Bidirectional EV Charging With BESS for Battery Degradation Control
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Solution Overview
Problem
The repeated charge-discharge cycles of electric vehicle batteries for balancing grid energy demand lead to battery degradation, reducing their lifespan and driving range, and existing systems lack efficient methods to mitigate this degradation while utilizing vehicle batteries for grid support.
Innovation Solution
A bidirectional charger and controller system that manages the discharge of both the vehicle's battery and a separate battery energy storage system to the grid, adhering to boundary conditions for reduced degradation, allowing simultaneous discharge based on demand and battery-specific parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the electric vehicle battery is used for repeated charge-discharge cycles to balance grid energy demand, then the grid can utilize distributed energy storage capacity, but the battery experiences degradation reducing lifespan and driving range
Solution Approach 1:
The system segments the energy storage function by introducing a separate battery energy storage system (BESS) distinct from the electric vehicle battery. The BESS handles the heavy lifting of grid balancing through repeated charge-discharge cycles, while the EV battery maintains its primary function for vehicle propulsion with minimal degradation from grid support activities.
Solution Approach 2:
The bidirectional charger acts as an intermediary between the EV battery, BESS, and electrical power grid. It intelligently manages power flow, enabling the EV battery to discharge to the grid when needed while respecting boundary conditions that prevent excessive degradation, and coordinating with the BESS to meet overall grid demands.
2Reliability
If the battery discharge rate is limited to reduce degradation, then battery lifespan is extended, but the ability to meet peak grid demand is reduced
Solution Approach 1:
The system merges the discharge capabilities of two battery systems - the EV battery and the BESS - to collectively meet grid demand. The EV battery contributes power within its degradation-boundary conditions, while the BESS supplements the discharge to ensure total grid power requirements are satisfied, thus maintaining both battery lifespan and grid power capability.
3Ease of operation
If the electric vehicle battery is charged in the evening when demand is high, then the vehicle is ready for use, but the electrical power grid experiences increased strain during peak demand periods
Solution Approach 1:
The system performs preliminary charging actions during off-peak hours when grid demand is low. The bidirectional charger and controller coordinate to charge the EV battery and/or BESS when electricity demand is lower, rather than waiting until evening when the vehicle is needed. This allows the vehicle to be ready for use while avoiding peak grid demand strain.
Data Source
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AI summary
This invention provides an electric vehicle charging system (100) comprising a bidirectional charger (110), a grid connection (300), a battery energy storage system (120), and a controller (130). The bidirectional charger (110) couples the charging system (100) to a charger inlet (210) of an electric vehicle (200). The battery energy storage system (120) is separate from the electric vehicle (200) and couples to the grid connection (300). The controller (130is configured to receive a boundary condition for reduced battery degradation of a battery (220) of the electric vehicle (200), to receive, from the electrical power grid (300), a demand for electrical power from the electric vehicle charging system (100), and to simultaneously discharge the battery energy storage system (120) and the battery (220) of the electric vehicle (200) to the electrical power grid (300) in dependence of the demand for electrical power and the boundary condition.