Sensorless Motor Polarity Detection via Current Injection
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Solution Overview
Problem
Existing methods for rotor magnet pole orientation in permanent magnet motor drives, particularly in sensorless control systems, face challenges in accurately differentiating between the positive and negative D axis, leading to incorrect alignment and potential instability, often requiring significant computations or time.
Innovation Solution
A method involving a stator current injector and error signal generator to introduce a predetermined error on an estimated reference axis, determining if the motor speed exceeds a threshold to adjust the control reference axis by 180°, facilitating rapid and reliable rotor magnet pole alignment using sensorless vector control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If position sensorless control algorithm is used to estimate rotor position, then device complexity is reduced, but measurement precision of rotor magnet polarity deteriorates
Solution Approach 1:
The patent applies preliminary action by performing an initial polarity detection routine before normal motor operation begins. The system injects a current pulse along the estimated D-axis and measures the resulting back-EMF to determine magnet polarity in advance, allowing the control system to establish correct reference frame alignment before sensorless vector control takes over, thus maintaining measurement precision without increasing operational device complexity
Solution Approach 2:
The patent introduces an intermediary measurement mechanism using back-EMF detection as a mediator between the current injection system and the control algorithm. By measuring the back-EMF generated in response to current injection, the system obtains polarity information without requiring direct mechanical sensors, thus resolving the contradiction between device complexity and measurement precision
2Device complexity
If conventional saliency detection techniques are used, then device complexity is reduced, but measurement precision of rotor magnet polarity deteriorates
Solution Approach 1:
The patent changes the measurement parameter from relying solely on saliency-based inductance variation to measuring back-EMF voltage directly. By injecting a known current pulse and measuring the resulting back-EMF voltage magnitude and polarity, the system achieves more precise magnet polarity detection while maintaining the same sensorless control hardware, thus resolving the contradiction between device complexity and measurement precision
3Measurement precision
If second technique is employed to resolve proper alignment with north pole, then measurement precision is improved, but productivity deteriorates
Solution Approach 1:
The patent performs the polarity detection and alignment resolution as a preliminary action during motor initialization before normal operation begins. The initial polarity detection routine executes once at startup, establishing correct reference frame alignment quickly, thereby avoiding continuous computational overhead during operation and maintaining high productivity while achieving precise north pole alignment
Solution Approach 2:
The patent rushes through the alignment determination process by using a direct back-EMF measurement approach during current injection rather than iterative computational methods. The system determines polarity and alignment in a single measurement cycle, skipping lengthy computation sequences, thus improving productivity while maintaining measurement precision
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 rapid and accurate detection of rotor magnet polarity with minimal disturbance, improving torque production and stability by differentiating between the rotor magnet north and south poles, thus enhancing the reliability of motor control.
Implementation Method 1
injecting a predetermined stator current on an estimated reference axis
Implementation Method 2
introducing predetermined error on the estimated reference axis... determining if a speed of the permanent magnet motor is greater than a predetermined threshold speed
Data Source
AI summary
Methods and apparatus are provided for aligning a control reference axis with a magnetic north of a permanent magnet motor. The method includes the steps of injecting a predetermined stator current on an estimated reference axis of the permanent magnet motor and introducing predetermined error on the estimated reference axis. The method further includes the steps of determining if a speed of the permanent magnet motor is greater than a predetermined threshold speed and setting the control reference axis to 180° added to the estimated reference axis if the speed of the permanent magnet motor is greater than the predetermined threshold speed or setting the control reference axis to the estimated reference axis if the speed of the permanent magnet motor is less than or equal to the predetermined threshold speed.