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thanhtuan
Joined: 03 Sep 2009
Posts: 3
Location: Vietnam
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| PID for Buck design |
 Posted: Wed Sep 23, 2009 10:24 pm |
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Hi everybody,
My project is MPPT for solar panel but in my project I have to use digital PID controller to control voltage output from buck converter. My input voltage is 12VDC. By using buck converter and PID controller I want to regulate the output voltage to an desirable value (this value is alternate, of course). In my circuit, the feedback voltage is divided by 2. And this is my code:
| Code: |
////////////////////////////////////////////////////////////////////////////////
/////////////////////***********************************////////////////////////
/////////////*****************************************************//////////////
// Project : TEST DIGITAL PID v2.1 //
// Hardware: PIC 16F877A, LCD, Buck converter (Extra: RS232 connect) //
// Software: PCM compiler v4.038 //
// Date : 14.09.2009 //
// Author : Nguyen Thanh Tuan (ENTETE) //
// Status : Not OK //
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
#include <16F877A.h>
#include <DEFS_16F877A.h>
#include <def_877A.h>
#device *=16 ADC=10
#use delay(clock=20000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7)
#fuses NOWDT NOPROTECT NODEBUG NOBROWNOUT HS
#use fast_io(C)
#use fast_io(A)
#include <stdlib.h>
#include <lcd_lib_4bit.c>
//int1 startPID; // PID flag bit
int8 count,nghin, tram, chuc, donvi;
signed int16 feedback,error,pre_error,integral,derivative;
long control;
long temp, setpoint, feed;
float Kp, Ki, Kd, P, I, D, dt, value;
#INT_RTCC
void RTCC_IRS()
{
++count;
if(count==10)
{
count=0;
setpoint=115;
set_adc_channel(0);
feedback=read_adc();
error=setpoint-feedback;
integral+=error; // Accumulated sum of error
derivative=error-pre_error; // Derivative of error
if((error<5)&&(error>-5))
{
Kp = 0.0;
Kd = 0.0;
Ki = 0.0;
control = control; // Don't use PID
}
else
{
Kp = 8.0;
Ki = 5.0;
Kd = 0.0001; // Assign value for Kp, Ki, Kd
P=Kp*error;
I=Ki*integral*dt;
D=Kd*derivative/dt;
control=(int16)(P+I+D);
if(control >920)
{
control = 800; // Limit the maximum value control at 90%
}
if(control < 100)
{
control = 100; // Limit the minimum value control at 10%
}
}
set_pwm1_duty(control);
pre_error = error; // Update error
}
}
void LCD_Display() // Need display the value >= 10 ????
{
value = (float)(2*feed*5)/1024;
value = value*1000;
nghin = value/1000 + 0x30;
temp = (int16)value%1000;
tram = temp/100 + 0x30;
temp = temp%100;
chuc = temp/10 + 0x30;
donvi = temp%10 + 0x30;
LCD_putcmd(0x84);
printf(LCD_putchar,"V=");
LCD_putchar(nghin);
LCD_putchar(tram);
LCD_putchar(chuc);
LCD_putchar(donvi);
printf(LCD_putchar,"mV");
delay_ms(1000);
}
void main()
{
dt = 0.001; // Sample time = 1ms = 100us(overflow time)*10 (count)
control = 0;
derivative = 0;
integral = 0;
error = 0;
Kp = 0.0;
Kd = 0.0;
Ki = 0.0;
setup_CCP1(CCP_PWM); // Configre for PWM mode
setup_timer_2(T2_DIV_BY_16,255,1); // prescale=16, PR2=255, postscale=1
set_pwm1_duty(0); // --> fsw = 78.12 kHz
setup_adc(ADC_CLOCK_INTERNAL); // Configure ADC
setup_adc_ports(AN0_AN1_AN3); //
set_tris_a(0b00011111); // RA0 -> RA4 as input
set_tris_c(0x00); // Port C as output
LCD_init(); // Configure for LCD
LCD_putcmd(0x84);
printf(LCD_putchar,"Test PID"); // Display project's name
LCD_putcmd(0xc1);
printf(LCD_putchar,"Status: NOT OK");//
delay_ms(2000);
LCD_putcmd(0x01);
setup_timer_0(RTCC_DIV_2);
set_timer0(6); // T_overflow = 2*(256-6)*0.2us = 100us
enable_interrupts(INT_RTCC); // enable interrupts Timer0
enable_interrupts(GLOBAL); // enable global interrupts
while(true)
{
//set_adc_channel(0);
//feed = read_adc();
//LCD_display();
}
}
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In this code, when I change the setpoint value, the output voltage is not change.
Anyone can help me?
Thanks so much for your comment! |
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thanhtuan
Joined: 03 Sep 2009
Posts: 3
Location: Vietnam
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| Posted: Thu Sep 24, 2009 7:29 pm |
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| Anyone can help me, please? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Sep 24, 2009 8:19 pm |
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Take the code out of the #int_rtcc routine, and put it in main in a loop.
Don't use interrupts. Put in printf statements to display intermediate
values. Display the output in a terminal window on your PC.
Disconnect the PIC from the buck converter circuit. Connect a trimpot
to the AN0 pin. Turn the trimpot with your hand. Watch the display
of the values as you turn the trimpot. Look for anything that appears
to be incorrect. This will show you the problem area in your code.
If everything in your code (during the testing given above) is correct,
then connect the external Buck Converter circuits to your PIC again.
The code will still be in a while() loop in main(). Add a delay_ms()
statement to the while() loop, to simulate the #int_rtcc interval.
Add a printf statement after the read_adc() statement. Display the
value read from the ADC. It may not be in the correct range of values.
In other words, simplify the program, display intermediate values, and
trouble-shoot the problem by analyzing the behavior of the program. |
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thanhtuan
Joined: 03 Sep 2009
Posts: 3
Location: Vietnam
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| Posted: Thu Sep 24, 2009 8:34 pm |
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Thank you for your help, PCM programmer!
I'll do it and reply the result when it's OK.
Thanks again, |
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zamzam23
Joined: 25 Aug 2010
Posts: 47
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| Posted: Sat Oct 02, 2010 2:34 am |
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| What is the result? If you succeeded, can you share with us the full working code? Thanks |
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MiniMe
Joined: 17 Nov 2009
Posts: 50
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| Posted: Sat Oct 02, 2010 6:12 am |
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I tested and i tried to use this code in design.
From point of view of PID --- WORKS. It takes in 2 values and outputs 1 value. Works like PID should work.
In this code there are no scaled variable limit. Because of that values will overflow, for example from 32 768 to - 32 768.
Scaled means some variables are overgrowing faster... so whole thing is not compensated.
My suggestion use code from " AVR221: Discrete PID controller - Atmel" google it. Its 100 times faster and well done. |
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