Intelligent Battery Pack Modulation Index Improvement
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Solution Overview
Problem
Conventional electric vehicle battery packs with fixed terminal voltage lead to low modulation index during low power requirements, resulting in high electromagnetic interference (EMI) and total harmonic distortion (THD), as the inverter must switch frequently to maintain output voltage, increasing EMI and THD.
Innovation Solution
An intelligent battery pack with freely interconnectable energy modules, each containing at least one energy cell and two switches, is controlled to adjust series or parallel interconnections to match terminal voltage with load demands, optimizing input voltage for the inverter and reducing EMI and THD by maintaining a higher modulation index.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the battery pack uses fixed terminal voltage with standard modules, then the structure is simple and reliable, but the modulation index is low during low power requirements, resulting in high EMI and THD
Solution Approach 1:
The battery pack transitions from a fixed voltage configuration to a dynamic reconfigurable system. The controller dynamically switches between series and parallel connections of energy modules based on real-time load demand, enabling the terminal voltage to adapt flexibly to different operating conditions and maintain optimal modulation index across varying power requirements
Solution Approach 2:
The system changes the electrical parameters of the battery pack by reconfiguring the interconnection topology of energy modules. By switching between series connections (higher voltage) and parallel connections (lower voltage), the terminal voltage parameter is adjusted to match load demands, thereby improving modulation index and reducing EMI and THD during low power operations
2Object-affected harmful factors
If the inverter switches frequently to maintain output voltage with fixed input voltage, then the output voltage stability is maintained, but the modulation index decreases, increasing EMI and THD
Solution Approach 1:
The input voltage parameter to the inverter is dynamically changed by reconfiguring the battery pack's energy module connections. This parameter adjustment allows the inverter to operate with an optimized voltage ratio between input and output, reducing the need for frequent switching while maintaining output stability and improving modulation index
Solution Approach 2:
The controller implements feedback control by monitoring load demand and adjusting the battery pack configuration accordingly. This closed-loop control ensures that the terminal voltage matches the required load demand, enabling the inverter to operate efficiently with higher modulation index and reduced EMI and THD
3Object-affected harmful factors
If the battery pack reconfigures energy modules to match terminal voltage with load demand, then the modulation index is improved and EMI is reduced, but the system complexity increases
Solution Approach 1:
The battery pack is segmented into multiple independent energy modules, each capable of being connected in series or parallel configurations. This segmentation allows flexible reconfiguration to achieve different terminal voltages while maintaining modular simplicity, reducing EMI by optimizing voltage matching without requiring complete system redesign
Solution Approach 2:
The energy modules are designed with universal switching capability, where each module can serve multiple functions by being reconfigured between series and parallel connections. This multi-functionality allows the same hardware components to adapt to different load demands, improving modulation index and reducing EMI without proportionally increasing system complexity
Data Source
AI summary
A method for improving the modulation index using an intelligent battery pack, in which method a battery pack includes a plurality of freely interconnectable energy modules. An energy module has at least one energy cell and at least two switches, and in which method series or parallel interconnection of a respective energy module with at least one adjacent energy module of the battery pack is implemented by a controller. A terminal voltage of the battery pack, which terminal voltage results from the respective interconnection, is adjusted in accordance with a respectively prespecified load demand on at least one N-phase electrical machine. The terminal voltage is connected as an input voltage to at least one multi-stage inverter, and an N-phase alternating current for supplying a respective N-phase electrical machine is formed by the at least one multi-stage inverter on the basis of a level of the input voltage.