Research On Control Strategy Of Parallel Active Power Quality Compensation

In recent years,the increasing demand for electricity in society and the large-scale application of loads that have an impact on the power quality of power grids have led to many power quality problems.Parallel Active Power Quality Compensation(PAPQC)is one of the effective devices for controlling reactive current,unbalanced current,and harmonic current caused by unbalanced loads and non-linear loads.In this paper,the LCLCL three-phase three-wire two-level topology is used to conduct in-depth research and analysis on the key control strategies of the parallel power quality control device.The main research contents of the thesis are as follows:The characteristics of the output filter determine the compensation effect of PAPQC.In this paper,the characteristics of LCLCL filter and its basic six passive damping strategies are studied and analyzed,and design examples are given.Based on the topological structure,the mathematical model of PAPQC in three-phase stationary coordinate system and positive sequence synchronous rotating coordinate system of fundamental wave is derived.The AC small-signal model is established and a multi-objective unified compensation strategy for grid current is proposed.The strategy compensates the reactive current and the unbalanced current based on positive sequence synchronous rotating coordinate system of fundamental wave,and compensates the harmonic current based on the two-phase stationary coordinate system.Because the current source type harmonic compensation device may cause harmonic amplification effect when compensating the voltage source type nonlinear load,the effect will cause the system output current to exproposes hibit low frequency resonance,and there is a risk of causing load damage.The paper a harmonic amplification effect suppression strategy based on fuzzy controller,which limits the harmonic compensation rate and then effectively suppresses the harmonic amplification effect.In order to effectively improve the compensation capacity of the equipment,this paper studies the key control strategies of multiple PAPQC parallel.In order to improve the compensation performance and reliability of equipment in parallel connection,in this paper,an improved instruction allocation strategy and hardware simulation bus are proposed,so that the system compensates according to the improved instruction allocation strategy in the normal mode,and compensates according to the system capacity ratio by hardware simulation bus in abnormal mode.In order to verify the above control strategy,in this paper,a prototype of 400V/60A modular PAPQC is designed and the key implementation technology of the prototype is discussed.Finally,the system experiments were carried out on the modular prototype,and the effectiveness of the proposed control strategies was verified by comparing the experimental results.