Stability Limits of Linear Feedback Control Systems

A new method is presented for determining the stability limits of open loop gains in linear feedback controlled systems. The method does not require finding the roots of multiple polynomials in k, the loop gain, as in the case of the commonly used algebraic Routh array technique. Instead, the roots of a single polynomial in s (the Laplace variable) of order at least one less than that of the system are evaluated to directly determine where the root locus crosses the imaginary axis.