Simulation Study Of Control Technology For Photovoltaic Inverter

The exploitation of new energy is very important due to the rapid growth of population and the economic development while the traditional energy is limited. As the cleanness natural resources in abundance, solar energy is a deal alternative. The photovoltaic inverter (usually called as "PV inverter") making the energy of sunlight convert into electric energy must be paid more attention.The mathematical model is built after the analysis of photovoltaic inverter principle in this thesis. Three control strategies and the maximum power point tracking of cells are analyzed on the base of the mathematical model. The main work about this thesis contains two parts discussed as below:Firstly, three control strategies of PV inverter are analyzed in detail is based on the theory of photovoltaic inverter. The first one is the dq closed-loop control technology under the ideal grid voltage. The stability of the DC voltage, power factor regulator can be achieved by this method. However, there will be a negative sequence component when grid voltage drops. The simultaneous existence of negative sequence component and the inductor results in the fluctuations of bus voltage. So the dq control technology doesn’t perform well on the control. Thus, the second method called as separation of positive and negative sequence dq control technology is introduced. The bus voltage fluctuations will be suppressed but not totally eliminated with this control technology. If the fluctuations described as previous are total eliminated, the inductor will not be included in the control loop because of the inherent negative sequence component under the unbalanced grid voltage. So the third control method is suggested, which performs the stability of the DC voltage and power factor regulator. And the third control strategy of the PV inverter is designed in detail in this thesis. Simulation models are established by matlab simulator.The simulation results show that the second control strategy is better for both the balanced and unbalanced grid voltage. Power scheduling and bus voltage stability are verified under the third control strategy by the simulations. The third control strategy owing to the more stable bus voltage is prior to the second.Secondly, these algorithms about MPPT have been researched in this thesis. The conclusions of advantages and disadvantages of several conventional MPPT methods can be obtained by doing the comparison. Then the perturbation and observation method will be optimized by adding another sampling point. In the improved solution, the voltages and power of three different points chosen from the P-U curve are compared respectively, and the change of next perturbation is depended on the compared results. Simulation and verification of the improved maximum power point tracking (MPPT) algorithm are finished by MATLAB. The simulation proves that the maximum power point tracking can be achieved excellently and the system is more stable by using the optimized algorithm model.