归首士学 NORTHWESTERN POLYTFCHNICAL UNTVERSITY §4.4 绘制根轨迹的基本法则(21 G(S) K(TS+1) s(s+1)(s+2) D(s)=(S+1)(S+2)+K"(Ts+1)=0 K=20 K T K"=6 +3s2+2s+K 3 K=20 K=20 20T 0 +3s2+2s+20 20T5 (S+385)s+0.425±j22351 虚轴交点:D(s)=s3+332+(2+207)s+K"=0 Re[D(jo)=-302+20=0 =2.582 Im|D(io)=-03+(2+207)=0T=0.233§4.4 绘制根轨迹的基本法则(21) ( 1)( 2) ( 1) ( ) * s s s K Ts G s 虚轴交点: ( ) ( 1)( 2) ( 1) 0 * D s s s s K Ts 3 2 * * * 3 2 ( ) s s s K K Ts G s ( ) 3 (2 20 ) 0 3 2 * D s s s T s K 20 * K 6 * K 3 * K 20 * K 3 2 20 20 ( ) 3 2 * s s s Ts G s ( 3.85)[ 0.425 2.235] 20 ( ) * s s j Ts G s Im[ ( )] (2 20 ) 0 Re[ ( )] 3 20 0 3 2 D j T D j 0.233 2.582 T