Research And Design Of Photovoltaic Micro Inverter Based On Bidirectional Symmetric Four-switch Power Coupling Circuit

The rapid consumption of fossil energy has led to energy crisis and environmental pollution,and renewable energy has attracted the attention of countries all over the world.As a renewable energy,solar energy has the advantages of endless use,wide distribution and no pollution,which has become the focus of development and utilization of countries around the world.,among which distributed photovoltaic power generation is one of the main ways of using solar energy.Micro-inverters are gradually used in distributed photovoltaic power generation because of the advantages of small size,large power generation,flexible and convenient installation,low cost,easy expansion and hot swap.However,in the photovoltaic micro-inverter,the photovoltaic module outputs constant power,while the power transmitted to the grid side contains double frequency disturbances,the input and output power are unbalanced,which results in the presence of secondary pulsating power in the photovoltaic micro-inverter,which leads to the reduction in the efficiency of the photovoltaic power generation system and the reduction in the output current quality of the photovoltaic microinverter.The traditional method to solve the double frequency power disturbance in photovoltaic micro-inverters is to connect large capacitance electrolytic capacitors in parallel on the intermediate bus,the service life of the large electrolytic capacitor is short and the volume is too large,which makes the service life of the whole photovoltaic micro inverter reduce and the volume become larger.Therefore,it is of great significance to study to replace large electrolytic capacitors and extend the service life of the photovoltaic micro-inverter.A photovoltaic micro-inverter based on bidirectional symmetrical four-switch power coupling circuit is designed in this paper,the photovoltaic micro-inverter system consists of a boost circuit,a full-bridge inverter and a bidirectional symmetrical four-switch power coupling circuit,the power coupling circuit is connected in parallel with the output of the full-bridge inverter to buffer the secondary pulsating power in the traditional photovoltaic micro-inverter and replace the electrolytic capacitor.Four different working modes of the power coupling circuit are analyzed,and the main control switches are controlled by Pulse Energy Modulation(PEM)signals.The expression of the duty ratio of the PEM signal and the set value of the coupling inductor current in different operating modes during a switching cycle is derived to obtain the corresponding PEM signal pulse.At the same time,the small signal model of the boost circuit is established,and the control block diagram of current closed-loop of the boost circuit and the control block diagram of the current inner loop and voltage outer loop of the full-bridge inverter are designed.The Matlab/Simulink R2014 a simulation software was used to simulate the photovoltaic micro-inverter based on the bidirectional symmetrical four-switch power coupling circuit.At the same time,the hardware design of the boost circuit,the full-bridge inverter and the bidirectional symmetrical four-switch power coupling circuit are designed,and the experimental platform of photovoltaic micro-inverter based on bidirectional symmetric four-switch power coupling circuit is established with TMS320F28335 as the main control chip.Simulation and experimental results show that the power coupling circuit effectively suppresses the secondary ripple in the photovoltaic micro-inverter,greatly reduces the capacitance value of the bus capacitor,avoids the use of large electrolytic capacitors with short life,and improves the service life and reliability of photovoltaic micro-inverters.