PTC Heater Control Using Resistance Feedback to Prevent Overheating
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Solution Overview
Problem
In high voltage applications, such as electric vehicles, PTC heating resistors can reach temperatures higher than 200°C, potentially damaging nearby plastic components due to insufficient inherent protection against overheating.
Innovation Solution
A method using two conditions to detect dangerous temperature increases, where if either condition is met, the heating power is turned off to prevent overheating, with Condition A assessing power and its gradient, and Condition B evaluating prolonged elevated resistance, ensuring robust operation and reliable overheating prevention without additional hardware or sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high voltage is applied to the PTC heating resistor to increase heating power, then heating efficiency is improved, but temperature control reliability deteriorates due to insufficient inherent protection
Solution Approach 1:
The patent implements a feedback control mechanism by continuously monitoring the electrical resistance of the PTC heating resistor and comparing it against a predetermined threshold value. When the resistance exceeds the threshold (indicating dangerous temperature), the control unit automatically interrupts or reduces power supply. This closed-loop feedback system ensures reliable temperature control in high voltage applications where inherent PTC protection is insufficient.
Solution Approach 2:
The patent replaces the reliance on inherent thermal-mechanical protection characteristics of PTC resistors with an electrical control system that uses electronic sensing and control circuitry. Instead of depending solely on the material's intrinsic temperature-resistance properties, the system uses electrical resistance measurement and electronic switching to achieve precise temperature control.
2Measurement precision
If additional temperature sensors are added to improve temperature monitoring accuracy, then temperature detection precision is improved, but device complexity increases
Solution Approach 1:
The patent employs the PTC heating resistor itself as the sensing element by utilizing its inherent temperature-dependent electrical resistance characteristic. The same component that generates heat also serves as the temperature sensor, eliminating the need for separate temperature sensing devices. This self-service approach achieves temperature monitoring without adding external sensors or increasing system complexity.
Solution Approach 2:
The PTC heating resistor performs dual functions: it serves as both the heating element and the temperature sensor. By exploiting the correlation between its electrical resistance and temperature, the system achieves multi-functionality from a single component, simplifying the overall device architecture while maintaining accurate temperature detection capability.
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 method effectively prevents overheating in high voltage applications by reliably detecting temperature increases and allowing sufficient cooling time before reactivation, enhancing the safety of PTC heating devices in electric vehicles.
Implementation Method 1
a pulse width modulated voltage is supplied to the PTC heating resistor
Implementation Method 2
The temperature-resistance characteristic of PTC resistors, especially of ceramic PTC resistors, shows a marked increase of electrical resistance at elevated temperatures
Data Source
Figure 1
AI summary
Disclosed is a method for controlling a heating device comprising a PTC heating resistor, wherein a pulse width modulated voltage is applied to the PTC heating resistor, said pulse width modulation having a first time period. According to the invention, the voltage is switched off for a second time period that is at least a hundred times larger than the first period, if a condition A or a condition B are fulfilled, wherein condition A requires that power is below a power threshold and a gradient of power is below a power gradient threshold, and wherein condition B requires that electrical resistance is above a resistance threshold for a third time period that is larger than the first time period, but smaller than the second time period.