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The Nyquist plot for () = + + with s = jω.. In control theory and stability theory, the Nyquist stability criterion or Strecker–Nyquist stability criterion, independently discovered by the German electrical engineer Felix Strecker [] at Siemens in 1930 [1] [2] [3] and the Swedish-American electrical engineer Harry Nyquist at Bell Telephone Laboratories in 1932, [4] is a graphical technique ...
Stability criterion. In control theory, and especially stability theory, a stability criterion establishes when a system is stable. A number of stability criteria are in common use: Stability may also be determined by means of root locus analysis. Although the concept of stability is general, there are several narrower definitions through which ...
The Nyquist stability criterion can now be found in many textbooks on feedback control theory. His early theoretical work on determining the bandwidth requirements for transmitting information laid the foundations for later advances by Claude Shannon , which led to the development of information theory .
Tools include the root locus, the Nyquist stability criterion, the Bode plot, the gain margin and phase margin. More advanced tools include Bode integrals to assess performance limitations and trade-offs, and describing functions to analyze nonlinearities in the frequency domain.
The M circle with M = 0.45 is highlighted in red and intercepts the Nyquist plot at frequencies . Hall circles (also known as M-circles and N-circles) are a graphical tool in control theory used to obtain values of a closed-loop transfer function from the Nyquist plot (or the Nichols plot) of the associated open-loop transfer function.
These systems can be solved by powerful frequency domain mathematical techniques of great generality, such as the Laplace transform, Fourier transform, Z transform, Bode plot, root locus, and Nyquist stability criterion. Nonlinear control theory covers a wider class of systems that do not obey the superposition principle.
Alexander Lyapunov in the 1890s marks the beginning of stability theory. Harold S. Black invented the concept of negative feedback amplifiers in 1927. He managed to develop stable negative feedback amplifiers in the 1930s. Harry Nyquist developed the Nyquist stability criterion for feedback systems in the 1930s.
Bode plot, Nyquist stability criterion, Nichols plot, and root locus are the usual tools for SISO system analysis. Controllers can be designed through the polynomial design, root locus design methods to name just two of the more popular. Often SISO controllers will be PI, PID, or lead-lag.