Battery Inverter AC Self-Heating for Cold-Weather Charging
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Solution Overview
Problem
Battery electric systems without a resident thermal management system face inefficiencies in heating battery packs, particularly in cold conditions, as traditional heating methods like heating blankets or ambient heating are slow and energy-inefficient, preventing charging operations in lithium ferrophosphate batteries until they reach a certain temperature.
Innovation Solution
The implementation of an AC waveform-based self-heating circuit topology using a DC voltage bus, an inverter, and electrical switches controlled by a battery controller to generate an AC waveform through the battery pack, allowing for faster and more energy-efficient heating to a predetermined temperature, enabling charging even in cold conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional heating methods (heating blanket or ambient heating) are used to heat the battery pack, then the battery pack can be warmed in cold conditions, but the heating process is slow and energy inefficient
Solution Approach 1:
The battery pack heats itself by utilizing its own internal resistance and the existing DC voltage bus. The controller switches the battery connections to create a self-heating configuration where current flows through the battery cells, generating heat internally without requiring external heating devices or energy input beyond what's already in the system.
Solution Approach 2:
The system changes the electrical configuration parameters of the battery pack by switching between series and parallel connections. During self-heating mode, the controller reconfigures the battery strings to increase current flow through the cells, thereby increasing internal heat generation. This parameter change enables rapid heating while maintaining energy efficiency.
2Temperature
If traditional heating methods are used, then the battery pack can reach charging temperature, but the heating process takes excessive time
Solution Approach 1:
The battery pack performs its own heating function using internal resistance heating (Joule heating). By configuring the battery connections through the controller and utilizing the existing voltage bus, the system generates heat rapidly within the battery cells themselves, eliminating the time delay associated with external heating methods.
Solution Approach 2:
The controller implements periodic switching of the battery configuration between charging mode and self-heating mode. This allows the battery to rapidly alternate between receiving charge and generating internal heat, achieving temperature targets faster than continuous external heating could provide.
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 enables rapid and energy-efficient self-heating of battery packs, allowing charging to proceed once the battery reaches the required temperature, overcoming the limitations of traditional heating methods and ensuring efficient operation in cold conditions without the need for external heating systems.
Implementation Method 1
generating, via the inverter, an AC waveform through the battery pack at a controlled amplitude
Data Source
AI summary
A battery electric system includes an inverter connected to a battery pack and a direct current (DC) voltage bus, first and second electrical switches, and a battery controller. The first switch is connected between the inverter and battery pack, and opens during an alternating current (AC) self-heating mode of the battery pack. This mode includes generating an AC waveform through the battery pack via the inverter at a controlled amplitude. The second switch, which is connected to the inverter and the first switch, closes during the self-heating mode. The controller, in response to calibrated entry criteria, opens the first switch, closes the second switch, and controls ON/OFF conducting states of the power switches to self-heat the battery pack using the AC waveform. The entry criteria includes required charging of the battery pack while a temperature of the battery pack is less than a calibrated temperature limit.