Motor speed controllers are electronic devices that control motor speed. They take a signal for the needed speed and drive a motor to that speed. There are a variety of motor speed controllers available.

DC Motor Power-Op-Amp Speed Controller. Video Credit: Engamsi

Drive Type

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

Choices for alternating current (AC) motors include:

• Induction motors
• Synchronous motors
• Pole number control drives
• Sensor-less vector drives
• Vector or feedback drives
• Servos or brushless motors

Choices for direct current (DC) motors include

• Brushed motors
• Brushless motors
• Servomotors

Drive-type categories for stepper motors include

• Unipolar stepper
• Bipolar stepper
• Permanent magnet stepper
• variable reluctance stepper
• Hybrid stepper
• Full-step
• Half-step
• Mini-step
• Micro-step products

Additional drive types include:

• Linear motors
• Voice coil motors
• Pneumatic motors
• Hydraulic motors

Selection Criteria

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

Product Specifications

There are four product classification specifications for motor speed controllers:

• Number of axes or motorsthe device can control.
• Rated power is the maximum power to be used with the motor.
• Resolution describes the number of binary digits (bits) the device uses to characterize an analog signal.
• Bus type for computer-based products, are used to transmit data within and between computer systems and the controller.

Electrical Specifications

Selecting motor speed controllers requires an analysis of electrical specifications.

• Supply voltage (AC) is the range of AC input voltage that will operate the drive or controller.
• Supply voltage (DC) is the range of DC input voltage that will operate the drive or controller.
• Maximum output voltage is the voltage that the device outputs. This output must match the system's processes.
• 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 input phase
  • Single-phase is used for lower voltage applications and is the more common phrase.
  • Three-phase is used for higher voltage.
• AC input frequency is the frequency the device will accept. There are three choices for AC input frequency: 50, 60, and 400 Hz.

Operating Parameters

There are five main categories to consider for the operating parameter of the motor speed controller:

• Setup and control describes how the speed controller is operated. The users can implement a joystick, control panel, computer interface, disk, or wireless communication in order to control the speed of the motor. It is important to consider operating environment and ease of access when selecting a setup and control mechanism.
• Modes of operation include digital position feedback, analog feedback, velocity mode, and current (torque) mode.
• Motor feedback choices include Hall effect, resolver, tachometer, incremental encoder, absolute encoder, analog position, sine and cosine.
• Mounting style is the configuration of the controller. The device can be mounted onto a IC/PCB board, OEM module, panel, DIN rail, rack, PC board or it can stand alone. The mounting depends on the size of the system.

Features

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.

Applications

Multi-axis controllers can control multiple and/or monitor multiple independent axes of motion.

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

Microcontroller-based 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.

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.

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.

Variable speed drives are used for industrial motor applications to monitor and adjust speed.

References

Speed Controllers

A BEGINNER'S GUIDE TO DIGITAL SIGNAL PROCESSING

Image credits:

Ametek | Bodine Electric