Research On Control Strategy Of The Cascaded STATCOM

With a large number of renewable energy access to the distribution system,in order to improve the power quality of the distribution system,the static synchronous compensator(the static synchronous compensator,STATCOM)is proved to be not only in the control of reactive power and voltage regulation on the premise of very efficient operation efficiency and ability to improve the transmission efficiency and capacity of the power grid.The surface plays an important role,and it can also maintain the reliability of the power system.The cascaded STATCOM is a parallel compensation device,which is generally used to solve the problem of reactive power compensation in the distribution system.In order to satisfy the target control and prevent the degradation of the whole system performance,the study of the control strategy of the cascaded STATCOM is particularly important.Based on this,the main contents of this paper are as follows:1.According to the three phase star type main circuit structure,the working principle of the cascaded STATCOM is introduced.The linear STATCOM state space model and the nonlinear switching periodic average model are set up in the coordinate system and the coordinate system respectively.Finally,the small signal model of the cascaded STATCOM in the two phase synchronous rotating coordinate system is derived.It provides theoretical basis for analyzing the controller and improving the system performance.2.The current inner loop controller designed for reactive power compensation is a key part of the cascaded STATCOM.In order to improve the compensation precision and dynamic response speed of the cascaded STATCOM steady state,the control principle of current decoupling is introduced,and the design method of current loop parameters is introduced in detail.3.The difference in the loss of each unit in the chain will lead to the imbalance of the DC side voltage.In order to ensure the stable operation of the device,the balance control of the capacitance voltage of the DC side is needed.In this paper,the capacitor charge and discharge process of H-bridge is analyzed,and the principle of energy balance is expounded.Based on this,the three level DC side capacitor voltage balance strategy in the whole,phase and phase is proposed.Through three levels of voltage balance strategy,the command voltage superimposed to the modulated signal is obtained,and the balance stability of the capacitance voltage of the DC side is realized.Finally,the block diagram of control strategy for chain STATCOM is given.4.To verify the control strategy,the cascaded STATCOM prototype is built,including the design of the main circuit structure and parameters,the design of the hardware control board,the sampling board and the driving board,the design of the underlying FPGA and DSP control algorithms.Based on this hardware platform,the effectiveness of the control strategy is verified by experiments.