Lecture 6

Question 1

Give the equation (and it’s name) relating motor torque and current in the armature circuit

Answer 1

tm = Kt*ia

electro-mechanical coupling

Question 2

What is Kirchhoff’s second law?

Answer 2

va - (sum of component potential differences) = 0

Question 3

What is eb?

Answer 3

The back electro-motive-force

Question 4

What is the equation for generation of EMF?

Answer 4

eb = Kb*(dtheta/dt)

Question 5

What is the potential difference across an inductor?

Answer 5

eL = L*(dia/dt)

Question 6

What is the potential difference across a resistor?

Answer 6

eR = ia*R

Question 7

What does Kirchoffs law when applied to the electric motor circuit result in

Answer 7

va - (eb +eR + eL) = 0

Question 8

What is the combined circuit equation for an electric motor

Answer 8

va = Kb dtheta/dt + iaR + Ldia/dt

Question 9

What is the Laplace transform for the circuit equation of an electric motor

Answer 9

Va(s) = KbsTHETA(s) + Ia(s)R + LsIa(s)

Question 10

What is the coupling equation for an electric motor

Answer 10

tm = Kt*ia

Question 11

What is the input and output of an electric motor

Answer 11

Va(s) is the input, and THETA(s) is the output, or s*THETA(s) to convert from angle (position control) to angular speed (speed control)

Question 12

What are the steps in a linear system for deriving a transfer function

Answer 12

System equations using laws of physics
Identify inputs and outputs (and intermediate variables)
Take Laplace transforms 
Eliminate unknown variables
Rearrange to obtain output/input ratio