| As energy shortage and environmental pollution become more serious,more and more researchers begin to pay attention to renewable energy utilization and distributed generation technology.As a typical renewable energy distributed generation system,photovoltaic systems are generally integrated into the power grid with power electronics.Compared with the traditional synchronous generator,its lack of inertia and damping will affect the safety and stability of the power grid in severe cases.The virtual synchronous generator technology provides inertial support through the installation of energy storage units in the PV system,so that the photovoltaic power generation system has the inertia and damping characteristics as the synchronous generator.In this process,the virtual inertia and damping parameters can be regulated independently according to the physical constraints such as charging and discharging power and residual capacity of the energy storage unit.The flexible inertia and damping capacity make it possible for the system frequency and voltage to be effectively suppressed at the initial stage of disturbance.Firstly,the key components of the photovoltaic energy storage system are modeled in detail.This paper establishes a photovoltaic cell model and analyzes the maximum power control strategy of the photovoltaic power generation system.The advantages and disadvantages of each type of energy storage are compared,lead-acid batteries are selected because of the high cost performance.The three-order dynamic model of lead-acid battery is analyzed and a comprehensive battery model is established.After that,the correlation between the traditional synchronous generator and the virtual synchronous generator is analyzed,and the control strategy of the virtual synchronous generator is introduced.Then,the simulation model of the combined power generation system of the CCDC bus is established and verified.Then,this paper analyzes the situation of isolated island and grid connection.The characteristics of the system are compared by simulation,and the influence of different parameters J?D?Kp on the operating characteristics of the system is compared.Furthermore,the improved inertial adaptive control strategy is proposed.Compared with the control strategy of constant inertia,the system performance is further improved.Since energy storage is the physical source of inertia in a photovoltaic system,the optimal configuration of energy storage unit under different damping ratio is analyzed.In order to analyze the adjustable range of inertia and damping of the virtual synchronous generator,the under-damping second-order system is selected,considering the energy storage capacity,charging and discharging power and the power rate.Therefore,the correctness of the parameter boundary and the validity of the control method are verified,which provides an analytical approach for the reliable operation of the virtual synchronous generator and the parameter adaptive control.Finally,this paper considers the typical application of photovoltaic energy storage system in the first end of' distribution network feeder.A new model of solid-state transformer(MPR-SST)is proposed in this paper,which combines the photovoltaic system controlled by the virtual synchronous generator and the solid state transf'ormer system based on multi-pulse rectifier.The feasibility of the model is verified by the prototype test and the application of virtual synchronous generator control in MPR-SST is verified by simulation. |
PDF Full Text Request