Control strategy for DC series-connected wind farm without energy curtailment

Abstract

With lower construction costs and power losses, the DC wind farm (DCWF) based on series-connected DC wind turbines (DCWT) is a potential collection scheme for large-scale offshore wind power. However, energy curtailment caused by unequal wind speed exists in DCWTs and results in energy waste, weakening the advantages of DCWTs. The energy curtailment mechanism is analyzed for DCWF, where single active bridge (SAB) is used as DC/DC converter in DCWTS and a full-bridge modular multilevel converter (FB-MMC) as the receiving end converter. The linear relationship between input and output of single active bridge (SAB) is interpreted, and a novel coordinate control strategy for DCWF is proposed to solve the wind energy curtailment caused by unequal wind speed. In addition, an auxiliary control strategy for receiving end converter is proposed to reduce the loss on HVDC link. A complete DCWF is built in PSCAD/EMTDC software package, and the results show that the proposed control strategy makes DCWF can operate well without energy curtailment under unequal wind speeds.