Motor Controllers Information

Motor controllers receive supply voltages and provide signals to motor drives that are interfaced to motors. They are used to start, stop, and run motors in a programmed manner. Motor controllers can be used to gradually start or increase the speed of a motor, increase torque, or reverse rotational direction of the motor. They can also be used to reduce cost by using smaller wire and reduced-amperage devices to control the motor. Controllers are used due to the demands of the operating system, installation requirements, or to increase motor efficiency.

There are two basic types of controllers: electronic and electromechanical.

  • Electronic units are very sophisticated and include features such as soft starting and variable frequency drives. Electronic units can be programmed to respond to system inputs and pre-set running conditions.
  • Electromechanical units make use of electromagnetic contractors or relays to stop, start, and reverse the motor's direction.

Motor controller components include a power supply, amplifier, user interface, and position control circuitry. Below is a video which describes the motor controller system. 

Drive Type

Drive type describes the category of motor system that is driven or controlled.

  • Brushed motors commutation with physical contacts.
  • Brushless motors do not use physical contacts.
  • Induction motors induce current into the rotor windings without any physical connection to the stator windings.
  • Synchronous motors are non-slip devices that operate at constant speed up to full load. They include both reluctance motors and servomotors.
  • Pole changing motors (PCM) use pole number control, a method for changing the number of poles on the primary winding.
  • Vector drive motors provide independent control of both the voltage and frequency. In some designs, encoders or resolvers are used to provide feedback about position and speed.
  • Linear motors generate force in only the direction of travel. Common technologies include moving coil and moving magnet designs.
  • Many types of stepper motors use motor controllers
    • Full-step motors
    • Half-step motors
    • Mini-motors
    • Micro-motors
    • Unipolar stepper motors
    • Bipolar stepper motors
  • Pneumatic motion control systems
  • Hydraulic motion control systems

Selection Criteria

The Engineering360 SpecSearch database allows industrial buyers to select motor speed controllers by product specifications, electrical specifications, operating parameters, and features.

Electrical Specifications

Electrical ratings include

  • Maximum output voltage is the voltage that the device outputs. This output must match the system's processes.
  • Rated power is the maximum power to be used with the motor.
  • Continuous output current is the term used to describe the current which a device will carry continuously in air without exceeding temperature limits.
  • Peak output current is the capacity current output for a short period of time
  • AC supply voltage is the range of AC input voltage that will operate the drive or controller.
  • DC supply voltage is the range of DC input voltage that will operate the drive or controller.
  • Motor controllers use either 50, 60, or 400 Hz AC input frequency. Input frequency is the frequency the controller will accept from the motor.
    • Single-phase inputs are used for lower voltage applications and is the more common phrase.
    • Three-phase inputs are used for higher voltage applications. They can be used to overcome high starting loads by starting the motor with higher torque. When the initial inertial load is overcome, they switch to a more efficient low-torque delta configuration.
  • Computer-based motor controllers use many different types of buses and communication standards.
    • Bus types include advanced technology attachment (ATA), peripheral component interconnect (PCI), integrated drive electronics (IDE), industry standard architecture (ISA), general-purpose interface bus (GPIB), universal serial bus (USB), and VersaModule Eurocard bus (VMEbus).
    • Communications standards include ARCNET, AS-i, Beckhoff I/O, CANbus, CANopen, DeviceNet, Ethernet, small computer systems interface (SCSI), and smart distributed system (SDS). Many serial and parallel interfaces are also available.

Operating Parameters

Operating parameters include specifications for

  • Setup and control describes how the controller is operated by the user.
    • Manual controls such as
      • Knobs
      • DIP switches
      • Jumpers
      • Potentiometers
    • Computer controlled or aided, including
      • Joystick
      • Digital control panel
      • Computer interface
      • Slots for PCMCIA cards
  • Control programs are stored on removable, nonvolatile storage media.
  • Hand held devices are designed to be programmed remotely.
  • Wireless and web-enabled controls are also available.
  • Configurations for motor controllers include several mounting styles. Most devices mount on a
    • Chassis
    • DIN rail
    • Panel
    • Rack
    • Wall
    • Printed circuit board (PCB)
    • Standalone devices
    • Integrated circuit (IC) chips that mount on PCBs


Motor speed controllers are available with several different feature options.

  • Soft start is controlled circuitry, which allows the motor to ramp up to full speed over time. This is often a safety feature for motors moving large or delicate loads, and as a preventive measure for excessive current draw.
  • Braking

Dynamic braking is the method of the braking in which the power supply is disconnected from the motor windings. The motor then essentially becomes a generator and the power (heat) is dissipated through a resistor shunt across the windings.

Injection braking is applicable to AC motors only. The AC power is disconnected and the DC power is "injected" into the windings. This creates a magnetic field opposing the motor rotation and slowing or stopping the motor.

Regenerative braking is similar to dynamic braking. The motor is removed from the power and the power generated from the rotating motor is sent back to the supply. The generated power can be used to recharge a battery that supplies the power to the system.

  • Brake output is a switch or relay designed to activate or control an external brake
  • Home/limit switch inputs are used to indicate start, stop, or end-of-travel positions of the associated axes.
  • Auxiliary input/output channels can be included for communications with or feedback from the device
  • Status monitoring functions include an alarm and monitor one or more parameters. In the case of a fault or non-compliant operation, such as overvoltage, overcurrent, overspeed production, and temperature changes, a signal will be generated to alert the operator.
  • Self-configuration or auto-tuning devices will detect operating conditions and automatically adjust its setting for optimal system performance.
  • Self-diagnosing motor speed controllers can detect system problems and report the problem to the operator or control system.
  • Electric vehicle design is used for control of electric motors in industrial, recreational, or other electric vehicles. Many include application-specific features such as reverse alarm output, signal for speedometers and tachometers.


Selecting motor controllers requires an analysis of application categories. Motor speed controllers are application-specific devices used to control machines such as conveyors.

Multi-axis controllers are used to control and monitor multiple, independent axes of motion

Robotic motion controllers use digital motion control hardware and software for the coordinated multi-axis control of industrial robots and robotic systems

Servo amplifiers are electronic modules that convert low level analog command signals to high power voltages and currents

Inverter drives convert AC power inputs to DC outputs

High frequency drives supply power to AC motors at frequencies that are considerably higher than those used in standard-power applications

Regenerative drives support motor braking

Variable speed drives support speed control and adjustment

Microcontrollers are computer systems on a chip where real-time manipulation of large amounts of digital data is required in order to improve or modify it. They are used for fast and high resolution motion control, and special programming equipment is used to program the DSP chip.

Silicon controlled rectifiers (SCR) are used in DC motor drives to rectify the AC input to produce the DC current drive.


Digital signal processors (DSP)are microprocessors which use real-time data, such as audio, video, temperature, pressure, or position and mathematically manipulate the digital data to improve or modify it. They are used for fast and high resolution motion control, and special programming equipment is used to program the DSP chip.


Pulse width modulation (PWM) is also known as Scalar of V/F Control. A PWM drive converts AC voltage and frequency to DC and then uses a PMW to simulate a sine wave. PMW drives are not suited for producing high torque at low speeds because torque and speed are controlled indirectly.



Basic Principles of Motor Control

What is Motor Control?


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