Analysis of control strategies of a full converter in a direct drive wind turbine

As wind energy evolves, it is tending towards a direct drive connection using synchronous generators without a gearbox. Variable speed wind turbines with synchronous machines require the conversion of the full power. One alternative is using full converters with a DC link. The objective of this paper is to study different control strategies of a back-to-back DC-link full converter for grid connected direct drive wind turbines. Traditionally, the generator side converter controls the electromagnetic torque, and thus, the generated power, while the grid side converter regulates the DC link voltage as well as the input power factor. In this paper we reverse the control function of each converter, so that, the generator side converter will regulate the DC link voltage, and the grid side converter will control the electromagnetic torque. Both alternatives are analysed and compared by means of simulations based on Matlab/Simulink models. The behaviour of both strategies is examined under abrupt wind speed variations and grid disturbances. Differences in rotor speed tracking, power generated, DC voltage, and grid currents are also analysed.