| In recent years,along with the promotion of smart grid construction and the application of new electrical equipment,the power industry has been developing rapidly.However,with more and more nonlinear and three-phase unbalanced loads connected to the grid,power quality problems such as harmonic pollution,substandard power factor and three-phase current unbalance in the power system are becoming more and more prominent,which have become important factors limiting the reliability and energy efficiency of the power system and have caused serious impacts on production and life.Therefore,it is important to study the comprehensive power quality management device of low-voltage distribution network.In view of the above problems,this thesis designs a joint management device based on Distribution Static Synchronous Compensator(D-STATCOM)and passive filter for distribution network.The device adopts a combination of active and passive structures,which not only avoids the problem of amplification of harmonic currents on the load side that may be caused by the pure active treatment device when treating harmonics,but also solves the problem of over-compensation or under-compensation that may occur when the pure passive treatment device compensates for reactive power.The device can optimize cost control while satisfying the compensation capacity and treatment effect,and has remarkable practicality and economy.This thesis firstly constructs the overall topology of the joint management device,including the D-STATCOM part to compensate reactive power and three-phase current imbalance and the passive filter part to control harmonics.Among them,the D-STATCOM selects the I-type three-level topology with lower switching loss and better output quality,elaborates the working principle,and selects the sinusoidal pulse width modulation strategy to realize the control through modeling analysis.To address the harmonic problem,this thesis proposes a new type of passive filter,which uses the coupling effect of the balanced reactor to generate a harmonic voltage corresponding to the number of harmonic currents,and applies this voltage to both ends of the filter branch to achieve the purpose of filtering harmonics.The working principle is derived in detail,and a parameter solution method considering the overall filter network is proposed.Second,based on the three-phase four-wire i _p-i_q current detection method,this thesis proposes a i _p-i_q current detection algorithm based on an improved second-order generalized integrator,which solves the error problem of the phase-locked loop(PLL)in the case of three-phase voltage asymmetry,etc.,and improves the accuracy of component extraction.By analyzing the current tracking control strategy,a composite control strategy based on quasi-PR control,PI control,and repetitive control is used to improve the current tracking control effect under transient and steady state.Finally,a simulation model of the joint governing device is constructed by MATLAB/Simulink,aiming to verify the effectiveness of the current detection algorithm as well as the tracking control strategy in this thesis.Simulation analysis is also conducted under different load conditions to fully evaluate the performance of the device.The hardware and software design of the device was completed based on the current detection algorithm,tracking control strategy and the main circuit topology.The test platform is set up in the laboratory environment,and the data and waveforms are measured by FLUKE power quality analyzer before and after the treatment,so as to verify the feasibility of the hardware and software solutions of the joint treatment device proposed in this thesis. |
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