Sensorless Commutation for Single Coil BLDC Motors
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Solution Overview
Problem
Existing methods for controlling single coil brushless DC motors lack robustness during non-steady state operations and are prone to excessive inrush currents and noise, especially in low-cost applications, due to the reliance on Hall sensors and complex calculations for accurate rotor position estimation.
Innovation Solution
A method that utilizes timing information from phase current zero crossings and derivative zero crossings to determine the shape and timing of driving signals, allowing for sensorless commutation and reducing the need for predictive time information, thereby enabling robust control and minimizing torque ripple and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall sensors are used for commutation control, then rotor position detection accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the position detection function from physical Hall sensors and implements it through sensorless estimation using back-EMF voltage monitoring and current waveform analysis. This removes the Hall sensor component while maintaining position detection capability through electrical signal processing.
Solution Approach 2:
The patent replaces the mechanical/electrical Hall sensor system with a software-based estimation algorithm that processes current and voltage waveforms. This substitutes physical sensing components with computational methods to achieve position detection.
2Device complexity
If BEMF voltage is monitored for sensorless commutation, then device complexity is reduced, but measurement precision deteriorates due to current interference
Solution Approach 1:
The patent segments the electrical cycle into distinct phases: acceleration phase where current is actively controlled, and coasting phase where current naturally decycles. BEMF monitoring is performed specifically during the coasting phase when current interference is minimal, separating the measurement function from the torque generation function.
Solution Approach 2:
The patent performs preliminary current cycling before BEMF measurement by allowing the current to naturally decay to zero during the coasting phase. This preliminary action of letting current settle creates optimal conditions for accurate BEMF detection before the next commutation event.
3Measurement precision
If predictive time information is used for commutation timing, then commutation accuracy is improved, but reliability deteriorates during non-steady state operations
Solution Approach 1:
The patent implements feedback by continuously monitoring actual current zero-crossing moments and using this information to adjust and refine commutation timing predictions. The system learns from actual motor behavior during acceleration and adapts predictive algorithms to match real-world conditions, improving reliability during transient operations.
Solution Approach 2:
The patent transitions from static predictive timing to dynamic adaptive timing. During non-steady state operations, the system uses real-time current waveform analysis and zero-crossing detection to dynamically adjust commutation timing, allowing the control strategy to adapt to changing motor conditions rather than relying on fixed predictions.
4Productivity
If inrush current is not limited during startup, then productivity is improved, but harmful factors increase due to excessive current
Solution Approach 1:
The patent applies periodic square wave voltage pulses during startup instead of continuous voltage application. This periodic excitation allows the motor to build speed in discrete steps while naturally limiting peak current through the inductive properties of the motor windings and the timing of voltage application relative to rotor position.
Solution Approach 2:
The patent performs preliminary rotor position estimation and synchronization before applying full power drive signals. By initially using lower power levels to establish rotor position and speed synchronization, the system prepares the motor for efficient operation without subjecting it to damaging inrush currents during the critical startup phase.
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
The method provides a robust and efficient control mechanism for single coil brushless DC motors, reducing noise and inrush currents while maintaining performance, even in low-cost applications, by using phase current and derivative information to estimate rotor position and adjust driving signals effectively.
Implementation Method 1
a current sensor (220) configured for monitoring the phase current through the coil of the single coil brushless DC motor during the generator mode period
Implementation Method 2
For driving the rotor by applying a suitable driving current waveform to one or more stator coils it is important to know the rotor position in relation to the stator coils
Implementation Method 3
Such sensorless methods may for example monitor the BEMF (back electromotive force) voltage for estimating the position of the rotor
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~5
AI summary
A method for controlling a single coil brushless DC motor, the method comprising at least a first EHP sequence which comprises: driving (120) the motor using a driving signal during a torque generating period, to accelerate the motor, such that during a subsequent generator mode period a phase current goes in generator mode; driving (130) the motor during the generator mode period using a generator mode signal, which allows the phase current to be in generator mode; monitoring (140) the phase current during the generator mode period thereby obtaining phase current information; and determining (110) parameters of a next EHP sequence based on the obtained phase current information.