This document describes the implementation of a current regulator for BLDC motor control. It provides an overview of various approaches for obtaining current feedback and analyzes the limitations of each approach. The document also presents a simple, linear, and cost-effective method of implementing the inner current loop by sampling the DC link current at the mid-point of PWM 'on time' with ST7FMC. Experimental results are also discussed.
The document outlines various approaches for obtaining current feedback in BLDC motor control, analyzing the limitations of regulating average DC link current, monitoring all three winding currents, and regulating peak current. It identifies sampling the DC link current at the midpoint of the PWM on-time as a simple, linear, and cost-effective solution for torque control.
The note details the implementation of this approach using the ST7FMC microcontroller's motor control macro cell. It explains how the U event interrupt, which occurs at the center of the PWM on-time, is used to read the instantaneous DC link current to derive the average phase current. The document includes experimental results and schematic diagrams for a sensorless control setup.
The system samples the DC link current at the midpoint of the PWM on time to determine the average load current.
The typical conversion time is approximately 3-4 microseconds.