Coordinated control strategy for voltage support in AC-DC hybrid system with high penetration of renewable energy

Abstract

With the advancement of the DC transmission mode for renewable energy bases, the hybrid cascaded HVDC system has emerged as a dominant structural configuration. To tackle voltage stability issues in weak grid conditions at the sending end, this paper formulates a novel coordinated control strategy between the sending and receiving ends by leveraging the DC current dead band, aiming to integrate multiple voltage regulation resources within the system. Initially, the critical reactive power regulation resources in the hybrid cascaded system are identified through an analysis of voltage support requirements. Subsequently, the reactive power support capabilities and operational constraints of Line Commutated Converters (LCC) and Modular Multilevel Converters (MMC) are quantitatively assessed. Building on device safety limits, a differentiated adaptive coordinated control strategy for the LCC grid connection point voltage is developed, utilizing the DC current dead band. This approach enables transient voltage optimization through adjustments in DC electrical quantities without relying on communication. Validation conducted on a real-time digital simulation platform confirms that the proposed strategy effectively enhances system voltage stability.