Permanent magnet synchronous motors (PMSMs) need magnetic flux position feedback for the torque or speed control algorithm. Conventionally, this magnetic flux position feedback system consists of N pairs of permanent magnets arranged in a ring shape and two Hall sensors. This position feedback system has many problems associated with it—including inaccurate magnetic pole lengths, inaccurate distribution of magnetic field strength along the magnetic rings, electromagnetic field influence on the Hall sensors, inaccurate axial position of two Hall sensors, error due to radial separation between two Hall sensors, and temperature and applied voltage variation between two Hall sensors—that produce inaccuracies in magnetic flux position calculation. The N pair of magnetic poles and ring structure make this setup very expensive.
This session presents a new setup consisting of a cam mounted on a rotor shaft, a pair of magnetic poles, a single 2-axis Hall sensor mounted on cam link rod, and software algorithms to calculate accurate magnetic flux position. The cam has grooves equal to half of the number of pole pairs. A one-way trip of the Hall sensor over the magnetic pole pair will determine the position of the rotor permanent magnetic field for one pole pair. This setup can be outside the motor casing, reducing electromagnetic influences on Hall sensor signals.
