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EVM430-F6779: Performed an evaluation using a 3-phase 3-wire motor as the load

O.H
Genius 5595 points
Part Number: EVM430-F6779

Hi experts,

My customer performed an evaluation using a 3-phase 3-wire motor as the load.
When compared with a wattmeter made by another company(=Comparison), the voltage values were different, and the active power and reactive power were also showing slightly different values.
I will first explain the details of the situation, and at the end I would like to ask you a few questions.

[Confirmation environment]

  • 3-phase 3-wire connection system: Δ (delta) connection
  • Load: 3 layer 3 wire motor

[Connection diagram with EVM including load]

  • Connect the EVM's Phase A/B/C terminal voltage and CT to each terminal of the load motor, and Neutral is not used.
  • In this state, compare the voltage, current, and power of Phase A/B/C with other companies' meters.

[Measurement result]

  • The EVM has been calibrated in a single-phase environment, and it has been confirmed that it shows the same value as the power meter of the measuring device.
  • But but a difference occurred in the voltage value in a three-phase.
  • There is also a slight difference in active power and reactive power.
  • 　 Comparison TI-EVM
    Display value Display value
    Active power 0.078 kW 0.090 kW
    Current Ph_A 1.723 A 1.746 A
    Ph_B 1.745 A 1.827 A
    Ph_c 1.815 A 1.760 A
    Voltage Ph_AtoB 204.4 V 111.3 V
    Ph_BtoC 204.9 V 125.9 V
    Ph_CtoA 202.7V 117.1 V
    Frequency 50 Hz 49.9 Hz
    Power factor 0.13 -
    Reactive power 0.625 KVAR 0.599 KVAR
    Arithmetic method Δconnection? Y connection?

[Calculation formula for Y (star) connection and Δ (delta) connection in 3-phase AC wiring method]

  • Y (star) connection (208Y/120 type)
    • The line voltage between each phase and Neutral is "phase voltage x √3", and the relationship between the phase voltages is "line voltage/√3".
    • Line current = phase current
  • Δ (Delta) connection
    • There is no neutral wire
    • Line voltage = phase voltage
    • Line current is "√3 x phase current", and the phase current has the relationship of line current/√3

[Inquiry]

Q1:
Assume that the information displayed on the electricity meter being compared is correct.
Is it correct to recognize that the calculation process is correct based on the measurement results?
Also, is it correct to assume that there will be no difference in the confirmation results when confirmed in a Y (star) connection environment?
TI-EVM performs calculations on the assumption of Y (star) connection, so when checking in a Δ (delta) connection environment, the displayed phase voltage will have a relationship of 1/√3.
They understand that the current value is phase current = line current because the calculation is based on a Y (star) connection.

Q2:
Is there any firmware that can be checked for Δ (delta) connection?
If not, if you have any reference materials, could you please share them?

Q3:
When supporting both Δ (delta) connection and Y (star) connection, is it correct to recognize that this can be done by changing only the calculation formula?
The calculation formula for Δ (delta) connection is created from Y (star) connection, but I would like to know if there are any points to be careful about in the calculation processing inside the microcontroller.

Best regards,
O.H

  • 0
    TI__Mastermind 35150 points

    I think the result between Y and Δ connection, can be transmited by a fix parameter. 

    What you need to do is to do the calibration one by one under three phase not a single phase. That means, you don't need a new software or a new calculation formula. Besides, you need to do the phase calibration at the same time.

  • 0 in reply to Eason Zhou
    Genius 5595 points

    Hello Eason Zhou,

    Sorry for the late reply.

    The customer performed additional checks and questions arose.
    Please tell me about the following.

    Q4:Does EVM perform calculations assuming a Y connection or a Δ connection?
    Q5:Also, are you calculating the line voltage between Phase-A and Phase-B?
    Q6They believe that TI-EVM is designed to display phase voltage, but is it possible to display line voltage?

    They confirmed the Y (star) connection and Δ (delta) connection using a resistor.

    The Y (star) connection Neutral terminal and EVM Neutral are not connected.
    While other companies' power meters display voltages from Phase A-Phase B, Phase B-Phase C, and Phase C-Phase A, TI-EVM seems to display voltages between Neutral and each Phase.

    Assuming that the Y and Δ connections have the following relationship, the current value is displayed the same as other companies' power meters, but the voltage value is different.
    This also suggests that there is a difference in the method of calculating voltage values.

    Y connection Δconnection 
    Line voltage Phase voltage (Neutral-Phase voltage) x√3 same as phase voltage
    Line current same as phase current Phase current x√3

    They checked the power input terminal of the actual EVM with a tester.
    As long as you check both the Y-connection phase voltage and line voltage at the EVM's power supply terminal, it seems that the TI-EVM is designed to display the phase voltage.
    They did a similar check with the delta connection, but as long as I checked the EVM input voltage with a tester, the correct voltage was being input.
    From this, it seems that the line voltage during delta connection and Y connection is not taken into account.
    By making it compatible with line voltage, they thinks possible to display it in the same way as other companies' power meters.

    Regarding microcontroller calculations, we also checked the actual microcontroller input voltage waveform from the voltage value displayed on the GUI and calculated backwards.
    We calculated the theoretical value of the microcontroller input voltage from the value displayed on the GUI and compared it with the actual waveform, but we also confirmed that the calculated value was almost the theoretical value.

    For your reference, the threads that touch on delta and triangle connections are expanded below.
    High order THD calculation and Delta-type (3P3W) for 3-phase emeter on F6779
    MSP430F67791A: What modes or configurations are supported for 3-phase Power Meters?

    Best regards,
    O.H

  • 0 in reply to O.H
    TI__Mastermind 35150 points

    Hi,

    Q4:Does EVM perform calculations assuming a Y connection or a Δ connection?

    [Eason]: It is  Δ connection.
    Q5:Also, are you calculating the line voltage between Phase-A and Phase-B?

    [Eason]: It will not calculate the line voltage based on phase voltage.
    Q6They believe that TI-EVM is designed to display phase voltage, but is it possible to display line voltage?

    [Eason]: It dones't support this, but you can do the calculation by yourself.

    Another reason why the acitve and reactive power is different may be because the code doesn't add this function:https://www.magnelab.com/wp-content/uploads/2015/01/Current-transformer-phase-shift-compensation-and-calibration.pdf Can you tell me what e-meter GUI that customer is using? If they use the EMDC, same like the one I shown before. It will have this problem.

    Eason

  • 0 in reply to Eason Zhou
    Genius 5595 points

    Hi Eason,

    Thank you for the reply.

    Eason Zhou said:
    Can you tell me what e-meter GUI that customer is using? If they use the EMDC, same like the one I shown before. It will have this problem.

    They use EMDC. And  they are experimenting based on the sample code below.
    :EnergyMeasurementDesignCenter_1_40_00_03\EnergyMeasurementDesignCenterWorkspace\EVM430-F6779_CT_3V_3C_50Hz

    Is there any sample code to implement this application note? 

    Best regards,
    O.H

  • 0 in reply to O.H
    TI__Mastermind 35150 points

    Hi OH,

    I think that maybe the reason. As EMDC lib is not open source to customer. The best solution would be:https://www.ti.com/tool/TIDM-THDREADING?keyMatch=TIDUB70A. It use this FIR table to handle the different phase shift caused from the current sensor.

    Another suggestion is to refer to this more accurate calibration flow:

    2021-06-23 EMDC Calibration Process.docx

    I only play with signle phase meter and can just give some  suggestion.

    Eason

  • 0 in reply to Eason Zhou
    Genius 5595 points

    Hi Eason,

    Sorry for late reply. 

    Thank you for the information.
    I am still in the process of confirming the information I received, but please let me ask question.

    Eason Zhou said:

    Q4:Does EVM perform calculations assuming a Y connection or a Δ connection?

    [Eason]: It is  Δ connection.

    Q7:The E2E below says does not support Δ(Delta) connection and the Y(Star) connection support, but is it really correct that it is Δ(Delta)?
    [Edit 2024/01/11]
    :e2e.ti.com/.../msp430f67791a-what-modes-or-configurations-are-supported-for-3-phase-power-meters

    Eason Zhou said:

    I think that maybe the reason. As EMDC lib is not open source to customer. The best solution would be:https://www.ti.com/tool/TIDM-THDREADING?keyMatch=TIDUB70A. It use this FIR table to handle the different phase shift caused from the current sensor.

    Q8:Could you please tell me how to integrate "TIDCBM3" (especially the function of "metrology-fir-table.c") used in "TIDM-Threading" into EMDC?
    I downloaded it, but since the content was for IAR, it cannot be built using CCS. (Based on Driverlib's Empty project.)
    Since there is no .txt or .hex, operation cannot be confirmed.

    Best regards,
    O.H

  • 0 in reply to O.H
    TI__Mastermind 35150 points

    Hi,

    I would suggest you to use  the code in EnergyMeasurementDesignCenter_1_40_00_03\EnergyMeasurementDesignCenterWorkspace\EVM430-F6779_CT_3V_3C_50Hz. 

    If you want to implement the FIR function into the EMDC code, I would say it is not easy... that part of code is really hard to understand. Anyway, if you want the source code of EMDC for adjusting this part, please connect TI sales. He will help you get that code.

    Eason

  • 0 in reply to Eason Zhou
    Genius 5595 points

    Hi Eason,

    Thank you for the reply.

    Considering the current evaluation situation, it may be necessary to understand the calculation algorithms in the library.
    We will consult with Japan TI as necessary.

    Best regards,
    O.H

  • 0 in reply to O.H
    TI__Mastermind 35150 points

    OK. You can share the E2E link to them as well.

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