DC motor speed controle thoery
November 19, 2009
I am struggling to grasp the principles of pulse width modulation, current stability and motor selection. To my understanding the pulse with modulation is the time period the current is switched on and off. This allows the motor to slow down and speed up but at a time frame that is considered as “smooth” for the motor and the current physical load that is on the motor. During this time the current will be with in a preset rang of units that are controlled by the oscillator and its frequency. Allowing for motor speed control.
Is my understanding correct?
Now for the real problem, I have no idea if this is correct but is the current stability percentage the time frame between the unit of time the current is on and off, or could it be seen like this? The only reason I am asking is because I figure if you draw a graph of the current and PWM the lowest values of the 2 graphs would be in unison with each other before a new PWM is produced and the current rises again. If this is your current stability percentage then it would explain to me why there is a limiting condition for the frequency of the PWM. How do I calculate the minimum frequency for a motor? Does it depend on the work load the motor has to do? Is the motor ripple the tolerance of the time frame that the motor is switch on and of giving a certain “dwell” period for the motor?
Please correct me if my understandings are not up to date or if something does not stick well.