Research Of 5kW Single Phase Energy Storage Hybrid Inverter

With the increasing environmental pollution problems,China has introduced a number of policies to encourage the development of clean energy,of which the most powerful is solar energy.However,the use of new energy such as photovoltaic is seriously affected and limited by natural conditions,including weather,seasons,time,regions,topography,and so on.Compared with traditional fossil fuel energy,the main renewable energy sources cannot provide stable and continuous energy supply.The actual power grid is not the ideal active and reactive power source with unlimited infinite impedance,and the power levels of medium and small-capacity power sources are scattered and the equivalent impedance is relatively large.The energy storage inverter stores electric energy when the photovoltaic power is greater than the load demand,and provides power to the load when the photovoltaic power generation power cannot meet the load demand,and collects and utilizes the renewable energy with maximum efficiency.Realizing local peak-shaving and valley-filling can maximize the use of new energy and reduce the impact and dependence on the grid.Firstly,the relationship between leakage current and photovoltaic inverter topology is analyzed,and the unipolar modulation HERIC full-bridge topology is selected as the inverter part of the energy storage inverter,which significantly reduces the system loss and ground leakage current,and improves the system conversion efficiency.A detailed theoretical analysis of the main circuit component parameters for calculation and selection,HERIC inverter partial grid-connected phase-locked control principle,and a detailed analysis of grid-connected current and off-grid voltage control.Secondly,the implementation of wide-range MPPT is discussed under off-grid and grid-tie conditions.When the sunshine conditions are poor,the open circuit voltage of the module is lower than the reference voltage of the bus 400 V.The photo voltaic output voltage is boosted to the bus reference voltage through the BOOST circuit,and the MPPT function is implemented by the method of disturbing the duty cycle.When the sunshine conditions and temperature are relatively good,the DC bus voltage is directly disturbed to achieve MPPT maximum power tracking.Then analyze the working principle of high frequency isolated bidirectional DC converter.The DC side adopts a two-stage structure,that is,the former is a constant-duty-duty LLC DC transformer and the latter is an output-regulated BUCK-BOOST circuit.The circuit can achieve soft switching within the full load range,achieve high efficiency under full load conditions,and increase power density.On this basis,the current closed-loop control strategyand voltage control strategy of the two-stage DC-DC converter and the conversion process of the two modes are analyzed.Finally,the energy management strategy of energy storage system is studied.Several common power control strategies are introduced.The usage scenarios of PQ control mode and VF control are analyzed,and the switching process of the two control modes is analyzed.