Using MCPWM for AC dimming

[ytan86]

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]

1.  
2. #include <stdio.h>
3. #include "string.h"
4. #include "freertos/FreeRTOS.h"
5. #include "freertos/task.h"
6. #include "freertos/queue.h"
7. #include "esp_attr.h"
8. #include "soc/rtc.h"
9. #include "driver/mcpwm.h"
10. #include "soc/mcpwm_periph.h"
11. #include "esp_task_wdt.h"
12.  
13.  
14. #define GPIO_PWM0A_OUT 19   // Pin output - connect to Triac gate
15. #define GPIO_SYNC0_IN   2   // Pin input - connect to ZC circuit
16.  
17. static void mcpwm_example_gpio_initialize(void)
18. {
19.     printf("initializing mcpwm gpio...\n");
20.     mcpwm_gpio_init(MCPWM_UNIT_0, MCPWM0A, GPIO_PWM0A_OUT);
21.     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
22.     gpio_pulldown_en(GPIO_SYNC0_IN);   //Enable pull down on SYNC0  signal
23. }
24.  
25. /**
26.  * @brief Configure whole MCPWM module
27.  */
28. static void mcpwm_example_config(void *arg)
29. {
30.     // mcpwm gpio initialization
31.     mcpwm_example_gpio_initialize();
32.  
33.     // initialize mcpwm configuration
34.     printf("Configuring Initial Parameters of mcpwm...\n");
35.     mcpwm_config_t pwm_config;
36.     pwm_config.frequency = 100;    //frequency = 100Hz , double of AC 50Hz since we drive for two halves of the waveform
37.     pwm_config.cmpr_a = 0.0;      
38.     pwm_config.counter_mode = MCPWM_DOWN_COUNTER;
39.     pwm_config.duty_mode = MCPWM_DUTY_MODE_0; // active high
40.     mcpwm_init(MCPWM_UNIT_0, MCPWM_TIMER_0, &pwm_config);  
41.  
42.     // Syncronization configuration
43.     mcpwm_sync_enable(MCPWM_UNIT_0, MCPWM_TIMER_0, MCPWM_SELECT_SYNC0, 850); // % phase offset
44.    
45.     const int MIN_PWM_DUTY = 0;
46.     const int MAX_PWM_DUTY = 75;
47.  
48.     // vary duty cycle
49.     float x = 0;
50.     float delta = .1;
51.     for(;;)
52.     {
53.         if(MAX_PWM_DUTY<x) delta = -.1;
54.         else if(MIN_PWM_DUTY>x) delta = .1;
55.        
56.         mcpwm_set_duty(MCPWM_UNIT_0, MCPWM_TIMER_0, MCPWM0A, x);
57.        
58.         vTaskDelay(5 / portTICK_PERIOD_MS);            
59.         x+=delta;
60.     }
61. }
62.  
63. void app_main(void)
64. {
65.     printf("Testing MCPWM for AC dimming...\n");
66.     xTaskCreate(mcpwm_example_config, "mcpwm_example_config", 4096, NULL, 5, NULL);
67. }
68.  

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