| Co-phase power supply system is a new railway traction power supply system, the advanced co-phased traction power supply system based on three-phase to single-phase converter has been widespread concerned and deeply studied due to it’s completely solving the existing problems such as problems of power imbalance in existing systems, locomotive passing phase problem, low power factor and phase imbalance of power quality problems. As the multi-level power electronics research has become increasing mature and can adjust to the capacity and the interface voltage of the system, three-phase to single-phase converter based on Module Multilevel Converter is used for advanced co-phased traction power supply system in this paper which focuses on the circuit characteristics of MMC converter and Grid-connection control strategy.First of all, the paper analyses the working principle of sub-module of MMC and sets up the mathematical model of single bridge arm. On the basis of it the four quadrant operating principle of MMC is discussed. The composition of circulating current of single-phase and suppression strategy is presented. Furtermore the voltage harmonic content of capacitance of each sub-module is studied. Finally the above analysis are verified by simulations.Secondly, it describles the topology structure and working principle of the three-phase five level PWM converter based on MMC. Combined with mathematical model of its port voltage under the dq coordinate three-phase active reactive power decoupling control strategy based on Id/Iq is adopted. The topology structure and working principle of single phase five level full-bridge PWM converter based on MMC are studied. Improving the dq coordinates cross decoupling control of active and reactive so that it can output voltage whose frequency, phase and amplitude is controllable and can deliver reactive power to the traction network. The capacitor voltage balance and stability control strategies of sub-modules of three-phase and single-phase and the modulation strategy of MMC are studied.Then, a three-phase PWM rectifier, single-phase full-bridge PWM Rectifier and three-phase to single-phase converter system simulation model is built through Matlab/simulink simulation platform. The steady-state and dynamic simulation results of voltage of dc side and the voltage and current of ac side are analyzed under various conditions, and the correctness of the grid control strategies of three-phase to single-phase PWM converter is verified.Finally, the small power experiment system of three-phase to single-phase converter based on Field Programmable Gate Array is constructed, completing the three-phase, single-phase PWM rectifier experiment, and three-phase to single-phase grid-connected operation experiment. The experimental results verifies the voltage control, power factor control of three-phase rectifier, grid voltage control and reactive power control of single-phase PWM converter and the feasibility of grid-connected control of three-phase to single-phase converter system is as well verified. |
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