STPM32 datasheet(29/89 Pages) STMICROELECTRONICS

29 / 89 page

8.4.1

Active power and energy calculation

The signal chain for the active power, energy calculations and related frequency conversion are shown in

Figure 33. The instantaneous power signal p(t) is generated by multiplying the current and voltage signals. This

value can be compensated by the active power offset calibration block (OFAx[8:0] in DSP_CR9 and DSP_CR11

registers). DC component of the instantaneous power signal (average power) is then extracted by LPF (low-pass

filter) to obtain the active power information.

Figure 33. Active power and energy calculation block diagram

IIPx

IINx

PLNA

VIPx

VINx

HPF

ROCOIL

INT

BHPFVx

BHPFCx

ROCx

Vx Data [23:0]

Vx [23:0]

Cx [23:0]

bsV

bsC

CHVx[11:0]

CHCx[11:0]

Phase

Compensation

Phase

Compensation

Cx Data [23:0]

LPF

Offset

LED

ADC

OFAx[9:0]

PHx Momentary Active Power[28:0]

PHx Active Power[28:0]

PHx Active Energy[31:0]

The active power is calculated simultaneously and independently for primary and secondary current channels.

Results of the calculated quantities are stored in the registers as follows:

EP1 = primary current channel active energy PH1 ACTIVE Energy[31:0]

P1 = primary current channel active power PH1 Active Power[28:0]

p1(t) = primary current channel instantaneous active power PH1 Momentary Active Power [28:0]

EP2 = secondary current channel active energy PH2 Active Energy[31:0]

P2 = secondary current channel active power PH2 Active Power[28:0]

p2(t) = secondary current channel instantaneous active power PH2 Momentary Active Power[28:0]

Active power measurements have a bandwidth of 3.6 kHz and include the effects of any harmonic within that

range.

8.4.2

Fundamental active power and energy calculation

The signal chain for the fundamental active power, energy calculations and related frequency conversion are

shown in Figure 34. The signal flow is the same as the active energy wideband, but voltage and current

waveforms are filtered to remove all harmonic components but the first (45 - 65 Hz). Power value can be

compensated by the active power offset calibration block (OFAFx[8:0] in DSP_CR9 and DSP_CR11).

STPM32, STPM33, STPM34

Functional description of hardwired DSP

DS10272 - Rev 13

page 29/89

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