Theory And Simulation Research On Dynamic Voltage Restorer

Dynamic Voltage Restorer (DVR) is considered as the most effective device to compensate the voltage sag. DVR is able to compensate distortions of the line voltage by "missing" voltage of the system into the line, which can compensate both steady state and dynamic voltage quality problems, The distortions of voltage include: voltage sag, voltage swell, three-phase voltage unbalance, voltage harmonic, etc. In order to enhance the dynamic performance of DVR and make it running more economically, this paper do research in voltage sag detection algorithm, control methods, as well as the calculation methods of compensation voltage of DVR. The major contributions of this paper are detailed as follows:A rapid algorithm integrating dq transformation with morphological filter is put forward for the first time. Dq transformation has merit in real time operation, and morphological filter has strong points in short time delay and high measure precision. The algorithm proposed has all these characteristics. By using this new algorithm, voltage sag can be detected instantaneously with duration, magnitude and phase-angle jump when it comes through dq transformation and morphological filtering.Considering the definition of voltage tolerance of different load and the limitation of DVR output voltage, a novel method for calculating optimal compensation voltage is presented. By making changes of reference voltage phase diagrams of load, this method can enlarge the compensation range and decrease the energy output of DVR. Furthermore, it can restrain efficiently absorbing energy from power system to ensure the safety of DVR when compensating voltage swell.A new control method, feed-forward integrated with PD adjustment, is proposed to resolve the current defects of DVR feed-forward control system. By analyzing the transfer function between the input and output, the disturbance and output, the advantages of this control method are as follows: it can enhance system damp, improve steady margin, and speed up system dynamic response. Meanwhile it can improve the adaptability of load variation.Comparing the design schemes of 4 main parts of DVR, the main circuit topology of three-phase four-wire DVR is confirmed, which is index to the distribution system with the consideration of reliability, economic, and synthesis of DVR. The topology structure is also suit for single-phase and three-phase three-wire DVR.A simulation model of the three-phase four-wired DVR based on PASCAD/EMTDC is proposed. A great deal of research on compensating voltage sag, swell, unbalance, and harmonics of DVR are carried out in use of the methods presented in this paper. The simulation results validated that the three-phase four-wired DVR meets the designing request.