ADE9178 datasheet(47/122 Pages) AD

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Data Sheet

ADE9178

THEORY OF OPERATION

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Rev. A | 47 of 122

Figure 67. 4-Wire WYE, 4-Wire Delta Phase-Sequence Error from a Phase

Voltage Dropping below ZXTHRSH with SEQ_CYC = 1

MEASUREMENTS ONLY FOR CURRENT

CHANNELS

Neutral Current Mismatch

The ADE9178 calculates the RMS of the sum of AI + BI + CI sam-

ple by sample and stores the result in the ISUMRMS register. The

ISUMRMSOS register allows offset calibration of this measurement.

The scaling is the same as for the other xIRMS and xIRMSOS

registers. Additionally, any one of the six auxiliary ADC path can

be selected by configuring the ISUM_AUXSEL bits in CONFIG0

be either added or subtracted from the sum of phase channels by

configuring ISUM_CFG bits in CONFIG0 register.

In some cases, the application requires to get an interrupt if the

RMS of the sum of current channels exceeds a threshold. This

threshold value can be set in the ISUMLVL register.

ISUMMISMTCH bit of STATUS0 is set when ISUMRMS exceeds

ISUMLVL.

To calculate ISUMLVL, use the following formula:

ISUMLVL= INOMIFS ×

% of nominal ×

RMSFS_CODES

(36)

where, INOM is the nominal current, IFS is the current that gives

full scale at the ADC current input (system specific), % of nominal

is the required percentage of nominal for ISUMLVL, and RMSFS_CO-

DES is the RMS output value when full-scale input is applied to the

ADC input.

For example, if INOM is 10 A, IFS is 44.188 A, and the required

ISUMLVL is 5% of INOM, ISUMLVL is calculated as:

ISUMLVL= 1044.188 × 0.05 × 107310840

=1214253

decimal=0x12872D

PEN FAULT DETECTION

This feature is designed to detect PEN faults according to the

BS7671:2018 Amendment 1:2020 standard.

The ADE9178 provides additional RMSONE calculation and dip/

swell detection on certain channels to enable easy PEN fault

detection. 3-channels are used for PEN fault detection, PEN_CHA-

NA, PEN_CHANB, and PEN_CHANC. The PEN channels can

be configured using the PEN_CHANSELA, PEN_CHANSELB, and

PEN_CHANSELC bits in the PEN_CONFIG register. The PEN

channels can be any of the 12 ADC channels AV, BV, CV,

AI, BI, CI, AUX0, AUX1, AUX2, AUX3, AUX4, and AUX5. CON-

FIG0:RMSONE_SRC_SEL selects samples either before or after

the HPF.

RMS of PEN Fault Channels

Four additional one-cycle RMS values (same as RMS of One Cycle

section) are calculated on the following signals:

1. VSUMRMSONE = (PEN_CHANA + PEN_CHANB +

PEN_CHANC)/3

2. VABRMSONE = PEN_CHANA − PEN_CHANB

3. VACRMSONE = PEN_CHANA − PEN_CHANC

4. VBCRMSONE = PEN_CHANB − PEN_CHANC

RMSONE_SRC_SEL bit in the CONFIG0 register decides and se-

lects samples either before or after the HPF. Period is calculated for

any one of the selected PEN channels based on PEN_LP_SEL bits

in the PEN_CONFIG and is stored in the PEN_PERIOD register

(for formula to convert to seconds, see Table 14). This period value

is used for the PEN channel RMS measurements. Separate RMS

offset calibration registers are also provided for each of PEN chan-

nel (VSUMRMSONEOS, VABRMSONEOS, VACRMSONEOS, and

VBCRMSONEOS). The PEN channel RMS offset register format is

the same as the other RMS offset registers (xxRMSOS).

For example, if PEN_CONFIG is set up in the following configura-

tion:

PEN_CHANSELA = 0000 = AV data processing path

PEN_CHANSELB = 0010 = BV data processing path

PEN_CHANSELC = 0100 = CV data processing path

PEN_LP_SEL = 11 = Combined PEN channels (AV + BV − CV)/2

Then the PEN fault output registers is calculated as follows:

VSUMRMSONE = (AV + BV + CV)/3

VABRMSONE = AV − BV

VACRMSONE = AV − CV

VBCRMSONE = BV − CV

PEN_PERIOD = Period of combined PEN channels

Dips and Swells on PEN Fault Channels

Swells can be detected based on VSUMRMSONE value while both

dips and swells can be detected on the 3-phase to phase voltage

RMS values (VABRMSONE, VACRMSONE, and VBCRMSONE).

Separate dip/swell levels and cycle configuration registers (VxxDI-

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