u(t C(s)= @, 1 (S+a mn)SS(S+@,)S 临界阻尼情况下的二阶系统的单位阶跃响应称为临界阻尼响应 h(o=l-e@, t-e '=l-e/(1+o,1 t20 (3-24) 当5=1时,二阶系统的单位阶跃响应是稳态值为1的无超调单调上升过程 d (3)过阻尼(5>1)0ver- damped Case C(s) (S-SXS-S2)Ss+o(5-22-1)S+on(5+ A O,s 1)5+On(5 A A2 +On(5 A3 √2-1(5+√2-1) h(t)=1 -(4+V2-1)on1t≥ 1) (3-25) 6161 S r t u t R s 1 ( ) ( ) , ( ) n n n n n S S S S S C s 1 ( ) 1 1 ( ) ( ) 2 2 2 临界阻尼情况下的二阶系统的单位阶跃响应称为临界阻尼响应 ( ) 1 1 (1 ) 0 h t e t e e t t n t t n t n n n (3-24) 当 1 时,二阶系统的单位阶跃响应是稳态值为 1 的无超调单调上升过程, t n n e dt dh t ( ) 2 (3)过阻尼( 1 ) Over-damped Case 1 2 S1,2 n n S S S S S S S S C s n n n n [ ( 1)][ ( 1)] 1 ( )( ) ( ) 2 2 2 1 2 2 ( 1) ( 1) 2 3 2 1 2 n n A S A S A 1 A1 ( 1) 1 2 2 S n A 2 1( 1) 1 2 2 3 A 0 2 1( 1) 1 2 1( 1) 1 ( ) 1 ( 1) 2 2 ( 1) 2 2 2 2 h t e e t t t n n (3-25)