AN2281 Datasheet, PDF (1/38 Pages) STMicroelectronics – Low cost self-synchronizing PMAC motor drive using ST7FLITE35

AN2281
Application note
Low cost self-synchronizing PMAC
motor drive using ST7FLITE35
Introduction
Due to their high efficiency, power by size ratio and silent operation, Permanent Magnet AC
(PMAC) motors are increasingly used in many applications. They are becoming the
predominant type of motor used in applications where the above advantages are required,
especially fans, compressors and pumps.
Since PMAC motors are synchronous machines, to get the best efficiency from them, the
excitation must be switched from one motor phase to another in exact synchronism with the
rotor motion. This concept, commonly known as self-synchronization, uses direct feedback
of the rotor angular position to ensure that the PMAC machine never loses synchronization.
This application note describes a low-voltage single-sensor three-phase AC permanent
magnet motor, also known as PMAC or BLAC (brushless AC) control system.
It includes a depiction of:
● Reference schematics, which can be used for up to 12V-50W PMAC motors and based
on ST7LITE35 microcontroller and on STS8C5H30L complementary P-channel and N-
channel MOSFETs,
● Firmware library, developed with the Cosmic C compiler and STVD7 release 3.x.x. It is
composed of several C modules containing a set of convenient functions for sinusoidal
waveform generation, synchronization mechanism and closed loop control of PMAC
motors.
March 2006
Rev 1
1/38
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