AN2388 Datasheet, PDF (1/54 Pages) STMicroelectronics – Sensor field oriented control

AN2388
Application note
Sensor field oriented control (IFOC)
of three-phase AC induction motors using ST10F276
Introduction
AC Induction motors are the most widely used motors in industrial motion control systems,
as well as in home appliances thanks to their reliability, robustness and simplicity of control.
Until a few years ago the AC motor could either be plugged directly into the mains supply or
controlled by means of the well-known scalar V/f method. When power is supplied to an
induction motor at the recommended specifications, it runs at its rated speed. With this
method, even simple speed variation is impossible and its system integration is highly
dependent on the motor design (starting torque vs maximum torque, torque vs inertia,
number of pole pairs). However many applications need variable speed operation. The
scalar V/f method is able to provide speed variation but does not handle transient condition
control and is valid only during a steady state. This method is most suitable for applications
without position control requirements or the need for high accuracy of speed control and
leads to over-currents and over-heating, which necessitate a drive which is then oversized
and no longer cost effective. Examples of these applications include heating, air
conditioning, fans and blowers.
During the last few years the field of electrical drives has increased rapidly due mainly to the
advantages of semiconductors in both power and signal electronics and culminating in
powerful microcontrollers and DSPs. These technological improvements have allowed the
development of very effective AC drive control with lower power dissipation hardware and
increasingly accurate control structures. The electrical drive controls become more accurate
with the use of three-phase currents and voltage sensing.
This application note describes the most efficient scheme of vector control: the Indirect Field
Oriented Control (IFOC). Thanks to this control structure, the AC machine, with a
speed/position sensor coupled to the shaft, acquires every advantage of a DC machine
control structure, by achieving a very accurate steady state and transient control, but with
higher dynamic performance.
In this document we will look at the complete software integration and also the theoretical
and practical aspects of the application.
October 2006
Rev 1
www.st.com
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