Optimum Feedback Amplifier Design For Control Systems

Many designers think of control system feedback loop compensation only in terms of stable or unstable. In reality, there is an optimum error amplifier transfer function for any given loop crossover frequency and phase margin. The optimum design is shown to be the one with the highest gain below crossover and the lowest gain above crossover. There is a unique pole-zero placement to achieve optimum performance. This pole-zero placement and resultant circuit component values can be determined without trail-and-error. In addition, there is an optimum open loop crossover frequency (loop bandwidth) or any given phase margin. Optimizing the Performance Optimizing the performance of a feedback control loop can be done with techniques that are simple, effective, and easy to apply. These techniques can be used on single or multiple loop systems of any type, and will yield optimum results without the usual trial-and-error process. Three new concepts are introduced: the concept of phase boost as the single variable of importance in loop stability, K-Factor as a convenient method of defining both phase boost and the shape of the Bode gain curve, and the concept of a Figure of Merit for evaluating the relative performance of various loop compensations.