BLDC Rotor Polarity Detection Without Motion Ambiguity
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Solution Overview
Problem
Current methods for detecting the orientation of rotor polarity in BLDC motors with ironless or slotless windings are ineffective due to weak saturation effects and inverter distortion, and require rotor movement, which is not acceptable in many applications.
Innovation Solution
A method involving high-frequency current sampling during zero voltage periods after injecting voltage pulses in the α-β plane to process current waveforms and determine rotor polarity, using a mathematical model that neglects stator voltage terms and identifies parameters using least squares algorithms, allowing precise detection without rotor motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If saturation effects-based detection method is used, then rotor polarity detection is possible without rotor movement, but the method fails for BLDC motors with ironless or slotless windings due to weak saturation effects
Solution Approach 1:
The patent applies preliminary action by injecting voltage pulses before performing current sampling to create measurable current waveforms. The voltage pulses are injected at specific angles in the α-β plane to generate current responses that reveal rotor polarity information, enabling detection before actual rotation occurs.
Solution Approach 2:
The patent uses periodic action through alternating positive and negative voltage pulses applied to the motor windings. This periodic excitation creates corresponding current waveforms that can be sampled and analyzed to determine rotor polarity, providing a systematic approach to extracting polarity information.
2Measurement precision
If rotor oscillation method is used to detect position based on back EMF, then rotor polarity can be detected, but rotor movement is required which is not acceptable in many applications
Solution Approach 1:
The patent replaces mechanical rotor oscillation with electrical voltage pulse injection. Instead of mechanically moving the rotor to generate back EMF for polarity detection, the method uses electrical excitation through voltage pulses applied to the windings, followed by current sampling during zero-voltage periods, thereby eliminating the need for mechanical movement.
3Measurement precision
If high-frequency current sampling is performed during zero voltage periods, then accurate current waveform representation is obtained, but increased computational processing is required
Solution Approach 1:
The patent extracts only the essential information from the current waveforms by focusing on specific sampling periods (zero voltage periods) and using mathematical models to process the data. This selective extraction approach reduces the processing burden compared to analyzing entire waveforms, while still achieving accurate polarity detection.
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 method effectively eliminates the 180° ambiguity and provides accurate rotor polarity detection for BLDC motors with small saturation effects, overcoming inverter distortion and enabling detection without rotor movement, suitable for ironless and slotless windings.
Implementation Method 1
The idea is to cause oscillatory movement of the rotor that creates enough back EMF and then to use standard techniques based on back EMF estimation in order to detect the rotor position.
Data Source
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AI summary
The invention refers to a method for detecting the orientation of the rotor polarity of a BLDC motor, especially with an ironless winding or slotless winding, i.e. eliminating a 180° ambiguity, comprising the following steps: determining the position of the rotor, i.e. the rotor angle with a 180° ambiguity, injecting at least one voltage pulse with an orientation in the in the α-β plane that matches the position of the rotor determined in the previous step, taking current samples with especially high frequency resulting from the at least one voltage pulse during a period where zero voltage is applied in order to gain a representation of the resulting current waveform, processing the current samples to determine small variations in the current waveform indicative for the orientation of the rotor polarity. The invention also refers to a motor system for detecting the orientation of the rotor polarity according to the method of one of claims 1 - 15.