What makes the inductive load like a motor heat up when used on a modified sine wave inverter. Is it because of the back emf caused by sudden drop of voltage by the square wave?
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1\$\begingroup\$ Which part heats up? \$\endgroup\$– winnyCommented Feb 14, 2022 at 12:45
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\$\begingroup\$ The motor itself and there is a whining/buzzing sound that can be heard. \$\endgroup\$– kuchiCommented Feb 14, 2022 at 12:49
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\$\begingroup\$ Thanks. Please edit the question to reflect this. It's not clear at the moment. \$\endgroup\$– winnyCommented Feb 14, 2022 at 13:30
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4 Answers
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I think the idea is as follows: any repetitive wave form may be decomposed in a sum of sine waves with frequencies multiples of the base one (Fourier series). The base frequency part produces work, but other frequencies are two fast and the slip is too much so their energy is lost whithout producing work, or better said the ratio of losses to work produced is too high.
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\$\begingroup\$ I think this is the easiest to understand explanation. I did more googling and some inverter manufacturers did mention this. \$\endgroup\$– kuchiCommented Jul 18, 2022 at 13:13
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Modified sinewave inverters do not necessarily produce a pure sine wave: -
Image from here.
Because of the harmonics of the "modified sinewave", eddy current losses are increased (due to the higher frequency harmonics) and, this causes heat increases over and above the heat produced when driven by a pure sinewave: -
Image taken from this article.
Maybe this is what you refer to?
Is it because of the back emf caused by sudden drop of voltage by the square wave?
No.
answered Feb 14, 2022 at 13:42
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\$\begingroup\$ Thank you. This is what I've been looking for. \$\endgroup\$– kuchiCommented Feb 16, 2022 at 4:34
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\$\begingroup\$ @kuchi please take the two minute tour to understand what motivates folk to give there free time to help you. \$\endgroup\$– Andy akaCommented Feb 16, 2022 at 9:03
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Motors heat up, regardless of being on a "modified sine wave" inverter or standard AC main for a variety of reasons. Those include:
- Resistive losses in the windings.
- Eddy current losses in the core materials.
- Friction losses in the bearings of the moving parts.
Back EMF does not cause losses.
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Back EMF will be a sinewave.
The difference between the drive waveform and the back EMF is the voltage driving current in the motor. Normally, the drive would also be a sinewave, so the difference would be relatively small and proportional to the torque demand from the load.
With modified sine, even at no torque load (above friction, windage) the difference is relatively large, (and far from sinusoidal) causing relatively large currents to produce heating.