BLDC Commutation Timing Using Linear Rotor Position Sensing
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Solution Overview
Problem
Current methods for controlling brushless DC motor commutation, such as using Hall sensors or sensorless back EMF zero-crossing analysis, face challenges in achieving high precision and efficiency due to low rotor position resolution, complex and expensive sensors, or limitations at low speeds.
Innovation Solution
A method utilizing one or more linear sensors to provide variable outputs based on motor rotational angle, sampling these outputs between commutation events, determining angular position and motor speed, and calculating the next commutation time using a hardware timer to optimize commutation timing precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If discrete Hall sensors are used to sense rotor position, then commutation control is achieved, but rotor position resolution is very low (6 increments per electrical rotation)
Solution Approach 1:
The patent replaces discrete Hall sensors with a linear position sensor that provides continuous output. This substitution transitions from a discrete mechanical sensing system to a continuous linear sensing system, achieving high-resolution rotor position measurement without the limitations of incremental Hall sensor outputs.
Solution Approach 2:
The patent changes the output parameter from discrete digital signals (Hall sensors) to continuous analog output (linear position sensor). This parameter change enables continuous rotor position measurement, providing high resolution for both block and sine commutation modes.
2Reliability
If sensorless back EMF zero-crossing analysis is used to determine commutation time, then cost is reduced, but operation at low speed is poor and block commutation is limited
Solution Approach 1:
The patent performs preliminary determination of rotor position and speed using the linear position sensor before commutation events occur. This preliminary action enables accurate commutation timing calculation regardless of motor speed, allowing reliable operation at low speeds where back EMF methods fail.
Solution Approach 2:
The patent introduces a microcontroller as an intermediary that processes linear position sensor output to calculate both rotor position and speed. This intermediary enables the system to overcome the limitations of sensorless methods by providing explicit position and speed information for commutation control.
3Measurement precision
If linear position sensor with continuous output is used to derive commutation time, then position resolution is improved, but processing time and jitter cause weak precision
Solution Approach 1:
The patent performs preliminary sampling of the linear position sensor output at known time instances between commutation events. This preliminary action captures position and speed information in advance, enabling the microcontroller to calculate the next commutation time without processing delays affecting precision.
Solution Approach 2:
The patent dynamically adjusts commutation timing based on real-time rotor position and speed measurements. By continuously updating position and speed information from the linear sensor, the system adapts to changing motor conditions, maintaining high precision commutation timing even during acceleration or deceleration.
Data Source
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AI summary
A method of controlling the commutation of a brushless direct current motor (BLDC) comprising: a) providing one or more sensors, said sensors adapted to provide a variable output dependent on the rotational angle of the motor or the relative position of the stator and rotor of the motor; b) sampling the output from said sensor(s) signals at a time tn between a past commutation event Cm-1 and the next commutation event Cm to be implemented; c) determining an angular position αn between rotor and stator at time tn at said time since the last commutation event from step b); d) determining the time Tm of next commutation event Cm based on commutation the next commutation angle (Cm), motor speed ω, and output from step c).