Research On Small Photovoltaic Grid-connected Inverter And Its Cloud Service Monitoring System

Under the background of the increasing exhaustion of traditional energy and environmental pollution,solar energy as one of the new energy has been paid more and more attention.With the reduction of the cost of photovoltaic cells and the strong support of the government,the rapid development of photovoltaic distributed generation,relying on urban and rural buildings,constitutes a part of the local micro-grid,eliminating the loss caused by long-distance transmission,is an important part of the construction of smart micro-grid.Photovoltaic power generation is very vulnerable to external factors,resulting in fluctuations in power generation,and a photovoltaic power generation system uses more photovoltaic cells,inverters and other equipment,both photovoltaic power plants and distributed photovoltaic power generation have regulatory difficulties.In order to maximize the efficiency,safety and reliability of power generation system,it is particularly important to monitor the photovoltaic power generation system systematically,real-time and effectively.Relying on the concept of photovoltaic distributed generation technology and ubiquitous power Internet of Things,integrating the current trend of Internet of Things and cloud computing,in order to further improve the power generation efficiency and safety and reliability of photovoltaic power generation system,this paper designs a single-phase photovoltaic grid-connected inverter with a power of 1 kW,and develops a remote monitoring system for photovoltaic based on Baidu cloud platform.Firstly,according to the analysis of the topology of the inverters,a two-stage non-isolation structure is adopted.The Boost circuit is used in the front stage to complete DC boost and photovoltaic maximum power point tracking control,and the full-bridge inverters are used in the back stage to complete the inverters and grid-connected control.The main circuit and its driving circuit,sampling and conditioning circuit,filtering circuit and auxiliary power supply circuit of the inverter are designed.The calculation and selection of parameters of the main circuit of the inverter are emphatically introduced.The control scheme of two-stage grid-connected photovoltaic inverters is analyzed in detail.The conductance increment method is used as MPPT control algorithm and double closed-loop PI regulation to realize the grid-connected inverters control.At the same time,the feed-forward control method of grid voltage is introduced into the current loop to restrain the influence of grid disturbance on the system.Simulink simulation platform is used to compare the MPPT algorithm and the whole machine simulation experiment,and the experimental prototype is built on this basis.The simulation and experimental results show that the designed inverter has good dynamic performance and high efficiency,and the grid-connected harmonics are small enough to meet the grid-connected requirements.Taking the above inverters as the monitoring object,the remote monitoring system of photovoltaic power generation based on cloud service is studied and designed.The system structure is simplified as equipment layer,network transmission layer and application layer.The device layer includes information acquisition point and gateway module to complete the bidirectional transmission of acquisition information and control commands in the cloud.The network transport layer uses Baidu cloud platform to complete the construction of cloud server.The application layer uses the monitoring client to interact with the user.The user can view the collection point information remotely and in real time,and send instructions to the device layer.MQTT protocol is used for communication between layers.The gateway module is designed with STM32 as the main control unit,and the communication connection with cloud is completed with W5500 hardware protocol stack chip.Finally,the monitoring software is developed and designed with Winform,which realizes the bidirectional communication from the device layer to the application layer and achieves the monitoring purpose.