Universal DC Motor Control Algorithms

Speed control of Universal Motors typically employs two schemes:

  1. Phase angle Control
  2. PWM Chopper control

Phase Angle Control

It is the simplest method to control the speed of a universal motor. Speed control is achieved by the varying the firing angle for the TRIAC. Phase angle control is very cost effective solution but not very efficient and prone to EMI.

Phase Angle Control of a Universal Motor

Figure above shows the Phase Angle Control mechanism typically employed for speed control of the TRIAC. A phase shift of the TRIAC gate's pulses allows the effective voltage, seen by the motor to be varied and hence the speed of the motor. A Zero Crossing Detection circuit is used to establish a timing reference for delaying the firing of the gate pulses.

PWM Chopper Control

PWM control is a more advanced solution for controlling the speed of a universal motor. In this method rectified AC line voltage is switched at a high frequency by a Power MOFSET or IGBT device to generate time varying voltage for the motor.

PWM Chopper Control of a Universal Motor

The switching frequency is usually in the range of 10 to 20 KHz so as to eliminate acoustic noise. This method of universal motor control can achieve better current control, better EMI behavior and hence more efficient.

 Control MethodsMCU RequirementsSuggested MCUs
RL78 FamilyRX FamilyRH850 FamilyRZT1 Group
Universal / DC Motor ControlTRIAC ControlGPIO, Timers, Interrupts, A/D Channels   
PWM Chopper ControlPWM Channel, Timers, A/D Channels