ECE 442 Power Electronics 1

Elementary Two-Pole Motor

ECE 442 Power Electronics 2

Elementary Two-Pole Generator

ECE 442 Power Electronics 3

Voltage induced in the coil, e

• Flux through the coil window is sinusoidal

• Φ = Φmaxsin(ωt)

• Voltage induced in coil,e• e = N(dΦ/dt)

• e = NωΦmaxcos(ωt)

• Emax = ωNΦmax

• Emax = 2πfNΦmax

• Erms = 4.44fNΦmax

ECE 442 Power Electronics 4

Directions of induced voltage and current

• Develop CCW counter-torque

• “Bunching” must occur at the top of coil side B and the bottom of coil side A

• Coil current is CCW as viewed from south pole

ECE 442 Power Electronics 5

Basic DC Generator

Separately Excited Shunt Generator

ECE 442 Power Electronics 6

ff

p

ff G

a p G

N I

nN I kE n k

R

R

ECE 442 Power Electronics 7

Generator Action

• Permanent-magnet field

• One-turn armature

• Drive so that Ea>Ebat

• Current Ia flows to charge Ebat

ECE 442 Power Electronics 8

From a Circuit Point-of-View

• “Generate” voltage Ea

• When supplying current, the machine develops a “counter-torque” in opposition to the driving torque

ECE 442 Power Electronics 9

Motor Action

• “Uncouple” the Prime Mover

• Eventually, Ea will decrease so that Ea<Ebat

• Ia flows as shown

• Armature turns in the same direction

ECE 442 Power Electronics 10

From a Circuit Point-Of-View

• Counter-emf, Ea, is induced, opposing the driving voltage Ebat

• Machine develops a driving torque