Brushless DC Motor Controller Offset Voltage Calibration
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Solution Overview
Problem
Precise detection of phase current in brushless DC motor systems is hindered by offset voltages and currents within the detection circuitry, affecting the accuracy of commutation timing and stability of motor operation.
Innovation Solution
A motor controller with a current detector and a microcomputer-based system that calculates and removes offset voltage from detected current information by determining the offset voltage through specific phase current analysis and modifying the detected values to exclude it, ensuring accurate rotor position determination and stable motor control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current detector is used to detect phase current for accurate commutation timing, then measurement precision is improved, but offset voltage and circuitry errors affect detection accuracy
Solution Approach 1:
The system performs preliminary action by detecting and storing offset voltage values during specific switching periods (when only one phase current flows) before actual motor operation. This pre-detection allows the offset voltage to be characterized and removed from subsequent current measurements, improving detection precision without being affected by offset errors during normal operation.
Solution Approach 2:
The invention converts the harmful offset voltage into a beneficial element by using it as a calibration reference. During specific switching periods when only one phase is active, the offset voltage becomes the dominant signal, allowing the system to deliberately measure and store it. This measured offset is then subtracted from all subsequent current measurements, transforming the previously harmful offset into a useful calibration parameter that improves overall measurement accuracy.
2Measurement precision
If voltage detection across current detecting resistor is used, then current detection is achieved, but the extremely small voltage is easily affected by amplifier properties and temperature
Solution Approach 1:
The system implements feedback by continuously monitoring the offset voltage during specific switching periods and using this information to correct subsequent current measurements. The detected offset voltage is fed back to the current calculation process, where it is subtracted from the raw measurements, creating a closed-loop correction system that compensates for amplifier drift and temperature variations.
Solution Approach 2:
The invention changes the operating parameter by selecting specific switching periods where only one phase current flows, causing the differential voltage to be dominated by offset voltage rather than phase current. This parameter change (selecting specific time windows for offset detection) allows the system to separate offset voltage measurement from phase current measurement, enabling accurate offset characterization that can then be used to improve reliability under varying temperature and amplifier conditions.
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
Enhances the precision of phase current detection, reducing the impact of circuitry-related errors and improving the stability and accuracy of commutation timing in brushless DC motor control.
Implementation Method 1
a resistor type current detector that detects a current value as a voltage value
Implementation Method 2
a Hall element type current detector that detects count of magnetic flux generated by DC current
Data Source
AI summary
A motor controller is disclosed. The motor controller includes a current detector that is provided in a direct current side of a power converter and that detects direct current information. A determiner determines a size of an offset voltage contained in the detected current information. The determiner calculates the offset voltage by canceling a positive current component by a negative current component both pertaining to the same one phase and contained in the detected direct current information. A modifier modifies the detected direct current information based on the calculated offset voltage.