VSG Based LVRT Control Method Study And Equipment Development Of Photovoltaic Grid-connected Inverter

Photovoltaic grid-connected power generation has become one of the inevitable choices of the energy supply security and sustainable development of national economy with the tightening of energy resources.However,as a weak inertial system,the photovoltaic power generation equipment is very possible to off-grid at a large scale and can even cause the local paralysis of the power grid,resulting in incalculable economic losses when there is a voltage drops fault in the power grid.While,the Virtual Synchronous Generator(VSG)based on PV Inverter is hard to actively support the grid voltage and frequency under the fault.Thus,it is of great significance to ensure the safe and stable operation of the system by studying the control strategy of the VSG's Low-Voltage Ride Through(LVRT).Based on the project of 'key technology and model application of the active support of power grid in new energy power station' and taking the VSG based on PV Inverter as the research object,the structure of the VSG based on PV Inverter,the control parameters design are studied in this paper and the control method of LVRT's integrated current limiting,which is of great significance to improve system reliability,high efficiency and high quality operation,and promote the development of smart grid.The main works and innovative points in this paper are as follows:(1)Firstly,a deep analysis is made on the current research situation of photovo-ltaic power generation technology.At the same time,the requirements of the grid-connected standard to new energy grid-connected power generation faults are described,and the current research situation of-the VSG technology and LVRT control of photovoltaic grid-connected power generation are analyzed.(2)Secondly,the system structure of VSG based on PV Inverter is studied and the principle of active and reactive power control of VSG is analyzed in this paper.The mechanical and electrical characteristics of the VSG are researched,and then the active and reactive power controller as well as the control parameter of the VSG are designed.On this basis,a simulation model of VSG grid-connected network system is built to verify the effectiveness of the virtual synchronization control method.(3)Then,the two conventional LVRT control methods of phasor current limiting and virtual resistance current limiting are studied,and it is found that they can' t control the fault transient and steady current of VSG under the deep drop of the grid voltage at the same time and have some limitations.Based on that,the LVRT integrated current limiting of VSG is put forward by combining the advantages of them.Besides,the superiority of the proposed LVRT control method is verified by simulation analysis of PSIM.(4)Finally,a prototype of 10kW VSG and a VSG based on PV inverter are developed and built.The software and hardware design and implementation process of the equipment are expounded,and the structure,parameter design and component selection of each module unit are made analysis of.Finally,the effectiveness of the proposed control strategy is verified by equipment experiment.