Study On Control Strategy Of Cascade H-bridge SVG In Reactive Power Compensation

With the requirement of the power electronic devices in industrial production,the existence of nonlinear loads make the power quality of system become more and more serious. Reactive power compensation fast and efficiently is of great significance to improving the power factor of the system, reducing the capacity of equipment, reducing power loss and so on. Because of its fast speed adjustment, wide operation range, the low harmonic content of the output current, small volume and low cost, Static Var Generator(SVG) is used in the application of reactive power compensation more and more widely.At present, the focus of SVG research is how to improve the accuracy and speed of reactive power compensation. This paper improved the speed of reactive power compensation, which maintained the premise of reactive power compensation more than 99%.Firstly, this paper according to the basic principle of SVG, the equivalent circuit structure is analyzed. For H-bridge cascaded SVG modulation strategy,this paper analysis of the unipolar SPWM modulation method and bipolar SPWM method. By comparing the output level and output voltage harmonic component, this paper choose unipolar SPWM modulation method.Secondly, this paper introduces two detection methods of reactive current:dq method andd qi-i method. On the basis of this, the detection method of reactive current based on power factor mode is introduced in detail: according to the set power factor of the power grid, the reactive power given signal is obtained according to certain algorithm, and the reactive current is obtained from the reactive closed loop control.Then, based on the introduction of the two current control methods: direct current control and indirect current control, this paper adopted two kinds of improved control methods: current control method based on power factor mode and control method of current inner loop based on reactive power mode. The central idea of the two methods is to obtain the reactive current of the reactive power according to the given signal, and then control the SVG reactive currentto track the given current in order to achieve the purpose of reactive power compensation.The detailed function of PSCAD software is introduced in this paper,cascade H-bridge SVG main circuit model is built in the PSCAD software. Two control methods are simulated in this paper, and the simulation results show that the methods are effective.