What type of motor controller uses a solid state and other devices to regulate speed?

A variable speed controller utilizes solid-state devices primarily to regulate the speed of electric motors. This is achieved by manipulating the voltage and current supplied to the motor, often employing techniques like pulse-width modulation (PWM). By adjusting these parameters, the controller can effectively change the motor's operating speed without the need for mechanical alterations to the motor or drive system.

In contrast, while a direct-on-line starter is designed to start a motor by directly connecting it to the power supply, it does not modulate speed and is primarily used for simple operations. A capacitor start motor employs a capacitor to enhance starting torque and is generally fixed in speed. An induction motor controller, while it can regulate speed, does so in a different manner and may not always employ solid-state devices, making it less applicable as a general term for variable speed regulation. Thus, the focus of variable speed controllers on solid-state technology is fundamental to their operation in varying motor speeds efficiently.