CS5484 datasheet(19/67 Pages) CIRRUS

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CS5484

DS981F3

4.8.2 Line-cycle Synchronized Averaging

When operating in Line-cycle Synchronized Averaging

mode, and when line frequency measurement is

enabled (see section 5.4 Line Frequency Measurement

on page 22), the CS5484 uses the voltage (V) channel

zero crossings and measured line frequency to

automatically adjust N such that the averaging period

will be equal to the number of half line-cycles in the

CycleCount register. For example, if the line frequency

is 51Hz, and the CycleCount register is set to 100, N will

4000

(100/2)/51 = 3921

during

continuous

conversion. N is self-adjusted according to the line

frequency, therefore the averaging period is always

close to the whole number of half line-cycles, and the

low-rate calculation results will minimize ripple and

maximize resolution, especially when the line frequency

varies. Before starting a low-rate conversion in the

Line-cycle

Synchronized

Averaging

mode,

the

SampleCount register should not be changed from its

default value of 4000, and bit AFC of the Config2

host processor should not change the SampleCount

4.8.3 RMS Current and Voltage

The root mean square (RMS in Figure 11) calculations

are performed on N instantaneous current and voltage

samples using Equation 1:

4.8.4 Active Power

The instantaneous voltage and current samples are

multiplied to obtain the instantaneous power (P1, P2)

(see Figures 9 and 10). The product is then averaged

over N samples to compute active power (P1AVG,

P2AVG).

4.8.5 Reactive Power

Instantaneous reactive power (Q1, Q2) are sample rate

results obtained by multiplying instantaneous current

(I1, I2) by instantaneous quadrature voltage (V1Q,

V2Q),

which

are

created

phase

shifting

instantaneous voltage (V1, V2) 90 degrees using

first-order integrators (see Figures 9 and 10). The gain

of these integrators is inversely related to line

frequency, so their gain is corrected by the Epsilon

power (Q1AVG, Q2AVG) is generated by integrating the

instantaneous quadrature power over N samples.

4.8.6 Apparent Power

By default, the CS5484 calculates the apparent power

(S1, S2) as the product of RMS voltage and current, as

shown in Equation 2:

The CS5484 also provides an alternate apparent power

calculation method. The alternate apparent power

method uses real power (P1AVG, P2AVG) and reactive

power (Q1AVG, Q2AVG) to calculate apparent power.

See Equation 3:

The APCM bit in the Config2 register controls which

method is used for apparent power calculation.

4.8.7 Peak Voltage and Current

Peak current (I1PEAK, I2PEAK) and peak voltage

(V1PEAK, V2PEAK) are calculated over N samples and

recorded in the corresponding channel peak register

documented in the register map. This peak value is up-

dated every N samples.

4.8.8 Power Factor

Power factor (PF1, PF2) is active power divided by ap-

parent power. The sign of the power factor is deter-

mined by the active power. See Equation 4:

RMS

–



--------------------

VRMS

–



----------------------

[Eq: 1]

SVRMS IRMS



[Eq: 2]

SQAVG2 PAVG2

[Eq: 3]

PACTIVE

----------------------

[Eq: 4]

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