Variable frequency operation of a HVDC-VSC interconnected type 1 offshore wind power plant

Abstract

A Department of Energy study showed wind power generation may reach 330 GW and 20% penetration of total energy production by 2030. Of this, 54 GW of wind power will be generated at offshore wind power plants. The deployment of offshore wind power plants requires power transmission from the plant to the load center inland. Depending on the distance to shore, the use of high-voltage direct current (HVDC) transmission may be economically justified. The use of HVDC has many operational and reliability advantages, and among them is the possibility of variable frequency operation of the sending-end (offshore wind power plant) power converter. This will allow the offshore wind power plant to operate at variable frequency but constant volt/hertz ratio. In this paper, a variable frequency constant volt/hertz operation will be applied to the Type 1 wind turbine (induction generator) for offshore wind power plants. The benefits of such variable frequency constant volt/hertz application include (a) low-cost variable speed wind turbines (no need to install a power converter at each turbine), (b) improved energy capture of the wind turbine by variable speed operation, and (c) enhanced compliance in energy conversion from aerodynamic to mechanical to electrical power. Various control aspects of Type 1 generators at the plant level and at the turbine level will be investigated. The potential impact of the proposed system on lowering the cost wind power will be investigated as well.