Study On Direct Power Control For Open Winding BDFG Fed By Dual 3-level Converters

In recent years,with the rapid development of China's economy as background,energy demand increased,the traditional fossil resources and the lack of utilization and over-exploitation and other issues.Wind energy as abound renewable clean energy on the surface,has been widespread concerned both at home and abroad.At present,permanent magnet synchronous generator and doubly fed induction generator are mainly used in wind power generation system,which the first generator has problems such as high capacity of converter required and high costs,while the last generator has problems such as regularly maintenance required and complicated control method required.Brushless doubly-fed generator as a low-cost generator,which doesn't require frequent maintenance,is especially suitable for wind power system.In this paper,with the project supported by National Natural Science Foundation of China "composite rotor open-winding brushless doubly-fed wind power generator and its direct power control strategy"(project approval number: 51277124)as the background,with the brushless doubly-fed generator regarded as the research object,the direct power control strategy based on open-winding dual 3-level converters is researched,so as to realize power tracking control for open-winding brushless doubly-fed generator system.The research emphases are as follows:Firstly,the working principle of the brushless doubly-fed generator and its three running modes is analyzed,and the power flow between the windings under different operating modes is deeply studied.On this basis,the brushless doubly-fed generator mathematical model in the rotating coordinate system is established,and its simulation model is established to study its running performance.Secondly,The control winding of the brushless doubly fed generator is designed as an open winding structure,and the two ends are respectively connected with a three level converter.Aiming at the topology,direct power control is proposed to realize power tracking control.The direct power control method has the advantages of fast power response,no need of complex coordinate transformation and small computation.In addition,the voltage space vectors of the open-winding brushless doubly-fed generator fed by dual 3-level converters are analyzed,and their different characteristics are compared for providing basis for the design of the direct power control method and re-enactment of space voltage vector selection table.Finally,according to the different characteristics of different voltage vectors in the dual 3-level converters,the control method is improved,and the vector space is partitioned by three different methods,such as 12 sectors,24 sectors and asymmetric 36 sectors partition methods.The direct power control method based on comparing the power error is designed and compared.In the Matlab/Simulink environment,the three kinds of running modes of the open-winding brushless doubly-fed wind generator direct power control system based on the three sector division methods are simulated when the speed and power are changed.The simulation results show that all of the three methods can meet the control requirements of the active power and reactive power,and they can be chosen according to different application situation.