SPWM pure sine wave inverter

[basofias]

Hello people,

I´m building at this moment a DC-AC pure sinewave inverter, and i have some questions in the power conversion in a tri level PWM architecture, for driving a H-bridge (Mosfet or IGBT).

- The first question is:

I am using a microcontroler ATMEGA328 for generation a two independent PWM signals, based on this code:

The PWM signals are complementary!

/* based on code by srnka
 Generating of PWM signals for single phase inverter circuit
 generating of sine signals with freq from 33 Hz to 61 Hz
 output values: PWM signals on 2 PWM outputs: one inverted and one non-inverted
*/
int i;  //i...for cycle
int j=64; //for setting the correct number of steps for the selected frequency (initial is the nr. of samples at 61Hz)
int z=0; //for selecting the correct value from the sinetable
int x=0;  //frequency selector - setting initial freq to 61 Hz
int y=0;  //setting of loop counter
int s=30;  //this value is the speed of frequency changing - later it could be controlled by a variable resistor connected to analog input
float phase;      // For calculating value of phase
//setting of sin table for half-period of 8 frequencies

//      steps     frequency
//sin1	64	61,03515625
//sin2	70	55,80357143
sin3	78	50,08012821
//sin4	86	45,42151163
//sin5	94	41,55585106
//sin6	102	38,29656863
//sin7	110	35,51136364
//sin8	118	33,10381356

//======================:.-"-.:    S I N E T A B L E   :.-"-.:====================================
//values are calculated from sinus values and amplidude is corrected based on tests
int sinus[]= {127, 133, 140, 146, 152, 158, 164, 170, 176, 182, 188, 193, 199, 204, 209, 213,
      218, 222, 226, 230, 234, 237, 240, 243, 245, 247, 249, 251, 252, 253, 254, 254, 254, 254, 253,
      252, 251, 249, 247, 245, 243, 240, 237, 234, 230, 226, 222, 218, 213, 209, 204, 199, 193, 188,
      182, 176, 170, 164, 158, 152, 146, 140, 133, 127,
      
      127, 132, 138, 143, 148, 153, 158, 163, 168, 173, 178, 183, 187, 192, 196, 200, 204, 208, 212,
      215, 219, 222, 225, 227, 230, 232, 234, 236, 238, 239, 241, 242, 242, 243, 243, 243, 243, 242,
      242, 241, 239, 238, 236, 234, 232, 230, 227, 225, 222, 219, 215, 212, 208, 204, 200, 196, 192,
      187, 183, 178, 173, 168, 163, 158, 153, 148, 143, 138, 132, 127,
      
      127, 131, 136, 140, 144, 149, 153, 157, 161, 165, 169, 173, 177, 181, 185, 188, 192, 195, 199,
      202, 205, 208, 211, 213, 216, 218, 220, 222, 224, 226, 228, 229, 230, 231, 232, 233, 233, 234,
      234, 234, 234, 233, 233, 232, 231, 230, 229, 228, 226, 224, 222, 220, 218, 216, 213, 211, 208,
      205, 202, 199, 195, 192, 188, 185, 181, 177, 173, 169, 165, 161, 157, 153, 149, 144, 140, 136,
      131, 127,
      
      127, 131, 134, 138, 142, 145, 149, 152, 156, 159, 163, 166, 169, 173, 176, 179, 182, 185, 188,
      191, 194, 196, 199, 201, 204, 206, 208, 210, 212, 214, 216, 217, 219, 220, 221, 222, 223, 224,
      225, 225, 226, 226, 226, 226, 226, 226, 225, 225, 224, 223, 222, 221, 220, 219, 217, 216, 214,
      212, 210, 208, 206, 204, 201, 199, 196, 194, 191, 188, 185, 182, 179, 176, 173, 169, 166, 163,
      159, 156, 152, 149, 145, 142, 138, 134, 131, 127,
      
      127, 130, 133, 136, 139, 142, 145, 148, 151, 154, 157, 160, 163, 166, 168, 171, 174, 176, 179,
      181, 184, 186, 189, 191, 193, 195, 197, 199, 201, 203, 204, 206, 207, 209, 210, 211, 212, 213,
      214, 215, 216, 216, 217, 217, 218, 218, 218, 218, 218, 218, 217, 217, 216, 216, 215, 214, 213,
      212, 211, 210, 209, 207, 206, 204, 203, 201, 199, 197, 195, 193, 191, 189, 186, 184, 181, 179,
      176, 174, 171, 168, 166, 163, 160, 157, 154, 151, 148, 145, 142, 139, 136, 133, 130, 127,
      
      127, 130, 132, 135, 137, 140, 142, 145, 147, 150, 152, 155, 157, 160, 162, 164, 167, 169, 171,
      173, 175, 177, 179, 181, 183, 185, 187, 189, 190, 192, 194, 195, 197, 198, 199, 201, 202, 203,
      204, 205, 206, 206, 207, 208, 208, 209, 209, 210, 210, 210, 210, 210, 210, 210, 210, 209, 209,
      208, 208, 207, 206, 206, 205, 204, 203, 202, 201, 199, 198, 197, 195, 194, 192, 190, 189, 187,
      185, 183, 181, 179, 177, 175, 173, 171, 169, 167, 164, 162, 160, 157, 155, 152, 150, 147, 145,
      142, 140, 137, 135, 132, 130, 127,
      
      127, 129, 131, 133, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164,
      166, 168, 170, 171, 173, 175, 176, 178, 180, 181, 183, 184, 185, 187, 188, 189, 190, 192, 193,
      194, 195, 196, 196, 197, 198, 199, 199, 200, 200, 201, 201, 201, 202, 202, 202, 202, 202, 202,
      202, 202, 201, 201, 201, 200, 200, 199, 199, 198, 197, 196, 196, 195, 194, 193, 192, 190, 189,
      188, 187, 185, 184, 183, 181, 180, 178, 176, 175, 173, 171, 170, 168, 166, 164, 162, 160, 158,
      156, 154, 152, 150, 148, 146, 144, 142, 140, 138, 136, 133, 131, 129, 127,
      
      127, 129, 131, 132, 134, 136, 138, 140, 141, 143, 145, 147, 148, 150, 152, 153, 155, 157, 158,
      160, 161, 163, 164, 166, 167, 169, 170, 171, 173, 174, 175, 177, 178, 179, 180, 181, 182, 183,
      184, 185, 186, 187, 188, 188, 189, 190, 190, 191, 191, 192, 192, 193, 193, 193, 194, 194, 194,
      194, 194, 194, 194, 194, 194, 194, 193, 193, 193, 192, 192, 191, 191, 190, 190, 189, 188, 188,
      187, 186, 185, 184, 183, 182, 181, 180, 179, 178, 177, 175, 174, 173, 171, 170, 169, 167, 166,
      164, 163, 161, 160, 158, 157, 155, 153, 152, 150, 148, 147, 145, 143, 141, 140, 138, 136, 134,
      132, 131, 129, 127};

//14 steps of frequency ramping (actually just 8 different freq. in loop)    
int fbase[]={64,70,78,86,94,102,110,118,110,102,94,86,78,70};        

//======================:.-"-.:    S E T U P   :.-"-.:============================================
void setup()
{

  
 //=====setting of timer0 for fast PWM method====
 //frequency PWM is fosc/(8*256) (by 16MHz oscil. = 7812,5)
 //timer 0, 8-bit timer, pins 5,6(+)   128us  
 TCCR0A=0b10110011;   // generate inverted PWM signals in output
 TCCR0B=0b00000010;   // set of source of clock signal + prescaller fclk/8
  
 //setting of PWM ports 5 and 6 to output (one is inverted - frequency is the same all the time)
 pinMode(5,OUTPUT);
 pinMode(6,OUTPUT);

}

//======================:.-"-.:  M A I N   L O O P  :.-"-.:============================================
void loop()
{

 //when "2*s" number of loops are made, the frequency is changed
 //(2*s to get whole sine wave - 360deg, no matter what the value of "s" is,
 //since j is the number of steps in half of sine period (at startup it is set to 64, so the infinite loop can) start

  if(y==2*s*j)   //check if some frequency has been looped for 2*s times (since j is a number of steps in 1/2 period
   { x=x+1;     //here the frequency change is done with "x" (initial value is 0!)
   if(x==14){   //if x is higher than 13 i.e. when x==14 it needs to be set to 0 again
     x=0;}
   }

   j=fbase[x];   //setting the freq. to the selected one  / first the x=0, so j=64 (frequency is 61 Hz)
    //change of polarity
    TCCR0A = TCCR0A ^ 0b01010000;
   //cycle for half period
  for(i=0; i<j;i++)
  {
   //setting the correct "z" for the selected frequency
    if(j==64){                   //           61Hz
      z=i;                  
     }
    if(j==70){                  //           55Hz
      z=i+64;  //+64
     }
    if(j==78){          
      z=i+134; //70+64          //            50Hz
     }
    if(j==86){
      z=i+212;  //78+70+64      //            45Hz
     }
    if(j==94){
      z=i+298; //86+78+70+64      //            42Hz
     }
    if(j==102){
      z=i+392; //94+86+78+70+64     //      38Hz
     }
   if(j==110){
      z=i+494; //102+94+86+78+70+64      // 35Hz
     }
    if(j==118){
      z=i+604; //110+102+94+86+78+70+64    //33Hz
     }
   //generating of value OCR0x, but output frequency is the same, since they are toggled outputs
   //(it's just that when one sine wave raises the other decreases)
    phase=sinus[z];
    OCR0A=byte(phase);
    OCR0B=byte(phase);

 }  
 //******************************************************
 y=y++;  //loop counter
}

For tri level PWM we should have something similar to this:


But we have only 2 independent PWM in thir format:
View attachment TEK0000.BMP View attachment TEK0002.BMP

How we can split our PWM signals to match with the first SPWM1 & SPWM2 picture???

Thanks,

Best regards

Basofias

:roll::roll::roll::roll::roll::roll:

 

[D.A.(Tony)Stewart]

if using sine to create PWM bipolar signals then use cosine to create SPWM1 for positive cycle & SPWM2 with negative cycle.

 

[basofias]

Hello friend,

I am trying to generate a spwm signal with the atmega328 micro.

I do not have a sine refrence for generate other sine wave.

See my attached file with the explanation of my question.

thanks!!!

Basofias

:roll::roll::roll:

 

[D.A.(Tony)Stewart]

normally PWM sine is trivial with quadrature analog oscillator, and comparator, and mux the PWM to enable each bridge leg.
Since you had Sin values in table, you can generate cosine values too and H bridge ON state values as well from quadrature wave state table.
Create your State Transition Table or **broken link removed**for each output then mix with PWM.. or use your State>Sine/Cosine lookup table method..

edit:
Add example application.
Then when you are done, build a unicycle here
or just video

 

[D.A.(Tony)Stewart]

It's not trivial but if you use your method, I found this partial solution **broken link removed**

 

[basofias]

Hello SunnySkyguy,

See my explanation!

My method are trivial for me!

Today i'm going to tests and, afther these tests i post the results.


Thanks for the help!!!

Basofias

 

[basofias]

Oooops!

I forgot the attachment!!!!



Thanks!

 

[goldsmith]

Dear basofias
Hi
If you need a three level SPWM , to achieve a three level inverter , you'll need a sine wave and another with 180 degree phase shift . then you can compare them with a main triangular wave , to achieve two SPWM , and then you'll need 4 dead time creator circuits , with an schmitt trigger not gate and an RCD network . ( for each section ) . this network will give you , SPWMA and SPWMA' and SPWMB and SPWMB' and with enough dead time .
Q1 and Q4 will get command from one section ( A and A' ) and Q3 and Q2 will get B and B' . don forget to use a good filter at your out put .
See my blogs , you'll find some things about SPWM , i think those literatures can be helpful to you !.
Best Wishes
Goldsmith

 

[basofias]

Hello goldsmith,

I'm trying to generate the PWMs with this method:

The Atmega328 create a 2 PWM signals, and one are inverted in relation to de first one, but with atmega I can not stop the PWM counters.

Well, I use "and" logic gates to do this function, you understand?

Se the pictures in the previous thread please, I make the dead time with the micro Atmega and use the same signal to drive in low frequency the other FET of bridge.

Where I can see your blog????

It would be interesting to learn more about this subject!!!

Thanks for all help!

Basofias

---------- Post added at 01:27 ---------- Previous post was at 01:17 ----------

Hello other one,

https://www.edaboard.com/attachment.php?attachmentid=70649&d=1331509455

This is my objective, but make this PWMs only with microcontroller, and some additional parts!!!

Can you give me more examples!

Thanks

Basofias

 

[goldsmith]

Dear Basofias
Hi
About , blog , it is simple , go to my profile , and then at top of that page click on the blog ( you can see all of my blogs ).
Best Luck
Goldsmith

 

[basofias]

Hello goldsmith,


I'm now testing H Bridge of my inverter:

Drivers are based on International Rectifier IR2110S, one for each arm of the bridge (Low Side and High Side).

This is my design:



These are my wave forms:





My question is the High outputs of the IR2110's are always on and not pulsate like the High inputs.

My H bridge is based on International Rectifier IRFZ24N (MosFET) for testing waveform only with DCBUS = 12V, in the future my H Bridge will be based on IGBT for DCBUS = 350V aprox.

Can you help-me with this problem?

Thanks for all help!

Basofias

 

[goldsmith]

Dear Basofias
Hi
Sorry for my delaying to reply .
Did you tested it in practice ? or perhaps you just simulated it ?
If you checked it in practice , did you check the wave forms of Lin and Hin ? were them correct ?
Best Wishes
Goldsmith

 

[basofias]

Hello goldsmith,

My problem is just solved.

My circuit design have a little problem in the connections of the bootstrap capacitor. (I was missing the ground connection in de negative pin of the bootstrap cap).

I have now other question, how do I make a dead time in the PWMs for the H bridge???

It is possible make them with hardware circuit? Or It is possible make them in the software of the ATMEGA???

Thanks for the help!

Basofias

 

[goldsmith]

Hi again
I'm very happy , because your first problem solved .
And for Dead time , see below , please , i used this simple circuit for many times in my designs :

Good luck
Goldsmith

 

[basofias]

Hello goldsmith,

I appreciate your help in this forum.

About the dead time, I'm go test your circuit, and post the result of the tests.

Thanks for all,

Basofias

 

[longcrystal]

Hi again
I'm very happy , because your first problem solved .
And for Dead time , see below , please , i used this simple circuit for many times in my designs :
View attachment 74142
Good luck
Goldsmith

Hi gold smith i also doing this project using 24V dc input and PIC16F877A as my switching pulse to setting the spwm....i just do it simple the switching frequency i just use 50Hz and using BJT to do switching pulse....but i heard a lot ppl said that use Mosfet to do switching pulse is better...but i didnt revision much for the Mosfet....so i just use familiar BJT to do my inverter.....but i wanna ask about do u know how to calculate the LC circuit and suitable for Filter 50Hz in my last output....because right now i design 50HZ switching pulse and transformer to Sinusoidal my LC value of component tested by software is L =8.8H C=1000nF ...then i get a good sine wave...but i not quite understanding about this kind of oscillation ...what value will be suitable for switching pulse 2kHz 5kHZ ???for make the LC circuit ...for i success to make oscillation the sine wave just depend on my guess.....but can u teach me how to calculate about this knowledge...just want to reduce my component value ...because L=8.8H it is to hard purchase this component...want to make it small value as possible ....but knowledge still limited havent research about the LC filter theory .....**broken link removed**

Uploaded with ImageShack.us


**broken link removed**

Uploaded with ImageShack.us


actually my question is ....if i use 24V H-bridge 50Hz to make spwm and oscillate the sine wave 50Hz ....for my software testing success is L=8.8H to 9.8 and C=1000nF

but i want to know that if i use 24V H-bridge 1kHz to 5Khz to make spwm and oscillate the sine wave 50Hz ..how do i assume what value of L and C can be generate Sine Wave...maybe this is simple question....but i still cannot imagine that how to oscillate the shape of sine wave if i change my switching pulse cycle of frequency ...

hope u will be guide me a bit ....

 

[mahmoudomar91]

Hi
i am trying to do a single phase inverter with V over F control but the sine wave i generated has distortions can you please tell me how could you get such a PWM
by the way i am using Atmega32.
thanks alot in advance