Battery Energy Storage with Controllable Voltage Source for Ripple Isolation
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Solution Overview
Problem
Battery energy storage systems in power systems face challenges due to voltage ripple from DC link capacitors, which can cause resistive heating and shorten the lifespan of electro-chemical batteries, and existing solutions like DC/DC converters are costly, especially for high voltage devices.
Innovation Solution
A battery energy storage system with a controllable voltage source that injects a voltage opposite to the voltage ripple of the DC link capacitor, using an active direct current filter device or a switched capacitor circuit, connected in parallel to the power converter, to stabilize the voltage and protect the batteries from harmonic current ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a battery energy storage is connected in parallel with the DC capacitor, then the ripple current is shared between the battery energy storage and the DC capacitor, but a significant amount of ripple goes into the batteries causing resistive heating and shortening their service life
Solution Approach 1:
A DC/DC converter is introduced as an intermediary device between the battery energy storage and the DC capacitor. This converter acts as a mediator that decouples the ripple current from the battery, allowing the battery to provide active and reactive power support without directly承受ing the harmful ripple current. The converter transforms and regulates the power flow, protecting the battery while maintaining system functionality.
Solution Approach 2:
The patent employs a DC/DC converter with rating significantly lower than the full battery voltage (e.g., rated for only a portion of the battery voltage). This allows using a less expensive, lower-rated converter instead of requiring a costly high-voltage-rated converter. The converter handles only the ripple current component rather than the full power, making the solution more cost-effective.
2Reliability
If a DC/DC converter is used to interface the battery energy storage with the DC capacitor, then the battery is protected from ripple current, but the DC/DC converter has to be rated for the full battery voltage which renders the solution costly, especially for high voltage devices
Solution Approach 1:
The DC/DC converter is designed to handle only the ripple current component rather than the full battery power. By rating the converter for a fraction of the total power (e.g., sized for ripple current only rather than full load), the system achieves adequate protection while dramatically reducing converter cost and complexity.
Solution Approach 2:
The patent changes the voltage rating parameter of the DC/DC converter from full battery voltage to a lower value sufficient for ripple current handling. This parameter change allows using standard, lower-voltage-rated converters that are more economical and easier to manufacture, while still achieving the protective function through proper control strategies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively isolates the DC link current ripple from the battery module, providing a stable voltage and extending the service life of batteries while being cost-efficient by using modular and standardized components, reducing the need for high-rated DC/DC converters.
Implementation Method 1
a controllable voltage source adapted to inject a voltage opposite to a voltage ripple of the direct current capacitor
Implementation Method 2
the active filter device comprises a direct current to alternating current converter and a coupling transformer
Implementation Method 3
A primary side of the coupling transformer is connected to a first pole of the battery module and arranged to be connected to the DC link capacitor. A secondary side of the coupling transformer is connected to the AC side of the direct current to alternating current converter
Implementation Method 4
the controllable voltage source comprises a switched capacitor circuit. The switched capacitor circuit comprises a capacitor and four power electronic switches arranged in an H-bridge circuit
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The disclosure relates to a battery energy storage 14 arranged to be connected to a direct current capacitor 13, which is connected in parallel to a power converter 12. The battery energy storage 14 comprises a battery module 15 and a controllable voltage source 16 adapted to inject a voltage opposite to a voltage ripple of the direct current capacitor 13. The disclosure also relates to a power system 10 comprising such battery energy storage 14 and a direct current capacitor 13.