A Modular Multilevel Converter-Based Interface for Utility-Scale Energy Storage Integration

Abstract

The prompt realisation of renewable energy sources into modern power systems has aggravated issues around intermittency, fluctuation of the voltage and the instability of the frequency. Utility-scale energy storage systems (ESS) and battery energy storage systems (BESS in particular) have proven useful in providing flexibility, reliability and quality of power to the grid. In this paper, a modular multilevel converter (MMC)-based interface to effectively and easily incorporate utility-scale ESS in the grid is outlined. An extensive system architecture is also created and a mathematical model of the MMC is fully developed to include the arm current interactions, balancing of capacitor voltages etc. In order to provide stable bidirectional power flow and enhanced dynamic performance under conditions of the changing grid conditions, a hierarchical control strategy, which involves regulation of dq-axes currents, is applied. The suggested system is tested against MATLAB/Simulink simulations with various conditions of operation such as load disturbances and grid fluctuations. It has been shown that performance evaluation lowers the total harmonic distortion (THD) to less than 3 per cent, improves voltage regulation and increases rapid transient response compared to traditional two-level voltage source converters (VSC)-based interfaces. Also, the scalability and operational reliability of the high-power use is also increased with the modular structure of the MMC. These findings affirm that the suggested MMC-based interface is a useful and effective tool to integrate energy storage at scale in power systems with a high amount of renewable energy sources.