ADE7953 datasheet(31/68 Pages) AD

31 / 68 page

Data Sheet

ADE7953

Rev. A | Page 31 of 68

APPARENT POWER CALCULATION

Apparent power is defined as the maximum power that can be

delivered to a load. VRMS and IRMS are the effective voltage

and current delivered to the load, respectively. The apparent

power can, therefore, be defined as the product of VRMS and

IRMS. This relationship is independent of the phase angle

between the voltage and current.

Equation 26 provides an expression for the instantaneous

apparent power signal in an ac signal.

)

sin(

ωt

VRMS

V(t)

(23)

)

sin(

ωt

IRMS

I(t)

(24)

P(t) = V(t) × I(t)

(25)

P(t) = VRMS × IRMS × cos(θ) −

(26)

VRMS × IRMS × cos(2ωt + θ)

The ADE7953 computes the apparent power simultaneously

on Current Channel A and Current Channel B and stores the

resulting measurements in the AVA (Address 0x210 and

Address 0x310) and BVA (Address 0x211 and Address 0x311)

registers, respectively.

The apparent power measurement is taken over a bandwidth

of 1.23 kHz and includes the effects of any harmonics within

that range. The apparent power registers are updated at a rate of

6.99 kHz and can be read using the waveform sampling mode

(see the Instantaneous Powers and Waveform Sampling section).

APPARENT ENERGY CALCULATION

The apparent energy is given as the integral of the apparent

power.

∫

Power(t)dt

Apparent

Energy

Apparent

(27)

The ADE7953 achieves the integration of the apparent power

signal in two stages. In the first stage, the apparent power

signals are accumulated in an internal 48-bit register every

143 μs (6.99 kHz) until an internal fixed threshold is reached.

When this threshold is reached, a pulse is generated and is

accumulated in 24-bit, user accessible accumulation registers.

The internal threshold results in a maximum accumulation rate

of approximately 206.9 kHz with full-scale inputs.

This process occurs simultaneously on Current Channel A and

Current Channel B, and the resulting readings can be read in the

24-bit APENERGYA (Address 0x222 and Address 0x322) and

APENERGYB (Address 0x223 and Address 0x323) registers.

Note that the apparent energy register contents roll over to full-

scale negative (0x800000) and continue to increase in value

when the power or energy flow is positive. Conversely, if the

power is negative, the energy register underflows to full-scale

positive (0x7FFFFF) and continues to decrease in value.

APENERGYA and APENERGYB are read-with-reset registers

by default. This means that the contents of these registers are

reset to 0 after a read operation. This feature can be disabled

by clearing Bit 6 (RSTREAD) of the LCYCMODE register

(Address 0x004).

The ADE7953 includes two sets of interrupts that are triggered

when the apparent energy register is half full (positive or

negative) or when an overflow or underflow condition occurs.

The first set of interrupts is associated with the Current

Channel A apparent energy, and the second set of interrupts is

associated with the Current Channel B apparent energy.

These interrupts are disabled by default and can be enabled by

setting the VAEHFA and VAEOFA bits in the IRQENA register

(Address 0x22C and Address 0x32C) for Current Channel A,

and the VAEHFB and VAEOFB bits in the IRQENB register

(Address 0x22F and Address 0x32F) for Current Channel B.

Apparent Energy Integration Time Under Steady Load

The discrete time sample period (T) for the accumulation

registers is 4.83 μs (1/206.9 kHz). With full-scale sinusoidal

signals on the analog inputs, a pulse is generated and added

to the APENERGYA and APENERGYB registers every 4.83 μs,

assuming that the AVAGAIN and BVAGAIN registers are set

to 0x00. The maximum positive value that can be stored in the

24-bit APENERGYA and APENERGYB registers is 0x7FFFFF

before the register overflows. The integration time under these

conditions can be calculated as follows:

Time = 0x7FFFFF × 4.83 μs = 40.5 sec

(28)

CURRENT RMS

CHANNEL

A OR B

xVAOS

VOLTAGE

RMS

INTERNAL

ACCUMULATION

FIXED INTERNAL

THRESHOLD

APPARENT

POWER

SIGNAL

APENERGYx

xVAGAIN

Figure 55. Apparent Energy Accumulation Signal Chain

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