Research On Power Balance Control Strategy Of Three-phase Photovoltaic Cascaded H-bridge Multilevel Inverter

Energy crisis and environmental pollution have attracted worldwide attention,and the use of renewable energy for grid-connected power generation has become a way to solve these problems.In order to improve the capacity of large-scale photovoltaic grid-connected power generation,the photovoltaic grid-connected power generation system based on cascaded H-bridge inverters has been widely used.Due to the inconsistency of light intensity and temperature for large-scale photovoltaic modules,cascaded H-bridge multilevel inverters work in power unbalance,which leads to the unbalance of grid-connected current and has a negative impact on power quality.In order to solve the problem of power imbalance,this paper focuses on the power balance control strategy of three-phase photovoltaic grid-connected power generation system based on cascaded H-bridge multi-level inverters.From the topology of cascaded H-bridge to the modulation method,and from the control method of inverters to the power inversion control strategy of hybrid cascaded H-bridge,these technologies have gradually matured,which makes the cascaded H-bridge as a photovoltaic grid-connected inverter have a deeper theoretical basis.Based on the theory of a single H-bridge unit,this paper analyses the principle and modulation method of the inverter cascaded by three H-bridge units,which provides theoretical support for the photovoltaic grid-connected cascaded H-bridge multi-level inverters,and deepens the understanding through simulation and experiment.In this paper,the engineering model of photovoltaic cells and the mathematical model of isolated full-bridge DC-DC converter are established,and the photovoltaic power generation model based on DC-DC converter is built.The maximum power point tracking function is realized.Then the double closed-loop control method of voltage and current of the inverter is analyzed in detail.Finally,aiming at the problem that the inter-phase power imbalance exists in three-phase photovoltaic grid-connected cascaded H-bridge multi-level inverters,which leads to the asymmetry of output current and can not be connected smoothly,and because of the limitation of the traditional zero-sequence injection method,this paper adopts an optimal zero-sequence component injection method to solve the serious imbalance of inter-phase power.A simulation model of three-phase photovoltaic grid-connected power generation system based on cascaded H-bridge multi-level inverters is built.The proposed zero-sequence voltage injection method is simulated under the condition of serious unbalanced power.The results verify the feasibility and validity of the proposed method.