Ian this wave normal?

[Gaber Mohamed Boraey]

Hello everyone
I have inverter with modified sine wave output and 50hz , customer complaints that it doesn’t work normal with electric fans at home, say the fan work but slow and with noise sound also he can smell burning smell after a while

I’ve checked the output wave of this inverter and it looks like this “ attached “

Ive measured the output voltage and it’s within range 220vac , the inverter work normal with other loads for example a tungestin
Lamp

Does the modified sine wave signal not suitable for electric fans?

 

[betwixt]

Modified sine rarely works with inductive loads such as motors.
The 'modified' sine you show is actually more like a square wave with settling time, instead of rising and falling gradually along a sine curve, it produces full positive, zero, full negative, zero, full positive, zero repeatedly. The inductive load doesn't take kindly to the abrupt rising and falling edges. Non-inductive loads don't care what the waveform is and would even work on pure DC.

Brian.

 

[crutschow]

Is your 'scope input set for DC, which it should be?
The rounded waveform display would suggest it's AC.

 

[D.A.(Tony)Stewart]

What's wrong with the flyback voltages?
What will selecting different capacitors for speed for impedance and phase shift do with harmonics?
Why are the harmonics audible yet not the fundamental f from lower impedance harmonics and edge-noise spectrum?

The tri-level inverter almost looks tri-state but not in one direction towards 0.

What's wrong with this picture? besides not being a sinewave.

You cannot use a square wave inverter or even a Triac on AC cap-controlled-speed fans due to these harmonics not shifting the phase properly.

 

[Easy peasy]

Unless the modified shine wave is an active short circuit in the dead time - then it is hopeless for powering things like fans.

very few modified sine inverters are built like this, usually the impedance P-N in the dead time is unknown and the energy stored in the transformer output wires flies about in an effort to reset the core flux to zero.

remember real mains has a low Z at all times, including near the zero crossings - where fan current often flows due to its inductive nature.

 

[BradtheRad]

Look into the diode-clamped converter. It's suitable for powering inductive loads. Its waveform is bipolar AC similar to the 'modified sine' inverter. Its switching sequence keeps free-wheeling diodes connected to the load for a brief portion of each idle cycle.