Research On STATCOM Integrated With Distribution Transformer Based On Passivity Control Method

In recent years,with rapid development of micro grid and energy Internet,the penetration of distributed generation equipments in distribution network increases year by year.The reactive power and voltage of the distribution power grid is more complex with widely used converter,electric vehicle and other small inertia power electronic load,which highlights the importance of dynamic reactive power compensation.STATCOM has been widely used in energy saving and power quality optimization control of modern distribution power grid.Conventional high voltage STATCOM suffers from high voltage stress,complex power topology and high cost.The low voltage distribution STATCOMs have low overall efficiency,because they are always installed separately and lack of coordination.To overcome the above shortages,this paper proposes that the distribution transformer which is at the intersection of voltage level is regarded as an important and effective reactive power compensation point.Distribution transformer integration STATCOM(DT-STATCOM)and nonlinear passivity based control method(PBC)are adopted,which can effectively reduce the voltage stress and initial investment,enhance the integration of the equipment,and improve the performance of the dynamic reactive power compensation.It has application prospect in the field of centralized reactive power compensation of medium and high voltage distribution power grid.Firstly,the principle and technical scheme of cascaded DT-STATCOM are studied.According to the actual distribution powe grid,the topology of the integrated STATCOM with Dyn11 type distribution transformer at high voltage central winding is introduced.This paper studies the voltage stress of DT-STATCOM.The steady state vector analysis method is used to quantitatively study the distribution law of the winding current after the injection compensation current.In this paper,medium voltage STATCOM,D-STATCOM and DT-STATCOM are compared,and it is proved that DT-STATCOM has better technical and economical performance.The current distribution of the distribution transformer is verified by simulation,which ensures that the transformer winding will not overload.The traditional PI controller for STATCOM reactive current loop has some problems such as poor system robustness,slow response to transient conditions and difficulty in setting PI parameters.In this paper,the description method of STATCOM system based on Lagrangian analysis method is studied.Based on Euler-Lagrange(EL)equation,the DT-STATCOM mathematical model with LCL filter is established from the energy point of view.On this basis,the strict passivity of STATCOM system with LCL filter is proved,and the reactive current control law based on PBC is designed.The virtual damping injection method is used to accelerate the dissipation of the system,and the influence of the virtual damping injection on STATCOM is revealed.The three level structure of DC capacitor voltage balance control strategy is designed to realize the stability control of capacitor voltage.Based on the Matlab/Simulink platform,DT-STATCOM with LCL filter simulation model is built.Finally,DT-STATCOM system dynamic experiment platform is developed,and the hardware and software of the control system is designed.The distribution of the winding current and the reactive power compensation performance of the DT-STATCOM system are tested on the developed DT-STATCOM experiment platform.The correctness of the mechanism analysis is verified by experiments.The experiment results show that the DT-STATCOM system has good reactive power compensation performance and fast dynamic response characteristics.