The post discusses a single phase variable frequency drive circuit or a VFD circuit for controlling AC motor sped without affecting their operational specifications.
What is a VFD
Motors and other similar inductive loads specifically do not "like" operating with frequencies that might be not within their manufacturing specs, and tend to become a lot inefficient if forced to under such abnormal conditions.
For example a motor specified for operating with 60Hz may not be recommended to work with frequencies of 50 Hz or other ranges.
Doing so can produce undesirable results such as heating up of the motor, lower or higher than the required speeds and abnormally high consumption making things very inefficient and lower life degradation of the connected device.
However operating motors under different input frequency conditions often becomes a compulsion and under such situations a VFD or a variable frequency Drive circuit can become very handy.
A VFD is basically as the name suggests s device which can be used for operating an inductive load with the any desired frequency which might be most suitable for it as per its company specs.
This is normally done using the given control in the form of a variable knob scaled with different frequency calibration.
Making a VFD at home may sound to be a difficult proposition, however a look at the design suggested below shows that after all it's not so difficult to build this very useful device (designed by me).
Circuit Description
The circuit can be fundamentally divided into two stages: The half brige driver stage and the PWM logic generator stage.
The half bridge driver stage uses the half bridge driver IC IR2110 which single handedly takes care of the high voltage motor drive stage incorporating two high side and low side mosfets respectively.
The driver IC thus forms the heart of the circuit yet require just a few components for implementing this crucial function.
The above IC however would need a high logic and a low logic in frequencies for driving the connected load at the desired specific frequency.
These hi and lo input logic signals become the operating data for the driver IC and must include signals for determine the specified frequency as well as PWMs in phase with the mains AC.
The above info are created by another stage comprising a couple of 555 ICs and a decade counter. IC 4017.
The two 555 ICs are responsible for generating the modified sine wave PWMs corresponding to the full wave AC sample derived from a stepped down bridge rectifier output.
The IC4017 functions as a totem pole output logic generator whose alternating frequency rate becomes the MAIN frequency determine parameter of the circuit.
This determining frequency is plucked from pin#3 of IC1which also feeds the IC2 triggering pin out and for creating the modified PWMs at pin#3 of IC2.
The modified sine wave PWMs are scanned at the outputs of the 4017 IC before feeding the IR2110 in order to superimpose exact "print" of the modified PWMs at the output of the half bridge driver and ultimately for the motor which is being operated.
Cx and the 180k pot values should be appropriately selected or adjusted in order to provide the correct specified frequency for the motor.
The high voltage at the drain of the high side mosfet must also be calculated appropriately and derived by rectifying the available mains voltage AC after suitably stepping it up or stepping it down as per the motor specs.
The above settings will determine the correct volts per Hertz (V/Hz) for the particular motor.
The supply voltage for both the stages can be made into a common line, same for the ground connection.
TR1 is a stepped down 0-12V/100mA transformer which provides the circuits with the required operating supply voltages.
The Half-Bridge Driver Circuit
The PWM Controller Circuit
Correction in the above Finalized Design
A careful investigation reveals that the diode feeds from IC2 in the above diagram is wrongly connected with the LIN/HIN inputs of the mosfet driver IC.
For a correct implementation of the VFD operation and the intended controls, the diodes must be integrated with the gates of the respective MOSFETs as indicated in the following corrected version:
The finalized integrated design of the above circuits may be witnessed in the following diagram, as drawn by Mr. Vuleek Unteeluv
R1 is for frequency adjustment, and R8 for Voltage Adjustment, both of these controls could be used for optimizing the V/Hz ratio for a particular motor, manually.
Note: Pin#16 of IC is shown configured with a PNP transistor stage which ensures that the IC 4017 keeps the mosfets powered only as long as its pin#14 is supplied with the cock pulses. This arrangement makes sure that under no circumstance the output of IC 4017 hangs and keeps one of the mosfets permanently ON and the other OFF, however if you feel the PNP stage is not crucial you may remove it and connect pin#16 directly with the supply positive.
Important: Make sure to connect the SD pin of the half-bridge driver IC with the negative or the ground line, otherwise the IC will not work.
Update:
Simplified and Improved Design
The above discussed simple single VFD design can be further simplified and improved by using a self oscillatory full bridge IC IRS2453, as shown below:
Here the IC 4017 is completely eliminated since the ful bridge driver is equipped with its own oscillator stage, and therefore no external triggering is required for this IC.
Being a full bridge design the output control to the motor has a full range of zero to maximum speed adjustment.
The pot at pin#5 of IC 2 can be used for controlling the speed and the torque of the motor through PWM method.
For V/Hz speed control the Rt/Ct associated with the IRS2453 and R1 associated with IC1 can be respectively tweaked (manually) for getting appropriate results.
ayanda says
Hi Mr Swag i redesigned my H bridge driver and if i test it with motor ,my ic driver just brew up and the only pin that may course this problem is pin 5 since it connected to high voltage and there is no diode or resistor across it ,is it correct like this? im scared to put another one if it blow again i will be in short of them
Swag says
Hi Ayanda, As you will understand that the H-bridge design is a standard design taken from the datasheet of the IC, so it has to be correct in every manner, pin#5 of the IR2110 is correctly configured, since it is as per the diagram in the datasheet.
Configuring an H-bridge using driver IC is always a little problematic unless it si done on a well designed PCB, and make sure to add 1k resistors across gate/drain of each mosfets, this might help to safeguard, but you can be never sure unless you have the most correctly designed PCB layout for the H-bridge.
If you want to avoid a driver IC, you can probably opt for the following H-bridge concept:
https://www.homemade-circuits.com/arduino-full-bridge-h-bridge-sinewave-inverter-circuit/
you can connect the NAND inputs to the IC 4017 outputs
ayanda says
thanks bro i will do that ,maybe there is a little infomation that i have missed but protecting it would help me
Swag says
Wish you all the best bro!
mohammed says
Dear MR Swag,
i want to make this circuit of VFD but using arduino as the designed one in https://www.homemade-circuits.com/arduino-full-bridge-h-bridge-sinewave-inverter-circuit/
but i need to vary the frequency using the arduino itself.will be any need for the 555 timers and ic 4017 ?? and will be the arduino Uno effective in changing the frequency ?
Swag says
Mohammad,
It may be possible to replace IC1, IC2 and the 4017 with an Arduino, but designing the program can be complex. However if you only want the frequency adjustment to be implemented from the Arduino, in that case you can replace IC section with any Arduino frequency generator stage
mohammed says
Thanks for the reply mr swag,
what i really need is to control motor speed using arduino and the power source for the circuit is from AC 220 volt which is available in any home not a DC batteries as implemented in https://www.homemade-circuits.com/arduino-full-bridge-h-bridge-sinewave-inverter-circuit/
Swag says
Mohammad, for this you will have to have an adjustable PWM output from the same Arduino board, this pwm could be configured with the low side mosfet gates for implementing the required motor control action
mohammed says
thanks Mr Swag for your reply,
thank god , i found a code for varying the frequency using arduino but now i want to change speed for 240 v AC induction motor and the output of the arduino is 5 volt.
will the use of nand concept of ic4093 useful with arduino which now vary the frequency or not ?? and how can i reach to 240 v of the ac motor Will the transformer concept 12-240 will be useful and will be the output frequency from the transformer variable or fixed ??
Swag says
Muhammad, please specify the pinouts and the configuration of your pwm control output. I may try to solve it
I just now remembered that the pwm control can be implemented through an arrangement that may allow the SPWM width control for this design:
https://www.homemade-circuits.com/arduino-full-bridge-h-bridge-sinewave-inverter-circuit/
mohammed says
Dear Mr Swag,
thank you so much for your support;
i just need two pins from arduino as 9 and 10 for pwm as you mentioned in
https://www.homemade-circuits.com/arduino-full-bridge-h-bridge-sinewave-inverter-circuit/
so that the arduino can change the frequency from 0 to 50 to control motor speed.
the AC induction motor specification 250W 1.5A 240 V. by varying the output frequency of the motor from 0 to 50 hz the speed of the motor will change but i do not want to use a battery as a power source for the circuit i just need to get its power from home ac electricity(220 V).the speed control of the motor will be by arduino. will the nand concept mentioned in
https://www.homemade-circuits.com/arduino-full-bridge-h-bridge-sinewave-inverter-circuit/ be helpful for my case?
Swag says
Mohammad, I was asking about your Arduino circuit which you found from another source. I wanted to know about it, since you said you found the PWM control codes.
Swag says
OK, I understood, you are referring to my recommendation, regarding varying of 8 and 9 pin PWM widths…let me think about it.
mohammed says
Dear Mr Swag
the source for varying the frequency in single phase motor
https://github.com/Terbytes/Arduino-Atmel-sPWM
https://www.youtube.com/watch?v=3DjKxDL_Qc0&t=925s
Swag says
OK, but this will need to be included in the Arduino system which is explained in the full bridge Arduino article??
mohammed says
ok mr swag but my question is will be the output frequency of transformer fixed or variable and i read that the current will step down in the case of using transformer and i don’t want to use a battery how can i achieve this using AC as the power source for the circuit ??
Swag says
frequency would be fixed because we won’t be using V/Hz principle, we would be using a PWM control based principle. You can use AC by feeding rectified DC 220V to the mosfet supply lines.
mohammed says
Thanks sir for your response.but if i connect pin 3 of ic1 automatically to ct of IRS what will be the benfit of ic2 ?? and i could not find IRS2453 in my city are there other replacements ?? and what about the previous circuit which uses IR2110 is it synchronized with the SPWM from the IC 555 or has the same issue ?
Swag says
Hi Mohammad, IC2 is for generating the SPWM, IC1 is for generating sample triangle waves for IC2, all are interdependent with each other.
You can Google “full bridge driver IC”, or half bridge driver IC, and see which one is available in your area.
Swag says
The previous one is synchronized through IC 4017.
mohammed says
hi sir,
if i have AC 220 V 1/4 hp compressor of household refrigerator and i want control its speed what is configuration suitable for Rt/Ct associated with the IRS2453 and R1 associated with IC1 ??
Swag says
Hi Muhammad, the full bridge stage is actually not synchronized with the SPWM from the IC 555, therefore the output may not be correctly optimized AC. Therefore I would suggest to eliminate Rt/Ct, and feed the Ct pin of the IC with frequency from pin#3 of IC1.
IC1 frequency may be set at the desired output frequency by measuring the output of IRS IC with a frequency meter and simultaneously setting the R1 220K preset…this will allow the full bridge stage to be synchronized with the SPWM control frequency and also allow to get the required 50Hz frequency at the output
ayanda says
Thanks bro,one more question ,why is it necessary for Drain pin in HO side is connected to power while the other one is connected to load. will this not affect the mosfet ?,just asking i did read about the mosfet from the page you shared yesterday.
Swag says
Ayanda, actually you have asked a very important, I am sorry I think the half bridge configuration which was taken from the datasheet itself is not correctly connected. The connection should be in the following manner, I’ll correct all the diagrams soon
https://i.stack.imgur.com/nC6WK.jpg
AYANDA says
Thank you very much Swag we appreciate your help bro.i have learnt a lot now and i’m hoping to get this done before the second of may which is two weeks from now and i will be presenting my project but i’m still working on it.
Swag says
You are most welcome Ayanda, I have done the necessary correction in the design, you may check it out now.
Satyajeet says
Hey swag .
Plzz give me a motor rating …??my project is 1 phase vfd for 0.5hp induction motor can I used your circuit in my project ..??? Plzz help me broo
Swag says
Hi Satyajeet, the motor rating will depend on the mosfet rating and the applied voltage to the drains of the mosfets, or vice versa, meaning the mosfet and the supply voltage could be selected as per the motor specifications.
ISZ says
Hi Mr. swagatam.
can u help me with single phase VFD run with arduino . MATLAB/SIMULINK code has been done to drive the bipolar full bridge PWM signal to MOSFET with variable frequency and modulation and will upload to the arduino.
So, my problem is how to make circuit for gate drive the MOSFET to drive the 240V 70W ceiling fan.? can u give me any suggestion. Thanks..
Swag says
Hi ISZ, An exactly similar question was asked many days ago by one of the readers and I had provided him and appropriate diagram for implementing the same, now it may be very difficult for me to search that particular comment.
Anyway if you are trying to feed the bipolar pulses into a n-channel based full bridge mosfet configuration then you might require a bootstrapping mechanism for the high side mosfets, right? Without this you won’t be able to drive the high side mosfets, so have you taken care of this??
mohammed says
hello sir ,i made a simulation for this circuit in multisim program but it doesn’t work for me.i can send you a photo from the simulated circuit if you wish sir :).
Swag says
Hello Mohammad, Simulators can produce wrong and misleading results, how can you confirm it is giving you the right results? If you build this circuit step wise with proper understanding the circuit will surely work…
mohammed says
Ok,thank you so much sir.I will do my best with god permission.
Benjamin says
Hello Mr. Swagatam, could you explain why the output (pin3) of the second 555 is connected to the HO and HI outputs with inversely polarized diodes? regards
Swag says
Hello Mr. Benjamin, that is not correct, and I have mentioned about this and have presented the finalized design at the end of the post….the diode links must be connected with the mosfet gates.
Benjamin says
Hello Mr. Swagatam, would you be so kind as to send me the image of the last scheme that has the corrections to my email? Since when downloading the image you can not see the values of the components well. Greetings Benjamin
Swag says
Hello Benjamin, I’ll try to update the diagram in the article soon with larger component numbers.
Benjamin says
Okay,thank you.
Farhan says
Thanks man
Swag says
Welcome dear!!
Farhan says
Hello again .
With all due respect brother I have one more question .
1. Why 2nd 555’s I mean ic2 output is directly going to mosfet’s gate ?
Please clearify this what’s purpose of it . If we remove ic2 from circuit it’s still working .
Swag says
Hi, If you are not including R8 pot and not integrating the IC2 output with the mosfet gates, then you won’t be able to control the speed of the motor, the option will be simply lost.
IC2 helps to transform or chop the mosfet gate drive into an SPWM format, and R8 allows the PWM control of this SPWM, meaning by rotating R8 you can reduce or increase the SPWM duty cycle or the width of the pulses. narrow width will cause decrease in motor speed, wider pulses will allow higher speeds.
farhan says
hello sir,
we have completed this project and i have a few questions please answer these questions it will be a great help 1.why we are using 2 555 ic’s ?
2. why we using pin 2 and 7 of 4017 ?
3. we have used ct also for protection i will share the pictures .
Swag says
Hello Farhan,
The two IC 555 are used for creating SPWMs in response to the 100Hz sinewave ripple sample achieved from the bridge at pin#5 of IC2
The actual sequencing of IC 4017 is from pin#3 > 2 > 4 > 7…by skipping pin#3 and pin#4, we are trying to insert a good “dead time” for the mosfets, although this can also result in significant amount of voltage drop at the output.
Also, the use of a half bridge at the output could result in further drop in voltage.
so the above things must be considered….
the half-bridge could be replaced with a full-bridge driver circuit for ensuring the correct level of output for the motor.
sure, the images will be greatly welcomed here,,,keep up the good work.
C4 says
We have hooked up the vfd in stages and began testing with and oscilloscope. We are getting a square wave coming out of pin three of ic2 and 1c1. We also looked through the previous comments and removed the 557 and other components as you stated. What should we be looking for on the oscilloscope going to the 4017 and further more on the ir2110?
Swag says
isolate the IC1/IC2 entirely and test it separately, connect the upper arm of the R8 pot at pin#5 of IC2 with the positive line.
varying this pot should create a variable PWM at pin#3 of IC2. The frequency of this PWM can be varied by adjusting R1.
Once this is confirmed, connect the R8 upper arm with 100Hz from the bridge, and check whether pin#3 of the IC 2 is producing an SPWM or not, it should.
Once this is confirmed you can integrate the IC4017 with this stage and verify the alternating pulses across pin#2 and pin#7.
similarly confirm the motor half bridge driver separately and finally integrate it with the IC 4017 output
C4 says
I have hooked up the whole circuit and i am able to vary my current. The problem is i am feeding the top mosfet with 170 v dc to run a 120vac motor but I’m only seeing about 4vac across where the motor would go. Any thoughts on the possible issue?
Swag says
Hooking up the whole circuit is not the right way to go, you must build it stages-wise and confirm the stages separately, once confirmed then you can integrate them together for the finals results….as you can see there are many stages in the design, unless you are sure each one of them are doing their job correctly you cannot be sure of the output performance.
please check the mosfet gates with an oscilloscope, check what waveform you get here? If it’s an SPWM then it is fine otherwise you may have to go right back and begin investigating from the IC1, Ic2 stages.
Benjamin says
Okay, to Know, in what frecuency ranges can you works
Swag says
you can set the frequency by adjusting R1 to the correct range, this can be set using a frequency meter.
Benjamin says
Thanks for answering Mr. Swagatam. Excuse me I thought the circuit was for that purpose (vary the speed). But could I use it for that purpose or not?
Swag says
Benjamin, you should only use the voltage control pot for varying speed, not the frequency pot
Benjamin says
Hello Mr. Swagatam, first I wanted to thank you for all your contributions to fans like me.
I have a doubt about the circuit, by reducing the frequency of the motor this consumes more current, how do you solve that problem. As far as I know, the voltage applied to the motor must be reduced, but I do not see that system in the circuit. Greetings Ben.
Swag says
Thank you Benjamin,
The frequency adjustment here is not for controlling speed, it is for ensuring that the motor operates with the correct frequency as specified by its manufacturer. It is specifically used when a 60Hz motor is being used with a 50 Hz source and vice versa, and then the pot may be used for correcting the frequency as per the spces.
the voltage output can be varied by adjusting the pot at pin#5 of IC2
Stephen says
Good morning sir. Pls, after putting up the circuit, I realised that there was no signal entering into pot 14 of IC4017. Sir, pls, wat do u think could be the problem? Thanks in anticipation as I await your response.
Swag says
Good morning stephen,
if you put up the whole circuit together, it is never going to work for sure, and that’s true for most of the circuits which have different stages.
you should build and confirm them stagewise, and this will require some serious understanding regarding the various stages.
anyway, by pot 14 you mean to say pin#14?
from where is pin#14 getting its signal? it is from pin#3 of IC1 right?, so check whether your IC1 is oscillating or not…keep verifying all the stages in the same manner.
by the way the following parts can be removed from the last diagram
T2, R9, R10, C7, C6, and connect pin#16 of IC 4017 directly to the positive line
Stephen says
I have done what u told me to do but what I realized is that it is only the pin Ho dat has voltage on it while the pin Lo does not and variation of the two potentiometer does not have effect on the Ho and Lo voltage. Sir, what else do u think I can do.
Swag says
did you check whether IC1 was generating the oscillations or not…. in response to these osculations at pin#14 of the IC4017 it is supposed to generate alternating ON/OFF voltage across its pin2 and pin#7, isolate the respective stages and first confirm them separately….checking HIN and LIN can be done later on…
IC2 pin#3 should be generating varying PWM in response to a varying voltage at its pin#5, this is the next possible thing that you must confirm
Stephen says
Thank u sir, will give it a trial and get back to you.
Swag says
you are welcome?
ayam says
when the R8 potentiometer is adjusted, what is the variable parameter here? its variable the voltage or variable the ripple frequency 100Hz to pin 5?
Swag says
the variable parameter is the voltage of the ripple input, or the amplitude of the applied ripples…
Stephen says
Good day sir. Pls, I don’t know if you can help me with a mathematical analysis of how you arrived at the values of each of those components used in the circuit. Thanks in anticipation.
Swag says
Stephen, sorry, that will be a lot of explanation, won’t be possible at this moment.
Prithak K Bhattacharyya says
Will a 1HP, 230V motor work with this circuit? Please reply ASAP cuz i am making this as my project and need to submit it within a couple of days. Thank you.
Swag says
motor power rating can be matched by suitably upgrading the mofet rating, so any desired motor rating can be used…
however make sure you have understood the circuit and stages perfectly before you try it.
the circuit will need to be built stage-wise, by confirming and testing each one step-wise, and then integrate them for the final outcome
Prithak k B says
So if I use a 230V motor, I will have to give the ‘motor voltage’ as 230V too?
Swag says
actually It should be 330V DC for a 220V motor
Prithak k B says
If we supply it with 330V DC, won’t it affect the circuit? Cuz the voltage will get supplied to other parts of the circuit too right?
Swag says
330V DC must go only to the mosfet drain, not to any other section of the circuit.
Prithak k B says
We are getting a DC output across where we are supposed to connect the motor for output….around 200mV, we haven’t given any motor voltage yet….So basically without motor voltage and motor….we are getting a 200mV DC output…is it working that means? And also….we are using a bred board so how are we supposed to make the ground connection to 0?
Swag says
sorry, that’s not the right way to check…you must verify the various stages separately.
using an oscilloscope first confirm whether the IC 555 stage is delivering the PWMs or not ( by varying the respective presets)
then verify whether the IC 4017 is responding accordingly or not, and then finally verify the output from the half-bridge and check if it is producing the PWM based chopped square cycles across its output pins…all these will need to be done via an oscilloscope.
Swag says
ground connection refers to the negative line from the power supply, all the negative lines must be connected in common, including the motor supply’s negative line.