Research On Single-phase Inverter Control Technology Based On Virtual Synchronous Generator

Distributed energy as the environmental-friendly and uncontaminated clean energy,has been extensively developed in the world,for example,it has been used in electric vehicle charging and buliding equipment power applications.The single-phase inverter is the key interface device of the microgrid and it has the characteristics of plug and play function,high efficiency and low cost,and the demand for low-voltage microgrid will become more extensive.Because Virtual Synchronous Generators(VSG)technology mimics the external characteristics of synchronous generators(SG),which greatly improves the stability of the paralleled or grid-connected inverter system,it enables the inverter to have a high performance of transient transition capability when dealing with different load or grid power sudden changes,and it has gradually become a new reseach hotspot for the operation of the inverter.The operation strategy of single-phase inverter in the grid-connected and off-grid mode based on the VSG technology is presented in this paper,and the main contents are summarized as follows:1)The background of the research subject is introduced,and aiming at the operation scheme of inverter as the microgrid interface,the main traditional control strategies of the inverters are discussed.The research status of three-phase VSG and single-phase VSG is also summarized respectively.2)The mathematical model of the single-phase VSG based on the second-order model of the SG is established,and the reactive-voltage loop is improved by adding an intergral term.Meanwhile,the influence of key parameters on the operation stability of VSG is analyzed based on the small signal mathematical model of VSG.The tracking accuracy of the reactive-voltage loop with integral term and the correctness of the design parameters are verified by simulation.3)In view of the stable operation of single-phase VSG in microgrid,the implementation schemes of VSG inner loop control,virtual impedance,seamless switching technology and low voltage ride through(LVRT)ability are described in detail.The parameters of inner loop control and virtual impedance are quantitatively analyzed to make the equivalent feeder impedance of VSG mainly inductance,and it can meet the power decoupling condition.Based on the principle of phase-locked loop of 2-order generalized integrator(SOGI-PLL),a voltage presynchronization link of single-phase VSG is designed to realize the seamless switching between islanded microgrid and gird-connected microgrid.Aming at the LVRT ability for voltage sag,a reactive power compensation strategy based on single-phase PQ reactive current is proposed to ensure that VSG can provide the reactive power and maintain the safe operation of the power grid.All the proposed control strategies are vefified by simulation.4)In order to reduce the current sensor of the single-phase VSG inductor,the inner loop control scheme based on the state observer is designed,the luenberger observer and kalman filter observer are designed to estimate the value of the inductor current respectively,the pole position of the luenberger observer is optimized by the pole configuration method,and the VSG inner loop control scheme based on the state observer is simulated and verified.5)An experimental platform for a single-phase inverter based on the VSG control method was built,and the feasibility and correctness of the proposed control scheme was verified by the experimental results.