Research On Control Strategy And Decision Of Interconnection Location Of Microgrid

During the operation of microgrid,output power of the distributed generation is often affected by environmental factors,maximum power point tracking strategy can guarantee its efficiency;inverter control strategy is related to automatic adjustment of the microgrid voltage and frequency,and stability input and output of distributed generation and load.When the droop control strategy is applied to the low-voltage microgrid,droop controller would fail to guarantee the normal operation of the system due to the power coupling,the stability and flexibility of the microgrid will be affected.In addition,microgrid as a special power system,when access to the distribution network,often changes the structure of the distribution network,making voltage distribution,power transmission and even stability of the power distribution system change.Based on this,the main study of this paper are as follows:(1)According to the mathematical model of the equivalent circuit of photovoltaic cell,the simplified model of photovoltaic cell is established.Based on the comparison of the commonly used maximum power point tracking strategies,comprehensive analyzed the mathematical model of the DC-DC converter and the power curve of the converter,a maximum power point tracking strategy without voltage detection is deduced,and optimized the strategy with variable step tracing.The simulation results show that the proposed maximum power tracking algorithm has better tracking performance.(2)Based on the analyses of the power transmission characteristics of the low-voltage microgrid,the power coupling characteristic of the inverter is analyzed by the relative gain array.The power decoupling is realized by introducing the virtual negative resistance in the droop controller.The range of virtual negative resistance is studied by means of the stability analysis theory of the control system.The analysis of the frequency characteristics shows that the introduction of the virtual negative resistance can make the output impedance of the inverter capacitive and improve the line voltage drop and reactive power compensation configuration.The inverter parallel system simulation model is built by MATLAB,the simulation results show that within the virtual negative resistance,the inverter can be stable to provide a 220 V three-phase AC,the frequency deviation is limited to ±0.2Hz,inverters' total harmonic distortion is reduced to 0.93%and 1.08%.(3)Took the siting of microgrid as purpose,oriented by the reducing of voltage deviation and network loss while the microgrid were accessed to the distribution network,a multi-target decision method for the siting of microgrid based on considering the network loss,voltage deviation,voltage deviation improvement level,network loss improvement level and static voltage stability index is proposed in thispaper.Connected the microgrid to each node in the distribution network system,and the five indexes are calculated according to the power flow.Then,by constructing the ideal optimal object and the ideal worst object,the nodes under selection are divided into three categories by means of fuzzy clustering,and the Euclidean distance method is used to further refine the clustering results,so as to realize the sorting of the nodes.Finally,the accuracy and rationality of the sorting results are verified by the simulation results of a typical microgrid connected to a IEEE14 distribution network.