Research On Operation And Control Half-substantiation Simulation Of Distributed PV System Based On RT-LAB

With the rapid development of economy and the raise of peoples’living standard, there has been more and more consumption of fossil fuel, which has brought much pressure on global environment, leading to the problems about shortage of resources, the greenhouse effect, the environmental pollution and so on. Therefore, it means much to make use of renewable sources. Solar energy has the advantages of environmental friendly, renewable and abundant, which has been payed more and more attention to, the main method of making use of solar energy is being connected to the power system.Solar energy is a type of intermittent energy, Photovoltaic Power System can be effected by different kinds of external conditions, including illumination intensity, environment temperature and so on, it has become the current research focus on making full use of solar energy concerning the external conditions, photovoltaic cells should be dealt with DC/DC rectification and DC/AC inversion, in this paper, Boost circuit is applied to realize the DC/DC conversion and the MPPT(maximum power point tracking) of photovoltaic cells, full bridge inverter is adopted, together with the double closed-loop of voltage and current method, realizing the connection to the power system.Model testing methods of Photovoltaic Grid-connected systems concludes digital simulation and physical simulation, digital simulation has the advantages of simple operation and varying parameter, while the accuracy is inferior to that of physical simulation, also, much physical phenomenon can’t be simulated. Physical process of much physical phenomenon can be observed directly, while the scale of system can’t be too big, Parameter adjustment range of physical devices is limited, configuration of physical parameters before testing and changing of operation mode are complex. Digital simulation and physical simulation are equipped with different kinds of characteristics and application scopes, thus it is the best way of making up each other’s differences. Therefore, in this paper, digital simulation and physical simulation are combined to carry out research of operation and control simulation of distributed PV system based on RT-LAB.Firstly, this paper describes the current development of digital simulation and physical simulation, also, conclusion of the advantages and disadvantages are carried out. Then the conclusion is researched that digital simulation and physical simulation should be combined to make up each other’s differences. Also, a brief description of the main elements of the research is carried out.Secondly, in this paper, the simulation model of photovoltaic cells in MATLAB/siumlink is established according to mathematical expression of photovoltaic principle, also, analogue simulation and data analysis about photovoltaic cells’output characteristics considering different kinds of illumination intensity and environment temperature is carried out. Then, different methods of MPPT are concluded, the model of different methods in MATLAB/siumlink is established to carry out comparison and data analysis at same simulation step size, in addition, comparison and data analysis at different comparison and data analysis is given to make a conclusion of different MPPT methods’advantages and disadvantages. Furthermore, analysis of typical grid-connection topological structure and control methods are conducted, the voltage and current double closed-loop control strategy is adopted in this paper to carry out real time simulation, considering that it has the advantages of simple, reliable and partical, also, increment PID control takes the place of position type PID control to raise the accuracy of real time simulation takeing the hardware error into account.Thirdly, this paper describes the design methods of real time simulation adapting to different kinds of control algorithm. Analysis of the control circuit realizing MPPT control and the voltage and current double closed-loop control strategy is carried out, in this paper, chip MC56F8257 of Freescale is adopted as physical control circuit, also, characteristics of the chip and programming of control are carried out.At last, establishment and testing of real time simulation based on RT-LAB are carried out, at first, a brief description of RT-LAB is carried out, then real time transformation of MATLAB/Simulink simulation model to RT-LAB simulation model is developed. Also, this paper carries out design of hardware controller by researching different kinds of MPPT algorithms together with the improved MPPT algorithm, then digital-analog hybrid real-time simulation is carried out based on the digital main circuit using RT-LAB developed by Opal-RT company, effectiveness and superiority of the improved MPPT algorithm are verified in comparison with control effects of the improved MPPT algorithm and control effects of traditional MPPT algorithms. In addition, effectiveness and superiority of the voltage and current double closed-loop control strategy are verified by digital-analog hybrid real-time simulation.