Page 673 - Mechatronics with Experiments

ELECTRIC ACTUATORS: MOTOR AND DRIVE TECHNOLOGY 659
are connected between the OUT1 and OUT2 ports. DC supply voltage and ground are
connected to the V and GND terminals.
cc
Logic voltage is internally derived from the V . The operation of the TPIC0107B is
cc
controlled by two input pins: DIR (IN1) and PWM (IN2). The PWM pin should be connected
to the PWM output port of a microcontroller, whereas the DIR pin can be connected to
any digital output. The PWM switching frequency is 2 kHz. The state of OUT1 and OUT2
(H-bridge output) follows the signal in the PWM pin. The actual PWM signal needs to
be formed by the PWM port of the microcontroller. For instance, the current control loop
must be implemented in the microcontroller. The IC is capable of sensing over-voltage,
under-voltage, short-circuit, over and under current, over temperature conditions and shuts
down bridge output and sets the status output pins to indicate the error code (STATUS1 and
STATUS2 pins).
Example: PM DC Motor Consider a permanent magnet DC motor. The armature
resistance is measured to be R = 0.5 Ω. When V = 120 V is applied to the motor, it reaches
t
a
1200 rpm steady-state speed and draws 40 A current. Determine the back EMF voltage, IR
power losses, power delivered to the armature, and torque generated at that speed.
The basic relationship for the motor,
di(t)
V (t) = L ⋅ + R ⋅ i(t) + V bemf (8.224)
t
dt
120 V = 0 + 0.5 ⋅ 40 Ω A + V bemf (8.225)
V bemf = 100 V (8.226)
where the transient effects of inductance is neglected in steady-state. The IR power loss is
2
2
2
P = R ⋅ i = 0.5 ⋅ 40 Ω A = 800 W (8.227)
IR a
and torque generated,
V bemf 100 V
K = = (8.228)
E
̇ 1.2krpm
K = 9.5493 ⋅ 10 −3 ⋅ K Nm/A = 0.7958 Nm/A (8.229)
E
T
T = K ⋅ i = 31.83 Nm (8.230)
T
and the electrical power converted to mechanical power,
P = T ⋅ w (8.231)
m
= 4000 W (8.232)
= P e (8.233)
P = V bemf ⋅ i a (8.234)
e
= 100 V ⋅ 40 A = 4000 W (8.235)
Since the motor speed is constant, the motor torque generated by the torque must be used
by a total load torque of equal magnitude but in the opposite direction.

8.5 AC INDUCTION MOTORS AND DRIVES

AC induction motors have been used in constant speed applications in huge quantities. They
have been the work horse of the industrial world. In recent years, they have also been used
as closed loop position servo motors with a sophisticated current commutation algorithm
in the drive being the key to the increased capabilities. Three-phase AC motors are more