Research On Control Of Three-Phase Four-Wire Dual-Mode PCS For Energy Storage

To solve the serious energy problem,the research on renewable energy power generation technology has been gradually deepened,which has been widely used in distributed power generation systems.Moreover,the energy storage systems are introduced to suppress the volatility of renewable energy power generation and to increase the penetration rate of distributed power generation.The power converter system(PCS),as the core of the energy storage system,is used to transmit the energy between the energy storage equipment and the grid.Besides,the PCS can also improve the output power quality of the converter.Therefore,research and development of various operational functions of the PCS can further promote the development of renewable energy technologies.In this paper,the PCS is taken as the research object,with conditions of the islanding mode under unbalanced load condition and the grid-connected mode under weak grid conditions.The control strategy,modulation strategy,unbalance suppression strategy,harmonic suppression strategy,and other methods are deeply explored.The main research work and innovation of the paper are as follows:Considering the influence of unbalanced load and weak grid,the converter topology is selected as three-phase four-wire neutral point clamped topology.Compared with the three-phase four-bridge topology,the zero-sequence component can be controlled under a simpler control strategy with the NPC topology.On this basis,the mathematical models of the system are established in both the three-phase stationary coordinate system and the synchronous rotating coordinate system.Besides,the control parameters of the droop control and the voltage-current double closed-loop are reasonably designed,providing a certain theorecticals basis for unbalance control and background harmonic control.In view of the problem of voltage unbalance at the point of common coupling(PCC)caused by the unbalanced load in island mode,the novel negative-sequence and zero-sequence voltage weighting control are introduced in the voltage-current double closed-loop control,which effectively suppress the unbalanced voltage at the PCC.Aiming at the voltage harmonic problem at the PCC caused by the weak grid terminal connection in grid-connected mode,the novel background harmonic voltage coordinated control strategy is proposed,including harmonic extraction strategy and harmonic voltage weighting control,which can effectively extract and suppress the harmonic voltage at the PCC.Finally,the control strategies proposed in this paper are verified by Matlab/Simulink simulation,and the experiments are carried out on physical platform and Starsim HIL semi-physical experimental platform.The effectiveness of the proposed strategies is verified by the simulation and experimental results.