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Reseaseh On Suppression Strategy Of Inverter Parallel Circulation Based On Virtual Synchronous Generator

Posted on:2021-01-08Degree:MasterType:Thesis
Country:ChinaCandidate:W Q LvFull Text:PDF
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With the decrease of traditional fossil energy,microgrid has gained wide attention due to its environmental protection concept.The distributed generation unit is connected to the micro grid through the inverter.The micro grid is a self-powered local grid formed by a variety of energy structures in a certain area and connected to the large grid through the switch device(circuit breaker).The traditional control strategy of the inverter is droop control strategy,which is characterized by fast response speed.However,when the load changes due to this characteristic,the system cannot timely adjust,bringing uncertainty to the normal operation of the load.The reference frequency of traditional droop control has a sudden change,which is a big challenge to the normal operation of microgrid.Referring to the conventional Synchronous Generator(SG)used in general large power grid,SG can provide rotational inertia and damping characteristics for the system.SG can also incorporate the energy from the rotor into the power grid system in case of interference.These features of SG make the stability of the large grid very obvious.So some scholars put forward simulation SG rotational inertia and damping characteristics of inverter control strategy,this strategy is called Virtual Synchronous Generator(Virtual Synchronous Generator,VSG)control strategy,by controlling the switch of the inverter,the control strategy to simulate the characteristics of SG,can be simulated in the inverter rotational inertia and damping characteristics of SG,can effectively change the micro grid system is the moment of inertia,for stable power output voltage and output power have obvious effect.In practical application,inverters are all operated in parallel,but there are also many problems in parallel operation of inverters.Due to the difference in line impedance and the difference in instantaneous voltage amplitude at output end of each inverter,circulation is easy to occur.The circulation will lead to the increase of inverter loss,which will affect the output efficiency of the microgrid.Therefore,it is of great significance to study circulation suppression strategies.This paper first introduces the research background and significance of microgrid,introduces the research status of VSG at home and abroad,and analyzes the voltage and current control strategies according to the research status at home and abroad.The causes of inverter circulation in parallel are simply analyzed and the current mainstream circulation suppression schemes are simply introduced.Secondly,this paper analyzes the SG mathematical model,and makes a comprehensive analysis of the VSG mathematical model,establishes the VSG mathematical model,and introduces the concept of virtual moment of inertia,and then through Matlab/Simulink simulation software to model the VSG,analyzes the VSG key parameters on the operation of the VSG.Moreover this paper analyzed the VSG parallel runtime and the reason of the circulation was proposed based on virtual impedance of VSG algorithm,join the virtual impedance voltage current double closed loop,because VSG on the characteristics and mechanism is a good way to simulate SG,through the VSG virtual impedance voltage and current double closed-loop control to join to simulate the large inductance,both can inhibit the circulation in the parallel system,also can effectively suppress the output voltage drop.And the calculation is simple and easy to realize.Matlab/Simulink simulation verifies that the proposed control strategy can suppress the system circulation,ensure the stability of the system output voltage,and greatly improve the power quality.Finally,the hardware and software structure of the system is introduced,including hardware circuit and software flow chart.The hardware parameters and device selection are analyzed deeply,and the program flow chart is designed for the system software implementation.
Keywords/Search Tags:microgrid, VSG, virtual impedance, Circulation suppression, Double closed loop control
PDF Full Text Request
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