Research On A Dual Channel Micro Grid Inverter With High Cost Performance

In recent years,with the continuous development of photovoltaic industry,the photovoltaic grid-connected micro-inverter is a trend in the current development.Compared with above average power of photovoltaic inverter power,photovoltaic grid-connected micro-inverter with small power level has many advantages.With the development of technology,the market has put forward higher requirements for high power density,high cost performance,and high efficiency of photovoltaic grid-connected micro-inverter.Compared with the traditional high-power grid-connected inverter,the current photovoltaic grid-connected micro-inverter has high cost and low power density,which leads to low cost performance,and severely limits the micro-inverter marketing.In this case,this paper presents a scheme of two photovoltaic modules sharing a photovoltaic inverter,that is,a dual-channel photovoltaic grid-connected micro-inverter.In this scheme,two photovoltaic modules are respectively connected to two high-frequency isolated DC circuit in the dual-channel photovoltaic grid-connected micro-inverter,which are in parallel at the output to share an inverter circuit and a filter circuit,and the main circuit share a common control unit,thus greatly reducing the cost of micro-inverter and improving the power density.By comparing several circuit topologies of photovoltaic grid-connected micro-inverter,their advantages and disadvantages are summarized in this paper.On this basis,the flyback circuit is chosen as the high-frequency isolated DC circuit of the dual-channel PV grid-connected micro-inverter.When the flyback circuit works,a large ripple current is produced in both the input side and output side of the inverter module.Therefore,each high-frequency isolated DC circuit of the two channels in this paper adopts the two-way interleaved parallel flyback circuit,and a interleaving control strategy is presented for 4 flyback circuits in the dual channels.that is,the phase of control pulses on switches in the 4-way flyback circuits shifts 90 degrees in turn,thus it can greatly reduce the current ripple of DC input side and AC output side of the photovoltaic inverter,and can reduce the DC side and the output side of the filter at the same time.Therefore,the power density is improved and the cost is reduced.In order to further improve the power density and the cost performance of photovoltaic grid-connected micro-inverter,a current detection method based on the on resistance of the primary switch of the flyback circuit for dual-channel photovoltaic grid-connected micro-inverter is presented in this paper,and no additional current sensor is needed.Compared with the resistance sampling method,it improves the efficiency,and compared with the current sensor sampling method,it reduces the cost.On this basis,the paper further presents a fast algorithm of maximum power point tracking(MPPT)based on primary peak current of the flyback transformer,which does not need to calculate the average power,and can determine the maximum power point with the comparison of peak current.Therefore,it occupies fewer digital controller resources,does not need to sample the input voltage,and can further reduce costs with no voltage sensor.Then,the maximum power point tracking control can be achieved through the disturbance observation method.In order to improve the efficiency of dual-channel grid-connected micro-inverter,a quasi-resonant peak current compensation method based on the controllable switching period is put forward in this paper.When the switch is turned off,selecting the appropriate drain-source voltage resonant to turn on the switch.This quasi-resonant method of the controllable switching period calculates the new primary and secondary peak currents following the principle of equal average grid current,thus turn-on and turn-off times of the switch are obtained.The presented method in this paper can effectively control the switching period and reduce the switching loss.In this paper,a 600W dual-channel photovoltaic grid-connected micro-inverter is designed,and the design method of main circuit parameters is given.The correctness of the principle and method presented in this paper is verified by simulation and experiment.