ADE7816 datasheet(21/48 Pages) AD

21 / 48 page

Data Sheet

ADE7816

Rev. 0 | Page 21 of 48

The content of the active energy register overflows from full-scale

positive (0x7FFFFFFF) to full-scale negative (0x80000000) and

continues to increase in value when the active power is positive.

Conversely, if the active power is negative, the energy register

underflows from full-scale negative (0x80000000) to full-scale

positive (0x7FFFFFFF) and continues decreasing in value. Bit 0

(AEHF1) in the STATUS0 register (Address 0xE502) is set when

Bit 30 in the AWATTHR, BWATTHR, or CWATTHR register

changes, signifying that one of these registers is half full. Simi-

larly, Bit 1 (AEHF2) in the STATUS0 register is set when Bit 30

in the DWATTHR, EWATTHR, or FWATTHR register changes,

signifying that one of these registers is half full.

Setting Bit 6 (RSTREAD) in the LCYCMODE register

(Address 0xE702) enables a read-with-reset for all watt-hour

accumulation registers. When this bit is set, all energy accu-

mulation registers are set to 0 following a read operation.

REACTIVE ENERGY MEASUREMENT

Definition of Reactive Power and Reactive Energy

Reactive power is the product of the voltage and current when all

harmonic components of one of these signals are phase shifted

by 90°. Reactive power is the power dissipated in an induc-tive or

capacitive load and is measured as volt-ampere reactive (var).

Reactive energy is the accumulation of reactive power over time.

RP =

()

∫

= VI × sin(θ)

(3)

where:

V is the rms voltage.

I is the rms current.

RP is the reactive or real power.

T is the line cycle period.

Reactive Energy Registers

The ADE7816 has six reactive energy registers that accumulate

active energy for each of the six channels separately: AVARHR

(Address 0xE406), BVARHR (Address 0xE407), CVARHR

(Address 0xE408), DVARHR (Address 0xE409), EVARHR

(Address 0xE40A), and FVARHR (Address 0xE40B). All

reactive energy registers are in 32-bit, signed format. The

ADE7816 accumulates both positive and negative reactive

power. Negative reactive power indicates that the current

is leading the voltage by up to 180°. The ADE7816 provides

a signed accumulation of the power, where positive power

is added and negative is subtracted.

Reactive Energy Threshold

The ADE7816 accumulates energy in two steps. The first

is done internally using the threshold registers, VARTHR1

(Address 0x43AD) and VARTHR0 (Address 0x43AE). These

registers make up the most significant and least significant 24 bits,

respectively, of an internal threshold register that is used to control

the frequency at which the external xVARHR registers are updated.

The VARTHR1 and VARTHR0 registers affect all six reactive

energy measurements. For standard operation, the VARTHR1

0x0. This sets the update rate of the xVARHR registers to the

maximum of 8 kHz with full-scale inputs.

If the rate at which energy is accumulated in the xVARHR

registers must be reduced, VARTHR1 and VARTHR0 can be

modified as follows:

Threshold = 0x2000000 ×

(kHz)

kHz

Rate

Update

Required

(4)

Note that the maximum output with full scale inputs is 8 kHz.

The threshold should not be adjusted to try to produce more

than 8 kHz. Such an adjustment could result in saturation of the

output frequency and, therefore, a loss of accuracy.

The second stage of the accumulation is done in the external

registers, xVARHR. With the recommended values provided in

Equation 4, the reactive energy updates at a rate of 8 kHz with

full-scale inputs (see Figure 29).

Reactive Energy Accumulation and Register Roll-Over

The reactive energy accumulates at a maximum rate of 8 kHz

with full-scale inputs. The maximum positive value that the 32-bit,

signed xVARHR registers can store before they overflow is

0x7FFFFFFF. Assuming steady accumulation with full-scale

reactive energy inputs, the accumulation time is

Time = 0x7FFFFFFF × 125 μs = 74 hr, 33 min, 55 sec

Conversely, if the reactive power is negative, the energy register

underflows from full-scale negative (0x80000000) to full-scale

positive (0x7FFFFFFF) and continues decreasing in value. Bit 2

(REHF1) in the STATUS0 register is set when Bit 30 of the

AVARHR, BVARHR, or CVARHR register changes, signifying

that one of these registers is half full. Similarly, Bit 3 (REHF2)

in the STATUS0 register is set when Bit 30 of the DVARHR,

EVARHR, or FVARHR register changes, signifying that one

of these registers is half full.

VGAIN

HPF

IAGAIN

DIGITAL

INTEGRATOR

HPF

PCF_A_COEFF

AVARGAIN

AVAROS

ACCUMULATOR

VARTHR[47:0]

AVARHR[31:0]

32-BIT

TOTAL

REACTIVE

POWER

ALGORITHM

Figure 29. Reactive Energy Signal Path

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