Research On The Architecture Of Optical Storage And Grid-connection System Based On Nine-switch Converter

At present,the scheme adopted in the photovoltaic energy storage grid-connected system is that each photovoltaic and energy storage device is connected to the public DC bus through their own DC-DC converter,and connected to the grid through a centralized DC-AC converter.However,this scheme needs to use a large number of converter devices,with a large number of switches,many power conversion levels,low efficiency,large volume and large initial investment,and other problems,is not conducive to the application in remote areas.Therefore,how to realize the compact optical storage grid-connected system has a great application prospect.In order to solve the above problems,a new architecture of optical storage and grid-connection system based on nine-switch converter is proposed.Compared with the 12 switching converter used in the traditional optical storage and grid-connected system,the switching tube of the converter is multiplexed,the switching tube is reduced by 1/4,the power density of the system can be improved effectively,and the control performance is the same as that of the original optical storage and grid-connected system.The nine-switch converter consists of nine switch tubes arranged in a three-voltage port structure.In this paper,three voltage ports are connected with power grid,energy storage system and photovoltaic system respectively.The work in this paper is as follows:Firstly,this paper introduces the topology and working principle of traditional optical storage and grid-connection system based on nine-switching converter,analyzes and compares their advantages and disadvantages,and draws the conclusion that the grid-connection system based on nine-switching converter can greatly improve the power density of the system.The switching modulation strategy of nine-switch converter is described in detail.Then,based on the topology of nine-switch converter,the mathematical model of optical storage and grid-connection system is established.The effectiveness and rationality of the topology are verified by designing and building a simulation system of 380 V 9-switch converter on AC side.Secondly,the control scheme of the new optical storage system structure is studied.The scheme adopts the three-level grid-connected control strategy and the hierarchical coordinated control strategy of the energy storage system.The three-stage grid-connected control strategy includes independent MPPT control strategy,common DC bus voltage balance control strategy and grid-connected current power feedforward decoupling control strategy.Aiming at the problem of frequent charging and discharging of lithium batteries,an optimal power allocation algorithm is proposed in this paper,which determines the priority and working mode of battery charging and discharging sequence according to the SOC feedback value of lithium batteries,so as to ensure that lithium batteries do not appear high power and over-charging and discharging state.The effectiveness and rationality of the proposed control scheme are verified by designing and building the simulation model of the new optical storage and grid-connection systemFinally,this paper will be based on three harmonic injected into dc voltage utilization methods for application of the light grid storage system,the advantages of this approach is that both enhance the public utilization rate of dc voltage of the dc side,also enlarged the photovoltaic array input network side power constraints,which expands the light grid storage system power constraints of scope,improve the dynamic stability of the whole system.By designing and building a simulation model,the correctness of this method is verified.