Coil Zero-Crossing Detection for Electric Machine Short-Circuits
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Solution Overview
Problem
Existing methods for detecting rotor winding short-circuits in electric machines are prone to errors due to noise in signal curves, leading to ambiguous results and inefficient operation, with non-homogeneous temperature distribution causing mechanical tensions and reduced efficiency.
Innovation Solution
A method involving the arrangement of a coil in the air gap between the rotor and stator, calculating minimum zero crossing durations, recording and correcting signal curves to identify sequential zero crossings, and comparing half-waves to detect asymmetries indicative of winding short-circuits, allowing for precise detection without relying on accurate rotational speed measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the air-gap coil measuring method is used to detect winding short-circuits, then the detection can be performed during operation, but the noise signal in the signal curve causes identification errors of half-rotation and leads to ambiguous results
Solution Approach 1:
The patent applies preliminary action by pre-calculating the minimum duration of two immediately sequential zero crossings based on the rotational frequency and number of pole pairs before analyzing the signal curve. This predetermined threshold enables reliable identification of valid zero crossings even in the presence of noise, as the minimum duration criterion filters out spurious crossings caused by noise signals.
Solution Approach 2:
The patent changes the parameter of zero crossing evaluation by introducing a time duration criterion. Instead of simply detecting zero crossings, the method evaluates the time interval between sequential zero crossings and compares it against the pre-calculated minimum duration. This parameter change transforms the detection from a simple threshold-based approach to a time-interval-based approach that is robust against noise.
2Reliability
If winding short-circuits are detected using traditional methods, then the detection capability is provided, but the non-homogeneous operating temperature causes mechanical tensions and reduces efficiency
Solution Approach 1:
The patent replaces mechanical temperature measurement and evaluation systems with an electromagnetic field-based detection method. By using a coil to measure magnetic flux and analyzing zero crossings in the generated signal, the method detects winding short-circuits electrically rather than through mechanical temperature sensors and physical inspections, enabling earlier and more precise detection.
Solution Approach 2:
The detection method utilizes the existing operational signals of the electric machine itself. The coil measures the magnetic flux that is already present during normal operation, and the zero crossings are extracted from the signal curve generated by the machine's own magnetic field variations. This self-service approach eliminates the need for additional sensors or external testing equipment.
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 simple and precise detection of winding short-circuits, reducing mechanical tensions and improving efficiency by accurately identifying asymmetries in the magnetic field, thus enhancing the operational reliability of electric machines.
Implementation Method 1
arranging a coil (25) in an air gap (26) arranged between the rotor (21) and the stator (20) of the electric machine (24)... measuring the magnetic flux at locations between the rotor and the stator is measured by means of a coil
Data Source
AI summary
Method for detecting short-circuits in a coil in an electric machine, includes: a) arranging a coil in an air gap between the rotor and stator; c) recording signal curves generated by the coil; d) determining zero crossings of the curve and storing the times thereof; e) determining zero crossings of the curve corrected by an offset c, identifying a pair of immediately consecutive zero crossings, the time separation of which is longer than the minimum duration; f) in no pair is identified, repeating step e) until identified, wherein the offset c is varied from the zero point to a global extreme value of the curve; g) identifying at least one of the two stored times, which lies between and closest in time to the pair and; h) extracting two half-waves from the curve using times identified in step g), wherein each half-wave corresponds to half a revolution of the rotor.