基于开关频率调整的构网型变流器暂态过流能力稳定性约束增强方法

The short-term overcurrent capability is critical for grid forming (GFM) converters to provide support during grid fault transient. Although the transient overcurrent (TOC) capability enhancement strategy based on customized and oversized design for power converters has developed in recent studies, these solutions are still difficult to promote due to their high cost and complex hardware structures. To address this issue, this article introduces the switching frequency as the degree of freedom to improve the TOC capability of GFM converter at the software level. By actively reducing the switching frequency in the TOC stage, the rise in junction temperature caused by overrated current can be suppressed effectively. Moreover, the inherent control stability issue of the inner voltage vector control loop under the substantial decrease of the switching frequency is quantitatively studied. On this basis, a multiparameters coregulation strategy is further proposed to ensure sufficient stability margin of the control loop during the TOC stage with the decreasing switching frequency. This strategy solves the contradiction between control stability and thermal demands in the switching frequency-based TOC method and it can further enhance the TOC capability without redesigning the hardware. Finally, the proposed TOC capability enhancement strategy is verified in both the electrothermal simulation and experiment.