Research On Control Technologies Of Dynamic Voltage Restorer In 380V Distribution Network

With the deepening of human modernization,more and more power electronic devices and products have been widely used in industry and daily life.But the common voltage sags in power quality problems will affect the normal operation of power electronic devices.In the field of power quality issues,dynamic voltage restorer(DVR)is the most effective solution to voltage sag because of its fast dynamic response,flexible control system and high economy.In this paper,a 20 kVA three-phase dynamic voltage restorer is designed,and its topology,voltage sag detection technology,software phase-locked technology,control strategy and compensation strategy are studied.Firstly,the paper studies the operating principle of the DVR,compares different DVR topologies,and finally chooses three single-phase H-bridge topology as the main circuit topology,and uses grid-side rectification to obtain energy.According to the topology,the DC-side capacitance,LC filter and transformer ratio are designed,and the max voltage compensation capability of DVR is analyzed.Secondly,for the widely used dq transform and root mean square detection method used in DVR system,there is a long delay problem.The paper proposes a voltage sag detection algorithm based on minimum phase angle.The simulation result indicates that the algorithm can be applied to three-phase asymmetric system,and the detection delay can be reduced from ms level to μs level.And the phaselocked error of traditional SPLL is analyzed when the three-phase voltage is asymmetrical and contains harmonic and DC components.The structure of orthogonal signal generator is improved,and on the basis of this,a hybrid filter PLL is designed,which improves the accuracy of PLL in non-ideal power grid.Combining the filter module of SPLL with detection module,the algorithm can be applied to the occasion where the harmonic voltage in power grid is high.Thirdly,in this paper,the control strategy of DVR is studied,and the double closed loop feedback PR control strategy is adopted.The parameters of the controller are designed,and the stability of DVR control strategy is proved by the bird diagram.And the paper compares three commonly used DVR voltage compensation strategies using vector graph.According to the supply voltage requirements of load,the way of energy acquisition and the voltage compensation capability of DVR,the minimum voltage compensation method is selected as the compensation strategy of DVR.The accuracy of compensation for single-phase and three-phase voltage sag is verified by simulation.Finally,the experiment platform using DSP TMS320F28335 is built to control the DVR.The corresponding hardware circuit and software design are completed.The performance of the prototype and the control technology proposed in this paper are verified by experiments.The experimental results shows that the 20 kVA threephase DVR can effectively detect and compensate the voltage drop,accurately lock the voltage phase of the power grid,and meet the design requirements.