Research On The Loss Models Of High-Power Photovoltaic Inverter

As is known to all, the solar green energy, gain more and more attentions around the world in the low-carbon society today. Being strongly supported by the government, the photovoltaic industry has been rapidly developed.There is a boom in construction of photovoltaic plants. Grid-connected PV inverter is a key component of the grid-connected photovoltaic power generation system. The efficiency of photovoltaic grid-connected inverter system is an important indicator measuring the power generation system. The low efficiency will directly lead the impossibility of the grid-connected PV inverter’s connecting the grid. This paper focuses on the efficiency of the photovoltaic grid-connected inverter system. Based on the power loss on the high-power photovoltaic inverter, the mathematical loss modeling and simulation is analyzed. This paper can provide some reference on the design of elevating PV inverter’s efficiency, which shorten the R&D time.Based on the topology of the grid-connected PV inverter, the theory of the power loss about the IGBT power devices, the filter inductor, the filter capacitor, the DC bus capacitor is studied and their mathematics loss models are established at the same time. The numerical example about the power loss module of the IGBT, which was used in a500kW photovoltaic grid-connected inverter system, is calculated.According to the mathematics loss models, the power loss of the filter inductor and filter capacitor have strong correlation with their harmonic currents. This paper analyzes SVPWM Fourier transform decomposition and a method of calculating the grid current’s total harmonic distortion is given. According to the current’s harmonic distribution, the aluminum loss and iron loss in filter inductors and filter capacitor is solved.Then a simple and feasible grid-connected PV inverter LCL filter design method is provided. The closed-loop PV inverter control strategy is analyzed in details. Also a simulation, which realizes the power factor is one on the condition of different PV power, is built by Matlab/Simulink. The simulation testify that the grid current’s harmonic is almost the same with the calculated results and the method of calculating the harmonic current is correct.Finally, relying on the500kW photovoltaic grid-connected inverter system which produced by Sichuan Clou Electric Co.LTD, relevant experiments was accomplished. According to the European Efficiency Power test points, the experiment is done and the experimental results verify the correctness of the theoretical loss models. Some components of the inverter system power loss which account a large proportion, such as the loss of the IGBT and the filter inductor, is analyzed in details. The modulation, load current, switching frequency’s impacts on the power devices loss are mainly discussed. The flux density, material’s impacts on the filter inductor loss are also discussed. This paper suggest to use copperbelt to make filter or select a proper switching frequency elevate the PV inverter’s efficiency. So using the method given by the paper to calculate the PV inverter theory power loss value in advance can effectively reduce the power loss and elevate its devolopment efficiency.