Research On Inverter Of Photovoltaic Generation System

At present, while most countries all over the world are developing green and renewable energy, solar energy is accepted commonly because of its unusual advantages. Photovoltaic(PV) system is paid more attention to among its various applications. With price reduction of PV module, the role of PV generation system is gradually changed from supplemental energy to substitute energy. Stand-alone and grid-connected PV generation system will be the trend among PV applications. The main problems are inverter output voltage control of Stand-alone PV System and inverter parallel operation control of grid-connected PV generation system. The paper focuses the research on droop control method for parallel inverter and three-phase four-legged inverter through theory analysis and simulation.First study the single-phase inverter control before study three-phase four-legged inverter output waveform control, which based on a study single-phase inverter and submit a three-phase four-wire inverter control. A double feedback loop control scheme, which is outer control loop and inner control loop, is proposed for single-phase power supply through sinusoidal inverter. The proposed outer control loop uses two PI controllers for the independent control as magnitude and phase to ensure a highly steady precising of the voltage output from inverted power supply. The inner control loop added a proportion of the controller, reduced the filter inductor, to ensure a fast response to the voltage output and reduce waveform distortion. A new algorithm is proposed that using of Correlation function to detect the phase of sinusioidal voltage output from the inverter. The simulation results is showwing that the control system based on the proposed method has excellent dynamic and static characteristics to keep all voltage output waveforms highly sinusioidal under any loading conditions.The three-phase Four-legged inverter was proposed for ansymmetrical and nonlinear three-phase load. As the existence of the forth leg and the coupling effect of the filter inductance, so that the control of the three-phase voltage became very complicated. The paper proposed a new decoupling control strategy for the above problem. In this paper, the filter inductance is regarded as an inner resistance of the power source. A transformation relationship is proposed based on the idea of changing the inner resistance of the power source. Therefore the three-phase voltage can be decoupled entirely and the complex control problem can be changed into simple single-phase voltage control. We have adopted a 3rd harmonic injection method and have improved the utilization of DC bus voltage which based on single-phase inverter control. At the same time, this method gives how to choose the value of the fourth leg's inductance. In this paper, the control strategy is simple and easy to control. The simulation results were shown that this inverted power supply fits any load and has excellent dynamic and static characteristics.In analyzing the parallel operation of inverter, which apply the wireless droop control strategy. We adopt the traditional droop control theory for controlling the circulation current, output active power and reactive power of the parallel inverters. Moreover, we make a simple simulation for the parallel system, verifying the fact that the droop theory can be used in the parallel control system of the inverter.