The PID controller allowed the proportional gain to increase to 1.7,about 40% more than in the PI controller (Figure 6-5 in Part 2 ), and the integral gain toincrease to 120, about 20% more than the PI. PID controller open loop (55° PM, 8.5 dB GM). Closed-loop Bode plot of PID controller (359-Hz bandwidth, 1.0dBpeaking).įigure6-20. In addition to Figure 6-17 earlier, the results of the tuningprocedure illustrated are in Figure 6-18 above are graphed in Figure 6-19 and Figure 6-20 below.
The expectation is that the P and I gains will be about20-40% higher than they were in the PI controller. Next, the integral gain is tuned, much as it was in the PIcontroller. The P and Dgains together form the high-frequency zone. The next step is to add a little D gain to curethe overshoot induced by the higher-than-normal P gain. Typically, the P gain can be raised 25%-50% over the value from theP and PI controllers. The benefit of the D gain is that it allows the P gain to be sethigher than it could be otherwise.Īs shown in Figure 6-18 below ,the first step is to tune the controller as if it were a P controller,but to allow more overshoot than normal (perhaps 10%), understandingthat the D gain will cure the problem. The P and D gains jointlyform the higher frequency zone. Experiment 6D, a PID controller.Ī PID controller is a two-zone controller. As with the PI controller, thedifferential and integral gains will be in line with the proportionalgain note that many controllers place all three gains in parallel.įigure6-17. Here, a low-pass filter with a break frequency (2000 Hz by default)is added to the derivative path. The most common use ofdifferential gain is adding it in parallel with the PI controller shownin Figure 6-17 below.
The PID controller addsdifferential gain to the PI controller.