ADE7953ACPZ datasheet(38/68 Pages) AD

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ADE7953

Data Sheet

Rev. A | Page 38 of 68

POWER FACTOR

The ADE7953 provides a direct power factor measurement

simultaneously on Current Channel A and Current Channel B.

Power factor in an ac circuit is defined as the ratio of the active

power flowing to the load to the apparent power. The power

factor measurement is defined in terms of “leading” or “lagging,”

referring to whether the current waveform is leading or lagging

the voltage waveform.

When the current waveform is leading the voltage waveform,

the load is capacitive and is defined as a negative power factor.

When the current waveform is lagging the voltage waveform,

the load is inductive and is defined as a positive power factor.

The relationship of the current waveform to the voltage wave-

form is illustrated in Figure 59.

ACTIVE (–)

REACTIVE (–)

ACTIVE (+)

REACTIVE (–)

+60° = θ; PF = –0.5

–60° = θ; PF = +0.5

ACTIVE (–)

REACTIVE (+)

ACTIVE (+)

REACTIVE (+)

CAPACITIVE LOAD:

CURRENT LEADS

VOLTAGE

INDUCTIVE LOAD:

CURRENT LAGS

VOLTAGE

Figure 59. Capacitive and Inductive Loads

As shown in Figure 59, the reactive power measurement is

negative when the load is capacitive and positive when the

load is inductive. The sign of the reactive power can therefore

be used to reflect the sign of the power factor.

The mathematical definition of power factor is shown in

Equation 37.

Power Factor =

(37)

Power

Apparent

Power

Active

Power

Reactive

Sign

)

(

The power factor measurement includes the effect of all

harmonics over the 1.23 kHz bandwidth.

The power factor readings are stored in two 16-bit, signed

registers: PFA (Address 0x10A) for Current Channel A and

PFB (Address 0x10B) for Current Channel B. These registers are

signed, twos complement registers with the MSB indicating the

polarity of the power factor. Each LSB of the PFx register equates

to a weight of 2−15; therefore, the maximum register value of

0x7FFF corresponds to a power factor value of 1. The minimum

By default, the instantaneous active and apparent power

readings are used to calculate the power factor, and the register

is updated at a rate of 6.99 kHz. The sign bit is taken from the

instantaneous reactive energy measurement on each channel.

USING THE LINE CYCLE ACCUMULATION MODE

TO DETERMINE THE POWER FACTOR

If a power factor measurement with more averaging is required,

the ADE7953 can use the line cycle accumulation measurement

on the active and apparent energies to determine the power factor

(see the Active Energy Line Cycle Accumulation Mode section

and the Apparent Energy Line Cycle Accumulation Mode section).

This option provides a more stable power factor reading.

To use the line cycle accumulation mode to determine the power

factor, the ADE7953 must be configured as follows:

•

The PFMODE bit (Bit 3) must be set to 1 in the CONFIG

•

The line cycle accumulation mode must be enabled on

both the active and apparent energies by setting the

xLWATT and xLVA bits to 1 in the LCYCMODE register

(Address 0x004).

When using line cycle accumulation to determine the power

factor, the update rate of the power factor measurement is an

integral number of half line cycles. The number of half line cycles

is programmed in the LINECYC register (Address 0x101). For

complete information about setting up the line cycle accumula-

tion mode, see the Active Energy Line Cycle Accumulation Mode

section and the Apparent Energy Line Cycle Accumulation

Mode section.

POWER FACTOR WITH NO-LOAD DETECTION

The power factor measurement is affected by the no-load

condition if no-load detection is enabled (see the No-Load

Detection section). The following considerations apply only

when no-load detection is enabled and a no-load condition

occurs:

•

If the apparent energy no-load condition is true, the power

factor measurement is set to 1 because it is assumed that

there is no active or reactive power.

•

If the active energy no-load condition is true, the power

factor measurement is set to 0 because it is assumed that

the load is purely capacitive or inductive.

•

If the reactive energy no-load condition is true, the sign of

the power factor is based on the sign of the active power.

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