Research On "source-grid-load" Autonomous Control Method Based On Virtual Synchronous Machine Technology

In recent years,because a large amount of new energy and controllable load are connected to the power grid through power electronic devices,the proportion of traditional generator sets in the power system is continuously reduced,making the power grid more susceptible to power fluctuations and faults and thus reducing the system stability.The proposed virtual synchronous machine technology can provide a unified synchronization mechanism for “source-grid-load”,which can not only improve the survivability of new energy and controllable load in the power system,but also rely on the synchronization of the three to resist outside interference.This paper is mainly for the virtual synchronous machine technology that realizes the "source-network-load" friendly interaction.On the basis of the modeling and control of the converter system,the new energy photovoltaic power generation on the "source-grid" side and the virtual synchronous machine control strategy of electric vehicle on the "grid-load" typical are studied in depth.The main research contents of this paper are summarized as follows:(1)The main circuit topology and control block diagram of the converter are introduced.The control is mainly divided into outer-loop virtual synchronous machine control and inner-loop double closed loop control.The characteristics and classification of virtual synchronous machine technology are summarized.O n this basis,the virtual synchronous generator control for inverter and the virtual synchronous motor control applied to rectifier are modeled and analyzed.The corresponding model verification module function is built in the MATLAB/Simulink simulation platform.(2)Traditional photovoltaic virtual synchronous machines are usually equipped with energy storage devices,which have problems of increasing cost,space occupation and post-maintenance.A new two-stage photovoltaic virtual synchronous machine control strategy based on adaptive MPPT is proposed.Firstly,the traditional photovoltaic virtual synchronous machine configured with energy storage is compared with the proposed control system,and the operation scenario of the proposed PV-VSG control method is given.Secondly,based on the conductance increment method,combined with the DC bus voltage,the adaptive MPPT algorithm is obtained.Then,in order to cooperate with the pre-adaptive MPPT control,an improved VSG control strategy is designed.Finally,the proposed control strategy is simulated and verified in off-grid or grid-connected mode by setting load/scheduling power variation and illumination variation.(3)Aiming at the problem of grid frequency and voltage quality caused by frequent resumption of high-power charging load,a fast charging control scheme for electric vehicles based on new VSM technology is proposed.Firstly,the pre-stage three-phase voltage type PWM rectifier and the post-stage resonant LLC zero-voltage switching DC converter are used as the main circuit topology,and the pre-stage charging mode based VSM control strategy and the latter stage double closed-loop control are respectively designed.Then,in order to highlight the superiority of the proposed VSM control,a synchronous generator with primary voltage regulation and frequency modulation characteristics is used as the synchronous power grid.Finally,the electric vehicle controlled by the VSG should be verified with inertia,damping and primary regulation characteristics,and compared with the traditional electric vehicle control method that does not participate in the adjustment.