Rotor Temperature Determination Using Reactive Power and Loss Models
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Solution Overview
Problem
Existing methods for determining the rotor temperature of asynchronous machines are inaccurate due to reliance on time-consuming analytical or experimental loss calculations and are not effective in part-load ranges or when phase voltage is low, leading to unreliable torque accuracy and thermal protection.
Innovation Solution
A method that combines rotor temperature determination using reactive powers and losses, where the first temperature is plausibility-checked against the second temperature based on operating ranges, with system-dependent errors stored in a characteristic map, and an additional method for determining temperature at rest by operating the machine as a transformer to generate losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotor temperature is determined as a function of reactive powers using an electromagnetic model, then the determination can be performed without time-consuming loss calculations, but the accuracy deteriorates in part-load ranges or when phase voltage is low
Solution Approach 1:
The patent dynamically switches between two temperature determination methods based on the operating range of the electric machine. In normal operating ranges, the electromagnetic model based on reactive powers is used for fast determination. In part-load ranges or low voltage conditions, the thermal model based on losses is used for higher accuracy. This dynamic adaptation resolves the contradiction by selecting the appropriate method for each operating condition.
Solution Approach 2:
The patent changes the input parameters used for temperature determination based on operating conditions. When operating in ranges where the electromagnetic model is accurate, reactive powers are used as input. When operating in part-load ranges or low voltage conditions, the system switches to using loss calculations as input parameters, thereby maintaining accuracy across all operating ranges.
2Measurement precision
If the rotor temperature is determined as a function of losses using a thermal model, then the accuracy is improved, but the determination becomes time-consuming due to complex loss calculations
Solution Approach 1:
The system dynamically selects the determination method based on operating range. The thermal model with loss calculations is only activated when the operating conditions indicate it is needed (part-load ranges, low voltage), avoiding unnecessary time-consuming calculations during normal operation while maintaining high accuracy when required.
Solution Approach 2:
Instead of continuously performing the time-consuming loss calculations, the system applies them partially or selectively only when operating conditions warrant their use. This partial application of the thermal model maintains accuracy in critical operating ranges while avoiding the productivity penalty of continuous complex calculations.
3Device complexity
If only one method for determining rotor temperature is used, then the device complexity is reduced, but the reliability deteriorates in certain operating ranges
Solution Approach 1:
The control device is designed with multi-functionality, incorporating both the electromagnetic model and the thermal model within a single system. This universal approach allows the device to handle all operating ranges reliably by selecting the appropriate function based on conditions, rather than requiring separate systems for different operating ranges.
Solution Approach 2:
The system dynamically adapts its structure by activating only the necessary determination method for the current operating range. This dynamic configuration maintains reliability across all conditions while minimizing the effective complexity at any given moment by only using the required method.
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
Ensures reliable and accurate rotor temperature determination across various operating states, minimizing errors and maintaining robustness by leveraging both reactive power and loss-based methods, and providing a definitive temperature measurement even at rest.
Implementation Method 1
the electric machine is excited by an alternating current in order to determine an electric resistance of the electric machine, and the second rotor temperature is determined as a function of the electric resistance, as a definitive loss for the rotor temperature
Data Source
AI summary
The invention relates to a method for determining a rotor temperature of an electric motor, in particular an asynchronous motor, the rotor temperature being determined at least in accordance with reactive powers and/or in accordance with losses of the electric motor. A first rotor temperature is determined in accordance with the reactive powers and, depending on an operating range of the electric motor, plausibility-checked or replaced by a second rotor temperature, which is determined in accordance with the losses.