Research On Several Key Issues Of AC And DC Distribution Power System

The traditional AC distribution power system has the power quality problem such as three-phase unbalance, voltage fluctuations, voltage flicker, frequency fluctuations and harmonics, so it is difficult to meet the needs of users of high power quality. However, the DC-based distribution power system has advantages in transmission capacity, controllability and power quality, and it can effectively improve power quality. Thus, the study of the DC distribution power system has practical significance. The DC distribution power system modeling and simulation technology is the foundation of DC distribution power system, so it is studied in the paper. The study of DC distribution power system is in its infancy, AC distribution power system will still be in a dominant position, so how to improve the quality of existing AC distribution power system will continue to be a long-standing issue. Therefore, how to use the Unified Power Quality Conditioner to improve power quality of the AC distribution power system is studied in the paper.In the paper, the modeling and simulation technology of DC distribution power system and the distribution power system power quality control methods are studied. The main work is presented as follows:Based on the physical and mathematical models of the major components of DC distribution power system, the simulation models of individual components are established by PSCAD, and the accuracy of each element simulation model is verified. On the basis of the establishment of DC distribution power system’s element simulation model, a multiport, multi-level DC distribution power system simulation model which contains distributed energy and energy storage is established in PSCAD. The established simulation model of DC distribution power system can run stably in the setted operating condition, and the voltage of each node of the DC link can be maintained at near rated15kV.That is, the balance of power and voltage stability are achieved.Aiming at the problem of power quality such as voltage sag, three-phase unbalance, harmonics, power quality compensation device unified power quality regulator (UPQC) are studied. We learn topological structure and principle of the compensation device, including the series compensation unit and the parallel compensation unit. Power quality detection methods and control strategies for UPQC are studied. The paper analyzes the optimal steady-state power of UPQC, and energy optimization compensation strategy is proposed. Simulation results indicate that the proposed energy optimization control strategy of UPQC can effectively solve power quality problems and can also reduce the compensation energy of UPQC, thereby the economy of the compensation device is improved.