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| 7kwt LLC 45 khz transformer design issues |
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| axizep:
--- Quote from: blueskull on April 17, 2019, 02:40:56 am ---Do you have a high speed current probe? If so, please upload a current waveform of your primary winding current. Alternatively, do you have a thermal camera? If so, paint the transformer with black non-conductive paint, and take a picture. You need to do either of those above, as the goal is the same -- to tell which component is heating, the core, or the winding. As for your original design, yes, splitting resonant tank is a good idea. Not only it reduces effective resistance on the coils, it also reduces delta B on the core, which can be nasty. Keep in mind that the LLC inductor sees the FULL AC current, not just ripple current as seen in other topologies. BTW, do you need voltage regulation? If you can get around with fixed conversion ratio, I highly recommend the plain old push pull, in half bridge or full bridge form. It is one of the very few topologies that guarantee ZVS without resonation or a minimum load current. Sorry if my post doesn't help, but I don't do LLC that much. I'm a power module person, not a converter topology person. --- End quote --- Thank you,Blueskull,that you responded so quick! I feel pity,because i dont have thermal imaging,neither friends with to borrow it. but core is definitely only warm (45C or so).its the winding that is heating up like crazy. I have bought tektronix a6303 current porbe,bu its faulty (has problems with dc offset,guess its hall sensor fault). so i do current measurements with a current transformer or sometimes with LEM current sensor. ill attach waveform from a usuall current transformer,which i have integrated into the converter for controlling overcurrent situatiuons. yellow trace is gate drive,purple trace is one end of the secondary,and blue trace is current transformer. Also i have witnessed zvs,when i was watching for primary halfbridge node voltage in respect to a gate drive volltage. Resonant inductor was overheating few designs before,but i have installed bigger core for him,bigger gap increased turn count and used fine litz wire,and now i have no problem with him now,its fixed and working fine. About a pushpull,iam very surpirsed to know that pp topology could make a zvs (what stops current reflected from a secondary to charge a drain of a transistor at deadtime,which is about to open?) .but pp will not suite me because i have 750V voltage on my halfbridge ,so pp will be give 1.5kv on drains,which will be the problem. also iam very surprised to know that there is full bridge pp topology,i could not imagine it. |
| moffy:
I was looking at an article about a 5kw/10kw resonant converter: https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/04448897.pdf and they seem to have put a lot of effort into cooling the transkormer: 1. 90% efficient gives 700W of losses for Tx 2. 95% efficient gives 350W of losses for Tx 3. 97% efficient gives 210W of losses for Tx It is going to get hot under load. Maybe you need some heatsinking like the above article. |
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