Study On The Key Technologies Of The DC Storage Energy System In DVR

As the development of the control technologies,the computer controlled load in power system are increasing.These are so called the sensitive load which demand a high quality of the power supply and have a poor resistance to faults such as the voltage sag.The DVR,which contains the DC energy storage system as its active power supply unit, is used to mitigate the voltage sag and protect the sensetive load after faults.Considering the importance of the DC energy storage system in the mitigation of the voltage sag,this thesis launches a research on the constructure,the maths models and the control stretage of the it. At the beganning , the thesis makes a short introduction on the problem existing in the power system and the measures to get rid of these problems.Among these measures,DVR is usually used to mitigate the voltage sag.The function and structure of DVR is stated.As an important part of DVR,the DC energy storage system is mentioned and the key technologies is given.As the main study of this subject,this thesis proposed two DC energy storage forms, namely the battery DC energy storage system and the compoud of battery and supercapacitor DC energy storage system.By constructing the small signal models of the two energy storage system,an analysis of the stability of the system is made based on the Bode Figure.Then there is going on with the design the PI controller,making up a outer voltage control loop and a inner current control loop.To gain a better control result,a feedforward controller is showed,which achieves a composite control together with a feedback controller.As to test the performance of the control stretage and the whole DC energy storage system,we have a simulation under the PSCAD/EMTDC.The last of the paper studys the characters of two forms of DVR using PSCAD/EMTDC,that is the DVR with the battery energy storage unit and eith the battery-supercapcitor energy storage unit .A cimparation is made between the two different forms of DVR.At the end,we make a summary of the whole thsis and a fowardlooking on the subject.