You are given the block diagram of a dc motor (as shown below) with the followin

Question

You are given the block diagram of a dc motor (as shown below) with the following parameters. Derive the transfer function of rotor speed as the output with the load torque taken as the input for a dc machine operated with constant flux. Express the transfer functions in terms of the motor parameters K (back cmf and torque constant), L, R, J and b. omega/T_L = _______ Derive the transfer function of armature current as the output with the load torque taken as the input for a dc machine operated with constant flux. Express the transfer functions in terms of the motor parameters K (back emf and torque constant), L, R, J and b. i/T_L = _________ For a pulsating load torque with a peak value equal to 1 N-m (assume sinusoidal variation) at a frequency of omega_0 = 20 rad/sec, evaluate the amplitude (peak to peak) of the speed pulsations for the machine with the parameters given above. Delta omega = _________ rad/sec

Explanation / Answer

a) 1/Lp and 1 Ls and Rp are in negative feedbcak aplly (1/Lp*Ls)/ ((1+1/Lp*Ls*Rp))

multiply with kt and ke and add bp

the result will be negative feed back to 1/J and 1/S

hence w/TL can be obtained.

b) both i/TL solve both system left side and right side using g(s)/1+g(s) H(s)

where g(s) is forward path gain.

h(s) is feedback

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