A Natural Switching Surface Control for the ANPC Converter with Fast Frequency Response

To address the transient power surges and DC-link voltage fluctuations arising from fast frequency response demands in new power systems, this paper proposes a Natural Switching Surface (NSS) control strategy for active neutral-point clamped (ANPC) converters. First, the operating modes and working principles of the ANPC converter are analyzed, and the phase trajectory relationship between the inductor current and DC-side voltage under diverse operating conditions is mathematically derived. On this basis, a systematic NSS control law is established according to the piecewise mathematical model of the converter. Furthermore, a current-limited NSS control scheme is developed to suppress transient current spikes, which realizes smooth voltage and current output regulation and effectively mitigates power transients and DC voltage fluctuations induced by fast frequency response operations and external power disturbances. Comprehensive simulation and prototype experimental results validate the superior performance of the proposed method. Quantitative comparisons demonstrate that, compared with the conventional PI control, the proposed strategy shortens the converter startup time by 1.5 s, restricts the DC voltage drop within 15 V under power disturbance conditions (in contrast to over 60 V with PI control), and achieves faster dynamic recovery and higher operation stability. The proposed method provides an effective solution for high-performance fast frequency response and stable grid integration of renewable energy and energy storage systems.