To implement feed forward control. Firstly, the transfer function of the linear DC Motor model has to be obtained. Actually in our case, the input of the plant is current so the transfer function of the mathematical model in ratio of angular velocity to current has to be obtained. It is given by:

G(s)=Ω_1/I_a =R_A/K_M 1/(T_e s+1) where T_e=(J_meq R_A)/(K_m Cϕ) is electro-mechanical time constant.

The feed forward control could be determined using equation G_F=G^(-1)(2.64) as follows:

G_F (s)=K_M/R_A (T_e s+1)/(T_o s+1)

It can be clearly seen the transfer function G_F (s) is improper and not realizable.

Using a non-causal filter from G_F=G^(-1)/G_filter (2.65), might solve the problem. As the transfer function of mathematical model is in first order, the transfer function of filter can be chosen such that:

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So the Simulink HIL model for the speed control of a test motor is shown in Figure 5.1. The Simulink HIL model has input blocks, motor test bench subsystem and output blocks.

To perform an experiment on the test motor, firstly the test motor could be set by “Enable Maxon” block. Using the “Disable Maxon” block, the switch off time could be specified, which automatically sends a signal to the test motor to shutdown. During the operation of the test motor, the load motor should be switched off for the entire simulation time or if it is desired to add some disturbances on to the test motor, the load motor could be switched on after sometime to observe the effect of disturbances acting on the test motor. A specific speed is set using “Solldrehzahl” block. The PI Controller has been implemented in the Simulink HIL model for the purpose of controlling speed of the test motor at the specific speed. It is to be noted that the simulation time should be greater than the motor shutdown