This application note introduces a low cost sinusoidal control method for BLDC motors with Hall sensors using ST7FMC. This method can reduce the motor's noise and power consumption, and improve the motor's efficiency.
The document explains how to control Permanent Magnet Synchronous Motors (PMSM) as three-phase AC motors rather than traditional trapezoidal BLDC motors. This approach reduces audible noise, core losses, and power circuit dimensioning while improving efficiency compared to rectangular current drive methods.
It details an experimental implementation using the ST7FMC microcontroller for a three-phase PMSM with Hall sensors. The guide covers speed and absolute position estimation techniques (division method and PLL), PI controller configuration for closed-loop control, and load angle compensation to achieve unity power factor operation.
Controlling a PMSM as an AC motor results in sinusoidal currents which produce lower audible noise, lower core losses, and allow for optimized power circuit dimensioning compared to rectangular currents.
The microcontroller calculates rotor speed based on the time difference between two consecutive Hall sensor edges, which corresponds to a specific electrical angle (e.g., 60 degrees for three sensors).
Load angle compensation varies linearly with speed to maintain close to unity power factor at all speeds and results in appreciably lower phase currents and DC link currents under the same load conditions.