There are basically three types of Inverters in the market. These are,
- Squarewave Inverter
- Sinewave Inverter
- Modified Sinewave Inverter
Waveform Comparison
Most of the inverters in the market uses modified sinewave for better output at competitive cost. The modified sinewave unit uses a 50% fixed PWM squarewave and the hikes are balanced by a capacitor to produce almost a sine wave. This is called quasi sinewave having THD around 25-28% while squarewave inverters have 45% THD and pure sinewave inverters have just 3% THD.
So, to form a modified sinewave inverter of 220V, we have to generate a 4 phase signal which has 25% 0V, 25% +311V, 25% 0V and 25% -311V. Thus, by series resistor-ed capacitor, the waveform becomes a quasi sinewave. In the driving section of push pull MOSFET sets (2 sets) we have to provide the following pulse,
MOSFET set 1: 0,1,0,0-0,1,0,0-0,1,0,0…
MOSFET set2: 0,0,0,1-0,0,0,1-0,0,0,1…
Now this requires a controlled bistable multivibrator whose output is set to off in 50% time. But we will use here a simple replacement for that. It’s a 4017 decade counter IC. We’ll use it to generate 4 pulses and the fifth state would be reset and this creates our required pulse. Then we just connect two non-consecutive outputs to MOSFET section to generate output. But there’s a tricky part in the clock and frequency. Since 4017 decade counter IC don’t have inbuilt clock generator, it requires external CP. For this we’ll use 555 timer IC and for each CP the output changes one step, but we need 4 changes for a complete 360° cycle. Hence, to make a 50Hz output, we need to set 555 timer IC to 200Hz.
Please note that following circuit only shows upto outputs from oscillator, you need to connect MOSFET pairs at the outputs for driving the Inverter Transformer.
Thus the circuit becomes as follows.
Hi there
I just found your site and found it very nice, specially the inverters circuit diagrams. I am particularly interested in modified square wave inverters however there is a slight glitch in almost all diagrams I have found so and it is error correction circuit i.e. like one SG3524/3525 PWM ic’s provide where Inverter keep producing 220V, load independent. Can you please provide same functionality to above diagram.
Regards
Sam
I guess you have overlooked this one. LINK
Hello sir,
How shall I connect the mosfets ?Plz publish mosfet model & the rest of the circuit..
good
Hi Arup
thanks for the link and please note that I have not overlooked the linked. It is PWM based but still s quare wave inverter. I comments you have also indicated that a modified square wave inverter is possible with SG3524. I only wish how that is possible?
Regards
Sam
SG3524 allows you to adjust PWM ratio manually, hence modified squarewave can also be achieved through it.
hi i just connected up to mosfet connection it was perfect but when i connect transformer the mosfets blasted so what was the problem and what about 13th pin of 4017
Pin 13 will goto ground. I have updated the image to reflect this.
mosfet pair means two or four
Atleast two.
Hello Engr.Basak,
Kindly check my post and reply me.
Is important.
Thanks a lot.
Where?
Thanks for work you are doing. Pin 7 and pin 5 are missing ??
hi Arup how r u ,
can i run the Circuits on 3000 watt inverter??
please Inform me
Are the outputs going to mosfet gates