Sensorless DC Brushless Motor Control Circuit BEMF Detection Masking
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Solution Overview
Problem
DC brushless motors experience incorrect back electromotive force (BEMF) detections due to pulse width modulation (PWM) input signals, leading to mistaken phase switching and failure in maintaining steady speed operations.
Innovation Solution
A control method and circuit comprising an output circuit, pulse generating circuit, detecting circuit, and mask circuit that generates a digital output signal synchronous with the PWM signal to drive the motor, detects BEMF, and ceases detection in a predetermined time interval to prevent incorrect BEMF detection, using a mask signal to inhibit pulse generation during PWM signal changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PWM input signal is applied to control motor speed, then motor speed control is achieved, but incorrect BEMF detection occurs causing mistaken phase switching
Solution Approach 1:
The patent applies preliminary action by predicting the zero-crossing time of the BEMF signal in advance and proactively suspending PWM operations before the actual zero-crossing occurs. This prevents the PWM signal from interfering with the BEMF detection at the critical moment, thereby avoiding incorrect phase switching while maintaining speed control capability
Solution Approach 2:
The patent implements preliminary anti-action by introducing a mask signal that actively blocks or masks the BEMF detection circuit from receiving incorrect signals during the PWM transition period. This counter-measure is applied in advance to neutralize the harmful effect of PWM-induced false BEMF readings before they can cause mistaken phase switching
2Reliability
If BEMF detection is suspended to prevent incorrect detection, then phase switching accuracy is improved, but motor cannot operate at steady speed
Solution Approach 1:
The patent applies periodic action by implementing a cyclic pattern of PWM operation and BEMF detection suspension. The system periodically suspends PWM operations only during the brief intervals when zero-crossing detection is critical, while maintaining normal PWM operation during other periods. This periodic alternation ensures both accurate phase switching and overall motor stability
Solution Approach 2:
By predicting zero-crossing times in advance and suspending PWM operations only during these specific predicted intervals, the system maintains steady speed operation during the majority of the time while ensuring accurate phase switching at critical moments. The preliminary prediction allows for minimal disruption to overall motor performance
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
Prevents incorrect BEMF detection, ensuring continuous normal operation of the DC brushless motor by eliminating the impact of glitches on the detection signal, allowing correct zero crossing detection and maintaining motor stability.
Implementation Method 1
detecting a BEMF generated in accordance with the operation of the DC brushless motor
Data Source
AI summary
A method for controlling a direct current (DC) brushless motor, and a control circuit thereof are provided. The DC brushless motor is sensorless. In response to a digital output signal that is applied to drive the direct current brushless motor, detection of a back electromotive force (BEMF) is ceased in a predetermined time interval, so as to avoid detecting erroneous BEMF and keep normal operation of the direct current brushless motor.