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Fabricante

SA9604

THREE PHASE BIDIRECTIONAL POWER/ENERGY METERING IC WITH SERIAL SPI INTERFACE

South African Micro Electronic Systems 

7.2 Reactive Energy

With a pf close to 0 establish the phase error:

PhaseError = arctan (VARMeaured / ActiveMeasured)

For each measurement calculate the following:

SA9604A

VA

=

PHIcalibrated =

PHICorrected =

VARtrue =

ActiveMeasured2 + VARmeasured2

arctan (VARmeasured / ActiveMeasured)

PHIcalibrated - PhaseError

VA * sin(PHICorrected)

TYPICAL APPLICATION

In the Application Circuit (Figure 1), the components required for a three phase energy

metering application are shown.

Terminated current sensors (current transformers) are connected to the current sensor

inputs of the SA9604A through current setting resistors (R8 ..R13).

The resistor values for standard operation are selected for an input current of 16µARMS

into the SA9604A, at the rated line current.

The values of these resistors are calculated as follows:

Phase 1:

R8 = R9 = (IL1/16µARMS) * R18/2

Phase 2:

R10 = R11 = (IL2/16µARMS) * R19/2

Phase 3:

R

12

=

R

13

=

(IL3/16µARMS)

*

R /2

20

Where ILX

= Secondary CT current at rated conditions.

R18, R19 and R20 = Current transformer termination resistors for the three phases.

R1 + R1A, R4 and R15 set the current for the phase 1 voltage sense input. R2 + R2A, R5 +

P and R set the current for phase 2 and R + R , R and R set the current for phase

5

16

3

3A 6

17

3. The values should be selected so that the input currents into the voltage sense inputs

(virtual ground) are set to 14µARMS for the rated line voltage condition. Capacitors C1, C2

and C3 are for decoupling and phase compensation.

R

14

defines

all

on-chip

bias and

reference

currents.

With R

14

= 47kΩ, optimum conditions

are set. R may be varied by up to ± 10% for calibration purposes. Any changes to R

14

14

will affect the output quadratically (i.e: ∆R = +5%, ∆P = +10%).

XTAL is a colour burst TV crystal (f = 3.5795 MHz) for the oscillator. The oscillator

frequency is divided down to 1.78975 MHz on-chip, to supply the digital circuitry and the

A/D converters.

sames

15/20

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