Brushless Motor Drive With Hall-Based Sine Period Correction
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Solution Overview
Problem
Existing motor drive systems for brushless motors face challenges in reducing vibration, noise, and torque ripple due to inaccuracies in rotor magnet magnetization and low resolution of sine wave amplitude values, leading to increased complexity and cost, and limited versatility.
Innovation Solution
A motor drive apparatus that computes and updates the period of sine wave drive signals based on the mathematical expression S=T/(n/2), allowing for accurate synchronization and phase adjustment of sine wave drive signals for a wide range of brushless motors with varying magnetic pole numbers, using three magnetic pole detecting elements and an inverter with FETs for power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the accuracy of division in magnetization of the rotor magnet is increased to reduce variations in hall signal period, then the manufacturing precision improves, but the device complexity and cost increase
Solution Approach 1:
The patent changes the control parameter from using raw hall signal periods directly to using corrected periods calculated by the formula Tc = 2*T/(n/2), where T is the measured hall signal period and n is the number of magnetic poles. This parameter transformation allows the system to compensate for magnetization division inaccuracies without requiring higher manufacturing precision, thus resolving the contradiction between manufacturing precision requirements and device complexity.
2Manufacturing precision
If the resolution of sine wave amplitude values is increased to reduce torque ripples, then the manufacturing precision improves, but the device complexity and cost increase
Solution Approach 1:
The patent applies parameter transformation to the sine wave amplitude values by adjusting them according to the corrected hall signal periods. Instead of increasing the resolution of amplitude values directly, the system recalculates amplitudes based on the corrected periods Tc, which compensates for variations and reduces torque ripples without requiring higher resolution hardware, thereby avoiding increased device complexity.
3Measurement precision
If the motor drive apparatus is designed with specific arrangement for a fixed number of magnetic poles to achieve accurate sine wave drive, then the measurement precision improves, but the adaptability decreases
Solution Approach 1:
The patent implements a universal control method that can drive brushless motors with any number of magnetic poles n. The key is using the formula Tc = 2*T/(n/2) and adjusting sine wave amplitude values based on corrected periods, where n is a variable parameter. This allows the same drive apparatus to adapt to different motor configurations (different pole numbers) while maintaining accurate sine wave drive, thus achieving both measurement precision and adaptability.
4Reliability
If the accuracy of division in magnetization and resolution of sine wave amplitude values are increased to reduce variations, then the reliability improves, but the device complexity increases
Solution Approach 1:
The patent employs a feedback mechanism where the hall signal periods are measured, corrected using the formula Tc = 2*T/(n/2), and then used to adjust subsequent sine wave amplitude values. This closed-loop approach ensures that variations in hall signal periods are continuously compensated, improving the reliability and consistency of the sine wave drive signal without requiring permanently complex hardware arrangements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively cancels variations in hall signal periods caused by magnetization inaccuracies, enabling the drive of brushless motors with any magnetic pole number, reducing torque ripples and increasing versatility while maintaining cost-effectiveness.
Implementation Method 1
three magnetic pole detecting elements that detect a rotational position of the rotor magnet
Implementation Method 2
an inverter with FETs for power supply
Data Source
AI summary
A motor drive apparatus that can be used to drive a wide range of brushless motors without any limit to a magnetic pole number of a rotor magnet. One rotational period T of the rotor magnet is obtained, and one period S of the sine wave drive signal according to a mathematical expression of S=T/(n/2). The one period S of the sine wave drive signal is updated at intervals of one period of the output signal from one magnetic pole detecting element among the three magnetic pole detecting elements.