Research On Control Strategy Of Small Power Photovoltaic Grid Connected Inverter

As environmental pollution problems caused by conventional energy sources becomes more and more serious, the use of solar photovoltaic industries have been developing continuously, therefore, the requirements of grid connected inverter for photovoltaic power generation system are becoming more and more stringent. One of the most important is the inverter control method, in this paper, the control of grid connected inverter and the control of anti- island operation have done a thorough research. In order to improve the stability of photovoltaic power generation system, the conversion rate and the operation ability of anti islanding, improve the quality of grid current.In order to meet the characteristics of low cost and high efficiency, a novel topology of the inverter was adopted in this paper. The inverter consists of three parts, the DC/DC boost unit, the H6 inverter bridge and the LC filter, the working principle of each part is deeply analyzed.For traditional inverter output current control PI regulator can not be achieved without static error control directly, a simple quasi PR regulator was adopted in the current loop control. According to the requirement of system response control, the relevant parameters of the quasi PR regulator were designed, and the reasonable parameters setting method was given, got the frequency response characteristics to achieve the exchange amount directly without static error control. Simulation results showed that the method ensures that the grid current and grid voltage keep with the same frequency and phase and effectively solve the problem of the harmonic content.Aiming at the shortage of the traditional maximum power point tracking control, an optimal control method was proposed in this paper, in this method, three different P-U values ware sampled to determine the working state of PV panels in which kind of working state, and the maximum power point of PV panels was gradually made by different orders. Simulation results showed that the optimized control method can not only ensure that the PV panels work at the maximum power point, but also can make the PV panels re-work in the new maximum power point when the light intensity changed.The improved active anti-islanding protection will affect the power quality and the improved passive anti-islanding protection is too complex, so this paper proposed the combination of active and passive antiislanding protection method based on the detailed analysis of islanding detection principle, namely the passive anti islanding operation control plays a major role, when it failure the active anti-islanding control play a protective role. The main process is as follows: firstly, the voltage and frequency of the common coupling point is detected, and if the protection threshold is exceeded, the inverter is disconnected, if it does not go beyond then using the active implementation of positive feedback frequency shift method at the point of common coupling voltage frequency. In order to make the method more effective, the normfCQ ?0 coordinate system was used to analyze the non detectable region of this method, and the key parameters of the active frequency shift method were designed by the coordinate system.According to the theoretical analysis, the experimental scheme of photovoltaic grid connected inverter was determined. The experimental contents the effect of grid connected current control, the effect of the maximum power point tracking control, and the control effect of the inverter anti-island operation. The experimental dates and the results were analyzed in detail. The results showed that all the experimental results meet the experimental requirements.