Abstract
Modular multilevel converter with integrated battery energy storage system (MMC-BESS) has been proposed for energy storage requirements in high-voltage applications. The state-of-charge (SOC) equilibrium of batteries is essential for BESS to guarantee the capacity utilization. However, submodule voltage regulation can lead to over-modulation of individual submodules, which will limit the efficiency of SOC balancing control. Focusing on this problem, a modified SOC balancing control method with high efficiency is proposed in this paper. The tolerance for battery power unbalance is defined to quantize the convergence of SOC balancing control. Both the DC component and AC component are considered while regulating submodule voltage. The linear programming method is introduced to realize the maximum tolerance for battery power unbalance in different operation modes. Based on the analysis, by choosing appropriate submodule voltage regulation method, the efficiency of SOC balancing control is improved greatly. In addition, the SOC controller is also optimally designed to avoid over-modulation of submodules. Finally, the detailed simulation and experiment results verify the effectiveness of the analysis and proposed control strategy.
Highlights
In recent years, renewable resources are becoming more and more important, but they have great impact on grid due to their stochastic nature, reducing the voltage and frequency stability [1,2].Battery energy storage system (BESS) is necessary and effective in these applications to improve the stability [3]
The investigation indicates that the battery power unbalance efficiency of SOC balancing control
The investigation indicates that the battery power unbalance can can to over-modulation the over-modulation of submodules, limiting the efficiency of balancing leadlead to the of submodules, limiting the efficiency of SOC
Summary
Renewable resources are becoming more and more important, but they have great impact on grid due to their stochastic nature, reducing the voltage and frequency stability [1,2]. Battery energy storage system (BESS) is necessary and effective in these applications to improve the stability [3]. As the interface between batteries and grid, many researches focus on medium and high-voltage power conversion system (PCS). Due to the advantages in medium and high-voltage applications, modular multilevel converters (MMC) has been used in BESS (MMC-BESS). The series connection of massive batteries reduces the reliability and increases the complexity of energy management. In [5,6,7], batteries are integrated into submodules of MMC, constituting a modularized and distributed PCS. Compared with the centralized structure, the reliability and flexibility of distributed structure are greatly improved.
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