Is it possible to make an IGBT to work at duty cycles up to 100%? - Page 1
Forum section: electronics / general

author: yogece
author_rank: Contributor
timestamp: September 11, 2019, 08:51:31 am
content: I am designing an IGBT based chopper with single Low side switching IGBT (chosen low side switching because ease of driving the IGBT.)There are plenty of resources available for SMPS (buck, boost, buck-boost,) PFC chopper, inverters, welding power sources, UPS and motor control applications. I presume all those applications work under duty cycles up to 50% and for motor applications it may go up to 95% (only during the peak of the SPWM signal) but none of the applications mentioned made it to work continuously in the duty cycle range of 90% or above.I googled a lot and read the application notes, datasheets and reference designs of various IGBT/MOSFET manufacturers such as Infineon, ST, Semikron, Vishay, ROHM, Fuji, Mitubhishi, Hitachi, Toshiba, IXYS, ABB, Renesas, TI, NXP, Nexperia.Some of the applications listed below which uses IGBT close to 100% duty cycle operation.1. HVDC circuit breaker uses a hybrid approach. During operation the current will always flow through the bypass branch which has a mechanical circuit breaker and during the interruption of the current it will be allowed to pass through the IGBT, this application doesn’t help me to understand about the 100% operation of the IGBT.2. Another application which uses the duty cycle up to 100% is separately excited DC motor which can use IGBT, but I couldn’t find any reference for the implementation using IGBT and there are plenty of resources available for thyristor based choppers and simulation of the same.3. The DC electronic load which uses the MOSFET in DC operation and couldn’t find reference for high power electronics load using IGBT. Many of the manufacturers I googled a lot and read the application notes, datasheets and reference designs of various IGBT/MOSFET manufacturers such as Infineon, ST, Semof IGBT mentioned not to operate the devices in the linear region.I am intending to use IGBT modules of 1200V/400A (semikron SKM400GB125D half bridge module.) For the proof of concept I used discrete IGBT (IRFGP50B60PD) and drove it up to dutycycle of 50% @ 490Hz and it worked perfectly. The high power IGBT modules the manufacturer doesn’t provide FBSOA but they provide RBSOA and SCSOA details alone. For the short overload conditions recommend to refer the transient thermal impedance characteristics and for the steady state pulsing operations recommends to look at RthJ-C of IGBT & diode.Many manufacturers have simulators which allows to simulate the electrical and thermal details of our circuit, but for which I couldn’t get some pointers regarding how far the simulation and bench test correlates (correlation of simulation Vs implementation) Semikron Semisel, Infineon (uses PLECS,) Fuji electric. By the simulator, we can estimate the losses of the switch (switching loss and conduction loss) and junction temperatures.For the following questions I am expecting some inputs from the community:1. Is it possible to operate IGBT up to 100% duty cycle? I couldn’t find many application references for IGBTs, which works in the duty cycle close to 100%. The question is similar tohttps://www.researchgate.net/post/Can_the_IGBT_MOSFET_turn_on_all_time_long_just_as_a_diode2. Need some information regarding how far the simulation and bench test correlates (correlation of simulation Vs implementation.)3. Reference designs or some resources for DC chopper using IGBT/MOSFET.4. Suggest me some technical forum and resources dedicated to power electronics.

author: fourtytwo42
author_rank: Super Contributor
timestamp: September 11, 2019, 02:38:11 pm
content: Try turning the question on it's head, what possible reason could there be that you cannot turn an IGBT on indefinitely ? why do you think this is the case ?I have seen this same post on multiple fora just like a few otherposters around here

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 11, 2019, 02:41:54 pm
content: Bootstrap gate drivers need switching to stay powered on.Minimum pulse width may be an important consideration. Note that limits duty cycle to a middle rangeand0 and 100%, since 0 and 100% mean no pulse width to be worried about.Your diagram is probably missing a clamp diode from the collector terminal to a low impedance, usually a capacitor or another supply (may be including the same +600V supply the load has). Consider what the collector voltage will do if "LOAD" is inductive.Tim

author: yogece
author_rank: Contributor
timestamp: September 12, 2019, 03:25:59 am
content: I have a gate driver with much more capabilities Semikron SKYPER 32R it is having an isolated supply for gate driving supply.In the circuit diagram i haven't mentioned the snubber and decoupling capacitor near the IGBT.Every i am aware of the design constraints but don't have much information about continuous operation of IGBT in the duty cycles close to 100%.

author: yogece
author_rank: Contributor
timestamp: September 12, 2019, 03:48:18 am
content: The possible reasons for limiting 100% operation is hot spotting problem in the parallel IGBT cells.I am not asking someone to do design for me. i am looking for some resources for exampleDesign Considerations for using IGBT modules in Inverters and Drives(http://www.irf.com/technical-info/appnotes/an-1202.pdf)while copying from the word document i mistakenly pasted twice that's the reason ofpostI hope you understood

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 12, 2019, 05:25:23 am
content: Hot spotting is avoided by:1. Operating in saturation, so the voltage drop is small, the power density is low, and runaway is less likely;2. Using matched devices in parallel. Obviously, a single die is matched with itself, but matched dice are desirable for modules with higher current ratings;3. Using devices with positive tempco, if possible. These vary by type, with some having PTC, 0TC or NTC characteristics. Check the Vce(sat) vs Ic, Tj graphs. (This only matters if you are connecting discrete devices in parallel.)Ratings are DC. A device rated for 1200V 30A, will handle 1200V in the off state, forever, just as it will handle 30A in the on state, as long as it's adequately cooled in both cases.Tim