Research On CHBR Voltage Balance Control Based On MPC

High-speed railway is an important mode of traffic and transportation,which can provide convenient,safe and on-time transportation services,and provide great convenience for people’s travel and cargo transportation.With the development of power industry,power frequency traction transformer has exposed its shortcomings of large size,heavy weight,and low frequency harmonic content,so scholars began to explore how to use power electronic converter to replace it,so power electronic transformer has been widely concerned by people,and its related research is also of great significance.With the development of power electronics technology,various multilevel topologies continue to emerge,and H-bridge cascade multilevel structure is one of them.Cascaded HBridge Rectifiers(CHBR)are the input stages of cascaded Power Electronic transformers(PET).This structure helps to increase the voltage level of the input power electronic devices.Solve the power problem of a single switching tube;In addition,the multilevel input on the AC side and the appropriate increase of the switching frequency can suppress the harmonic component to a certain extent.In addition,if the device has good control performance,it can improve the quality of the DC voltage of the medium and high frequency DC-DC converter,and the whole traction system can operate better.Therefore,it is of great practical significance and value to study this device and design a scientific control strategy for it.To this end,the principle,topology and parameters of CHBR are introduced,and then the operation mode of single-phase H-bridge rectifier under single/bipolar modulation is compared and analyzed,and it is concluded that the performance of the system can be brought into play to a greater extent.Then the carrier cascade modulation and carrier phase-shift modulation strategies of CHBR are explained.Then,the state average model and small signal dynamic model of single-phase CHBR are created around unipolar modulation.The factors related to CHBR output voltage are analyzed to determine whether the load resistance at all levels is directly related to the output voltage balance.Secondly,the control strategy of cascade H-bridge rectifier composed of double closed loop control and voltage balance control is introduced and analyzed.The CHBR double closed loop control block diagram is analyzed.The total voltage of output side is kept constant by instantaneous direct current double closed loop control.In addition,the sinusoidal degree of input current is not good and there are many burrs,which will seriously affect the life of the switch.By analyzing its shortcomings,the voltage increment model prediction algorithm is proposed.The voltage increment model prediction algorithm not only reduces the rolling times,but also reduces the rolling times.It also reduces the computation of the traditional finite set control algorithm,minimizes the change of switching state in the cost function,realizes smooth modulation,makes the switching state correct,and has a good voltage equalization effect.The voltage balance process of this modulation strategy in a complete modulation period is analyzed.Finally,the three-module CHBR system is simulated and verified by experiments,which verifies the correctness of the proposed voltage balance strategy and the rationality of the Model Predictive Control(MPC)control.Simulation and experiments show that the MPC voltage balance algorithm designed in this paper can reduce the calculation amount,and the current has a good sinusoidal degree,and can achieve voltage balance and good dynamic response ability.