Nyquistkúrfa

Nyquistkúrfa, also known as the Nyquist plot, is a graphical representation of the frequency response of a dynamic system. It is a plot of the imaginary part of the open-loop transfer function against its real part, with the frequency as a parameter. The plot shows how the system's gain and phase shift change as the input frequency varies.

Developed by Harry Nyquist in 1932, the Nyquist plot is a fundamental tool in control theory for analyzing system stability. The stability of a closed-loop system can be determined by examining the encirclements of the critical point (-1, 0) by the Nyquist curve in the complex plane. The Nyquist stability criterion relates the number of clockwise encirclements of the critical point to the number of unstable poles of the open-loop system.

The Nyquist plot provides insights into the system's bandwidth, gain margin, and phase margin, all of which are important indicators of its performance and robustness. For a stable closed-loop system, the Nyquist curve must not encircle the critical point. The distance of the curve from the critical point indicates how close the system is to instability. Variations in system parameters can be visualized by observing how the Nyquist curve shifts. It is particularly useful for understanding the behavior of systems with delays and complex poles.