Battery Management Device Using Equivalent Circuit Model for SOC Estimation
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Solution Overview
Problem
Conventional storage battery systems face challenges in accurately estimating chargeable/dischargeable capacity during constant charging and discharging, leading to inefficiencies and potential system shutdowns due to incorrect SOC estimation.
Innovation Solution
A storage battery management device with a chargeable/dischargeable capacity table and controller that calculates actual capacity based on temperature, SOC, charge/discharge rate, and battery degradation rate, using an equivalent circuit model and internal resistance estimation to predict chargeable and dischargeable power amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a current integration method is used to estimate SOC, then the storage battery system can operate with simple measurement, but current measurement errors accumulate during constant charging and discharging, leading to incorrect SOC estimation
Solution Approach 1:
The patent introduces an equivalent circuit model as an intermediary between current measurement and SOC estimation. This model includes capacitors representing different time constants of battery response, allowing the system to account for transient effects and measurement errors without requiring direct integration of all current fluctuations. The model acts as a filter that separates meaningful charge/discharge signals from measurement noise.
Solution Approach 2:
The patent changes the estimation parameters by using voltage-based SOC estimation supplemented by current integration only during specific phases (charging phase and discharging phase). The system dynamically adjusts which parameters are used for estimation based on operational conditions, rather than continuously integrating current which accumulates errors.
2Reliability
If SOC estimation value is smaller than real value, then the storage battery system operates conservatively, but the apparent dischargeable capacity becomes smaller and the system cannot operate efficiently
Solution Approach 1:
The patent implements feedback mechanisms where the equivalent circuit model continuously monitors voltage responses to current changes and adjusts SOC estimation accordingly. The system uses voltage measurements during charging and discharging phases to feedback-correct the SOC value, preventing excessive conservatism while maintaining reliability. This closed-loop approach ensures the system operates near optimal capacity without risking premature shutdowns.
3Productivity
If SOC estimation value is larger than real value, then the storage battery system plans for greater capacity, but the storage battery reaches end-of-discharge voltage before SOC becomes 0%, causing unexpected system shutdown
Solution Approach 1:
The patent applies beforehand cushioning by using the equivalent circuit model to predict voltage behavior and SOC trends before actual discharge completion. The model anticipates when the battery will reach end-of-discharge voltage by analyzing voltage responses during discharging phase, allowing the system to plan capacity utilization with appropriate margins. This prevents unexpected shutdowns while maximizing usable capacity through accurate prediction rather than conservative limits.
4Reliability
If the storage battery repeats charging and discharging constantly to stabilize power system frequency, then the system prevents output fluctuations of natural renewable energy, but current measurement errors accumulate and SOC cannot be estimated correctly
Solution Approach 1:
The patent applies periodic action by structuring the estimation process to reset and recalibrate during each charging and discharging cycle. The equivalent circuit model is updated periodically with new voltage and current measurements from each phase transition, preventing error accumulation that would occur with continuous integration. Each cycle provides fresh data to refresh the model parameters and maintain accuracy despite constant cycling operations.
Data Source
AI summary
According to one embodiment, a storage battery management device includes a chargeable/dischargeable capacity table, a controller, and a communication controller. The chargeable/dischargeable capacity table stores therein in advance a chargeable/dischargeable capacity corresponding to a temperature, a state of charge (SOC), a required charge rate or discharge rate, and a battery degradation rate of a secondary battery. The controller calculates an actual chargeable/dischargeable capacity by referring to the chargeable/dischargeable capacity table based on the temperature, the SOC, the required charge rate or discharge rate, and the battery degradation rate of the secondary battery. The communication controller informs a host device about the chargeable/dischargeable capacity of the secondary battery.