Research On Control System Of Intelligent Hybrid Photovoltaic Inverter

Photovoltaic hybrid inverter,which is an ideal choice in small distributed power system,mentioned in this paper combines the function of grid-connected inverter and off-grid inverter.When grid is in abnormal state,the hybrid inverter works in off-grid mode and the output power can be used to support AC load.When grid is in normal state,hybrid inverter works in gridconnected mode and the output power will be put into power grid.So hybrid inverter makes up the shortcomings of those two inverters.However,there are still a lot of problems are not solved.Such as the efficiency of charging,the quality of output current under on-grid mode,the seamless switching between on-grid mode and off-grid mode.Therefore,this paper will study the above problems.First of all,the main circuit and control circuit of the dual mode photovoltaic inverter are designed.The circuit structure of grid-connected inverter including interleaved boost circuit and full-bridge inverter circuit.The circuit structure of off-grid inverter including battery pushpull circuit,full-bridge inverter circuit and full-bridge phase-shifted charging circuit.These two modes both use the full-bridge inverter circuit,and when the output of photovoltaic array is abnormal,at this time,the power grid can be used to charge battery through full-bridge topology,so the full-bridge topology,which constructs the bidirectional PWM converter,can work in two direction.The operating principle of these two main circuits is analyzed and then the key components are designed and selected.Secondly,the paper puts forward the control strategy of off-grid and grid-connected mode.The four-stage charging method of battery both under photovoltaic array and power grid is proposed.In this method,the pre-charging mode is added to the traditional three-stage charging method,which makes the whole charging process more smooth and prolongs the life of the battery.Moreover,the control method of full-bridge inverter has been proposed.What's more,the fuzzy control strategy,which enhances the stability of the whole system when connect to the nonlinear load,has been put into grid-connected inverter.And the MPP tracking method has been proposed in on-grid mode.Then in order to achieve efficient switching and management between sub patterns.An energy management strategy based on bus voltage hierarchical control has been proposed,thus,efficient switching and management among sub modes is achieved and switching method between off-grid and grid-connected mode is put forward.Finally,a 3.2KW photovoltaic hybrid inverter is designed.According to the four-stage charging method,the battery can be charged efficiently,the fuzzy deadbeat control in grid connected mode effectively reduces the current harmonics when connect to nonlinear load,the current harmoics is less than 3%.The switching between the on-grid mode and off-grid has been achieved,and the whole switching time is less than 2s and the real switching time is less than 20 ms.