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How to meter phase-phase energy with MSP430FE4232?

Vinicius Hoff
Prodigy 40 points
Other Parts Discussed in Thread: MSP430FE4232

hi

I want to use  the MSP430FE4232 for phase-phase energy metering. Is it possible?

Can I set the register "phase correction", which adjusts the angle between voltage and current, to adjust metering for phase-phase?
How else to do it?

  • 0
    Guru 227245 points

    Phase correction is for compensating the delay that appears on the current signal if it is taken by a current transformer rather than a current shunt. Due to the magnetic cuplingin a current transformer, the output current (and therefore the input voltage on the MSP) is a fixed delay behind the voltage that caused the current. So you have to delay the voltage reading by the same amount. That's what AFAIK the phase correction does.

    For metering, it doesn't matter whether you are sensinge phas-phase or phase-neutral. The maximum voltages differ, but as long as you also read the current between the two phases (and something else wouldn't make much sense), the software side is not different for both situations. Only the external hardware might require some changes, especially the power supply part, due to the missing dependency to ground. However, as long as there are only two connection points, voltage is voltage, current is current and power is power.

  • 0 in reply to Jens-Michael Gross
    Prodigy 40 points

    Thank you Jens-Michel

    Actually, I want to do something different. I want to have an approximate metering from a balanced three-phase system. For this, I pretend to measure the voltage between two phases and the current in the third phase. The problem is this way the current has a 45º delay. If I correct this delay with the "Phase Correction", the metering is the right?

  • 0 in reply to Vinicius Hoff
    Guru 227245 points

    Vinicius Hoff said:
    If I correct this delay with the "Phase Correction", the metering is the right?

    I think so. However, the critical part is the 'If'. I'm not sure whether the phase correciton register is capable of doign such a huge phase correction (normal ranges are below +-5°)

    If you sample with 14kHz (a usualy sampling rate for getting non-sinusodial current waveforms) , 45° phase difference would require buffering 1750 sampling values in a hardware FIFO.

    Well, I just checked the datasheet and on 4096Hz sampling frequency, the correction spans +-31.25ms. With 14kHz it still is +-9ms or ~+-160°. So it should work.
    However, the 'normal' range is much, much less. No idea why this 'normal' range is listed at all. Either it works over full range, or (if both ranges are given) it should be stated what the drawback is when leaving the normal range. But there is no info in the ESP guide that calrifies this.

    I have no own experience with this (we are using a preprogrammed ADE chip for the metering process in our devices), so I have to rely solely on the datasheet, which doesn't seem to give more information.

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