ADE7166 datasheet(64/144 Pages) AD

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ADE7566/ADE7569/ADE7166/ADE7169

Rev. A | Page 64 of 144

Reactive Power Gain Calibration

Figure 71 shows the signal processing chain for the

ADE7569/ADE7169 reactive power calculation. As explained in

the Reactive Power Calculation for the ADE7569/ADE7169

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]). Equation 25 shows

how the gain adjustment is related to the contents of the watt

gain register.

Output VARGAIN

⎟

⎠

⎞

⎜

⎝

⎛

⎭

⎬

⎫

⎩

⎨

⎧ +

VARGAIN

Power

Reactive

(25)

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 ADE7569/ADE7169.

Reactive Power Offset Calibration

The ADE7569/ADE7169 also incorporate a reactive power

offset register (VAROS[15:0]). This is a signed, twos complement,

16-bit register that can be used to remove offsets in the reactive

power calculation (see Figure 71). 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.

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 45 summarizes the relationship of the phase difference

between the voltage and the current and the sign of the resulting

VAR calculation.

Table 45. Sign of Reactive Power Calculation

Angle

Integrator

Sign

Between 0° to +90°

Off

Positive

Between –90° to 0°

Off

Negative

Between 0° to +90°

Positive

Between –90° to 0°

Negative

Reactive Power Sign Detection

The ADE7569/ADE7169 detect a change of sign in the reactive

power. The VARSIGN flag in the Interrupt Status 1 SFR

(MIRQSTL, 0xDC) records when a change of sign has occurred

according to the VARSIGN bit in the ACCMODE register

(0x0F). If the VARSIGN bit is set in the Interrupt Enable 1 SFR

(MIRQENL, 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 VARSIGN in the ACCMODE register (0x0F) is cleared

(default), the VARSIGN flag in the Interrupt Status 1 SFR

(MIRQSTL, 0xDC) is set when a transition from positive to

negative reactive power occurrs.

When VARSIGN in the ACCMODE register (0x0F) is set, the

VARSIGN flag in the Interrupt Status 1 SFR (MIRQSTL, 0xDC)

is set when a transition from negative to positive reactive power

occurrs.

Reactive Power No-Load Detection

The ADE7569/ADE7169 include a no-load threshold feature on

the reactive energy that eliminates any creep effects in the

meter. The ADE7569/ADE7169 accomplish this by not

accumulating reactive energy when the multiplier output is

below the no-load threshold. When the reactive power is below

the no-load threshold, the RNOLOAD flag in the Interrupt Status

1 SFR (MIRQSTL, 0xDC) is set. If the RNOLOAD bit is set in the

Interrupt Enable 1 SFR (MIRQENL, 0xD9), the 8052 core has a

pending ADE interrupt. The ADE interrupt stays active until the

RNOLOAD status bit is cleared (see the Energy Measurement

Interrupts section).

The no-load threshold level is selectable by setting the

VARNOLOAD bits in the NLMODE register (0x0E).

Setting these bits to 0b00 disables the no-load detection,

and setting them to 0b01, 0b10, or 0b11 sets the no-load

detection threshold to 0.015%, 0.0075%, and 0.0037% of

the full-scale output frequency of the multiplier, respectively.

REACTIVE ENERGY CALCULATION FOR THE

ADE7569/ADE7169

As for active energy, the ADE7569/ADE7169 achieve the

integration of the reactive power signal by continuously

accumulating the reactive power signal in an internal, nonreadable,

49-bit energy register. The reactive energy register (VARHR[23:0])

represents the upper 24 bits of this internal register. The

VARHR register and its function are available for the

ADE7569/ADE7169 but not for the ADE7566/ADE7166.

The discrete time sample period (T) for the accumulation register

in the ADE7569/ADE7169 is 1.22 μs (5/MCLK). As well as

calculating the energy, this integration removes any sinusoidal

components that may be in the active power signal. Figure 71

shows this discrete time integration or accumulation. The

reactive power signal in the waveform register is continuously

added to the internal reactive energy register.

The reactive energy accumulation depends on the setting of the

SAVARM and ABSVARM bits in the ACCMODE register (0x0F).

When both bits are cleared, the addition is signed and, therefore,

negative energy is subtracted from the reactive energy contents.

When both bits are set, the ADE7569/ADE7169 are set to be in

the more restrictive mode, the absolute accumulation mode.

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