Topology And Control Technology Of AT Co-phase Power Supply Device Based On Modular Multilevel Converter

The power quality problem,mainly harmonics,negative sequence,and reactive power,as well as the neutral section problem,are more prominent in the railway traction power supply system,affecting the safe and reliable operation of the power grid and trains.The existing power flow controller-based co-phase power supply scheme can solve the power quality and neutral section problems,however,it is not fully applicable to the auto-transformer(AT)power supply system,and there is still room for optimization.Therefore,in this dissertation,the topology scheme of AT co-phase power supply device is studied,based on which the basic operation control and the control concerning the engineering application of the scheme are thoroughly studied and explored.Lastly,a small-power experimental platform is built to verify the effectiveness and practicality of the proposed scheme.The main contents and innovations of this dissertation are as follows.Two AT co-phase power supply device topology schemes(MMC-5L1 CB and MMC-4L2CB)are proposed,which have various advantages over the existing scheme(MMC-5L).The proposed schemes replace the auto-transformer required in the existing scheme when applied to AT power supply systems by adding the capacitive branch to the topology.The proposed schemes are quantified and compared with the existing solution in the application context of AT power supply system.Compared to the existing scheme,the MMC-4L2 CB reduces the number of IGBTs and sub-module capacitors by20%,simplifying the complexity of the control system,and the MMC-5L1 CB increases system efficiency by 0.5% on the premise that the simulation verifies that the schemes all meet the requirements of the co-phase power supply functions well.For the basic operation and functional implementation of the scheme,the finite control set-model predictive control(FCS-MPC)is optimized,which is more suitable for multi-control objectives,multivariable coupling,and nonlinear systems like power electronic converters.An optimal inserted submodule-model predictive control(OIS-MPC)strategy is proposed to further reduce the computational burden of the existing FCS-MPC by reducing the number of level selections and the number of submodule conduction selections,which reduces the computational burden of the Modified-IL-MPC by nearly half while ensuring good output performance.Secondly,based on the basic operational requirements and functional requirements of the scheme,the OIS-MPC-based rectifier-side and inverter-side control schemes are proposed based on the establishment of discrete time-domain mathematical models of rectifier-side and inverter-side.Finally,the dynamic performance of the control scheme and the high-quality realization of the basic operational requirements and the co-power power supply functions are verified through the simulation of steady-state conditions and sudden load changes conditions.For the pre-charging process faced in engineering applications,the AC-side and DC-side pre-charging control strategies based on model predictive control are proposed,which have better dynamic response performance than the traditional PI control and stronger robustness than the deadbeat predictive control.The dynamic response performance of the proposed algorithm and the control performance of the charging current and sub-module voltage are verified by simulating the pre-charging process on the AC and DC sides.Then,a hybrid model predictive control-based master-slave grid-connection control strategy is proposed by combining model predictive control and droop control for the grid-connection process of the modular multilevel converter(MMC)as a power source,which eliminates the modulator and fully exploits the advantages of model predictive control and then improves the dynamic response performance of traditional droop control.The fast dynamic response performance of the algorithm and the control performance of the output voltage,current,and power are verified by simulating the grid-connected system with three loads and three substations.A scaled-down experimental platform is developed to verify the effectiveness of the proposed schemes.For MMC-5L1 CB and MMC-4L2 CB,the main circuit structure is designed,key parameters are calculated,devices are selected,half-bridge power modules are designed and developed.Then the scaled-down experimental platform is built to verify the MMC-5L1 CB and MMC-4L2 CB schemes,and steady-state and load mutation experiments are conducted.The experiments verify the effectiveness and practicality of the two proposed schemes.