Research On Configuration Of Hybrid Energy Storage System In Virtual Synchronous Generator

Virtual synchronous generator(VSG)improves the dynamic performance of micro-grid with distributed generation by introducing the inertia and damping of synchronous generator.As an essential part of the VSG system,the energy storage system can provide continuous inertial simulation capability for the VSG.In order to improve the overall output performance of the VSG system,this paper analyzes the mathematical model and control strategy of the VSG.Then,the hybrid energy storage system composed of the battery and ultracapacitor on the DC side of the VSG is studied from the two aspects of parameter configuration and control strategy.The detail content and innovations are reflected in:There are several virtual damping effect terms added to the swing equation of VSG to mimic the damping effect of real synchronous generator.Compare different representation methods from two aspects.The first aspect examines what type of damping effect form is the best to mimic the damping effect of synchronous generator while the second aspect exmines what kind of damping effect form is better to improve system frequency stability.This provides a theoretical basis for the construction of VSG swing equation.The key parameters inertia and damping are both virtual quantities.After qualitatively analyzing the swing equation of VSG,an inertia and damping cooperative adaptive control method is proposed to improve the transient performance of VSG and adapt to different operating conditions.Based on the detailed analysis of the mathematical modeling and control strategy of VSG,in order to improve the output performance of VSG system,the parameter configuration and control strategy of the hybrid energy storage system are analyzed.In the aspect of parameter configuration,the unbalanced power of the VSG system is decomposed according to the operating characteristics of each energy storage device.Then,an energy management strategy aiming at improving the overall economics of the system is proposed.On the basis of that,the lower system cost and higher energy efficiency are taken as the objective function,the system reliable operating and the energy storage devices working in a reasonable interval are regarded as constraints.After building an optimization model,the NSGA-? algorithm is used to calculate the parameter configuration of the VSG system with one year as the optimization cycle.It is confirmed that the proposed energy management strategy can make the hybrid energy storage system fully realize its economics under the premise of ensuring normal operation of the system.Finally,the control strategy of hybrid energy storage system is researched.When the power fluctuation is too large,the cycle life of the battery may be shortened because of overcharging or over-discharging.This paper proposes a VSG system control strategy with battery state of charge feedback.The control strategy of the system will be switched smoothly according to the state of charge of the battery.As a result,the energy storage system will always run within a predetermined reasonable range.