ADE5166 datasheet(59/148 Pages) AD

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ADE5166/ADE5169

Rev. 0 | Page 59 of 148

Reactive Power Gain Calibration

Sign of Reactive Power Calculation

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.

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

Integrator

Sign

Between 0° to +90°

Off

Positive

Between –90° to 0°

Off

Negative

Between 0° to +90°

Output VARGAIN =

⎟

⎠

⎞

⎜

⎝

⎛

⎭

⎬

⎫

⎩

⎨

⎧ +

VARGAIN

Power

Reactive

(23)

Positive

Between –90° to 0°

Negative

Reactive Power Sign Detection

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.

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

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).

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.

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.

The 256 LSBs (VAROS = 0x100) written to the reactive power

offset register are equivalent to 1 LSB in the WAVMODE register

(Address 0x0D).

VARGAIN[11:0]

VARDIV[7:0]

LPF2

CURRENT

CHANNEL

VOLTAGE

CHANNEL

TIME (nT)

MCLK

REACTIVE POWER

SIGNAL

VARHR[23:0]

UPPER 24 BITS ARE

ACCESSIBLE THROUGH

VARHR[23:0] REGISTER

FOR WAVEFORM

SAMPLING

WAVEFORM

VALUES

VAROS[15:0]

sgn

2–6 2–7 2–8

HPF

PHCAL[7:0]

90° PHASE

SHIFTING FILTER

OUTPUTS FROM THE LPF2 ARE

ACCUMULATED (INTEGRATED) IN

THE INTERNAL REACTIVE ENERGY

DIGITAL-TO-FREQUENCY

CONVERTER

Figure 67. Reactive Energy Calculation

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