The Design Of Power Cell Of Cascaded H Bridge SVG And Research On Control Strategy

With the raised requirement of electric power quality, flexible AC transmissionsystem has been rapidly developed in recent years. As one of the important memberin it, SVG has already become a hot research topic and direction of FACTSequipments because of its superior control performance and good compensationeffect. It can effectively suppress voltage fluctuation, and reduce harmonics.This paper analyzed the cascaded H-bridge SVG which avoids the high cost,huge volume, high loss and transformer ferromagnetic nonlinear caused by multipleof transformer structure and has series of advantages of simple structure, lessdevices, easy to achive modular design and packaging compared with othermultilevel structure. This paper analyzed the basic compensation principle of SVGfirstly, then compared and analyzed the two commonly used modulation strategies,finally, chose the unipolar of double frequence CPS-SPWM mode. It will raise theequivalent switching frequency2N times, with using a pair of inverting modulationwave to compare with the triangle carrier wave. Control strategies include DC sidecapacitor voltage control and AC side control, active voltage vector superpositioncontrol algorithm was applied to DC side to balance the capacitor voltage; the ACside was controlled by state feedback decoupled control, which can achievedecoupling completely of active and reactive power. Simulation result showed thatthe above methods can achieve fast dynamic response, provide better effect ofreactive power compensation, maintain the balance of DC capacitor voltage.Secondly, completed the design of power cell, which in the cascaded SVG.According to the specific functions, which to be achieved in the power cell, thispaper designed the driving circuit of IGBT, signal sampling circuit, power supplycircuit, optical fiber interface circuit and the SPWM producing circuit of FPGA.Also, analyzed loss and heat dissipation of the main circuit.At last, debugging the functions of the power cell through the experiment. andthe result were successful. The power cell designed in this paper is correct. All ofthese laid a solid foundation for cascaded SVG.