Three-phase power electronic transformer decoupling equalization control method based on feedback linearization

Abstract

The invention discloses a decoupling balance control method for a three-phase cascade type power electronic transformer (PET) based on feedback linearization, and aims to realize rapid stabilization of two-stage direct current voltage of three-phase intermediate direct current and output direct current of the cascade type PET and balance of the three-phase intermediate direct current voltage when the power is large in disturbance and the power grid voltage is unbalanced or three-phase parameters are inconsistent. The method is characterized in that a state feedback linearization method is adopted, nonlinear state equations of three-phase intermediate direct-current voltage and direct-current network side output voltage of the three-phase cascade PET are linearized and decoupled, voltage control is simplified into a first-order differential system, and then parameter design can be carried out through a PI controller and a zero-pole assignment method. According to the method, the transient performance of the PET equipment during power reverse large disturbance can be improved, voltage and power balance among three phases of the PET is realized, and the method has a better prospect in the aspects of ensuring the PET wide operation range stable control capability and promoting the application of the PET equipment in new energy high-proportion alternating current and direct current hybrid power grid engineering.

Description

Technical field [0001] The present invention relates to a three-phase power electronic transformer control method, in particular a three-phase cascaded power electronic transformer based on feedback linearization decoupling balanced control method, belongs to the field of power electronic transformer control technology. Background [0002] Based on cascaded H-Bridge (CASCAD H-Bridge, CHB) and dual active bridge (DAB) converter three-phase cascaded power electronic transformer (PET), can facilitate the input of three-phase medium and high voltage AC grid and low voltage high-power DC output, with the advantages of good multi-level waveform quality, small number of required components, easy modular expansion, etc., is the core equipment for building AC-DC flexible transmission and distribution systems and energy Internet. [0003] Each H-bridge module of the three-phase cascaded PET CHB is connected to the DC stage DAB through an independent intermediate DC capacitor, and all the D...

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Problems solved by technology

[0004] When the power of the PET DC grid side has a two-way large disturbance, the instantaneous power imbalance inside the device will first cause fluctuations in the DC bus voltage of the output capacitor and the intermediate capacitor. In addition, unbalanced grid voltage or inconsistency of module parameters between three phases will make the average DC voltage of the three phases unbalanced, and the risk of instability will be aggravated when the power is disturbed

[0005] In terms of DC voltage stability and balance control at all levels of cascaded PET, many studies have focused on single-phase cascaded PET. Or the DAB shift phase is corrected to achieve sub-module voltage balance control, but it cannot solve the problem of unbalanced phases in the three-phase PET topology

For the three-phase PET topology, one method is based on CHB level control, by introducing the reactive current correction component of each phase, or using the zero-sequence voltage injection method, to realize the independent distribution of three-phase active power to achieve the purpose of inter-phase voltage balance; the other The method is based on DAB-level independent control, and the phase-to-phase voltage balance is achieved by adding an input voltage equalization control loop on the basis of the DAB total output voltage control loop. However, these methods are all based on the main control loop. There is strong coupling between the controls of each layer, and the control design is based on the small-signal approximate linearization model, which is difficult to achieve the control target. It has a good dynamic response in the case of large disturbances in the power bidirectional full operating range.

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