STPM32 datasheet(57/89 Pages) STMICROELECTRONICS

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Parameter

Value

Correction factor

KV=0,125∙ CHV2048+0.75

KI=0,125∙ CHC2048+0.75

The above procedure must be repeated for all voltage/current channels.

Note:

for proper energy calculation of secondary channel in STPM33, the value of CHV1 calibrator must be copied

also in CHV2.

9.2.2

Phase calibration (PHVx, PHCx bits)

The STPM3x does not introduce any phase shift between voltage and current channels.

However, the voltage and current signals come from transducers, which could have inherent phase errors. For

example, a phase error of 0.1° to 0.3° is not uncommon for a current transformer (CT). These phase errors can

vary from part to part, and they must be corrected in order to perform accurate power calculations. The errors

associated with phase mismatch are particularly noticeable at low power factors.

The phase compensation block provides a method of digital phase correction of the phase shifting between

voltage and current channels which can be introduced by the external component intrinsic characteristics or by

external component mismatch.The amount of phase compensation can be set per each channel, and it is

executed delaying the currents and voltage samples using bits of the phase calibration configurators: PHCx[9:0]

and PHVx[1:0].

These registers act in the same way by delaying the desired waveform by a certain quantity given from the

equations below in degree:

Table 38. Phase delay

Parameter

Value

Current shift

φC=flineSCLK∙PHCx9:0 ∙360°

Voltage shift

φV=flineSCLK∙PHVx1:0 ∙29∙360°

Global phase shift

φ=flineSCLK∙ PHCx9:0 −PHVx1:0 ∙29 ∙360°

A capacitive behavior is determined by the current leading the voltage waveform to a certain angle. In this case,

there is the compensation by delaying the current waveform by the same angle through PHCx register. For a 50

Hz line the current channel waveform maximum delayed is:

φC ≤ 4.6035° with step ∆φC = 0.0045°

An inductive behavior has the opposite effect, so that current lags the voltage waveform. In this case, PHV

PHCx register for the fine tuning of the current waveform.

PHV impacts on the calculation of power and energies related to both current channels. For a 50 Hz line, the

voltage channel waveform maximum delayed is:

φV ≤ 6.912° with step ∆φV = 2.304°.

STPM32, STPM33, STPM34

Application calibration

DS10272 - Rev 13

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