Research On Combined Control Of Grid-connected Photovoltaic And Power Quality Regulatory Systems

With the energy shortages and increasingly severe environmental problems, research and development of renewable energy has been widespread concerned at home and abroad.The solar energy is favored for its huge reserves, clean and pollution-free characteristics. However, the photovoltaic characteristics of their own make it subject to changes in the weather impact, which means it needs frequent switches. That will bring a variety of adverse disturbances on the traditional power grid and the distribution network, which affects the power quality. In addition, with the increasing use of power electronic devices as well as a large number of non-linear loads, there are a lot of harmonics and reactive components of the grid, affecting the quality of power supply.This paper analyzed the theories starting from the grid-connected PV systems and the active power filter, and compared the similarities both in functions, structures and control strategies of the two systems. According to the analysis, this paper proposed to achieve a combined control system, which is both a photovoltaic grid power generation, but also for harmonic suppression and reactive power compensation. The basic topology and working principle of the combined control system were also introduced.According to the basic principle of photovoltaic cells, a mathematical model on engineering was derived, and the simulation and the analysis on performance characteristics were finished in the MATLAB/Simulink environment. Combined the basic principles of PV MPPT(Maximum Power Point Tracking, MPPT) control, this paper analyzed several conventional MPPT control methods, and improved to optimize the incremental conductance method. The flow charts of all methods were built, as well as the MATLAB/Simulation models, and the simulation results demonstrated the validity of the models.The mathematical model of the combined control system was built and the basic control principle was analyzed. Based on the three-phase circuit instantaneous reactive power theory, the models of p-q method and p qi-i method for simulation analysis were built to verify its feasibility.Analyze and design the synthesis of the combined control command signal, and calculated the active current signal of the PV array, also the DC voltage control signal. The synthetic chart was given, also. The system’s current loop control strategy was analyzed in detail. Combined with the traditional PI control, the quasi-resonant controller was introduced into the paper. Then a quasi-PIR control strategy was proposed, and the analysis shows that the strategy meets the design requirements of this article. When the grid voltage is unbalanced, a coordinated control strategy was proposed to get better control effect.Finally, the MATLAB/Simulink simulation model of the combined control system was built, and different operating conditions were considered in the simulations. The simulation results showed that the combined control system can inject active power to the grid while achieving power quality regulation.