STPM32 datasheet(31/89 Pages) STMICROELECTRONICS

31 / 89 page

Q2 = secondary current channel reactive power PH2 Reactive Power[28:0]

q2(t) = secondary current channel instantaneous active power PH2 Momentary Reactive Power[28:0].

8.4.4

Apparent power and energy calculation

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

Figure 36. The apparent power signal S is generated in two ways:

•

Vectorial methodology: uses the scalar product of active and reactive power. The active power is selectable

through the active power mode bit (APMx in DSP_CR1 and DSP_CR2) between wideband or fundamental.

Equation 2

Svec= P2+Q2

(2)

•

RMS methodology: uses the product of RMS data of voltage and current. This value can be compensated

by the apparent power offset calibration block (OFSx[8:0] in DSP_CR10 and DSP_CR12).

Equation 3

SRMS=VRMS∙IRMS

(3)

The apparent energy is calculated from vectorial or from RMS apparent power according to AEMx configuration

bit in DSP_CR1 and DSP_CR2.

Figure 36. Apparent power and energy calculation block diagram

Cx RMS Data [17:0]

Vx RMS Data [17:0]

Offset

√¯

APMx

S LED

AEMx

OFSx[9:0]

PHx Apparent Vectorial Power[28:0]

PHx Apparent Energy[31:0]

PHx Apparent RMS Power[28:0]

PHx Reactive Power[28:0]

PHx Fundamental Power[28:0]

PHx Active Power[28:0]

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

ES1 = primary current channel apparent energy PH1 Apparent Energy[31:0]

S1RMS = primary current channel apparent RMS power PH1 Apparent RMS Power[28:0]

S1vec = primary current channel apparent vectorial power PH1 Apparent Vectorial Power[28:0]

ES2 = secondary current channel apparent energy PH2 Apparent Energy[31:0]

S2RMS = primary current channel apparent RMS power PH2 Apparent RMS Power[28:0]

S1vec = primary current channel apparent vectorial power PH2 Apparent Vectorial Power[28:0]

8.4.5

Sign of power

Power measurements are signed calculations. Negative power indicates that energy has been injected into the

grid. DSP_SR1, DSP_SR2 status registers and DSP_EV1, DSP_EV2 registers include sign indication bits for

each calculated power.

If the sign of power is negative, the sign bit is set. SIGN = 0: positive power

SIGN = 1: negative power

In the calculation of the sign, a delay equal to half line period is included. If the period of signal is T = 20 ms (f =

50 Hz), the applied delay is 10 ms.

STPM32, STPM33, STPM34

Functional description of hardwired DSP

DS10272 - Rev 13

page 31/89

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