Research On Nonlinear Control Strategies For Distribution STATCOM

Reactive power compensation technology is one of important technologies to improve power quality and guarantee power grid safety. Distribution Static Synchronous Compensator (D-STATCOM) is a new device for the user side of reactive power compensation. It Can compensate the reactive power of the load real-time, fast and continuously, and can also be used to solve the grid voltage fluctuation and flicker, power grid harmonic pollution and other issues. This paper research on key technologies of D-STATCOM mathematical modeling, nonlinear controller design and reactive power and harmonic current detection method in deeply. The main achievements include the following aspectsBased on the D-STATCOM voltage and current vector analysis, D-STATCOM output power by the relation of power grid voltage and output voltage phase Angle is studied. Working principle of the D-STATCOM is described. Then the D-STATCOM three-phase circuit switching function model is established. The system mathematical model in d-q two-phase synchronous rotating coordinate system is established through Coordinate Transformation.For the nonlinear characteristics of the system mathematical model in d-q coordinates, this paper proposes a nonlinear control method using feedback linearization theory. The D-STATCOM meeting the feedback linearization design conditions is verified. Through multiple input multiple output feedback linearization method, the active power and reactive power of the system are decoupled. Feedback linearization coordinate transformation matrix is obtained. For linear system proportional control is used, to ensure the output current zero steady-state error tracks the current. SVPWM controller is designed, which transform the feedback linearization control quantity into PWM control signals, the design method of SVPWM controller is analyzed. Focuses on comparing several synthesis methods of instruction voltage, choose the optimal one.This paper discusses the three phase circuit instantaneous reactive power theory. Based on the theory, instantaneous reactive power and harmonic current detection methods are expounded. The methods are divided into the p-q method and the ip-iq method. For a view that under the condition of power grid voltage distortion condition the results of the p-q method and the ip-iq method are not accurate, the results of two reactive power and harmonic current detection methods under the condition of power grid voltage distortion are analyzed and compared. Proved that the detection results of p-q method under the condition of power grid voltage distortion is not accurate, and the ip-iq method is not affected by power grid voltage distortion, the detection results are accurate.Simulation model of the D-STATCOM is established. The makeup and function of each module in the model is expounded. To load respectively linear resistance-inductance and resistance-capacity situation, nonlinear and mutation situation has carried on the simulation analysis. The validity of the nonlinear controller design is proved. For grid voltage distortion of reactive power and harmonic current detection method has carried on the simulation analysis, which proved the ip-iq method is not influenced by power grid voltage distortion.