matlab - How to use `feedback` function in Matlab?

Question

Matlab's feedback function is used to obtain the closed loop transfer function of a system. Example:

sys = feedback(sys1,sys2) returns a model object sys for the negative feedback interconnection of model objects sys1,sys2. To compute the closed-loop system with positive feedback, use sign = +1, for negative feedback we use -1.

My question arises when we have a system of the following type:

According to these docs, we can use feedback to create the negative feedback loop with G and C.

sys = feedback(G*C,-1)

This is a source of confusion, shouldn't the above be: sys = feedback(G*C,1,-1)? These are not the same.

However, looking at these docs, for a unit loop gain k, you can compute the closed-loop transfer function T using:

G = tf([.5 1.3],[1 1.2  1.6 0]);
T = feedback(G,1); 

Why are we using 1 and not -1? This is still negative feedback and not positive feedback.

标签： matlab

Answer 1

G = tf([.5 1.3],[1 1.2  1.6 0]);
T = feedback(G,1); 

中的一个feedback(G,1)表示sys2并且由于该函数有两个输入，因此根据以下行，默认值将是负统一反馈

sys = feedback(sys1,sys2) 返回一个模型对象 sys，用于模型对象 sys1,sys2 的负 反馈互连。

考虑以下脚本

s = tf('s');
G = 1/s;
T1 = feedback(G,1)
T2 = feedback(G,1,-1)

T1 和 T2 相同。