Voltage Balancing And Active Power Decoupling Control Of Single-Phase Cascaded H-Bridge Rectifier

Power high-speed railway has developed rapidly in recent years because of its advantages of high efficiency,environmental protection,safety,comfort,fast and convenient,and large capacity of passengers.However,the traditional traction transformer with high-speed railway has large volume and single function,which restricts the lightweight development of power high-speed railway and the improvement of power density.The use of power electronic transformer instead of conventional transformer can greatly reduce the weight and volume,and has become domestic and foreign scholars'research hotspots.Considering the high voltage and wide fluctuation range of traction power grid(20-29 kV),the proposed power electronic traction transformer uses cascade H-bridge rectifier + intermediate frequency transformer isolated DC-DC converter + multi-level inverters.This paper focuses on the two key issues of voltage distribution equalization control and suppression of secondary power pulsation on the DC side of single-phase CHBR in order to ensure the efficient and reliable operation of the system.In the first chapter,the background and significance of the project are summarized.The current research status of power electronic transformer,voltage equalization control of single-phase cascaded H-bridge rectifier and active power decoupling technology are introduced and summarized.In the second chapter,the working principle of single-phase CHBR is analyzed in detail,the operation mechanism of its rectifier unit power factor is analyzed,and its high-efficiency phase-shifted pulse width modulation technology is studied.Then,aiming at the unbalanced DC voltage caused by inconsistent parameters and abrupt load changes among cascade rectifier units,a voltage balancing control strategy based on virtual power unit is proposed to ensure the voltage sharing capability of the system.In the third chapter,the mechanism of secondary ripple power generation of single-phase H-bridge rectifier is analyzed firstly.Aiming at single-phase CHBR independent active power topology,a comprehensive control strategy is proposed to simultaneously solve DC-side capacitor voltage equalization and secondary ripple voltage ripple suppression,so that the circuit works in the current intermittent mode and adopts the control mode of real-time allocation of decoupling link switch duty ratio.The zero-current switching-on of SiC device is realized,and the effect of suppressing secondary ripple voltage ripple on DC side is verified by simulation experiment.In Chapter 4,a single-phase CHBR hybrid active power decoupling topology is adopted to achieve secondary ripple power suppression without increasing the number of switches in the system.Firstly,by analyzing the working principle of single module composite active power decoupling control,an active power decoupling control strategy based on mathematical calculation and closed-loop control of decoupled inductance and current is proposed.Finally,voltage equalization and active power decoupling control are realized simultaneously with DC voltage equalization control strategy.In the fifth chapter,a two-module cascaded single-phase CHBR active power decoupling experimental platform is built,and the design of related hardware circuits is introduced and analyzed.Finally,the effectiveness of the proposed control strategy is verified by experiments.