ADE9078ACPZ datasheet(48/108 Pages) AD

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Data Sheet

ADE9078

Rev. 0 | Page 47 of 107

Power Accumulation

Figure 61 shows how AWATT low-pass filtered active power

samples are accumulated to provide an accurate active power

value in the AWATT_ACC register. The sign of the Phase A

total active power accumulation is monitored in the REVAPA bit

and interrupts can be enabled if the power changes sign. There

are corresponding x_ACC accumulations for each power on

each phase and REVx status bits in the STATUS0 register to

indicate if the power changes sign.

Power Accumulation Details

Figure 61 shows how AWATT values are accumulated into an

internal power accumulator and then are latched into the

xWATT_ACC register at a rate of PWRRDY.

PWRRDY is set after (PWR_TIME + 1) 4 kSPS samples

accumulate. The power accumulation time can be calculated

according to the following equation:

Internal Power Accumulation Time (sec) =















4000

_ TIME

PWR

The PWR_TIME[12:0] register allows up to (8191 + 1) =

8192 samples to be accumulated, which corresponds to

8192/4000 = 2.048 sec.

Internal Power Accumulation Time (sec) =

sec

048

4000

8191

















The internal power accumulator overflows at the same rate as

the internal energy accumulator (see the Internal Energy

Accessing the User Power Registers

The user accessible signed power accumulator is a 32-bit

x_ACC, as shown in Figure 67.

INTERNAL POWER ACCUMULATOR

AWATT_ACC

fDSP

AWATT

Figure 67. Internal Power Register to AWATT_ACC

Calculate the expected AWATT_ACC according to the

following formula based on the average AWATT value:

Internal Power Accumulation = AWATT × (PWR_TIME + 1)

Thus, AWATT_ACC is the 32 MSBs, which can be calculated by

rounding the following equation down to the nearest whole

number:

AWATT_ACC = ROUNDDOWN(User Power

Accumulation × 2−13)

where ROUNDDOWN()is a function to round down to the

nearest integer.

For example, if 4000 samples of AWATT are accumulated at

4 kSPS with full-scale inputs, the expected value of

AWATT_ACC is 0x009B 0003.

User Power Accumulation = 20,823,646 × (3999 + 1) =

83,294,584,000

AWATT_ACC = ROUNDDOWN(83,294,584,000 × 2−13) =

10,167,795 = 0x009B 25F3

Note that W/LSB varies with PWR_TIME accumulation time.

Power Sign Detection

The REVRPC, REVRPB, REVRPA, REVAPC, REVAPB, and

REVAPA bits in the STATUS0 register allow the user to monitor

if the active or reactive power on any phase has changed sign.

The PWR_SIGN_SEL bit allows the user to select whether the

power sign change follows the total or fundamental energies. To

track total active power, set the REVAPx power sign status bits,

PWR_SIGN_SEL = 0. To track fundamental VAR on the

REVRPx bits, write PWR_SIGN_SEL = 1.

The CVARSIGN, CWSIGN, BVARSIGN, BWSIGN, AVARSIGN,

and AWSIGN bits in the PHSIGN register indicate whether the

total or fundamental VAR selected in the PWR_SIGN_SEL bit

is positive or negative.

The power signs are updated at the same time as the

xWATT_ACC, xVAR_ACC, and xFVAR_ACC registers and

correspond to the sign of these registers. Note that the power

registers and signs are updated after the number of 4 kSPS

samples configured in the PWR_TIME register have elapsed,

from 500 μs to 2.048 sec. The power sign change indication in

the REVxPx bits are updated at the same time (see the Power

Accumulation Details section for more information).

The ADE9078 allows the user to accumulate total active power

and VAR powers into separate positive and negative registers:

PWATT_ACC and NWATT_ACC, PVAR_ACC and NVAR_ACC.

This accumulation is done by evaluating the AWATT, low-pass

filtered active power every 4 kSPS. If AWATT is positive, it is

added to the PWATT_ACC accumulation. If AWATT is negative,

the absolute value is added to the NWATT_ACC accumulation.

A new accumulation from zero begins after the power update

interval set in PWR_TIME has elapsed. The positive and

negative total active power and total VAR from all three phases

are added into the positive/negative active power and VAR

accumulations.

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