Research On Application Of Muti-Level Converter In Co-Phase Power Supply System

Reactive power, harmonic and negative sequence have been technical problems for years in traction power supply system of electrified railway. With the development of high-speed and heavy-duty railway, negative sequence problem is more and more prominent. The locomotive running speed is limited due to the presence of the lectricity sub-phase device. Simultaneously traction load is high voltage, large-capacity load, so the traditional two-level converter can not meet the requirements.In order to solve the above problems, the paper studies the cophase power supply system based on the novel YNvd balance transformer and diode clamped five-level structure power flow controller. For inherent capacitance voltage imbalance problem of diode clamped live-level converter, this paper studies a novel dc auxiliary regulator circuit based on single-stage capacitor, its structure is simple, easy to control and reliability. The circuit can be provided to achieve the balance of the voltage of the DC capacitor under conditions of any power factor, especially in the active power pass.In addition, this article also learn from the German model to study continuous cophase power supply system based AC-DC-AC power flow controller. In order to adapt to the high-voltage and large-capacity requirements of traction power supply, reducing the stress of switching devices, reducing the switching frequency, reducing output voltage harmonics, reducing the loss of the switching devices, improving the reliability and efficiency of power flow controller, two kinds of multi-level structure programs of power flow controller of continuous cophase power supply system are proposed, including diode clamped five-level structure of the program and cascade nine-level structure program of power flow controller. Which PWM modulation of the diode clamped five-level structure program, this article also research a fast SVPWM modulation algorithm. The algorithm will traditional αβ coordinates axes along the coordinate origin is rotated45degrees clockwise or counterclockwise to obtain a new still cartesian coordinates-α’β’coordinates. Just simple addition and subtraction, and multiplication of the calculation of the reference voltage vector positioning and basic vector acting time in the coordinate system, to avoid the the cumbersome computation of trigonometric and irrational numbers, calculations are quite simple.Finally, this paper attempts to study a cascade no output transformer power flow controller structure program of continuous cophase power supply system. AC-DC-AC power flow controller in this scheme constituted by the the five power unit cascade, in which each power unit is again based on a diode clamped five-level structure of AC-DC-AC converter. Through the cascade structure of the multi-cell, increase the voltage level of the output transducer, and so to cancel the output transformer, the power supply directly to the traction load.