Research On DVR With An AC/AC Converter

As the increasingly development of science and technology, the demand of the power quality is moreand more stricter. The power quality problems can bring great losses to the sensibility loads. Among allkinds of the problems, voltage sags are most frequently happened and can cost lots of losses.The DVRs,dynamic voltage restorers, are the most economic and useful solve way of the problem.At present, studies on DVRs are often with a VSI (voltage source inverter). The main structurecontains a large DC energy storage. The DC energy storage can not avoid the disadvantages of big volume,heavy weight, large cost and not easy integration. Recently, AC/AC converters are researched deeply andextensively. An AC/AC converter has a smaller volume, lighter weight, and can be integrated more easily.It has been a trend in the application of DVRs.This paper has analysed lots of AC/AC converter topologies, and then chooses the virtual rectifyingand inversing topology as the main circuit in the DVR, which can be without any commutation control. Atthe same time,there are many other elements can effect the DVR’s output characteristics,such as thelocation where the power supplies, the position of the isolation transformer, the form of the outputfilter,and so on.This paper has done detailed analysis and comparisons. Finally, supply on the line side,locate the isolation transformer on the inverter’s output, and use the leakage inductance of the transformeras a filtering inductance.In order to compensate the line voltage rapidly and accurately, the DVR should have a good dynamicresponse.However, the PI control in the DVR can reduce the output quality and make the voltage easilydistort across the zeros.Therefore, the paper uses one-cycle control, which can response rapidly and has agoof control robustness.The control equation of the system with one-cycle control has been deduced, whichcan be a design basis of the integral circuit. A large signal model has been built, the state variables havebeen analysed with phase planes, the elements which can influence the system stability have been obtained.Simulations with one-cycle control and PI control have been done to compare the steady, dynamicproperties, and abilities of input perturbation rejection and with a non-linear load.Finally, a1kVA AC/AC DVR prototype has been designed and the steady, dynamic experimentshave been done.The results verify the correctness and feasibility of the theory analysis andsimulations.