ADE7755 datasheet(13/20 Pages) AD | Energy Metering IC with Pulse Output

13 / 20 page

ADE7755

Rev. A | Page 13 of 20

NONSINUSOIDAL VOLTAGE AND CURRENT

The active power calculation method also holds true for non-

sinusoidal current and voltage waveforms. All voltage and current

waveforms in practical applications have some harmonic content.

Using the Fourier Transform operation, instantaneous voltage

and current waveforms can be expressed in terms of their

harmonic content.

(

∑

∞

≠

sin

)

(

hω

)

(1)

where:

v(t)

is the instantaneous voltage.

is the average voltage value.

is the rms value of the voltage harmonic, h.

is the phase angle of the voltage harmonic.

∑

∞

≠

)

sin(

)

(

hω

(2)

where:

i(t) is the instantaneous current.

IO is the current dc component.

Ih is the rms value of the current harmonic, h.

βh is the phase angle of the current harmonic.

Using Equation 1 and Equation 2, the active power (P) can be

expressed in terms of its fundamental active power (P1) and

harmonic active power (PH).

P = P1 + PH

(3)

where:

P1 is the active power of the fundamental component:

P1 = V1 × I1 cosΦ1

Φ1 = α1 – β1

and

PH is the active power of all harmonic components:

∑

∞

≠

cos

Φh = αh – βh

A harmonic active power component is generated for every

harmonic, provided that the harmonic is present in both the

voltage and current waveforms. The power factor calculation

previously shown is accurate in the case of a pure sinusoid;

therefore, the harmonic active power must also correctly

account for the power factor because it is made up of a series of

pure sinusoids.

Note that the input bandwidth of the analog inputs is 14 kHz

with a master clock frequency of 3.5795 MHz.

ANALOG INPUTS

Channel 1 (Current Channel)

The voltage output from the current transducer is connected

to the ADE7755 at Channel 1. Channel 1 is a fully differential

voltage input. V1P is the positive input with respect to V1N.

The maximum peak differential signal on Channel 1 should be

less than ±470 mV (330 mV rms for a pure sinusoidal signal)

for specified operation. Note that Channel 1 has a programmable

gain amplifier (PGA) with user-selectable gain of 1, 2, 8, or 16

(see Table 5). These gains facilitate easy transducer interfacing.

+470mV

–470mV

VCM

DIFFERENTIAL INPUT

±470mV MAX PEAK

COMMON-MODE

±100mV MAX

V1P

V1N

VCM

AGND

Figure 24. Maximum Signal Levels, Channel 1, Gain = 1

Figure 24 illustrates the maximum signal levels on V1P and

V1N. The maximum differential voltage is ±470 mV divided by

the gain selection. The differential voltage signal on the inputs

must be referenced to a common mode, for example, AGND.

The maximum common-mode signal is ±100 mV, as shown in

Figure 24.

Table 5. Gain Selection for Channel 1

Gain

Maximum Differential Signal (mV)

±470

±235

±60

±30

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