Motor Hall Sensor Offset Cancellation via Average Signal Subtraction
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Solution Overview
Problem
Conventional methods fail to accurately cancel the signal offset caused by external magnetic fields in Hall element sensors used for motor control, leading to inaccurate signal transmission to microcontrollers.
Innovation Solution
A motor drive system incorporating multiple Hall elements and a signal processing circuit that calculates an average signal across all phases to remove offset components, converting the resulting difference into a pulse signal for precise motor control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional offset cancellation circuits are used for Hall elements, then parasitic capacitance offset can be cancelled, but external magnetic field offset cannot be removed
Solution Approach 1:
The patent segments the offset cancellation process into two distinct stages: first cancelling parasitic capacitance offset using conventional circuits, then removing external magnetic field offset by calculating the average of three phase signals. This segmentation allows each type of offset to be addressed by a specialized method, achieving comprehensive offset removal that improves measurement precision while maintaining circuit simplicity.
2Measurement precision
If multiple Hall elements are used to detect rotor position, then measurement coverage is improved, but external magnetic field interference affects all sensors equally causing systematic offset
Solution Approach 1:
The patent extracts the external magnetic field offset component from individual Hall element signals by calculating the average of all three phase signals. Since external magnetic field interference affects all sensors equally, the average value represents the common-mode offset, which can be subtracted from each individual signal to remove the harmful external field effect while preserving the genuine rotor position information.
Solution Approach 2:
The patent converts the harmful effect of external magnetic field interference into a useful signal processing step. By recognizing that external magnetic fields affect all Hall elements equally, the system uses this uniform interference pattern as a reference to calculate and remove the offset, transforming what was previously a detrimental factor into a basis for improving measurement accuracy.
3Power
If signal processing circuits amplify Hall element outputs, then signal strength is increased, but offset components are also amplified
Solution Approach 1:
The patent performs preliminary offset removal by calculating the average signal and subtracting it from each phase signal before amplification. This preliminary action eliminates offset components from the signals, ensuring that subsequent amplification only amplifies the genuine rotor position information without simultaneously amplifying offset errors, thus maintaining a high signal-to-offset ratio.
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 removes external magnetic field-induced offsets, ensuring high-precision motor control by converting the average signal difference into a pulse signal, maintaining a 50% duty ratio and enhancing motor control accuracy without additional sensors.
Implementation Method 1
a plurality of magnetic sensors that output sine wave signals having a certain phase difference in order in accordance with rotation of a rotor
Data Source
AI summary
A motor according to a disclosed embodiment includes: a plurality of magnetic sensors that output sine wave signals having a certain phase difference in order in accordance with rotation of a rotor; a signal amplifier that amplifies a difference between an output signal of each of the plurality of magnetic sensors and an average signal that is an average of the output signals of the plurality of magnetic sensors; and a pulse signal generation unit that converts an output signal of the signal amplifier into a pulse signal.