Micropython SPWM #9342

marestudio2004

Hello,

does anyone have experience with generating a sine wave using pwm (on ESP32 or 8622), need to drive MOSFETs for a single phase inverter like:

https://www.homemade-circuits.com/arduino-pure-sine-wave-inverter-circuit/

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jimmo

28 days ago

Woah. Do not use this circuit to generate mains voltages! Buy a real inverter instead.

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robert-hh

28 days ago

The circuit in the link does not generate a sine wave. It create for each half of the sine wave a 7 cycle PWM signal which emulates the energy of a sine wave. A 50Hz transformer is slow, so it will not carry over much of that 350Hz PWM, and the remaining will be reduced by the capacitor in the output. That circuit does not look overly dangerous, because all you touch & work with is at the low voltage side. Using a 3.3V device could be a problem, because it needs like 5V to get into a low Rds state and switch higher currents w/o taking too much power itself.

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marestudio2004

marestudio2004

27 days ago

I understand your concern, but I didn't get an answer to the given question... I assume that with PWM, it is necessary to make a dynamic change in the duty cycle parameter in a certain range... Is there a ready-made function or something like that... .. what happens when LED lighting changes color, can this function be used somehow?

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1 reply

marestudio2004 27 days ago

robert-hh

27 days ago

You might be able to use machine.bitstream() for your purpose, which has the bitstream ready for one half cycle and is repeated with alternating the drives every half cycle. Repeating would be started by the timer at a rate of 100 (or 120) Hz.
But with 800Hz pulse rate and a timer it should be possible to make a software coded PWM, at least with the ESP32. The ESP8266 with Python is probably too slow. The timer would be called at the PWM rate. Here it's 800 Hz, and it would then set a Pin, wait a certain time taken from a table and then reset the pin. The board would hardly be able to do something else. Using the time will ensure a stable frequency.

marestudio2004

robert-hh

27 days ago

I hacked together a short script. Times to be varied.

from machine import Pin, Timer, idle
import time
table = (100, 200, 400, 600, 800, 800, 600, 400, 200, 100)
count = 0
alt = 0
p9 = Pin(9, Pin.OUT, value=0)
p10 = Pin(10, Pin.OUT, value=0)

def pulse(t):
    global table, count, alt
    global p9, p10
    if alt:
        p9(1)
        time.sleep_us(table[count])
        p9(0)
    else:
        p10(1)
        time.sleep_us(table[count])
        p10(0)
    count = (count + 1)
    if count == len(table):
        alt = 1 - alt
        count = 0

t = Timer(callback=pulse, freq=1000, mode=Timer.PERIODIC)
while True:
    idle()

It creates the following waveform at Pins 9 and 10:

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2 replies

marestudio2004 27 days ago

Thanks Mr. Rober! This is nice solution!

marestudio2004 27 days ago

This is table from C code, for DC/AC inverter SPWM based:

// choose 1 of the SPWM tables below:
const int sPWMArray[] = {500,500,750,500,1250,500,2000,500,1250,500,750,500,500}; // this is the array with the 50Hz SPWM values; change

them at will

// const int sPWMArray[] = {416,416,625,416,1041,416,1666,416,1041,416,625,416,416,7}; // use this table to obtain 60Hz

Values are given in us (microseconds)!

robert-hh

27 days ago

I had similar numbers initially, but changed them a little bit to make the difference more obvious in the diagram. The pulse lengths at the start and end must be longer.
Since the time can only be set up in periods of while ms, the slots per half wave are either 10 or 5. In my example, I use 10, but 5 should be fine as well. At 10 slots, each slots has a length of 1000µs, and 5 slots 2000µs. The code cannot use the full slot length, because the callback must return before the next timer IRQ. Using the timer ensures a stable frequency over time. But you can as well just use a permanent loop and accept the drift.

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@marestudio2004 · 2021-10-31T18:29:37+07:00

jimmo

26 days ago

I'm going to re-iterate for @marestudio2004 and anyone else who might be reading this in the future: This is a really bad idea. Inverters are cheap, just buy a real one.

You risk damaging your devices, not to mention electrocuting yourself, or starting a fire. This circuit has no safety protections and is a hazard.

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Programme Arduino

Objectifs de la vidéo

Analyses des performances d’un signal sPWM avec Arduino
Savoir mesurer la fréquence réelle d’un onduleur en utilisant le signal sPWM Savoir les limitations du code Arduino
Savoir paramétrer un signal sPWM avec Arduino
Analyse des d’un signal sPWM avec le port série
Comprendre la le principe du signal sPWM : PWM de type sinusoïdal Connaitre les paramètres d’un signal SPWM

Voir la vidéo pour plus de détails

Le Programme Arduino

Commande sPWM : Partie 3

#define   R_PWM       5
#define   L_PWM       6

#define   TestFreq    7
#define   TimerBit    7

#define   N
#define   TimerStep
#define   T0_us

Onduleur

unsigned long
unsigned long
unsigned long
bool

bool

// Commande 1 pont H
// Commande 2 pont H

// Mesure de la fréquence

        // Amplitude du  signal sinusoïdal 2^8
256     // Nombre d’échantillons du tableau) 512=2^9
16       // Pas d'incrémentation du Timer
100     // Période d'incrémentation du Timer

        // Période globale T=2*N*T0_us => F=1/F: Fréquence

MedSine[N];
TimerSPWM=0;
i_sin=0;
sPWM_l=false;
sPWM_r=true;

bool            sinePolar=false;

double          sine_val=0;

void setup()
{

  // Init sortie
  pinMode(R_PWM, OUTPUT);
  pinMode(L_PWM, OUTPUT);
  pinMode(TestFreq, OUTPUT);

  // Génération du signal sinusoïdal: 1/2 Période (2*N échantillons/période)
  for (unsigned int i=0; i<N; i++)
  {

    sine_val=(double)((2<<TimerBit)-1)*sin(PI*(double)i/(double)N);

    MedSine[i]=(unsigned int)round((sine_val));
  }

  // Port série affichage des signaux (sPWM + Sine )

  Serial.begin(9600);
}

void loop() {

  // Prévisualisation des signaux de l'onduleur + sin(t)
  /*
  Serial.print(MedSine[i_sin]); Serial.print(",");
  Serial.print(((2<<TimerBit)-1)*sPWM_l); Serial.print(",");
  Serial.println(((2<<TimerBit)-1)*sPWM_r);

  */
  // Incrémentation du Timer: Compteur rapide (signal triangulaire)
  TimerSPWM+=TimerStep;
  TimerSPWM%=N-1;

  // Incrémentation du Timer du signal: Compteur long (signal sinusoïdal)
  i_sin+=1;
  i_sin%=N-1;

  // Changement d'état
  if(!i_sin) sinePolar=!sinePolar;
  // Géneration des signaux PWM
  if(sinePolar)
  {

    sPWM_l =MedSine[i_sin] > TimerSPWM;

    sPWM_r =false;

} else {

    sPWM_l = false;

    sPWM_r =MedSine[i_sin] > TimerSPWM;
  }

  // Affectation des sorties PWM
  digitalWrite(R_PWM,sPWM_r);
  digitalWrite(L_PWM,sPWM_l);

  // Mise à jour signal du test

  digitalWrite(TestFreq,sinePolar);
}

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Arduino Nano SPWM generator

October 31, 2021

Continuing work on my previous project, namely the generation of pulse width modulated sinusoidal waves or called SPWM, I added an important function, namely voltage feedback in this project.

In addition, I also added voltage, temperature, and battery protection functions. Protection is to protect against over-voltage, low voltage, over-temperature and low battery.

Now I use Arduino Arduino Nano, so the SPWM generator module is compact.

In a previous project, I focused on generating a sinusoidal signal using the PWM port on the Arduino Uno.

SPWM generator Hard Ware

Nano-Inverter2 Download

Here I add a voltage divider circuit for low-batt detection, as well as a buzzer circuit.

The rest of the circuit is the same as in the previous project.

Nano-Inverter-PCB-top-1 Download

Nano-Inverter-PCB-Bottom-1 Download

Full-Bridge MOSFET

If you use a Full-bridge MOSFET as in my previous post, the 12V regulator does not need to be used. Just jumper the input and output pins of this 12V regulator, this is because the SPWM generator card will monitor the battery voltage for low-batt detection.

Arduino Nano Code

In this section, I add code that matches the hardware above.

In the previous project, I made code only for the 50Hz frequency, here I add it also for 60Hz.

To work at 60Hz use the code that I’m currently commenting as 60Hz and make the code marked as 50Hz a comment.

Voltage Feedback

The main program here performs voltage feedback processing and tries to stabilize the voltage by adjusting the output pulse width so that the voltage increases or decreases according to the error that occurs.
In addition, it also reads the temperature and battery voltage.

After that, the program will check all the inputs by calling the function feedBackTest.

Feed Back Test

This routine is tasked with checking all feedback inputs whether they exceed a predetermined limit.

Maybe you see the upper and lower limits of the voltage feedback on the program and in the comments are different, that’s because I tried to do the settings that best suit my needs.

If one of the limits is exceeded, this routine will call the alarmIndication a routine that matches the type of alarm that occurred.

Alarm Indication

When an alarm occurs this routine will turn off all SPWM outputs, then turn on the buzzer and LED according to the alarm that occurs.

The LED lights up and the buzzer sounds twice for under-voltage, three times for over-voltage and so on.

This alarm goes on continuously until it is reset because I made a continuous loop.

For more details, please see the program below

#include <avr/io.h>
#include <avr/interrupt.h>

/*
   SPWM_Nano_VFB3.ino

   Created : 8/11/2021
   Author  : yopie DIY

   Left bridge used for fundamental signal (50Hz/60Hz), Right bridge for SPWM (10kHz carrier freq.)
   Sampling per Cycle 
   ---> 10kHz/50Hz = 200 
   ---> 10kHZ/60hz = 166
   Look Up table entries use only half cycles (identical positive and negative cycles) 
   50 Hz --->  200/2 = 100 entries
   60 Hz --->  167/2 = 83 entries
   
   SPWM clock = fXTAL/freq. carrier = 16.000.000/10.000 = 1.600 clock. 
   WGM mode 8 is used, so ICR1 = 1.600/2 = 800 clk
   Look up tables for a half cycle (100 or 83 entries), max value = 800 (100% duty cycle)is loaded into register ICR1.

  This code is for 50Hz !!!
  for 60Hz use the Lookup Table for 60Hz and use the code marked on the ISR(TIMER1_OVF_vect) !!!
*/

const byte      vfbPin = A0,
                tfbPin = A1,
                battPin = A2;
volatile double percentMod;
int             phs;

//---------------------------------Look Up Table for 50 Hz---------------------------------------
int lookUp1[] = {
  0,  25, 50, 75, 100, 125, 150, 175, 199, 223, 247, 271, 294, 318, 341, 363, 385, 407, 429, 450,
  470, 490, 510, 529, 548, 566, 583, 600, 616, 632, 647, 662, 675, 689, 701, 713, 724, 734, 744, 753,
  761, 768, 775, 781, 786, 790, 794, 796, 798, 800, 800, 800, 798, 796, 794, 790, 786, 781, 775, 768,
  761, 753, 744, 734, 724, 713, 701, 689, 675, 662, 647, 632, 616, 600, 583, 566, 548, 529, 510, 490,
  470, 450, 429, 407, 385, 363, 341, 318, 294, 271, 247, 223, 199, 175, 150, 125, 100, 75, 50, 25, 0
};


/*
//---------------------------------Look Up Table for 60 Hz---------------------------------------
int lookUp1[] = { 
  0, 30, 60, 90, 120, 150, 179, 208, 237, 266, 294, 322, 349, 376, 402, 428, 453, 478, 501, 524, 
  547, 568, 589, 609, 628, 646, 664, 680, 695, 710, 723, 735, 747, 757, 766, 774, 781, 787, 792, 796, 
  798, 800, 800, 799, 797, 794, 790, 784, 778, 770, 762, 752, 741, 729, 717, 703, 688, 672, 655, 637, 
  619, 599, 579, 558, 536, 513, 489, 465, 441, 415, 389, 363, 335, 308, 280, 252, 223, 194, 164, 135, 
  105, 75, 45, 15, 0};
*/


void setup() {
  // Register initilisation, see datasheet for more detail.
  TCCR1A = 0b10110000;
  /*      10xxxxxx Clear OC1A/OC1B on compare match when up-counting. Set OC1A/OC1B on compare match when down counting
          xx11xxxx Set OC1A/OC1B on compare match when up-counting. Clear OC1A/OC1B on compare match when down counting.
          xxxxxx00 WGM1 1:0 for waveform 8 (phase freq. correct).
  */
  TCCR1B = 0b00010001;
  /*      000xxxxx
          xxx10xxx WGM1 3:2 for waveform mode 8.
          xxxxx001 no prescale on the counter.
  */
  TIMSK1 = 0b00000001;
  /*      xxxxxxx1 TOV1 Flag interrupt enable. */
  ICR1   = 800;      /* Counter TOP value (at 16MHz XTAL, SPWM carrier freq. 10kHz, 200 samples/cycle).*/
  sei();             /* Enable global interrupts.*/
  DDRB = 0b00011110; /* Pin 9, 10, 11, 12 as outputs.*/
  PORTB = 0;

  pinMode(13, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(2, INPUT_PULLUP);

  percentMod = 0.01;
  for (int i = 0; i < 75; i++) {              // Soft Start
    percentMod = percentMod + 0.01;
    delay(20);
  }
}


void alarmIndication(int alarm)
{
  TCCR1A = 0;                             // shutdown SPWM output
  TIMSK1 = 0;
  PORTB &= 0b11100001;
loopX:
  for (int i = 0; i < alarm; i++) {
    digitalWrite(7, HIGH);                // turn ON LED and Buzzer
    digitalWrite(13, HIGH);
    delay(200);
    digitalWrite(7, LOW);                 // then turn OFF
    digitalWrite(13, LOW);
    delay(200);
  }
  delay(1000);
  goto loopX;                           //never ending story... until reset
}

void feedBackTest(float vfbIn, int tfbIn, int battIn) {
  long alrm;
  static int alrmCnt;
  
  if (digitalRead(2) == LOW) return;
  if (phs != 1) return;
  
  alrm = constrain(vfbIn, 462, 660);
  if (alrm !=vfbIn) alrmCnt++; else alrmCnt=0;
  if (alrm == 462 && alrmCnt >= 150) alarmIndication(2);        // underVoltage @ 2.5V --> 2.75 / 5 x 1023 = 562
  if (alrm == 660 && alrmCnt >=15) alarmIndication(3);          // overVoltage @ 3.15V --> 3.15 / 5 x 1023 = 645
  if (tfbIn >= 924) alarmIndication(4);                         // over temp @ 80C --> 10k/(10k + 1.068k) x 1023 =924
  if (battIn <= 457) alarmIndication(5);                        // low batt @ 10.5V --> (2k7/12.7k x 10.5) / 5 x 1023 = 457
  if (tfbIn >= 725 && digitalRead(8) == LOW)  digitalWrite(8, HIGH);  // fan ON @45C --> 725
  if (tfbIn <= 679 && digitalRead(8) == HIGH) digitalWrite(8, LOW);   // fan OFF @40C --> 679

}

void loop() {
  static int vfbValue;
  static int vfbValue1;
  static int vfbRise = 0;
  static float vMax;
  float alrm = 0;
  static int alrmCnt = 0;
  float ampDiff;

  if (phs = 1) {
    vfbValue1 = vfbValue;
    vfbValue = analogRead(vfbPin);                              // vfbPin = 0 to 5V ---> vfbValue = 0 to 1023

    if (vfbValue > vfbValue1 && vfbValue > 200) vfbRise = 1;     //check for positif cycle, bigger than noise
     if (vfbValue < vfbValue1 && vfbRise == 1) {                 // maximum vfb value reached
      vfbRise = 0;
      vMax = vfbValue1;
      ampDiff = 614 - vMax;      
      if (ampDiff > 5 || ampDiff < -5) {
        percentMod = percentMod + (ampDiff / vMax);               // voltage correction
        if (percentMod > 0.97) percentMod = 0.97;               // limit duty cycle to 97%       
      }
        
     feedBackTest(vMax, analogRead(tfbPin), analogRead(battPin));
      vMax = 0;
    }
  }
}


/*---------------------------------------------------------------------------------------------------------*/
ISR(TIMER1_OVF_vect) {
  static int num;
  static int  ph;
  static int dtA = 0;
  static int dtB = 5;

  if (num >= 99) {    // <------------------ 50 Hz !!!
//  if (num >= 82) {    // <------------------ 60 Hz !!!
    if (ph == 0) {         // OC1A as SPWM out
      TCCR1A = 0b10110000; // clear OC1A, set OC1B on compare match
      dtA = 0;             // no dead time
      dtB = 5;            // adding dead time to OC1B
    } else {
      TCCR1A = 0b11100000; // OC1B as SPWM out
      dtA = 5;
      dtB = 0;
    }
    ph ^= 1;
  }
  OCR1A = int(lookUp1[num] * percentMod) + dtA; // SPWM width update
  OCR1B = int(lookUp1[num] * percentMod) + dtB; // note: 0.7 used to reduce inveter output voltage

  num++;
  if (num >= 100) {                   // toggle left bridge (50Hz) !!!
//  if (num >= 83) {                   // toggle left bridge (60Hz) !!! 
    delayMicroseconds(60);
    if (ph == 1) {
      digitalWrite(12, LOW);
      digitalWrite(11, HIGH);
      phs = 1;
    } else {
      digitalWrite(11, LOW);
      digitalWrite(12, HIGH);
      phs = 0;
    }
    num = 0;
  }
}

Until here is my post this time, have a nice day.

See on YouTube

1ère Générale NSI

Term. Générale NSI

Terminale STI2D SIN

Bts Ccst

Technico-commercial 3.0

Vidéos YouTube

Arduino pure sinus

Arduino Pure Sine Wave Inverter Circuit with Full Program Code

Circuit Operation

Powering the Arduino Board

Waveform Images for Arduino SPWM

Using BJT Buffer Stage as Level Shifter

Delay Effect

Adding an Automatic Voltage Regulator

How to Setup

Using CMOS Buffer

You'll also like:

About Swagatam

Have Questions? Please Comment below to Solve your Queries! Comments must be Related to the above Topic!!

Micropython SPWM #9342

Replies:8 comments 3 replies

Arduino Nano SPWM generator

SPWM generator Hard Ware

Full-Bridge MOSFET

Arduino Nano Code

Voltage Feedback

Feed Back Test

Alarm Indication

1ère Générale NSI

Term. Générale NSI

Terminale STI2D SIN

Bts Ccst

Technico-commercial 3.0

Vidéos YouTube

Arduino pure sinus

Circuit Operation

Powering the Arduino Board

Waveform Images for Arduino SPWM

Using BJT Buffer Stage as Level Shifter

Delay Effect

Adding an Automatic Voltage Regulator

How to Setup

Using CMOS Buffer

You'll also like:

About Swagatam

Have Questions? Please Comment below to Solve your Queries! Comments must be Related to the above Topic!!

Micropython SPWM #9342

Replies:8 comments · 3 replies

SPWM generator Hard Ware

Full-Bridge MOSFET

Arduino Nano Code

Voltage Feedback

Feed Back Test

Alarm Indication

Replies:8 comments 3 replies