Stability Analysis Of PV Inverter Based On Harmonic Balance And Floquet Theory

With growing global energy crisis, solar energy has great prospects for development as s new energy. In order to make the solar energy to replace traditional energy to meet the need of our daily lives, the study of photovoltaic inverter is an important link. The stability of the pv inverter (photovoltaic inverter) is the premise of the running of photovoltaic inverter. Hence, the focus of the research emphasis in this paper is the stability analysis of the photovoltaic inverter.Firstly the classification of the pv inverters is introduced according to the output filter. The grid-connected inverter with LCL-filter is chosen as the research object, which is suitable for the large capacity power system. The content of the research is stability analysis of the pv inverter under the passive damping control and PI control. The critical values of the damping resistor which make the pv inverter stable are obtained according to the conventional stability analysis method and the analysis method based on the harmonic balance and Floquet theory. Comparing the grid-connected current waveforms under the obtained damping resistor, it is concluded that the grid-connected current waveform under the damping resistor based on the harmonic balance and Floquet theory is better than the grid-connected current waveform under the damping resistor based on the conventional stability analysis method. And the essential reasons for this phenomenon is revealed.Then, the discrete model of the grid-connected inverter with LCL-filter is established based on the stroboscopic map. Then the stability analysis of the system is researched based on the bifurcation diagram and folded diagram. Because the discrete model is a nonlinear model and the model which is the basis of the former two methods is linear, the damping resistor based on the discrete model will make the system stable. The simulations prove the conclusion. At the same time, it is concluded that the damping resistor under the stability analysis method based on the harmonic balance and Floquet theory is more close to the damping resistor making the system stable. The PI control parameters and the input voltage range which make the system stable are obtained based on the bifurcation diagrams and folded diagrams. The correctness of the stability analysis is verified by simulations.And then the classification and the influence to the source of the nonlinear load are introduced. Howerver, traditional stability analysis of the inverter with nonlinear load is not fully reflect the characteristics of nonlinear load, which usually approximates the nonlinear load to linear load firstly. Thus being more and more strict with the precision of the equipment, a new stability analysis method is needed. The stability analysis method based on the harmonic balance and Floquet theory is suitable for this requirement, which can deal with the continuous and periodic nonlinear load accurately. Becuase in the process of stability analysis using the method based on the harmonic balance and Floquet theory, the characteristics of nonlinear load can be fully reflected, without approximating nonlinear load. Simulation and experimental results verify the correctness and accuracy of the stability analysis method.Because the output valtage of photovoltaic panels is low, photovoltaic inverter generally uses two-stage structure. The general method for the design and stability analysis of the two-stage inverter is to separate two stages to design. However when two stages are separately stable, the cascade system is not necessarily stable. Hence it is necessary to study the stability of the two stages as a whole. The two-stage inverter can be modeled and stability analysis as a whole using the stability analysis method based on harmonic balance and Floquet theory. The simulation and experimental results verify the accuracy of the stability analysis method.