Closed-Loop PI Controller
Figure 8 presents the closed-loop performance for three PI controller implementations using values from Table 2. All closed-loop tests were performed using the step profile that was used in Figure 6 and Figure 7, and with T = 500 . The top figure shows the result using moderate tuning values for T = 200 in Table 2. The middle and bottom figures show the results for moderate and aggressive tuning values forT = 500 in Table 2.
Comparing the results shown in Figure 8, the top figure shows a slower response time than the response time in the middle figure by approximately a factor of three, even though both are considered moderate tunings. Unlike the middle figure, the top figure represents the case in which the PI controller was tested at a slower loop rate than the rate at which it was tuned (i.e. 500 , versus 200 ). Clearly the loop rate is an important consideration when tuning a PI controller.
The middle and bottom figures represent moderate and aggressive tunings, respectively. The response times reflect these tuning strategies, with aggressive tuning realizing a speedup by nearly a factor of four 4 over moderate tuning. Figure 9 presents these performance differences in greater detail.
Figure 8 – Closed Loop Test
Figure 9: Closed-loop moderate tuning (left), aggressive tuning (right)