Motor Thermal Protection via State-Dependent Threshold Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional motor control devices fail to provide effective thermal protection when motor windings experience temperature differences between the detection point and the winding itself, leading to potential burning out due to inaccurate temperature detection, especially when the motor is locked or has poor thermal conduction, resulting in unnecessary activation of protection functions or failure to prevent overheating.
Innovation Solution
A motor control device equipped with a position detecting sensor to determine the motor's operational state, a speed controller to adjust motor speed based on position, a temperature estimation component that adjusts thresholds based on operational states, and a current controller to cut off power when the estimated temperature reaches a state-dependent threshold, ensuring optimal protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a temperature detector (thermistor or thermostat) is embedded in the motor winding to detect temperature, then thermal protection can be provided, but the temperature detector cannot accurately detect the motor winding temperature when there is a temperature difference between the detector and the winding, leading to potential burning out
Solution Approach 1:
The patent replaces the mechanical/physical temperature detector (thermistor or thermostat embedded in motor winding) with an electronic thermal system that calculates temperature based on current history and thermal time constants. This substitution eliminates the need for physical contact between detector and winding, avoiding the temperature difference problem while maintaining protection reliability.
Solution Approach 2:
The patent introduces an intermediary calculation model that uses current commands and thermal time constants to estimate temperature. This intermediary approach indirectly determines winding temperature without requiring direct thermal contact, thus avoiding the measurement inaccuracy caused by temperature differences between detector and winding.
2Reliability
If the motor is locked or has poor thermal conduction, then current may concentrate on one phase causing localized temperature rise, but the temperature detector cannot detect this localized temperature increase, leading to burning out
Solution Approach 1:
The patent replaces physical temperature detectors with an electronic calculation system that processes current history and thermal characteristics. This system can detect localized temperature rises by analyzing phase current distributions and applying appropriate thermal time constants, overcoming the limitation of physical detectors that rely on thermal conduction.
Solution Approach 2:
The patent dynamically adjusts the protection thresholds based on motor operational state (rotating or locked). When the motor is locked, the system recognizes the changed thermal conditions and adjusts the temperature threshold downward to account for localized heating, ensuring protection effectiveness under varying operational conditions.
3Device complexity
If a fixed temperature threshold is used for protection, then the protection function is simple to implement, but it causes unnecessary activation when the motor is rotating (where uniform temperature rise occurs) or failure to protect when the motor is locked (where localized temperature rise occurs)
Solution Approach 1:
The patent makes the protection threshold dynamic by adjusting it based on motor operational state. When the motor is rotating, a higher threshold is used since temperature rises uniformly. When the motor is locked, a lower threshold is applied to account for localized heating. This dynamic adjustment maintains protection accuracy without excessive complexity.
Solution Approach 2:
The patent changes the protection threshold parameter based on motor state (rotating vs. locked). The system monitors motor operation conditions and adjusts the temperature threshold accordingly, using different threshold values for different operational modes to optimize both protection accuracy and system simplicity.
4Reliability
If the thermal time constant of the motor winding is smaller than the detection delay of the temperature detector, then the temperature detector cannot detect the temperature in time, leading to burning out
Solution Approach 1:
The patent replaces physical temperature detectors with an electronic calculation system that computes temperature based on current history and thermal time constants. This electronic approach eliminates the detection delay inherent in physical detectors, providing timely protection that matches the actual thermal response of the motor winding.
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
The solution provides a more accurate and adaptive thermal protection mechanism that prevents motor winding overheating by adjusting thresholds according to the motor's operational state, reducing the risk of burning out and unnecessary protection activations.
Implementation Method 1
an electronic thermal system in which no temperature detector is used... protects objects to be protected by calculating a heating value and a heat release amount to estimate the temperature
Implementation Method 2
If thermal conduction from the motor winding to the temperature detector is poor... the temperature detector cannot detect the temperature of the motor winding correctly
Data Source
AI summary
A synchronous motor control device having an optimal protection function in accordance with an operational state of a motor is provided.The motor control device includes a position detecting sensor detecting an angular position of a motor, a speed controller controlling the speed of the motor based on the angular position of the motor detected by the position detecting sensor, a temperature estimation component that estimates the temperature of the motor from a current command value calculated by the speed controller or a torque command value and, when the estimated temperature reaches a threshold, outputs a current cutoff signal to a current controller that cuts off passage of current to the motor, and an operational state determination part determining an operational state of the motor based on the angular position of the motor detected by the position detecting sensor, wherein the temperature estimation component changes the threshold based on the operational state of the motor determined by the operational state determination component.