Research Of An Improved Deadbeatcontrol Strategy Applied To Distribution Static Synchronous Compensator

Nowadays, power quality issues are calling more and more attention. As one of the most important parts, reactive power pollution in the grid should not be ignored. Distribution Static synchronous Compensator(D-STATCOM) is the new generation of the reactive power compensation device. It can offer effective compensation of reactive power in the distribution network and is considered as a trend in the field. While in actuel grid, the reactive current fluctuates frequently due to the change of load. Therefore, it is of great practical significance for the safe and reliable operation of electric power lines to ensure a fast compensation of the reactive power in the grid.To achieve this goal, an improved deadbeat control strategy applied to a D-STATCOM with a three-phase two-level voltage source inverter topology is proposed in this paper. Firstly, a mathematical model of D-STATCOM is built in the two-phase stationary coordinate and its deadbeat form is deduced. Then, a deadbeat controller is designed as the current loop, while a conventional PI controller is used in the outer loop. After analyzing the stability of the current loop, a modified deadbeat controller is presented. Since the existing of inhence delay of the digital system, such as sampling and computing, a two beats prediction is made for the grid voltage and reference compensating current, to achieve a real deadbeat control.Deadbeat control is a control method based on system model, so that it is sensitive to the variation of system parameters. In this regard, a weighted recursive least squares method is applied to identify the filter inductor, in order to enhance the stability of the D-STATCOM deadbeat control system. Meanwhile, to improve the control accuracy, a repetitive state predictor is designed to predict the compensating current,and the stability of the whole current loop is analyzed as well. Since the grid frequency variation would result in poor performance of the repetitive controller, a modified FIR low-pass filter based repetitive predictor with frequency adaptive function is presented in this paper.On the basis of theoretical analysis, the simulation is carried out with the Matlab/Simulink software. Meanwhile, further experimental verification is made on the d SPACE hardware-in-the-loop experimental platform in the laboratory. The simulation and experimental results show that the D-STATCOM device applying the proposed deadbeat control strategy based on repetitive predictor can quickly compensate for reactive power and has both good steady-state performance and dynamic performance.