PWM Inverter
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
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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.
25 Responses to “PWM Inverter”
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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
Please can you send me the circuit of PWM inverter (12VDC-230VAC)
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
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
need more of this.
sir
this is the best information on pwm, it have helped me to understand the basics of pwm.
thank you
themba
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
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
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.
i have the best information .. thanks a lot
sir
i have best information about the pwm inverter , thank you sir
i am very grateful, ur write up has given has given a ride on to my B.ENG project theory. God bless.( from nigeria.)
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
Plea can you send the circuit of FM transmeter after 5km range
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
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
anyone with a low cost 1000W power inverter circuit diagram with tutorials that i can do practically plz help…..
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.
I need more detail infromation
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i want all information about PWM thanks
thanks for ur kind information
hey can someone publish the component list for making 3 phase pwm inverter…
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
jaya darling search in electronic circuits.. yo ll get more info