STPM32 datasheet(40/121 Pages) STMICROELECTRONICS

40 / 121 page

Theory of operation

STPM32, STPM33, STPM34

40/121

DS10272 Rev 8

ROCx = 0: channel x current sensor is CT or shunt

ROCx = 1: channel x current sensor is Rogowski coil

In case of ROCx = 1, integrator filter is included to integrate current signal coming from

Rogowski coil current sensor. Rogowski coil integrator is selectable independently for each

current channel.

8.3.5

Fundamental component filter

This low-pass filter on the voltage and current signals is used to calculate: zero-crossing,

period, phase-angles and fundamental active and reactive energy. Filtered voltage and

current components are available on DSP_REG6, DSP_REG7, DSP_REG8, DSP_REG9

named VxFund and CxFund.

8.3.6

Reactive filter

Reactive filter introduces a delay in current and voltage streams respectively; these signals

are used to calculate reactive power and energy.

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 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 12 for each configuration value. Maximum LED pulse width is anyway fixed to 81.92

STPM32 Datasheet(PDF) 40 Page - STMicroelectronics

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