Sensorless Motor Driving Device BEMF Detection
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Solution Overview
Problem
Existing motor driving devices face challenges in accurately detecting back electromotive force (BEMF) during both ON and OFF times of a PWM signal, especially at low rotation speeds, leading to misjudgments in commutation points due to insufficient zero-crossing events and unstable operating conditions.
Innovation Solution
A motor driving device and method that includes a PWM signal generating unit, a driving unit, a floating point selecting unit, a BEMF detecting unit, and a control unit, which can detect BEMF during both ON and OFF times of the PWM signal based on motor parameters such as duty cycle, operating voltage, and rotation speed, ensuring accurate commutation timing by switching detection modes accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If BEMF detection is performed during ON times of PWM signal, then commutation points can be correctly determined, but at low rotation speeds the ON times are greatly reduced and insufficient for detecting zero-crossing events
Solution Approach 1:
The patent dynamically switches between ON-time detection and OFF-time detection modes based on motor rotation speed. At high speeds, ON-time detection is used; at low speeds, OFF-time detection is activated. This dynamic adaptation resolves the contradiction by adjusting the detection timing according to operating conditions, ensuring sufficient detection opportunities across all speed ranges.
Solution Approach 2:
The patent changes the detection parameter from ON-time interval to OFF-time interval based on rotation speed conditions. By monitoring rotation speed and switching detection windows accordingly, the system overcomes the limitation of insufficient ON-time duration at low speeds while maintaining detection accuracy through parameter adaptation.
2Adaptability or versatility
If BEMF detection is performed during OFF times of PWM signal to determine commutation timings, then detection can occur at low rotation speeds, but misjudgments of commutation points often occur due to erroneous BEMF signals
Solution Approach 1:
The patent employs feedback mechanisms to verify BEMF detection results. During OFF-time detection, the system monitors the detected BEMF signals and compares them against expected patterns. If misjudgment is detected through feedback analysis, the system can correct or reject erroneous commutation point determinations, thereby maintaining reliability while enabling low-speed operation.
Solution Approach 2:
The patent performs preliminary verification of BEMF signals before finalizing commutation point determination. By pre-checking the validity of detected zero-crossing events and comparing against motor parameters, the system prevents erroneous commutation commands, ensuring reliable operation even when using OFF-time detection at low speeds.
3Measurement precision
If Hall sensor is used to detect rotor position, then sensing accuracy is maintained, but system volume and manufacturing costs increase
Solution Approach 1:
The patent enables the motor system to detect its own rotor position using built-in current sensors and BEMF detection circuits, eliminating the need for external Hall sensors. The motor's own electrical characteristics are exploited for position sensing, achieving self-service functionality that reduces component count, system volume, and manufacturing costs while maintaining adequate sensing accuracy.
Solution Approach 2:
The patent replaces the mechanical Hall sensor-based position detection system with an electrical field-based BEMF detection method. By substituting the mechanical sensing approach with electrical measurement of back electromotive force, the system achieves sensorless operation that reduces physical components and complexity while maintaining the ability to determine rotor position for commutation control.
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 solution prevents misjudgments of commutation points by ensuring sufficient BEMF detection during both ON and OFF times, even at low rotation speeds and unstable voltage conditions, thereby improving the reliability of motor operation.
Implementation Method 1
detect a back electromotive force (BEMF) of the floating phase during ON times or OFF times of the output PWM signal
Data Source
AI summary
A motor driving device includes a PWM signal generating unit, a control unit, a driving unit, a floating point selecting unit and a BEMF detecting unit. The PWM signal generating unit generates an input PWM signal having a duty cycle according to a rotation speed command. The control unit generates a driving signal having multiple phases and an output PWM signal. The floating point selection unit selects a floating phase of the motor that is not turned off, and the BEMF detecting unit receives detects the BEMF of the floating phase during ON times or OFF times of the output PWM signal, so as to output a commutation signal in response to zero crossing events occurring in the BEMF. The control unit controls the BEMF detecting unit to detect the BEMF of the floating phase under the ON times or the OFF times of the output PWM signal.