The Study Of Power Electronic Traction Transformer

Power electronic traction transformer (PETT), is applying the power electronic devices and power electronic converter technology to the train traction transformers, in order to achieve energy conversion and control, it can replace the traditional core transformer. Compared with the traditional transformer, power electronic transformer is small, light, and its no-load loss is small, beyond these, it makes the transformer’s secondary voltage, current and power highly controllable, and it can be used as the circuit breaker. The high-power electronic devices can turn off fault currents within a few microseconds, so the protection devices are not needed in power electronic transformer.In this paper, a detailed analysis and comparison of several power electronic traction transformer’s main circuit topology is done, and on this basis the feasibility and practical topology is determined. For the determined topology, parameters of the main circuit are obtained by theoretical calculation and the auxiliary circuit and control circuits are also designed. These theoretical analyses can play a guiding role in power electronic traction transformer prototype’s production.For the main circuit topology in this paper, the control strategy is analyzed in two respects, control of single unit and the balance control between units. The control of single unit includes the control of AC/DC converter and DC/DC converters. The control of AC/DC converter is the double closed-loop control of voltage and current, the voltage loop is PI control and the current loop is quasi-PR control with cascaded harmonic current compensator. The control of DC/DC converter is phase shift control. Cascaded H-bridge DC capacitor’s voltage balance control includes the carrier phase-shift modulation and the voltage balance compensation control. The control of power balance between DC/DC converters is the Voltage-droop control. These control strategies above are not only theoretical analyzed but also verified with simulation. The simulation results show the feasibility and effectiveness of the control strategies.In addition, experiments are done with the power electronic traction transformer prototype. The experiments are divided into two parts in the same way with simulations, experiment with single unit and experiment with cascade units. Experiments of signal unit include AC/DC converter’s experiment and DC/DC converter’s experiment. Results of AC/DC converter’s experiment indicate necessity and effectiveness of the use of quasi-PR control. Results of DC/DC converter’s experiment indicate feasibility of phase shift control. Experiments of cascade units include experiment of AC/DC converters with cascade H-bridge and experiment of parallel DC/DC converters. Experimental results of AC/DC converters with cascaded H-bridge indicate effectiveness of the carrier phase shift modulation technique and the control voltage balance compensation, Experimental results of parallel DC/DC converters indicate that the Voltage-droop control makes the currents equal.