| With the rapid development of renewable energy(such as photovoltaic cell,fuel cell,etc.)based on DC power supply,the popularity of new power loads(such as electric vehicle,laptop,mobile phone,LED lighting,etc.),and the large-scale application of power electronic converters,DC microgrid has been developed rapidly.Compared with AC microgrid system,these DC sources and loads can reduce the power conversion link,simplify the system structure and improve the efficiency of the system.In DC microgrid,the load driven by DC-DC converter usually shows constant power characteristics when the output is strictly controlled,and its input impedance often shows negative impedance characteristics,which will interact with the power supply unit,greatly attenuate the system damping and stimulate the system oscillation.In other words,even if the subsystem in DC micro network can operate stably,when large system is composed,the stability of the system is difficult to guarantee.In order to solve the stability problem of the system,the common method is to analyze the stability of the system,determine the stability boundary conditions and the optimal range of system parameters,and ensure the stability of the system by parameter optimization design.However,because the DC micro network contains source,load and a large number of power electronic transformation units,the system order is high and nonlinear is strong,which makes the stability analysis of the system very difficult.In order to solve the stability of the system,this paper proposes a new method of compound control which combines passivity-based control and extended high-gain state observer for the source side bidirectional DC-DC converter commonly used in DC micro network.The method proposes that the traditional PI control is replaced by passivity-based control,which ensures the stability of the bidirectional DC-DC converter r with constant power load.By introducing decentralized control,the system is still stable when each source has constant power load.In addition,the control performance of the system under disturbance,parameter uncertainty and model error is solved by introducing the extended high-gain state observer.The method proposed in this paper can effectively solve the problem of instability caused by the interaction of DC micro network factor system.The main contents of this paper are as follows:(1)In this paper,the structure,control architecture,causes of stability problems and solutions of DC microgrid are investigated,and the control status of source side converter is summarized.Through the investigation of the current situation,the distributed control architecture is determined as the DC microgrid control architecture,and the passivity-based control scheme of the common Bidirectional DC-DC converter on the source side is defined.(2)Lagrange dynamics method is used to model the traditional DC-DC converter,and the basic principle of the passivity-based control is briefly introduced.(3)The passivity-based control is applied to x(x≥2)parallel bidirectional Buck-Boost converters with constant power load,and its detailed design is carried out.The system simulation model is built on the platform of MATLAB / Simulink,and the simulation results verify the correctness and effectiveness of the passivity-based controller.(4)Based on the passivity-based control,an extended high-gain state observer is designed to improve the control performance of the system in the case of disturbance,parameter uncertainty and model error.The simulation based on the simulation model verifies the correctness of the method.(5)A small DC microgrid experimental platform is designed and built in the laboratory,which includes two micro sources(lithium battery and DC power supply,and the output of micro source enters DC bus through bidirectional buck boost converter with power level of 100W)and one load(electronic load).The experimental results verify the correctness of the proposed passivity-based controller and extended high-gain state observer. |
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