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Terrible Idea Boost Converter To Be Tested On Gocart

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pepelevamp:
this sounds like a real cool project. i am looking forward to seeing footage of you sitting in a go kart moving along off a 12v battery. maybe race a friend riding a power drill.

jbb:

--- Quote from: T3sl4co1l on January 03, 2020, 12:57:41 am ---You need a per-channel sense.  Think about current sharing, let alone compensation.

--- End quote ---


--- Quote from: i_am_fubar on January 03, 2020, 06:12:17 am ---...Or do you think that the channel characteristics will vary that much?...

--- End quote ---

Yes, you almost always need it per-channel.  This is because a small change in switch duty cycle translates to a small change in the DC operating point of the inductor.  Because your MOSFETs and inductors will be chosen to have low DC resistance, you will get a large current imbalance.

However, there is one way to get around that.  It will likely compromise the efficiency of your converter. Go to Discontinuous Conduction Mode (DCM).

Advantages:

* MOSFETs turn on near zero current.  No diode reverse recovery loss in synchronous rectifier diodes (which is good, because 200V MOSFETs have pretty crap body diodes)
* Inductor currents drop to zero each switching cycle, which reduces the system order and can make compensation design easier
* Current sharing will be largely - and stably! - determined by inductor tolerance
* Inductor values will be lower
Disadvantages are significant:

* Increased RMS currents in the converter mean higher conduction losses
* Increased current ripple will increase inductor core loss.  Inductors may end up being quite large and difficult
* Somewhat more difficult to control synchronous rectifiers
* Inductor currents drop to zero and will ring a bit (inductance + MOSFET capacitance = LC resonant tank at a few MHz).  This could make a lot of radio noise, and may require snubbers to damp it away.

Here's a question: do you really need a well controlled output voltage?  I assume you will have some kind of motor speed controller after this stage (so that you can control the motor speed down to zero)?

Getting a 1:10 step up out of a boost converter is a bit of an ask anyway, so why not use a fixed-ratio step-up converter (e.g. unregulated full bridge transformer)?

amyk:

--- Quote from: i_am_fubar on January 03, 2020, 06:12:17 am ---Re. Inverter. Considered it, but the goal is to get some experience designing high power switching systems. So not really applicable :(

--- End quote ---
You can take the inverter apart and learn from its design too.

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