Slow speed of fan in inverter mode

I've designed a PWM square wave inverter. inverter is ok. but feeling some problem. frequency is stabe 50.53Hz. Duty cycle is 50%. voltgae is 234 to 238AC. but if I load a fan, then speed is becoming 8/10 of its actual speed. I can't find any designing fault, but can't find why the speed is slower than the usual speed. Can anyone help me??? Pls inform me. email: mithun060@gmail.com

_Mithun

Added after 48 minutes:

I used SG3524 as the oscillator circuit as usual. Help me pls...

What kind of fan drive?

celling fans mainly. ratings: 220V AC,85W. But another problem I watched, the brightness of the clear ac lamps also goes low.

I can't find why. is there any problem in the wave shape?

I can show you the control circuit PCB design.

Added after 38 seconds:

https://obrazki.elektroda.pl/100_1273195380.jpg

Hi Mithun,

I think your inverter design does not have feedback, so when the fan is loaded, the voltage of the inverter drops and there is no compensation for this, so the fan rotates slowly and the lamps glows lower.

Hope this helps.
Tahmid.

Thanks a lot Tahmid vai,But I used a feed back ckt using 4N35 opto-couplar. o/p voltage is not changing yet. but voltage is lower with no load condition. If any waveshape problem there??? or noise? O/P is filtered by RC filter. but frequency meter shows various frequencies as 153/163 but if frequency meter is first connected and then inverter is turned on, it shows 50.53 Hz. pls see my design i posted.

Thanks
Mithun



Added after 37 seconds:

anyway, there is no sound in fan (usually fan produces a ceeeeeee sound for square wave). fan is running smoothly but slower. I've just done some changes, added more filter, and tap is changed. now fan is speedy, but voltage is 248AC. it may creat problems I think. I'm testing... If anyone have better idea pls help me.

Thanks
Mithun

The fans are inductive loads, and will be naturally be affexted by the waveform you are generation (PWM ) in your case, while the board suppplies sine. This is spped change can be usally seen in 90% of pwm inverters. It also depends on the core of the output transformer, the quality of the winding wires and the output drivers (wether mosfet, igbt or or transistors )

MOSFETs are not heated, but transformer is heated. and a sound is coming out from the transformer. is there any problem in the oscillator circuit?


can you help me to design a sine wave oscillator ckt?

Added after 3 hours 51 minutes:

Is it possible to convart square wave into sine wave using D/A converter circuit with bandpass filter??


Have you any idea? Please reply me.

Finally I found the problem for slow speed of fan. It was actually our measurement fault. we measured the o/p voltage using Digital Multimeter. In this case the o/p is noise mixed and have some spikes. as a result, DMM shows high voltage, so we tuned the PWM at 225VAC. but it was actually 180V AC. So I think we should use Analog voltmeter to measure high voltage AC.