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An AC induction motor is one of the simplest and most reliable types of electric motor, with the power ranging from a few watts to many kilowatts. There are many different ways to design and control such motors, from low cost with a single-phase input to high accuracy with a polyphase approach, and this type of system is the most widely used motor across the consumer and industrial markets.

We offer the entire range of power semiconductors including discrete IGBTs and power MOSFETs as well as power modules and intelligent power modules (IPM), high-voltage gate drivers and powerful STM32 microcontrollers needed to implement high-efficiency variable-frequency drive (VFD) motor control.

We have also developed a complete ecosystem with a range of evaluation boards, reference designs, firmware and development tools to help simplify and accelerate the design cycle.

    • induction motor An induction motor uses an alternating current in a stator, or stationary winding, to induce a magnetic field in a metal cage or wire winding as the rotor. The interaction of the electric and magnetic fields drives the motor without any connections between the moving parts via a slip ring, making it highly reliable.

      The motor speed control depends on the speed of rotation of the magnetic field, which depends on the frequency of the AC current and number of poles. The rotating magnetic field from the AC current in the stator results in a flux induced in the rotor, and the interaction of the electric and magnetic fields creates the rotation. As the induced current in the rotor lags the flux current in the stator, the rotor will never reach the full rotating magnetic field speed, also called the synchronous speed.

      A single-phase, constant-frequency AC current is used to drive smaller loads in household appliances, with the frequency producing a fixed speed. Variable Frequency Drives (VFDs) are used more in fans, pumps and compressors to enable the motor speed control. A three-phase induction motor provides a smoother motion with more control and accuracy of positioning for the motor, and there are designs of motors with five or more poles. These polyphase designs give higher accuracy for positioning the motor, allowing more precise delivery of fluids through pumps or positioning of blades of all kinds, but require more complex control systems. These motor control systems are also evolving from simple scalar systems to various types of field-oriented control (FOC) or vector control algorithms.

    • There are two main types of motor construction, one with a wound coil rotor and the other with a squirrel cage rotor. This squirrel cage rotor is a cylinder of steel laminations, with aluminum or copper conductors embedded in its surface where the magnetic field is induced.

      Both the wound coil and squirrel cage induction motors can be driven by a single- or three-phase AC current with a constant or variable frequency, giving a wide range of performance from small motors in the home to large industrial motors driving large pumps or compressors. This also leads to a wide range of control systems.

      A single-phase motor needs a starter configuration to provide the starting torque while a 3-phase motor can be inherently self-starting as the different phases can be manipulated to start the rotor moving. Power factor control and direct torque control can help to boost the performance of a three-phase induction motor drive.

      Single-phase induction motors

      A single-phase motor with a coil winding is the simplest type of AC motor but needs a starting mechanism. This leads to the three different types of single-phase induction motor: shaded-pole, split-phased, and capacitor motors.

      Starting the motor can be achieved by designing the stator with two windings, a main and auxiliary coil. Connecting a capacitor in series with the auxiliary winding means the current flows through both coils are out of phase. It is this phase difference that generates a torque to start the rotation.

      An electrolytic start capacitor is used to achieve the best phase angles between start and main windings and is disconnected from the start circuit when the motor reaches about 75% of full-load speed. It is designed for short-time duty, and using it for longer than necessary can cause problems, so the accurate control is essential.

      Shaded-pole induction motors

      A shaded-pole motor uses a squirrel cage rotor and usually range from 1/20th to 1/6th of a horsepower for small motors. This has additional windings in each corner of the stator, called shade windings. These are not connected but generate a current from the induced field. This inhibits the field, creating a low torque to get the motor moving.

      Split-phase induction motors

      A split-phase induction motor has two windings, a run winding and a secondary start winding, and usually operate up to 1/3 horsepower to drive blades on a ceiling fan, washing machines tubs, blower motors for oil furnaces, and small pumps.

      The higher power start winding gets the motor moving up to 75 to 80% of its speed, and then a centrifugal switch is used to switch over to the less powerful run coil to save energy.

      Single-phase AC motors are extremely common in all walks of life. The vast majority of motors powered by the household or light industrial mains supply are single phase.

      One of the keys is to size the motor correctly for the application. If the motor doesn’t generate enough torque for the design it will always be running at maximum, putting more strain on the components and generating too much heat. Similarly, if the motor is too big it will not operate efficiently and will waste energy.

      However, single-phase power sources can be used to generate a three-phase variable frequency supply to drive a 3-phase induction motor.

      A single-phase induction motor drive can also see torque ripple, which is a regular change in the output torque, and the difference between the maximum and minimum figure is often expressed as a percentage to highlight the controllability of the motor.

      Fault detection in single-phase induction motors usually requires sensors as there is not sufficient information to implement more complex sensorless algorithms.

3-phase Induction Motor (ACIM)
3-phase Induction Motor (ACIM)
Three-phase induction motors are brushless motors. The stator is copper-wound and the rotor is typically an aluminum squirrel cage...
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Single Phase AC Motor
Single Phase AC Motor
A single-phase AC induction motor is a brushless motor designed with a single stator coil. ST offers state-of-art, rugged...
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Technical Documentation

    • Description Version Size Action
      AN4694
      EMC design guides for motor control applications
      1.0
      2.13 MB
      PDF
      AN4606
      Inrush-current limiter circuits (ICL) with Triacs and Thyristors (SCR) and controlled bridge design tips
      2.2
      1,008.92 KB
      PDF
      AN4694

      EMC design guides for motor control applications

      AN4606

      Inrush-current limiter circuits (ICL) with Triacs and Thyristors (SCR) and controlled bridge design tips

    • Description Version Size Action
      DN0005
      A three phase induction motor drive using a V/F control
      2.1
      528.11 KB
      PDF
      DN0005

      A three phase induction motor drive using a V/F control

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      ACEPACK™ overview 1.1
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      ACEPACK™ overview

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      ACEPACK™: Adaptable, Compact, and Easier Packages Power Modules 1.0
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      SLLIMM™ 2nd Series Small Low-Loss Intelligent Molded Module 1.0
      1.38 MB
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      ST PowerStudio;The dynamic electro-thermal simulation software for power devices 1.0
      290.77 KB
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      T2550-12 Snubberless™ Triacs: 25 A, 1200 V SMD/Insulated Triacs for compact AC motor drive 1.0
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      ACEPACK™: Adaptable, Compact, and Easier Packages Power Modules

      SLLIMM™ 2nd Series Small Low-Loss Intelligent Molded Module

      ST PowerStudio;The dynamic electro-thermal simulation software for power devices

      T2550-12 Snubberless™ Triacs: 25 A, 1200 V SMD/Insulated Triacs for compact AC motor drive

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      Motor Control Reference Guide 15.10
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      Motor Control Reference Guide