Lecture 22 Second order system natural response Review Mathematical form of solutions Qualitative interpretation Second order system step response Related educational modules: –Section 2.5.4, 2.5.5
Second order input-output equations Governing equation for a second order unforced system: Where is the damping ratio ( 0) n is the natural frequency ( n 0)
Homogeneous solution – continued Solution is of the form: With two initial conditions:,
Damping ratio and natural frequency System is often classified by its damping ratio, : > 1 System is overdamped (the response has two time constants, may decay slowly if is large) = 1 System is critically damped (the response has a single time constant; decays “faster” than any overdamped response) < 1 System is underdamped (the response oscillates) Underdamped system responses oscillate
Overdamped system natural response >1: We are more interested in qualitative behavior than mathematical expression
Overdamped system – qualitative response The response contains two decaying exponentials with different time constants For high , the response decays very slowly As increases, the response dies out more rapidly
Critically damped system natural response =1: System has only a single time constant Response dies out more rapidly than any over- damped system
Underdamped system natural response <1: Note: solution contains sinusoids with frequency d
Underdamped system – qualitative response The response contains exponentially decaying sinusoids Decreasing increases the amount of overshoot in the solution
Example For the circuit shown, find: 1.The equation governing v c (t) 2. n, d, and if L=1H, R=200 , and C=1 F 3.Whether the system is under, over, or critically damped 4.R to make = 1 5.Initial conditions if v c (0 - )=1V and i L (0 - )=0.01A
Part 1: find the equation governing v c (t)
Part 2: find n, d, and if L=1H, R=200 and C=1 F
Part 3: Is the system under-, over-, or critically damped? In part 2, we found that = 0.2
Part 4: Find R to make the system critically damped
Part 5: Initial conditions if v c (0 - )=1V and i L (0 - )=0.01A
Simulated Response