Research On Photovoltaic Grid-connected System Based On Sliding Mode Control

With the increasing of the power demand and the exhaustion of non-renewable energy,solar energy more and more draws public attention.Besides,it becomes the most promising green energy internationally because of the advantage of cleanliness,environmental protection and renewableness,etc..The conversion efficiency of photovoltaic device is low.The maximum power point tracking(MPPT)technology is used to solve the problem.However,the efficiency and power supply quality are affected by the uncertainty of environment.It restricts the further development and expansion of the photovoltaic industry.Thus,in order to improve the efficiency of photovoltaic power generation system and the quality of power supply,the sliding mode variable structure control is used in MPPT and inverter control.In addition,this strategy can solve the problems of reliability of the MPPT under uncertain environment and the control quality of robustness.Firstly,the research status and the development trend of control technology about MPPT and inverter are introduced in this paper.Besides,the sliding mode variable structure control principle and the general design process of sliding mode controller are carried on in detail.In addition,the circuit structure of the two-stage photovoltaic grid-connected system is also discussed in this paper.The sliding mode control strategy is used not only in MPPT controller in the former-stage DC/DC circuit,but also in inverter controller in the post-stage DC/AC circuit.Afterwards,the former-stage DC/DC and the post-stage DC/AC circuit are combined to form a complete photovoltaic power generation system,and the MPPT and inverter grid control are achieved by sliding mode control.Secondly,in the former-stage DC/DC circuit,the switching surface is defined by a liner combination of the photovoltaic cells output voltage and current.What’s more,the least square method is applied to the MPPs which corresponds to the various radiation levels to determine the parameters of the switching surface.Besides,the sliding mode controller based on the incremental conductance algorithm is proposed to design and achieve MPPT with high precision tracking.Based on the topology and parameters of the inverter circuit and the filter circuit,the DC/AC circuit mathematical model is established.The sliding mode control algorithm is designed in inverter control,and the DC/AC conversion is achieved with high quality.Finally,the simulation and comparison analysis of MPPT and inverter control arecarried out under the MATLAB/Simulink environment according to the designed sliding mode controllers respectively.In addition,the sliding mode control simulation of the whole photovoltaic grid-connected power generation system is carried out.The simulation results show that the dynamic and static characteristics of the sliding mode control algorithm are better than the traditional algorithm.