Analog Devices ADE7753 z

ADE7753

–23–

REV. PrC 01/02

PRELIMINARY TECHNICAL DATA

E(t)

−R

S

T

U

V

W

4. (1+ 2. /8.9Hz) sin(4.

...)

ff ft

VIt

Figure 38 – Output frequency ripple

LINE CYCLE ENERGY ACCUMULATION MODELINE CYCLE ENERGY ACCUMULATION MODE

LINE CYCLE ENERGY ACCUMULATION MODE

In Line Cycle Energy Accumulation mode, the energy

accumulation of the ADE7753 can be synchronized to the

Channel 2 zero crossing so that active energy can be accumu-

lated over an integral number of half line cycles. The

advantage of summing the active energy over an integer

number of half line cycles is that the sinusoidal component in

the active energy is reduced to zero. This eliminates any

ripple in the energy calculation. Energy is calculated more

accurately and in a shorter time because integration period

can be shortened. By using the line cycle energy accumula-

tion mode, the energy calibration can be greatly simplified

and the time required to calibrate the meter can be signifi-

cantly reduced. The ADE7753 is placed in line cycle energy

accumulation mode by setting bit 7 (CYCMODE) in the

Mode register. In Line Cycle Energy Accumulation Mode

the ADE7753 accumulates the active power signal in the

LAENERGY register (Address 04h) for an integral number

of half cycles, as shown in Figure 39. The number of half line

cycles is specified in the LINECYC register (Address 1Ch).

The ADE7753 can accumulate active power for up to 65,535

half cycles. Because the active power is integrated on an

integral number of half line cycles, at the end of an line cycle

energy accumulation cycle the CYCEND flag in the Inter-

rupt Status register is set (bit 2). If the CYCEND enable bit

in the Interrupt Enable register is enabled, the IRQ output

will also go active low. Thus the IRQ line can also be used

to signal the completion of the line cycle energy accumula-

tion. Another calibration cycle will start as long as the

CYCMODE bit in the Mode register is set. Note that the

result of the first calibration is invalid and should be ignored.

The result of all subsequent line cycle accumulation is

correct.

From Equations 6 and 10.

()

∫∫ ⋅

































−=

nTnT

dttf

dtVItE

2cos

9.8

)(

(12)

where n is a integer and T is the line cycle period. Since the

sinusoidal component is integrated over a integer number of

line cycles its value is always zero.

Therefore:

E(t) VI dt

=+

(13)

E(t) VInT=

(14)

CALIBRATION

CONTROL

LINCYC

[

15:0

]

Power Phase B

LPF1

FROM

CHANNEL 2

ADC

ZEROCROSS

DETECT

ACCUMULATE ACTIVE POWER DURING

LINCYC ZERO-CROSSINGS

55 0

LAENERGY[23:0]

WDIV

23 0

Figure 39 – Energy Calculation in Line Cycle Energy Accu-

mulation Mode

Note that in this mode, the 16-bit LINECYC register can

hold a maximum value of 65,535. In other words, the line

energy accumulation mode can be used to accumulate active

energy for a maximum duration over 65,535 half line cycles.

At 60Hz line frequency, it translates to a total duration of

65,535 / 120Hz = 546 seconds.

POSITIVE ONLY ACCUMULATION MODEPOSITIVE ONLY ACCUMULATION MODE

POSITIVE ONLY ACCUMULATION MODE

In Positive Only Accumulation mode, the energy accumula-

tion is done only for positive power, ignoring any occurrence

of negative power above or below the no load threshold as

shown in Figure 40. The ADE7753 is placed in positive only

accumulation mode by setting the MSB of the MODE

off. Transitions in power going negative to positive or

positive to negative set the IRQ pin to active low if the

Interrupt Enable register is enabled. The Interrupt Status

Registers, PPOS and PNEG, show which transition has

occurred. See ADE7753 Register Descriptions.

Active Power

IRQ

Active Energy

PNEGPPOS PNEG

Interrupt Status Registers

No-load

threshold

No-load

threshold

PNEGPPOS PPOS

Figure 40 – Energy Accumulation in Positive Only

Accumulation Mode