Research On Power Quality Improvement Of Micro-grid With Active Control Strategy

With the rapid development of the world economy,human society is facing an increasingly serious energy crisis and pollution problems.Distributed new energy plays a pivotal role in the energy revolution because of its cleanliness and renewability.Microgrid is the main form of distributed energy utilization.At present,countries around the world have carried out research on microgrid systems engineering around new energy sources.Compared with the public power grid,the microgrid is more vulnerable to interference from the external environment and other factors.At the same time,its internal power electronics and non-linear loads will all lead to deterioration of power quality.Therefore,based on the control strategy of microgrid,this paper discusses the power quality control method with active control strategy.Firstly,in order to select the appropriate filter,this paper models the three commonly used filters,analyzes the amplitude-frequency characteristics of the transfer function,and selects the LCL filter as the filtering device of the microgrid from the filtering performance of each frequence band.For the control problem of the LCL interface inverter,the mathematical model of the three-phase static abc coordinate system,the two-phase staticαβcoordinate system and the two-phase rotating dq coordinate system is established,and the state equation of the interface inverter is obtained.In the equation of state,a new current control output is introduced to decouple the current,and the current is controlled separately.The PQ control of the interface inverter is realized by using the current inner loop power outer loop,and the vf control of the interface is realized by the current inner loop voltage outer loop.Secondly,considering the influence of parameters on the filter performance,the constraint conditions of the LCL filter are given,and the parameters of the LCL filter are designed and verified for an example.In order to weaken the resonance peak phenomenon in the frequency band of the LCL filter,four kinds of passive damping strategies and active damping strategies increase the system damping,and at the same time achieve the suppression of resonance peaks and high-performance filtering effects.Based on the advantages of active damping strategy,a constant power current double-inner loop control strategy combined with active damping is proposed,this paper adds the capacitance current of the LCL filter as feedback into the control loop,the active damping control of the LCL filter is achieved while achieving constant power control of the interface inverter.Then,considering the effect of parameters on filter performance,the classification and topology of active power filter are briefly introduced,and shunt active power filter is used as research object.Combined with the various modules of the active power filter,the basic working principle of the APF is described.For the key technologies of active power filter,harmonic extraction and current tracking,i_p-i_q extraction method and PI control current tracking loop combined with repetitive control strategy are proposed respectively,which can achieve fast,accurate and stable tracking of command current.Considering the idle capacity of the microgrid interface inverter,this paper proposes a microgrid power quality control method with active control strategy,the harmonic component detected by the load current is added into the interface inverter output current command control loop,so that the interface inverter acts as a power exchange device,and at the same time,it actively compensates for harmonic power quality problems in the system.Finally,in order to test the governance method proposed in this paper,the simulation model of microgrid was built by using Matlab/Simulink platform.The simulation of the LCL filtering microgrid control strategy with active damping is carried out.The results show that the LCL filter with active damping is better than the L filter in grid-connected state.The tracking effect of PI control combined with repetitive control is better than the traditional PI control.Constant voltage constant frequency control has good internal stable voltage and frequency effect.A simulation model of active power filter was built to verify the load current harmonic components in the detection system,and to generate tracking currents of equal magnitude and direction.The simulation of microgrid power quality control method with active control strategy was performed to verify the effectiveness of the interface inverter’s active compensation for harmonic power quality problems in the system.