Power Electronic Transformer And Its Application In Power System

Power electronic transformer (PET) is a kind of new intelligent power voltage device. It flexibly control original and vice edges voltage through introducing power electronic transform technique in traditional power transformer. With the enhancement of power electronic device manufacturing ability and improvement of power electronic transform control strategy, power electronic transformer is expected to solve many problems in modern power system.Based on the detailed analysis of PET basic principle, the mathematical model is gived, which can be applied to different topological structures. Forther more, it gives a three level control strategy. The input level uses the double loop decoupling control strategy with direct voltage in the outside loop and current in the inner loop.The inter-mediate link uses the open loop control strategy, because it could be viewed as a proportion amplifier. The output level also use the double loop control strategy, but its outside loop control the instantaneous AC voltage, and its inner loop control instantaneous AC current. The simulation results show that three level control strategies can get a good output voltage waveform.The traditional PI controller is analysed and gives its shortcomings, which only achieves zero steady-state error in the direct voltage control rather than in the alternating voltage control. On the basis of previous studies, it adds complex integral and differential blocks to traditional PI controller, and proposes a novel controller, named proportion complex-integration differentiation (PCID). The controller can be proved having a perfect result.PET is emulated in the platform environment of Matlab/Simulink, and results show its can effectively control power quality, especially in diverse abnormal condition. It can guarantee the stability of the output voltage. What’s more, the problem of frequency offset in the micro power grid, is discussed as a important question by building a grid connection system for wind farms. PET with a energy storage system can restrain the frequency offset.By simplifying PET topological structure, a simple physical experiment system is established, which is applied in single-phased break-line fault. The experimental results show that PET can reduce influences of the break-line fault, and guarantee basicly stable output voltages. This is an evidence to prove the advantage of PET.