PID shunt regulator

Projects General Guidance
1

Hi guys,
For a project I use a mosfet and a PWM signal to control voltage over a train (by using a different duty cycle I can change the resistance of the mosfet -> different voltage).
But my code doesn't seem to work, it only gives 0 as output.

#include <PID_v1.h>

const int SpanningTreinLezer= A0;
const int MosfetPin = 6;
const int WensSpanningLezer = A2;
double alpha;
double Kp=-5, Ki=0.5, Kd=0;
double WerkelijkeTreinspanning;
double WensTreinspanning;
PID myPID(&WerkelijkeTreinspanning,&alpha,&WensTreinspanning,Kp,Ki,Kd,DIRECT); //Normally this should attain voltage we want in 6sec
int PIDtijd = -6000;

void setup() {
  pinMode(MosfetPin,OUTPUT);
  myPID.SetMode(AUTOMATIC);
  Serial.begin(19200);


}

void loop() {
  double WerkelijkeTreinspanning = analogRead(SpanningTreinLezer)*20.0/1023.0; // Voltage that the train has on the moment.
  int beta;
  double WensTreinspanning = 4+analogRead(WensSpanningLezer)*5/1023.0; //Voltage we want the train to have
  if (WerkelijkeTreinspanning<4 && (millis()-PIDtijd)>6000)) {
     analogWrite(MosfetPin,beta);
  }
  if (WerkelijkeTreinspanning >4 && (millis()-PIDtijd)>6000) { // We give PID 6secs to calculate
    PIDtijd = millis();
    myPID.Compute(); // This should compute alpha but only gives 0!!
    int beta = alpha*255;
    analogWrite(MosfetPin,beta);
  Serial.println(alpha);
  }
}

The PID only gives alpha=0, and I don't know what's wrong.
I will also add system. Btw I can change wenstreinspanning (by turning a potentiometer).
Here's the circuit

167992368_284022453163519_4730905455436927489_n
167992368_284022453163519_4730905455436927489_n1732×811 253 KB

2

Hello
well at least the calculations using the millis() function requires the datatype unsigned long.

unsigned long PIDtijd = 0;
3

Thanks,
I'm using this library btw:
https://playground.arduino.cc/Code/PIDLibrary/

4

Which controller is used? Why *255?
Some Arduino only uses byte, 8 bits in analogWrite....

5

PI, I gave a Kc and Ti not equal to 0 and Td=0.
I use the *255, because the PI controller should give a duty ratio between 0 and 1
Which I will convert to a PWM signal (which needs the *255)

6

Okey, I misread one declaration.
Add some temporary Serial.println of the key variables just before analogWrite and watch Serial monitor to see where things go wrong.
Which controller?

7

Hi,
What model Arduino are you using?

Thanks.. Tom... :grinning: :+1: :coffee: :australia:

8

Uno.
Which controller? I guess a PI one.
I changed my code to the following:

#include <PID_v1.h>

const int SpanningTreinLezer= A0;
const int MosfetPin = 6;
const int WensSpanningLezer = A2;
double alpha;
double WerkelijkeTreinspanning;
double WensTreinspanning;
double Input,Output,Setpoint;
PID myPID(&Input,&Output,&Setpoint,5,0.5,0,REVERSE); //Normally this should attain voltage we want in 6sec
unsigned long PIDtijd = -6000;

void setup() {
  pinMode(MosfetPin,OUTPUT);
  myPID.SetMode(AUTOMATIC);
  myPID.SetSampleTime(6000);
  Serial.begin(19200);


}

void loop() {
  double WerkelijkeTreinspanning = analogRead(SpanningTreinLezer)*20.0/1023.0; // Voltage that the train has on the moment.
  int beta;
  double WensTreinspanning = 4+analogRead(WensSpanningLezer)*5/1023.0; //Voltage we want the train to have
  Input = analogRead(SpanningTreinLezer)*20.0/1023.0;
  Setpoint = 4+analogRead(WensSpanningLezer)*5/1023.0;
  if (WerkelijkeTreinspanning<4) {
     analogWrite(MosfetPin,255);
  }
  if (WerkelijkeTreinspanning >4 && (millis()-PIDtijd)>6000) { // We give PID 6secs to calculate
    PIDtijd = millis();
    myPID.Compute(); // This should compute alpha but only gives 0!!
    int beta = alpha*255;
    analogWrite(MosfetPin,beta);
  }
  else {
    analogWrite(MosfetPin,beta);
  }
  Serial.println(Output);
  }

As you can see my PID library generates an output (which I checked with serialprint) it indeed calculates something. Which is a duty cycle 'alpha' of a pwm so 0.8 means 80% of the time I want a high pwm pulse to my mosfetpin. (it's after the line myPID.compute())
But I don't how i can change the output signal in beta, can I do something like this: beta=Output*255?
Thanks, snor

9

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.