Research On Topology Of Improved Unified Power Quality Conditioner And Control Strategy

With the continuous increase of nonlinear loads in various types of power grid, power quality gets deteriorated continuously, so that it seriously endangers the security of power system and the interests of users. Conventional power quality compensation devices can not meet the increasing requirements to power quality of users. Unified Power Quality Conditioner (UPQC) as an integrated power quality compensator, not only can compensate the current quality problems of harmonic and reactive current caused by loads, but also can compensate the voltage problems of voltage swell, sag, asymmetry, flicker and fluctuation. UPQC is a new trend of consumer power technology.The current studies about UPQC mainly include topologies, operation principles, detection methods and control strategies. A lot of researches of control methods and control strategies about UPQC have been made before in our laboratory, and there are some achievements. This paper not only summarizes the preliminary work, but also makes some in-depth researches about different topologies. Taking the three-phase three-wire UPQC as the object and using super capacitor as the energy storage unit of the UPQC's DC side, this paper designed an improved UPQC topology. Making full use of super capacitor's large energy storage capability, this topology can well compensate a long time voltage drop or rising and short time interruptions.This paper sets the improved UPQC as the study object, to analyze the system structure, functions and working principles. Meanwhile, mathematical model of series and parallel converter and the DC energy storage unit is established, and the power flow characteristics are also analyses deeply.Fundamental positive sequence component extraction method based on Synchronous coordinate transformation is used as the amount of compensation detecting method, and the corresponding improvement was carried out. The impact between series and parallel compensation unit is analyzed and the corresponding improved control strategy is studied. Simulation results show that it can realize the voltage drop, voltage harmonics, current harmonics and reactive power compensation, improved control strategy is proved effective, and also illustrates the effectiveness of topology. On basis of the theoretical analysis and simulation study In this paper, on basis of simulation studies, corresponding control circuit and main circuit parameters are designed preliminarily. This design is prepared for the follow-up work.