Page 6 - Electric Drives and Electromechanical Systems

List of principal symbols

The following are the principal symbols used in this book. In general, they are also defined
within the text. Lower-case symbols normally refer to instantaneous values, and upper-case
symbols to constants. In practice, a symbol may refer to more than one quantity; however,
within a particular context, the meaning should be clear.

B Damping constant
B g Air-gap flux
C rr Coefficient of rolling resistance
d Duty cycle
Per-phase r.m.s. e.m.f.
e p
Steady-state error
e ss
Direct-current (d.c.) brushless motor back e.m.f.
E a , E b , E c
Tachogenerator voltage
E g
Kinetic energy
E k
Direct Current (d.c.) brushed-motor back e.m.f.
E m
Regenerative energy
E r
Supply frequency
f e
Sampling frequency
f p
PWM switching frequency
f s
F Force
Frictional force
F f
F L External linear force
I Moment of inertia; Current
Inertia referred to the output of the motor
I eff
I L Load inertia
I m Motor inertia
I tot Total inertia of a rotating system
I a Armature current
I f Field current
I m Induction motor magnetisation current
I r Induction motor rotor current referred to the stator
I r ’ Induction motor rotor current
Regenerative current
I R
Induction motor stator current
I S
K Shaft stiffness
Voltage constant for a direct current (d.c). brushed motor
K e
Tachogenerator voltage constant
K g
Proportional gain
K p
Effective stiffness of a joint
K s
Direct current brushed motor torque constant
K t
Induction-motor torque constant
K T
K T 0 d.c. brushless-motor torque constant
xi