Systems Analysis and Control

Systems Analysis and ControlMatthew M. PeetArizona State UniversityLecture 10: Routh-Hurwitz Stability CriterionOverviewIn this Lecture, you will learn:The Routh-Hurwitz Stability Criterion: Determine whether a system is stable. An easy way to make sure feedback isn t destabilizing Construct the Routh TableM. PeetLecture 10: Control Systems2 / 28A Stability TestWe know that for a system with Transferfunction G(s) =n(s)d(s)Input-Output Stability implies that all roots ofd(s)are in the Left Half-PlaneIAll have negative real (s)Re(s)CRHPQ uestion:How do we determine if all roots ofd(s)have negative real part?Example: G(s) =s2+s+ 1s4+ 2s3+ 3s2+s+ 1M. PeetLecture 10: Control Systems3 / 28A Stability TestAnother VariationDetermining stability is not that hard (Matlab).Now suppose we add feedback:Controller:Static Gain: K(s) =kClosed Loop Transfer Function: y(s) = G(s) K(s)1 + G(s) K(s) u(s)x1x2mcmwuClosed Loop Transfer Function:k(s2+s+ 1)s4+ 2s3+ (3 +k)s2+ (1 +k)s+ (1 +k)We know that increasing the gain reduces steady-state error.

Routh’s Method Step 3 Complete the third row. Call the new entries b 1; ;b k I The third row will be the same length as the rst two b 1 = det 4 a a 2 a 3 a 1 0 a 3 b 2 = det 4 a a a 3 0 a 3 b 3 = det a 4 0 a 3 0 a 3 The denominator is the rst entry from the previous row.

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