Chapter 9

# 9.6 Effect of PID Controller Modes on System Stability

PID Controller modes affect the overall system stability and Gain Margin. In general, if Proportional Mode is our reference, Integral (or Proportional + Integral) Control reduces relative stability of the closed loop system, while Proportional + Derivative Control increases relative stability of the closed loop system. Let’s consider again the example from Chapter 9.2, where G(s) was described by Equation 9‑3. The summary of stability analysis for all four modes of PID Controller for this example is shown in Table 9‑1. We shall return to this topic later, using Root Locus analysis for discussion.