The Research Of Dynamic Voltage Restorer Involtage Sags Detection And Control Strategies

As the development of science and technology ,a large number of sensitive electrical equipment put into use,these devices require high quality of power supply,so voltage sages have become a significant problem.Dynamic Voltage Restorer(DVR) is referred to as the most effective solution to solve this problem,and it can also compensate voltage harmonic and voltage unbalance. Voltage sages detection and control strategy are improtant section in the work flow of DVR, so this thesis will focus on the study of the two section.Firstly,this paper do research in common voltage sag detection algorithm, especially focusing on dq0 transformation method and its various improved method based on instantaneous reactive power theory .This paper also analyse the advantage and disadvantage that detection algorithm owned, construe the scope of thire application,and do simulation research for some method.The low-pass filter was used to separate the AC and DC component that come from dq transformation in voltage sag detection based on dq transformation,while the real time conflict with filter's effects in commonly low-pass filter.So the real-time of detection algorithm was impacted by low-pass filter.In this paper,Morphology that was used to signal processing was studied, combined with morphological filter theory,and considering the actual occurrence of the grid is the largest single-phase voltage sag problem.A single-phase voltage sag detection based on morphological filter was put forward and simulated.The simulation results show the method can improved the lack of low-pass filter and better meet the detection requirment of DVR.The traditional three-phase software PLL was facilely impacted by the negative sequence components in three-phase unbalance.This paper firstly do research in three-phase PLL in depth, and a software PLL that can be fit for the single-phase voltage sag detection was designed. Morphological filter was used to in this method to enhance its anti-interference ability.And the simulation results show that this method can meet the requirment of DVR on PLL.This paper established DVR's equivalent circuit and math model.By reason of shortage of the feed-forward control and feed-back control, a compound control strategy was emploied,that is combined with feed-forward control and feed-back control,and analysed the stability,dynamic response and load adaptability. The results show that the compound control strategy can meet the requirment of DVRcontrol system.