ADE7758 datasheet(37/68 Pages) AD

37 / 68 page

ADE7758

Rev. A | Page 37 of 68

VARG[11:0]

VARDIV[7:0]

° PHASE

SHIFTING FILTER

MULTIPLIER

HPF

CURRENT SIGNAL–i(t)

0x2851EC

0x00

0xD7AE14

VOLTAGE SIGNAL–v(t)

0x2852

0x00

0xD7AE

LPF2

SIGN

2–1 2–2 2–3 2–4

VAROS[11:0]

VARHR[15:0]

TOTAL REACTIVE POWER IS

ACCUMULATED (INTEGRATED) IN

THE VAR-HR ACCUMULATION REGISTERS

Figure 72. ADE7758 Reactive Energy Accumulation

Energy Accumulation Mode

When overflow occurs, the VAR-hr accumulation registers

content can rollover to full-scale negative (0x8000) and continue

increasing in value when the reactive power is positive. Con-

versely, if the reactive power is negative the VAR-hr accumulation

registers content can roll over to full-scale positive (0x7FFF)

and continue decreasing in value.

The reactive power accumulated in each VAR-hr accumulation

configuration of the CONSEL bits in the COMPMODE register

(Bit 0 and Bit 1). The different configurations are described in

Table 9.

Table 9. Inputs to VAR-Hr Accumulation Registers

By setting the REHF bit (Bit 1) of the mask register, the

ADE7758 can be configured to issue an interrupt (IRQ) when

Bit 14 of any one of the three VAR-hr accumulation registers

has changed, indicating that the accumulation register is half

full (positive or negative).

CONSEL[1, 0]

AVARHR

BVARHR

CVARHR

VA × IA’

VB × IB

VC × IC’

VA(IA’ – IB’)

VC (IC’ – IB’)

VA(IA’ – IB’)

VC × IC’

Reserved

Note that IA’/IB’/IC’ are the current phase shifted current waveform.

Setting the RSTREAD bit (Bit 6) of the LCYMODE register

enables a read-with-reset for the VAR-hr accumulation

registers, i.e., the registers are reset to 0 after a read operation.

The contents of the VAR-hr accumulation registers are affected

by both the current gain register (IGAIN) and the VAR gain

Integration Time Under Steady Load

The discrete time sample period (T) for the accumulation

on the analog inputs, and a 90° phase difference between the

voltage and the current signal (the largest possible reactive

power), and the VAR gain registers set to 0x000, the average

word value from each LPF2 is 0xCCCCD. The maximum value

that can be stored in the reactive energy register before it

overflows is 215 − 1 or 0x7FFF. As the average word value is first

added to the internal register, which can store 240 − 1 or 0xFF,

FFFF, FFFF before it overflows, the integration time under these

conditions with VARDIV = 0 is calculated as

Reactive Power Frequency Output

Pin 17 (VARCF) of the ADE7758 provides frequency output for

the total reactive power. Similar to APCF, this pin provides an

output frequency that is directly proportional to the total reactive

power. The pulse width of VARPCF is 64 × CLKIN if VARCFNUM

and VARCFDEN are both equal. If VARCFDEN is greater than

VARCFNUM, the pulse width depends on VARCFDEN. The

pulse width in this case is T × (VARCFDEN/2), where T is the

period of the VARCF pulse and VARCFDEN/2 is rounded to

the nearest whole number. An exception to this is when the

period is greater than 180 ms. In this case, the pulse width is

fixed at 90 ms.

second

0.5243

μs

0.4

0xCCCCD

FFFF

FFFF,

0xFF,

Time

When VARDIV is set to a value different from 0, the time

before overflow are scaled accordingly as shown in Equation 21.

() VARDIV

VARDIV

Time

(21)

A digital-to-frequency converter (DFC) is used to generate the

VARCF pulse output from the total reactive power. The TERMSEL

bits (Bit 2 to Bit 4) of the COMPMODE register can be used to

select which phases to be included in the total reactive power

calculation. Setting Bit 2, Bit 3, and Bit 4 includes the input to

the AVARHR, BVARHR, and CVARHR registers in the total

active power calculation. The total reactive power is signed

addition. However, setting the SAVAR bit (Bit 6) in the

COMPMODE register enables absolute value calculation.

ADE7758 数据表(PDF) 37 Page - Analog Devices

ADE7758 数据表(HTML) 37 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68

数据表下载