Transformer after PWM controlled 3 phase inverter

Discussion in 'General Electronics Chat' started by eimix, Dec 20, 2009.

  1. eimix

    Thread Starter Active Member

    Sep 2, 2008
    32
    0
    Hello,

    I'm making car electric conversion.

    I have an inverter 36-144V @10kW with 1-400Hz main frequency and 16kHz PWM,

    and 7kW motor with nominal 220V delta wiring. I know i can paralel some windings to reduce voltage to 1/2 or to 1/4.

    Also i could increse battery voltage by adding more batteries in series, but i do not want to play with more then 50V. Here goes my basic system structure:
    [​IMG]

    Is it possible to build step-up transformer and use it between inverter and motor? (with at least 90-95%eff)
    I assume that transformer would work on PWM frequency, am I right? As PWM frequency is high - transformer could be build using quite low induction coils.

    If yes- transformer could be small with low winding number on each side with 6-10 gauge wire? Some kind of microwave transformer remake.

    Is it possible?
    Have anybody build it?
    Any comments and suggestions are very welcome

    Thank you
     
  2. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    Asking a magnetic circuit to transform a PWM wave of 16 KHZ is asking for trouble, (in my humble opinion). The usual way that this is done is to start with a stiff high voltage DC Buss (with lots of capacity) and then switch the HV Mosfets as needed to follow the PWM regime. Filtering and switching noise suppression is done afterwards.

    Regards, DPW [ Spent years making heaters out of op-amps.]
     
  3. eimix

    Thread Starter Active Member

    Sep 2, 2008
    32
    0
    I guess that transforming 16kHz PWM wave would have allot of noise in output, but does it realy matter on AC induction motor?
     
  4. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    Heat...HEAT, and lots of it, thats what the 16kHz. frequency is going to produce in a transformer and the motor. And of course, your efficiencies are going to suffer as a result.

    Regards, DPW [ Spent years making heaters out of op-amps.]
     
  5. eimix

    Thread Starter Active Member

    Sep 2, 2008
    32
    0
    Thanks for info, but this way of stepping up voltage is still in my mind :)

    I searched allot on google trying to understand transformers, and i found out that Full-bridge topology is used in high power transformers.

    And my FVD has this topology :) 3phase fullbridge. And i still do not see reasons why my idea would not work :(
     
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