Sensorless BLDC Rotor Position Detection at Zero and Ultra-Low Speed
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Solution Overview
Problem
Existing brushless DC motors require position sensors for accurate rotor position detection, which increase system volume, weight, and cost, and existing sensorless methods are prone to errors and complexity, especially at low and zero speeds.
Innovation Solution
A control method that generates continuous voltage pulses and samples three-phase motor winding voltages to derive rotor position without sensors, using adjacent voltage pulses to measure phase inductances and switch between different detection methods based on speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position sensor is used to detect rotor position, then rotor position detection accuracy is improved, but system volume, weight, and cost increase
Solution Approach 1:
The patent replaces the mechanical position sensor system with an electrical measurement system. Specifically, it uses high-frequency signal injection to measure motor inductance, which indirectly detects rotor position without requiring physical sensors. This substitution eliminates the need for additional mechanical components while achieving accurate position detection through electrical parameter measurement.
Solution Approach 2:
The patent introduces motor inductance as an intermediary parameter to detect rotor position. Instead of directly measuring position with a sensor, the system measures inductance changes caused by rotor position variations. The inductance serves as a mediator that translates mechanical position information into electrical measurement signals, enabling sensorless position detection.
2Measurement precision
If high-frequency signal injection is used to detect rotor position, then rotor position detection accuracy is improved, but device complexity and sensitivity to motor parameters increase
Solution Approach 1:
The patent employs periodic high-frequency signal injection at specific frequencies to excite the motor windings. By injecting signals at predetermined frequencies and measuring the resulting current responses, the system periodically samples inductance values at different rotor positions. This periodic excitation strategy simplifies the control logic compared to continuous measurement while maintaining detection accuracy.
Solution Approach 2:
The patent utilizes changes in motor inductance parameters as rotor position varies. By monitoring how inductance values change with rotor position and comparing measured values against predetermined thresholds or lookup tables, the system determines rotor position without complex real-time calculations. This parameter-based approach reduces computational complexity while maintaining measurement precision.
3Device complexity
If salient pole effect method is used to detect rotor position, then system simplicity is improved, but reliability decreases due to difficulty in detecting permanent magnet pole
Solution Approach 1:
The patent performs preliminary rotor position detection using high-frequency signal injection and inductance measurement before switching to other control methods. This initial detection phase establishes accurate rotor position and identifies permanent magnet pole locations, providing a reliable foundation for subsequent motor control operations. The preliminary action ensures that critical position information is captured before the motor enters normal operating modes.
Solution Approach 2:
The patent implements feedback mechanisms where measured inductance values are continuously compared against expected values or thresholds. When deviations are detected that might indicate incorrect pole detection or rotor position errors, the system can trigger corrective actions or switch to alternative detection methods. This feedback loop enhances reliability by continuously validating detection accuracy and correcting errors when they occur.
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
Accurately detects rotor position at zero and ultra-low speeds with high reliability, reducing system size, weight, and cost, and adapts to varying motor parameters and power inverter characteristics.
Implementation Method 1
The first kind of method uses high-frequency signal injection, and the rotor position is detected by measured inductance
Implementation Method 2
The second kind of method uses the relationship between winding inductances and the rotor position caused by the salient pole effect
Data Source
AI summary
Disclosed is a system and a method for controlling a brushless direct current motor or a permanent magnet synchronous motor using inductance-based rotor position detection. Voltage pulses are applied to the motor windings and the resulting voltages are measured. The inductances of the windings are determined from the measured voltages, and the relationship between the measured inductances and their order is compared to determine the rotor position. The motor is then controlled based on the rotor position.