Abstract
Cell state-of-charge (SoC) balancing within each branch of a three-phase battery energy storage system (BESS) and among three branches is crucial to overcome the inability to fully utilise the available capacity of a three-phase BESS. The proposed topology is constructed with one branch instead of three branches to take advantage of its idle cells/modules (Ms) (one-third of the total cells/ Ms ) and to eliminate the need of SoC balancing among the branches. Contrary to conventional topologies, idle cells/ Ms can serve as redundant cells/ Ms or can be dropped out of a BESS, thereby leading to a reduction in the cost, control complexity, size, and losses of a BESS. A novel SoC balancing strategy for the proposed topology of a three-phase BESS is introduced in this paper. Moreover, the cell/ M activation algorithm is implemented to minimise the duration needed to activate the cells/ Ms required to generate voltage for the phases, thereby leading to an improvement of battery operational efficiency. Based on the simulation results, SoC balancing among 3996 cells, 2664 cells, 333/222 Ms , and 12 cells in M with the lowest and the highest average SoC is achieved in 53 min, 48 min, 38 min, 18 min and 53 min, respectively.
Highlights
The wide use of distributed generation based on renewable energy is one of the most effective solutions in the power industry for addressing global environmental issues [1]
Electrochemical energy storage technologies are rechargeable battery energy storage systems (BESSs) that store electrical energy in the form of chemical energy [5]. Compared with batteries, such as nickel-cadmium cell and lead-acid cell, lithium-ion (Li-ion) cells have been widely used in BESSs because they are characterised by several features such as high energy density, fast charge/discharge capability, long life span, and low self-discharge rate [6], [7]
SIMULATION RESULTS OF THE PROPOSED TOPOLOGY AND THE PROPOSED SOC BALANCING STRATEGY In order to verify the performance of the proposed topology [see Fig. 1a] and the proposed SoC balancing strategy [see Fig. 9], the simulation model has been constructed in MATLAB Simulink software (R2017b)
Summary
The wide use of distributed generation based on renewable energy is one of the most effective solutions in the power industry for addressing global environmental issues [1]. The proposed SoC balancing strategy can be summarised in two main steps: First, based on M -prioritised (as explained in Section III), Ms with lowest priority will be activated to generate two output voltages that have the lowest two relative currents. M -prioritised alone in the proposed topology for the following reasons: 1) The fundamental idea of the control strategy when using cell-prioritised alone is to activate the cells, one after another, during each Ts of the duty cycle based on CPL to generate the desired Vout. NUCs is the number of cells activated to generate the desired Vout , while
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