Steady-state power distribution in VSC-based MTDC systems and dc grids under mixed P/V and I/V droop control

Abstract

This paper proposes a steady-state power distribution derivation method for voltage source converter (VSC)-based multi-terminal HVDC (MTDC) systems and dc grids under mixed power/voltage (P/V) and current/voltage (I/V) droop control. P/V and I/V droop control are two commonly used control schemes, which can be combined to achieve co-regulation of powers & currents in MTDC systems and dc grids. The proposed method can be used to estimate the power distributions under different scenarios for MTDC systems and dc grids based on VSCs with mixed P/V and I/V droop control. After determining the initial operating point based on an estimation-correction algorithm, redistributed power due to power disturbances, current changes or converter outages is analyzed in detail considering converter overload. An excess power reduction strategy is further proposed to avoid violation of power limits after converter outage. The accuracy of the proposed method is validated through multiple scenarios in a modular multilevel converter (MMC)-based four-terminal dc grid. The comparison between the proposed method and other approaches in the current literature further demonstrates the advantages of proposed power distribution derivation method. • Determination of initial operating point for mixed P/V and I/V droop control by proposed estimation-correction algorithm. • Derivation of power redistribution after dc power/ current reference changes and converter outages. • Consideration of possible converter overloads caused by different system disturbances.