Research On The Application Of Cascaded Matrix Converters In Medium-voltage And High-power Wind Turbines

With the development of wind turbines,the capacity of wind turbines continues to increase.If the traditional 690 V low-voltage grid connection is still adopted,the grid connection current of wind turbines will be larger and larger,resulting in the increasing cost and loss of wind turbines,and bringing challenges to the operation and maintenance of wind turbines,The medium voltage wind power system based on PMSG has a broad application prospect.In this paper,the application of Cascaded Matrix Converter(CMC)in offshore wind power is studied,and the control strategy of Maximum Power Point Tracking(MPPT)operation and fault-tolerant operation of permanent magnet direct drive wind power system based on CMC is proposed.The power loss and junction temperature of IGBT module in steady-state operation of the unit under rated conditions are analyzed and calculated.The research content and work mainly include the following points:(1)The control strategy of MPPT operation of permanent magnet direct drive wind power system based on CMC is proposed.The modulation strategy of CMC,the four step commutation strategy of bidirectional switch and the vector control of PMSG are studied.Aiming at the problem of low reliability of CMC caused by too many switching devices,a fault-tolerant control strategy of the system is proposed.When there is a fault in the cell,the neutral point shift is used to realize the maximum balanced three-phase line voltage output of CMC,which improves the decrease of the maximum power tracking interval of the unit and is conducive to the improvement of the unit power generation.Finally,a simulation model of permanent magnet direct drive wind turbine based on CMC is built in Matlab/Simulink to verify the feasibility of the topology and the effectiveness of the proposed control strategy.(2)In medium voltage and high-power wind power system,most of the converter faults are caused by IGBT module failure,and IGBT module failure is largely affected by the thermal cycle impact in the working process,because the thermal expansion coefficient of each layer of IGBT module material is different,it will bear different degrees of thermal stress,and long-term accumulation will lead to device thermal fatigue failure.High junction temperature of IGBT module will lead to aging failure.It is of great significance to accurately obtain the junction temperature of IGBT module for system reliability evaluation.Therefore,this paper studies the maximum power loss and junction temperature of IGBT module when the unit operates under rated conditions,and finally carries out simulation verification in PLECS.(3)The hardware in the loop real-time simulation platform of RT-LAB is used to build the hardware in the loop simulation model.The main circuit runs on the FPGA board of the simulator by using RT-LAB software.The controller adopts TMS320F28335 of TI's C2000 series.The information interaction between them forms a closed loop,which verifies the effectiveness of the control strategy.