Author Topic: EEVblog #449 - Absopulse VFC500 Variable Frequency Converter Teardown  (Read 18878 times)

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Offline Yansi

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There is no "may be right", in this one, there are only facts. The topology you described, is just evil crap, if you don't understand that enough. Any sensible engineer won't use that anywhere, because of what I have tried to explain you. With that topology, you wont save anything apart from switching loss on one side. From the circuit design point of view, it is not simplier though. It is only negligence or lack of expirience or both, or whatever evil will make you use that kind of topology. I have never seen it anywhere, because it just don't work as on the paper. There is a big difference in between the slewrate of the 50Hz side and the output of the reconstruction LC filter, there will be crap on the output around zerocrossings, when changing the polarity of the output. And then the whole output floats on that squarewave.

It is evil in every aspect, almost none advantage, except that it is probably cheaper, cause the lack of one output choke and highspeed mosfet driver. (They can drive the slow halfbridge side using a few discretes). But cost cutdowns are NOT a valid excuse for not doin' that inverter right. And I will not advise anyone to build things that aren't right. So it is nice, that such topology exists (you will for sure find much more possibilities), but be aware some of them simply aren't going to work well or good enough.

Lowvoltage side sinusoidal modulators are a whole another category, please don't mix em here or make another topic for em.

That hybrid IGBT/NMOS topology with only lowside diodes needing to be fast does not make sense. Please describe it more or check that you aren't mixing things together.
 

Offline bktemp

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That hybrid IGBT/NMOS topology with only lowside diodes needing to be fast does not make sense. Please describe it more or check that you aren't mixing things together.
Here is a 250W HID metal halide electronic ballast using this configuration:
http://www.st.com/web/en/resource/technical/document/application_note/CD00192161.pdf
 

Offline NiHaoMike

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And I do not understand what other efficiency boost it will bring, than saving switching losses on one side. You still can use lower conduction loss transistors on both sides, regardles of the switching frequency.
There's a tradeoff between conduction and switching losses. You can't optimize for both at the same time.

The inverter I actually used the design in was supplied by an internal isolated DC/DC converter, so the output neutral was just bypassed to ground with a capacitor. As it was intended for motor loads, EMI wasn't a huge concern. It's certainly much less noisy than a common modified sine inverter or a filterless VFD.
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