BLDC Motor Torque Ripple Reduction via Pseudo-Random BEMF Sampling
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Solution Overview
Problem
Torque ripple in hard-disk drives (HDDs) caused by periodic perturbations in back electromotive force (BEMF) detection leads to inefficiencies, audible noise, and increased design complexities in sensorless drive systems, as the periodic sampling of BEMF signals introduces jitter and vibrations in the disk rotation.
Innovation Solution
Implementing pseudo-random sampling of BEMF signals to disrupt periodicity, spreading spectral energy across a wider frequency range, thereby reducing the amplitude of specific frequencies and minimizing torque ripple, which can be achieved by sampling at pseudo-random intervals or using a pseudo-random sequence for BEMF detection in BLDC motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If periodic sampling of BEMF signals is used for sensorless control, then motor position detection is achieved, but torque ripple and audible noise increase
Solution Approach 1:
The patent applies periodic action by using pseudo-random sampling sequences to detect BEMF signals at strategically chosen time intervals. This periodic yet varied sampling approach maintains accurate position detection while distributing the spectral energy of torque ripple across multiple frequencies rather than concentrating it at a single frequency, thereby reducing audible noise.
Solution Approach 2:
The patent changes the sampling parameters by using pseudo-random sequences with different frequencies and patterns. By varying the sampling timing based on these sequences, the system achieves accurate BEMF detection while spreading the torque ripple energy spectrum, converting the harmful concentrated noise into distributed low-level ripple across multiple frequencies.
2Ease of operation
If BEMF detection is performed at regular intervals, then control simplicity is maintained, but spectral energy concentrates at specific frequencies causing noise
Solution Approach 1:
The patent uses periodic pseudo-random sampling sequences that maintain a structured, repeatable pattern for control simplicity while introducing frequency variation. This approach keeps the control logic manageable through defined sampling sequences while effectively distributing spectral energy to reduce concentrated noise at specific frequencies.
Solution Approach 2:
The system uses feedback from the detected BEMF signals to adjust and refine the sampling timing based on the pseudo-random sequences. This feedback mechanism maintains control simplicity by automatically adapting to motor position while implementing the noise-reducing pseudo-random sampling pattern.
3Stability of the object's composition
If sine-wave phase currents are injected for constant torque, then torque ripple is minimized, but BEMF detection perturbations still cause noise
Solution Approach 1:
The patent changes the detection parameters by implementing pseudo-random sampling sequences for BEMF measurement. This approach maintains the sine-wave current injection for constant torque while modifying how position information is extracted, thereby reducing the noise caused by detection perturbations without sacrificing torque stability.
Solution Approach 2:
The patent converts the harmful effect of BEMF detection perturbations into a benefit by using pseudo-random sampling. The perturbations that would normally concentrate energy at specific noisy frequencies are instead distributed across a broader frequency spectrum, transforming concentrated noise into dispersed, less noticeable ripple while maintaining accurate position 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 approach significantly reduces torque ripple, minimizing audible noise and increasing system stability by distributing spectral energy over more frequencies, making the noise less annoying and reducing the overall perturbation energy, thus enhancing the operational efficiency and design simplicity of HDDs.
Implementation Method 1
detecting the motor position based upon a measurement of a back electromotive force (BEMF) generated by the coils of the motor
Data Source
AI summary
In BLDC motors driven via sensorless techniques, the BEMF signals in the motor coils may be used to detect the position of the motor such that speed of the motor may be accurately controlled. When detecting the BEMF signals, however, small perturbations occur which negatively impact the rotational torque of the motor. As a result, torque ripple may occur at regular intervals which may result in inefficiencies as well as audible noise. In various embodiments as described herein, the sampling of the BEMF signals may be done so at pseudo-random intervals such that the overall spectral energy that presents from the BEMF detections may be reduced at specific frequencies (such as fundamental sampling frequencies and harmonics thereof) and spread out over many more frequencies. Thus, despite the overall spectral energy being the same, the amplitude of any given frequency is lower as the sampling of the BEMF is less periodic.