ADE7978 datasheet(56/125 Pages) AD

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ADE7978/ADE7933/ADE7932/ADE7923

Data Sheet

Rev. D | Page 56 of 125

VOLTAGE RMS IN DELTA CONFIGURATIONS

In 3-phase, 3-wire delta configurations, Phase B is considered

the ground of the system, and the Phase A and Phase C voltages

are measured relative to it (see Figure 113). This configuration

is selected by setting Bits[5:4] (CONSEL[1:0]) equal to 01 in the

ACCMODE register (Address 0xE701). Table 24 lists all config-

urations where the ADE7978 can be used.

In the 3-phase, 3-wire delta configuration (see Figure 77), all

Phase B active, reactive, and apparent powers are 0. The ADE7978

subtracts the uncompensated and unfiltered instantaneous values

of the Phase A and Phase C voltages and sends them to the

regular Phase B datapath: VB = VA − VC. The rms value of the

result—that is, the line voltage between Phase A and Phase C—

is computed and stored in the BVRMS register. The BFVRMS

BVRMS line voltage.

The BVGAIN, BPHCAL, BVRMSOS, and BFVRMSOS registers

can be used to calibrate the BVRMS and BFVRMS registers

computed in this configuration.

In 3-phase, 4-wire delta configurations, the Phase B voltage is

not sensed, and the Phase A and Phase C voltages are measured

relative to the neutral line (see Figure 114). This configuration

is selected by setting Bits[5:4] (CONSEL[1:0]) equal to 11 in the

ACCMODE register.

In the 3-phase, 4-wire delta configuration (see Figure 78), the

ADE7978 calculates the opposite of the uncompensated and

unfiltered instantaneous value of the Phase A voltage and sends

the value to the regular Phase B datapath: VB = −VA.

PHASE A

ADE7933

PHASE C

ADE7933

ADE7978

AVGAIN[23:0]

HPFEN BIT

CONFIG[4]

HPF

DIGITAL

LPF

BVGAIN[23:0]

HPFEN BIT

CONFIG[4]

HPF

CVGAIN[23:0]

HPFEN BIT

CONFIG[4]

HPF

DIGITAL

LPF

FUNDAMENTAL VOLTAGE

RMS (BFVRMS) CALCULATION

VOLTAGE RMS (BVRMS)

CALCULATION

Figure 77. Phase B Voltage Calculation in 3P3W Delta Configuration (CONSEL = 01 in the ACCMODE Register)

PHASE A

ADE7933

ADE7978

AVGAIN[23:0]

HPFEN BIT

CONFIG[4]

HPF

DIGITAL

LPF

BVGAIN[23:0]

HPFEN BIT

CONFIG[4]

HPF

FUNDAMENTAL VOLTAGE

RMS (BFVRMS) CALCULATION

VOLTAGE RMS (BVRMS)

CALCULATION

–1

Figure 78. Phase B Voltage Calculation in 3P4W Delta Configuration (CONSEL = 11 in the ACCMODE Register)

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