Research On Control Strategy For A Single-phase PV Grid-connected And Grid-off Inverter With LCL Filter

With the worsening of the energy crisis,the development and utilization of new energy is imminent.The wide use of new energy can not only solve the problem of energy shortage,but also greatly reduce the damage of traditional energy utilization to the ecological environment,which is an important step for human's sustainable development.Solar energy occupies a large proportion in the new energy,and photovoltaic power generation is a major form of new energy utilization.With the continuous development of power electronics technology,photovoltaic power generation has been fully developed in the cost,efficiency and application range.The photovoltaic grid connected technology has no negligible significance to the photovoltaic power generation.In this paper,a single phase photovoltaic grid connected / off network inverter is selected as the research object,and the LCL filter is used as the output side filter of the inverter.Through the analysis of the bipolar and single stage frequency doubling SPWM modulation technology,the filter is more pertinent to the filtering of all the harmonics.In the mode of off network,the LC filter is used to filter the output voltage.In the mode of grid connection,the LCL filter is used to filter the grid current.At the same time,the capacitance current proportional feedback method is designed to damp the peak resonance produced by the LCL filter in the middle frequency phase.In the off grid mode,the mathematical model of the inverter's running state is established,and a double closed loop control method based on capacitance current is used to verify the method by using MATLAB simulation software.The grid connected mode,this paper adopts the control mode based on virtual vector,using the delay on the actual amount of virtual vector is orthogonal with the actual current and voltage,so as to meet the requirements of 2S/2R coordinate transformation,the mathematical models were built in the two-phase stationary coordinate and synchronous rotating coordinates.The coupling components of the LCL type filter on the dq axis are analyzed by the method of equivalent block diagram.In this way,the control of active power and reactive power is realized alone.Finally,the double closed loop control of capacitance current and grid current based on virtual vector is determined,and the simulation verification is carried out by using MATLAB simulation software.Aiming at the grid connected control strategy based on virtual vector,an indirectAFD islanding detection is established.The phase perturbation is applied to achieve the disturbance of grid current and frequency,so as to achieve islanding protection.The seamless switching technology of the dual mode inverter is described in detail.MATLAB simulation software is also used to simulate the simulation.At the end of this paper,an experimental prototype based on DSP TMS320F28335 is built,and the power is 2kW under the mode of grid connected and off network.The design of the hardware part mainly includes the construction of the PMOSFET main circuit,the design of the PMOSFET drive circuit,the sampling of voltage and current and the design of the conditioning circuit.The control flow of the software part is introduced in detail.