此系列属于胡寿松《自动控制原理题海与考研指导》(第三版)习题精选,仅包含部分经典习题,需要完整版习题答案请自行查找,本系列属于知识点巩固部分,搭配如下几个系列进行学习,可用于期末考试和考研复习。
自动控制原理(第七版)知识提炼
自动控制原理(第七版)课后习题精选
自动控制原理(第七版)附录MATLAB基础
第三章:时域分析法
Example 3.21
已知单位反馈系统的开环传递函数:
G ( s ) = 10 s ( s + 4 ) ( 5 s + 1 ) G(s)=\frac{10}{s(s+4)(5s+1)} G(s)=s(s+4)(5s+1)10
求输入信号为: r ( t ) = 2 + 4 t + 3 t 2 r(t)=2+4t+3t^2 r(t)=2+4t+3t2时,系统的稳态误差 e s s ( ∞ ) e_{ss}(\infty) ess(∞).
解:
系统为单位负反馈系统,根据开环传递函数,可得闭环系统特征方程:
D ( s ) = 5 s 3 + 21 s 2 + 4 s + 10 = 0 D(s)=5s^3+21s^2+4s+10=0 D(s)=5s3+21s2+4s+10=0
由赫尔维茨判据可知, n = 3 n=3 n=3,各项系数: a 0 = 5 , a 1 = 21 , a 2 = 4 , a 3 = 10 a_0=5,a_1=21,a_2=4,a_3=10 a0=5,a1=21,a2=4,a3=10均为正,且 a 1 a 2 − a 0 a 3 = 34 > 0 a_1a_2-a_0a_3=34>0 a1a2−a0a3=34>0.因此,系统稳定.
由
G ( s ) = 10 s ( s + 4 ) ( 5 s + 1 ) = 2.5 s ( 0.25 s + 1 ) ( 5 s + 1 ) G(s)=\frac{10}{s(s+4)(5s+1)}=\frac{2.5}{s(0.25s+1)(5s+1)} G(s)=s(s+4)(5s+1)10=s(0.25s+1)(5s+1)2.5
可知,系统为Ⅰ型系统,且 K = 2.5 K=2.5 K=2.5。
由于Ⅰ型系统在 1 ( t ) 、 t 、 1 2 t 2 1(t)、t、\displaystyle\frac{1}{2}t^2 1(t)、t、21t2信号作用下的稳态误差分别为: 0 、 1 K 、 ∞ 0、\displaystyle\frac{1}{K}、\infty 0、K1、∞,根据线性叠加定理有:
当系统输入为: r ( t ) = 2 + 4 t + 3 t 2 r(t)=2+4t+3t^2 r(t)=2+4t+3t2时,系统的稳态误差为: e s s ( ∞ ) = ∞ e_{ss}(\infty)=\infty ess(∞)=∞.
Example 3.22
已知控制系统如下图所示:
当局部反馈(内反馈)断开时,求:
- r ( t ) = 1 ( t ) , n ( t ) = 0 r(t)=1(t),n(t)=0 r(t)=1(t),n(t)=0时,系统的超调量、上升时间和调节时间;
- r ( t ) = 0 , n ( t ) = 1 ( t ) r(t)=0,n(t)=1(t) r(t)=0,n(t)=1(t)时,系统的超调量和调节时间;
- r ( t ) = t , n ( t ) = 1 ( t ) r(t)=t,n(t)=1(t) r(t)=t,n(t)=1(t)时,系统的稳态误差.
当局部反馈闭合时,求:
- r ( t ) = 1 ( t ) , n ( t ) = 0 r(t)=1(t),n(t)=0 r(t)=1(t),n(t)=0时,要求超调量降为 20 % 20\% 20%的 K t K_t Kt和调节时间;
- r ( t ) = 0 , n ( t ) = 1 ( t ) r(t)=0,n(t)=1(t) r(t)=0,n(t)=1(t)时, K t K_t Kt取值同上,系统的超调量和调节时间;
- r ( t ) = t , n ( t ) = 1 ( t ) r(t)=t,n(t)=1(t) r(t)=t,n(t)=1(t)时, K t K_t Kt取值同上,系统的稳态误差.
解:
【局部反馈断开】
-
r ( t ) = 1 ( t ) , n ( t ) = 0 r(t)=1(t),n(t)=0 r(t)=1(t),n(t)=0时的 σ % , t r \sigma\%,t_r σ%,tr和 t s t_s ts.
开环传递函数为:
G ( s ) = ω n 2 s ( s + 2 ζ ω n ) = 56 s ( s + 3 ) = 56 / 3 s ( 1 3 s + 1 ) G(s)=\frac{\omega_n^2}{s(s+2\zeta\omega_n)}=\frac{56}{s(s+3)}=\frac{56/3}{s\left(\displaystyle\frac{1}{3}s+1\right)} G(s)=s(s+2ζωn)ωn2=s(s+3)56=s(31s+1)56/3
可得:
ζ = 0.2 , ω n = 56 = 7.48 , ω d = ω n 1 − ζ 2 = 7.33 , K v = 56 3 \zeta=0.2,\omega_n=\sqrt{56}=7.48,\omega_d=\omega_n\sqrt{1-\zeta^2}=7.33,K_v=\frac{56}{3} ζ=0.2,ωn=56=7.48,ωd=ωn1−ζ2=7.33,Kv=356
可得:
β = arccos ζ = 78.46 ° = 1.37 σ % = e − π ζ / 1 − ζ 2 × 100 % = 52.7 % t r = π − β ω d = 0.24 , t s = 3.5 ζ ω n = 2.33 ( Δ = 5 % ) \begin{aligned} &\beta=\arccos\zeta=78.46°=1.37\\\\ &\sigma\%={\rm e}^{-\pi\zeta/\sqrt{1-\zeta^2}}\times100\%=52.7\%\\\\ &t_r=\frac{\pi-\beta}{\omega_d}=0.24,t_s=\frac{3.5}{\zeta\omega_n}=2.33(\Delta=5\%) \end{aligned} β=arccosζ=78.46°=1.37σ%=e−πζ/1−ζ2×100%=52.7%tr=ωdπ−β=0.24,ts=ζωn3.5=2.33(Δ=5%) -
r ( t ) = 0 , n ( t ) = 1 ( t ) r(t)=0,n(t)=1(t) r(t)=0,n(t)=1(t)时的 σ % \sigma\% σ%和 t s t_s ts.
C n ( s ) = − 1 2 s ( s + 3 ) + 112 N ( s ) = − 8.93 × 1 0 − 4 56 s ( s 2 + 3 s + 56 ) = − 8.93 × 1 0 − 4 [ 1 − 1 1 − ζ 2 e − ζ ω n t sin ( ω d t + β ) ] = − 8.93 × 1 0 − 4 [ 1 − 1.02 e − 1.5 t sin ( 7.33 t + 78.46 ° ) ] \begin{aligned} C_n(s)&=-\frac{1}{2s(s+3)+112}N(s)=-8.93\times10^{-4}\frac{56}{s(s^2+3s+56)}\\\\ &=-8.93\times10^{-4}\left[1-\frac{1}{\sqrt{1-\zeta^2}}{\rm e}^{-\zeta\omega_nt}\sin(\omega_dt+\beta)\right]\\\\ &=-8.93\times10^{-4}\left[1-1.02{\rm e}^{-1.5t}\sin(7.33t+78.46°)\right] \end{aligned} Cn(s)=−2s(s+3)+1121N(s)=−8.93×10−4s(s2+3s+56)56=−8.93×10−4[1−1−ζ21e−ζωntsin(ωdt+β)]=−8.93×10−4[1−1.02e−1.5tsin(7.33t+78.46°)]
由于是线性系统,且 ζ = 0.2 , ω n = 7.48 \zeta=0.2,\omega_n=7.48 ζ=0.2,ωn=7.48,故:
σ % = 52.7 , t s = 2.33 ( Δ = 5 % ) \sigma\%=52.7,t_s=2.33(\Delta=5\%) σ%=52.7,ts=2.33(Δ=5%) -
r ( t ) = t , n ( t ) = 1 ( t ) r(t)=t,n(t)=1(t) r(t)=t,n(t)=1(t)时的稳态误差.
e s s r ( ∞ ) = 1 K v = 0.054 e_{ssr}(\infty)=\frac{1}{K_v}=0.054 essr(∞)=Kv1=0.054
扰动作用下的稳态误差为:
e s s n ( ∞ ) = − lim s → 0 G 2 H 1 + G 1 G 2 H s N ( s ) e_{ssn}(\infty)=-\lim_{s\to0}\frac{G_2H}{1+G_1G_2H}sN(s) essn(∞)=−s→0lim1+G1G2HG2HsN(s)
其中: G 1 = 112 , G 2 = 1 2 s ( s + 3 ) , H = 1 , N ( s ) = 0.1 s G_1=112,G_2=\displaystyle\frac{1}{2s(s+3)},H=1,N(s)=\displaystyle\frac{0.1}{s} G1=112,G2=2s(s+3)1,H=1,N(s)=s0.1,则有:
e s s n ( ∞ ) = − 8.93 × 1 0 − 4 e_{ssn}(\infty)=-8.93\times10^{-4} essn(∞)=−8.93×10−4
故:
e s s ( ∞ ) = ∣ e s s r ( ∞ ) ∣ + ∣ e s s n ( ∞ ) ∣ = 0.0549 e_{ss}(\infty)=|e_{ssr}(\infty)|+|e_{ssn}(\infty)|=0.0549 ess(∞)=∣essr(∞)∣+∣essn(∞)∣=0.0549
【局部反馈闭合】
-
r ( t ) = 1 ( t ) , σ % = 20 % r(t)=1(t),\sigma\%=20\% r(t)=1(t),σ%=20%时的 K t K_t Kt和 t s t_s ts.
闭环特征方程为:
s 2 + ( 3 + 0.5 K t ) s + 56 = 0 s^2+(3+0.5K_t)s+56=0 s2+(3+0.5Kt)s+56=0
故
ω n = 56 = 7.48 , ζ t = 3 + 0.5 K t 14.96 \omega_n=\sqrt{56}=7.48,\zeta_t=\frac{3+0.5K_t}{14.96} ωn=56=7.48,ζt=14.963+0.5Kt
由
σ % = e − π ζ t / 1 − ζ t 2 × 100 % = 0.2 = 20 % \sigma\%={\rm e}^{-\pi\zeta_t/\sqrt{1-\zeta_t^2}}\times100\%=0.2=20\% σ%=e−πζt/1−ζt2×100%=0.2=20%
可得:
ζ t = 0.456 , K t = 7.64 , t s = 3.5 ζ ω n = 1.03 ( Δ = 5 % ) \zeta_t=0.456,K_t=7.64,t_s=\frac{3.5}{\zeta\omega_n}=1.03(\Delta=5\%) ζt=0.456,Kt=7.64,ts=ζωn3.5=1.03(Δ=5%) -
n ( t ) = 1 ( t ) , K t = 7.64 n(t)=1(t),K_t=7.64 n(t)=1(t),Kt=7.64时的 σ % \sigma\% σ%和 t s t_s ts.
C n ( s ) = − 8.93 × 1 0 − 4 ( 56 s 2 + 6.82 s + 56 ) N ( s ) C_n(s)=-8.93\times10^{-4}\left(\displaystyle\frac{56}{s^2+6.82s+56}\right)N(s) Cn(s)=−8.93×10−4(s2+6.82s+5656)N(s)
由于 ζ t = 0.456 \zeta_t=0.456 ζt=0.456和 ω n = 7.48 \omega_n=7.48 ωn=7.48不变,可得:
σ % = 20 % , t s = 1.03 ( Δ = 5 % ) \sigma\%=20\%,t_s=1.03(\Delta=5\%) σ%=20%,ts=1.03(Δ=5%) -
r ( t ) = t , n ( t ) = 1 ( t ) r(t)=t,n(t)=1(t) r(t)=t,n(t)=1(t)时的稳态误差.
G ( s ) = 56 s ( s + 3 + 0.5 K t ) = 56 s ( s + 6.82 ) = 8.21 s ( 0.147 s + 1 ) G(s)=\frac{56}{s(s+3+0.5K_t)}=\frac{56}{s(s+6.82)}=\frac{8.21}{s(0.147s+1)} G(s)=s(s+3+0.5Kt)56=s(s+6.82)56=s(0.147s+1)8.21
即, K v = 8.21 K_v=8.21 Kv=8.21,因此:
e s s r = 1 K v = 0.122 e_{ssr}=\frac{1}{K_v}=0.122 essr=Kv1=0.122
扰动作用下的稳态误差为:
e s s n ( ∞ ) = − lim s → 0 G 2 H 1 + G 1 G 2 H s N ( s ) e_{ssn}(\infty)=-\lim_{s\to0}\frac{G_2H}{1+G_1G_2H}sN(s) essn(∞)=−s→0lim1+G1G2HG2HsN(s)
其中: G 1 = 112 , G 2 = 0.5 s ( s + 6.82 ) , H = 1 , N ( s ) = 0.1 s G_1=112,G_2=\displaystyle\frac{0.5}{s(s+6.82)},H=1,N(s)=\displaystyle\frac{0.1}{s} G1=112,G2=s(s+6.82)0.5,H=1,N(s)=s0.1,则有:
e s s n ( ∞ ) = − 8.93 × 1 0 − 4 e_{ssn}(\infty)=-8.93\times10^{-4} essn(∞)=−8.93×10−4
故:
e s s ( ∞ ) = ∣ e s s r ( ∞ ) ∣ + ∣ e s s n ( ∞ ) ∣ = 0.123 e_{ss}(\infty)=|e_{ssr}(\infty)|+|e_{ssn}(\infty)|=0.123 ess(∞)=∣essr(∞)∣+∣essn(∞)∣=0.123
【结论】
接通测速内反馈可增大系统的阻尼比,不影响系统自然频率,但会降低系统的开环增益.因而,系统的超调量和调节时间均可减小,而斜坡输入时的稳态误差会增大.由于内反馈处于扰动作用点之后,因此内反馈对扰动产生的稳态误差没有影响.
Example 3.23
设前馈控制系统如下图所示,定义 e ( t ) = r ( t ) − c ( t ) e(t)=r(t)-c(t) e(t)=r(t)−c(t).
若输入信号 r ( t ) r(t) r(t)和扰动 n ( t ) n(t) n(t)都是单位斜坡函数,且 K > 0 , T > 0 K>0,T>0 K>0,T>0,要求:
- 计算 K d = 0 K_d=0 Kd=0时系统的稳态误差 e s s ( ∞ ) e_{ss}(\infty) ess(∞);
- 选择 K d K_d Kd值,使系统稳态输出 c ( t ) c(t) c(t)与希望输出 r ( t ) r(t) r(t)之间不存在稳态误差.
解:
-
K d = 0 K_d=0 Kd=0时系统的稳态误差 e s s ( ∞ ) e_{ss}(\infty) ess(∞);
当 K d = 0 , n ( t ) = 0 , r ( t ) = t K_d=0,n(t)=0,r(t)=t Kd=0,n(t)=0,r(t)=t,即 R ( s ) = 1 s 2 R(s)=\displaystyle\frac{1}{s^2} R(s)=s21时,系统的闭环传递函数为:
Φ r ( s ) = K T s 2 + s + K \Phi_r(s)=\frac{K}{Ts^2+s+K} Φr(s)=Ts2+s+KK
由于 K > 0 , T > 0 K>0,T>0 K>0,T>0,故闭环系统是稳定的.误差函数:
E r ( s ) = R ( s ) − C ( s ) = R ( s ) [ 1 − Φ r ( s ) ] = T s 2 + s T s 2 + s + K R ( s ) E_r(s)=R(s)-C(s)=R(s)[1-\Phi_r(s)]=\frac{Ts^2+s}{Ts^2+s+K}R(s) Er(s)=R(s)−C(s)=R(s)[1−Φr(s)]=Ts2+s+KTs2+sR(s)
由终值定理可知,
e s s r ( ∞ ) = lim s → 0 s E r ( s ) = lim s → 0 s ⋅ T s 2 + s T s 2 + s + K ⋅ 1 s 2 = 1 K e_{ssr}(\infty)=\lim_{s\to0}sE_r(s)=\lim_{s\to0}s·\frac{Ts^2+s}{Ts^2+s+K}·\frac{1}{s^2}=\frac{1}{K} essr(∞)=s→0limsEr(s)=s→0lims⋅Ts2+s+KTs2+s⋅s21=K1
当 K d = 0 , r ( t ) = 0 , n ( t ) = t K_d=0,r(t)=0,n(t)=t Kd=0,r(t)=0,n(t)=t,即 N ( s ) = 1 s 2 N(s)=\displaystyle\frac{1}{s^2} N(s)=s21时,系统的闭环传递函数为:
Φ n ( s ) = K f s ( T s + 1 ) ( T f s + 1 ) ( T s 2 + s + K ) \Phi_n(s)=\frac{K_fs(Ts+1)}{(T_fs+1)(Ts^2+s+K)} Φn(s)=(Tfs+1)(Ts2+s+K)Kfs(Ts+1)
误差函数:
E n ( s ) = R ( s ) − C ( s ) = − N ( s ) Φ n ( s ) = − K f s ( T s + 1 ) ( T f s + 1 ) ( T s 2 + s + K ) N ( s ) E_n(s)=R(s)-C(s)=-N(s)\Phi_n(s)=-\frac{K_fs(Ts+1)}{(T_fs+1)(Ts^2+s+K)}N(s) En(s)=R(s)−C(s)=−N(s)Φn(s)=−(Tfs+1)(Ts2+s+K)Kfs(Ts+1)N(s)
由终值定理可知,
e s s n ( ∞ ) = lim s → 0 s E n ( s ) = − lim s → 0 s ⋅ K f s ( T s + 1 ) ( T f s + 1 ) ( T s 2 + s + K ) ⋅ 1 s 2 = − K f K e_{ssn}(\infty)=\lim_{s\to0}sE_n(s)=-\lim_{s\to0}s·\frac{K_fs(Ts+1)}{(T_fs+1)(Ts^2+s+K)}·\frac{1}{s^2}=-\frac{K_f}{K} essn(∞)=s→0limsEn(s)=−s→0lims⋅(Tfs+1)(Ts2+s+K)Kfs(Ts+1)⋅s21=−KKf
故当 K d = 0 , r ( t ) = t , n ( t ) = t K_d=0,r(t)=t,n(t)=t Kd=0,r(t)=t,n(t)=t时,系统的稳态误差为:
e s s ( ∞ ) = e s s r ( ∞ ) + e s s n ( ∞ ) = 1 − K f K e_{ss}(\infty)=e_{ssr}(\infty)+e_{ssn}(\infty)=\frac{1-K_f}{K} ess(∞)=essr(∞)+essn(∞)=K1−Kf -
确定稳态误差为零时的 K d K_d Kd值.
当 K d ≠ 0 , n ( t ) = 0 , r ( t ) = t K_d≠0,n(t)=0,r(t)=t Kd=0,n(t)=0,r(t)=t,即 R ( s ) = 1 s 2 R(s)=\displaystyle\frac{1}{s^2} R(s)=s21时,系统的闭环传递函数为:
Φ r ( s ) = K ( 1 + K d s ) T s 2 + s + K \Phi_r(s)=\frac{K(1+K_ds)}{Ts^2+s+K} Φr(s)=Ts2+s+KK(1+Kds)
误差函数为:
E r ( s ) = R ( s ) − C ( s ) = R ( s ) [ 1 − Φ r ( s ) ] = T s 2 + ( 1 − K d K ) s T s 2 + s + K R ( s ) E_r(s)=R(s)-C(s)=R(s)[1-\Phi_r(s)]=\frac{Ts^2+(1-K_dK)s}{Ts^2+s+K}R(s) Er(s)=R(s)−C(s)=R(s)[1−Φr(s)]=Ts2+s+KTs2+(1−KdK)sR(s)
由终值定理可知,
e s s r ( ∞ ) = lim s → 0 s E r ( s ) = lim s → 0 s ⋅ T s 2 + ( 1 − K d K ) s T s 2 + s + K ⋅ 1 s 2 = 1 − K d K K e_{ssr}(\infty)=\lim_{s\to0}sE_r(s)=\lim_{s\to0}s·\frac{Ts^2+(1-K_dK)s}{Ts^2+s+K}·\frac{1}{s^2}=\frac{1-K_dK}{K} essr(∞)=s→0limsEr(s)=s→0lims⋅Ts2+s+KTs2+(1−KdK)s⋅s21=K1−KdK
当 K d ≠ 0 , r ( t ) = 0 , n ( t ) = t K_d≠0,r(t)=0,n(t)=t Kd=0,r(t)=0,n(t)=t,即 N ( s ) = 1 s 2 N(s)=\displaystyle\frac{1}{s^2} N(s)=s21时,
e s s n ( ∞ ) = lim s → 0 s E n ( s ) = − K f K e_{ssn}(\infty)=\lim_{s\to0}sE_n(s)=-\frac{K_f}{K} essn(∞)=s→0limsEn(s)=−KKf
要使系统稳态输出 c ( t ) c(t) c(t)与希望输出 r ( t ) r(t) r(t)间不存在稳态误差,有:
1 − K d K K − K f K = 0 \frac{1-K_dK}{K}-\frac{K_f}{K}=0 K1−KdK−KKf=0
故当 K d = 1 − K f K K_d=\displaystyle\frac{1-K_f}{K} Kd=K1−Kf时,系统稳态输出 c ( t ) c(t) c(t)与希望输出 r ( t ) r(t) r(t)间不存在稳态误差.
Example 3.24
设控制系统闭环传递函数为: Φ ( s ) = ω n 2 s 2 + 2 ζ ω n s + ω n 2 \Phi(s)=\displaystyle\frac{\omega_n^2}{s^2+2\zeta\omega_ns+\omega_n^2} Φ(s)=s2+2ζωns+ωn2ωn2.
如果:
- 0.707 ≤ ζ < 1 , ω ≥ 2 0.707≤\zeta<1,\omega≥2 0.707≤ζ<1,ω≥2;
- 0 < ζ ≤ 0.5 , 2 ≤ ω n ≤ 4 0<\zeta≤0.5,2≤\omega_n≤4 0<ζ≤0.5,2≤ωn≤4;
- 0.5 ≤ ζ ≤ 0.707 , ω n ≤ 2 0.5≤\zeta≤0.707,\omega_n≤2 0.5≤ζ≤0.707,ωn≤2;
在 s s s平面上绘出系统特征方程根可能位于的区域.
解:
闭环系统特征方程根在 s s s平面上的位置由以下量确定:
σ = ζ ω n , ω d = ω n 1 − ζ 2 , β = arccos ζ \sigma=\zeta\omega_n,\omega_d=\omega_n\sqrt{1-\zeta^2},\beta=\arccos\zeta σ=ζωn,ωd=ωn1−ζ2,β=arccosζ
-
0.707 ≤ ζ < 1 , ω ≥ 2 0.707≤\zeta<1,\omega≥2 0.707≤ζ<1,ω≥2;
{ 0.707 ≤ ζ < 1 ω ≥ 2 ⇒ { 0 ° < β ≤ 45 ° σ ≥ 1.414 \begin{cases} &0.707≤\zeta<1\\ &\omega≥2 \end{cases}\Rightarrow\begin{cases} &0°<\beta≤45°\\ &\sigma≥1.414 \end{cases} { 0.707≤ζ<1ω≥2⇒{ 0°<β≤45°σ≥1.414 -
0 < ζ ≤ 0.5 , 2 ≤ ω n ≤ 4 0<\zeta≤0.5,2≤\omega_n≤4 0<ζ≤0.5,2≤ωn≤4;
{ 0 < ζ ≤ 0.5 2 ≤ ω n ≤ 4 ⇒ { 60 ° ≤ β < 90 ° 0 < σ ≤ 2 1.73 ≤ ω d ≤ 4 \begin{cases} &0<\zeta≤0.5\\ &2≤\omega_n≤4 \end{cases}\Rightarrow \begin{cases} &60°≤\beta<90°\\ &0<\sigma≤2\\ &1.73≤\omega_d≤4 \end{cases} { 0<ζ≤0.52≤ωn≤4⇒⎩ ⎨ ⎧60°≤β<90°0<σ≤21.73≤ωd≤4 -
0.5 ≤ ζ ≤ 0.707 , ω n ≤ 2 0.5≤\zeta≤0.707,\omega_n≤2 0.5≤ζ≤0.707,ωn≤2;
{ 0.5 ≤ ζ ≤ 0.707 ω n ≤ 2 ⇒ { 45 ° ≤ β < 60 ° 1 ≤ σ ≤ 1.414 0 ≤ ω d ≤ 1.73 \begin{cases} &0.5≤\zeta≤0.707\\ &\omega_n≤2 \end{cases}\Rightarrow \begin{cases} &45°≤\beta<60°\\ &1≤\sigma≤1.414\\ &0≤\omega_d≤1.73 \end{cases} { 0.5≤ζ≤0.707ωn≤2⇒⎩ ⎨ ⎧45°≤β<60°1≤σ≤1.4140≤ωd≤1.73
【特征方程根可能位于的区域】
Example 3.25
设系统闭环传递函数如下,当输入为的单位阶跃函数时,确定系统的动态性能指标,并画出其单位阶跃响应曲线.
Φ ( s ) = 9 s 2 + 3 s + 9 \Phi(s)=\frac{9}{s^2+3s+9} Φ(s)=s2+3s+99
解:
由系统闭环传递函数可知,系统的自然频率和阻尼比分别为:
ω n = 3 , ζ = 0.5 \omega_n=3,\zeta=0.5 ωn=3,ζ=0.5
则系统的动态性能指标为:
超调量: σ % = e − π ζ / 1 − ζ 2 × 100 % = 16.3 % 峰值时间: t p = π ω n 1 − ζ 2 = 1.21 s 调节时间: t s = 4.4 ζ ω n = 2.93 s ( Δ = 2 % ) \begin{aligned} &超调量:\sigma\%={\rm e}^{-\pi\zeta/\sqrt{1-\zeta^2}}\times100\%=16.3\%\\\\ &峰值时间:t_p=\frac{\pi}{\omega_n\sqrt{1-\zeta^2}}=1.21s\\\\ &调节时间:t_s=\frac{4.4}{\zeta\omega_n}=2.93s(\Delta=2\%) \end{aligned} 超调量:σ%=e−πζ/1−ζ2×100%=16.3%峰值时间:tp=ωn1−ζ2π=1.21s调节时间:ts=ζωn4.4=2.93s(Δ=2%)
【系统单位阶跃响应】
Example 3.26
设单位反馈系统的开环传递函数为: G ( s ) = 4 s ( s + 2 ) G(s)=\displaystyle\frac{4}{s(s+2)} G(s)=s(s+2)4,写出该系统的单位阶跃响应和单位斜坡响应表达式.
解:
依题意可得:
G ( s ) = 4 s ( s + 2 ) = ω n 2 s ( s + 2 ζ ω n ) G(s)=\frac{4}{s(s+2)}=\frac{\omega_n^2}{s(s+2\zeta\omega_n)} G(s)=s(s+2)4=s(s+2ζωn)ωn2
可得系统自然频率和阻尼比:
ω n = 2 , ζ = 0.5 \omega_n=2,\zeta=0.5 ωn=2,ζ=0.5
自然频率与负实轴的夹角为: β = arccos ζ = 60 ° \beta=\arccos\zeta=60° β=arccosζ=60°.
【单位阶跃响应表达式】
c ( t ) = 1 − 1 1 − ζ 2 e − ζ ω n t sin ( ω n 1 − ζ 2 t + β ) = 1 − 1.155 e − t sin ( 1.732 t + 60 ° ) \begin{aligned} c(t)=1-\displaystyle\frac{1}{\sqrt{1-\zeta^2}}{\rm e}^{-\zeta\omega_nt}\sin(\omega_n\sqrt{1-\zeta^2}t+\beta)=1-1.155{\rm e}^{-t}\sin(1.732t+60°) \end{aligned} c(t)=1−1−ζ21e−ζωntsin(ωn1−ζ2t+β)=1−1.155e−tsin(1.732t+60°)
【单位斜坡响应表达式】
c ( t ) = t − 2 ζ ω n + 1 ω n 1 − ζ 2 e − ζ ω n t sin ( ω n 1 − ζ 2 t + 2 β ) = t − 0.5 + 0.577 e − t sin ( 1.732 t + 120 ° ) c(t)=t-\frac{2\zeta}{\omega_n}+\frac{1}{\omega_n\sqrt{1-\zeta^2}}{\rm e}^{-\zeta\omega_nt}\sin(\omega_n\sqrt{1-\zeta^2}t+2\beta)=t-0.5+0.577{\rm e}^{-t}\sin(1.732t+120°) c(t)=t−ωn2ζ+ωn1−ζ21e−ζωntsin(ωn1−ζ2t+2β)=t−0.5+0.577e−tsin(1.732t+120°)
【响应曲线】
Example 3.27
宇宙飞船控制系统简化结构图如下所示,已知控制器的时间常数 T = 3 T=3 T=3,力矩与惯量比 K 1 J = 2 9 \displaystyle\frac{K_1}{J}=\frac{2}{9} JK1=92.求系统的阻尼比及各项动态性能指标.
解:
由图可得,系统闭环传递函数为:
Φ ( s ) = K 1 T s + K 1 J s 2 + K 1 T s + K 1 = ( 2 / 3 ) s + ( 2 / 9 ) s 2 + ( 2 / 3 ) s + ( 2 / 9 ) \Phi(s)=\frac{K_1Ts+K_1}{Js^2+K_1Ts+K_1}=\frac{(2/3)s+(2/9)}{s^2+(2/3)s+(2/9)} Φ(s)=Js2+K1Ts+K1K1Ts+K1=s2+(2/3)s+(2/9)(2/3)s+(2/9)
从 Φ ( s ) \Phi(s) Φ(s)形式可知,该系统是比例-微分控制二阶系统,其标准形式为:
Φ ( s ) = ω n 2 z s + z s 2 + 2 ζ d ω n s + ω n 2 \Phi(s)=\frac{\omega_n^2}{z}\frac{s+z}{s^2+2\zeta_d\omega_ns+\omega_n^2} Φ(s)=zωn2s2+2ζdωns+ωn2s+z
由
( 2 / 3 ) s + ( 2 / 9 ) s 2 + ( 2 / 3 ) s + ( 2 / 9 ) = ω n 2 z s + z s 2 + 2 ζ d ω n s + ω n 2 \frac{(2/3)s+(2/9)}{s^2+(2/3)s+(2/9)}=\frac{\omega_n^2}{z}\frac{s+z}{s^2+2\zeta_d\omega_ns+\omega_n^2} s2+(2/3)s+(2/9)(2/3)s+(2/9)=zωn2s2+2ζdωns+ωn2s+z
可得:
z = 1 / 3 , ω n = 2 / 3 , ζ d = 2 / 2 = 0.707 z=1/3,\omega_n=\sqrt{2}/3,\zeta_d=\sqrt{2}/2=0.707 z=1/3,ωn=2/3,ζd=2/2=0.707
由于:
r = z 2 − 2 ζ d ω n z + ω n 2 z 1 − ζ d 2 = 1.414 ψ = − π + arctan ω n 1 − ζ d 2 z − ζ d ω n + arctan 1 − ζ d 2 ζ d = − π + π 2 + π 4 = − 0.785 β d = arctan 1 − ζ d 2 ζ d = π 4 = 0.785 \begin{aligned} &r=\frac{\sqrt{z^2-2\zeta_d\omega_nz+\omega_n^2}}{z\sqrt{1-\zeta_d^2}}=1.414\\\\ &\psi=-\pi+\arctan\frac{\omega_n\sqrt{1-\zeta_d^2}}{z-\zeta_d\omega_n}+\arctan\frac{\sqrt{1-\zeta_d^2}}{\zeta_d}=-\pi+\frac{\pi}{2}+\frac{\pi}{4}=-0.785\\\\ &\beta_d=\arctan\frac{\sqrt{1-\zeta_d^2}}{\zeta_d}=\frac{\pi}{4}=0.785 \end{aligned} r=z1−ζd2z2−2ζdωnz+ωn2=1.414ψ=−π+arctanz−ζdωnωn1−ζd2+arctanζd1−ζd2=−π+2π+4π=−0.785βd=arctanζd1−ζd2=4π=0.785
【系统动态性能指标】
峰值时间: t p = β d − ψ ω n 1 − ζ d 2 = 4.72 s 超调量: σ % = r 1 − ζ d 2 e − ζ d ω n t × 100 % = 20.8 % 调节时间: t s = 4 + ln r ζ d ω n = 13.04 s ( Δ = 0.02 ) \begin{aligned} &峰值时间:t_p=\frac{\beta_d-\psi}{\omega_n\sqrt{1-\zeta_d^2}}=4.72s\\\\ &超调量:\sigma\%=r\sqrt{1-\zeta_d^2}{\rm e}^{-\zeta_d\omega_nt}\times100\%=20.8\%\\\\ &调节时间:t_s=\frac{4+\ln{r}}{\zeta_d\omega_n}=13.04s(\Delta=0.02) \end{aligned} 峰值时间:tp=ωn1−ζd2βd−ψ=4.72s超调量:σ%=r1−ζd2e−ζdωnt×100%=20.8%调节时间:ts=ζdωn4+lnr=13.04s(Δ=0.02)
【系统单位阶跃响应曲线】
Example 3.28
设电子心律起搏器系统如下图所示,其中模拟心脏的传递函数相当于一纯积分器.
- 若 ζ = 0.5 \zeta=0.5 ζ=0.5对应最佳响应,问起搏器增益 K K K应取多大?
- 若期望心速为 60 次 / m i n 60次/{\rm min} 60次/min,突然接通起搏器,问 1 s 1s 1s后实际心速为多少?瞬时最大心速多大?
解:
-
求解增益 K K K.
由图可知,系统开环传递函数为:
G ( s ) = K s ( 0.05 s + 1 ) = 20 K s ( s + 20 ) = ω n 2 s ( s + 2 ζ ω n ) G(s)=\frac{K}{s(0.05s+1)}=\frac{20K}{s(s+20)}=\frac{\omega_n^2}{s(s+2\zeta\omega_n)} G(s)=s(0.05s+1)K=s(s+20)20K=s(s+2ζωn)ωn2
若 ζ = 0.5 \zeta=0.5 ζ=0.5对应最佳响应,则取起搏器增益 K = 20 K=20 K=20. -
求实际心速和瞬时最大心速.
满足 ζ = 0.5 \zeta=0.5 ζ=0.5的系统的闭环传递函数为:
Φ ( s ) = 400 s 2 + 20 s + 400 \Phi(s)=\frac{400}{s^2+20s+400} Φ(s)=s2+20s+400400
系统的自然频率和阻尼比分别为:
ω n = 20 , ζ = 0.5 \omega_n=20,\zeta=0.5 ωn=20,ζ=0.5
系统的单位阶跃响应表达式为:
c ( t ) = 1 − 1 1 − ζ 2 e − ζ ω n t sin ( ω n 1 − ζ 2 t + arccos ζ ) = 1 − 1.155 e − 10 t sin ( 17.32 t + 60 ° ) c(t)=1-\frac{1}{\sqrt{1-\zeta^2}}{\rm e}^{-\zeta\omega_nt}\sin(\omega_n\sqrt{1-\zeta^2}t+\arccos\zeta)=1-1.155{\rm e}^{-10t}\sin(17.32t+60°) c(t)=1−1−ζ21e−ζωntsin(ωn1−ζ2t+arccosζ)=1−1.155e−10tsin(17.32t+60°)
若期望心速为 60 次 / m i n 60次/{\rm min} 60次/min,突然接通起搏器,设 1 s 1s 1s后实际心速为 c ( 1 ) c(1) c(1),则:
c ( 1 ) = 60 × [ 1 − 1.155 e − 10 sin ( 17.32 + π / 3 ) ] = 60.0015 次 / m i n c(1)=60\times[1-1.155{\rm e}^{-10}\sin(17.32+\pi/3)]=60.0015次/{\rm min} c(1)=60×[1−1.155e−10sin(17.32+π/3)]=60.0015次/min
由于 0 < ζ < 1 0<\zeta<1 0<ζ<1,故该系统为欠阻尼二阶系统,动态性能指标为:
超调量: σ % = e − π ζ / 1 − ζ 2 × 100 % = 16.3 % 峰值时间: t p = π ω n 1 − ζ 2 = 0.18 s \begin{aligned} &超调量:\sigma\%={\rm e}^{-\pi\zeta/\sqrt{1-\zeta^2}}\times100\%=16.3\%\\\\ &峰值时间:t_p=\frac{\pi}{\omega_n\sqrt{1-\zeta^2}}=0.18s \end{aligned} 超调量:σ%=e−πζ/1−ζ2×100%=16.3%峰值时间:tp=ωn1−ζ2π=0.18s
设瞬时最大心速为 c max c_{\max} cmax且发生在 t p = 0.18 s t_p=0.18s tp=0.18s时,则
c max = 60 × ( 1 + σ % ) = 69.78 次 / m i n c_{\max}=60\times(1+\sigma\%)=69.78次/{\rm min} cmax=60×(1+σ%)=69.78次/min
故若期望心速为 60 次 / m i n ) 60次/{\rm min}) 60次/min),突然接通起搏器,则 1 s 1s 1s后实际心速为 60.0015 次 / m i n 60.0015次/{\rm min} 60.0015次/min,瞬时最大心速发生在 0.18 s 0.18s 0.18s时,为 69.78 次 / m i n 69.78次/{\rm min} 69.78次/min. -
【系统单位阶跃响应曲线】
Example 3.29
已知二阶系统的单位阶跃响应为: c ( t ) = 10 − 12.5 e − 1.2 t sin ( 1.6 t + 53.1 ° ) c(t)=10-12.5{\rm e}^{-1.2t}\sin(1.6t+53.1°) c(t)=10−12.5e−1.2tsin(1.6t+53.1°),求系统的闭环传递函数、超调量 σ % \sigma\% σ%和峰值时间 t p t_p tp、调节时间 t s t_s ts.
解:
该二阶系统单位阶跃响应为:
c ( t ) = 10 − 12.5 e − 1.2 t sin ( 1.6 t + 53.1 ° ) = 10 [ 1 − 1.25 e − 1.2 t sin ( 1.6 t + 53.1 ° ) ] c(t)=10-12.5{\rm e}^{-1.2t}\sin(1.6t+53.1°)=10[1-1.25{\rm e}^{-1.2t}\sin(1.6t+53.1°)] c(t)=10−12.5e−1.2tsin(1.6t+53.1°)=10[1−1.25e−1.2tsin(1.6t+53.1°)]
由上式可知,该系统放大系数为: 10 10 10,但放大系数不影响系统的动态性能.
标准的二阶系统单位阶跃响应为:
c ( t ) = 1 − 1 1 − ζ 2 e − ζ ω n t sin ( ω n 1 − ζ 2 t + β ) c(t)=1-\frac{1}{\sqrt{1-\zeta^2}}{\rm e}^{-\zeta\omega_nt}\sin(\omega_n\sqrt{1-\zeta^2}t+\beta) c(t)=1−1−ζ21e−ζωntsin(ωn1−ζ2t+β)
则有:
ζ ω n = 1.2 , 1 1 − ζ 2 = 1.25 , ω n 1 − ζ 2 = 1.6 , β = arccos ζ = 53.1 ° \zeta\omega_n=1.2,\frac{1}{\sqrt{1-\zeta^2}}=1.25,\omega_n\sqrt{1-\zeta^2}=1.6,\beta=\arccos\zeta=53.1° ζωn=1.2,1−ζ21=1.25,ωn1−ζ2=1.6,β=arccosζ=53.1°
解得:
ζ = 0.6 , ω n = 2 \zeta=0.6,\omega_n=2 ζ=0.6,ωn=2
故系统的闭环传递函数为:
Φ ( s ) = 40 s 2 + 2.4 s + 4 \Phi(s)=\frac{40}{s^2+2.4s+4} Φ(s)=s2+2.4s+440
由于 0 < ζ < 1 0<\zeta<1 0<ζ<1,故该系统为欠阻尼二阶系统,其动态性能指标为:
超调量: σ % = e − π ζ / 1 − ζ 2 × 100 % = 9.5 % 峰值时间: t p = π ω n 1 − ζ 2 = π 2 × 0.8 = 1.96 ( s ) 调节时间: t s = 3.5 ζ ω n = 3.5 1.2 = 2.92 ( s ) ( Δ = 5 % ) \begin{aligned} &超调量:\sigma\%={\rm e}^{-\pi\zeta/\sqrt{1-\zeta^2}}\times100\%=9.5\%\\\\ &峰值时间:t_p=\frac{\pi}{\omega_n\sqrt{1-\zeta^2}}=\frac{\pi}{2\times0.8}=1.96(s)\\\\ &调节时间:t_s=\frac{3.5}{\zeta\omega_n}=\frac{3.5}{1.2}=2.92(s)(\Delta=5\%) \end{aligned} 超调量:σ%=e−πζ/1−ζ2×100%=9.5%峰值时间:tp=ωn1−ζ2π=2×0.8π=1.96(s)调节时间:ts=ζωn3.5=1.23.5=2.92(s)(Δ=5%)
Example 3.30
已知各系统脉冲响应如下,求传递函数:
- c ( t ) = K ω sin ω t c(t)=\displaystyle\frac{K}{\omega}\sin\omega{t} c(t)=ωKsinωt;
- c ( t ) = 0.02 ( e − 0.5 t − e 0.2 t ) c(t)=0.02({\rm e}^{-0.5t}-{\rm e}^{0.2t}) c(t)=0.02(e−0.5t−e0.2t);
- c ( t ) = 0.01 t c(t)=0.01t c(t)=0.01t;
解:
系统的脉冲响应的拉普拉斯变换对应系统的闭环传递函数.
-
c ( t ) = K ω sin ω t c(t)=\displaystyle\frac{K}{\omega}\sin\omega{t} c(t)=ωKsinωt;
Φ ( s ) = L [ c ( t ) ] = K s 2 + ω 2 \Phi(s)=L[c(t)]=\frac{K}{s^2+\omega^2} Φ(s)=L[c(t)]=s2+ω2K -
c ( t ) = 0.02 ( e − 0.5 t − e 0.2 t ) c(t)=0.02({\rm e}^{-0.5t}-{\rm e}^{0.2t}) c(t)=0.02(e−0.5t−e0.2t);
Φ ( s ) = L [ c ( t ) ] = 0.02 ( 1 s + 0.5 − 1 s − 0.2 ) = − 0.014 ( 2 s + 1 ) ( 5 s − 1 ) \Phi(s)=L[c(t)]=0.02\left(\displaystyle\frac{1}{s+0.5}-\frac{1}{s-0.2}\right)=\frac{-0.014}{(2s+1)(5s-1)} Φ(s)=L[c(t)]=0.02(s+0.51−s−0.21)=(2s+1)(5s−1)−0.014 -
c ( t ) = 0.01 t c(t)=0.01t c(t)=0.01t;
Φ ( s ) = L [ c ( t ) ] = 0.01 s 2 \Phi(s)=L[c(t)]=\frac{0.01}{s^2} Φ(s)=L[c(t)]=s20.01