The Arduino code is developed by me, and it is my first Arduino code, ...and it looks pretty good 🙂
What is SPWM
I have already explained how to generate SPWM using opamps in one of my earlier articles, you could go through it for understanding how it can be created using discrete components and regarding its importance.
Basically, SPWM which stands for sine wave pulse width modulation, is a type of pulse modulation where the pulses are modulated to simulate a sinusoidal waveform, so that the modulation is able to attain properties of a pure sine wave.
To implement a SPWM the pulses are modulated with an initial narrower widths which gradually get broader at the center of the cycle, and finally end being narrower at the end to finish the cycle.
To be more precise, the pulses begin with narrowest widths which gradually get broader with each subsequent pulses, and gets broadest at the center pulse, after this, the sequence continues on but with an opposite modulation, that is the pulses now gradually begin getting narrower until the cycle finishes.
This constitutes one SPWM cycle, and this repeats throughout at a particular rate as determined by the application frequency (usually 50Hz or 60Hz). Typically, SPWM is used for driving power devices such as mosfets or BJTs in inverters or converters.
This special modulation pattern ensures that the frequency cycles are executed with a gradually changing average voltage value (also called the RMS value) , instead of throwing sudden Hi/low voltage spikes as normally witnessed in flat square wave cycles.
This gradually modifying PWMs in a SPWM is purposely enforced so that it closely replicates the exponentially rising/falling pattern of a standard sinewaves or sinusoidal waveform, hence the name sinewave PWM or SPWM.
Generating SPWM with Arduino
The above explained SPWM can be easily implemented using a few discrete parts, and also using Arduino which will probably enable you to get more accuracy with the waveform periods.
The following Arduino code can be used for implementing the intended SPWM for a given application.
Gosh!! that looks awfully big, if you know how to shorten it, you may certainly feel free to do it at your end.
digitalWrite(9, HIGH);
/*
This code was based on Swagatam SPWM code with changes made to remove errors. Use this code as you would use any other Swagatam’s works.
Atton Risk 2017
*/
const int sPWMArray[] = {500,500,750,500,1250,500,2000,500,1250,500,750,500,500}; // This is the array with the SPWM values change them at will
const int sPWMArrayValues = 13; // You need this since C doesn’t give you the length of an Array
// The pins
const int sPWMpin1 = 10;
const int sPWMpin2 = 9;
// The pin switches
bool sPWMpin1Status = true;
bool sPWMpin2Status = true;
void setup()
{
pinMode(sPWMpin1, OUTPUT);
pinMode(sPWMpin2, OUTPUT);
}
void loop()
{
// Loop for pin 1
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin1Status)
{
digitalWrite(sPWMpin1, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = false;
}
else
{
digitalWrite(sPWMpin1, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = true;
}
}
// Loop for pin 2
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin2Status)
{
digitalWrite(sPWMpin2, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin2Status = false;
}
else
{
digitalWrite(sPWMpin2, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin2Status = true;
}
}
}
Nice work one Swagatem, you have officially made it to my Top 5 911 Engineering List, I appreciate all your hard work to this blog.
I have 2 questions:
1. Will the circuit give regulated VAC output constantly?
2. How can i better the circuit to carry things like fan etc?
Thanks again
Thanks Miebaka, I am so glad you liked my site!
Since the PWM delays would be constant from the Arduino or may be tweaked as per the users preference and transformer winding rating, the output can be expected to be very accurate and no external regulator would be required for fixing the RMS.
as for the fan operation, a properly calculated filter circuit at the output of the trafo will be quite sufficient to allow you to operate inductive loads efficiently.
only the switching frequency is 30KHz. but the main output is 60Hz. as my appliances needed. i am using SPWM right now generated by arduino UNO.
there should not be more than 4 to 6 pillars on each waveform, as implemented in my SPWM, I think you are using some other code not the above one.
yes i am having different codes. i am using interrupt. since arduino loop function is very slow. because it has other code executed because of translating the code. it will affect the code inside the loop like speed.
OK, but make sure the pillars on each waveform does not exceed 6, but anyway your issue is current(amp) related not waveform.
I never tried high current h bridge., maybe I will try to build a high current h bridge so that I can check the output if it is going well., will update after I build., thanks always for the help.,
sure! my pleasure!
hi swatagam. could you check my h bridge circuit? i dont think ir2110 can drive 3 mosfet per in.
https://www.dropbox.com/s/zln57f64dleta7h/fsdf.png?dl=0
Hi Isak, it looks good to me, why do you think it cannot drive 3 or more parallel mosfets?
mosfets have high gate impedance…so current is never an issue for their gates.
so its okay to drive more than 3 mosfet for one driver?
did i choose the right value for the bootstrap capacitor?
yes you can, according to me! but first verify the results with a single pair, if it works good then go ahead with the parallel connections. you can check the cap value in the datasheet, and use it as per the instructions provided there.
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high swatagam, could you help me designing an filter for this?
here is my spwm, i used arduino uno. could you try simulate?
switching freq is 31Khz
freq:60 Hz
Hi Isak, I am sorry I am not good at simulating circuits, since I mostly depend on my brain simulation for all my designs.
hi swatagam, i tried simulation but. the value of capacitor is verry big about 20uf.
how can is reduce it? see my simulation please
https://www.dropbox.com/s/5s1kt37dfs92flh/simulation.png?dl=0
Hi Isak, that looks misleading, that’s why I never depend on simulators….if you check it practically you will find that a much smaller capacitor doing the job perfectly, because the transformer secondary itself will act like a filter and to a great extent smoothen the waveform even without a capacitor…
by the way you can try putting a load in the simulation and check the effect
its hard to tell weather i put a right caps because i don’t have oscilloscope. i tried this with 2.2uf and it can run the stand fan. but not at great speed. i think it is not smooth as i expect because trying to switch at low speed the fan turn at very low speed. tried to compare the output at the grid. it has a big difference.
without a scope you cannot verify an inverter output, it is a must.
and the fan speed is more related to current and wattage from the trafo not the waveform…..please read this post for learning regarding voltage drop issues
http://www.homemade-circuits.com/2017/07/inverter-voltage-drop-issue-how-to-solve.html
i can use an 8v – 230v transformer since i have a high switching frequency. now i set it to 30KHz. voltage drop is not much the problem.. the transformer is just a salvage from old ups. my code can change amplitude so that i can stabilize the voltage output. i can also change the switching frequency while system is running. but the main problem is the filter for 230 out.
you mean to say instead of 50Hz or 60Hz you are using 30kHz for driving the fan? That’s highly not recommended, and moreover the current consumption is the main aspect, check your battery current it must fulfill the fan’s rated consumption.
your transformer output must produce an AC that matches your grid AC characteristic in every respect.
Made some changes and put it on paste bin to make things easy
https://pastebin.com/1sQAi9vr
could you please throw some light regarding how this modification would help to improve the performance of the PWM output, I am sure the readers will love to know about it.
// Some changes made by Atton Risk for Swagatam
const int sPWMArray[] = {500,500,750,500,1250,500,2000,500,1250,500,750,500,500}; // This is the array with the SPWM values change them at will
const int sPWMArrayValues = 13; // You need this since C doesn’t give you the length of an Array
// The pins
const int sPWMpin1 = 8;
const int sPWMpin2 = 9;
// The pin switches
bool sPWMpin1Status = true;
bool sPWMpin2Status = true;
void setup()
{
pinMode(sPWMpin1, OUTPUT);
pinMode(sPWMpin2, OUTPUT);
}
void loop()
{
// Loop for pin 1
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin1Status)
{
digitalWrite(sPWMpin1, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = false;
}
else
{
digitalWrite(sPWMpin1, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = true;
}
}
// Loop for pin 2
for(int i(0); i != sPWMArrayValues; i++)
{
if(sPWMpin1Status)
{
digitalWrite(sPWMpin1, HIGH);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = false;
}
else
{
digitalWrite(sPWMpin1, LOW);
delayMicroseconds(sPWMArray[i]);
sPWMpin1Status = true;
}
}
}
Thank you very much Atton, I hope the readers will benefit immensely from this information! I appreciate it a lot!
No problem I hope we can work together in the future.
sure we can!
Halo sir.
I will try your code and the driver as pure sine wave inverter.
If I successful to make it, may I re-post this article?
at least for arduino code only.
Thank you.
Yogi S.
Hello Yoyo,
you can submit the details to me, I'll post it in the above article with your credentials in it, but if you use it for your own website then that could be a copyright violation….
Hi,
The output 8 and 9 of the arduino represents the positive and negative cycle of the sine wave? Sorry I am quite new to arduino but how do the output pins recognize that it is negative or positive since the code looks the same? Is the delay used in this code arbitrary chosen? If I need 50Hz, should the delay change as well?
Hi,
as per the given code pin8/9 will alternately produce SPWM pulses at the rate of 50Hz. The total delay periods across the two pins are calculated to produce 50Hz frequency
The SPWM waveform rate (delays) is arbitrarily set in the code, you can tweak it to create a different RMS value depending upon your transformers primary voltage rating.
alternatively the Arduino code could be further upgraded for responding to a feedback from the transformer output and for achieving an automatic RMS adjustment
Hi sir,
Its good to see you involving in arduino projects, I hope you will soon master in this field too 🙂
I would like to point some errors in the code:
1) we must not use pin 13 in arduino, unless we run out of pins, since it is always connected with LED, it will deviate our results. we can use other pins say 8 and 9.
2) we cannot use delay for less than 1ms and we can't use decimal place in delay function like delay(1.25); . Instead use delayMicroseconds(); for instance delayMicroseconds(500); for 500us and delayMicroseconds(1250); for 1.25ms. You may replace all delay with this function.
The above errors won't show up while compiling but, it affects our end result.
Regards
Thank you Girish,
Although I hardly find time, I did this just to have some fun … 🙂
I will surely correct the above code as per your suggestions, as soon as possible..
I appreciate your help very much and I am sure the readers will also get an opportunity to learn from this discussion.
Thanks again, and keep up the good work!