Characteristics Of VSC-HVDC Based On ABB Cascaded Two-level Tecnology

As the global energy shortage and environmental pollution have become increasingly prominent, all countries in the world are looking for the more economical, environmental, reliable transmission mode.The high-votltage direct current system based on VSC(VSC-HVDC) becomes an ideal choice, because of its flexibility and reliability, and it has broad application prospects. In this paper, the working principle, mathematic model, operation range and parameter analysis and design of VSC-HVDC system have been detailed theoretical derivated; VSC-HVDC system based ABB cascaded two-level technology has been modeled using PSCAD simulation software, and comprehensive comparative analysis of the cross coupling flow control, decoupling flow control and so on have been made. This paper puts forward a new combination power flow control method, and proves its validity; Harmonic characteristics of ABB cascaded two-level converter and different modulation mode have been carried out a detailed analysis and discussion, and then the relationship of the harmonic and cascaded module number is obtained. The simulation results show that the control strategy of CPS-SPWM techonology is simple. The techonology can increase the equivalent switching frequency without changing the switching frequency, and reduce switching loss.In addition, the paper analyzes the AC system fault, converter valve fault and DC line fault of VSC-HVDC system, obtains the voltage and current stress changes of main components during the fault occurrence and development process of system, and according to the criterion mades reasonable fault protection strategy. It is intended to provide beneficial reference for the future engineering design of VSC-HVDC.