Voltage Ripple Suppression And Voltage Balancing Control Of Single-Phase Cascaded H-Bridge Rectifier

As the key equipment of power transmission in the field of rail transit,the stability and efficiency of traction transformer is very important for the development of high-speed railway locomotive.Compared with traditional traction transformer,power electronic traction transformer(PETT)has a significant improvement in power density and wide application prospects.Single phase cascaded H-bridge rectifier(CHBR),as an important part of multistage PETT,has secondary voltage pulsation,which is easy to cause voltage imbalance and seriously endangers the operation safety of equipment.Therefore,this paper focuses on the DC side voltage secondary ripple suppression and voltage balance control method between cascaded modules of single-phase CHBR.Firstly,the operation mechanism of CHBR is analyzed,the state average space model is established,and the small signal dynamic model is established by introducing small signal disturbance,which provides the basis for the design of control system.At the same time,the model shows that the parameters of CHBR have high coupling degree and strong nonlinear characteristics.It is difficult to design the controller of CHBR system.Secondly,aiming at the problem of secondary voltage ripple in CHBR and low power density caused by large filter volume,active power decoupling(APD)technology is introduced to actively transfer and store the ripple power,so as to achieve the goal of reducing DC side voltage ripple.By analyzing the working principle of CHBR with APD,a ripple suppression strategy based on DC ripple voltage feedforward is proposed,which extracts the ripple current information from the ripple voltage for compensation,so as to reduce the dependence of APD on system parameters in discontinuous current mode.The voltage stability is controlled by decoupling capacitor average voltage feedback,which enhances the controllability and stability of APD module.The introduction of APD into CHBR system effectively reduces the demand of DC filter capacitor.Thirdly,aiming at the problem of poor dynamic response of CHBR,a proportional resonant grid side current controller based on feedback linearization is designed,and linear active disturbances rejection controller(LADRC)is used to control the average output voltage of DC side.Through mathematical transformation and disturbance compensation,the nonlinear system is equivalent to a linear system to improve the dynamic response performance of the system.Aiming at the problem of voltage balance between modules,a strategy of balancing control based on dynamic reference voltage is proposed in static coordinate system.By calculating the power deviation between modules in real time and compensating accurately quickly,the voltage balance of modules is realized,so as to improve the dynamic response performance and anti-disturbance capability of the system.In addition,the current sharing strategy of parallel dual active bridge(DAB)converter based on direct power control,CHBR control strategy and APD control strategy constitute the efficient overall control scheme of PETT.Finally,the three module CHBR test prototype based on NI PXIe-7846 real-time controller and wide band gap semiconductor SiC MOSFET is developed,and the effectiveness of the voltage suppression control strategy and the voltage balancing control strategy between CHBR modules are verified by experiments.