Sensorless Brushless DC Motor Position Detection
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Solution Overview
Problem
Brushless DC motors without sensors face challenges in accurately detecting the rotation position at startup, leading to potential reverse rotation, as existing sensorless methods often result in a 30-degree alignment error between detected and controlled rotation angles.
Innovation Solution
A rotation control apparatus that supplies current to multiple coil paths in a brushless DC motor, measures current values, and judges their order to detect the rotation position using a position detecting unit and a table for correspondence, allowing accurate position detection at startup without sensor assistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless motor control is used to reduce device complexity, then the motor can operate without sensors, but the rotation position detection accuracy deteriorates due to 30-degree alignment error at startup
Solution Approach 1:
The patent applies preliminary action by performing position detection before normal motor operation begins. The system detects the rotor position at startup using a specific detection method, then uses this pre-detected position information to initialize the control system, avoiding the 30-degree alignment error that would otherwise occur during normal operation.
Solution Approach 2:
The patent changes the detection parameter by measuring current flow through different coil paths instead of using traditional back-EMF detection. By supplying current to specific coil paths and measuring the resulting current values, the system determines rotor position based on magnetic resistance variations, achieving accurate position detection without sensors.
2Device complexity
If traditional sensorless position detection is used, then device complexity is reduced, but manufacturing precision deteriorates due to reverse rotation at startup
Solution Approach 1:
The system performs preliminary position detection before startup to determine the correct rotation direction. By detecting the rotor position in advance using the current measurement method, the control system can initialize with accurate position information, preventing reverse rotation and ensuring correct startup direction.
Solution Approach 2:
The patent implements feedback by continuously monitoring the current flow through different coil paths and using this information to determine rotor position. The measured current values provide feedback about the magnetic resistance state, which is used to accurately determine position and control rotation direction without reverse rotation.
3Ease of operation
If rotation position is detected at 60 degree intervals during driving, then control is simplified, but position detection accuracy deteriorates when the motor is stopped
Solution Approach 1:
The patent applies preliminary action by performing high-precision position detection before motor startup when the motor is stationary. This preliminary detection uses current measurement through multiple coil paths to determine exact rotor position, which then serves as the initial condition for subsequent 60-degree interval control during operation.
Solution Approach 2:
The patent segments the position detection process into two distinct phases: (1) preliminary high-precision detection at startup using current measurement through multiple paths, and (2) routine 60-degree interval detection during operation. This segmentation allows each phase to use the most appropriate method for its specific requirements.
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 rotation position at startup, minimizing reverse rotation and aligning the detected position with driving control, thus improving motor control accuracy.
Implementation Method 1
measuring a current flowing through a plurality of different paths including the coils, judging an order of the measured current values, and detecting a rotation position of the motor based on the order
Data Source
AI summary
A technology for correctly detecting a rotating position of a rotator at the time of rotation start. A rotation control apparatus controls rotation of a motor, which includes a stator provided with a plurality of coils and a rotor having magnetism. At the time of detecting a position of the motor when the motor is stopped, a control part supplies a current to a plurality of different paths including the coils, a stopped position detecting part measures the current flowing in each of the plurality of paths, judges the order of the measured current values, and a rotating position of the motor is detected based on the order. Based on a combination of a path showing the highest current value and a path showing the second highest current value, the stopped time position detecting part judges a position of the motor.