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  • Pulse Width Modulation or PWM technology is used in Inverters to give a steady output voltage of 230 or 110 V AC irrespective of the load. The Inverters based on the PWM technology are more superior to the conventional inverters. The use of MOSFETs in the output stage and the PWM technology makes these inverters ideal for all types of loads. In addition to the pulse width modulation, the PWM Inverters have additional circuits for protection and voltage control.

    The quality of the output wave form (230 / 110 volt AC) from the inverter determines its efficiency. The quality of the inverter output wave form is expressed using Fourier analysis data to calculate the Total Harmonic Distortion (THD). THD is the square root of the sum of the squares of the harmonic voltage divided by the fundamental voltage.

    THD = √ V2 2 + V3 2 + V4 2…………. Vn 2 / V1
    Based on the output waveforms, there are three types of Inverters. These are Sine wave, Modified Sine wave or Quasi sine wave and Square wave inverters.

    Sine wave

    Alternating current has continuously varying voltage, which swings from positive to negative. This has an advantage in power transmission over long distance. Power from the Grid is carefully regulated to get a pure sine wave and also the sine wave radiate the least amount of radio power during long distance transmission. But it is expensive to generate sine wave in an inverter. Its quality is excellent and almost all electrical and electronic appliances work well in sine wave inverter.

    Sine Wave

    The sine wave is the AC waveform we get from the domestic lines and from the generator. The major advantage of sine wave inverter is that all of the house hold appliances are designed to operate in sine wave AC. Another advantage is that the sine wave is a form of soft temporal rise voltage and it lacks harmonic oscillations which can cause unwanted counter forces on engines, interference on radio equipments and surge current on condensers.

    Modified Sine wave or Quasi Sine wave

    Modified sine wave is designed to simulate a sine wave since the generation of sine wave is expensive. This waveform consists of a Flat Plateau of positive voltage, dropping abruptly to zero for a short period, then dropping again to a flat plateau of negative voltage. It then go back to zero again and returning to positive. This short pause at zero volts gives more power to 50 Hz fundamental frequency of AC than the simple square wave.

    Inverters providing modified sine wave can adequately power most house hold appliances. It is more economical but may present certain problems with appliances like microwave ovens, laser printers, digital clocks and some music systems. 99% of appliances run happily in modified sine wave. Instruments using SCR (Silicon Controlled Rectifier) in the power supply section behave badly with modified sine wave. The SCR will consider the sharp corners of the sine wave as trashes and shut off the instrument. Many of the Laser printers behave like this and fail to work in inverters and UPS providing modified sine wave power. Most variable speed fans buzz when used in modified sine wave inverters.

    Square wave

    This is the simplest form of output wave available in the cheapest form of inverters. They can run simple appliances without problems but not much else.Square wave voltage can be easily generated using a simple oscillator. With the help of a transformer, the generated square wave voltage can be transformed into a value of 230 volt AC or higher.

    Advantage of Pulse Width Modulation

    In a standard Inverter without the PWM technology, the output voltage changes according to the power consumption of the load. The PWM technology corrects the output voltage> according to the value of the load by changing the Width of the switching frequency in the oscillator section. As a result of this, the AC voltage from the Inverter changes depending on the width of the switching pulse. To achieve this effect, the PWM Inverter has a PWM controller IC which takes a part of output through a feedback loop. The PWM controller in the Inverter will makes corrections in the pulse width of the switching pulse based on the feedback voltage. This will cancel the changes in the output voltage and the Inverter will give a steady output voltage irrespective of the load characteristics.

    PWM Inverter Block Diagram


    How it Works?

    To design an Inverter, many power circuit topologies and voltage control methods are used. The most important aspect of the Inverter technology is the output waveform. To filter the waveform (Square wave, quasi sine wave or Sine wave) capacitors and inductors are used. Low pass filters, are used to reduce the harmonic components. Resonant filter can be used if the Inverter has a fixed output frequency. If the inverter has adjustable output frequency, the filter must be tuned to a level above the maximum fundamental frequency. Feedback rectifiers are used to bleed the peak inductive load current when the switch turns off.

    As per the Fourier analysis, a square wave contains odd harmonics like third, fifth, seventh etc only if it is anti-symmetrical> about 180 degree point. If the waveform has steps of certain width and heights, the additional harmonics will be cancelled. If a Zero voltage step is introduced between the positive and negative parts of the square wave, the harmonics that are divisible by three can be eliminated. The width of the pulse should be 1/3 of the period for each positive and negative steps and 1/6 of the period for each of the Zero voltage steps. This leaves on the fifth, seventh, eleventh, thirteenth harmonics etc
    .
    The Pulse Width Modulation technology is meant for changing the characteristics of the square wave. The switching pulses are Modulating, and regulating before supplied to the load. When the Inverter requires no voltage control, fixed pulse width can be used.

    Multiple Pulse Width Modulation (MPWM) Technology

    In Multiple Pulse width technology, waveforms that contain a number of narrow pulses are used. The frequency of these narrow pulses is called Switching or Carrier frequency. The MPWM technology is used in Inverters driving variable frequency motor control systems. This allows wide range of output voltages and frequency adjustments. More over the MPWM technology overall improves the quality of the waveform.

    PWM Inverter Characteristics

    In order to increase the efficiency of the PWM inverter, the electronic circuit is highly sophisticated with battery charge sensor, AC mains sensor, Soft start facility, output control etc. The PWM controller circuit uses PWM IC KA 3225 or LM 494 .These ICs have internal circuits for the entire operation of the pulse width modulation. The Oscillator circuit to generate the switching frequency is also incorporated in the IC. Output driver section uses Transistors or Driver IC to drive the output according to the switching frequency. Output section uses an array of Switching MOSFETs to drive the primary of the stepping transformer. Output voltage is available in the secondary of the stepping transformer.

    attentionThe author D Mohankumar is not an active member anymore. Please take into consideration that the presented information might not be correct.
    
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    40 Responses to "PWM Inverter"

    1. ameer ahmed says: on July 8, 2010 at 10:01 am

      thanks this is the best information about pwm. you have any circuit take 110 volts from 220 volts without using stepdown transfarmer.
      with best regards
      Ahmed

    2. Please can you send me the circuit of PWM inverter (12VDC-230VAC)

      • mallikarjuna says: on March 25, 2012 at 9:55 am

        hai,now i am studying in final year BE so i need information from pwm inverter for giving seminar .if it is possible send me the slides based on pwm.
        thank you

      • Thanks. Please can you send me the circuit of PWM inverter (24VDC-230VAC)

    3. Ahmed, Hello, I live the U.S.A. so I am not sure where your 220 is coming from or how, if you are talking mains ac,,here in the states we have three incoming lines a, 110 pos, a neg,”or nuetral” and a 110 positive. the two positives alternate through the neutral this gives us 220Volts,,if you are talking transformer dc ,,I believe you have a center tapp on the out putsecondary that gives you your sorta neutral and the two outter leads would be the independent 110′s as far as drawing from one I am not sure this works without adverse effects to the other

      • Dear Ed,
        Thanks allot and sorry for the late reply.
        i live in pakistan and there is fixed 220 volts coming from power station along with a neutral wire.i have some equipments that are operating with the 110 volts.that’s why i am looking for any circuit that convert 220V to 110V with heavy amperes.
        Thanks With Best Regards
        Ahmed

    4. kipngetich says: on July 16, 2010 at 1:51 pm

      need more of this.

    5. themba mahlinza says: on August 4, 2010 at 7:35 pm

      sir

      this is the best information on pwm, it have helped me to understand the basics of pwm.

      thank you
      themba

    6. I purchased a tripp lite Model #: APSINT3636VR
      It says PWM sine wave
      can it be considered pure sine wave?
      is it suitable for running telecom equipment and servers?

      Thanks,
      Dave

    7. pls i need you to teach me on how to calculate inverter output power. Like if an inverter is rated 3kva, how can i calculate to know the components required. Pls help me out

    8. oloko isaac says: on December 28, 2010 at 7:01 pm

      i need to regulate the output of my inverter to 230+/-1% with PIC18F452 , Can you help please?. i am willing to pay for it.
      regards,
      isaac.

    9. kailash rangaraj says: on February 4, 2011 at 2:06 am

      i have the best information .. thanks a lot

    10. neppolian.n says: on February 15, 2011 at 12:27 pm

      sir
      i have best information about the pwm inverter , thank you sir

    11. eghosa edosomwan says: on February 26, 2011 at 11:46 am

      i am very grateful, ur write up has given has given a ride on to my B.ENG project theory. God bless.( from nigeria.)

    12. hello..i doing project inverter which 12vdc to 240vac..i using pic 16f877 for produce pwm..so can u help with schematic n program software..need help..tq

    13. CH.SRINIVAS RAO says: on March 1, 2011 at 10:45 am

      Plea can you send the circuit of FM transmeter after 5km range

    14. Daniel L. says: on March 25, 2011 at 11:34 am

      Thanks again for Your clearifing tutorial ! Can You make a tutorial abaud calculating the transformers,chokes and other inductors because this is still hocus-pocus for me !
      And not only me, I’m shore !
      Thanks, DL

    15. i am doing a project on a 12Vdc to 220Vac and i am looking for a circuit diagram for a 1000W modified sine wave inverter that i can do practically and understand easily and that will not

    16. anyone with a low cost 1000W power inverter circuit diagram with tutorials that i can do practically plz help…..

    17. Enough of all this stupid theory ! Get to the bottom of things. Come out with a real circuit and explain. Else shut-up ! Don’t copy from books and paste that crap here.

    18. I need more detail infromation

    19. i want all information about PWM thanks

    20. indumathy.m says: on October 27, 2011 at 5:08 pm

      thanks for ur kind information

    21. hey can someone publish the component list for making 3 phase pwm inverter…

    22. hey can you please provide me the circuit diagram .. and details about the components .. it will be easy to compare with my inverter…

      thanks
      ppatel

    23. jaya darling search in electronic circuits.. yo ll get more info

    24. kintu hamza says: on May 30, 2012 at 8:42 pm

      hallo how r u i need a pmw circuit diagram using mosfets thank u nice day

    25. Waliur Rahman says: on July 14, 2012 at 12:16 pm

      Dear sir,
      thanks this is the information about pwm inverter.I need a 500va pwm Inverter(single phase), Which convert 12v to 230v for my university project. so i want to circuit diagram of that inverter. Please can you send me the circuit diagram of PWM inverter.
      I will grateful to you.

      Best Regards

      Waliur Rahman
      Dhaka, Bangladesh

    26. i doing project inverter which 12vdc to 240vac…so can u help with schematic n program software..

    27. The best (PWM) inverter generate (modified sine wave) inverter controller (Ic) is (sg3524) and 3 phase transformer to deliver exactly (50Hz-60Hz)

    28. This is a real fact file in electronics today that most of the electronics=author are not well %aware% of this..i know that many electronics{student}fermilialize with CD4047..as an astable mutivibrator..for project… .but i will let you known that..iccd4047,ne555,cd4060+cd4017 and any order chip are low §cost ¤pwm¤(inverter)….the best chip pwm inverter that generate $ine%wave,!!modified $ine%wave,controller chip is {sg3524}this is a §high cost that is very useful to all f=i=n=a=l%s=t=u=d=e=n=t..so you make come across pwm inverter in any {website} i can asure that the circuit is full error correction.the best and correct circuit of this is not post to any {website}absolutely speaking.. the chip is have 16 pin…pin1=in pin2=inf pin3=osc out pin4=currentlimit pin5=currentlimit pin6=RT pin7=CT pin8=GND power pin pin9=comparator pin10=shutdown pin11=emitter 1 pin12=collector1 pin13=collector 2 pin14=emitter 2 pin15=Vcc power pin pin16=5volt regulator output so the frequency is determined by the value capacitor RT AND CT connected to pin6 and pin7 respectively using the formular below f=1.30/RtCt………

    29. Pls; kindly assist him ellaborate the theory of 12v dc to 230ac inverter and please the circuit diagram will also be needed,
      thanks and God bless.

    30. starjeya23 says: on January 10, 2013 at 12:55 pm

      sir, i want the verilog code for generation of PWM inverter. I need the code to control the mosfets so that the switching can be done and pulse width sine wave is produced. Thank You.

    31. Ahmad asg says: on July 16, 2013 at 8:21 am

      high power ac 230V PWM for inductive load

      Hello !
      I Pleased if you help me !
      I need to a circuit for High power ( 30kw) PWM ( or dimming ) for inductive load Voltage Setting (with protection for load short circuit )
      Thanks for all .
      yours truly – Ahmad asghari

    32. sudheer kumar says: on November 19, 2013 at 11:46 am

      i need more answer

    33. sudheer kumar says: on November 19, 2013 at 11:50 am

      hai i am sudheer i doing inverter project work i need to know how pwm technique in inverter works

    34. this is best information on PWM, thanks a lot. Please I will need a 2kv and 5kv PWM inverter circuit diagram. Thank you

    35. prashanth suvarna says: on February 23, 2014 at 10:34 pm

      Hello every1. Have “Dropped in” often2ur very good&well in4med site. M put off by rude comments put up by half baked folks who don’t have the patience or the more probably the capacity 2nderstand the insight working of anything more than a few simple but well designed and well thought out circuits….a little patience&a bit of help on a 1:1 basis with a rather cooperative colleague will of course go a long way…Bye

    36. can u plz explain the differences in circuit diagram of Square wave inverter and sine wave inverter? mainly IC make the output to become sine wave?? i dun understand it clearly.. i’m a student.. thank you..

    37. Hi, I need a circuit of the microwave pulse. Please give me tips. Thanks

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