Grid-connected/Standalone And Switching Control Method Of Micro Grid Inverter

Smart grid is considered as an effective way to alleviate the current energycrisis and the effective way to deal with grid failure for users. People around theworld focus on the research of smart grids. In a distributed power generation system,inverter is the main control device to regulate the performance of distributed powergeneration system. This paper studies the control strategy of distributed generationsystem interface device which is called inverter in the grid-connected and islandmode as well as the situation when switching between the two modes.In the grid-connected mode, this thesis studies how to control the current flowsinto the main grid. In this dissertation we use PID control method which is widelyused in egineering in the synchronous rotating coordinate and the static coordinateof the system, then tune the parameters of the control system. For system’s couplingproblems we designed decoupling control, then do the simulating and analyzing. Inthe island mode, due to loss of the support of main gird’s voltage and frequency, wechose the voltage and current double closed-loop to control the voltage andfrequency of the system.The new switching control scheme we proposed is based on the analysis of theexsiting scheme. We put forward the switching control algrithm based on the LCfilter. The changes for each variable in the process of switching are analyzed. Wecontrol the voltage and frequency of the system by the clipper, the current harmonicsuppression effect is poor for the LC filter, the efficiency and response speed of theinverter will deteriorate if we simply increase the value of inductance. The T-typefilter can effectively solve the problems above, this paper discusses the parametersof the filter design process in detail. L-type and T-type filter filters are equivelent inlow frequency and the capacitance effect can be ignored, we simplified controllerdesign process for this property, then build system model. Compare with LC filter insuppressing current harmonics, T-type filter does have obvious improvement. Thesimulation results proves that proposed switching control scheme is reasonable.