Research On Topological Structure And Control Strategy For Dual Two-level Inverter Of Open Winding Brushless Doubly-fed Wind Power Generator

People has created remarkable achievements in the transformation of natural,economic development and industrial production during the long history of struggle,but at the same time,the irrational exploitation and utilization of natural resources has led to global pollution and ecological damage.Wind energy has been the concern of people as a kind of non-polluting and sustainable development energy,and the doubly-fed induction generator has become the main wind turbine model because of its variable frequency constant frequency power generation characteristics.Brushless doubly-fed generator not only inherits the advantages of doubly-fed induction generators,but also omits the slip ring and other structures and reduces the failure rate,which is especially apply to offshore wind power occasions.In this paper,the brushless doubly-fed generator(BDFG)is taken as the research object,and a direct power control(DPC)strategy of the generator is proposed which is suitable for the open winding structure.The main research contents are as follows:(1)This paper summarizes the working principle of BDFG,the three modes of operation and its power flow relations in different operating modes;The rotor of the BDFG is designed with a new type of mixed rotor structure with more stronger coupling ability.The control winding of the stator is designed as an open winding structure.In order to establish its equivalent circuit,this paper deduces the mathematical model of brushless doubly-fed wind power generator into the MT rotating coordinate system.(2)The principle of DPC and instantaneous power theory are researched.The DPC strategy has the advantages of the fast power response,simple calculation and less dependence on the generator parameters,which is especially suitable for wind power generation.Aiming at the special structure of the hybrid rotor open-winding BDFG,the DPC strategy is improved.According to the amplitude of the space voltage vectors,they are divided into long vectors,middle vectors and short vectors,and the different effects of each kind of space voltage vectors in the DPC strategy is summarized.(3)This paper analyzes the space voltage vectors are generated by the double dual-level converters under the open winding structure.In this paper,the generation mechanism and its harm of the common mode voltage and common mode current in the open winding structure of the common DC bus is analyzed.Aiming at the hybrid rotor open-winding BDFG systembased on double-two-level converter,a common-mode voltage elimination control strategy based on DPC is proposed.The proposed method is based on MATLAB / Simulink software.The control method is simulated by MATLAB / Simulink software.The results show that this control method can greatly improve the power control precision of the control system,and ensure the stability of the output voltage and current of the power winding,and effectively eliminates the common mode voltage in the system.(4)This paper designs a control system with TMS320F28335 DSP based on two four-quadrant converters.Build the experiment system of hybrid rotor open winding BDFG with rated power of 23 kW with common DC bus based on the DPC system,and carry out experimental research.Prove the feasibility of the common mode voltage control elimination strategy based on DPC.