Study On The Control Strategy Of Multi-Function Grid-Connected Inverter In Microgrid

As a special kind of distributed generation system,microgrid has become a research priority in distributed generation area by integrating the advantages of all kinds of distributed resources and reducing the impact of distributed generation units on grid.As the key equipment in the microgrid system,the control technology of grid-connected inverter has been developed rapidly.Compared with the traditional grid-connected inverter which has no inertia damping and can only transmit active power into the grid,the multi-function grid-connected inverter(MFGCI)which has more flexible control and more diverse functions has been paid more attention.In this paper,the power quality control and virtual inertia damping control of MFGCI are studied.In order to realize the power quality control function of MFGCI,The harmonic and reactive current detection algorithm based on FBD theory is used to obtain the comprehensive current,and the MFGCI control strategy with both grid-connected power generation and power quality management is studied.Considering the limited capacity of a single MFGCI for power quality management,how to control harmonics and reactive power components in a targeted and optimized way is necessary.Based on analytic hierarchy process(AHP),the comprehensive evaluation model of harmonic and reactive power is established,which fully considered the difference of power quality indicators;On this basis,an optimal compensation strategy is designed to achieve the same comprehensive power quality index and minimize the input compensation capacity,and the optimal compensation coefficients of reactive power and harmonic current in the optimal compensation strategy are determined by Lagrange multiplier method,so as to realize the flexible management of power quality of MFGCI.In order to realize the virtual inertia damping function of MFGCI,the virtual synchronous generator control is used to simulate the inertia damping characteristics of synchronous generator,which provides a certain support for the stability of the power grid.By systematically analyzing the mathematical model of the virtual synchronous generator and the control structure of the power loop,the small signal model of the power loop is deduced;the influence of inertia,damping and other parameters on the output of the system and the design method are discussed in detail.In order to make full use of the flexibility of MFGCI control and improve its property in the transient process,based on the adaptive control of traditional inertia,an improved adaptive control of virtual inertia damping algorithm is proposed,which can effectively shorten the transient response time and reduce the fluctuation of system frequency and power in the transient process.Based on the Typhoon HIL experimental platform,the experiments of MFGCI power quality management control and virtual inertia damping control are completed.The experimental results verify that the power quality optimization compensation strategy can effectively realize the MFGCI to control the power quality in a targeted and optimized way;and verify that the improved adaptive control of inertia and damping can effectively improve the transient performance of the system.There are 75 figures,14 tables and 81 references in this paper.