Stator Winding Temperature Measurement Using Torque-Free Bias Currents
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Solution Overview
Problem
Conventional methods for determining the temperature of stator windings in rotating field electric machines lack accuracy and require temperature sensors, with existing methods relying on resistance measurements that are sensitive to current measurement tolerances and motor model accuracy.
Innovation Solution
The method involves utilizing additional degrees of freedom in n-phase systems to establish current components that do not affect torque production, allowing for more accurate determination of ohmic resistance in stator windings through vector-based control methods, such as closed-loop vector control, and expanding the Clarke transformation for n-phase systems to enable precise temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional resistance measurement methods are used to determine stator winding temperature, then temperature can be determined without temperature sensors, but the measurement accuracy is insufficient due to sensitivity to current measurement tolerances and motor model accuracy
Solution Approach 1:
The patent changes the operating parameters by introducing specific current components with particular frequency characteristics and torque effectiveness levels. By controlling the torque effectiveness to be between 0 and 20% of total torque, and using current frequencies between 100-1000 Hz, the method optimizes the relationship between ohmic resistance measurement and temperature determination, thereby improving measurement accuracy while maintaining reliability
Solution Approach 2:
The patent replaces direct physical temperature sensing with an indirect electrical measurement system. By substituting mechanical/physical temperature sensors with electrical resistance measurements combined with vector-based current control, the system achieves temperature determination through electrical parameter analysis rather than direct thermal sensing
2Measurement precision
If additional current components are introduced to improve temperature measurement accuracy, then ohmic resistance determination is improved, but torque production is affected
Solution Approach 1:
The patent applies partial action by introducing current components that contribute only partially to torque production (0-20% torque effectiveness). This partial contribution is sufficient to obtain accurate ohmic resistance measurements for temperature determination, while minimizing the impact on primary torque production requirements
Solution Approach 2:
The patent employs periodic high-frequency current components (100-1000 Hz) superimposed on the fundamental motor currents. These periodic current injections occur in controlled intervals and allow resistance measurement without creating continuous torque disturbances, thus maintaining steady torque production while enabling periodic temperature monitoring
3Speed
If high frequency current components are used for temperature measurement, then measurement speed is improved, but the influence of ohmic resistance decreases
Solution Approach 1:
The patent optimizes the frequency parameter within the 100-1000 Hz range to balance measurement speed and precision. By selecting frequencies in this intermediate range rather than using extremely high frequencies, the method maintains sufficient ohmic resistance influence for accurate measurement while achieving rapid temperature determination
Solution Approach 2:
The patent implements feedback control where the measured resistance values are continuously used to update temperature estimates. This feedback mechanism allows the system to compensate for decreasing ohmic resistance influence at higher frequencies by adjusting measurement strategies and control parameters in real-time
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
This approach enables more accurate temperature determination of stator windings without the need for temperature sensors, allowing for improved thermal management and additional functions like self-testing and harmonic handling, while avoiding torque production and reducing the influence of ohmic resistance at high frequencies.
Implementation Method 1
impinge upon the phase currents at least in part with bias currents that are determined by the vector-based method in such a way that they exhibit no torque effectiveness in the rotating field machine
Implementation Method 2
an ohmic resistance of the stator windings is ascertained
Data Source
AI summary
A method for energizing the stator windings of a rotating field machine operable in motor mode, the stator windings respectively being impinged upon with phase currents that are predefined using a vector-based method. The phase currents are impinged upon at least in part with bias currents that are determined by the vector-based method in such a way that they exhibit no torque effectiveness in the rotating field machine.