Power electronic transformer enabling high quality of electric energy output, and control method thereof

Abstract

The invention provides a power electronic transformer enabling the high quality of electric energy output, and a control method thereof. A topologic structure of the power electronic transformer includes an input stage, an intermediate isolation stage and an output stage. The output stage is an inverter of a three-phase four-leg structure, wherein the previous three phase legs adopts a dual-closed loop control strategy based on an output voltage outer loop of a PIR controller and an inductance current inner loop of a PI controller, and the fourth leg adopts a neutral current independent control method based on proportion resonance. The frequency characteristic curve and root locus of the frequency domain theory and other relevant methods are utilized to carrying out frequency division setting for dual-closed loop PIR-PI controller parameters. Therefore, the stability is effectively improved, and stable errors and robustness requirements of a system are also taken into consideration.

Description

technical field [0001] The invention relates to the technical field of power equipment, in particular to a power electronic transformer. Background technique [0002] Power electronic transformer (Power Electronic Transformer, PET), also known as solid-state transformer, is an intelligent power electronic device that realizes multiple functions such as voltage conversion, electrical isolation, reactive power compensation, and renewable energy grid connection. The function of AC-DC hybrid interface and relay protection has a very broad application prospect. The low-voltage distribution network system generally has a three-phase four-wire structure, and its loads are mostly unbalanced nonlinear mixed loads. These loads will not only generate fundamental positive sequence currents, but also inject negative sequence and zero sequence harmonics into the system. wave current. The power electronic transformer can support the distribution network voltage through proper control, su...

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Problems solved by technology

However, this scheme has the following disadvantages: (1) Using more rotating coordinate transformations and low-pass filters will increase the complexity of the control and generate delays, which will affect the control accuracy

(2) The inner loop and the outer loop of the controller are related to each other, and designing the parameters of the inner loop or outer loop alone cannot guarantee the performance of the system

It is possible to take advantage of the characteristic of the large gain of the AC component of the proportional resonance controller, and use the proportional resonance controller on the α-axis, β-axis and 0-axis respectively to realize the non-difference control of the AC quantity, but this technical solution has the following disadvantages: (1) The harmonic component is still the same frequency AC quantity in the αβ0 coordinate system, and the influence of nonlinear load is not considered

(2) The αβ0 axis only uses a proportional resonant voltage loop controller, and the lack of a current closed loop affects the dynamic response of the system

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