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TIDA-010025: Neutral requirement in 3 phase 6 switch pfc converter

Anoop kumar N
Intellectual 908 points
Part Number: TIDA-010025

Hello, Experts,

This is for my customer; the front-end converter is 3 phase PFC with 3 PFC chokes and 6 Mosfet operated using SVPWM without neutral. But customer asking for neutral line, they argued that neutral can bypass unbalanced current in case of any disturbance happened. 

Qn1: Incase if there is no neutral if an unblance happen; what will be the after effect ?

Qn2: if the grid is unbalanced (say RY phase 420Vac, YB phase 400Vac) and there is no neutral. weather my controller will taken care ? (by making proper adjustments in the modulating signal ) ?

Qn3: If i am taking neutral? how it is being connected to the converter without changing the topology. ? Spitted DC link capacitor with neutral at the middle point. ?

Thanks and regards

Anoop kumar 

  • 0
    TI__Expert 3570 points

    Dear Anoop,

    Thank you for your interest in TIDA-010025 reference design. This reference design was developed for use with industrial drives to drive 3-phase AC motors and we assumed a balanced 3-phase AC input voltage vs. Neutral, hence VDC+ + VDC-= 0V.  

    Just to clarify: Are you planning to use TIDA-010025 as DC/AC to drive a 3-phase motor or are are you planning to use TIDA-010025 to implement a 3-phase PFC?

    Assuming you use as 3-phase inverter to drive a 3-phase AC motor.

    Q1: If your 3-phase input voltage is unbalanced vs. Neutral, than the 3-phase AC output voltage will be unbalanced vs. Neutral too.

    Q2: No, the TIDA-010025 design creates a 3-phase AC voltage which is scaled to the rectified DC-input voltage (VDC+ and VDC-) and the equivalent 0V will be VDC/2. If there's no imbalance VDC/2 will be equal to Neutral, if there's an imbalance, VDC/2 (VDC+ +VDC-) will be not equal to the AC grid Neutral.  
    Of course the SVPWM can be modified to compensate for a small DC voltage offset, but this is needs to be implemented on the MCU and was out of the scope of TIDA-010025 hardware design. For support of this with C2000 MCU, please contact the C2000 E2E forum. 

    Q3: You need to ensure that the VDC+ and VDC- are balanced with TIDA-010025 versus Neutral, as we only switch between VDC+ and VDC-. 

    Please let me know if this answered your question.

    Thanks.

    Regards,

    Martin Staebler

  • 0 in reply to Martin Staebler
    Intellectual 908 points

    Thank you Martin for your time. 

    Im just taking TIDA-010025 as reference for designing 3 phase system, but not using it because my application is 3 phase PFC, input is 415Vrms (line to line 50Hz ) and output is 750Vdc.  Currently the design was going on without taking neutral, and now some arguments are arises for avoiding the neutral. so engaging neutral in the converter can by pass the unbalanced current, becuase in the previous testing of the converter we faced common mode issue like our CM choke is heating too much, phase to earth  points showing 1kV of voltage.  so these issues drag the neutral requirement in the converter.

  • 0 in reply to Anoop kumar N
    TI__Expert 3570 points

    Hello Anoop,

    thank you for the info. In that case, I'd like to point you to reference design from my colleges in the grid team.

    https://www.ti.com/tool/TIDA-01606, 10-kW, bidirectional three-phase three-level (T-type) inverter and PFC reference design. 

    https://www.ti.com/tool/TIDM-1000: Vienna Rectifier-Based Three Phase Power Factor Correction Reference Design Using C2000 MCU

    I am aware it's a different topology though may give some more info in general.

    Regards, 
    Martin Staebler