STPMC1 ST Microelectronics, STPMC1 Datasheet - Page 38

• Manufacturer Part Number: STPMC1
• Description: Programmable poly-phase energy calculator IC
• Manufacturer: ST Microelectronics

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Theory of operation
9.16
9.16.1
9.16.2
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Calibration (configuration bits: PM, TCS, CIX, CVX, CCA,
CCB, CPX)
Voltage and current channels calibration
The 8-bit calibration values CVX and CIX (where X stands for N, R, S or T) are used as
static data for the channel
K
When configuration bit PM is set, a 2-bit CvX or CiX is appended to each CVX or CIX
respectively:
K
CvX bits are part of the CCA configuration byte while CiX are part of CCB configuration
byte.
Phase compensation
The STPMC1 does not introduce any phase shift between voltage and current channel.
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 STPMC1 provides a means of digitally calibrating these small phase errors introducing
some delay. The amount of phase compensation can be set per each phase using the 4 bits
of the phase calibration configurators (CPR, CPS, CPT).
A vector method of phase shift compensation is implemented.
The compensating voltage vector, which is produced from a frequency compensated signal
of integrated voltage vector multiplied by a given compensation constant per each phase
and is almost perpendicular to the input voltage vector, is subtracted from the input voltage
vector at the input of the decimation filter.
Those phase compensators are merged from a common coarse part CPC and from each
phase 4-bit phase error compensator CPX:
CPC[1] = 0: K
CPC[1] = 1: K
When either PM or TCS are set, a 2-bit CpC is appended to CPC to produce the following
factor:
CPC[1] = 0: K
CPC[1] = 1: K
CpC bits are part of the CCA configuration byte.
The equation for phase compensation in degree is:
X
X
= (4096 - 1024 + 4CXX)/4096
= (8192 - 1024 + 4CXX + CxX)/8192
PHC
PHC
PHC
PHC
= - (16 CPC[0] + CPX)/1024
= (16 - CPX)/1024
= - (32 CpC + 16 CPC[0] + CPX)/4096
= (64 - 32 CpC + 16 CPC[0] + CPX)/4096
calibrators, multiplying their streams to the following factor:
Doc ID 15728 Rev 1
(± 6.25 %)
(± 12.5 %)
STPMC1