Page 74 - Servo Motors and Industrial Control Theory -

4.2 Types of Power Unit 67

Fig. 4.2 The basic operation Power Supply
of a single-phase half recti- V c
fication thyristor controlled 0180 360 V q Output Voltage
DC motors V

R

p Armature
L

M Statar

Fig. 4.3 Types of available
power units Power Units

Thyristor Thyristor Pulse Width
Thyristor Controlled Controlled Modulated
Controlled With Current With Current
With Current Freq. Frq. of Freq. of
of 50 HZ 100 HZ 300 HZ

Fig. 4.4 Output voltage from Mark
pulse width modulated power
unit

Space

frequency is possible. A typical frequency may be as high as 2 kHz. This kind of
frequency is often used for application where a high performance from the motor is
required. In PWM power unit, transistors are used for smaller motors and thyristor
are used for larger motors to control the voltage supplied to the motor. When thyris-
tor is used, forcing circuits must be used to stop the conduction of thyristor because
once triggered, it will continue to conduct until the current becomes zero.