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inverter question

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Hello Everyone!

Is there a big difference between pure sine wave inverters and (modified sine wave, square wave) inverters?

If the inverter is powering a device with a full wave bridge rectifier, is there really any difference between the two?


Yes there is a difference.  The waveform will vary depending on how well designed the inverter is, and how much it costs.  The utility of various waveforms will depend on the application.

In other words, there is no simple answer.  Some loads don't much care about waveform; others do.  And the noise will vary.

There is a very big difference in the output, whether that greatly affects the device you're trying to power is impossible to say without knowing more about the device in question. Anything with an iron transformer or motor will tend to buzz noticeably when connected to a "modified sine" which is just a square wave with dead time. Some devices like phase control dimmers won't work at all, and I've seen other devices burn up but most stuff like computers and modern TVs and other stuff with switching power supplies doesn't really care. If you need it for a specific application then modified sine may be just fine, but for more general purpose use pure sine is always preferable.


--- Quote from: vivi-d on July 26, 2021, 07:21:41 pm ---If the inverter is powering a device with a full wave bridge rectifier, is there really any difference between the two?

--- End quote ---

There are not many devices left around with such a simple input as for most products PFC has been mandated for many years and that is certainly waveform sensitive. I think modified sinewave has largely been consigned to the dustbin of history except for those offshore copycat manufacturers who know no better and the unfortunate unaware consumers who still buy them (presumably because they are dirt cheap).

The main difference between them is the harmonic content of the output voltage. Many loads, as well as the mains, require harmonics above the fundamental one to have an amplitude below certain levels. This can be achieved by adding a filter between the converter and the load, which can add a significant volume, cost and weight to the product. Therefore, different modulations can be used to reduce the harmonic content and, as a consequence, the required filter (modified sine wave, PWM, symmetric PWM, etc).

A pure sine wave inverter would be the best solution in terms of EMC as it ideally does not produce high frequency harmonics. However, if it is implemented with bipolar transistors, the efficiency of the converter will probably be quite low, which is not great in case it will be used for supplying high amounts of energy. On the other hand, resonant converters have really high efficiencies at their nominal operating point, but they can be difficult to design.

Consequently, as previous comments have stated, the topology used in each product needs to be chosen according to the requirements of the load and the expected cost of the final product


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