Voltage Equalization Control Strategy Of Boost Converter In Photovoltaic DC Collection System

At present,large-scale photovoltaic power plant collection methods adopt AC collection,and there are problems such as poor parallel stability of multiple inverters,low system efficiency,and large line loss.Photovoltaic itself is a DC component.The form of DC collection enables better access to photovoltaic power generation,improves solar energy utilization,and is more economical.The high-voltage and high-power DCboost converter is the core part of the photovoltaic DC-collecting system.With the current voltage and current capacity levels of power electronic devices,it cannot meet the high current and output of the input side of the high-power photovoltaic DC-boost converter.The high voltage requirement on the side requires a multi-module input parallel output series(IPOS)structure to achieve high ratio ratio boost,while equalization and current sharing are common problems of IPOS structure converters,IPOS When the converter is connected to the PV array,the issue of Maximum Power Point Tracking(MPPT)of the PV module should also be considered.A new current sharing and equalization control strategy needs to be proposed.When a plurality of photovoltaic power plants adopt a series connection method to realize direct current collection,since the illumination conditions of different photovoltaic power plants are inconsistent,a pressure equalization problem occurs between the series type boost converters.The main research contents are as follows:(1)Analyzed the topology of the series-collecting system and the IPOS-type boost converter in the DC boosting and collecting system of large-scale photovoltaic power plants,DC/DC converters and modular multilevel converters(Modular Multilevel Converter,The control strategy of MMC)lays the foundation for further study of the output voltage equalization control between the series boost converter and the equalization control between the IBFBC inside the IPOS boost converter.(2)The problem of current sharing and equalization inside the IPOS converter when accessing the PV array is studied.In order to solve the problem that the output uniform voltage can not be achieved well when the parameters of the IPOS-type converter sub-modules are inconsistent with the traditional unified duty-duty control strategy,this paper proposes a current-flow equalization MPPT control method.The method enables one sub-module of the IPOS type converter to realize the MPPT control of the photovoltaic module,and the other sub-modules adopt the input current sharing control to realize the internal voltage equalization of the IPOS type converter.On the basis of the current sharing type MPPT control,this paper Furthermore,the current sharing equalization type MPPT control strategy is proposed to solve the problem of the equalization of the equalization pressure control ability of the current sharing type MPPT control.(3)The equalization control strategy between series boost converters is studied.Aiming at the problem of unbalanced output voltage between series converters when the illumination between the photovoltaic power plants is inconsistent,this paper proposes a hierarchical control strategy based on power weight to solve the problem ofoutput voltage imbalance;When the sub-module of the streamer adopts the IBFBC converter,there is a limitation of the duty ratio,which causes the sub-module MPPT control to fail.The power weight layered control strategy is improved to improve the MPPT control failure when the illumination intensity is severely unbalanced.problem.(4)Based on the above discussion and analysis,the corresponding simulation model is built for the IPOS boost converter and the series boost converter in Matlab/Simulink.Through the analysis of the simulation results,the correctness of the internal voltage equalization analysis of the IPOS boost converter is verified.The designed control strategy can realize the voltage equalization between the converters.The series boost converter is verified.The theoretical analysis of the equalization problem of the device,the rationality of the design of the simulation parameters,by designing the coordinated control between the DC/DC converter and the MMC converter station to achieve the unbalanced illumination,between the series converters Output voltage equalization control.