Sensorless Brushless DC Motor Rotor Position Detection
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Solution Overview
Problem
Sensorless brushless DC motors face challenges in accurately detecting the rotational position of the rotor at startup, leading to potential reverse rotation issues, especially in applications like spindle motors for hard disks, where minimizing reverse rotation is crucial.
Innovation Solution
A rotation control apparatus that supplies test currents through different paths of a motor's coils when stopped, converts these currents into detection voltages, compares voltage values, and determines the rotational position based on the order of current values, optimizing test current flow and electrical conduction time to improve detection precision and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a sensorless motor is used to make the motor smaller, then the device size is reduced, but the ability to detect rotational position at startup is lost
Solution Approach 1:
The system performs preliminary actions by supplying test currents to different coil paths before the motor starts rotating. This preliminary current injection allows the detection of rotor stop position through voltage measurements, establishing the initial rotational position information needed before normal operation begins.
Solution Approach 2:
The patent replaces the mechanical sensor-based detection system with an electrical field-based detection method. By injecting test currents and measuring resulting voltages, the system electronically determines rotor position without physical contact or additional mechanical components, maintaining motor compactness.
2Ease of operation
If the motor starts with unknown rotational position, then the motor can start without sensors, but the rotor may rotate in the reverse direction
Solution Approach 1:
Before initiating normal motor operation, the system performs a preliminary detection phase by supplying test currents to different coil paths and measuring the resulting voltages. This preliminary action determines the correct rotation direction based on the detected rotor stop position, ensuring reliable startup without reverse rotation.
Solution Approach 2:
The system implements feedback by measuring the voltages generated during test current injection and using this information to determine the correct rotation direction. The detected voltage values provide feedback about the rotor's stop position, which is then used to adjust the startup sequence and ensure correct rotation direction.
3Measurement precision
If test currents are supplied to detect rotational position, then position detection accuracy is improved, but the detection precision depends on motor characteristics
Solution Approach 1:
The system dynamically adjusts the test current injection strategy by measuring the time required for detection voltages to reach reference levels. This dynamic approach allows the detection method to adapt to different motor characteristics (R and L values) while maintaining consistent detection accuracy across various motor types.
Solution Approach 2:
The patent changes the detection parameters by measuring not just the magnitude but also the time characteristics of the detection voltages. By incorporating time measurements of when voltages reach reference levels, the system creates a detection method that is less sensitive to variations in motor electrical characteristics.
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 rotational position of the motor when stopped, allowing for correct motor control and minimizing reverse rotation, thus ensuring proper operation and reducing errors in position detection.
Implementation Method 1
a stop position detector configured to convert the test currents flowing through the plurality of paths into detection voltages for measurement
Implementation Method 2
The proposed sensorless motor obtains positional information by detecting an induced voltage generated in a coil by measuring a potential of a central point of a wiring of the motor
Data Source
AI summary
A rotation control apparatus includes: a controller configured to supply test currents to a plurality of different paths of a motor when the motor is stopped; and a stop position detector configured to detect a rotational position of the motor based on an order of current values of the test currents. The controller causes one of the test currents to flow through one of the plurality of different paths, measure time taken until the corresponding detection voltage reaches a reference voltage, and set electrical conduction time of the test currents based on a result of the measurement.