Research On Sliding Mode Control Strategy Based On Photovoltaic MPPT And VSG Inverter Technology

In order to improve the power generation efficiency and stability of photovoltaic microgrid,it is very important to study its key technologies.Combined with Virtual Synchronous Generator(VSG)technology and Sliding Mode Control(SMC)algorithm,the photovoltaic array,Maximum Power Point Tracking(MPPT)control,battery energy storage technology and inverter control of the photovoltaic micro-grid are studied in this paper.In the study of photovoltaic array,this paper elaborates on the photovoltaic effect of photovoltaic cell,and deduces the theoretical mathematical model and engineering mathematical model of photovoltaic cell respectively.The simulation results show that,the engineering mathematical model is superior to the theoretical mathematical model in the practicability of the model and the ideal degree of the output characteristic curve.Because the tracking step of traditional Incremental Conductance(INC)algorithm is fixed,it is very difficult for tracking-effect to strike a balance between the tracking speed and the steady-state amplitude.For this,combining the minimum variance adaptive algorithm,this paper adopts adaptive step size INC algorithm.The simulation results show that the Adaptive Incremental Conductance(AINC)algorithm is superior in tracking speed and steady-state amplitude.To further improve the tracking effect,a conventional SMC strategy based on adaptive INC algorithm is proposed in this paper,and the adaptive observation is added to the sliding mode control law to weaken the inherent chattering of SMC.It is proved that the improved strategy not only effectively reduces chattering,but also further shortens the tracking time by the simulation,and even when the environment changes,MPPT can be implemented efficiently.In order to improve the stability of the photovoltaic system,this paper adds a battery energy storage device on its dc-side.Firstly,the working principle of Buck/Boost bidirectional DC-DC converter is described.Then,the traditional double closed loop control strategy and predictive current control strategy are analyzed respectively.Finally,the simulation results prove that,the steady-state amplitude of the dc-side voltage obtained by the latter method is smaller and the waveform is smoother,and the dc-side voltage can be well stabilized even when the environment or the load changes.In inverter control,this paper adopts the double-layer control structure,and proposes the Fuzzy Sliding Mode Control(FSMC)strategy based on VSG inverter.In the upper control,the VSG algorithm is used to provide reference voltage for the underlying control,so that the inverter system has strong inertia.Using the classical second-order model of synchronous generator,the ontology algorithm of VSG is designed,including rotor motion equation and stator electrical equation.At the same time,referring to the principle of power frequency regulation and excitation regulation of synchronous generator,the power frequency regulator and excitation regulator of VSG are designed respectively,and the main control parameters in VSG are analyzed and designed.In order to enhance the robustness of the system,this paper adopts SMC strategy in the underlying control,and combines fuzzy control in the switching control law to correct the switching coefficient in real time,thus weakening the chattering.Simulation results show that this strategy not only improves the robustness of the system,but also effectively weakens the chattering,and reduces the harmonic distortion rate of the inverter output waveform,which can realize the inverter quickly and stably even when the load changes.