Brushless Motor Zero Crossing Detection with Adaptive Windowing
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Solution Overview
Problem
Existing methods for detecting the zero crossings (ZCs) of the back-electromotive force (BEMF) in brushless motors with misaligned polar couples suffer from noise filtering delays, impacting speed detection accuracy.
Innovation Solution
A monitoring device that adjusts the period of time for detecting zero crossings by modifying the electric revolution time based on the occurrence of ZCs within specific time zones, centered around expected instants, to ensure accurate detection without modifying speed monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If noise filtering is applied to detect zero crossings in motors with misaligned polar couples, then detection accuracy is improved, but detection delay increases and impacts speed monitoring accuracy
Solution Approach 1:
The patent pre-calculates and stores expected zero crossing instants based on the nominal electric revolution period before actual detection begins. During operation, the detector compares actual zero crossing signals against these pre-established time references, enabling immediate identification of deviations without requiring post-detection filtering or analysis, thus eliminating detection delay while maintaining accuracy
Solution Approach 2:
The patent implements a feedback mechanism where the detected zero crossing instants are used to update and refine the expected instants for subsequent cycles. The system calculates the deviation between actual and expected zero crossings, then adjusts the reference timeline accordingly, creating a self-correcting system that maintains accuracy without requiring noisy filtering operations
2Reliability
If the detection period is extended to capture zero crossings in motors with significant polar misalignment, then detection reliability is improved, but detection time increases
Solution Approach 1:
The system pre-establishes a detection window around each expected zero crossing instant based on the maximum anticipated misalignment. This predetermined window is sufficient to capture all possible zero crossing variations without requiring extended detection periods, as the window boundaries are calculated in advance based on known motor characteristics and misalignment tolerances
Solution Approach 2:
The patent dynamically adjusts the detection window timing for each cycle based on previously detected zero crossing instants. Rather than using a fixed static window, the system shifts and resizes detection windows adaptively to track the actual zero crossing pattern, maintaining optimal detection coverage while minimizing the active detection period duration
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 approach enables precise detection of zero crossings with reduced noise interference and shorter detection times, even in motors with significant polar misalignment, while maintaining speed control accuracy and reducing circuit complexity.
Implementation Method 1
detection of the position of the rotor during rotation generally involves the output stage of a winding of the motor, for example the output stage of winding La, being put into high impedance status, and the use of a circuit 3 suitable for detecting a Pbemf signal showing the polarity of the induced back-electromotive force (BEMF) of said winding
Data Source
AI summary
A monitoring device for an electric motor has in input a signal representing zero crossings of the back-electromotive force of the motor and comprises a monitor that detects the signal in first periods of time arranged around instants of time in which the zero crossings are expected. The device comprises a setting circuit that sets second periods of time that are less than the first periods of time and each second period of time is centered on the instant of time in which the zero crossing is expected. The monitor comprises a detector that tests whether each actual zero crossing occurs inside the second period of time and a controller that modifies by a quantity the subsequent period of electric revolution time between two consecutive expected instants of zero crossing if said actual zero crossing occurs outside the second period of time.