ADE7880 datasheet(63/104 Pages) AD

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Data Sheet

ADE7880

Rev. A | Page 63 of 104

HPGAIN

HXWATTOS

HXWATT

HPGAIN

HYWATTOS

HYWATT

HPGAIN

HZWATTOS

HZWATT

HPGAIN

HXVAROS

HXVAR

HPGAIN

HYVAROS

HYVAR

HPGAIN

HZVAROS

HZVAR

Figure 86. Harmonic Active and Reactive Powers Signal Processing

The harmonic distortions of the three harmonic components

are stored into the HXVHD, HXIHD, HYVHD, HYIHD,

HZVHD, and HZIHD 24-bit registers in 3.21 signed format.

This means the ratios are limited to +3.9999 and all greater

results are clamped to it.

As a reference, Table 20 presents the ADE7880 harmonic engine

outputs when one phase is analyzed and the registers in which

the outputs are stored.

Harmonic Calculations When the Neutral is Monitored

When the neutral current and the sum of phase currents are

monitored, only the harmonic rms related registers are updated.

The registers HX, HY and HZ identify the index of the harmonic,

including the fundamental. When a phase is analyzed, the

fundamental rms values are calculated continuously and the

results are stored in dedicated registers FIRMS and FVRMS.

When the neutral is analyzed, the fundamental information is

calculated by setting one of the harmonic index registers HX,

HY or HZ to 1 and the results are stored in harmonic registers.

The maximum index allowed in HX, HY and HZ registers is 63.

The no attenuation pass band is 2.8 kHz, corresponding to a

−3 dB bandwidth of 3.3 kHz, thus all harmonics of frequency

lower than 2800 Hz are supported without attenuation.

HXIRMS, HYIRMS and HZIRMS registers contain the harmonic

rms components of the neutral current and HXVRMS, HYVRMS

and HZVRMS registers contain the harmonic rms components

of ISUM. Note that in this case, the rms of the fundamental

component is not computed into FIRMS or FVRMS registers,

but it is computed if one of the index registers HX, HY and HZ

is initialized with 1.

If the HX register is initialized to 1, the ADE7880 computes the

harmonic distortions of the other harmonics identified into HY

HYVHD, HYIHD, HZVHD, and HZIHD 24-bit registers. The

distortions of the neutral current are saved into HYIHD and

HZIHD registers and the distortions of the ISUM are stored

into the HYVHD and HZVHD registers. As HX is set to 1, th

HXIHD and HXVHD registers contain 0x1FFFFF, a number

representing 1 in 3.21 signed format.

As a reference, Table 21 presents the

and HZ registers and stores them in 3.21 signed format into the

DE7880 harmonic engine

ate Rate

From

isters,

ic engine output registers is

o ways to manage the harmonic

FG)

outputs when the neutral current and ISUM are analyzed and

the registers in which the outputs are stored.

Configuring Harmonic Calculations Upd

The ADE7880 harmonic engine functions at 8 kHz rate.

the moment the HCONFIG register is initialized and the

harmonic indexes are set in the HX, HY and HZ index reg

the ADE7880 calculations take typically 750 ms to settle within

the specification parameters.

The update rate of the harmon

managed by Bits[7:5] (HRATE) in HCONFIG register and i

independent of the engine’s calculations rate of 8 kHz. The defaul

value of 000 means the registers are updated every 125 μsec

(8 kHz rate). Other update periods are: 250 μsec (HRATE =

001), 1 ms (010), 16 ms (011), 128 ms (100), 512 ms (101),

1.024 sec (110). If HRATE bits are 111, then the harmonic

calculations are disabled.

The ADE7880 provides tw

computations. The first approach, enabled when Bit 0 (HRC

of HCONFIG register is cleared to its default value of 0, sets Bit

19 (HREADY) in STATUS0 register to 1 after a certain period

of time and then every time the harmonic calculations are updated

at HRATE frequency. This allows an external microcontroller to

access the harmonic calculations only after they have settled.

The time period is determined by the state of Bits[4:3] (HSTIME)

in the HCONFIG register. The default value of 01 sets the time

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