STPM32_V02 datasheet(39/89 Pages) STMICROELECTRONICS

39 / 89 page

Figure 44. Swell detection process

VFUND

CFUND

SWV_THR

SWC_THR

SWV_EV/SWC_EV = 0000

0001 0010

0101

1011

SWV_TIME / SWC_TIME

0110

SWELL Event

Start

SWELL Event

End

SWELL Event

Start

Overflow

Reset state

SWELL Event

End

Sag and swell threshold calculation

Thresholds for sag voltage detection are calculated below, according to the following input parameters:

VL: line voltage nominal RMS value

VSAG: target RMS value of sag voltage

R1, R2: voltage divider resistors

AV = 2, voltage channel gain

DSAG= 210, length of sag threshold register

calV = 0.875, calibrator mid value

Table 15. Voltage sag

Parameter

Value

SAG peak voltage

VSAG_peak=VSAG∙ 2

Input signal

Vin_SAG_peak=VSAG∙ 2∙ R2R1+R2 V

Percentage of FS input

Vin_SAG_peak FS = VSAGVref∙AV∙calV∙ 2∙ R2R1+R2

SAGV=VSAGVref∙AV∙ 2∙ R2R1+R2∙calV∙DSAGHEX

LSBSAG_V= Vref∙R1+R2

AV∙ 2∙R2∙calV∙DSAG V

To calculate the filtering time for the sag event, we consider the time in which the nominal instantaneous voltage

is below the sag threshold, that is:

Equation 15

time=2∙arcsin VSAGVL ∙10002πfL ms

(15)

To correctly distinguish between normal sinusoidal voltage and sag event, the filtering time should be added to

this component, for example half line period (10 ms at 50 Hz). Since LSB of SAG_TIME_THRx register is 8 μs

(FCLK = 125 kHz), the value to set is:

Equation 16

TIME= time+dt8us HEX

(16)

STPM32, STPM33, STPM34

Functional description of hardwired DSP

DS10272 - Rev 13

page 39/89

STPM32 Datasheet(PDF) 39 Page - STMicroelectronics

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