Demagnetization Detection via Power Control Unit
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Solution Overview
Problem
Existing methods for detecting demagnetization in permanent magnet motors are inaccurate due to the inability of temperature sensing elements in the stator to accurately measure rotor temperature, leading to uncertainties in determining whether a permanent magnet is demagnetized, which can result in reduced operational torque and safety issues in electromobiles.
Innovation Solution
A demagnetization detection device and method that uses a power control unit connected to a DC power source, featuring a memory, voltage detector, current detector, and processing unit to calculate and compare power values, determining demagnetization by comparing testing power values to standard values at standard torque and rotation speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensing elements are disposed in the stator to sense temperature, then temperature measurement is possible, but the rotor temperature and permanent magnet temperature cannot be accurately detected
Solution Approach 1:
The patent uses power consumption as an intermediary parameter to indirectly detect rotor temperature and permanent magnet temperature. Instead of directly measuring temperature with sensors in the rotor, the system measures electrical parameters (voltage, current, frequency) and calculates power consumption, which serves as a mediator reflecting the thermal state of the permanent magnet without requiring direct temperature sensing in the rotor.
Solution Approach 2:
The patent replaces the mechanical/physical temperature sensing system with an electrical measurement system. Instead of using temperature sensors that would need to be physically installed in the rotor, the system uses electrical parameter measurements (voltage, current, frequency) processed by a microcontroller to infer temperature and detect demagnetization, substituting direct thermal measurement with electrical characterization.
2Productivity
If full-range flux-weakening control is adopted to deliver ideal output performance, then torque and speed requirements are satisfied, but the permanent magnet is exposed to demagnetizing field causing heat accumulation
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors power consumption and compares it against predetermined thresholds. When the power consumption exceeds the threshold (indicating excessive heat accumulation and potential demagnetization), the system provides feedback to adjust or limit the flux-weakening control, thereby protecting the permanent magnet while allowing optimal performance within safe operating limits.
3Reliability
If the permanent magnet temperature exceeds the limitation of the magnetic flux density-magnetic field strength curve, then demagnetization occurs, but temperature sensing cannot detect this condition accurately
Solution Approach 1:
The patent changes the detection parameter from direct temperature measurement to power consumption measurement. By monitoring changes in electrical parameters (voltage, current, frequency) and calculating power consumption, the system detects demagnetization through electrical characteristic changes that occur when the permanent magnet's magnetic properties deteriorate, avoiding the limitations of temperature sensing.
Data Source
AI summary
A demagnetization detection device and a demagnetization detection method thereof are provided. The demagnetization detection device is for use in a power control unit which is electrically connected to a testing permanent magnet motor. The power control unit is electrically connected to a direct current power source. The demagnetization detection device is configured to detect a testing voltage value and a testing current value of the direct current power source, and to compute a testing power value of the direct current power source according to the testing voltage value and the testing current value. The demagnetization detection device determines the difference between the testing power value and a standard power value, and then determines whether the testing permanent magnet motor is in a demagnetization status according to the difference.