Battery Relay Switching Order for Thermal Load Management
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Solution Overview
Problem
In parallel-connected battery systems, varying Open Circuit Voltages (OCV) between batteries can cause inrush currents when relays are switched on, leading to thermal loads and potential damage to relays, especially when switched on at different timings.
Innovation Solution
The order of switching relays from the OFF to the ON state is dynamically changed based on estimated thermal damage, with the relay suffering less damage being switched last, and a third relay is used to control charge and discharge between batteries, while an information output section notifies users of relay lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If relays are switched from OFF to ON in parallel-connected battery systems with varying OCV, then charge and discharge functionality is enabled, but inrush current flows causing thermal load and relay damage
Solution Approach 1:
The patent applies preliminary action by calculating the OCV difference between batteries before switching relays and determining the switching order in advance. The controller identifies which relay should be switched last based on the OCV comparison, ensuring that the relay experiencing minimal thermal load is switched last. This preemptive planning prevents excessive thermal damage before it occurs.
Solution Approach 2:
The patent implements dynamics by making the relay switching order adaptive rather than fixed. The controller dynamically determines the switching sequence based on real-time OCV measurements and differences between batteries. This dynamic adjustment ensures that the relay with the smallest OCV difference to the source battery is always switched last, optimizing thermal load distribution under varying operating conditions.
2Reliability
If relay switching order is fixed, then control logic is simple, but one relay consistently suffers more thermal load and deteriorates faster
Solution Approach 1:
The patent applies parameter changes by using OCV values as the basis for determining relay switching order. Instead of a fixed sequence, the controller changes the switching order based on OCV parameter differences between batteries. By comparing OCV parameters and identifying the battery with the closest OCV to the source, the system dynamically adjusts which relay switches last, distributing thermal load more evenly while maintaining relatively simple control logic.
3Object-affected harmful factors
If the relay with smallest OCV difference is switched last, then thermal load is minimized, but requires real-time OCV measurement and calculation
Solution Approach 1:
The patent applies self-service by utilizing the OCV information that is already being measured and monitored by the battery management system for other functions. The controller uses existing OCV measurements and calculations to determine relay switching order, rather than requiring separate dedicated measurement systems. This approach minimizes additional measurement complexity while achieving thermal load reduction.
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 approach shares thermal loads between relays, reduces relay deterioration, and extends their lifespan by alternating the switching order and providing timely notifications for relay replacement.
Implementation Method 1
The relay is used to allow or prohibit charge and discharge of each of the assembled batteries
Implementation Method 2
an inrush current may flow from the assembled battery having a higher OCV to the assembled battery having a lower OCV
Implementation Method 3
an inrush current may flow to the relay which is turned ON last, and that relay may be subjected to a thermal load due to the inrush current
Data Source
Figure 1
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Figure 3~4
AI summary
[PROBLEM] To suppress deterioration of a relay. [SOLVING MEANS] A battery system includes a first battery (10) and a second battery (20) connected in parallel and performing charge and discharge. A first relay (SMR-B1) is switched between an ON state in which the charge and discharge of the first battery are allowed and an OFF state in which the charge and discharge of the first battery are prohibited. A second relay (SMR-B2) is switched between an ON state in which the charge and discharge of the second battery are allowed and an OFF state in which the charge and discharge of the second battery are prohibited. A controller (41) controls the ON state and the OFF state of each of the first relay and the second relay. The controller also changes the order in which the first relay and the second relay are switched to the ON state, in performing the charge and discharge of the first battery and the second battery.