This document discusses different methods of controlling the speed of DC motors, focusing on pulse width modulation (PWM). PWM works by rapidly switching the voltage to the motor on and off to vary the average power and control motor speed. A higher duty cycle (proportion of time the voltage is on) results in a higher average voltage and faster motor speed. Examples are provided of calculating duty cycles and switching frequencies for different speed control applications.

1. Industrial Electronics DEK 3113 DC motor speed control

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4. Multi-Axis Conveyor System Vertical Operation Feeding Materials Rotational Operation Variable Speed Conveyor Applications for Speed Control Systems

11. Speed control circuit -When Q1 is ON,Ia will go through La and motor will start to move.At this time La will start to charge and magnetic field exist. -When Q1 is OFF after ON, energy in La need to discharge. This is done by discharge through D1. -This kind of circuit is for safety so Q1 is not damage by very high voltage or current. -Please refer to Figure 6.9 for full bridge circuit for reverse and forward movement of motor.

12. Chopper -the relatives ON-OFF thyristor determine the average of the motor. -when thyristor is ON,Ia will flow through L and motor will start to move. -when motor is move until around 75% speed of motor,commutating switch will closed. This will caused thyristor off. -when thyristor off after time t1,armature current decline through freewheeling diode as energy stored in a circuit inductance is applied to the armature. -motor will slow down(since thyristor OFF),then commutating switch will be open and thyristor ON again. -diode serve a path to maintain the armature current which no longer flow through external circuit. -as the ratio ON/OFF increased,the average motor Vm rises. -This process will be repeated.