STPM32 datasheet(43/121 Pages) STMICROELECTRONICS

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DS10272 Rev 8

43/121

STPM32, STPM33, STPM34

Theory of operation

121

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

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).

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

CxData [23:0]

LPF

Offset

LED

ADC

OFAx[9:0]

PHxMomentary Active Power[28:0]

PHx Active Power[28:0]

PHx Active Energy[31:0

GIPG1703140852LM

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