Single-phase Cascaded H-bridge Multilevel Converter Direct Power Control

Locomotives can run through the neutral sections normally without electric arc and voltage shock when the ground's auto passing neutral section system(GAPNSS)based on single-phase cascaded H-bridge multilevel converter is adopted.The GAPNSS is beneficial for rapid passenger-transport and heavy freight-transport of Chinese electrified railway system.The GAPNSS is composed of single-phase cascaded H-bridge multilevel inverter and three-phase two-level pulse rectifiers.Direct power control of the converters in the GAPNSS is studied in this thesis.Firstly,the topology and main composition of single-phase cascaded H-bridge multilevel converter in the GAPNSS is introduced.The single-phase cascaded H-bridge multilevel inverter and the three-phase two-level pulse rectifiers are back-to-back connected through their corresponding DC-sides.The mathematical model and working principal of rectifier-side and inverter-side are also introduced respectively.An improved single-phase cascaded H-bridge multilevel inverter structure,which adopts an affiliate-voltagecompensation inverter application,is presented.The affiliate inverter could improve the power quality of the traction grid,which is powered by the single-phase cascaded multilevel H-bridge inverter under low switching frequency.The power control of the single-phase cascaded H-bridge multilevel inverter becomes more robust due to this affiliate inverter.Secondly,the principal and implementation of direct power control strategy of improved single-phase cascaded H-bridge multilevel inverter is introduced.On-line module power estimation algorithm for single-phase cascaded multilevel H-bridge inverter,which adopts direct power control and nearest level modulation,is proposed.Then,simulation results via Matlab/Simulink software are given to verify the correctness and effectiveness of direct power control strategy and module power estimation algorithm.The advantage of the improved single-phase cascaded H-bridge multilevel inverter structure is summed.Additionally,predictive direct power control with fast dynamic performance under low switching frequency for three-phase two-level pulse rectifier is introduced.In order to achieve more stable DC-voltage sources,the control outer loop of rectifiers adopt loads' and capacitors' power feed-forward.Then,simulation results via Matlab/Simulink software are given to verify the correctness and effectiveness of control strategy of the three-phase two-level pulse rectifier.At last,the model of GAPNSS is established in Matlab/Simulink software and the control strategy for single-phase cascaded H-bridge inverter and three-phase two-level pulse rectifiers is studied via simulation.AC currents on the rectifier-side and the inverter-side of the converter are of high quality.DC-side voltages of the converter have fast dynamic performance with less voltage fluctuation compared with the reference value.In order to verify the adopted strategies further,the model of GAPNSS is established in RT-LAB platform.Control and modulation strategies for the converter are implemented in DSP+FPGA digital controller.The hardware-in-the-loop experiment results show good agreement with the simulation results and the correctness and effectiveness of control strategies for converter in the GAPNSS are verified.