Research On Passivity-Based Control Of Three-phase Four-legs D-STATCOM Based On Improved FBD Algorithm

The three-phase four-legs low-voltage distribution static synchronous compensator(D-STATCOM)is an active comprehensive compensation device,which can solve the three-phase unbalance,harmonic pollution and low power factor power quality problems in three-phase four-wire low-voltage distribution network comprehensively and effectively.D-STATCOM can realize the ideal compensation function.The key is the reference command current detection and output current tracking control.In this paper,according to the poor characteristics of real-time and dynamic performance of the traditional current measurement algorithm,the improved design of the traditional Fryze-Bucholz-Dpenbrock(FBD)power current method is presented.In order to change the inherent delay problem in the process of traditional detection,which brought by the detection error of PLL and the analog low-pass filter.The method of extracting the reference voltage using the symmetrical component method is proposed to avoid the error caused by the three-phase voltage distortion or unbalance.The cascade first order inertial filter is used to replace the analog low-pass filter.The MATLAB simulation results show that the improved FBD algorithm obviously reduces the inherent delay.According to the characteristics of D-STATCOM nonlinear and variable structure,the mathematical model of abc static coordinate system and dq0 coordinate system is established.The strict passivity of D-STATCOM is demonstrated in detail based on the Euler-Lagrange(EL)model.In order to accelerate the convergence of the system,an Energy-Shaping-and-Damping-Injection method(ESDI)is used to design the nonlinear passive controller(PBC).At the same time,the results of current compensation based on the classical proportional integral(PI)controller,the quasi proportional resonant(PR)controller and the introduced passivity-based controller(PBC)is analyzed and compared.The simulation results show that the compensation effect of the traditional PI controller is poor and the PR controller parameters are difficult to be adjusted.PBC nonlinear control theory can be used to track the reference current quickly and accurately.After compensation,the three-phase current waveform is ideal,the three-phase unbalance degree is obviously reduced,and the controller parameters areeasy to be adjusted.In the field of nonlinear system,it is worth to be studied and applied in practical engineering.Finally,the hardware platform of 50 KVA three-phase four-legs D-STATCOM is built.The parameter selection of the main circuit components,the design of the hardware circuit board of each module and the software design of the system have been done.Experimental study on harmonic suppression and a comparative analysis of the current after compensation under PBC controller and PI controller are discussed.The results show that the PBC control algorithm can realize the harmonic suppression function effectively.At the end of the paper,an overview of the summary and follow-up study of the subject are elaborated.