MSP430F6779A: Energy Measurement - Reactive Power

Federico

Part Number: MSP430F6779A

Using the MSP430-ENERGY-MEASUREMENT (1.40.00.03) library with the MSP430 (MSP430F6779AIPZ) I have a problem in the reactive power measurement.

The following table compares the measurements made with the MSP430 and a laboratory instrument.

Comparision table

As you can see there is a big difference in the reactive power value (1078,27 vs 26,83).

What could be the reason why I am getting this error? Thanks.

over 3 years ago

0 Brandon Fisher94 over 3 years ago

TI__Mastermind 28075 points

Hi Federico,

Your reactive power measurement is quite far off, but it also looks like your apparent power is about 12% off, and your power factor is about 13% off as well.

To me your issue sounds similar to this thread: https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/913227/ccs-msp430f6779a-power-factor-reactive-power-and-apparent-power-reading-incorrectly

Which points to an incorrect or missing phase calibration value as a potential cause. If you're using the EMDC GUI the video linked in that thread shows how to perform the phase calibration.

Regards,
Brandon Fisher

0 Federico over 3 years ago in reply to Brandon Fisher94

Prodigy 15 points

Hi Brandon,
thank you.

I did the calibration manually and I also have the doubt that the phase calibration is wrong.
What is the meaning of the "Phase Correction" parameter that I left at the default value of 0x0080?

The power clamp I use introduces a phase shift between 3 and 4 degrees.

So, according the guide:

which in my case is:
(360 * 50) / (32 * 2048) = 0.275 Deg

So how to use this value to correct the phase error of my power clamp?

Thanks,
BR.

+1 Brandon Fisher94 over 3 years ago in reply to Federico

TI__Mastermind 28075 points

Hi Federico,

Ill have to check with some of my colleagues to be sure, but that Phase Correction value is used for setting fractional sample delays. Assuming you need just a 3-4 degree phase shift, you should be able to make the correction in this register (because your required phase shift is less than a single sample time - see this other e2e thread for details).

By default this register is set to 0x0080, which if I'm not mistaken would be interpreted as 128*0.275Degrees (your resolution) = 35.2degrees. So I believe you should be able to set your 3-4 degree phase by setting this register somewhere around hex 0x0B.

Best Regards,
Brandon Fisher

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MSP430F6779A: Energy Measurement - Reactive Power