Research On Dynamic Voltage Compensation Device For Distribution Newwork

With the continuous development of China's economy and modernization,various kinds of harmonics and impact loads are emerging,and users also have higher requirements for power quality than ever before.Voltage quality problems mainly include voltage sags,voltage swells,voltage harmonics,and three-phase imbalances.Among them,the frequency of voltage sags is the highest,resulting in the largest economic losses.Dynamic voltage restorer(DVR),as a kind of series compensation device,can solve various voltage quality problems well,and is one of the effective means to guarantee voltage quality at present.The working principle and topology of DVR are analyzed in this thesis,and the advantages and limitations of different multilevel converters used in DVR are compared and analyzed,and diode-clamped multilevel converters or cascade multilevel converters serves as the inverter unit of the DVR are chose,and research the corresponding SVPWM modulation method.The control strategy of DVR device is designed,and the compensation effects and applicable occasions of three common voltage compensation strategies are studied and compared;three-phase voltage detection method based on instantaneous reactive power theory and single-phase voltage conversion detection method adopts single-phase voltage structured of three-phase voltage are analyzed in detail.To solve the problem of three-phase dq0 detection method can only be applied to three-phase voltage balance and single-phase voltage method can only detect the voltage of one phase only,a voltage detection algorithm based on SOGI-QSG are proposed,and the feasibility of the algorithm is verified through simulation;As an example of the rectifier unit using three-phase half-bridge PWM converter,inverter unit using 5L-NPC converter,the DC side voltage regulation and control strategy are introduced.The main circuit design and parameter calculation of the diode-clamped multilevel DVR and cascaded multilevel DVR are completed respectively;the DVR simulation model based on diode-clamped converter and H-bridge converter is built in the SIMULINK software,the simulation of common power quality problems in the distribution network verify the feasibility of the topology.On the basis of the research work,a dynamic voltage compensation device is designed and developed.The experimental results verify the compensation ability of DVR device for voltage fluctuation and harmonic problem.