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High order THD calculation and Delta-type (3P3W) for 3-phase emeter on F6779

Other Parts Discussed in Thread: MSP430F6779, EVM430-F6779, TIDM-THDREADING

Champs,

My customer is interested in MSP430F6779 for 3-phase emeter as in the following link.

Would you please help clarify and provide us solutions about below?

1) How many orders does the THD calculation we have now? We want to have up to 31-order THD calculation as well as each order harmonic output on voltage and current. Is the solution inside the reference code? If not, do you have any solution?

2) It seems the reference design is with 3-phase/4-wire (Y-type with reference ground). Do you have any reference design (example code and demo board) for 3-phase/3-wire (Delta-type, no reference ground)?

Wayne Huang

  • Hi Wayne,

    We are currently working with metering experts to answer this question and appreciate your patience while a response is formulated.

    Regards,
    Ryan
  • Wayne,

    1. Please note that the EVM430-F6779 does not automatically support the THD. One has to use the same EVM, but overwrite the SW with the SW available on the TIDM-THDREADING TI Design, which is on the web today. However, this TID, does not support harmonic distortion or harmonic content by the order. It calculates the total harmonic distortion versus fundamental in the measurement without breaking it down further. If one needs to get harmonic content for multiples of the fundamental, we have to do extensive processing via bandpass filtering or Frequency domain processing of the samples for voltage and current seperately. The MSP430F6779 might not have enough CPU MIPS to do harmonics for voltage and current. It maybe possible but with very limited accuracy. We have not tried it yet. 

    2. Currently, we do not have any 3-phase 3-wire solution on MSP today. 

    Thanks

    Kripa

  • Kripa,

    1. Does that mean we cannot guarantee customers to do that on F6779 even if they want to try it? Do you have any plan to verify if F6779 can be used for high-order THD and its harmonic contents on voltage and current?

    2. Do you have any plan to develop 3-phase/3-wire solution on MSP?

    Wayne
  • 1. No, it doesnt mean that at all. Several customers use F6779 and understand the limitations and work towards a solution that is basic in nature. Time domain processing is less computationally compared to frequency domain processing using FFT. Higher the order THD, more will be the processing needs. In time domain, one can use a simple band-pass filter to just take the band of interest. For example, the customer needs fundamental for voltage and current, this is doable. In addition, if they want to pick a few of the orders, then they can implement some band pass filters in time domain and then focus on getting the THD for those only. You can also implement lower order FFT for Frequency domain processing, but that will limit the level of accuracy achieved for the THD.

    2. We currently do not plan to do 3-phase, 3-wire, but if there is a strong need from our customers, we can think about adding to our roadmap of designs.

    Thanks

    Kripa 

  • Kripa,

    Thank you very much for your information.

    Wayne
  • Kripa,

    If we want convert 3 phase 4 wire system into 3 phase 3 wire system,
    Need add any component or only modify source code??

    Thanks

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