Research On Operation Control Strategy Of Power Electronic Transformer Based On Novel Individual Phase Current Control

Modern power grids are entering a "new energy + Internet" post-carbon era characterized by actively developing energy internet,is a main strategy to deal with the energy revolution of China.Especially the AC&DC hybrid distribution network with a lot of the power electronics technology has become an important direction for future distribution network construction.The key component of the distribution network equipment is the traditional distribution transformer which realizes isolation,energy transfer and other basic functions.But its poor controllability and compatibility make it far from being able to meet the future with the hybrid AC&DC Power distribution network.Therefore,a highly controllable power electronics transformer(PET)becomes the coordinated control electricity distribution network centre.A high-frequency DC-DC transformer module is implemented as a high-frequency power electronics transformer isolation,the key unit of energy transfer and transforming voltage levels becomes the main content of this paper analysis.Firstly,this paper proposes a structure for power electronics transformer based on CLLC resonant converters,a detailed study of the working principle of CLLC resonant converters,and based on the equivalent circuit analysis of the CLLC resonant converter steady-state output gain special type of leakage inductance in the resonance frequency is constant characteristics.At the same time,the optimal design of the cascade PET structure based on the CLLC resonant converter structure is presented.The equivalent mathematical model of cascaded PET structure is established,which provides a theoretical basis for the proposed independent phase current control strategy.In this paper,an novel individual phase current control strategy is proposed,which can make the PET run stably regardless of whether the grid voltage is balanced or not,and the working principle of the control strategy is studied in detail.The decoupling control is realized by the linear phase change,the novel individual phase lock technique and the zero sequence current compensation control for the line voltage,so that the PET can run in a stable state regardless of whether the grid voltage is balanced.Compared with the traditional control strategy,the control strategy of the novel individual phase current control system is greatly simplified because of the clamping characteristics of the CLLC resonant converter,and the control mode is more flexible.Secondly,the power analysis for novel individual phase current control strategy of power electronics transformer,a detailed analysis of the various conditions of reduced load and thecorresponding calculation formula have been recommended.The power analysis includes the active power and reactive power analysis,thus improving the proposed system of the novel individual current control.Finally,when voltage is normal,unbalance or fault,a 10Kv/50Hz/900Vdc-760 Vdc power electronics transformer experimental verification has been made in PSCAD/EMTDC.Based on the experimental waveforms measured,it can fully verify the validity of the system of the independent current control.Meanwhile,according to the experimental waveforms,the power characteristics based on novel individual phase current control strategy is analyzed,and the reactive power compensation scheme is proposed.All of them are provided as a more accurate theory and data base for the optimization of the control structure in the future.