Sensorless Rotor Position Detection in Low-Saliency Electrical Machines
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Solution Overview
Problem
Existing methods for sensorless position detection in electrical machines, particularly in low-saliency machines, face challenges such as requiring additional connections, high-frequency switching, and sensitivity issues, especially at low speeds and standstill conditions.
Innovation Solution
A method and apparatus that apply an electrical test signal to one phase terminal of an electrical machine with respect to a star point or other phase terminals, performing differential measurements to estimate the relative position, which eliminates offset issues and allows for continuous drive signal operation without additional connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If impedance measurement is used for sensorless position detection in low-saliency machines, then position detection at low speeds and standstill becomes possible, but measurement precision deteriorates due to very slight impedance changes (down to around 1%)
Solution Approach 1:
The patent segments the impedance measurement into differential components by measuring impedance between phase terminals rather than to a common reference. This segmentation allows extracting position information from the differential impedance changes while eliminating common-mode offsets, thereby improving measurement precision for low-saliency machines operating at low speeds
Solution Approach 2:
The patent changes the measurement parameter from absolute impedance to differential impedance between phase terminals. By measuring the difference in impedance between different phase combinations, the system can detect the subtle 1% impedance changes in low-saliency machines with sufficient precision for position detection at low speeds
2Use of energy by stationary object
If signal injection is implemented using the drive circuit, then continuous drive signals can be maintained, but device complexity increases due to high-frequency switching requirements
Solution Approach 1:
The patent makes the drive circuit multi-functional by enabling it to perform both drive operations and impedance measurement functions. By injecting test signals through the same drive circuit switches and using the same current sensors for both drive current measurement and impedance measurement, the system achieves continuous drive operation without adding dedicated measurement hardware or increasing switching frequency requirements
3Reliability
If additional position sensors are used, then position detection reliability improves, but device complexity and cost increase
Solution Approach 1:
The patent enables the electrical machine to detect its own position using its inherent electrical characteristics (impedance) and the existing drive circuit infrastructure. By measuring the impedance variations caused by rotor position through the stator windings and using the drive circuit for signal injection and measurement, the system achieves reliable position detection without any additional position sensors, thereby maintaining reliability while reducing device complexity
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 rotor position detection in low-saliency machines at low speeds and standstill conditions, improving reliability and reducing the need for additional connections or high-frequency switching.
Implementation Method 1
measuring the machine impedance or measuring the back emf... The impedance of the machine can be measured and the rotor position information can be extracted
Data Source
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AI summary
An apparatus for detecting the position in an electrical machine (1) when the machine is driven by a drive circuit (4) comprises an injection source (61) and a differential measurement unit (62). • The injection source (61) is arranged to apply a test signal to one phase terminal (2") of the electrical machine (1 ), with respect to a star point (2"') or to at least two other phase terminals (2, 2"); • The differential measurement unit (62) is arranged to perform a differential measurement of a response to the test signal on at least two phase terminals (2, 2') of the electrical machine (1), wherein these two phase terminals are different from the phase terminal (2") to which the test signal is applied. The apparatus further comprises a position estimating unit (10) arranged to determine, from a result of the differential measurement, an estimate of the relative position of the second and the first part (11a, 1 lb).