Research On Control Strategy Of Single-phase Unified Power Quality Controller

With the rapid development of power electronics technology,power switching devices and other non-linear loads are widely used in power systems,injecting a large number of harmonics and reactive currents and voltages.The consequence is the distortion of voltage and current in the power grid.The rate rises.Especially in single-phase low-voltage distribution networks such as rural power grids,power quality has problems such as a lack of reactive power,large harmonic content,and unqualified voltage quality.The single-phase unified power quality controller(UPQC)has both voltage and current compensation functions,which can solve a variety of power quality problems together.The main circuit topology of single-phase UPQC is analyzed.From the perspective of system compensation effect,the topology of left series and right parallel is selected,and its working compensation principle is analyzed,and the mathematical model is established;considering the compensation effect of the parallel side output,the LCL filter is connected to the power grid;The inverter using LCL filter is modeled,the inherent resonance problem of LCL filter is discussed,and capacitive current feedback active damping is used pertinently,the damping effect under different feedback coefficients is analyzed,and The conditions of system stability are analyzed,and the effective damping of the natural resonance of the filter is finally realized.The control of the parallel-side converter is analyzed in detail.From the perspective of improving the accuracy of the command current,the structure and parameters of the phase-locked loop have been improved and parameter adjusted;the advantages and disadvantages of several harmonic and reactive current detection methods have been compared,and how the methods can be implemented in a single-phase system,Considering the accuracy of reactive power and harmonic current detection links in the case of grid voltage distortion and load fluctuations;the control method of parallel side compensation is described,and the converter is analyzed under the proportional resonance(PR)control strategy.And the stability and frequency response characteristics of the controller.The control of the series-side converter is analyzed in detail.From the perspective of improving the accuracy of compensation,a complete compensation strategy is selected among the three compensation strategies.The control method of series-side compensation is described,and feedback,feedforward and hybrid control are analyzed.Considering the voltage change rate of capacitance current reaction,the use of voltage and capacitance current dual-loop feedback control is analyzed and determined,and the control strategy is analyzed.The stability and frequency response characteristics of the converter and controller.The compensation effect of single-phase UPQC is verified in the simulation environment and experiments.The reactive current is simulated by the way of series reactors,and the harmonics of the power grid are simulated by the way of non-linear loads.The above methods are used for compensation under different conditions,which verifies the theoretical analysis of this article.