Consider the dynamics of a DC motor speed control system and its current mode amplifier. Consider the the motor torque-speed transfer function is a first-order filter and the current mode amplifier input-output dynamics is also a first-order filter. W(s)/T(s)=Km/tms+1
T(s)=Kt. i
i(s)/i(cmd)=Ka/tas+1
Assume that there is a load torque acting as a disturbance on the motor and that it is in the form of
(i) step function,
(ii) a ramp function.
If we want to make sure that the steady-state speed error due to the load torque is zero, what kind of controller is required in order to deal with each type of disturbance (load) torque? Why can't a PD type controller do the job?