The Study And Design Of Digital Photovoltaic Array Simulator

Nowadays solar energy is playing a very important role in new energy power generation. Manufacturers and laboratories dedicated to photovoltaic (PV) equipment research and development are arising continuously. With the real PV modules as test platform in the development of photovoltaic systems, it is hard to perform all-weather tests on PV equipment due to the environmental limitations. The PV array simulator, as a new type specific power supply, can emulate the I-V characteristic of real PV arrays under any working conditions, which makes the all-weather tests and developments of PV systems possible, thus greatly reduces time and improves the efficiency of the products development. The contents of this study are as follows:Firstly, the developments of solar energy and PV array technology are reviewed, according to the internal structure and the equivalent circuit of the photovoltaic array, a mathematical model of solar battery is established, and its output current-voltage characteristic is given. The relationship between I-V characteristic and its working condition has been fully analyzed. In view of the superiority of the digital PV simulator, it has been chosen to perform the simulation task in this paper.Secondly, the structure of a typical solar power system is introduced, and its operational principle has been reviewed. The working principle of MPPT circuit, which is being connected directly with PV arrays, has been fully discussed, and a conclusion is drawn that, the simulator should vary its output current value according to the changes of voltage. Comparison between several simulation schemes has been done, at last, the system structure and current control strategy is designed.Thirdly, detailed design method of the hardware and software system of PV array simulator is presented. Hardware system consists of the following parts: main power board based on full-bridge DC-DC converter, functional circuits and digital control circuit based on TMS320F2809. Software system includes: current control algorithm design and its parameters tuning, the digital controller programming based on C language and Assembly language. All the modules have been tested and they can work properly, which lays a good foundation for the final experiments.At last, simulation and experimental results are presented. Both of the steady state and dynamic results are favorable. A good tracking precision of the I-V table working point is realized, which can be seen from the steady state results. Dynamic experimental results prove that the PV array simulator has a good transient response characteristic, and it meets the requirement of the latter MPPT circuits. The validity of the proposed simulation scheme and control strategy has been proved.