STPM32 datasheet(27/89 Pages) STMICROELECTRONICS

27 / 89 page

Input streams for reactive filter are VxFund and CxFund signals.

8.4

Functional description of hardwired DSP

From the decimation and filtering block, signals are fed to hardwired DSP to compute the following quantities for

primary and secondary channels:

•

Active power and energy wideband 0 Hz (4 Hz) - 3.6 kHz

•

Active power and energy fundamental 45 - 65 Hz

•

Reactive power and energy

•

Apparent power and energy from RMS data

•

Apparent power vectorial calculation

•

Signal measurement: RMS, period, zero-crossing, phase-delay, sag and swell, tamper

Each power signal is accumulated in the correspondent energy register every new sample, so at a rate of 7.8125

kHz.

Energy registers are up-down counters. The accumulation is signed so that the negative energy is subtracted

from the positive energy. When the measured power is positive, the energy register increases its content from

0x00000000 up to the maximum value, 0xFFFFFFFF, then it rolls from 0xFFFFFFFF back to 0x00000000.

Vice versa, when the power is negative, the register decreases its content; from 0x00000000 rolls to 0xFFFFFFFF

and continues decreasing till 0x00000000.

To monitor each energy register overflow and power sign, status bits are available on DSP_SR1 and DSP_SR2.

When an energy threshold is reached, a pulse is generated on LED pin.

This pulse is generated by monitoring two consecutive bits of the energy register: the LED signal goes high when

the two selected bits commute to 01 and goes low when the bits change to 11.

The configuration bits LPWx[3:0] in DSP_CR1 and DSP_CR2 shift the default bits for pulse generation, thus

changing the default pulse frequency of a given factor, indicated in Table 11 for each configuration value.

Maximum LED pulse width is anyway fixed to 81.92 ms (640 periods of 7812.5 Hz clock).

Table 11. LPWx bits

LPWx

LED_PWM

0000

0.0625

0001

0.125

0010

0.25

0011

0.5

0100

0101

0110

0111

1000

1001

1010

1011

128

1100

256

1101

512

1110

1024

1111

2048

The signal chain for each power, energy calculations and related frequency conversion are explained in the

following section.

STPM32, STPM33, STPM34

Functional description of hardwired DSP

DS10272 - Rev 13

page 27/89

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