Multi-Phase Motor Driving Device BEMF Initial State Detection
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Solution Overview
Problem
Existing methods for driving multi-phase brushless DC motors, such as fan motors, face challenges in accurately determining the initial state of the motor when it starts, particularly in the absence of sensors, leading to potential noise and inefficiencies due to the need for non-conduction periods and increased costs with sensor-based systems.
Innovation Solution
A device that includes a back electromotive force (BEMF) detecting comparator and an initial state detecting unit, which uses BEMF and hall detection signals to determine the rotation state of the motor, allowing for accurate identification of forward, reverse, or stopped states without the need for sensors, by measuring time durations and phase relationships between these signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a hall sensor is used to detect rotor position, then the position detection accuracy is improved, but the cost increases
Solution Approach 1:
The patent extracts the position detection function from the hall sensor and implements it through software-based back electromotive force detection. The BEMF detection unit detects the back electromotive force generated in the coil during the non-conduction period to determine rotor position, eliminating the need for physical hall sensors while maintaining position detection capability
Solution Approach 2:
The patent replaces the mechanical/electrical hall sensor system with an electromagnetic field-based detection method. By detecting the back electromotive force generated during the non-conduction period, the system substitutes physical sensor hardware with electromagnetic measurement, reducing cost while achieving the same functional goal
2Device complexity
If the back electromotive force is used for rotor position detection, then the cost is reduced, but the driving waveform becomes distorted and noise increases
Solution Approach 1:
The patent applies preliminary action by detecting the back electromotive force during the non-conduction period before the next conduction phase begins. This timing allows position detection to be completed in advance, enabling the controller to prepare the appropriate driving waveform without distortion, thus eliminating noise while maintaining cost advantages
Solution Approach 2:
The patent implements feedback by using the detected back electromotive force signal to continuously adjust and optimize the driving waveform. The BEMF detection unit provides real-time rotor position information that feeds back to the control unit, which then generates appropriate driving signals to prevent waveform distortion and minimize noise generation
3Measurement precision
If the non-conduction period is extended to detect back electromotive force, then the position detection accuracy is improved, but the productivity decreases
Solution Approach 1:
The patent applies periodic action by utilizing the natural switching cycles of the motor phases. The back electromotive force is detected during each non-conduction period, which occurs periodically as different phases are switched. This periodic detection provides continuous position information without requiring extended non-conduction periods, maintaining both detection accuracy and operating speed
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
Enables accurate detection of the motor's initial state upon startup, reducing noise and costs by eliminating the need for sensor-based systems and allowing for appropriate sequence control, thereby improving motor control efficiency.
Implementation Method 1
a back electromotive force (BEMF) detecting comparator connected to one of the plurality of coils to compare BEMF generated in one end of the one of the plurality of coils with a midpoint voltage of the plurality of coils
Implementation Method 2
a hall detection signal corresponding to a result of comparing a pair of hall signals indicating a position of a rotor
Data Source
AI summary
A driving device of a multi-phase motor having a plurality of coils is provided. The driving device includes a back electromotive force (BEMF) detecting comparator connected to one of the plurality of coils to compare BEMF generated in one end of the one of the plurality of coils with a midpoint voltage of the plurality of coils and generate a BEMF detection signal, when the multi-phase motor starts to be driven; and an initial state detecting unit configured to detect a rotation state of the multi-phase motor based on the BEMF detection signal and a hall detection signal.