Design Process

Possible Designs - PWM vs. MCU

NAU Motor Systems formulated two major designs for their motor controller, one designed around a microcontroller and the other using a pulse width modulation (PWM) IC. Below are short descriptions of both designs.

PWM

A pulse width modulation IC internally generates a pulse waveform. This waveform is output to a pin on the IC and is used to control the MOSFET drivers. A PWM chip has an input that controls the frequency of the pulse via a resistor. For this design a variable resistor known as a potentiometer is used. The specific type of potentiometer used in this design is called a throttle pot and is the device of choice used for controlling the speed of electric cars. Some PWM chips have specific inputs used to stop the pulse output used for safety reasons. For this design choice a current sensor would be used to indicate to the PWM chip when an overload of current is passing to the motor to shut the system down. PWM ICs are more inexpensive that microcontrollers.

Microcontroller

With a microcontroller design the pulse waveform is created via software. The device would still use a potentiometer to control the frequency of the waveform, but this would also require software control. The device would offer many more features such as rpm calculation, monitoring of each MOSFET individually for failure and software controlled motor direction for reverse via motor and not transmission. The client can benefit from much more control of the system via software if using this design but the cost of a microcontroller is much higher than a PWM IC.