Rotor Temperature Determination via Stator Flux Saturation Saliency
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Solution Overview
Problem
Existing methods for determining the rotor temperature of electric induction machines are inaccurate and unreliable, especially at low speeds, and often require additional sensors or complex thermal models, which increase costs and complexity.
Innovation Solution
The method determines rotor temperature by analyzing inherent machine saliencies, specifically using stator flux saturation saliency angles, which are independent of load values and do not require additional sensors, leveraging existing components for speed sensorless control and machine models to adjust rotor resistance and time constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a sensor on the stator winding is used to estimate rotor temperature based on thermal models, then the system complexity is reduced, but the measurement precision of rotor temperature deteriorates
Solution Approach 1:
The patent replaces physical temperature sensors with an electrical measurement approach. By measuring rotor resistance variations through electrical signals and using these to infer temperature through a machine model, the system eliminates the need for physical sensors while achieving accurate rotor temperature determination.
Solution Approach 2:
The patent utilizes the change in rotor resistance parameter with temperature. By monitoring how rotor resistance varies as temperature changes and using this parameter variation to determine temperature, the system achieves accurate temperature measurement without physical sensors.
2Measurement precision
If direct detection of rotor resistance variations is used to estimate temperature, then the measurement precision improves, but the device complexity increases due to requirements for precise injected stator voltage knowledge
Solution Approach 1:
The patent makes the system self-sufficient by using the machine's own operational parameters (rotor resistance variations) to determine temperature. The method uses information already available from the machine's operation without requiring external sensors or complex additional measurement systems.
Solution Approach 2:
The patent implements a feedback mechanism where the determined rotor temperature is used to adapt the machine model parameters. This closed-loop approach continuously refines the temperature determination by comparing measured rotor resistance with model predictions and adjusting accordingly.
3Device complexity
If fundamental wave representation is used for sensorless control, then the device complexity is reduced, but the reliability deteriorates at low speeds and zero frequency
Solution Approach 1:
The patent transitions from fundamental wave analysis to analyzing non-fundamental wave properties, specifically rotor flux saturation saliencies. By changing the frequency domain approach to focus on saturation effects, the system achieves reliable sensorless control across the entire speed range including zero and low speeds.
Solution Approach 2:
The patent exploits the saturation saliency effects which manifest as periodic variations in the rotor flux linkage. By detecting these saturation-induced variations, the system can determine rotor position and speed information without physical sensors, even at standstill and low speeds where fundamental wave methods fail.
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 allows for accurate, reliable, and fast determination of rotor temperature without additional sensors or complex thermal models, maintaining system reliability and reducing costs, especially at low speeds.
Implementation Method 1
the temperature of the rotor significantly influences the rotor resistance and thus the rotor time constant
Data Source
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Figure 4~5
AI summary
The invention relates to a method and an apparatus of determining a temperature of a rotor (RT) of an electric induction machine (1) comprising the steps of: - determining a set of temperature-independent comparative stator flux saturation saliency angles (CSA) in a reference frame, - determining an actual stator flux saturation saliency angle (ASA) in the reference coordinate frame depending on a machine model (MM) comprising at least one rotor temperature-dependent parameter, - determining a temperature-independent comparative stator flux saturation saliency angle (CSA), - determining a deviation between the actual stator flux saturation saliency angle (ASA) and the temperature-independent comparative stator flux saturation saliency angle (CSA), - determining the rotor temperature (RT) as the temperature which minimizes said deviation.