Battery energy storage and power system
View Patent ↗Battery energy storage arranged to be connected to a direct current capacitor, which is connected in parallel to a power converter. The battery energy storage includes a battery module and a controllable voltage source adapted to inject a voltage opposite to a voltage ripple of the direct current capacitor. A power system including such battery energy storage and a direct current capacitor is also disclosed.
1. A battery energy storage arranged to be connected to a direct current capacitor, which is connected in parallel to a power converter, the battery energy storage comprising:
a battery module, and
a controllable voltage source that is electrically connected to the battery module via an electrical conductor and that electrically isolates a DC link current ripple of the direct current capacitor from the battery module by electrically injecting, directly into the electrical conductor, a voltage opposite to a voltage ripple of the direct current capacitor and provides the battery module with a steady DC terminal voltage.
2. The battery energy storage as claimed in claim 1 , wherein the controllable voltage source comprises an active direct current filter device electrically connected to the battery module.
3. The battery energy storage as claimed in claim 2 , wherein the active filter device comprises a direct current to alternating current converter and a coupling transformer.
4. The battery energy storage as claimed in claim 3 , wherein the direct current to alternating current converter has a DC side connected to two poles of the battery module and is powered by the battery module.
5. The battery energy storage as claimed in claim 3 , wherein a primary side of the coupling transformer is connected to a first pole of the battery module and arranged to be connected to the direct current capacitor, and a secondary side of the coupling transformer is connected to an AC side of the direct current to alternating current converter.
6. The battery energy storage as claimed in claim 3 , wherein the coupling transformer comprises an air-cored transformer.
7. The battery energy storage as claimed in claim 3 , wherein a current required to inject the voltage opposite to the voltage ripple is limited to a magnetizing current of the coupling transformer.
8. The battery energy storage as claimed in claim 3 , further comprising a controller that controls the controllable voltage source,
wherein the controller filters out the voltage ripple in the DC link and determines a reference voltage based on the voltage ripple.
9. The battery energy storage as claimed in claim 8 , wherein the reference voltage is scaled in view of a turn ratio of the coupling transformer.
10. The battery energy storage as claimed in claim 9 , wherein the turn ratio of the coupling transformer is ratio between a nominal voltage and a ripple peak voltage ripple.
11. The battery energy storage as claimed in claim 9 , wherein the controller determine the reference voltage by calculating a difference between a DC link voltage and an average of DC link voltage.
12. The battery energy storage as claimed in claim 3 , wherein the coupling transformer is connected in series with a pre-charge circuit, said pre-charge circuit is electrically connected between the coupling transformer and the direct current capacitor.
13. The battery energy storage as claimed in claim 3 , wherein the direct current to alternative current converter comprises an H-bridge converter.
14. The battery energy storage as claimed in claim 1 , wherein the controllable voltage source comprises a switched capacitor circuit, the switched capacitor circuit comprising a capacitor and four power electronic switches arranged in an H-bridge circuit.
15. The battery energy storage as claimed in claim 1 , wherein the controllable voltage source is adapted to receive a reference voltage based on a voltage measured over the direct current capacitor, wherein the reference voltage is equal to the injected voltage.
16. The battery energy storage as claimed in claim 1 , wherein the controllable voltage source and the battery module are electrically connected in series.
17. A power system for connection to an alternating current load, the power system comprising:
a power converter for connection to the load,
a direct current capacitor connected in parallel to the power converter, and
a battery energy storage connected in parallel to the direct current capacitor, the battery energy storage comprising a battery module and a controllable voltage source that is electrically connected to the battery module via an electrical conductor and that electrically isolates a DC link current ripple of the direct current capacitor from the battery module by electrically injecting, directly into the electrical conductor, a voltage opposite to a voltage ripple of the direct current capacitor and provides the battery module with a steady DC terminal voltage.
18. The power system as claimed in claim 17 , wherein the power converter comprises a single-phase power converter, a single phase converter module, a multilevel converter, a modular multi-level converter or a cascaded H-bridge converter structure.
19. The power system as claimed in claim 17 , further comprising a pre-charge circuit, wherein the battery energy storage comprises a direct current to alternating current converter and a coupling transformer, the pre-charge circuit being electrically connected in series with the direct current capacitor and the coupling transformer.