A simple discrete-time PID controller.

pid.py

# A simple discrete-time PID controller. If plot is true, this will use matplotlib to show a graph.
# Otherwise, it will simply print out the successive values of the controller.

plot = True

if __name__ == '__main__':
	if plot:
		import matplotlib.pyplot as plt

	v = [0] * 100
	v[0] = 200
	setpoint = 150
	e0 = 0
	e1 = 0
	e2 = 0
	kp = 0.3
	td = 0.25
	ti = 3
	h = 1
	
	for i in range(99):
		e3 = e2
		e2 = e1
		e1 = (setpoint - v[i]) / (1 + (i+1) * 0.1)
		v[i+1] = v[i] + kp * (e1 - e2) + kp * h * e1 / ti + kp * td * (e1 - 2 * e2 + e3) / h
		if (plot == False):
			print v[i+1]

	if (plot == True):
		plt.plot(v)
		plt.show()