Hybrid Forklift Battery SOC Estimation and Power Allocation
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Solution Overview
Problem
Conventional battery control systems for hybrid forklift trucks face challenges in accurately estimating state of charge (SOC) due to temperature influences and frequent charging/discharging cycles, leading to errors in SOC estimation and potential battery deterioration, excessive discharge/charge, and inefficient power allocation between engine and motor generator.
Innovation Solution
A battery control device with a SOC estimating device that determines SOC from established relationships between battery voltage and SOC, revises and resets SOC based on constant discharge current periods, and integrates current to achieve accurate SOC estimation, coupled with a drive power allocation control device that manages discharge/charge currents to prevent excessive battery usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SOC is estimated based on voltage and integrated current in conventional hybrid forklift trucks, then the estimation method is simple, but the accuracy of SOC estimation deteriorates due to temperature influences and frequent charging/discharging cycles
Solution Approach 1:
The patent applies dynamics by making the SOC estimation method adaptive to operating conditions. The controller dynamically selects between different estimation approaches (voltage-based, current integration-based, or combined methods) depending on whether the battery is charging, discharging, or idle, and adjusts for temperature effects. This dynamic adaptation resolves the contradiction by maintaining high accuracy without requiring a permanently complex system structure.
Solution Approach 2:
The patent changes parameters by introducing temperature compensation factors and state-dependent weighting coefficients in the SOC estimation algorithm. By adjusting these parameters based on measured temperature and operating state, the system achieves high accuracy across varying conditions without adding physical hardware complexity.
2Adaptability or versatility
If the battery operates with frequent charging and discharging cycles, then the hybrid power unit provides flexible power allocation, but the error in SOC estimation increases leading to battery deterioration
Solution Approach 1:
The patent implements feedback by continuously monitoring battery voltage, current, and temperature, then using this information to update SOC estimates and adjust power allocation in real-time. The controller receives feedback on battery state and adjusts charging/discharging rates to prevent excessive cycles, thereby maintaining reliability while preserving power allocation flexibility.
Solution Approach 2:
The patent applies beforehand cushioning by establishing protective control strategies that prevent SOC from reaching extreme levels. The controller proactively limits charging when SOC approaches 100% and prevents excessive discharge, cushioning against conditions that would cause battery deterioration before they occur.
3Productivity
If SOC estimation error increases due to temperature and frequent cycles, then power allocation between engine and motor generator becomes inefficient, but reducing control complexity would sacrifice accuracy
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal power allocation strategies in lookup tables or rule sets that account for different temperature and SOC conditions. The controller quickly retrieves appropriate strategies based on current state, achieving efficient power allocation without requiring complex real-time calculations that would compromise accuracy.
Data Source
AI summary
A hybrid forklift truck is provided with an engine, a battery-driven motor generator, and a battery control device that prevents excessive exhaustion or charging of the battery. The state of charge (SOC) of the battery is determined from the battery voltage and SOC when battery current is zero for at least a predetermined time period and from the battery voltage, current and SOC when discharge current is constant for at least a predetermined time period. SOC is revised whenever battery current is zero or constant for at least the predetermined time period, and SOC at any point of time in operation of the forklift truck is estimated by integrating battery current from the SOC revision and subtracting the integrated current from the revised SOC. Drive power of the engine and motor generator are allocated according to a relationship between permissible discharge and charge current and SOC of the battery.