Development Of Cascaded H-bridge Photovoltaic Grid-connected Inverter

The deteriorating environmental problems and the continuous depletion of fossil fuels make the new energy become the focus of attention.Solar energy has become the darling of the new era as a kind of pollution-free energy.Human beings in order to make full use of solar energy,but also through the means of science and technology to make long-term use of solar energy.Again under the background of photovoltaic grid-connected inverter by the attention of scientific research workers.Cascade H-bridge research has been very deep,relatively mature technology,from the cascade H bridge structure to the modulation strategy,from the inverter control strategy to the hybrid cascade H bridge power balance control,these technologies continue to mature The H-bridge as a photovoltaic grid-connected inverter has a deep theoretical support.Based on the theory of single power unit,this paper analyzes the principle of multiple power unit cascade inverters and the way of modulation.These are the theoretical basis for the research of photovoltaic grid-connected inverter.In this paper,a photovoltaic module for engineering is established.Based on the engineering PV module,the mathematical model of the PV grid-connected inverter is established.The linear control model of the inverter is established,and the double closed-loop control of the single-phase photovoltaic grid-connected inverter is analyzed Strategy,PI controller has many advantages,but the linear control of mathematical model analysis found that the exchange of traffic for the control object will have a lot of problems,based on this,this paper presents a single-phase PCI control method,PCI control PI The controller is introduced into the complex field,and the controller has an infinite gain at the fundamental frequency by introducing the amount of-j to achieve the purpose of eliminating the steady-state error and compensate for the deficiency of the PI controller.PCI control is applied to the three-phase dq coordinate system,through the all-pass filter to meet the single-phase use of PCI conditions,set up a simulation model,the simulation results further illustrate the correctness of this paper method.Finally,based on the three-phase grid-connected inverter,the three-phase cascaded H-bridge photovoltaic grid-connected inverter is analyzed,and the output voltage is asymmetrical for the three-phase photovoltaic grid-connected inverter.Can not be successfully connected to the problem,this paper with zero sequence voltage injection method to solve the problem of unbalanced phase power.By extracting the zero-sequence voltage of the network side voltage,it is injected into the control to achieve the balanced three-phase output voltage and correct the three-phase gridconnected current to realize the grid connection of the three-phase cascaded H-bridge photovoltaic grid-connected inverter.