Research On Encapsulation Parameters Design Of Bridge Arm Reactor Of Flexible DC Converter

Bridge arm reactor is connected in series in each branch of converter of VSC-HVDC system.As a key component,it has the problem of uneven temperature rise distribution,which will induce a series of thermal faults and threaten the stable operation of power grid.With the continuous expansion of the hybrid scale of AC/DC transmission projects,the working conditions of bridge arm reactors are becoming more and more complex.The existing design methods are not suitable for AC/DC superposition conditions,and can not effectively solve the problem of excessive local temperature rise.Thus,it is of great significance to balance the current distribution among the encapsulations by designing,so as to avoid the overheating of a certain encapsulation during the operation of bridge arm reactors.The research results obtained in this paper are as follows:For the electromagnetic calculation of the bridge arm reactor,two targeted optimization design methods for encapsulation parameters are proposed based on the existing design methods.Firstly,the modular calculation of multi-encapsulations inductors under different placement modes is completed,and then the equivalent voltage equations of parallel branches are derived.On this basis,combined with the actual design of the bridge arm reactor,the advantages and disadvantages of the equal current density method,the equal resistance voltage method and the isothermal rise method are obtained.At the same time,the existing design methods could not satisfy multiple constraints,a comprehensive optimization design methodology based on weight coefficient hybrid constraints is proposed,for the Wudongde ±800 kV bridge arm reactor,the comprehensive performance is improved by 24.3%and 28.5%compared with equal resistance voltage method and isothermal rise method.In order to improve the encapsulation temperature rise distribution and match encapsulations’ heat-generating and heat-dissipating performance at different positions,a differential constrained optimization design methodology of inner and outer encapsulations is proposed,for the Wudongde ±800 kV bridge arm reactor,compared with equal resistance voltage method and isothermal rise method,the encapsulation temperature difference decreases by 16.4%and 12.5%respectively.A set of design methods suitable for AC and DC combined working conditions of bridge arm reactor is formed.An equivalent electromagnetic model is established for the AC/DC superposition working conditions of the bridge arm reactor.In addition,the actual overload and harmonic conditions are taken into account in the calculation,and the distribution law of the alternating current and the direct current among parallel branches are obtained.Based on the restriction and influence of actual working conditions to design,a set of parameter adjustment methods suitable for this situation is proposed based on gradient descent method.For the Wudongde ±800 kV bridge arm reactor,as the optimization target facing equal temperature rise,the difference between maximum and minimum temperature rise among encapsulations is reduced to 0.9 K,as the optimization target facing equal resistance voltage,the difference between the maximum voltage and the minimum voltage of each encapsulation resistance is reduced to 0.1 V.Two new reactor structures are proposed to improve the encapsulation temperature rise distribution.The axial partition structure and radial layered structure of the reactor are proposed.The effective heat loss per unit area of each encapsulation is increased by segmentation,and the heat dissipation area is increased to improve the temperature rise distribution of encapsulations.For the Wudongde ±800kV bridge arm reactor,compared with the traditional integrated structure,the encapsulation temperature difference of the axial partition structure decreases from 45.6 K to 37.4 K,and the hot spot temperature rise of the encapsulation decreases from 58.3 K to 44.5 K.The hot spot temperature rise of the radial layered structure decreases by 33.9%.A set of modular functional design software for the bridge arm reactor is formed,which can reflect the calculation details.Various design methods are included in the software,optimization design is carried out according to the specific AC/DC superposition working conditions,and all kinds of information involved in the reactor design process are effectively graphed.Finally,the effectiveness of design is verified by the prototype temperature rise test.