Maximizing Vanadium Redox Flow Battery Efficiency: Strategies of Flow Rate Control

Vanadium redox flow batteries (VRFBs) are one of the most promising technologies for large-scale energy storage due to their flexible energy and power capacity configurations. The energy losses evaluation assumes a very important rule on the VRFB characterization in order increase the efficiency of the battery. Very few papers describe the relations between hydraulic, electrical and chemical contributions to the system energy losses, especially in a large size VRFB system. In the first part a fluid dynamics characterization of a 9kW / 27 kWh VRFB test facility has been conducted. In particular, we will consider the internal resistance as the sum of an ohmic and a transport resistance. Secondly, an overall loss assessment based on both numerical and experimental results has been carried out. Finally, some improvements in the battery management strategy and in stack engineering are proposed, that results from this work and can help the future designer to develop more efficient VRFB stack with a compact design

Ageing Mitigation and Loss Control Through Ripple Management in Dynamically Reconfigurable Batteries

Dynamically reconfigurable batteries merge battery management with output formation in ac and dc batteries, increasing the available charge, power, and life time. However, the combined ripple generated by the load and the internal reconfiguration can degrade the battery. This paper introduces that the frequency range of the ripple matters for degradation and loss. It presents a novel control method that reduces the low-frequency ripple of dynamically reconfigurable battery technology to reduce cell ageing and loss. It furthermore shifts the residual ripple to higher frequencies where the lower impedance reduces heating and the dielectric capacitance of electrodes and electrolyte shunt the current around the electrochemical reactions.Comment: 8 pages, 8 figure

HVDC Transmission and Energy Storage for Wind Power Plant

This thesis will investigate the effects of an energy storage system incorporated into the submodules of a modular multilevel converter connected to a HVDC line. A simulation has been made to see the effects of energy storage on the transmission of power from a generator connected to the grid via a HVDC line with two MMCs connected in each end, one of which incorporates the energy storage system

Comprehensive assessment of fault-resilient schemes based on energy storage integrated modular converters for AC-DC conversion systems

Due to the scalability and flexibility of various modular power electronic converters, integrating split energy storage components (such as batteries and supercapacitors) is feasible and attractive. This paper investigates the operational and economic characteristics of different ac/dc fault-resilient schemes using energy storage integrated modular converters in ac-dc conversion applications. Based on the topological features between the energy storage system (ESS) and the ac and/or dc system, four energy storage based modular converter deployment schemes are presented. Through a case study, operational performance including fault isolation and power compensation under extreme ac/dc fault conditions are verified using time-domain simulation. System losses are evaluated, whereas detailed design considerations, major component usage and estimated capital costs are articulated. The four schemes are compared and selection guidelines are presented. In general, the schemes with independent ESSs would be preferable for such ac-dc conversion applications due to their high operational flexibility

A comparison of power conversion systems for modular battery-based energy storage systems

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.A modular battery-based energy storage system is composed by several battery packs distributed among different modules or parts of a power conversion system (PCS). The design of such PCS can be diverse attending to different criteria such as reliability, efficiency, fault tolerance, compactness and flexibility. The present paper proposes a quantitative and qualitative comparison among the most widely proposed PCSs for modular battery-based energy storage systems in literature. The obtained results confirm the high performance of those PCSs based on the parallel connection of different modules to a single point of common coupling, also identifying those based on modular multilevel cascaded converters as promising concepts according to the assumptions of the present paper.Postprint (author's final draft

Advanced Control of a Multi-Port Autonomous Reconfigurable Solar Power Plant

The multi-port autonomous reconfigurable solar power plant (MARS), which is an integration of photovoltaic (PV) and energy storage system (ESS) to the transmission ac grid and a high-voltage direct current (HVdc) link, is designed to provide frequency response and reject disturbances in the grid with continued operation and reduced transient instability. The complex architecture of the MARS and the intermittent nature of PV underlies the need for developing simple, efficient, and easily generalizable control methods for MARS and MARS-type systems that integrate multiple power sources to the submodules (SMs) in each arm. The presence of different sources such as PV and ESS in each arm of the MARS causes uneven distribution of active power among different SMs present in MARS, thereby leading to unbalanced modules’ capacitor voltages that may impact system stability under various operating conditions. Moreover, in the case of partial shadings, shaded PV SMs will suffer from decreased injected PV power, causing power mismatch between different SMs in the MARS system. An energy balancing control (EBC) method is introduced to balance the capacitor voltages of different types of SMs. Moreover, the system operation region is explored through data-driven method and a machine learning-based EBC criteria are proposed to improve the system efficiency and reduce the switching frequency. The proposed EBC criteria can disable/enable the EBC depending on the MARS input power dispatch commands with high accuracy according to the operation region. To simplify the design process and improved the system performance, the thesis further proposed a neural network-based power mismatch elimination (NNPME) strategy. The NNPME strategy employs ESS to its maximum capacity and the dc and ac circulating currents to transfer power between the SMs, arms, and legs of the MARS and stabilize the system under partial shedding conditions. The aforementioned controls are data-driven methods that require a large amount of simulation data. A model predictive control (MPC) is proposed for more accurate and efficient control of MARS. It can optimally allocate uneven power of ESS and PV in one arm and counteract capacitor voltage deviations. The system dynamic response is largely improved with the implementation of MPC. The proposed advanced controls facilitate the efficient control and energy management of a system with multiple input power sources like MARS to fully utilize its potential with an extended operating region while maintaining high efficiency.Ph.D