ti = 1e9;
td = .1;
kt = 90.63e-6;
t = 1/20000;
J = 8.6556e-3;
 
k = kt; 
kp = k-k*t/(2*ti); 
kd = k*td/t;
ki = k*t/ti;

num = t^2/(2*J)*[kd+ki+kp,-kd+ki,-kd-kp,kd];
den = [1,-3,3,-1,0];

hold off;
rlocus(tf(num,den,t));

tita = 0:0.01*pi:2*pi;
x = sin(tita);
y = cos(tita);
hold on;
plot(x,y,'o1');