Electric Motor Magnet Temperature Detection Without Rotor Position
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Solution Overview
Problem
Existing methods for determining magnet temperatures in electric motors are costly and complex, requiring temperature sensors on the rotor and assuming a rotating state with known rotor position, which is impractical and expensive.
Innovation Solution
A method involving a test mode and a normal mode to determine magnet temperatures using current values measured at predefined and operation-dependent magnet temperatures, without the need for rotor position information, by applying voltage-time areas at specific angles and comparing current values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensors are installed on the motor rotor to measure magnet temperature, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses current values as an intermediary to indirectly determine magnet temperature. Instead of directly measuring temperature with sensors on the rotor, the method measures electrical current values and compares them with reference current values from test mode to infer temperature, thus avoiding direct temperature sensing on the rotating component.
Solution Approach 2:
The patent replaces the mechanical/physical temperature sensing system with an electrical measurement system. By substituting physical temperature sensors with electrical current measurements and comparisons, the method achieves temperature determination without the complexity of installing and maintaining sensors on the rotor.
2Measurement precision
If EMF evaluation or field current signal injection methods are used to determine magnet temperature, then measurement precision is improved, but device complexity and operational requirements increase
Solution Approach 1:
The patent performs preliminary actions by conducting test mode measurements beforehand to establish reference current values for different temperatures. This preliminary characterization allows the normal mode operation to simply compare current values without requiring complex real-time calculations or additional sensors during actual motor operation.
Solution Approach 2:
The patent creates a copy of the motor in test mode with identical structure but different operational conditions. By measuring and storing reference current values from this test copy at various temperatures, the system establishes a lookup table that simplifies temperature determination during normal operation without requiring complex real-time analysis.
3Measurement precision
If rotor position information is required for temperature determination, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The patent extracts the temperature determination method from dependence on rotor position information. By designing the measurement approach to be independent of rotor position, the method removes this additional requirement, allowing temperature determination to proceed with simpler measurements that do not need angular position data.
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 precise determination of magnet temperatures with reduced complexity and cost, applicable to both stationary and rotating motors, improving torque calculation accuracy.
Implementation Method 1
Due to saturation in the iron or more specifically inductive saturation, currents flowing in the magnetic field direction in windings of electric motors, i.e. in the direction of the magnets disposed on the electric motor, are greater than currents less closely oriented to the magnetic field of the magnets when voltage-time areas are impressed.
Data Source
AI summary
A temperature determination method for magnet temperatures on magnets of electric motors has a test mode. A first voltage is applied to a test winding of a test motor with test magnets for impressing a first voltage-time area at first angles of a test motor rotating field. The test magnets are subject to a predefined magnet temperature. First current values are ascertained at the first angles and stored based on the predefined magnet temperature. In a normal mode, a second voltage is applied to a motor winding of an operations motor with motor magnets for impressing a second voltage-time area at second angles of a motor rotating field. The motor magnets have an operation-dependent magnet temperature. Second current values are determined at the second angles and stored based on the operation-dependent magnet temperature. The operation-dependent magnet temperature is determined by comparing a second current value with a first current value.