Battery SOC Calibration via Partial Charge Cycles
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Solution Overview
Problem
Conventional elevator systems face inefficiencies due to peak power demand sizing, energy dissipation during regeneration, voltage sag issues, and inaccurate state-of-charge (SOC) estimation of batteries, leading to reduced efficiency and shorter battery life.
Innovation Solution
A regenerative elevator power system with an electrical energy storage system (EES) that controls power distribution between primary and secondary sources based on demand and SOC, using a controller to monitor and calibrate SOC through partial charging/discharging, minimizing depth of discharge to extend battery life and reduce errors in SOC estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SOC estimation methods are used, then the system can operate continuously, but the SOC estimation accuracy deteriorates with cumulative error reaching ±15%
Solution Approach 1:
The patent applies partial action by performing incomplete charge-discharge cycles (micro-cycles) rather than full cycles. The controller executes partial charging when SOC is below a threshold and partial discharging when SOC is above a threshold, accumulating small corrections over time. This approach bounds cumulative error without requiring complete battery cycles, resolving the contradiction between maintaining accuracy and minimizing operational disruption.
2Measurement precision
If full charge and discharge calibration is performed, then SOC estimation accuracy is reset, but battery life is reduced due to accelerated degradation
Solution Approach 1:
The patent performs only partial charging and discharging operations during calibration micro-cycles, typically changing SOC by small amounts (e.g., 1-5%) rather than complete cycles. This partial action approach maintains SOC estimation accuracy by periodically correcting cumulative errors while minimizing stress on the battery, thereby extending battery life compared to full charge-discharge calibration methods.
Solution Approach 2:
The calibration process is implemented as periodic micro-cycles executed at scheduled intervals or when SOC thresholds are reached, rather than continuous full cycles. The controller performs brief charge-discharge micro-cycles that incrementally correct SOC estimation error, maintaining precision without subjecting the battery to repeated full-stress conditions that would accelerate degradation.
3Duration of action of stationary object
If battery SOC is maintained in a narrow optimal range, then battery life is extended, but the system cannot meet peak power demand
Solution Approach 1:
The patent implements dynamic SOC management where the optimal SOC range is not fixed but adapts based on system conditions. The controller adjusts charge-discharge thresholds and micro-cycle parameters in real-time, allowing the battery to operate in narrow ranges during normal conditions to extend life, while permitting wider excursions when peak power demand requires it. This dynamic approach resolves the contradiction between longevity and power capability.
Data Source
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AI summary
Calibration of the state-of-charge (SOC) of a battery-based energy storage system used with a regenerative drive uses an SOC-open circuit voltage (V?oc#191) correlation. The battery is partially charged or discharged to assure operation defined by V?oc#191 following a known V?oc#191-SOC profile, such as a charge or discharge boundary curve. The partial charging/discharging may be synchronized with a traffic profile of an elevator system driven by the regenerative drive. A V?oc#191 measurement is made, and by enhancing the relaxation dynamics of V?oc#191 through regulating battery usage with a reference to traffic profile, a V?oc#191 is estimated more reliably. Using the estimate V?oc#191 and the known V?oc#191-SOC profile, state-of-charge of the battery is determined.