Research On DC Bias Suppression Strategy Of Series Compensation Transformer Between Microgrid And Distribution Network

The research topic of this paper is from the National Science Foundation of China,"Research on coordination control of series compensation links and bus interface power converter in AC/DC hybrid micro-grid"(U1610121).With the rapid development of new energy distributed generation technology,AC/DC hybrid micro-grid has gradually become a new research hotspot in the field of electrical engineering research.Since the operation state of the distribution network is very likely to affect the AC/DC hybrid micro-grid in the grid-connected operation state,this situation is improved by adding a series link between the AC/DC hybrid micro-grid and the distribution network,so the grid-connected AC/DC hybrid micro-grid can maintain ride-through capability and improve power quality when the distribution network fails.At the beginning of the fault of the distribution network,the series compensation transformer in the series link is prone to DC bias,which affects the power quality.Generally,this problem is solved by designing the core of the series compensation transformer to twice the rated value,but this will greatly increase the volume and cost of the series compensation transformer.In order to ensure the reliable,stable and safe operation of the series link between the AC/DC hybrid micro-grid and the distribution network,and to reduce the volume and cost of the series compensation transformer,it is necessary to suppress the DC bias of the series compensation transformer.The specific content of the full text is as follows:(1)Introduced the basic structure and operating principle of the series link respectively.Firstly,the structural characteristics of a typical AC/DC hybrid micro-grid and a series-connected AC/DC hybrid micro-grid are introduced respectively,and a detailed analysis of the specific topology of the proposed series link is made.Then it analyzes the basic principle of the series link working in voltage compensation mode.Finally,the mathematical model of the series link is established under the abc three-phase stationary coordinate system and the dq two-phase rotating coordinate system.(2)Three voltage compensation control methods in series are introduced.Firstly,the four commonly used voltage change detection methods are compared and introduced,and the instantaneous voltage dq detection method based on the instantaneous reactive power theory is derived in detail.Then the voltage-compensated feedforward control method,feedback control method and a composite control method are analyzed.Finally,on the Matlab/Simulink simulation environment and d SPACE experimental platform,the above-mentioned composite control method is used to achieve the function of series link voltage compensation.(3)A DC bias suppression strategy suitable for series compensation transformers in AC/DC hybrid microgrids is proposed.Firstly,the cause of DC bias in series compensation transformer is analyzed.Then combined with the aforementioned voltage compensation composite control method,a DC bias suppression strategy is proposed by controlling the amplitude of the first half period of the output voltage of the series link.Finally,the Simplier/Matlab/Maxwell simulation environment and d SPACE experimental platform realize the DC bias suppression function of the series compensation transformer,which improves the power supply quality of the series link and the economy of the system.