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hisham.i
Joined: 22 Aug 2010
Posts: 43
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| Sine wave generation problem |
 Posted: Sun Jan 29, 2012 5:01 am |
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Hello,
I am designing sine wave inverter with pic18f2331, so am producing sine wave over 180degree using a predetermined sine wave table, and i update duty cycle each timebase interrupt period which is 1/10khz where 10khz is the switching frequency.
But i got this result on my scope after filtering the output signal.
The output stays sinusoidal with the correct amplitude for some number of cycles then it drops and starts increasing again sinusoidally, and so on.
I want to attach a picture for the output wave form but it seems it is not possible to attach a picture from my pc.
I don't know if the problem is hardware or software, so please if you can help me to find any problem in my code.
This is the code
| Code: |
#include<18F2331.h>
#fuses H4, NOWDT, NOPROTECT, NOBROWNOUT, NOPUT, NOLVP
#use delay(clock=10MHZ)
#define POWER_PWM_PERIOD 999 // 10 KHz pwm freq with 40 MHz osc.
// Sine Wave Lookup Table
long duty[100] =
{120,240,360,519,639,759,879,999,1118,1238,
1359,1479,1598,1718,1798,1918,2038,2158,2238,2358,
2438,2557,2637,2717,2837,2917,2997,3077,3157,3237,
3317,3357,3437,3516,3556,3596,3676,3716,3756,3796,
3836,3876,3916,3916,3916,3916,3916,3916,3916,3916,
3916,3916,3916,3916,3916,3916,3916,3876,3836,3796,
3756,3716,3676,3596,3556,3516,3437,3357,3317,3237,
3157,3077,2997,2917,2837,2717,2637,2557,2438,2358,
2238,2158,2038,1918,1798,1718,1598,1479,1359,1239,
1119,999,879,759,639,519,360,240,120,120
};
/***H2110112***Out*/
long i,d0,d1,d2,j,k;
//The Program takes a value from the lookup table each 0.1ms, and put this number in the duty
//cycle of the power pwm...
//The duty cycle is changed according to interrupt service routine, which is PWM_TB
#INT_PWMTB
void duty_int()
{ //ELEMINATE EVERY THING CONCERNIG J AND K IF YOU HAVE TO MAKE MONOPHASE SYSTEM.//
if(i>99){
if(j>99) {
d1 = 120;
i =0;
} else {
d1 = duty[j];
j++;
d0 = 120;
}
} else {
d0 = duty[i];
i++;
d1 = 120;
j = 0;
}
set_power_pwm0_duty(d0);
set_power_pwm2_duty(d1);
}
void main()
{ float v;
int d3 = 50;
i=0;
j=100;
k=132;
d0 = 120;
d1 = 120;
// Setup the 4 Power PWM channels as ordinary pwm channels.
setup_power_pwm_pins(PWM_COMPLEMENTARY, PWM_COMPLEMENTARY, PWM_OFF, PWM_OFF);
// Mode = Free Run
// Postscale = 1 (1-16) Timebase output postscaler
// TimeBase = 0 (0-65355) Initial value of PWM Timebase
// Period = 999 (0-4095) Max value of PWM TimeBase
// Compare = 0 (Timebase value for special event trigger)
// Compare Postscale = 1 (Postscaler for Compare value)
// Dead Time =3 which correspond to >120ns real time value
/*******************************************
dead time = deadtime value/(Fosc/prescalar)*
********************************************/
setup_power_pwm(PWM_FREE_RUN|PWM_DEAD_CLOCK_DIV_2, 1, 0, POWER_PWM_PERIOD, 0, 1,4);
ENABLE_INTERRUPTS(GLOBAL);
ENABLE_INTERRUPTS(INT_PWMTB);
while(1){
}
}
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stoyanoff
Joined: 20 Jul 2011
Posts: 375
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| Posted: Sun Jan 29, 2012 5:53 am |
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If the problem is in the hardware it can be a restarting of your controller.
If you have a load after your invertor it can cause dropdown of the supply voltage.
Do you have big capacitators in the filter of the power supply???
Have you put 2 caps near by the controller - 1 electrolite(100uF) and 1 non-electrolite(150nF). The extra caps with big one in the filter should prevent any restarts.
If you have a load ofter your invertor it can cause dropdown of the supply voltage.
Another thing! If you structurise well your program it won`t be nesseccary to use interrupts! |
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hisham.i
Joined: 22 Aug 2010
Posts: 43
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| Posted: Sun Jan 29, 2012 6:06 am |
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No i didn't put a load at the output, and yes i filtered the input, and for every supply pin of the controller i put 0.1uF capacitor.
I don't think that the controller is restarting, if it is so why it will start making a sine wave with a small amplitude until it reaches its correct amplitude, and then it drops again?
Is there any thing in the configuration bits that may cause the controller to restart? |
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temtronic
Joined: 01 Jul 2010
Posts: 9241
Location: Greensville,Ontario
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| Posted: Sun Jan 29, 2012 7:08 am |
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software ??
Normally for debugging purposes, you'ld printout the variables to 'see' what's going on.In your case I,J,D0,D1,duty[i],duty[j].
One of your counters could be corrupted, your 'IF' logic might be wrong,array pointer might be bad, any number of possibilties.
I'd slow down the ISR to allow sending the data to a PC with a 'file capture' program running, then after say 5 minutes, stop the program and look at the captured data.Compare the numbers to what you think should be happening to what is shown...
hardware??
Yes, one of the config fuses might be incorrect...there are a few !!!
Perhaps coding a 'Hello World' program and running it ( without any PWM of course) will confirm this. If it runs fine, then fuses and PIC is OK...problem lies in the PWM code. If it fails...probably a 'fuse' is incorrect or other setup. |
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