Research On Control Strategy Of H-bridge Cascade SVG

In recent years,with the rapid development of power electronics technology,the demand for electronic devices in industrial production has been continuously increasing.The input of non-linear loads has raised the issue of power quality in power grids,and The rapid and efficient reactive power compensation has become a research of high-voltage high-power compensators.Hot spot.This article is based on the static var generation(SVG)of cascaded H-bridge inverters.The main work is as follows:First,the working principle of the H-bridge inverter unit is introduced.The equivalent circuit and the main circuit topology of the cascaded SVG are analyzed.The three-phase,eleven-level cascaded SVG main circuit structure required in this paper is designed.For the carrier phase-shift modulation strategy of cascaded H-bridge SVG,the single-pole frequency multiplication and bipolar SPWM modulation is analyzed and compared,and the single-pole multiplier with higher output level and less harmonic component of output voltage is selected.Frequency CPS-SPWM modulation method.Secondly,for the accurate and rapid extraction of voltage and current under three-phase unbalanced conditions,a positive and negative sequence decoupling control strategy based on double synchronous frames is proposed and a mathematical model is established.The feasibility of this control.In the aspect of reactive current detection,a traditional and improved reactive current detection method based on instantaneous reactive power theory is briefly introduced.Then,the three-phase star-connected Cascade SVG control system is described in detail.Aiming at the problem of DC-side voltage equalization under three-phase unbalance,this paper introduces the hardware voltage-sharing method and software voltage-sharing method,and proposes a DC-side capacitive voltage equalization control method,namely the overall control,phase-to-phase control and phase-to-phase control.In the balanced control strategy,an active voltage vector is superimposed on the overall DC-side voltage control to achieve the balance control of the sub-module units.Simulations verify the correctness of this strategy.Finally,a three-phase star 11-level cascaded SVG with a rated voltage of 3kV and a capacity of ±5Mvar is designed,including the main circuit parameter design of the device and the hardware design of the control circuit.Through the reasonable debugging of the main circuit and the control circuit,the correctness of the circuit design described in this chapter was verified by MATLAB simulation.