Studies On Integrated Variable-Speed Constant-Frequency Wind Turbine Models And The Application

With the rapid development of wind power technology, variable-speed constant -frequency (VSCF) wind turbine has been widely utilized in MW level wind turbine. In this paper, models of integrated VSCF wind turbine are studied, which are used to calculate and analyze installed capacity limit of wind farm and the voltage stability problem.1) According to the mechanical torque characteristic of wind turbine and rotation speed-torque characteristic of doubly-fed machine, mechanical torque characteristic of VSCF wind turbine is obtained.2) On the basis of steady state model of doubly-fed machine, steady state model of VSCF wind turbine for intergration analysis is established. In this model, power distribution in stator winding and rotor winding is calculated according to both wind-power curve and rotation speed control law of VSCF wind turbine. Method of determining reactive power capacity limit of VSCF wind turbine is also presented, which can be used in power system voltage stability analysis.3) On the basis of dynamic model of doubly-fed machine, dynamic model of VSCF wind turbine for intergration analysis is established. The model is composed of three parts, i.e. machenical part of turbine, doubly-fed machine and control system. Three kinds of wind speed model used in VSCF wind turbine dynamic simulation are introduced.4) With Power System Analysis Software Package (PSASP) developed by CEPRI, steady state simulation and dynamic simulation of grid conneted with VSCF wind turbine are realized, in which VSCF wind turbine models are estabilished using User Program Interface (UPI) of PSASP.5) Methods of calculating wind farm installed capacity limit using power system steady and dynamic simulation are presented. With steady state simulation method, cases under different load levels and wind speed variation are considered. With dynamic simulation method, transient stability under wind speed disturbances and grid faults are investigated.6) Static approaches to analyze wind farm voltage stability are introduced in this paper; named P-V curve method and V-Q curve method, reactive power characteristic of VSCF wind turbine and CSWT are analyzed, and voltage stability of wind farm composed of VSCF wind turbine and CSWT is analyzed respectively.Study results of this paper provide simulation tools for analysis of VSCF wind turbine intergration, which can be used either to analyze the characteristic of single VSCF wind turbine, or to perform power system analysis for grid intergrated with VSCF wind turbines.