ADE75 datasheet(63/148 Pages) AD

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Preliminary Technical Data

ADE75xx/ADE71xx

Rev. PrE | Page 63 of 148

VARDIV[7:0]

VAROS[15:0]

VARGAIN[11:0]

LPF1

LVARHR [23:0]

ACCUMULATE REACTIVE

ENERGY IN INTERNAL

THE LVARHR REGISTER

AT THE END OF LINCYC

HALF LINE CYCLES

OUTPUT

FROM

LPF2

FROM VOLTAGE

CHANNEL

ADC

LINCYC [15:0]

ZERO CROSS

DETECTION

CALIBRATION

CONTROL

DIGITAL TO FREQUENCY

CONVERTER

Figure 48 Line Cycle . Reactive Energy Accumulation Mode

APPARENT POWER CALCULATION

The apparent power is defined as the maximum power that can

be delivered to a load. Vrms and Irms are the effective voltage and

current delivered to the load; the apparent power (AP) is defined

as Vrms × Irms. Equation 28 gives an expression of the

instantaneous power signal in an ac system with a phase shift.

()

sin( )

rms

i(t) =

)

sin(

ωt

I rms

(27)

)

(

)

(

)

(

p(t) =

)

cos(

)

cos(

−

rms

(28)

The apparent power is defined as Vrms × Irms. This expression is

independent from the phase angle between the current and the

voltage.

Figure 49 illustrates the signal processing in each phase for the

calculation of the apparent power in the ADE75XX/ADE71XX.

Vrms

Irms

0x1A36E2

APPARENT POWER

SIGNAL (P)

CURRENT RMS SIGNAL – i(t)

VOLTAGE RMS SIGNAL – v(t)

MULTIPLIER

0x00

0x1CF68C

0x00

0x1CF68C

VAGAIN

DIGITAL TO FREQUENCY

CONVERTER

Figure 49. Apparent Power Signal Processing

The apparent power signal can be read from the waveform

the WFSM bit in the Interrupt Enable Register 3 SFR

(MIRQENH, 0xDB). Like the current and voltage channels

waveform sampling modes, the waveform date is available at

sample rates of 27.9 kSPS, 14 kSPS, 7 kSPS, or 3.5 kSPS.

The gain of the apparent energy can be adjusted by using the

multiplier and VAGAIN register (VAGAIN[11:0]). The gain is

adjusted by writing a twos complement, 12-bit word to the

VAGAIN register. Equation 29 shows how the gain adjustment

is related to the contents of the VAGAIN register.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎭

⎬

⎫

⎩

⎨

⎧ +

VAGAIN

Power

Apparent

OutputVAGA

(29)

For example, when 0x7FF is written to the VAGAIN register, the

power output is scaled up by 50%. 0x7FF = 2047d, 2047/212 =

0.5. Similarly, 0x800 = –2047d (signed twos complement) and

power output is scaled by –50%. Each LSB represents 0.0244%

of the power output. The apparent power is calculated with the

current and voltage rms values obtained in the rms blocks of

the ADE75XX/ADE71XX.

Apparent Power Offset Calibration

Each rms measurement includes an offset compensation

value—see Current Channel RMS Calculation and Voltage

channel RMS Calculation sections. The voltage and current

channels rms values are then multiplied together in the

apparent power signal processing. Since no additional offsets

are created in the multiplication of the rms values, there is no

specific offset compensation in the apparent power signal

processing. The offset compensation of the apparent power

measurement is done by calibrating each individual rms

measurement.

Apparent Energy Calculation

The apparent energy is given as the integral of the apparent

power.

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