Research On Control Strategy Of Multi-Interconnected Converters In Hybrid Microgrids

The microgrid is a small power generation and distribution system connected to the medium and low voltage distribution network,which is mainly composed of distributed generation units,energy conversion devices,and energy storage devices.The distributed power generation unit needs to be connected to the microgrid through the converter.converter,as a DC/AC converter,is the core power electronic device for micro-grid system to realize the conversion ofnew energy.Parallel converters are widely used in hybrid microgrids due to their high reliabiliy,good stability and low cost.The application of traditional interconnection droop control between parallel inverters can achieve load sharing,but due to the influence of circuit impedance,there are problems of power cycling and excessive stress between inverters.These problems increase the loss of the power system,reduce the life of the interconnected.converter,occupy the capacity of the interconnected converter and easily lead to system instabiliy.This paper introduces an improved droop control method based on frequency superposition.TheDC voltage in the DC converter is superimposed with a small AC signal.The frequency of theAC signal is proportional to the output power.The converter and the droop control based on the superimposed frequency are coordinated together to solve the power problem.Problems withcirculation,circulating current between converters and uneven power distribution.However,due to the inherent disadvantages of droop control due to the fixed droop coefficient,he system willbe unbalanced due to excessive voltage and frequency deviation.Therefore,this paper adopts thesegmented droop control method,even if the load changes in a specific area,it can maintain aconstant reference value,by using the droop characteristic curve with a combination of linear and quadratic functions to improve the response speed and reduce the steady-state errors.Then the modeling and simulation of the control method of the designed hybrid micro-grid parallel converter are carried out.The results show the effectiveness of the strategy.