Submarine Battery String Synchronization via DC-DC Converters
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Solution Overview
Problem
Submarine propulsion systems face challenges in evenly discharging and charging battery strings due to differences in state of charge, leading to potential deep discharge or overcharging, which shortens battery life and complicates communication and control efforts.
Innovation Solution
A method where a battery management system synchronizes the state of charge of battery strings by adjusting string voltages using DC-DC controllers based on measured state of charge, ensuring no overcharging or deep discharge, and allowing for even discharging and charging by setting the string voltage according to a characteristic curve specific to each battery string.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If parallel battery strings are connected without decoupling, then the system complexity is reduced, but unequal charging and discharging occurs leading to deep discharge or overcharging
Solution Approach 1:
DC-DC converters are introduced as intermediary devices between parallel battery strings to enable controlled power transfer. These converters act as mediators that regulate current flow based on state of charge differences, allowing equalization without direct battery connection. This resolves the contradiction by providing a controlled interface that prevents unequal charging/discharging while maintaining system functionality.
Solution Approach 2:
The system dynamically changes operating parameters (power transfer amount, string voltage) based on real-time state of charge measurements. By adjusting these parameters according to battery conditions, the system achieves uniform discharge/charge behavior. This parameter adaptation allows the system to maintain reliability while managing complexity through intelligent control rather than hardware redundancy.
2Reliability
If DC-DC converters are used to decouple battery strings, then battery string uniformity is improved, but the load on individual battery strings increases due to independent charging and discharging
Solution Approach 1:
The control system continuously monitors state of charge of each battery string and uses this feedback to regulate DC-DC converter operation. Power transfer is dynamically adjusted based on real-time SOC differences, ensuring that charging and discharging occur only when necessary to maintain uniformity. This feedback mechanism prevents excessive loading by activating equalization only when SOC imbalances exist.
Solution Approach 2:
The system applies partial equalization action rather than continuous full-power transfer. DC-DC converters operate at reduced power levels during equalization, transferring only the necessary amount of energy to balance SOC differences. This partial action approach minimizes the additional load on battery strings while still achieving the goal of uniform discharge/charge behavior.
3Reliability
If communication and control devices are added to coordinate battery strings, then battery string uniformity is improved, but the device complexity and communication effort increase
Solution Approach 1:
Each battery string's DC-DC controller independently determines power transfer requirements based on local SOC measurements and communicated string voltages. The system uses a distributed control architecture where each controller serves its own battery string autonomously, requiring minimal central coordination. This self-service approach reduces communication overhead while maintaining uniformity through decentralized decision-making.
Solution Approach 2:
The control system is segmented into independent DC-DC controllers, each managing a specific battery string. This segmentation allows each controller to operate autonomously with minimal communication, reducing the overall communication burden. Each segment (controller-string pair) handles its own equalization needs independently, dividing the complex coordination task into manageable independent units.
4Productivity
If battery strings are discharged frequently with high cycle numbers, then productivity is improved, but uneven charging and discharging leads to overcharging and total discharge
Solution Approach 1:
The DC-DC converters enable continuous equalization action during charging and discharging cycles. Rather than periodic intervention, the system continuously monitors and adjusts power distribution to maintain SOC uniformity throughout operation. This continuous action ensures that even with high cycle frequencies, battery strings remain balanced and prevent overcharging or total discharge conditions.
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 ensures even discharging and charging of battery strings, extending their service life and maintaining consistent power supply to submarine systems, even under varying load conditions.
Implementation Method 1
the string voltage of each battery string is set by the respective DC-DC controller using a characteristic for the respective battery string depending on the measured SOC
Data Source
Figure 1~2
Figure 3
AI summary
Submarines have a propulsion network (10) for supplying an electric drive. A plurality of parallel battery strings (11, 12) is associated with the propulsion network (10) for continuous energy supply. The parallel connection of battery strings (11, 12) is problematic, because equalizing currents can flow between the battery strings (11, 12). The avoidance of equalizing currents by means of DC-DC converters (13, 14) can lead to overcharging and deep discharging of the individual strings (11, 12). The invention relates to a submarine and to a method for operating a drive system of a submarine, wherein the states of charge (SOC) of at least two battery strings (11, 12) of a propulsion network (10) are synchronized in that the respective states of charge of the battery strings (11, 12) are measured by respective battery management systems (BMSs) (19) and respective string voltages of the battery strings (11, 12) are set by respective DC-DC converters (13, 14) in accordance with the respective measured states of charge.