MCP39F511A datasheet(48/68 Pages) MICROCHIP

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MCP39F511A

DS20006044A-page 48

 2018 Microchip Technology Inc.

9.4

Calibrating the Phase

Compensation Register

Phase compensation is provided to adjust for any

phase delay between the current and voltage path.

This procedure requires sinusoidal current and voltage

waveforms, with a significant phase shift between

them, and significant amplitudes. The recommended

displacement power factor for calibration is 0.5. The

procedure for calculating the phase compensation

Determine what the difference is between the

angle corresponding to the measured power

factor (PFMEAS) and the angle corresponding to

the expected power factor (PFEXP), in degrees.

EQUATION 9-7:

Convert this from degrees to the resolution

provided in Equation 9-8. There are 56 samples

per line cycle. One line cycle is 360 degrees, so

for each sample the angle is 360 degrees/56

samples = 6.42857 degrees/sample. Since the

phase compensation has a bit of sign, the

maximum angle error that can be compensated

is only half, that is ±3.21 degrees. Converting

the angle to 8-bit resolution gives 256/6.42857

degrees = 39.82 with 40 as an approximation.

EQUATION 9-8:

Combine this additional phase compensation to

whatever value is currently in the phase

compensation,

and

update

the

Equation 9-9 should be computed in terms of an

8-bit 2's complement-signed value. The 8-bit

result is placed in the least significant byte of the

16-bit Phase Compensation register.

EQUATION 9-9:

Based on Equation 9-9, the maximum angle in degrees

that can be compensated is approximately ±3.2

degrees. If a larger phase shift is required, contact your

local Microchip sales office.

9.5

Offset/No-Load Calibrations

During offset calibrations, it is recommended that no

line voltage or current be applied to the system. The

system should be in a no-load condition.

9.5.1

AC OFFSET CALIBRATION

There are three registers associated with the AC Offset

Calibration:

• Offset Current RMS

• Offset Active Power

• Offset Reactive Power

When computing the AC offset values, the respective

gain and range registers should be taken into

consideration according to the block diagrams in

Figures 5-2 and 5-4.

After

successful

offset

calibration,

Save Registers to Flash

command can then be

issued to save the calibration constants calculated by

the device.

9.5.2

DC OFFSET CALIBRATION

In DC applications, the high-pass filters on the current

and voltage channels are turned off. There are two

registers associated with the DC Offset Calibration:

• DC Offset Current RMS

• DC Offset Active Power

In addition to that, full access to the ADC's internal

24-bit Offset registers is provided.

MEAS

Value in PowerFactor Register

32768

---------------------------------------------------------------------------

ANGLE

MEAS 



MEAS

 180



---------



acos

ANGLE

EXP 



EXP

 180



---------



acos



ANGLE

MEAS

ANGLE

EXP

–

 40



PhaseCompensation

NEW

PhaseCompensation

OLD



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