Sensorless DC Brushless Motor Startup via BEMF Differential
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Solution Overview
Problem
Conventional methods for starting a DC brushless motor without a sensor require complex operational procedures, increasing assembly difficulties and production costs, especially in small motors, as they rely on detecting back electromotive force (BEMF) for rotor position determination.
Innovation Solution
A control apparatus comprising a sense amplifier, differential circuit, and control circuit that measures and calculates the differential value of BEMF across unenergized windings to switch current between windings in a specific sequence, eliminating the need for sensors and complex operations by utilizing the steady-state equilibrium point for motor startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensor (e.g., Hall sensor) is placed within the motor to detect rotor position, then the rotor position detection accuracy is improved, but the assembly difficulty and production cost increase
Solution Approach 1:
The invention extracts the rotor position detection function from the mechanical sensor domain and relocates it to the electrical signal domain. By measuring the back electromotive force (BEMF) of the non-conducted winding, the system obtains rotor position information without physical sensors, thereby eliminating assembly complexity while maintaining detection precision.
Solution Approach 2:
The BEMF signal serves as an intermediary carrier that conveys rotor position information. Instead of directly measuring mechanical position with a sensor, the system uses the electrical BEMF signal generated by the motor's own operation as a mediator to infer rotor position, simplifying the manufacturing process.
2Ease of manufacture
If complex operational procedures are used to start the motor without a sensor, then the need for sensors is eliminated, but the control complexity increases
Solution Approach 1:
The system performs preliminary action by pre-charging the non-conducted winding capacitor during the startup sequence. This preliminary charging of the capacitor with BEMF signal enables the subsequent zero-crossing detection to work effectively, simplifying the overall control logic by preparing the detection mechanism in advance.
Solution Approach 2:
The control system continuously monitors the BEMF signal and uses feedback from the zero-crossing detection to determine when to switch phases. This feedback mechanism automates the startup sequence, reducing control complexity by allowing the system to self-regulate based on real-time electrical conditions rather than requiring complex external control procedures.
3Ease of manufacture
If BEMF detection is used to determine rotor position for motor startup, then sensorless operation is achieved, but the operational complexity and control difficulty increase
Solution Approach 1:
The invention uses the zero-crossing point of the BEMF signal as a distinctive electrical 'marker' or 'color change' event to indicate specific rotor positions. This zero-crossing event serves as a clear, easily detectable signal that simplifies the control logic by providing unambiguous position information without requiring complex signal processing or additional sensors.
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 simplifies the startup process by switching current between windings based on BEMF differential values, ensuring successful motor operation without the need for sensors or complex procedures, thereby reducing production costs and assembly challenges.
Implementation Method 1
a back electromotive force (BEMF) generated across the rotor winding in response to the rotational movement thereof is detected as the reference for determining the rotor position
Implementation Method 2
calculating a differential value of the first BEMF
Implementation Method 3
supplying a current to two of the windings to excite a first phase, and to switch the current to the other two windings in a specific sequence
Data Source
AI summary
An apparatus for starting a direct current brushless motor and a method thereof are provided. The direct current brushless motor comprises a plurality of windings. The control apparatus comprises a sense amplifier, a differential circuit, and a control circuit. The sense amplifier is configured to detect a first back electro-motive force of a non-electrified first winding. The differential circuit is configured to calculate a differential value of the first back electro-motive force. The control circuit is configured to provide a current to two of the windings and to switch the current to another two of the windings to start the direct current brushless motor.