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MSP430F6736A: Single Phase Electric bidirectional "NET" meter

dflohr
Expert 1140 points
Part Number: MSP430F6736A
Other Parts Discussed in Thread: MSP430F6779, TIDM-THDREADING, MSP430F6736, MSP430F6749, MSP430F6749A, EVM430-F6779,

Need some help with bidirectional 60 Hz AC electric flow measurement.

Does TI has a reference design or some guidance on an electrical "NET" meter?  These meters are  capable of  measuring and separately storing watt hour measurements where sometimes electricity will be flowing through the meter from the power grid and other times electricity will be flowing through the meter to the power grid.

Thanks.

  • 0
    TI__Intellectual 1370 points
    Hi Daniel,

    Have you had a chance to look at the reference designs for e-metering?

    www.ti.com/.../smart-e-meter-amr-ami

    Regards,
    Ryan
  • 0
    TI__Mastermind 49692 points

    Hello Daniel,

    Please refer to the Total Harmonic Distortion Measurement For Energy Monitoring Reference Design (TIDM-THDREADING). This design supports bi-directional (four-quadrant) energy measurement and is based on the MSP430F6779(A). However, it could be ported to the MSP430F6736(A) quite easily.

    Hope this helps.

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Expert 1140 points
    James: Thanks for the note. Since we want to do just single phase, measuring current on L1 and L2 and voltage on L1-N and also L2-N, can the part MSP430F6749 be used instead? Saves a few $.

    Dan
  • 0 in reply to dflohr
    TI__Mastermind 49692 points

    Hello Dan,

    Yes, after a quick comparison, the MSP430F6749 should work fine, especially since you only need 4 Sigma Delta channels and not 7. Depending on your Flash, RAM, and other peripheral requirements, you may be able to find an even cheaper device (the filters and compare feature in the parametric search should be very helpful). However, I would highly recommend that you use the A version of the device (MSP430F6749A) rather than the non-A version (MSP430F6749). The A version is recommended for new designs and functionally equivalent. Please read the Differences Between MSP430F67xx and MSP430F67xxA Devices app note for more details.

    It sounds like your application is actually two-phase (two SD channels per phase). Thus, I would still recommend using the poly-phase EVM430-F6779 for your development, since you can just use two out of the three phases. Then, just port the code from the MSP430F6779(A) to MSP430F6749(A).

    Hope this helps!

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Expert 1140 points

    Meter Config.pdfJames,  Would you please review the "modified" TI drawing attached and confirm this is a valid approach and use of this IC.   Also some thoughts on creating the running "virtual" KWH meters.  Can IC do this or will we do this outside the IC by continually polling and integrating registers?  Thanks,  Dan

  • 0 in reply to dflohr
    TI__Mastermind 49692 points

    Hello Daniel,

    Here's some feedback based on the diagram that you shared.

    1. I'm not sure why you'd need duplicate CT's in series (e.g. A&D, B&C). They'd measure the same current. Instead, maybe you want to remove the duplicates and add one to the Neutral to measure cumulative current on the return path.
    2. For measuring VRMS on Phase 1 and Phase 2, please be sure to reference the negative ADC inputs to Neutral and connect the GND of the MCU to Neutral.

    I've never heard of virtual meters. The source code for the design mentioned above supports both negative and positive energy. The "polling and integrating registers" sounds like an approach for a standalone (non-MCU based) ADC. The data available in the ADC conversion registers are available based on the sampling frequency.

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Expert 1140 points
    James.

    Thanks for comments above.

    The CTs are on the same phases but not physically next to each other.

    Inverter 1 is the 60 Hz output from a solar panel inverter. Power goes one way only onto the two phases,

    Inverter 2 is independent, connected to the same two phases but they are at the inverter that handles the batteries. The CTs (even though on the same phases), measure the power used for battery charging as well as for discharging onto the grid.

    They are clearly measuring different things. You maybe took the drawing physically too literally.

    We want to take frequent KWH readings and populate an off-site SQL database with many time stamped "meter readings". "Reading" the meter will be done by looking at the offsite database rather than the meter itself which is why we call it a virtual meter.

    Will the IC registers hold frequently updating KW measurements? Are there registers for running KWH?

    Make sense?

    Thanks

    Dan
  • 0 in reply to dflohr
    TI__Mastermind 49692 points

    Hello Daniel,

    Yes, I was focused on the diagram that you provided and was not aware of the additional details. It makes more sense now. Moving forward, I would recommend getting familiar with the MSP430F6736A device by reading through the datasheet and user's guide and also getting familiar with the TI Design(s) that I mentioned earlier (both its user's guide and the source code).

    Basically, this design will do what you need to do. There's a background process that gets triggered by the Sigma Delta ADC interrupt (frequency defined by the sampling rate) and calculates the energy consumption (and many other metrology values) based on the data captured by the ADC. Then, every 1 second a foreground process gets triggered which accumulates the energy consumption and updates the related variables. The application code then has access to these variables and reports them to the GUI. In your case, rather then reporting to the GUI, you would change the code (and add wireless hardware) to send the values to the cloud.

    Does this make sense?

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Expert 1140 points

    James,

    Perfect.  We have experience with TI 8051 and ARM SOCs and are familiar with TI BLE and ZigBee stacks.  This will be different but should be able to get through it.  The development board ordered and the schematics/gerbers being worked on.

    Thank you.

    Dan

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