Improved Nearest Level Modulation Strategy for Cascaded H-Bridge Multilevel Converters

With the increasing demand for high-voltage, high-power energy conversion in large-scale energy storage systems, cascaded H-bridge (CHB) multilevel converters have gained significant attention due to their modular structure and voltage scalability. This paper focuses on the nearest level modulation (NLM) strategy commonly used in CHB converters and proposes an improved NLM method. The improvement integrates sinusoidal pulse-width modulation (SPWM) within each voltage step interval and doubles the carrier period to reduce the effective switching frequency. These enhancements not only improve the tracking accuracy of the output waveform with respect to the reference signal, but also significantly suppress harmonic distortion while reducing switching losses. A detailed analysis of the CHB topology, conventional NLM principles, and the proposed strategy is provided, followed by simulation verification. Results show that the improved method effectively balances output quality and switching efficiency, offering a promising modulation strategy for high-performance CHB multilevel systems in energy storage applications.