Author Topic: Power electronics snubber circuits.  (Read 735 times)

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Offline Kemme

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Power electronics snubber circuits.
« on: October 14, 2016, 04:53:22 pm »
Hello all

I had an opportunity to examine high power voltage source inverter and I found out that there is a snubber circuit in the rectifier section. The snubber consists of a capacitor and resistor across the DC+ and DC- outputs of the rectifier so I assume that they are just dV/dt limiters. But, are they really needed? I know that it is sometimes essential to design snubber circuits on the inverter side to minimize the voltage overshoots and current rise times during the switching but I have absolutely no idea why are they needed on the rectifier side.

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Offline SeanB

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Re: Power electronics snubber circuits.
« Reply #1 on: October 14, 2016, 05:53:07 pm »
The rectifiers create a change in current as they turn on or off, and with the unknown line and load inductance this can make for a large voltage spike, especially if you have the line reactor installed to increase the input impedance on a low impedance supply.

If you have a very low impedance supply ( typical in an industrial environment, where you could literally have a supply impedance in the low milliohm range) the turn on spikes can be very large, definitely enough to damage the junctions from overvoltage or from concentrating the current in a small spot on the die as the slow portions of the diode turn on or off. If you look at the datasheets for all inverters you see the need to increase supply impedance in certain conditions with a line reactor.
 


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