An effective power electronic transformer applied to distribution system

The paper proposes a new power electronic transformer (PET), for the application in the distribution system, which is composed of the three-stage power circuits. The input stage uses three-phase three-level PWM rectifier to reduce the voltage stress rating of components, where the reactive power and high-voltage dc-link voltage closed-loop controls provide the ability to adjust the reactive power and stabilize the dc-link voltage in the high-voltage side. The isolation stage employs the low-voltage dc-link voltage closed-loop control with a high-frequency step-down transformer to maintain the constant low dc voltage and isolate the low-voltage side from the high-voltage side. In the third-stage, three-phase two-level inverter outputs the desired voltage and power to the load through the output voltage closed-loop control. With the three-stage control strategy, the PET´s input currents and the output voltages have quality sinusoidal waveforms, and the input power factor is controllable. The PET model is established on MATLAB/SIMULINK, and this system is also implemented in laboratory based on DSP TMS320F2812. The simulation results and experimental results verify the proposed PET system.