Brushless DC Motor Control via Back-EMF Phase Difference
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Solution Overview
Problem
Existing control methods for brushless DC electrical drives face challenges in accurately determining rotor position and speed, requiring multiple sensors and lacking a unified approach, which leads to inefficiencies and inaccuracies.
Innovation Solution
A controller that uses phase differences of periodic electrical signals as an information parameter to control brushless DC motors, allowing for precise positioning by comparing current rotor position with a target position and applying drive signals to balance torques across stator magnetic poles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple sensors (phototransistors, encoders, Hall-effect sensors, potentiometers, resolvers) are used to determine rotor position and speed, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent extracts the position sensing function from separate external sensors and integrates it into the motor's own phase windings. The back-EMF signals naturally generated by the motor phases are used directly for position detection, eliminating the need for dedicated sensors like Hall-effect sensors or encoders.
Solution Approach 2:
The phase windings serve dual functions: they act as both the actuating components that generate motor torque and as the sensing elements that provide rotor position information through back-EMF signals. This multi-functionality reduces the overall component count while maintaining measurement capability.
2Adaptability or versatility
If different sensors are used for position and speed determination, then measurement flexibility is improved, but lack of unified approach increases device complexity
Solution Approach 1:
The same phase windings are used for both position and speed determination. The back-EMF signals from these windings provide both pieces of information, creating a unified approach that eliminates the need for separate sensor systems and their respective auxiliary circuits.
Solution Approach 2:
The patent merges the position sensing and speed sensing functions into a single integrated system using the motor's phase windings. Both position and speed information are derived from the same back-EMF signals, eliminating the need for separate sensor systems.
3Measurement precision
If conventional sensor-based methods are used, then position determination capability is improved, but inability to achieve high accuracy worsens measurement precision
Solution Approach 1:
The motor uses its own operational characteristics (back-EMF signals from phase windings) to determine its position, rather than relying on external sensors. This self-service approach eliminates errors introduced by sensor-motor mismatches and provides more accurate position detection.
Solution Approach 2:
The system uses the back-EMF signals from the phase windings as feedback to continuously determine rotor position. This feedback mechanism provides continuous, high-resolution position information that is more accurate than discrete sensor measurements.
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 approach enables accurate and efficient control of brushless DC motors by creating stable and flexible operational modes, reducing vibration and increasing positioning accuracy, and allows for a unified standard in motor control systems.
Implementation Method 1
the drive signals are formed in such a way that a torque exerted by one phase against the rotor is counterbalanced by a torque exerted by at least another phase against the rotor
Data Source
AI summary
A controller for brush less DC motors includes an angular position sensor and control logic to detect the phase difference between a target position signal and a current angular position signal. The detected phase difference is the basis for generating motor drive control signals to position the rotor of the motor to the target position.