Electric Heater PWM Control to Limit Peak Current
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Solution Overview
Problem
Existing electric heaters in battery electric vehicles face challenges in maintaining control and regulation over a wide voltage range, leading to excessive maximum current and overload of the supply network, which exceeds predefined current limit values.
Innovation Solution
The electric heater is designed with at least two resistor elements connected in parallel, operated with a pulse-width-modulated voltage, and controlled through duty cycles to manage heating power and current within specified limits across varying voltage ranges, using a control unit with IGBTs for efficient regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM control is used to regulate heating power at high voltages, then controllability is improved, but maximum current cannot be reduced and overloads the supply network
Solution Approach 1:
The patent applies periodic action by switching between series and parallel connections of resistor elements at different voltage ranges. At high voltages (above 450V), elements are connected in series to reduce current, while at lower voltages (below 450V), they switch to parallel connection. This periodic switching based on voltage thresholds enables both controllability and current reduction, resolving the contradiction between PWM control benefits and supply network overload.
2Use of energy by moving object
If the heater is designed for high voltage operation, then efficiency is improved, but adaptability to wide voltage range (250V-900V) is reduced
Solution Approach 1:
The heater employs dynamic connection configuration that adapts to different voltage ranges. The control unit monitors voltage levels and automatically switches between series and parallel resistor element connections. This dynamic adaptability allows the heater to operate efficiently across the wide voltage range of 250V-900V, resolving the contradiction between high-voltage efficiency and broad voltage range adaptability.
Solution Approach 2:
The heater achieves multi-functionality by incorporating both series and parallel connection capabilities within a single device. This universal design allows the same heater to efficiently operate across diverse voltage conditions (250V-900V), making it adaptable to different battery states of charge and operating conditions. The multi-functional connection strategy resolves the contradiction between optimized high-voltage performance and broad voltage range compatibility.
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 allows for effective control and regulation of heating power between minimum and maximum requirements while minimizing the maximum current, reducing load on the supply network, and ensuring efficient operation across a wide voltage range.
Implementation Method 1
When the voltage is applied to the heater, heat can be generated in the thick-film elements
Implementation Method 2
heat can be generated in the thick-film elements and then transferred to the fluid
Data Source
Figure 1~2
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Figure 6~7
AI summary
The invention relates to a method (2) for operating an electric heater (1) with at least two resistor elements (TFR1, TFR2). A pulse-width-modulated operating voltage (U) is applied to the resistor elements (TFR1, TFR2) in such a way that the voltage pulses of the individual voltages (U_TFR1, U_TFR2) at the resistor elements (TFR1, TFR2) are shifted in time and the maximum current (I_MAX) in the heater (1) is thereby reduced. The invention also relates to an electric heater (1) for carrying out the method (2) according to the invention.