Modeling And Equivalence For The Wind Farm Equipped With Direct-Driven Permanent Magnet Synchronous Generators

This paper addresses the issues associated with the directly driven wind turbine with permanent magnet synchronous generators(D-PMSG), focusing on studies of wind turbine models, control strategies as well as operational characteristics in relation , having established mathematical models of all different components including the aerodynamic system , the current collection system , the driving system and PMSG , thoroughly studied control principles of converters based on the topology——'uncontrolled rectifier bridges'plus'the Boost chopper'plus'PWM controlled inverters', built up converter models and transfer function relations. Having analysed wind turbine's power controlling principles, the paper researches on power flow calculations of different types of wind turbines, puts forward a simplified power flow calculation method of doubly-fed induction generators based on its complicated models that have already exsited. Calculation analysis of numerical samples shows that the simplified model has approximate power flow calculation results with the original one , yet is greatly simplified about the calculation procedure with a higher convergence rate and better applicability . Different reactive power controlling methods of variable speed constant frequency (VSCF) wind turbines adopt different power flow calculations , and power flow calculations under the condition of constant voltage control as well as the condition of constant power factor control are respectively analysed and compared. The paper builds a complete simulation model of D-PMSG under Matlab/Simulink environment, simulates short-circuit current characteristics of D-PMSG , focuses on the situation when the severest three-phase short circuit fault happens at the bus of the exit of wind farms . The simulation results show that the injection current to the grid, which can even be neglected at rough calculations, has been greatly limited due to the adoption of current limiting link. In addition, this paper has simulated current characteristics of single-phase grounding fault and voltage sags, which are common at the exit bus of wind farms. When three-phase short circuit fault happens, the converter efficiently isolates the generator due to which the fault would have little influence on the generator. The core issues during the fault are DC-link voltage rises and rotor speed-ups, which can be dealt with by the adding of energy release device. The studies of this text can provide basis for PMSG's connecting to the grid, the power flow calculation model proposed in the paper applies for power flow calculations of bulk power system with wind farms connected to. The analysis of system modeling sets basis for in-depth study of wind turbines'operational characteristics, while the analysis on fault current behaviors and dynamic characteristics could be applied in areas such as PMSG's connecting to grid analysis and secondary system arrangement and etc.