Autonomous-synergic Operation For Photovoltaic And Energy Storage System Based On Flexible Virtual Inertial Control

Compared with the traditional synchronous generators,the distributed generators using power electronic interfaces lack rotational inertia,it has fluctuations and uncertainties,and poor anti-interference ability,which causes the stability of the system to decrease.The virtual synchronous generator(VSG)technology has become an important method to solve this problem.However,various factors affecting the stable operation of the system,as constraints to adjust the virtual inertia in the VSG system,will directly affect the system’s operating performance and power quality.In addition,the parallel operation of multiple sets of VSG units is widely used in actual engineering.The coordinated operation between VSG units can be achieved by adjusting the virtual inertia.Therefore,this paper studies the flexible adjustment method of multi-constrained virtual inertia and the cooperative operation control between multiple optical storage VSG systems.The main research results are as follows:(1)Firstly,the topological structure of a typical virtual synchronous generator system with distributed power and the control principle of traditional VSG technology are introduced in this paper.In view of the disadvantages of traditional VSG control with poor flexibility and controllability,the flexible virtual synchronous generator(FVSG)is introduced.The advantages of flexible and adjustable of the power electronic equipment can be given full play in this control technology.However,this method has a single constraint condition and only considers the change of frequency.Therefore,a multi-constrained flexible virtual inertia(M-FVI)control strategy is proposed in this paper,which takes into account the state of charge(SOC)of the energy storage unit,the change rate of the system frequency,the inverter capacity and the power adjustable amount of the system in unit time.The virtual inertia can be adjusted with multiple constraints on the stability of the system.The virtual inertia is adaptively adjusted based on the exponential function and arc tangent function to reducing the degree of influence of various factors and improve the equipment operation performance.At the same time,the power quality of the system is improved.The proposed control strategy can be more suitable for practical engineering.The control-level hardware-in-the-loop experimental platform is established to validate the effectiveness of the proposed M-FVI control strategy.(2)Since the control parameters in the proposed M-FVI control strategy directly affect the system’s virtual inertia level,which affect the system stability,a four-terminal microgrid small-signal model with an optical storage VSG unit is established in this paper.The influence of the main control parameters on the system stability and the principles for parameter designing are obtained by the root locus analysis,stable operation boundary,analytic hierarchy process,and three-dimensional surface graph.Therefore,the control effect of the virtual inertia is optimized,and the theoretical basis can be provided by the design of parameters in the proposed control strategy provides.(3)Aiming at the problem of virtual inertia coordination in multi-VSG systems in practical engineering applications,a multi-optical storage VSG system cooperative operation control strategy based on a three-VSG parallel system in proposed in this paper.The TOPSIS method is used to evaluate the virtual inertia adjustment capability of each VSG unit,and the inertia level provided by each VSG unit is adjusted according to the evaluation results and the principle of inertia allocation to achieve the control effect of "decentralized autonomy and centralized coordination",so that the frequency stability can be improved,the overcurrent shutdown phenomenon can be avoided and the damage to equipment can be reduced.The cooperative operation control strategy has certain reference value for engineering applications.A multi-optical storage VSG system simulation platform was built by Matlab/Simulink,and the effectiveness of the proposed control strategy was verified.