Research On Control Strategy Of Electronic Power Transformer

ABSTRACT:Electronic Power Transformer (EPT) is a new type of transformer with the ability of the voltage regulation and power transmission of power system. Compared with the traditional transformer, its significant advantage is that the current of the primary side, the voltage of the second side and the power factor can be flexibly controlled. EPT can not only promote the power quality, improve the system stability, but also conform a variety of distributed power resources, to achieve flexible power transmission. So, the researches on EPT are significant for the smart grid.This paper, firstly, gives a summary of the development and current state of EPT, and analyzes some representative structures, then proposes a new electronic power transformer (EPT), for the application in the distribution system, which is composed of the three-stage topology. 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. The control strategy of the three stages and the operation principle of the system are analyzed in detail. With the three-stage control strategy, the EPT's input currents and the output voltages have quality waveforms, and the input power factor is controllable.Basing on the above contents, The EPT model is established on MATLAB/SIMULINK, and the simulation results verify the proposed EPT system. Further, this system is also implemented in laboratory based on DSP TMS320F2812, the hardware of system is discribled in detail, including the main circuit and the control circuit topology, and the parameters of component elements are calculated in theory either. Then the program flow of three stages in DSP2812 is shown. The experimental results show that the input currents and the output voltages have quality waveforms, and verify the proposed EPT system.