Sangam: A Confluence of Knowledge Streams

A High-Efficiency Grid-Tie Battery Energy Storage System

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dc.contributor Electrical and Computer Engineering
dc.contributor Lai, Jih-Sheng
dc.contributor Meehan, Kathleen
dc.contributor Lindner, Douglas K.
dc.contributor Nelson, Douglas J.
dc.contributor Yu, Wensong
dc.creator Qian, Hao
dc.date 2014-03-14T20:16:22Z
dc.date 2014-03-14T20:16:22Z
dc.date 2011-08-31
dc.date 2011-09-17
dc.date 2011-10-25
dc.date 2011-10-25
dc.date.accessioned 2023-02-28T17:19:58Z
dc.date.available 2023-02-28T17:19:58Z
dc.identifier etd-09172011-124632
dc.identifier http://hdl.handle.net/10919/29008
dc.identifier http://scholar.lib.vt.edu/theses/available/etd-09172011-124632/
dc.identifier.uri http://localhost:8080/xmlui/handle/CUHPOERS/266343
dc.description Lithium-ion based battery energy storage system has become one of the most popular forms of energy storage system for its high charge and discharge efficiency and high energy density. This dissertation proposes a high-efficiency grid-tie lithium-ion battery based energy storage system, which consists of a LiFePO4 battery based energy storage and associated battery management system (BMS), a high-efficiency bidirectional ac-dc converter and the central control unit which controls the operation mode and grid interface of the energy storage system. The BMS estimates the state of charge (SOC) and state of health (SOH) of each battery cell in the pack and applies active charge equalization to balance the charge of all the cells in the pack. The bidirectional ac-dc converter works as the interface between the battery pack and the ac grid, which needs to meet the requirements of bidirectional power flow capability and to ensure high power factor and low THD as well as to regulate the dc side power regulation. A highly efficient dual-buck converter based bidirectional ac-dc converter is proposed. The implemented converter efficiency peaks at 97.8% at 50-kHz switching frequency for both rectifier and inverter modes. To better utilize the dc bus voltage and eliminate the two dc bus bulk capacitors in the conventional dual-buck converter, a novel bidirectional ac-dc converter is proposed by replacing the capacitor leg of the dual-buck converter based single-phase bidirectional ac-dc converter with a half-bridge switch leg. Based on the single-phase bidirectional ac-dc converter topology, three novel three-phase bidirectional ac-dc converter topologies are proposed. In order to control the bidirectional power flow and at the same time stabilize the system in mode transition, an admittance compensator along with a quasi-proportional-resonant (QPR) controller is adopted to allow smooth startup and elimination of the steady-state error over the entire load range. The proposed QPR controller is designed and implemented with a digital controller. The entire system has been simulated in both PSIM and Simulink and verified with hardware experiments. Small transient currents are observed with the power transferred from rectifier mode to inverter mode at peak current point and also from inverter mode to rectifier mode at peak current point. The designed BMS monitors and reports all battery cells parameters in the pack and estimates the SOC of each battery cell by using the Coulomb counting plus an accurate open-circuit voltage model. The SOC information is then used to control the isolated bidirectional dc-dc converter based active cell balancing circuits to mitigate the mismatch among the series connected cells. Using the proposed SOC balancing technique, the entire battery storage system has demonstrated more capacity than the system without SOC balancing.
dc.description Ph. D.
dc.format application/pdf
dc.publisher Virginia Tech
dc.relation Qian_H_D_2011_Revised4.pdf
dc.rights In Copyright
dc.rights http://rightsstatements.org/vocab/InC/1.0/
dc.subject Microgrid
dc.subject rectifier mode
dc.subject inverter mode
dc.subject bidirectional ac-dc converter
dc.subject battery management system
dc.subject battery energy storage system
dc.subject lithium-ion battery
dc.title A High-Efficiency Grid-Tie Battery Energy Storage System
dc.type Dissertation


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