Novel Hybrid Modulation Method for Modular Multilevel Converter Based Energy Storage System

This paper focuses on introducing a modular cascaded battery energy storage system and establishing a mathematical model for both the AC and DC sides of the energy storage system. Based on this, a corresponding control strategy is proposed. To achieve a specific trade-off between switching times and output harmonics, a new hybrid modulation strategy (NHPWM) is proposed that combines the characteristics of NLM and CPS-PWM commonly used in traditional modular cascaded topologies. With this hybrid modulation strategy, the modulation of each sub-module can be flexibly configured, allowing the system to coordinate device loss and output harmonic characteristics in real time according to system requirements. Additionally, this paper proposes a calculation method based on the theory of double Fourier series expansion to derive the analytical solution of the NHPWM harmonic distribution, providing a theoretical basis for sub-module modulation mode configuration. Finally, the correctness and effectiveness of the modulation strategy and theoretical calculation were verified by simulation and experiment. The proposed method in this paper has demonstrated clear advantages over traditional HPWM and CPS-PWM in terms of harmonics and efficiency, as shown by the experimental results.