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Research On An Improved Hybrid Cascaded H-Bridge Inverter-Based STATCOM

Posted on:2014-01-14Degree:MasterType:Thesis
Country:ChinaCandidate:P P LiFull Text:PDF
GTID:2232330398959223Subject:Power electronics and electric drive
Abstract/Summary:PDF Full Text Request
As a converter circuit consisted of full-controlled semiconductor devices, STATCOM of multilevel topological structure can make devices of lower withstand voltage used in high-voltage high-power occasion. It also has excellent response speed, adjust range and stability. With so predominant performance, STATCOM of multilevel topological structure is treated as the development direction of dynamic reactive power compensation set.Hybrid cascaded multilevel topology not only inherited the characteristics of cascaded structure——easy to extend, low cost and low loss, but also avoid the contradiction between the device power and switching frequency to some extent. So this kind of topology gradually becomes one of the research focus in high-capacity STATCOM. In this paper, we use the hybrid cascaded inverter as the main circuit topology of STATCOM, study the working principle and PWM control method, and analysis its dynamic reactive power compensation performance in the ideal and non-ideal conditions.First, based on the research of several kinds of typical multilevel cascaded type in resent years, an improved cascaded H-bridge topology is proposed. This is2H-3H hybrid cascaded topology of3:2DC voltage ratio, which is suitable for high-power and high-voltage occasion. To fit the special structure, the hybrid frequency carrier PWM modulation is selected to control the inverter and analyze the harmonic characteristics of the output voltage.Secondly, with the simulation software MATLAB/Simulink, the dq decoupling control strategy and the modulation is all been simulated. The results show that it has the ideal compensation effect in a given reactive power mutation, as well as an un-unit power factor load.Then, considering the unbalance problem voltage of DC capacitor, exchanging the trigger pulse is chosen to ensure the DC capacitor energy balancing. Based on the theoretical basis and defects of the existing Pulse Cycle Transposition, a advanced method, Pulse Sorting Transposition is proposed. It controls the DC voltage value as a constant to ensure the dynamic response speed, and its feasibility has been verified by simulation.At last, to further improve the function of STATCOM and ensure its safety in abnormal conditions, the system adopted the sequence control strategy based on asymmetric component method. The simulation verifies the compensation effect of three kinds of situations, asymmetric load, asymmetric system voltage, and system voltage mutation.Further more, A large number of simulation waves are accompanied with the principle analysis to explain the main circuit topology and prove the accuracy and validity of the proposed control methods.
Keywords/Search Tags:STATCOM, Hybrid Cascaded, Multilevel, DC Capacitor Voltage Unbalance, Asymmetric Control
PDF Full Text Request
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