ADE5166_08 AD [Analog Devices], ADE5166_08 Datasheet - Page 59

• Manufacturer Part Number: ADE5166_08
• Description: Single-Phase Energy Measurement IC with 8052 MCU, RTC, and LCD Driver
• Manufacturer: AD [Analog Devices]

Reactive Power Gain Calibration
Figure 67 shows the signal processing chain for the ADE5169
reactive power calculation. As explained in the Reactive Power
Calculation (ADE5169) section, the reactive power is calculated by
applying a low-pass filter to the instantaneous reactive power
signal. Note that, when reading the waveform samples from the
output of LPF2, the gain of the reactive energy can be adjusted by
using the multiplier and by writing a twos complement, 12-bit
word to the var gain register (VARGAIN[11:0], Address 0x1E).
Equation 23 shows how the gain adjustment is related to the
contents of the var gain register.
The resolution of the VARGAIN register is the same as the
WGAIN register (see the Active Power Gain Calibration section).
VARGAIN can be used to calibrate the reactive power (or energy)
calculation in the ADE5169.
Reactive Power Offset Calibration
The ADE5169 also incorporates a reactive power offset register
(VAROS[15:0] (Address 0x21). This is a signed, twos complement,
16-bit register that can be used to remove offsets in the reactive
power calculation (see Figure 67). An offset can exist in the reactive
power calculation due to crosstalk between channels on the PCB
or in the IC itself. The offset calibration allows the contents of
the reactive power register to be maintained at 0 when no power
is being consumed.
The 256 LSBs (VAROS = 0x100) written to the reactive power
offset register are equivalent to 1 LSB in the WAVMODE register
(Address 0x0D).
Output VARGAIN =
⎛
⎜
⎝
CURRENT
CHANNEL
Reactive
VOLTAGE
CHANNEL
Power
HPF
×
PHCAL[7:0]
SHIFTING FILTER
⎧ +
⎨
⎩
1
90° PHASE
VARGAIN
2
2
12
T
⎫
⎬
⎭
⎞
⎟
⎠
REACTIVE POWER
LPF2
MCLK
sgn
SIGNAL
5
TIME (nT)
VAROS[15:0]
2
6
Figure 67. Reactive Energy Calculation
2
+
5
+
2
WAVEFORM
REGISTER
–6
VALUES
Rev. 0 | Page 59 of 148
(23)
2
–7
FOR WAVEFORM
2
–8
SAMPLING
VARGAIN[11:0]
Sign of Reactive Power Calculation
Note that the average reactive power is a signed calculation.
The phase shift filter has −90° phase shift when the integrator
is enabled and +90° phase shift when the integrator is disabled.
Table 46 summarizes the relationship of the phase difference
between the voltage and the current and the sign of the resulting
var calculation.
Table 46. Sign of Reactive Power Calculation
Angle
Between 0° to +90°
Between –90° to 0°
Between 0° to +90°
Between –90° to 0°
Reactive Power Sign Detection
The ADE5169 detects a change of sign in the reactive power.
The VARSIGN flag (Bit 4) in the Interrupt Status 1 SFR
(MIRQSTL, Address 0xDC) records when a change of sign has
occurred according to the VARSIGN bit (Bit 5) in the ACCMODE
register (Address 0x0F). If the VARSIGN bit is set in the Interrupt
Enable 1 SFR (MIRQENL, Address 0xD9), the 8052 core has a
pending ADE interrupt. The ADE interrupt stays active until the
VARSIGN status bit is cleared (see the Energy Measurement
Interrupts section).
When the VARSIGN bit (Bit 5) in the ACCMODE register
(Address 0x0F) is cleared (default), the VARSIGN flag (Bit 4)
in the Interrupt Status 1 SFR (MIRQSTL, Address 0xDC) is set
when a transition from positive to negative reactive power occurs.
When VARSIGN in the ACCMODE register (Address 0x0F) is
set, the VARSIGN flag in the Interrupt Status 1 SFR (MIRQSTL,
Address 0xDC) is set when a transition from negative to positive
reactive power occurs.
DIGITAL-TO-FREQUENCY
VARDIV[7:0]
CONVERTER
%
TO
+
+
48
23
V ARHR[23:0 ]
OUTPUTS FROM THE LPF2 ARE
ACCUMULATED (INTEGRATED) IN
THE INTERNAL REACTIVE ENERGY
REGISTER
Integrator
Off
Off
On
On
ADE5166/ADE5169
0
UPPER 24 BITS ARE
ACCESSIBLE THROUGH
VARHR[23:0] REGISTER
Sign
Positive
Negative
Positive
Negative
0