PWM Heating Control for Sensorless Overheating Detection

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Solution Overview

Problem

Existing electrical heating devices in vehicles face challenges in detecting overheating efficiently, particularly in high-voltage systems, which can lead to component damage or fire, and current temperature sensing methods add cost, weight, and complexity.

Innovation Solution

A method using pulse-width modulated drive signals to detect overheating by monitoring the duty cycle and amplitude of electrical current through resistive elements, eliminating the need for additional temperature sensors by defining detection thresholds based on supply voltage and setpoints.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If an additional temperature sensor is used to detect overheating, then temperature measurement accuracy is improved, but device complexity and cost increase

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The heating device uses its own existing components (control unit, pulse-width modulated drive signal, and resistive elements) to detect overheating conditions. The control unit monitors the duty cycle of its own drive signal and compares it against threshold values, allowing the system to self-detect overheating without requiring external temperature sensors. This eliminates the need for additional measurement devices while maintaining effective temperature monitoring.

Inventive Principle:

Principle #25Self-service

2Reliability

If an additional temperature sensor is installed, then overheating detection capability is improved, but weight increases

Engineering Contradiction:

Improveoverheating detection capabilityVSAvoiddevice weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The control unit performs multiple functions: it controls the heating elements via pulse-width modulation and simultaneously monitors for overheating conditions by analyzing the duty cycle of its own drive signal. This multi-functionality eliminates the need for separate temperature sensing hardware, thereby avoiding additional weight while maintaining reliable overheating detection capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Speed

If thermal probe is placed close to heating modules, then temperature detection speed is improved, but risk of sensor damage increases

Engineering Contradiction:

Improvetemperature detection speedVSAvoidsensor reliability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The duty cycle of the pulse-width modulated drive signal serves as an intermediary parameter that indirectly indicates temperature conditions. Instead of placing a physical sensor near the heating modules where it would be exposed to extreme temperatures, the system uses the electrical characteristic (duty cycle) of the drive signal as a mediator to infer temperature status, thereby avoiding sensor damage while maintaining detection capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Device complexity

If duty cycle monitoring is used for overheating detection, then device complexity is reduced, but measurement precision may decrease

Engineering Contradiction:

Improvesystem complexityVSAvoidtemperature measurement precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The system implements feedback by continuously monitoring the duty cycle of the drive signal and comparing it against pre-established threshold values that correspond to safe operating temperatures. When the duty cycle exceeds the threshold, the system detects overheating conditions. This feedback mechanism provides sufficient precision for safety-critical temperature monitoring without requiring complex measurement systems.

Inventive Principle:

Principle #23Feedback

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

Enables real-time detection of overheating without additional sensors, preventing damage to surrounding components and reducing system complexity and weight, while maintaining safety and efficiency.

Implementation Method 1

the heating modules comprise resistive elements that for example have a positive temperature coefficient (PTC), i.e. elements such as PTC ceramic resistors

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

the ohmic value of PTC resistive elements increases very rapidly beyond a preset temperature threshold

Methodology Applied

Scientific EffectPositive temperature coefficient effect: Thermistor

Data Source

PatentUS12253866B2Method for detecting overheating of a heating device, and corresponding control unit

Publication Date: 2025.03.18 VALEO SYST THERMIQUES SAS

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.