ADE9078ACPZ datasheet(40/108 Pages) AD

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Data Sheet

ADE9078

Rev. 0 | Page 39 of 107

Fundamental Reactive Power

The fundamental reactive power in the ADE9078 is calculated

using a proprietary algorithm that requires initialization of the

network frequency and of the nominal voltage measured in the

voltage channel. The SELFREQ bit in the ACCMODE register

selects whether the system is 50 Hz or 60 Hz. For a 50 Hz system,

clear the SELFREQ bit, and for a 60 Hz system, set the SELFREQ

bit to 1. The SELFREQ selection must be made prior to writing

1 to the run register.

The VLEVEL register indicates the nominal value of the voltage

channel. Calculate VLEVEL according to the following equation:

VLEVEL = X × 1,144,084

where X is the dynamic range that the nominal input signal is at

with respect to full scale.

It is recommended to set the voltage channel input so that the

nominal voltage, for example 240 V rms, corresponds to one half of

the analog input signal range of the ADE9078. The ADE9078

can support ±1 V peak, 0.707 V rms inputs, so it is recommended

to scale the voltage channel inputs to 0.353 V rms. Then, with a

nominal input of 240 V, the input signal is at half of full scale and X

is equal to 2. Write 2,288,168d to the VLEVEL register to configure

this feature.

VLEVEL = 2 × 1,144,084 = 2,288,168

After configuring the SELFREQ and VLEVEL parameters, the

ADE9078 tracks the fundamental line frequency within ±5 Hz

of the 50 Hz or 60 Hz frequency selected in SELFREQ. If a larger

frequency range than ±5 Hz is required in the application, monitor

the line period (xPERIOD) and change the SELFREQ selection

accordingly. Note that the run register must be set to 0 before

changing the SELFREQ setting and must then be set to 1 again.

The fundamental current signal is shifted by 90° and multiplied

by the fundamental voltage signal. This is then gained by

APGAIN and offset correction is applied according to the

AFVAROS register.

APGAIN

AFVAROS

AFVAR

AI_PCF

AV_PCF

FUNDAMENTAL

VAR

ENERGY/

POWER/CF

ACCUMULATION

Figure 59. Fundamental Reactive Power, AFVAR

The fundamental reactive power at a power factor of 0 has a similar

ripple to the total active power at a power factor of 1 (see Figure 56).

xFVAROS has the same scaling as xFVAR (see the Total Active

Power section to understand how to calculate this register value.

Table 18 shows the settling times for fundamental reactive

power for a 50 Hz signal.

Table 18. Fundamental Reactive Power Settling Time

Fundamental Reactive Power

SettlingTime (sec)

Configuration

FS = 99%

FS = 99.90%

Integrator On, HPF On,

and LPF2 On

0.86

1.11

Integrator Off, HPF On,

and LPF2 On

0.86

1.11

Power Factor

The total active power and total apparent power are

accumulated over 1.024 sec. Then the power factor is calculated

on each phase according to the following equation:

sec

1.024

over

accumulate

AVA

sec

1.024

over

accumulate

AWATT

APF =

The sign of the APF calculation follows the sign of AWATT.

To calculate what quadrant the energy is in, look at the sign of

the total or fundamental reactive energy in that phase along

with the sign of the xPF or xWATT value, as indicated in Figure 60.

The quadrants with capacitive power factors are indicated in

dark gray whereas the quadrants with inductive power factor

are indicated in light gray. Note that for most applications, the

watts are received (imported) from the grid and so the active

power and VAR stay within Quadrant I and Quadrant IV.

CAPACITIVE:

CURRENT LEADS

VOLTAGE

INDUCTIVE:

CURRENT LAGS

VOLTAGE

WATT

90° LAGGING

INDUCTIVE:

CURRENT LAGS

VOLTAGE

CAPACITIVE:

CURRENT LEADS

VOLTAGE

WATT (–)

VAR (+)

QUADRANT II

WATT (+)

VAR (+)

QUADRANT I

WATT (–)

VAR (–)

QUADRANT III

WATT (+)

VAR (–)

QUADRANT IV

WATT(+) INDICATES POWER RECEIVED (IMPORTED FROM GRID)

WATT(–) INDICATES POWER DELIVERED (EXPORTED TO GRID)

θ2 = 60° PF2 = 0.5 IND

θ1 = –30° PF1 = 0.866 CAP

Figure 60. Active Power and VAR Sign for Capacitive and Inductive Loads

The power factor results is stored in 5.27 format. The highest

power factor value is 0x07FF FFFF, which corresponds to a power

factor of 1. A power factor of −1 is stored as 0xF800 0000. To

determine the power factor from the xPF register value, use the

following equation:

Power Factor = APF × 2−27

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