| With the rapid development of power electronics technology, a large number of non-linear load characteristics of electrical equipment will inject into the system a lot of harmonics and pollute the grid, but also bring a series of power quality problems, such as serious voltage sag problem, voltage fluctuation problem, and voltage interruption problem; with the rise and development of high-technology, information industry, precision manufacturing, automation and control operations, and other related electrical equipment industry have been widely used in power systems, such power equipment interference in the system is very sensitive to power quality, so the power quality requirements for the corresponding sensitive electrical equipment are increasing. Among many power quality problems, voltage sag problem is the main cause to the abnormal operation of sensitive electrical equipment. Statistics show that, power quality problems caused by voltage sag accounted for70%-90%of its total numbers. The dynamic voltage restorer is considered as one of the most economical and effective means to offset the voltage sag problem. This paper examined a large number of domestic and foreign relevant literature, on the basis of an in-depth understanding of the dynamic voltage restorer of the current research status and analysis of its basic working principle, the typical composition structure and basic functions and features of each component unit, the detection algorithm of voltage sag and compensation strategy and control algorithm of dynamic voltage restorer have been studied.This thesis describes the working principle of dynamic voltage restorer as well as several major functional units of the main circuit topology, a detailed comparative analysis of the structure and characteristics of each unit have been carried out, on this basis, combining the characteristics of low voltage distribution network, DVR main circuit topology has been designed. For the problem of the disadvantage that the traditional LC filter attenuating a high frequency component takes a long time, a new LCC filter has been designed, the new filter wire holds LC filter characteristics of the second order, and has much shorter time on the steady-state adjustment than the LC filter, and through the simulation, the performance of the new LCC filter is better than ordinary LC filter.Voltage sag detection has a great influence on the compensation effect. In this thesis, several commonly used detection algorithm have been analyzed and compared, focused on dq transformation method based on instantaneous reactive power, especially for abc-dq transformation and αβ-dq transformation method applicable for single-phase voltage sag. Based on this study, a detection algorithm by delaying a small variable angle to configure the αβ coordinate system in order to carry on dq transformation has been studied, the algorithm reduces the amplification of harmonics, has a good real-time property, and satisfies the DVR design requirements.In this paper, For the shortcomings of feed-forward control algorithm and feedback control algorithm, the complex control algorithm with the reference of voltage feed-forward and feedback of the inverter output voltage has been used, the complex control algorithm combines the advantages of feed-forward control algorithm and feedback control algorithm, has good dynamic response characteristics and improved damping system, increas the stability of the system. the complex control algorithm improved the compensation effect of the dynamic voltage restorer. Papers based on PSCAD simulation platform to build the simulation model of dynamic voltage restorer access to low-voltage distribution grid and get a lot of simulation results by setting different voltage sag depth and duration of voltage sag, through simulation curve of the compensated load voltage to verify the detection algorithm, control algorithm designed in this paper and the whole dynamic voltage restorer’s compensation performance. |
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