AN1162 - Sensorless Field Oriented Control (FOC) of an AC Induction Motor (ACIM)

AN1162 Sensorless Field Oriented Control (FOC) of an AC Induction Motor (ACIM) operate at a speed that is roughly proportional to the Author: Mihai Cheles input frequency. As you decrease the frequency of the Microchip Technology Inc. drive voltage, you also need to decrease the amplitude Co-Author: Dr.-Ing. Hafedh Sammoud by a proportional amount. Otherwise, the motor will APPCON Technologies SUARL consume excessive current at low input frequencies. This control method is called Volts-Hertz control. The benefits of field oriented control can be directly INTRODUCTION realized as lower energy consumption. This provides higher efficiency, lower operating costs and reducesThe requirement of low-cost, low-maintenance, robust the cost of drive components.electrical motors has resulted in the emergence of the AC Induction Motor (ACIM) as the industry leader. In sensorless field oriented control, the speed and/or Typical applications requiring the use of an induction position are not directly measurable; their values are motor drive range from consumer to automotive estimated using other parameters such as phase applications, with a variety of power and sizes. voltages and current, that are directly measured. Where efficiency, low cost, and control of the induction For additional information on the ACIM modeling motor drive is a concern, the sensorless Field Oriented equation and other induction motor topologies, see Control (FOC), also known as vector control, provides "References" for a complete list of related the best solution. The term "sensorless" does not documentation available from Microchip. represent the lack of sensors entirely, but the fact that in comparison with other drives from the same category Control Strategy of field oriented control, it denotes that the speed and/or position sensor is missing. This feature Traditional control methods, such as the Volts-Hertz decreases the cost of the drive system, which is always control method described above, control the frequency desired, but this is not the only reason for this and amplitude of the motor drive voltage. In contrast, approach, as some applications have requirements field oriented control methods control the frequency, concerning the size, and the lack of additional wiring for amplitude and phase of the motor drive voltage. The sensors or devices mounted on the shaft (due to hostile key to field oriented control is to generate a 3-phase environments such as high temperature, corrosive voltage as a phasor to control the 3-phase stator contacts, etc.). current as a phasor that controls the rotor flux vector and finally the rotor current phasor. The intent of this application note is to present one solution for sensorless Field Oriented Control (FOC) of The key to understanding how field oriented control ® Digital Signalinduction motors using a dsPIC works is to form a mental picture of the coordinate Controller (DSC). reference transformation process. If you picture how an AC motor works, you might imagine the operation from the perspective of the stator. From this perspective, a OVERVIEW sinusoidal input current is applied to the stator. This time variant signal causes a rotating magnetic flux to be AC Induction Motor generated. The speed of