Research On Phase Locking Technology Of Photovoltaic Grid-connected Inverter Under Non-Ideal Grid Conditions

Solar energy has become the representative of the new green energy because of its clean.efficient and rich resources,so the development and utilization of the solar energy has been paid more and more artention.The grid connected inverter is one of the core parts of the photovoltaic system.In order to ensure the inverter and grid to maintain synchronous operation,it must effectively track the phase of the voltage,which requires phase locked loop has good performance.In the access to a large number of photovoltaic power grid,the characteristics of the weak network is obvious,so the voltage is prone to distortion and unbalance.At the same time,the DC offset will be generated when the grid is transient,The current phase locked loop has good adaptability to the voltage distortion unbalance,but the phase locked performance is poor when the grid contains asymmetric DC offset.Therefore,it is one of the key points to realize the stability of the grid connected photovoltaic inverter,which is to design a better phase locked loop technology to adapt to these non-ideal grid conditions.The paper firstly analyzes and describes the performance requirements of the grid connected inverter for the phase locked loop and the disadvantages of the single synchronous reference frame software phase locked loop(SSRF-SPLL)which is not suitable for voltage unbalance.Secondly,the dual second-order generalized integrator-software phase locked loop(DSOGI-PLL)which is suitable for voltage unbalance is not suitable for the shortcoming of voltage asymmetric DC offset and proposes the improved dual second-order generalized integrator-software phase locked loop(IDSOGI-PLL).The application of Matlab/Simulink to IDSOGI-PLL,DSOGI-PLL and SSRF-SPLL under non-ideal grid,at the same time,the IDSOGI-PLL is used to simulate the grid connected photovoltaic inverter.The results show that the IDSOGI-PLL achieves the expected design goal and the photovoltaic inverter with IDSOG1-PLL can achieve stable grid connection under non-ideal grid conditions.Finally,the phase locked loop experimental platform based on TMS320F28335 is designed,which verifies the performance of SSRF-SPLL,DSOGI-PLL and IDSOGI-PLL.In addition,the grid connected photovoltaic inverter with three kinds of PLL is verified on the My Way experimental platform.The results show that the IDSOGI-PLL provides a reliable guarantee for the photovoltaic inverter to stabilize the grid under non-ideal grid conditions.