Lead Angle Estimation for BLDC Motors via Phase-Sample Difference
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Solution Overview
Problem
Existing methods for sensorless control of brushless DC motors face challenges in estimating the lead angle between voltage and current vectors, particularly when using continuous sine wave currents, as traditional BEMF sensing is not possible, and existing solutions require high processing power or complex sensor setups, which increase costs and acoustic noise.
Innovation Solution
A method and system that utilize a lead angle estimator with a sampling unit and processing unit to calculate the difference of phase-samples during an extremum period, normalizing the difference to estimate the lead angle independently of current size, allowing for efficient motor control without position sensors and reducing acoustic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional BEMF sensing is used for sensorless control, then lead angle estimation is possible, but it requires high-impedance motor phase without current which creates sensing windows and generates acoustic noise
Solution Approach 1:
The patent replaces the traditional BEMF sensing method (which requires mechanical interruption of current flow to create sensing windows) with an electrical measurement approach. By measuring phase current during voltage extrema when current is naturally at extremum points, the method eliminates the need for mechanical-like current interruption while still enabling lead angle estimation, thereby reducing acoustic noise.
Solution Approach 2:
The patent changes the measurement parameter from BEMF voltage (which requires high-impedance and current interruption) to phase current measurement during voltage extrema. This parameter change allows continuous operation without creating sensing windows, thus eliminating the source of acoustic noise while maintaining lead angle estimation capability.
2Measurement precision
If Field-Oriented-Control is used for sensorless control, then lead angle control is achieved, but it requires high processing power due to multiple transformations which increases IC cost
Solution Approach 1:
The patent extracts only the essential measurement information needed for lead angle control by measuring phase current at specific voltage extrema points. This selective extraction of information eliminates the need for complex multi-axis transformations required by Field-Oriented-Control, significantly reducing processing power requirements while maintaining control accuracy.
Solution Approach 2:
Instead of implementing the full Field-Oriented-Control methodology with complete transformations, the patent applies a partial approach by measuring current at only the critical voltage extrema moments. This partial action provides sufficient lead angle information for effective control without the excessive processing burden of complete FOC implementation.
3Measurement precision
If BEMF voltage is sampled when phase current is zero, then lead angle can be determined, but it requires creating sensing windows which reduces continuous sine wave operation and increases acoustic emissions
Solution Approach 1:
Instead of sampling BEMF voltage when current is zero (traditional approach), the patent inverts the approach by sampling phase current when voltage is at extrema. This inversion allows measurement during continuous sine wave operation without creating sensing windows, thereby eliminating acoustic emissions while achieving lead angle determination.
Data Source
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AI summary
A lead angle estimator (110) for estimating a lead angle of a brushless DC motor. The lead angle being the angle between a phase-voltage-vector of a phase-voltage, and a phase-current-vector of a phase-current. The lead angle estimator comprises a sampling unit (114) and a processing unit (112). The sampling unit (114) being adapted for obtaining phase-samples which are a measure of the phase-current. The processing unit (112) being adapted for estimating the lead angle by calculating a difference of the phase-samples in a extremum period around a maximum or around a minimum of the phase-voltage, and by normalizing the obtained difference.