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Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I have been reading older posts on the CM300DY-24H operating frequency and opinions seems to vary on upper limits. From 70kHz to 200kHz. For this IGBT, what would be considered the max Freq (using UD2.5 driver with phase shift) at 700A peak primary current for it to run reliably with minimal heating?
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
I've tried personally these CM300DY-24H on a 198kHz DRSSTC,- nothing happens.. I guess, the long ON-and-OFF times cannot work with the fast switching requirement of the coil. I also tried using CM200DY-12NF series on that same coil, and it works properly., no heating has been noticed since I'm using a Phase Lead driver and at very low duty cycle (Low BPS) .
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve, how low do you think the switching loss in a ZCS condition can be compared to 100% hard switching? I guess it can not be zero even in perfect ZCS. Maybe a ratio of something like 1:10 or 1:5? It will be worse with increasing frequency.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
That's quite a difficult question, which I'll answer as best I can.
First of all, there is no such thing as ZCS because the current is only zero at one point in time, but the device takes a finite amount of time to switch. If we want the switching process to complete at zero current, then we have to start it while the current is still relatively high. The higher the frequency, the higher the current we have to initiate switching.
For example, if we are running 1000A at 100kHz, the rate of change of current around the zero crossing is 1000 *2pi*100000/1e6= 628A/us.
If we say that our Powerex H series brick takes about 500ns to switch, then we will begin the switching process when the collector current is 314A.
Then, we can approximate the collector current during the switching process as a linear decay to zero. This cuts the turn-off losses by at least a factor of 2, compared to hard switching of an inductive load. In practice the factor is somewhat more than 2 because turn-off consists of a delay period followed by a fall period, and the losses occur mainly during the fall period, so they benefit from a lower current.
This then gives us the result, that for ZCS of a 1000A peak sinusoidal current at 100kHz, the turn-off loss per switching event is a bit less than one-half of the datasheet value for hard switching at 314A.
The same argument can be applied to the turn-on process with the same conclusions.
If we start the turn-off process late, then we get lower turn-off losses because the current naturally passes through zero before the switching process is complete. The problem is that the current commutates to the antiparallel diode which then undergoes forced recovery when the other bridge leg turns on. The device turning on has to handle the load current plus a large diode recovery current, so the increased turn-on losses and diode recovery losses more than cancel out the lower turn-off losses.
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CM300DY-24H Frequency
