Research On Parallel Control Strategy Of Multiple Inverters In Large-scale Photovoltaic Power Plants

In recent years,the rapid development of social economy has made energy consumption increasing,fossil energy is facing depletion and shrinking,and the development and utilization of renewable energy has achieved unprecedented development,promote the maturity of the multiparallel inverter control technology based on photovoltaic power plants,and the application will be more extensive.However,the multi-parallel inverter is affected by the difference in the capacity of the equipment itself,the output voltage is not equal,the wiring impedance and the measurement impedance are different,and the system circulating current will be generated.The increase of circulating current will not only lead to a series of problems such as reduced working efficiency,increased power consumption,and shortened life of power electronic devices,but also will damage the electrical environment and affect the power quality.Therefore,starting from the design structure of large-scale photovoltaic power plants,this thesis studies the key technical problem of multi-parallel inverter circulating current suppression in the power generation system.First,establish the power generation system structure and multi-inverter parallel operation structure of a large-scale photovoltaic power station,deeply understand their working principles,summarize the advantages and disadvantages of each structure,and determine the system framework of this thesis,give full play to the advantages of inverter parallel redundancy,high flexibility and good economy.Secondly,the equivalent physical model of a single inverter is extended to the equivalent physical model of multiple inverters in parallel,and the corresponding mathematical model is established to conduct detailed power analysis,taking the parallel connection of two inverters as an example,the mechanism of circulating current generation of parallel inverters is deeply analyzed.The main factors of circulating current in multi-inverter parallel system of large photovoltaic power station are determined.Thirdly,the traditional circulation suppression control strategy is deeply analyzed,and based on the traditional droop control,two improvements are made in view of its existing limitations.By improving the method of droop control design and optimizing circuit parameter design,the advanced technology of voltage and current double closed-loop control technology,virtual complex impedance technology and optimized robust droop controller is used,an improved robust droop control strategy based on voltage and current double closed-loop is proposed,and the system circulating current suppression strategy is studied to solve the power sharing problem.Finally,in the MATLAB/Simulink simulation environment,the theoretical model of the parallel system of three photovoltaic inverters with the same capacity is built.By comparing the output voltage,current and circulating current waveforms of each inverter under different control methods,the effectiveness of the proposed control strategy on circulating current suppression is verified;the output power waveform and switching frequency of each inverter are also compared,and the results show that the control strategy also improves the power distribution accuracy and reduces the switching frequency fluctuation.Moreover,through the construction of the physical experimental platform,the design concept and control strategy of this thesis are verified,which is expected to provide theoretical guidance for engineering practice and have a good promotion and application value.