我试图实现一个简单的脚本执行PI控制的巡航控制应用程序，但我发现一些问题的组成部分。下面是我的代码：

function [] = PI_cruisecontrol()
clc; close all;
t0 = 0; tfinal = 50; dt = 0.001;                % time parameters
r = 10;                                         % reference of 10 m/s
m = 1000;                                       % mass
b = 50;                                         % friction coeff. (depends on v)
yp = zeros(tfinal/dt,1); t = yp;                % initialize speed and time array
Ki = 40;                                        % integrarl constant
Kp = 800;                                       % proportional constant
int = 0;                                        % itinialize int error
% CONTROL LOOP (Forward-Euler integrator is used to solve the ODE)
for i=t0+2:tfinal/dt
    err   = r-yp(i-1);                          % update error
    int   = int+err;                            % integral term
    u     = (Kp*err)+(Ki*int*dt);               % action of control
    yp(i) = yp(i-1)+((-b*yp(i)/m) + (u/m))*dt;  % solve ode for speed  
    t(i)  = t(i)+dt*i;                          % log the time                
end
% Results
figure(1)
plot(t,yp)
title ('Step Response')
xlabel('Time (seconds)')
ylabel('Amplitud')
axis([0 20 0 12])
hold on
reference = ones(tfinal/dt,1)*10;
plot(t,reference,':')
end

这是它应该是如何，使用预定义的matlab函数：

function [] = PI_cruisecontrol2()
m = 1000;
b = 50;
r = 10;
s = tf('s');
P_cruise = 1/(m*s + b); 
Kp = 800;
Ki = 40;
C = pid(Kp,Ki);
T = feedback(C*P_cruise,1);
t = 0:0.1:20;
step(r*T,t)
axis([0 20 0 12])
end

我在代码中做错了什么？谢谢！