300 ms

and the ripple attenuation is 128 dB. Figure 72 shows the

frequency response of LPF2 when LPFSEL is 0 and Figure 73

shows the frequency response of LPF2 when LPFSEL is 1.

The ADE7880 stores the instantaneous total phase active

powers into the AWATT, BWATT, and CWATT registers. Their

equation is

∑

∞

xWATT

cos(φk – γk) × PMAX ×

(21)

where:

UFS, IFS are the rms values of the phase voltage and current when

the ADC inputs are at full scale.

PMAX = 27,059,678 it is the instantaneous power computed

when the ADC inputs are at full scale and in phase.

The xWATT[23:0] waveform registers can be accessed using

various serial ports. Refer to the Waveform Sampling Mode

section for more details.

–5

–10

–15

–20

–25

0.1

FREQUENCY (Hz)

Figure 72. Frequency Response of the LPF Used to Filter Instantaneous Power

in Each Phase When the LPFSEL Bit of CONFIG3 is 0 (Default)

–10

–20

–30

–40

0.1

FREQUENCY (Hz)

Figure 73. Frequency Response of the LPF Used to Filter Instantaneous Power

in Each Phase when the LPFSEL Bit of CONFIG3 is 1

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