Study On Power Conversion System Of Virtual Synchronous Generator

In the mode of island operation,to prevent the system frequency and voltage amplitude from abrupt changes,restore system power balance,and ensure that the system output AC parameters are within the normal range,the power conversion system faces the fluctuation of the load power,uses the power of the energy storage device,adopts the virtual synchronous generator control strategy,and simulates the features like the ontology model of the synchronous generator,active frequency modulation,and reactive power regulation.The above process is a adjustment of VSG.VSG's adjustment is composed of two parts,including active frequency control and reactive power control.Essentially,it's a droop control,which belongs to the differential regulation.Although the virtual synchronous generator has similar virtual inertia and damping as the synchronous generator,the virtual synchronous generator and the synchronous generator are not completely equivalent,and the configuration of VSG's control parameters is relatively flexible.This paper is based on the power conversion system of virtual synchronous generator as the research content.The emphasis is laid on the analysis and research of traditional virtual synchronous generator technology,and advance a new virtual synchronous generator strategy which can make the droop coefficient adjust itself according to the actual situation.This control strategy not only maintain the power balance of microgrid in mode of island operation,but also realize the small deviation of frequency adjustment and voltage amplitude adjustment.The main research work of this paper can be divided into the following parts:First of all,It is clear that the function of the power conversion system in the microgrid is mainly dependent on the power converter.By analysising the mathematical model and control system structure of power converter,It is obvious that the control system of the power converter is made up of the inner loop controller and the outer loop controller.The inner loop controller determines the characteristics of the power converter itself.The outer loop controller determines the function of the power converter in the microgrid.In addition,by means of control strategy commonly used in power converter.I am further aware of the essence of the traditional control strategy for power quality regulation,and what are the shortcomings.Secondly,by analyzing and studying the mathematical model of synchronous generator,I lead to the problem of how the virtual same generator technology is how to simulate a DC/AC converter into a synchronous generator.Through the analysis and study of the mathematical model of the virtual synchronous generator,it is clear that how to design the controller of the power converter based on the virtual synchronous generator and how to choose each parameter.Thirdly,the problem of the bias of frequency modulation and voltage regulation in the of island operation mode.It is possible to analyze the features in virtual synchronous generator,including the relationship of between active power change and frequency change,reactive power change and voltage change,alone with the dynamic characteristics of power regulation.Taking droop coefficient as an optimization object and introducing parameter self-adaptive adjustment method,an improved virtual synchronous generator is proposed to adjust the droop coefficient according to the actual situation.The simulation experiment platform is built through MATLAB/Simulink,and the simulation show that improved control strategy has better performance compared with the traditional virtual synchronous generator,which not only maintain the power balance of microgrid,but also achieve the small deviation of frequency adjustment and phase voltage amplitude adjustment.Last but not least,by building the physical platform of the power conversion system,I verify the improved control strategy.The experimental results demonstrate the correctness and feasibility of the proposed control strategy.