Hybrid Battery SOC Control via Variable Coefficient to Prevent Engine Hunting
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Solution Overview
Problem
Existing battery charge and discharge control systems for hybrid vehicles face challenges in quickly converging the state of charge (SOC) to a target SOC without causing uncomfortable oscillations in engine power, leading to a hunting phenomenon that affects vehicle occupants.
Innovation Solution
A charge and discharge control apparatus that sets a hunting allowable period and calculates the charge and discharge amount by multiplying the SOC difference with a coefficient based on this period, allowing controlled oscillations that do not discomfort vehicle occupants, and adjusts this period according to driving state parameters like vehicle speed and engine power changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the inclination of charge and discharge amount with respect to SOC difference is increased to improve convergence properties, then the SOC converges to target SOC quickly, but the discharge and charge of the battery are frequently repeated causing hunting phenomenon
Solution Approach 1:
The patent applies dynamics by making the charge and discharge coefficient variable rather than constant. The coefficient is dynamically adjusted based on the difference between current SOC and target SOC, allowing rapid convergence when the difference is large while preventing hunting when the difference is small. This dynamic adjustment resolves the contradiction between fast convergence and engine power stability.
Solution Approach 2:
The patent changes the parameter of charge and discharge coefficient from a fixed value to a variable value that depends on SOC difference. By changing this parameter based on system state, the system achieves both fast convergence (when coefficient is high) and stability (when coefficient is reduced), resolving the technical contradiction.
2Productivity
If the charge and discharge coefficient is increased to quickly converge SOC to target SOC, then convergence properties improve, but hunting phenomenon occurs making driver or passenger feel uncomfortable
Solution Approach 1:
The patent changes the charge and discharge coefficient from a constant parameter to a variable parameter that depends on the SOC difference. When SOC difference is large, the coefficient is high for fast convergence. When SOC difference becomes small, the coefficient is reduced to prevent hunting. This parameter change resolves the contradiction between convergence efficiency and eliminating harmful hunting phenomenon.
Solution Approach 2:
The system dynamically adjusts the charge and discharge coefficient based on real-time SOC difference, transitioning from a static to a dynamic control approach. This dynamic adjustment allows the system to achieve high productivity during convergence while eliminating the harmful hunting phenomenon that occurs with fixed high coefficients.
3Loss of time
If the charge and discharge coefficient is simply increased to improve convergence, then SOC reaches target SOC faster, but the battery undergoes frequent charge-discharge cycles
Solution Approach 1:
The patent changes the charge and discharge coefficient from a fixed high value to a variable value that decreases as SOC approaches target SOC. This parameter change allows the system to minimize time to converge (by using high coefficient when needed) while reducing frequent charge-discharge cycles (by lowering coefficient near target), thus protecting battery cycle life.
Solution Approach 2:
The dynamic adjustment of the charge and discharge coefficient based on SOC difference allows the system to optimize both convergence speed and battery durability. The coefficient is high only when necessary for fast convergence and automatically reduced to minimize unnecessary battery cycling, resolving the contradiction between reducing time loss and preserving battery duration.
Data Source
AI summary
A charge and discharge control apparatus is provided with: a setting device which is configured to set a hunting allowable period (T), which is a hunting period in which hunting of engine power is allowed; and a calculating device which is configured to calculate a charge and discharge amount of a battery by multiplying a difference between a state of charge (SOC) of the battery and a target SOC, which is a target value of the SOC, by a charge and discharge coefficient determined on the basis of the hunting allowable period.