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TIDA-00951: Cold-start Mechanism Purpose

Swathika Rao
Prodigy 240 points

Part Number: TIDA-00951

I understand the cold start mechanism is added to start-up the DC bus when it is completely discharged. But why cant it be directly started from the bidirectional converter? Why an additional boost converter for start-up??

  • 0
    TI__Intellectual 2815 points

    Hi Swathika,

    The current fed converter's operation can be understood by examining a standard boost converter (with isolation).

    When all the four low side full-bridge converter switches are turned on simultaneously, the inductor current builds up. When a pair of these switches are turned-off. the  Δv across the current fed inductor can be giving as (N*Vout – Vin), where is Vin is the voltage on the 400V DC Bus and Vin is the battery voltage. Since Vout is ver low at cold-start, the Δv at turn-off appearing across the inductor can be negative or very low. This can lead to a inductor current build up higher than its saturation current at startup.

    In order to avoid this an additional cold-start converter is used to precharge the 400V Bus to greater than 150V to 200V.

    Best  Regards,

    Ram

  • 0 in reply to Ramkumar S
    Prodigy 240 points

    Thank you  very much for your explanation Sir.  Really appreciate it.