| As static components,Photovoltaic array and energy storage devices will have negative effects on system inertia after accessing to grid,because the power is decoupled from system frequency.In order to improve dynamic stability of system,this essay will establish contact between system frequency and energy storage devices power,and make the research on virtual inertia of hybrid energy storage system,then provide inertia support.Aimed at the different principles and power regulating characters of two portions in the hybrid energy storage system,battery and supercapacitor,this paper distributes the power of hybrid energy storage system,in order to prolong their life.The main research results are as follows:(1)According to the different principles and power regulating characters of two portions in the hybrid energy storage system,the power of high-power-density supercapacitors is called firstly.If the energy demand is larger than supercapacitors' energy supply,the power of high-energy-density batteries is called.In this way,the large-current impacting caused by batteries frequent fast charge and discharge is avoided,then the life of energy devices are prolonged.(2)Energy transformation relation was set up between energy of battery and supercapacitor and rotor kinetic energy of synchronous generator.Definition of virtual inertia based on two kinds of static energy in hybrid energy storage system was proposed.In this way,system frequency was decoupled with hybrid energy.(3)Charging or discharging of hybrid energy storage system can provide inertia support to system frequency when system frequency was fluctuating.Meanwhile,according to the different characters of two kinds of energy storage system,energy needed was distributed to them,in order to reduce the adverse impact on battery life.In order to avoid overcharge or overdischarge,states of charge(SOC)of supercapacitor and battery were monitored simultaneously.(4)The small-signal models of batteries and supercapacitors were derived,and the small-signal model of two-region interconnected power system with hybrid energy storage devices.According to the state equation,the change of characteristic roots of interconnected power system is analyzed when virtual inertia and damping are changed as controllable parameters,and the virtual inertial integrated control is carried out for the virtual inertial of energy storage elements in different regions.(5)Based on Matlab/Simulink,a dynamic simulation model with 30% proportion photovoltaic-energy-storage system and a dynamic interconnected power system simulation model with 40% proportion photovoltaic-energy-storage system were established to validate the control strategies effectiveness.Hybrid energy storage system under the virtual inertia control strategy can not only realize the frequency response,but prolong the life of hybrid energy storage system.Further more,the power oscillation characteristics of interconnected power system can be improved by adjusting the virtual inertia in two regions as controllable parameters... |
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