Motor Drives and Their Types

Motor drives are electronic devices that control torque, position outputs, and manage motor speed. They are available in a variety of forms and are used to power machines, robots, equipment, and other machinery. That being said, this blog will outline motor drives, allowing you to better understand their purpose and importance.

To begin, it is important to preface this blog by detailing that the terms “motor controllers” and “motor drives” are often used interchangeably since controller circuits are normally combined with drive circuits to produce a single unit. More than that, there are varying types of motors and motor drives. The four most common types of motor drives include DC, AC, stepper, and servo variations. Each type is equipped with input power types that are tailored to the output function of their applications.

DC Drives

DC motor drives convert alternating current into direct current to power a DC motor. Typically, DC drives are power modules that serve as an interface between a DC motor and a controller. In most cases, the motor is supplied with a controller to help power the control signals that communicate with the drive. DC drives are often called variable speed drives as most types have the ability to adjust shaft speed. Furthermore, they are characterized by their dependable speed regulation, broad speed range, and voltage transfer capabilities.

DC drives are used to power the following motors:

-      Linear motors

-      Brushed motors

-      Brushless motors

AC Drives

AC drives convert AC inputs to DC. Shortly after this conversion, the DC current is converted back into AC to fuel the motor. Essentially, they are frequency inverters or amplifiers that serve as an interface between an AC motor and controller. It makes the voltage compatible with the motor by converting the controller’s step and direction inputs into the desired voltage. They are often called variable frequency drives as the majority of AC motor drives adjust input frequency.

AC drives are used to power the following motors:

-      Synchronous motors

-      Induction motors

-      Sensorless vector drives

Servo Motor Drives and Controllers

Exclusively used to power servo motors, servo drives help generate precise movements to rotate parts of your machine. They modify the input power via an alternating or constant current source and turn it into a pulsed current output that ranges in pulse frequency and duration. This series of movements control position, torque, and motor speed. There are two primary types of servo motors. Standard servo motors offer great speed and power to the motor system. In contrast, small servo motors do not supply a lot of power but work for compact spaces.

Stepper Drive

A stepper motor drive and controller change alternating or constant current sources into a stepped current output that adjusts the stepper motor’s input power. Often called step amplifiers or pulse drives, stepper motor drives monitor and adjust input power through permanent magnets. Moreover, there are poles in the stator and rotor that transmit DC current to help generate stepwise rotation. Since a stepper drive’s rotational output is not continuous, the input power must be controlled in a way that allows groups of stator poles to either energize or de-energize. Steppers are used in a wide range of applications, some of which include micro-positioning, robotics, medical equipment and more.  


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