Datasheet

Data Sheet ADE7880
Rev. A | Page 63 of 104
HARMONIC
COMPONENTS
CALCULATIONS
HPGAIN HXWATTOS 2
2
÷
HXWATT
HPGAIN HYWATTOS 2
2
÷
HYWATT
HPGAIN HZWATTOS 2
2
÷
HZWATT
HPGAIN HXVAROS 2
2
÷
HXVAR
HPGAIN HYVAROS 2
2
÷
HYVAR
HPGAIN HZVAROS 2
2
÷
HZVAR
10193-061
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
e
DE7880 harmonic engine
ate Rate
From
isters,
ic engine output registers is
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t
o ways to manage the harmonic
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A
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