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AC Induction Motors (ACIMs)

The AC Induction Motor (ACIM) is the workhorse of the motor world. It is the most common motor type, used in everything from consumer products to heavy industry. Its simple design with no brushes makes it highly reliable and allows it to be manufactured at a low cost. However, it is less efficient than other motors like the Permanent Magnet Synchronous Motor (PMSM), which is partially related to the heat generation in the rotor windings. The open-loop Voltage/frequency (V/f) drive technique is traditionally used to control ACIMs, and it can be implemented on simple 8-bit PIC® and AVR® microcontrollers (MCUs). This drive technique is not very efficient, so for applications that need higher efficiency, an advanced control solution like Field-Oriented Control (FOC) can be applied. Implementing this advanced control requires high-performance dsPIC33 Digital Signal Controllers (DSCs) or 32-bit PIC32MK or SAM MCUs.

Applications

  • Blowers
  • Home appliances
  • Pumps
  • Air conditioner and refrigerator compressors
  • Automation/industrial applications
  • Power tools

Recommended Products for AC Induction Motor Control

ProductsOn-Off
Control
TRIAC-Phase
Control
Variable
Frequency
(V/Hz, V/f)
Sensored
FOC
Sensorless
FOC
Microcontrollers
(MCUs).
Digital Signal
Controllers
(DSCs) and
Field-Programmable
Gate Arrays (FPGAs)
8-bit PIC® and AVR® MCUs  
  dsPIC33 DSCs
  32-bit PIC32MK and SAM MCUs
  IGLOO®2 FPGAs
  SmartFusion® SoC FPGAs

 

3-Phase Gate DriversMIC4604
MIC4605
MIC4607

How an ACIM Works

The ACIM, sometimes called a squirrel cage motor, is one of the most popular motors used in consumer and industrial applications. Induction machines are by far the largest group of all industrial electrical machines, converting approximately 70-80% of all electrical energy into mechanical form. They have a very robust rotor construction, which makes them suitable for high-speed applications. With proper design, they have good overloading and field weakening characteristics.

The ACIM is comprised of a simple cage-like rotor and a stator containing three windings. The changing field produced by the AC line current in the stator induces current in the rotor which interacts with the field and causes the rotor to rotate. The rotor does not have any moving contacts, which eliminates sparking.

BrushedDCMotorDesignFlowchart

Implementing ACIM Control

How It Works

The AICM is comprised of a simple cage-like rotor and a stator containing three windings. The changing field produced by the AC line current in the stator induces a current in the rotor which interacts with the field and causes the rotor to rotate. No brushes are necessary in this design. The base speed of the AC motor is determined by the number of poles built into the stator windings and the frequency of the AC input voltage. Variable speed control of an AC motor can be accomplished by increasing or decreasing the input frequency.

A load on the motor causes the motor to slip in proportion to the load. The slip occurs when the rotor turns at a slower speed than the rotating field produced by the stator. This slip is responsible for energizing the rotor. The ACIM is available in single-phase and three-phase versions. A three-phase ACIM is usually the best choice for variable-speed applications.

Microcontroller Features for ACIM Control

InputDigital or analog input signals for speed, frequency position, direction
Capture/Compare/Pulse-Width Modulation (CCP)Generation of space vector PWMs for three-phase inverter and speed sensing using input capture
ComparatorsOvercurrent detection and protection
Analog-to-Digital Converter (ADC)Measurement of phase current for torque control and for sensorless control, measurement of voltage for inverter and measurement of analog input signals
Quadrature Encoding Interface (QEI)Optical encoder interfacing for position sensing
Communication Peripherals (I2C, SPI, CAN)Torque, speed, position and/or direction information exchange

ACIM Control Considerations:

  • Smooth control at low speeds
  • Efficient control at high speeds
  • Variable speed and torque control using complex vector control
  • Eliminate rotor position sensor using sensorless vector control strategies
  • Must know rotor position (velocity) for slip and vector control
  • Sensorless control does not work at low motor speeds

FPGAs for Multi-Axis Motor Control

Build safe and reliable multi-axis deterministic motor control on a single System-on-Chip (SoC) FPGA. FPGAs provide many advantages for motor control applications, including:

  • Compact solution to save board space and reduce product size
  • Motor speeds exceeding 100,000 RPM for sensorless Field Oriented Control (FOC).
  • Low latency of 1 μs for FOC loop from ADC measurement to PWM generation allows switching frequencies up to 500 kHz
  • Design flexibility with modular IP suite
  • Advanced safety features such as rotor slip, overload detection and overcurrent protection
  • SoC integration of system functions reduces Total Cost of Ownership (TCO)

Motor Control Hardware and Software Solutions

Featured Software Tools

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Motor Control Application Algorithm and Application Software

To support the development of motor applications, we provide motor control libraries and examples for Field-Oriented Control (FOC), windmilling, DC-link compensation, field weakening and many other control algorithms.

Motor Control Library Diagram

Motor Control Library

The Motor Control Library contains FOC function blocks that are optimized for the dsPIC33 families of DSCs. The library functions are designed to be used within any application framework, providing an efficient and flexible solution for implementing a motor control application.

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MPLAB® X Integrated Development Environment (IDE)

MPLAB X Integrated Development Environment (IDE) is an expandable, highly configurable software program that incorporates powerful tools to help you discover, configure, develop, debug and qualify embedded designs for Microchip’s microcontrollers and digital signal controllers.

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MPLAB Code Configurator (MCC)

MPLAB Code Configurator (MCC) is a free, graphical programming environment that generates seamless, easy-to-understand C code to be inserted into your project.

Featured Hardware Tools

dsPICDEM MCHV-3 High-Voltage Motor Control Development Board

dsPICDEM MCHV-3 High-Voltage Motor Control Development Board