The Study On Three-Phase Three-Wire Low-Voltage Static Var Generator

With the continuous development of power electronics technology, more and more compensation devices using power electronics have been applied in the electric power system. As an important part of the modern Flexible AC Transmission System (FACTS), Static Var Generator (SVG) can continuously compensate the grid reactive power between capacitive and inductive, and it has a lot of advantages, such as flexible control and rapid response, etc. In this paper, a deeply research of the low-voltage three-phase three-wire SVG system based on full bridge inverter with an LCL filter has been conducted by means of theoretical analysis, mathematical modeling, simulation experiment and system implementation.Firstly, this paper describes the necessity of power grid reactive power compensation, development and research status of reactive power compensation devices. The properties of reactive power in three-phase circuit and the compensation principle of SVG system are also introduced. Then build a main circuit mathematical model according to the principle of circuit and the theory of coordinate transformation. On the basis of mathematical model, a closed-loop control block diagram for SVG using the direct control method of the inverter-side inductance current is derived. In addition, the principles of reactive current detection, grid voltage phase locking and space vector modulation are introduced. Meanwhile, a design method of the voltage and current regulator in frequency domain is given.In order to suppress the selective harmonic components in steady-state output current of SVG, an optimization method based on the sliding DFT harmonic detection and the feed-forward compensation by the selective harmonic current of the grid-side inductance is proposed. Furthermore, a simulation model based on this method is also built in the Matlab platform to verify its effectiveness.Finally, a prototype of the low-voltage three-phase three-wire SVG is designed. The prototype is tested in the experimental platform by the open-loop and closed-loop reactive power compensation experiments. Experimental results not only show that the performance meets the design specifications and requirements, but also demonstrate the effectiveness of the control method and the correctness of the hardware design.