Machine Drives Module 3.06 Electric Drives

1
Machine DrivesModule 3.06Electric Drives

• Lecturer
• Dr Vesna Brujic-Okretic
• (in place of Professor Graham Parker)
• Ext 9676 and 9681
• Email mes1vb_at_surrey.ac.uk

2
Separately excited DC motor
Steady-state regime equations
3
Series-wound DC motor

• Field armature circuits are connected in
  series, as shown in the Figure below so IaIf
• assuming linear dependence of flux on the field
  current (approximately), we have, in a
  steady-state

4
Series-wound DC motor

• Torque-Speed and Torque-Current steady-state
  characteristics

stall torque
5
Shunt-wound DC motor

• equivalent circuit

Ideal case KT Ka gives
6
Shunt-wound DC motor

• w is directly related to Ia

7
Permanent Magnet DC Motor

• Stall torque, T0, and no-load speed, w0 are

When Vs varies, torque-speed characteristics are
parallel straight lines (with the same
gradient) (Vs2 gt Vs1) T0 and w0 change
accordingly
8
Set of Equations

• La and Lf are the armature and field circuit
  inductance

TM motor torque
TL load torque
Friction w TFcw
II Newton's Law for rotation
9

• Motor Gearbox

10
Motor gearbox

• If load driven through a gearbox - load inertia
  must be converted to its equivalent value on the
  motor shaft
• N is the gearbox ratio

11
Referred Inertia
Nl, Nm - the number of teeth at the load and
motor shafts,respectively ql, qm - the angular
travels wl, wm - the angular velocities
Assuming perfect contact
Power on either side must be the same (assuming
no losses)
Tl,m - the torques
The stored kinetic energy - the same
Jl - moment of inertia of the load, at the load
shaft Jm - moment of inertia of the load,
referred to the motor shaft
12
Referred Inertia

• The total inertia that the motor must overcome
  is
• similarly, the inertia at the load shaft is
• Optimum value of N - when the equivalent load
  inertia on the motor shaft motor inertia

13
Leadscrew Mechanism

• load driven through a leadscrew