| The widespread application of high proportion renewable energy combined with high proportion power electronic equipment has led to a gradual decrease in the rotational inertia of the power system.When renewable energy generation or load undergoes random fluctuations,the frequency of the power system will experience significant fluctuations due to the hysteresis of traditional units and the low inertia characteristics of the system.Therefore,in the face of high penetration rate of new energy,the system frequency will continue to deteriorate,Introducing the Battery Energy Storage System(BESS)into power grid frequency regulation can optimize and improve frequency quality.Energy storage converters have the advantages of fast response speed,high response accuracy,flexible control,and bidirectional charging and discharging.This article applies Virtual Synchronous Generator(VSG)technology to the control of energy storage converters,enabling them to have a certain amount of rotational inertia and participate in frequency regulation control of the power grid.For energy storage converters based on VSG control,this paper aims to explore the potential of energy storage frequency modulation and conducts research on adaptive control strategies for energy storage participation in primary and secondary frequency modulation of the power grid.Firstly,based on the VSG control principle,the parameters of the current,voltage and power control loops are designed to achieve the "current voltage power" three closed-loop control under the VSG,and the effect of energy storage batteries on the frequency regulation of the power grid is demonstrated.Secondly,a dual layer constrained energy storage adaptive comprehensive control strategy is proposed for the participation of the energy storage converter system in the primary frequency regulation of the power grid.The correlation coefficients are designed based on the hyperbolic tangent function,and the State of Charge(SOC)of energy storage and system frequency are considered to form a dual layer constraint.Using an adaptive virtual synchronous machine control strategy outside the frequency modulation dead zone to achieve energy storage adaptive output under inertia and droop effects;Within the frequency modulation dead band,the energy storage adopts a joint control strategy of frequency modulation and recovery.When the SOC of the energy storage battery is within the set threshold,frequency modulation control is used,and when it is outside the threshold,SOC recovery control is used.Then,for the energy storage converter system participating in the secondary frequency regulation of the power grid,segmented adaptive changes in the integration coefficient are achieved based on the characteristics of the frequency change of the power grid during frequency regulation.If the frequency of the power grid exceeds the frequency boundary when the secondary frequency regulation is turned on,an integration link is introduced on the basis of the energy storage participating in the primary frequency regulation of the power grid,which not only promotes the recovery speed of the power grid frequency but also adjusts the power grid frequency without error.Optimize the design of adaptive coefficients to achieve better performance in frequency modulation under complex power and load fluctuations,and achieve more suitable tracking and dynamic performance.Finally,a semi physical experimental platform based on Matlab/Simulink simulation and "HIL platform+DSP controller" verified the effectiveness of the proposed control strategy in improving the frequency regulation characteristics of the power grid and the superiority of the adaptive secondary frequency regulation strategy. |
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