A Dual-closed-loop Control PWM Converter Of Co-phase Power Supply System

The operation mode of high-power locomotive and the mode of single-phase power supply make the traction power supply system of high-speed railway have some outstanding problems,such as heavy load and frequent fluctuation,high load ratio,high reliability requirement,long power supply time,unbalanced three-phase power system,large harmonic and large negative sequence current.In view of the problems of electric power quality,such as phase separation,negative sequence and harmonics,and the disadvantages of overload capacity in the current traction power supply system in China,a three phase-single phase commutator is proposed as the main equipment of the same phase supply mode.In the circuit structure,the forward circuit adopts the three-phase PWM rectifier circuit and the rear circuit adopts the full bridge single-phase inverter circuit.In the control aspect,due to the use of large intermediate energy storage electrolytic capacitance to support the intermediate bus voltage,the Advanced circuit and the rear circuit realize decoupling in the model,so they can be studied and designed separately,and the double closed loop control strategy with the inner loop of current and the outer loop of voltage is adopted at both front and back stages.In this paper,a system circuit is established to realize the same phase power supply,namely,a converter composed of a three-phase PWM rectifier,a DC link and a single-phase PWM inverter,and push to the realization of multilevel,the structure of diode clamped five levels rectifier and grade H bridge nine levels inverter is adopted in front and back stages respectively.Secondly,the realization of the front and rear primary circuits,the establishment of the mathematical model and the designation of the controller are introduced in detail.The dual closed-loop control strategy of the internal loop of current and external loop of voltage is introduced in both rectifier and inverter.Then the rationality and effectiveness of the controller design are verified by simulation.Then,the phenomenon of DC capacitance voltage drift is analyzed in detail.On this basis,the principle of capacitance auxiliary voltage equalization circuit is analyzed torestrain the phenomenon of capacitance voltage drift.Based on the above mentioned,the harmonic analysis of the system is carried out.Finally,by analyzing the working principle and power supply performance of the same phase power supply system,a simulation model is built in MATLAB / Simulink to verify the accuracy and feasibility of the same phase power supply system and control strategy.