scientist1234
Newbie level 1
I have been trying to understand how the "zoneless"induction cooktop of De dietrich Piano works. I have found a introduction movie on youtube and it shows the internal workings of the cooktop although at not great resolution because they do not want you to copy it.
https://www.youtube.com/watch?v=7ePgUtekGdE (you see at 18 seconds the PCBs of the cooktop)
What I have found so far from the movie is when the coils and metal sheets are removed you see the pcb boards with the drivers (SEE also the attached image of the pcb boards). As far as I can see in the back are the fans for the heatsinks. the heatsinks are the large grey rectangles. on the long side of the heatsinks you see the black and whitish blocks, those are very likely the IGBTs, 6 on each site of the heatsink making 36 in total for 36 coils. In front of the heatsink there is a black square which most likely is the chip that controls the IGBTs and monitors the system.
Now comes the question of the mysterious electrical component in the image and video you see next to the IGBTs location a white square with a silver colored cross (probably solder). There are in total 36 of these components, equal to the number of IGBTs so they are probably connected. The white components (with silver cross) are I estimate about an inch high and an inch wide and about a maximum of a 1/4 inch thick.
I did some research into the components of an induction cooktop and have come up with some possible candidates for the components. However I have not been able to find a picture matching the component. For an induction cooker to work on the components that lead to the induction coil that generate the magnetic field you need a capacitor in series with the induction coil. A current transformer (often a toroidal coil) that monitors power consumption, and an igbt driver circuit (most likely a simple ic).
I can therefore only deduce that components (white square with silvery cross) are ceramic type capacitors. However I have not been able to find any ceramic capacitors that look that way, so I am at a loss what the component could be. It looks familiar, like I have seen it more often but I can not remember anaything about it.
Also the components do not get excessively hot since they are not connected to the heatsink.
Does someone here maybe know what the components could be or could maybe point in a direction where to look because I am at a loss.
I have also found that the igbts are most likely dual igbt meaning 2 IGBTs in 1 package because you need 2 IGBT per coil.
Thanks in advance
In addition I have found that most IGBTs in induction cookers are protected by snubber circuits to absorp the voltage spikes of the collapse of the magnetic field in the coil. These snubber circuits contain capacitors, resistor and diodes.
I have found a link in this forum https://www.edaboard.com/threads/225668/
Were mtwieg says this
Re: Half Bridge Induction Cooker
Originally Posted by resonant
I have them there to suppress transient voltages. Could they be the source of my problem?
Reply from mtwieg
Those caps will definitely increase the dissipation in the IGBTs. Every time either IGBT turns on, it will dissipate all the energy stored in those "snubber" caps. At 50V, that's 58.75uJ and at 28KHz that's 1.645W per IGBT. At 100VDC that will quadruple, and so on.
There are a few ways to properly snub a half bridge. First is to put good snubber caps on the DC rail, right next to the IGBT terminals. Second is to fit the half bridge output with a good RC snubber. The sizing of the snubber components must be done carefully in order to get good performance and not cause significant heating.
However, when driving a resonant load, snubbers should hardly be necessary, since you should be switching the IGBTs at zero current. I've worked on solid state tesla coils (just a dual resonant load) and we switch currents over 1KA easily at ~30KHz, and no snubbers are necessary as long as you are driving on resonance. Doing so greatly reduces the stress on the IGBTs, allowing us to push the current far beyond its ratings.
Could the white square components with silver cross be those snubber caps on the DC rail as mentioned above or maybe a package containing the snubber circuit for after the IGBT?
https://www.youtube.com/watch?v=7ePgUtekGdE (you see at 18 seconds the PCBs of the cooktop)
What I have found so far from the movie is when the coils and metal sheets are removed you see the pcb boards with the drivers (SEE also the attached image of the pcb boards). As far as I can see in the back are the fans for the heatsinks. the heatsinks are the large grey rectangles. on the long side of the heatsinks you see the black and whitish blocks, those are very likely the IGBTs, 6 on each site of the heatsink making 36 in total for 36 coils. In front of the heatsink there is a black square which most likely is the chip that controls the IGBTs and monitors the system.
Now comes the question of the mysterious electrical component in the image and video you see next to the IGBTs location a white square with a silver colored cross (probably solder). There are in total 36 of these components, equal to the number of IGBTs so they are probably connected. The white components (with silver cross) are I estimate about an inch high and an inch wide and about a maximum of a 1/4 inch thick.
I did some research into the components of an induction cooktop and have come up with some possible candidates for the components. However I have not been able to find a picture matching the component. For an induction cooker to work on the components that lead to the induction coil that generate the magnetic field you need a capacitor in series with the induction coil. A current transformer (often a toroidal coil) that monitors power consumption, and an igbt driver circuit (most likely a simple ic).
I can therefore only deduce that components (white square with silvery cross) are ceramic type capacitors. However I have not been able to find any ceramic capacitors that look that way, so I am at a loss what the component could be. It looks familiar, like I have seen it more often but I can not remember anaything about it.
Also the components do not get excessively hot since they are not connected to the heatsink.
Does someone here maybe know what the components could be or could maybe point in a direction where to look because I am at a loss.
I have also found that the igbts are most likely dual igbt meaning 2 IGBTs in 1 package because you need 2 IGBT per coil.
Thanks in advance
In addition I have found that most IGBTs in induction cookers are protected by snubber circuits to absorp the voltage spikes of the collapse of the magnetic field in the coil. These snubber circuits contain capacitors, resistor and diodes.
I have found a link in this forum https://www.edaboard.com/threads/225668/
Were mtwieg says this
Re: Half Bridge Induction Cooker
Originally Posted by resonant
I have them there to suppress transient voltages. Could they be the source of my problem?
Reply from mtwieg
Those caps will definitely increase the dissipation in the IGBTs. Every time either IGBT turns on, it will dissipate all the energy stored in those "snubber" caps. At 50V, that's 58.75uJ and at 28KHz that's 1.645W per IGBT. At 100VDC that will quadruple, and so on.
There are a few ways to properly snub a half bridge. First is to put good snubber caps on the DC rail, right next to the IGBT terminals. Second is to fit the half bridge output with a good RC snubber. The sizing of the snubber components must be done carefully in order to get good performance and not cause significant heating.
However, when driving a resonant load, snubbers should hardly be necessary, since you should be switching the IGBTs at zero current. I've worked on solid state tesla coils (just a dual resonant load) and we switch currents over 1KA easily at ~30KHz, and no snubbers are necessary as long as you are driving on resonance. Doing so greatly reduces the stress on the IGBTs, allowing us to push the current far beyond its ratings.
Could the white square components with silver cross be those snubber caps on the DC rail as mentioned above or maybe a package containing the snubber circuit for after the IGBT?
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