AN3322 datasheet(31/38 Pages) STMICROELECTRONICS

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AN3322

Computational issues and compensation algorithms

The voltage and IL are shifted by two samples:

Equation 31

Tshift_I_L ~ 2 samples ~3 µs ~ 0.05 deg.

The voltage and IH are shifted by four samples:

Equation 32

Tshift_I_H ~ 4 samples ~ 6 µs ~ 0.1 deg.

Table 6 shows what level of the phase shift correction is necessary to be reached in order to

lower the error caused by the phase shift to an acceptable value. It can be seen that we

need to correct the phase shift to a value lower than 0.1 deg. This value can be easily

reached by the phase shift compensation filter introduced in Section 2.7.3, compensating

with the step of 0.013 deg. The value 0.013 deg. allows negligible error of the instant power

caused by the phase shift to be reached.

Data from Table 6 are depicted in Figure 19, Figure 20, and Figure 21.

Table 6. Error of instant power caused by phase shift

Sampling time trigger shifted

by [deg.]

Error of instant power [%]

for PF = 1

Error of instant power [%]

for PF = 0.5

0.01

0.000002

0.030232

0.02

0.000006

0.060466

0.05

0.000038

0.151200

0.1

0.000152

0.302500

0.2

0.000609

0.605200

0.5

0.003808

1.515300

0.015230

3.038100

0.060917

6.105700

0.380500

15.476300

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