| With the rapid development of economy,the demand for energy is increasing.A large number of fossil energy consumption lead to energy crisis and environmental pollution worsening.Solar energy is widely distributed,renewable,no environmental pollution,the world has increased the intensity of the development of clean energy,has become the focus of energy development.Recently,the National Energy Administration of China issued guidelines of energy development.The guidelines proposed several policy advice including developing distributed energy,releasing the distributed power construction in the user-side and encouraging diversified investment.Micro-inverter has the advantages of easy expansion,low cost,high efficiency and modular design,and it is becoming the trend of distributed photovoltaic inverter in the future,so it is of great significance to study it.PV module output constant power by MPPT(MaximumPower Point Tracking)control,while the power transmitted to the grid includes double-frequency ripple power.So the energy buffer circuit is needed in the inverter circuit.The traditional buffer circuit is usually connected a large capacity electrolytic capacitor in parallel with input terminal of the inverter.At the same time,in order to ensure the life of the PV module,the voltage ripple needs to be controlled within 2%.These restrictions that result in the decoupling capacitor is very large,which can only used electrolytic capacitor as decoupling capacitor.The large capacity electrolytic capacitor is not only large in size but also short in life,which severely limits the service life of the micro-inverter.Many scholars have put forward different solutions to prolong the service life of the micro-inverter.Such as long-life electrolytic capacitor technology or micro-inverter without using electrolytic capacitor.A power decoupling micro-inverter for photovoltaic gird-connected power generation is designed in this paper.This paper is based on the conclusion that the decoupling capacitance is inversely proportional to the average value of the capacitor voltage and the voltage ripple in the case of the single-phase inverter power and the grid frequency.The micro-inverters in parallel by the basic buck-boost circuit and the current source from the high-frequency inverter circuit.Decoupling capacitors connected in series between the two circuits.Peak current control method is used to increase the voltage across the capacitor and the voltage ripple,reduce the capacitance requirements and prolong the lifetime of inverter.During each switching cycle,the output power of the PV module is transferred to the decoupling capacitor.Secondly,based on the above ideas,this paper puts forward the inverter topology which is connected in series with the boost circuit and the flyback converter,which can alsoachieve the purpose of reducing the decoupling capacitance value;Then,five working states of the micro-inverter circuit areinvestigated.The corresponding circuit parameters and peak current control strategy are designed.Thirdly,according to the working characteristics and design requirements of the photovoltaic micro-inverter,the key components of the circuit are designed,and the power switching devices are selected according to the voltage and current stress;According to the design of the circuit parameters,simulations of the proposed circuit are performed with PSIM and the results show that the proposed topology and control strategy are reasonable. |
