Sensorless Rotor Position Detection in Switched Reluctance Motors
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Solution Overview
Problem
Existing sensorless methods for determining rotor position in switched reluctance motors are prone to noise and require detailed knowledge of motor parameters, making them unreliable and inefficient.
Innovation Solution
A method that involves applying a voltage to a phase winding, sampling the current signal, detecting a feature of the second temporal derivative, and determining the rotor position based on this feature, which includes zero crossing points and sign changes of the third temporal derivative, without needing prior knowledge of motor parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensorless methods based on inductance measurements are used, then rotor position can be determined without sensors, but the method requires complex look up tables and detailed knowledge of motor parameters
Solution Approach 1:
The patent extracts only the essential feature needed for position determination - the zero crossing point of the second temporal derivative of current - while eliminating the need for complex look up tables and detailed motor parameters. This extraction approach simplifies the system by focusing on the critical signal characteristic that directly indicates rotor position.
Solution Approach 2:
The method uses the motor's own current signal and its temporal derivatives to determine rotor position, without requiring external sensors or pre-stored look up tables. The system serves itself by utilizing inherent electrical characteristics of the motor operation to generate the positioning information.
2Measurement precision
If detection of zero current slope (di/dt=0) is used to determine commutation point, then position information can be obtained, but the method is prone to noise and detection becomes unreliable
Solution Approach 1:
Instead of analyzing the first derivative of current (di/dt) in the time domain, the patent transitions to analyzing the second temporal derivative in the time domain. This dimensional change in the derivative order provides a more robust feature (zero crossing point) that is less susceptible to noise interference and provides more reliable commutation detection.
3Ease of operation
If inductance based methods with threshold conditions are used, then commutation can be controlled, but the method requires prior knowledge of integral motor parameters such as inductance, resistance, flux linkage or inertia
Solution Approach 1:
The system determines rotor position using only the measured current signal and its temporal derivatives, without requiring any pre-programmed motor parameters such as inductance, resistance, or inertia. The motor effectively determines its own position through the characteristics of its operating current, eliminating the need for external parameter databases.
4Adaptability or versatility
If voltage pulses are applied during motor run to provide current peaks, then position information can be obtained during coasting, but the method requires additional voltage application logic
Solution Approach 1:
The patent continuously monitors the second temporal derivative of the current signal during normal voltage application, providing uninterrupted position information throughout motor operation including coasting periods. This eliminates the need for separate voltage pulse injection sequences while maintaining continuous positioning capability.
Data Source
AI summary
A method for determining the position of a moving rotor in a switched reluctance motor includes the steps of applying a voltage to a phase winding of the reluctance motor, sampling a signal representative of the current magnitude in this phase winding, detecting a feature of the second temporal derivative of the signal, and determining the position of the moving rotor taking into account the occurrence of this feature. Apparatus for carrying out the method is described.