Research On Bi-directional Photovoltaic Micro-inverter

In view of the fact that the severe energy situations we face and the negative impact on productions exist in domestic,the state actively promotes the new energy generation to ameliorate situation that lives on account of the traditional power generation mode.With the advantages of stable,reliable,flexible configuration,high efficiency and clean,photovoltaic micro-inverter has attracted more and more attention.The micro-inverter including the battery module,considering as the breakthrough point,is studied and effectively reducing the effect of weather factors on the reliability and improving the energy utilization ratio of the photovoltaic panel.Firstly,the micro-inverter only with the simple on-grid and off-grid modes which is considered as traditional micro-inverter in this paper is analyzed.Mathematical model of fly-back circuit is established and the maximum power point tracking(MPPT)is introduced in the on-grid mode.Adaptive resonant controller is introduced to achieve zero error tracking of on-grid sinusoidal current and the controller of the power grid and the load part is designed in the on-grid and off-grid modes respectively.And the control effect is verified by simulation.Secondly,in order to solve the problem of low energy utilization ratio of photovoltaic panels,the research focuses on the introduction of the battery module added to the traditional micro-inverter.A bi-directional DC/DC circuit is designed,and the topology of one way fly-back circuit and inverter circuit is improved.A novel bi-directional fly-back circuit and the bi-directional DC-AC circuit make the energy transfer in the reverse circuit the battery circuit in two directions.The mathematical model of boost chopper circuit and buck chopper circuit are built and the working mode of the improved micro-inverter is analyzed under different illumination conditions.Then,the controller of the battery part is designed separately in the modes of on-grid and off-grid.And the control effect of the four working modes is verified in simulation.Thirdly,since the output power of the micro-inverter is only a few hundred watts and the efficiency of the system must be improved,it is necessary to reduce the hardware loss as much as possible.In this paper,the parameters of the main power board are strictly designed and components in circuitry are analyzed at the same time.The loss,establishing the mathematical model,in each part of the circuit uses control variables method to compare the loss of one-way fly-back circuit and bi-directional fly-back circuit when the operating frequency or input power is changed.An experimental platform is constructed to test the efficiency of the circuit and select the optimal topology.Finally,the physical experiment platform of 250 W photovoltaic inverter is built to verify the output waveform and control method under the new operating mode.