Sensorless Brushless Motor Driver Using Multi-Frequency Signal Detection
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Solution Overview
Problem
Conventional DC brushless motors require position sensors for phase switching, which increase size, assembly difficulty, and cost, limiting their application, especially in smaller motor systems where sensorless methods struggle with immediate detection of zero back electromotive force or phase current.
Innovation Solution
A system and method utilizing a look-up table module, oscillator circuit, and multi-frequency signal generator circuit to output driving signals based on oscillating signals with different frequencies, allowing for accurate and instantaneous detection of back electromotive force and phase current, reducing switching loss and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a position sensor is disposed in the DC brushless motor to detect rotor position, then the motor can rotate normally with phase switching, but the size, assembly difficulty, and cost of the motor increase
Solution Approach 1:
The patent extracts the position detection function from a physical sensor and implements it through sensorless detection using back electromotive force (BEMF) signals. The controller detects rotor position by analyzing BEMF characteristics without requiring any physical position sensor in the motor structure, thereby eliminating the complexity while maintaining operational reliability
Solution Approach 2:
The patent replaces the mechanical/electrical position sensor system with an electronic signal processing system. Instead of using physical sensors to detect rotor position, the system uses electronic detection of BEMF signals and phase current characteristics to determine rotor position and control phase switching
2Device complexity
If conventional sensorless driver devices use back electromotive force or phase current for position detection, then the motor can operate without sensors, but zero values cannot be detected immediately
Solution Approach 1:
The patent dynamically adjusts the detection frequency of phase current and back electromotive force based on the operating conditions. By increasing detection frequency during critical periods when zero-crossing detection is needed, the system achieves high measurement precision without requiring continuous high-frequency operation, thus maintaining structural simplicity while improving detection accuracy
Solution Approach 2:
The patent performs preliminary detection and analysis of phase current and back electromotive force signals at multiple frequencies to predict and prepare for zero-crossing events. This allows the system to detect zero values more immediately by having advance information about upcoming zero-crossing points through multi-frequency signal analysis
3Device complexity
If the motor operates without position sensors using conventional methods, then size is reduced, but switching loss and power consumption increase due to delayed zero detection
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors phase current and back electromotive force signals at multiple frequencies, detects zero-crossing points, and uses this information to optimize switching timing. This feedback loop enables precise control of phase switching, reducing switching losses by ensuring switches occur at optimal moments rather than relying on fixed or delayed timing
Solution Approach 2:
The system dynamically adjusts detection and switching parameters based on real-time signal analysis. By varying detection frequency and analyzing signal characteristics dynamically, the system optimizes switching timing to minimize switching losses while maintaining the sensorless simple structure
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 efficient motor operation by accurately detecting phase current and back electromotive force with high frequency and resolution, improving motor efficiency and reducing size and assembly complexity by eliminating the need for position sensors.
Implementation Method 1
an oscillator circuit, a multi-frequency signal generator circuit. The oscillator circuit is configured to generate a plurality of oscillating signals having different frequencies from each other
Implementation Method 2
Many conventional driver devices of the DC brushless motors determine the position of the rotor and switch the rotor to any other phases of the DC brushless motor according to a back electromotive force (BEMF) induced by a stator of the DC brushless motor
Data Source
AI summary
A system and a method for driving a motor with a frequency conversion mechanism are provided. The system includes a look-up table module, an oscillator circuit, a multi-frequency signal generator circuit, and a motor driver circuit. The look-up table module stores a preset driving signal. The oscillator circuit generates oscillating signals having different frequencies. The multi-frequency signal generator circuit outputs a multi-frequency signal according to the oscillating signals. One waveform segment of the multi-frequency signal in a modulation region has a first oscillating frequency. Another waveform segment of the multi-frequency signal outside the modulation region has a second oscillating frequency lower than the first oscillating frequency. When a back electromotive force or a phase current of the motor reaches zero within a time interval of the modulation region, the motor driver circuit drives the motor according to the preset driving signal and the multi-frequency signal.