Research On Power Quality Control And Active Power Fluctuation Smoothing Method Of Integrated Power Flow Controller

Distributed photovoltaic integration into the distribution network is an important way to consume new energy.However,photovoltaic power generation has the characteristics of intermittent fluctuations,coupled with low natural power factor,nonlinearity,and severe three-phase imbalance in the distribution network load,which exacerbates the power quality issues and energy losses of the power grid.The grid connected converter can effectively solve the power quality problem of the distribution network,and the energy storage converter can also effectively smooth out the power fluctuation of the load.The comprehensive power flow controller combining the grid connected converter and energy storage can integrate to solve the power quality and power fluctuation problem of the distribution network,which has positive practical significance for promoting the realization of the dual carbon goal.This thesis mainly studies the active and reactive power control methods of a comprehensive power flow controller for low-voltage distribution network power quality control and active power fluctuation smoothing.This thesis aims to smooth the active power fluctuations in low-voltage active distribution networks and improve the power quality of low-voltage active distribution networks.The circuit topology and system control scheme of the integrated power flow controller are studied.The grid connected converter is used to stabilize the DC bus voltage and improve the power quality of the power grid.The DC side cascaded energy storage converter is used to compensate for the active power fluctuations,including photovoltaic power generation and load.A mathematical model of a comprehensive power flow controller was established,and circuit parameters were selected for design.The capacity of the supercapacitor was determined based on the time-frequency characteristics of photovoltaic power fluctuations.This thesis studied the power quality control method of the integrated power flow controller,extracted non fundamental positive sequence components from the load current as compensation instructions,and completed the tracking control of compensation current instructions based on a composite control strategy of PI+repetitive control.Considering the impact of energy storage charging and discharging current on DC bus voltage stabilization control,the introduction of charging and discharging current feedforward control in the DC bus voltage control loop improves the anti-interference performance of DC bus voltage control and power quality control.This thesis studied the smoothing of active power fluctuations and optimization strategies for charging and discharging in the integrated power flow controller.The fluctuation components of active power were extracted from photovoltaic and load power as the charging and discharging power instructions for supercapacitors.Under the premise of stable DC voltage control,the smooth compensation of power fluctuations was completed based on charging and discharging current control.An improved moving average filter(MAF)algorithm is proposed,which improves the extraction performance of power fluctuation components and the smoothing effect of power fluctuation by adaptively adjusting the size of the sliding window and MAF phase correction based on power prediction;A self recovery fuzzy control method for supercapacitor SOC based on power fluctuation prediction is proposed,which reduces the depth of supercapacitor charging and discharging,improves the smoothing efficiency and residual smoothing ability of unit charging and discharging depth.This thesis have established a MATLAB/Simulink simulation model for a comprehensive power flow controller and an RT-LAB real-time simulation experimental platform.We have conducted simulations and experiments on power quality control and power fluctuation smoothing under various operating conditions and control strategies,and the results show the effectiveness of the control strategy used in this thesis.The comparison of experimental results from different methods indicates that the improvement strategy proposed in this thesis has superiority in compensation performance and utilization efficiency of supercapacitors.