Research On Voltage Regulation Method Of Grid-connected Photovoltaic Inverter

In recent years,as the world has paid more and more attention to environmental protection,the proportion of new energy sources has also increased,so photovoltaic power generation has developed rapidly.In the process of photovoltaic power generation,photovoltaic inverters are needed to convert solar energy into electrical energy.Traditional two-level inverters generate higher harmonic components during operation,resulting in large losses during conversion.Conducive to economics.After continuous research,it is found that the T-type three-level inverter can achieve low harmonic components and low loss.Therefore,in order to better control the voltage,it is necessary to improve the two-stage photovoltaic inverter.This paper will mainly study the two-stage T-type three-level PV inverter,which can be decomposed into the maximum power point tracking(MPPT)and control strategy for the topology.The maximum power tracking point is completed by the pre-stage DC/DC boost control circuit,and the implementation of the control strategy is performed by the downstream DC/AC inverter control circuit.In this paper,we will study the two parts independently and complete the purpose of controlling the voltage.Firstly,the topology of the two-stage T-type inverter is studied.The topology,switching characteristics and commutation characteristics of the T-type inverter are analyzed.Combined with the structural characteristics of the pre-stage DC/DC boost chopper circuit,a two-stage T-type three-level photovoltaic grid-connected mathematical model was established.According to the switching characteristics of the T-type inverter,the mathematical model of the T-type inverter under different coordinates is constructed.Secondly,based on the research of pre-level DC/DC control strategy,the operating principle of photovoltaic cells is studied.According to the characteristics of traditional photovoltaic cells,the photovoltaic cell model is built using Simulink.Then the model is simulated on Matlab to obtain the battery output characteristic curve,and the change rule is obtained.In order to solve the problem that the traditional maximum power point tracking control algorithm has slow tracking speed and low accuracy,this paper proposes a tracking algorithm that uses the conductance increment method to control the integral regulator.Through simulation,it is found that the algorithm can better track and control the photovoltaic cells,improve the accuracy and improve the output of the photovoltaic cells,and effectively regulate the voltage.In this paper,the control technology of the inverter is improved,and the sinusoidal pulse width modulation technology is used to realize the voltage and current double closed loop control.On this basis,this paper proposes a fast three-level sinusoidal pulse width modulation algorithm,which makes the division of the sector interval simple,shortens the time of vector action and simplifies the calculation to improve the calculation speed.The fastness of the algorithm is verified by simulation,which makes the inverter control more efficient and effectively regulates the voltage.Finally,in order to verify the applicability of the two independent control algorithms studied in this paper in the overall photovoltaic power generation system,the Simulink simulation model of the overall two-stage photovoltaic grid-connected inverter system was built,and the simulation was carried out with relevant experimental parameters.When the external illumination PV changes to a large extent,the two-stage T-type photovoltaic grid-connected system can still achieve stable power transmission and have a good control effect on the voltage.