AN INTELLIGENT IMPLEMENTATION OF IMPROVED NONLINEAR DROOP CONTROL SCHEME IN MTDC NETWORKS USING FUZZY SEARCH

摘要

Multi-terminal direct current (MTDC) networks typically operate under active power and DC voltage (P-U_(dc)) droop control. Such control arrangement facilitates active power dispatch, and its design is greatly influenced by DC network characteristics. Therefore, the first part of this paper analyzes P-U_(dc) droop characteristics when implemented on Grid-Side Voltage Source Converters (GSVSCs) of a MTDC network, in which the variations of DC cables' resistances with temperature are taken into account. The analysis establishes that the actual droop characteristics of GSVSCs are nonlinearity, which are contrary to the widely assumption of linear relationships. These findings of presented analysis is fundamental for the design of accurate power dispatch for the GSVSCs. Therefore, an improved droop control scheme using fuzzy search (VDCFS) for MTDC networks is proposed. The proposed improved droop control performs real-time search to capture the droop curves of the GSVSCs over full range of permissible DC voltages and active powers. The proposed droop control is implementation without the assumption of prior knowledge of the DC network parameters which are subject to variations and uncertainty, and instead the droop curves are periodically obtained and updated. The technical viability of the proposed improved droop control has been tested on a four-terminal HVDC network simulation model established in MATLAB/Simulink. Simulation results confirm the accuracy and superiority of the proposed VDCFS scheme over the traditional linear droop scheme in general, and particularly, under the scenario of DC cable resistance changes and power flow variations.