Research On Balance Control For DC-Link Capacitor Voltages Of Cascaded H-bridge Rectifier

The new advantages of non power frequency transformer cascade power converter with its modular structure,high net side power factor,low breakdown voltage,easy to expand multi-level,in power transmission,static reactive power compensation,new energy and other places have been successfully applied.The cascade H bridge converter can be directly connected to high voltage power grid,thus eliminating the traditional power frequency transformer topology,reducing the converter area;the suppression of power of the AC side current harmonics,unit power factor,two-way flow of energy to complete the system,because in recent years,more and more studies on transformerless cascaded type converter.Firstly,this thesis based on analyzes the running principle of cascaded H-bridge rectifier,the mathematical model of single-phase and three-phase cascaded H-bridge rectifier system is established,and the mathematical model is optimized.The AC side current is subjected to d-q rotation coordinate transformation.The method of feedforward decoupling is used to realize independent control of reactive current and active current.Aiming at the single-phase cascaded H-bridge rectifier system,a control strategy based on three-dimensional modulation is proposed.According to the AC side of the detected voltage and the synthesis of each bridge DC capacitor voltage,select the appropriate adjustment of the modulation track,bridge the duty ratio of the active power regulation of each bridge in unit time of absorption,the realization of the H-bridge DC capacitor voltage balance control fast.Secondly,three-dimensional modulation control strategy application is studied in three-phase cascaded H-bridge rectifier system.Aiming at the problem of voltage balance three-phase cascaded H-bridge rectifier system and adopts the method of negative sequence voltage,the negative sequence voltage to three-phase rectifier system with adjustable active power absorption of each phase,phase voltage balance;phase voltage balance is still using the balance control method of three-dimensional modulation.Finally,the simulation model based on MATLAB / Simulink and based on RT-lab the real-time simulation experiment platform are constructed.The theoretical analysis of single-phase and three-phase system is carried out.The simulation results show that when the system is started and the post of the operating characteristics of the analysis.