Improvement in Applying of Nyquist Criterion in Special Systems

Nyquist criterion on non- minimum phase systems is error- prone,and the curve is easy to stagger.What's more,the supplement of the frequency characteristics for the Bode diagram is extremely complicated. To solve the above problems,this paper studied the characteristics of two special systems based on the theory of the Nyquist criterion in logarithmic coordinates. It proposed a way to improve the complexity of the stability judgment method on non- minimum phase systems. Through extracting the common characteristic of Nyquist curve and Bode diagram,unifying them in one formula,we solved the problems of the difficulty in judgment of curve numbers. The paper precisely defined the half- through and its expansion,which enlarged the application scope of the Nyquist criterion.Through the three steps,which are addition,calculation and determination,the difficulty is highly reduced. What's more,the accuracy is also improved.