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A 3-phase induction motor uses current delivered in three phases in a sequence into the coils of a stator to create a rotating magnetic field. This induces an electric field in a coil or squirrel cage to drive a rotor. The difference in speed between rotor, the synchronous speed and the rotating magnetic field is called the slip.

We offer the entire range of power semiconductors and ICs 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.

To help reduce and simplify the design cycle, we offer a complete ecosystem of hardware, evaluation boards and reference designs, as well as firmware and software libraries.

    • In a 3-phase AC induction motor, there are three stator windings, each usually in two halves, with the rotor winding short-circuited by end rings. As the current passes through the coils on opposite sides of the stator, a two-pole electromagnet is established, creating a two-pole motor. Applying a phase to each of the electromagnets in turn creates the rotating magnetic field that is strong enough to start moving the rotor.

      three phase ac induction motor

      More winding can create more poles in the motor, with more complex control required but more accuracy in positioning the rotor. A four-pole motor is regarded as optimum for the torque and responsiveness needed to for the motor drives of electric cars, for example. But higher pole counts are only possible with more sophisticated control schemes.

      The typical drive has three half-bridges, each delivering a sine-wave voltage to the stator. This uses power MOSFETs or IGBTs with high-voltage gate drivers, or power modules that combine the three half-bridges and related gate drives. These can use scalar algorithms that vary the voltage to determine the frequency of the phases, or volts/hertz. More sophisticated algorithms such as vector control or Field-Oriented Control (FOC) are used to control the frequency of multiple phases in high-end motors are now increasingly popular across the range of three-phase induction motors.

      Polyphase motors generally cover three-phase motors using multiple poles.

    • A soft-start controller is used in three-phase AC induction motors to reduce the load on the self-starting motor and the current surge of the motor during start-up. This reduces the mechanical stress on the motor and shaft, as well as the electrodynamic stresses on the attached power cables and electrical distribution network, extending the lifespan of the system.

      Induction motors can have inrush currents seven to ten times that of the operational current. Starting torques can be 3 times higher to overcome the starting conditions, causing mechanical stress on the components in the motor. So electronic soft starters use a control system to reduce the torque by temporarily reducing the voltage or current input until the induction motor reaches its synchronous speed.

      A digital soft-starter controller continuously monitors the voltage during start-up, adjusting to the load of the motor to provide a smooth acceleration and the speed control. This is often done with connected silicon-controlled rectifiers (thyristors) controlling each phase separately to give the optimum control.

    • The torque generated in the rotor of a 3-phase induction motor is proportional to the flux generated by each stator pole, the rotor current and the power factor of the rotor. Direct torque control (DTC) is a technique used in variable frequency drives. It comes from estimating the magnetic flux from the voltage and current of the motor. This is compared to a reference value to control the torque.

      This allows the flux and the torque to be changed quickly by changing the references, making the motor more efficient and reducing power losses as only the exact current is used. This also avoids the rotor overshooting, allowing more accurate control over the motor.

    • Three-phase induction motors are a key part of almost every industrial process. So there are many methods for fault detection and diagnosis to make sure that the motors keep the production lines running.

      However, despite the high level of reliability of these motors, most of the methods require a good deal of expertise to apply successfully, looking at the voltage, current, vibration or the thermal profile. Simpler approaches are needed so that any line operators can make reliable decisions. And motor makers want to reduce the number of sensors in the motor as they can fail and cause reliability problems.

      Rotor faults may occur during production as small faults, or may result from production faults or mechanical, environmental, electromagnetic or thermal pressure on the rotor when the motor runs. Even if these faults are small at first, the faults grow over time, and a broken or cracked rotor can cause neighboring components to fail from increased currents and thermal activity.

      Machine learning is increasingly being used to monitor the performance of motors, comparing the patterns of different types of data used in the control systems to predict any potential failure.

Block diagram: 3-phase induction motor control

Featured Products

    • This starter kit is particularly suited to drive 3-phase brushless motors (either AC induction or permanent magnet types) and demonstrates how effectively the STM8 microcontrollers can be used in real-world motor control applications.
      Solution Components
      Part Number Description Status Core Products Price (US$)*
      Order / Download
      STSW-STM8041
      Configuration software for STM8S motor control kit
      Active
      -
      Software
      Part Number Marketing Status Supplier Software Version Download
      STSW-STM8041 Active ST 1
      STSW-STM8042
      STM8S motor control firmware library builder
      Active
      -
      Software
      Part Number Marketing Status Supplier Software Version Download
      STSW-STM8042 Active ST 1.0.2
      STSW-STM8041

      Description:

      Configuration software for STM8S motor control kit

      Price (US$)*

      -
      Software
      Part Number Marketing Status Supplier Software Version Download
      STSW-STM8041 Active ST 1
      STSW-STM8042

      Description:

      STM8S motor control firmware library builder

      Price (US$)*

      -
      Software
      Part Number Marketing Status Supplier Software Version Download
      STSW-STM8042 Active ST 1.0.2

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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
      AN4768
      SLLIMM™ 2nd series small low-loss intelligent molded module
      4.0
      23.7 MB
      PDF
      AN3338
      SLLIMM™ small low-loss intelligent molded module
      5.0
      4.15 MB
      PDF
      AN4840
      SLLIMM™-nano 2nd series small low-loss intelligent molded module
      1.0
      3.63 MB
      PDF
      AN4043
      SLLIMM™-nano small low-loss intelligent molded module
      2.1
      4.83 MB
      PDF
      AN1904
      ST7MC three-phase AC induction motor control software library
      3.4
      1.12 MB
      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

      AN4768

      SLLIMM™ 2nd series small low-loss intelligent molded module

      AN3338

      SLLIMM™ small low-loss intelligent molded module

      AN4840

      SLLIMM™-nano 2nd series small low-loss intelligent molded module

      AN4043

      SLLIMM™-nano small low-loss intelligent molded module

      AN1904

      ST7MC three-phase AC induction motor control software library

    • Description Version Size Action
      TN1221
      Mounting instruction for SLLIMM™ -nano 2nd series (N2DIP-26L)
      1.0
      542.38 KB
      PDF
      TN1220
      Mounting instruction for SLLIMM™ 2nd series (SDIP2F-26L full molded and SDIP2B-26L DBC based)
      1.0
      604.33 KB
      PDF
      TN1037
      SLLIMM™-nano mounting instructions and heatsink
      3.0
      1.21 MB
      PDF
      TN1221

      Mounting instruction for SLLIMM™ -nano 2nd series (N2DIP-26L)

      TN1220

      Mounting instruction for SLLIMM™ 2nd series (SDIP2F-26L full molded and SDIP2B-26L DBC based)

      TN1037

      SLLIMM™-nano mounting instructions and heatsink

    • Description Version Size Action
      RN0010
      ST7MC three-phase AC induction motor control software library Release 2.0
      2.5
      114.75 KB
      PDF
      RN0010

      ST7MC three-phase AC induction motor control software library Release 2.0

    • 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

Publications and Collaterals

    • Description Version Size Action
      ACEPACK™: Adaptable, Compact, and Easier Packages Power Modules 1.0
      818.5 KB
      PDF
      ST PowerStudio;The dynamic electro-thermal simulation software for power devices 1.0
      290.77 KB
      PDF
      T2550-12 Snubberless™ Triacs: 25 A, 1200 V SMD/Insulated Triacs for compact AC motor drive 1.0
      1.8 MB
      PDF

      ACEPACK™: Adaptable, Compact, and Easier Packages Power Modules

      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

    • Description Version Size Action
      Motor Control Reference Guide 15.10
      2.61 MB
      PDF
      STM32F3 series - Mainstream 32-bit MCUs 17.09
      2.18 MB
      PDF

      Motor Control Reference Guide

      STM32F3 series - Mainstream 32-bit MCUs

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