PWM Duty-Cycle Overheating Detection in Electric Heaters
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Solution Overview
Problem
Existing methods for detecting overheating in electric heating devices for vehicles are costly, space-intensive, and prone to additional failure points, relying on additional sensors that increase weight and complexity.
Innovation Solution
A method using pulse width modulation (PWM) control signals to monitor and control the electrical power supply to resistive elements in electric heating devices, allowing for real-time detection of overheating by analyzing the duty cycle of the PWM signal without the need for additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an additional thermal probe sensor is used to directly measure the temperature of the electric heating device, then the temperature detection accuracy is improved, but the device complexity, cost, and weight increase
Solution Approach 1:
The control unit utilizes existing operational parameters (PWM duty cycle, supply voltage, current intensity) to self-diagnose overheating conditions without requiring external sensing components. The system monitors its own operational state through parameters already being measured for control purposes.
Solution Approach 2:
The patent uses intermediary parameters (duty cycle, voltage, current) that mediate between the heating elements and the control unit to indirectly detect temperature conditions. These parameters serve as proxies for direct temperature measurement, allowing inference of thermal state without thermal contact.
2Measurement precision
If an additional thermal probe sensor is used to directly measure the temperature, then the temperature detection accuracy is improved, but the cost and weight of the device increase
Solution Approach 1:
The control unit utilizes existing operational parameters (PWM duty cycle, supply voltage, current intensity) to self-diagnose overheating conditions without requiring external sensing components. The system monitors its own operational state through parameters already being measured for control purposes.
Solution Approach 2:
Instead of using a physical thermal probe that copies the temperature measurement function, the patent creates a virtual copy of temperature information by calculating thermal state from electrical parameters (duty cycle, voltage, current), eliminating the need for physical sensing mass.
3Measurement precision
If an additional thermal probe sensor is used to directly measure the temperature, then the temperature detection accuracy is improved, but the reliability decreases due to additional failure points
Solution Approach 1:
The control unit utilizes existing operational parameters (PWM duty cycle, supply voltage, current intensity) to self-diagnose overheating conditions without requiring external sensing components. The system monitors its own operational state through parameters already being measured for control purposes.
Solution Approach 2:
The existing control unit and its measurement of electrical parameters serve multiple functions: controlling the heating elements and simultaneously detecting overheating conditions. This multi-functionality eliminates the need for dedicated temperature sensing components that would add failure points.
4Speed
If the duty cycle detection threshold is set to detect overheating early, then the detection speed is improved, but false detection may occur when the device is in cold state
Solution Approach 1:
The control unit performs preliminary assessment of the heating device state by evaluating multiple parameters (duty cycle, supply voltage, current intensity) before triggering overheating detection. This preliminary analysis ensures that detection thresholds are only applied when the device is in an operational state where overheating is possible.
Solution Approach 2:
The system continuously monitors the relationship between duty cycle and actual heating effect through current intensity measurements, providing feedback that adjusts the interpretation of duty cycle values. This feedback mechanism distinguishes between high duty cycle due to cold state (normal) and high duty cycle due to overheating (abnormal).
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 effective and real-time detection of overheating in electric heating devices, preventing damage to surrounding components while reducing costs, weight, and complexity by eliminating the need for additional sensors.
Implementation Method 1
The electric heating device comprises electric heating modules... The heating modules comprise resistive elements, for example with a positive temperature coefficient (PTC)... The resistive elements may be powered by an on-board electrical voltage source
Implementation Method 2
the heating modules comprise resistive elements, for example with a positive temperature coefficient (PTC), such as PTC stones... the ohmic value of PTC resistive elements increases very quickly beyond a predetermined temperature threshold
Data Source
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AI summary
The present invention relates to a method for detecting overheating of an electrical heating device comprising a plurality of resistive elements configured to be supplied electrically using a control signal by pulse width modulation according to a setpoint, comprising the following steps: - detecting the setpoint, - detecting the duty cycle (PWM_system; PWM_subsystem), - defining a threshold value for detecting the duty cycle according to the setpoint, or a value of at least one parameter for monitoring an incidence of overheating, - comparing the detected duty cycle value with the detection threshold value, and - detecting an incidence of overheating when the detected duty cycle value reaches the detection threshold value. The invention also relates to a corresponding control unit.