Research On Application Of Unified Power Quality Conditioner In Active Distribution Networks And Its Control Strategy

In active distribution network,unified power quality conditioner can solve all kinds of power quality problems in distribution network.It is a powerful supplement to the regulation technology of active distribution network,and affects the stable operation of the whole active distribution network to a large extent.At the same time,the unified power quality regulator is also a distributed terminal for the user side.Its compensation performance affects the power quality of the power supply of the user,especially the safe power supply of the sensitive equipment.Therefore,the research of unified power quality conditioner is very important.Considering the characteristics of the complex structure,large weight and high cost of the traditional unified power quality regulator,and its difficult to compensate for the deep sags and harmonic components,a topology of the single phase transformerless UPQC is proposed in this paper.On this basis,the research contents and objectives of this topic are as follows:First,the UPQC topology of the single phase non isolation transformer is expounded.On this basis,the mathematical modeling is carried out,the power flow of the topology compensation work is analyzed,and the mechanism of the DC bus ripple is derived,and the DC bus capacitance is designed accordingly.Secondly,the series compensation control method of the unified power quality regulator is studied.In this paper,the voltage sags compensation control strategy based on the minimum current injection method and the non harmonic detection link voltage sags harmonic compensation control strategy is proposed.They can compensate the grid voltage depth drop without increasing the maximum output current limit of the series side converter,and broadens the compensation range of the sag.The unified power quality regulator can effectively compensate the harmonic components of the grid voltage,improve the power quality of the load side,and make maximum use of the series compensation capacity of the unified power quality regulator to ensure the continuous and stable power supply of the load.The feasibility of the proposed control method is verified by simulation comparison and analysis.After that,the difficulty of DC component detection in the parallel side harmonic detection algorithm is studied.The traditional harmonic extraction algorithm based on the instantaneous reactive power theory is analyzed and compared.On this basis,a harmonic extraction control algorithm based on the three order + two order generalized integrator is proposed.It can effectively suppress the interference of DC components in power grid current to harmonic detection.At the same time,a DC bus control algorithm based on PIR controller is proposed to solve the problem of UPQC topology DC bus ripple of half bridge structure without isolation transformer.The simulation results show that the proposed control method can achieve the compensation of the specific harmonic current and the DC bus voltage without fluctuation.Finally,the hardware circuit design and the software control algorithm of the single phase transformerless structure unified power quality regulator are analyzed in detail,and the previous part of the research is verified by the simulation and experiment.