ESP32 Forum

Posted: **Sat Oct 03, 2020 6:59 am**

Hi

I am generating a 100Hz MCPWM signal that is synchronised with the AC signal. Although it works well, when I increase the PWM duty cycle to a point, it starts to glitch.

It seems that this phenomenon occurs when the high side of the PWM gets close to the trigger signal. (See the glitch at t=6s to t=7s)

Does anyone know what causes this?

Thanks.

My code:

Code: [Select all] [Expand/Collapse]

 
#include <stdio.h>
#include "string.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/queue.h"
#include "esp_attr.h"
#include "soc/rtc.h"
#include "driver/mcpwm.h"
#include "soc/mcpwm_periph.h"
#include "esp_task_wdt.h"
 
 
#define GPIO_PWM0A_OUT 19   // Pin output - connect to Triac gate
#define GPIO_SYNC0_IN   2   // Pin input - connect to ZC circuit
 
static void mcpwm_example_gpio_initialize(void)
{
    printf("initializing mcpwm gpio...\n");
    mcpwm_gpio_init(MCPWM_UNIT_0, MCPWM0A, GPIO_PWM0A_OUT);
    mcpwm_gpio_init(MCPWM_UNIT_0, MCPWM_SYNC_0, GPIO_SYNC0_IN); // need to modify esp_rom_gpio_connect_in_signal in components/drivers/mcpwm.c
    gpio_pulldown_en(GPIO_SYNC0_IN);   //Enable pull down on SYNC0  signal
}
 
/**
 * @brief Configure whole MCPWM module
 */
static void mcpwm_example_config(void *arg)
{
    // mcpwm gpio initialization
    mcpwm_example_gpio_initialize();
 
    // initialize mcpwm configuration
    printf("Configuring Initial Parameters of mcpwm...\n");
    mcpwm_config_t pwm_config;
    pwm_config.frequency = 100;    //frequency = 100Hz , double of AC 50Hz since we drive for two halves of the waveform 
    pwm_config.cmpr_a = 0.0;       
    pwm_config.counter_mode = MCPWM_DOWN_COUNTER;
    pwm_config.duty_mode = MCPWM_DUTY_MODE_0; // active high
    mcpwm_init(MCPWM_UNIT_0, MCPWM_TIMER_0, &pwm_config);   
 
    // Syncronization configuration
    mcpwm_sync_enable(MCPWM_UNIT_0, MCPWM_TIMER_0, MCPWM_SELECT_SYNC0, 850); // % phase offset
    
    const int MIN_PWM_DUTY = 0; 
    const int MAX_PWM_DUTY = 75; 
 
    // vary duty cycle 
    float x = 0;
    float delta = .1;
    for(;;)
    {
        if(MAX_PWM_DUTY<x) delta = -.1;
        else if(MIN_PWM_DUTY>x) delta = .1;
        
        mcpwm_set_duty(MCPWM_UNIT_0, MCPWM_TIMER_0, MCPWM0A, x);
        
        vTaskDelay(5 / portTICK_PERIOD_MS);            
        x+=delta;
    }
}
 
void app_main(void)
{
    printf("Testing MCPWM for AC dimming...\n");
    xTaskCreate(mcpwm_example_config, "mcpwm_example_config", 4096, NULL, 5, NULL);
}
 

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Using MCPWM for AC dimming

Using MCPWM for AC dimming