Sensorless BLDC Circuit for Accurate Back-EMF Zero-Crossing Detection
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Solution Overview
Problem
Existing BLDC motors face challenges in accurately detecting the back electromotive force (BEMF) zero-crossing point due to the use of filters that affect the phase of the BEMF voltage, leading to reduced detection accuracy.
Innovation Solution
A sensorless motor circuit that includes a BLDC motor, a driving circuit, a voltage adjustment circuit, a virtual neutral point circuit, and a control circuit, which generates a virtual neutral voltage and compares it with divided terminal voltages to detect the BEMF zero-crossing point without using filters, ensuring accurate detection and reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter is used to filter out noise in the back electromotive force voltage, then noise is reduced, but the phase of the back electromotive force voltage is affected, reducing the accuracy of detection of the BEMF zero-crossing point
Solution Approach 1:
The patent extracts and eliminates the filter component from the BEMF detection circuit. By removing the filter that causes phase delay, the system directly detects the BEMF voltage without phase distortion, thereby maintaining accurate zero-crossing point detection while still addressing noise through alternative means in the control algorithm.
Solution Approach 2:
The patent introduces a virtual neutral point as an intermediary reference. By comparing the BEMF voltage against this virtual neutral point rather than using a filtered signal, the system achieves accurate zero-crossing detection without the phase distortion introduced by traditional filtering methods.
2Object-affected harmful factors
If a filter is used to filter out noise in the back electromotive force voltage, then noise is reduced, but the phase of the back electromotive force voltage is affected, reducing the accuracy of detection of the BEMF zero-crossing point
Solution Approach 1:
The patent removes the filter component from the circuit, thereby reducing device complexity. The system achieves noise management without requiring additional filtering hardware, simplifying the overall circuit design while maintaining detection accuracy.
Solution Approach 2:
The system uses the existing virtual neutral point circuitry to serve dual purposes: establishing a reference for BEMF detection and enabling accurate zero-crossing detection without requiring separate filtering components. This self-service approach reduces overall system complexity.
3Measurement precision
If a virtual neutral point circuit is used to generate virtual neutral voltage and compare with divided terminal voltages, then detection accuracy of BEMF zero-crossing point is improved, but device complexity increases
Solution Approach 1:
The virtual neutral point circuit serves multiple functions simultaneously: it provides a stable reference voltage for BEMF detection, enables accurate zero-crossing point detection, and eliminates the need for separate filtering circuits. This multi-functionality justifies the added complexity by consolidating multiple roles into a single circuit element.
Solution Approach 2:
The virtual neutral point acts as an intermediary reference that simplifies the comparison process. By providing a stable mid-point reference voltage, it enables direct comparison with terminal voltages to detect zero-crossing points accurately without requiring complex filtering or signal conditioning circuits.
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 solution allows for precise detection of the BEMF zero-crossing point without phase delays, enhancing the accuracy of rotor position tracking and reducing manufacturing costs by eliminating the need for filters.
Implementation Method 1
The voltage adjustment circuit is coupled to the first terminal of the third winding, and is used to generate a divided voltage according to a terminal voltage of the third winding
Implementation Method 2
The comparator is coupled to the voltage adjustment circuit and directly coupled to the virtual neutral point circuit, and is used to compare the divided voltage with the virtual neutral voltage to generate a comparison signal
Implementation Method 3
The motor system may track the rotor position according to the zero-crossing points of the back electromotive force voltage of the BLDC motor
Data Source
AI summary
A sensorless motor circuit includes a brushless direct current motor, a driving circuit, a voltage adjustment circuit, a virtual neutral circuit, a comparator and a control circuit. The brushless direct current motor includes the first to third windings. The driving circuit outputs a PWM voltage to the first winding, couples the second winding to a ground terminal, and floats the third winding. The voltage adjustment circuit outputs a divided voltage according to a terminal voltage of the third winding. The virtual neutral circuit generates a virtual neutral voltage. The comparator compares the divided voltage with the virtual neutral voltage to generate a comparison signal. The control circuits determine a sampling time according to a duty cycle of the PWM voltage, and samples the comparison signal at the sampling time to detect a back electromotive force zero-crossing event, so as to perform commutation.