BLDC Motor Startup Using Phase Current Ratio Monitoring
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Solution Overview
Problem
Existing methods for starting three-phase sinusoidal BLDC motors are not reliable, particularly at low speeds, and often result in high noise due to the need for open-winding measurements and complex algorithms.
Innovation Solution
A method involving current sensing to determine the initial angular position of the rotor magnet, applying sinusoidal energizing signals to move the rotor to different angular positions, and monitoring current ratios to determine optimal commutation points, allowing for closed-loop control and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BEMF measurement technique is used to determine commutation points, then commutation timing can be determined, but the method is not reliable at low speeds and requires open-winding measurements
Solution Approach 1:
The patent introduces current sensing as an intermediary measurement method instead of directly measuring BEMF. By measuring phase currents and using them to infer rotor position and commutation timing, the system avoids the complexities of open-winding BEMF measurements while maintaining reliability at low speeds.
Solution Approach 2:
The patent replaces the electrical measurement approach (BEMF measurement) with a different physical measurement approach (current sensing). This substitution allows commutation determination to work reliably at low speeds where BEMF signals are too weak, without requiring complex open-winding measurement circuits.
2Measurement precision
If complex algorithms are used for commutation control, then precise commutation timing can be achieved, but algorithmic complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where phase currents are continuously monitored and fed back to the control system. This feedback allows the system to automatically determine commutation timing based on actual current conditions, achieving precise commutation without requiring complex predictive algorithms.
Solution Approach 2:
The system uses its own operating parameters (phase currents) to determine commutation timing, eliminating the need for external sensors or complex reference algorithms. The motor's own current signatures provide the information needed for precise commutation control.
3Measurement precision
If open-winding measurements are performed for BEMF detection, then commutation points can be identified, but acoustic noise increases
Solution Approach 1:
The patent uses current sensing as an intermediary that does not require opening motor windings. This indirect measurement method avoids the mechanical disturbances and acoustic noise generated by physically opening and closing winding connections during BEMF measurement.
Solution Approach 2:
The patent skips the noisy open-winding measurement step entirely by using continuous current sensing during normal closed-winding operation. This allows commutation timing to be determined without ever opening the windings, thus eliminating the source of acoustic noise.
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 reliable and low-noise startup of BLDC motors with low algorithmic complexity, suitable for simple hardware implementations, and scalable for various motor types and speeds, reducing acoustic noise and torque ripple.
Implementation Method 1
monitoring two of the motor phase currents flowing through two of the phase windings using the current sensing means
Implementation Method 2
applying a first set of sinusoidal energizing signals to the phase windings for causing first stator currents to flow in the windings thereby generating a first magnetic field oriented in a first direction
Implementation Method 3
maintaining the first set of energizing signals for allowing the rotor to move to a first angular position different from the initial angular position, the rotor movement causing BEMF voltages to be induced
Data Source
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AI summary
Method of starting a three-phase sinusoidal BLDC motor, comprising: a) determining an initial position of the rotor; b) applying a first set of sinusoidal energizing signals to the windings, corresponding to a set of sinusoidal waveforms shifted apart by 120° and 240° sampled at a first angle (φ1); and maintaining the energizing signals for allowing the rotor to move to a first angular position; c) while maintaining the energizing signals, monitoring two of the phase currents, and determining whether a predefined condition is satisfied, comprising testing whether a ratio of two total current values is equal to a predefined value, and if true, to repeat steps b) and c), but with second and further sinusoidal energizing signals sampled at a second or further angular position, selected from a limited group of discrete angular positions.