Simulation Research On Three-phase Current Source Multiple Grid-connected Inverter Based On Phase-shifted Control

With the large-scale exploitation and utilization of solar energy, the rapid development of photovoltaic(PV) industry and the continuous growth of installed capacity of the PV power generation system, the high power PV grid-connected inverter becomes the major research emphasis. Multiple superposition method is a main technology to expend the capacity of inverter, when inverter uses multiple superposition method, its switching frequency is low, its circuit structure is simple, its construction is easy to modular and its power supply reliability is guaranteed through the module redundancy. Until now, the research of grid-connected inverter has been mainly about the voltage source inverter, but the current source inverter can be better suitable for the current source characteristic of PV cell, so the research of current source inverter gets more and more attention.The current source multiple PV grid-connected inverter is regarded as the research object and its grid-connected control strategy is mainly researched. Firstly, the multiple superposition principle of three-phase current source square wave inverter is described. The three-phase current source triple inverter connecting in parallel with transformers is taken as an example, Fourier expression of the output current is deduced and the harmonic of output current is analyzed. The phase-shifted technology is applied to adjust the output current. Based on this phase-shifted technology, the main circuit of grid-connected inverter is built up by using two parts of three-phase current source triple inverter. Secondly, the mathematical model of solar PV cell is built up, the simulation model is established and its electrical characteristics are tested. The mathematical model of CL filter is deduced in three-phase static, the two-phase static and two-phase rotary coordinate. Thirdly, the control diagram of system based on the two-phase rotary coordinate is obtained through analysis. The design of current regulator is finished by a double loop control of a filter capacitor voltage inner loop and a grid–connected current outer loop. The calculation of phase-shifted angle is got through phase-shifted principle. The track of grid voltage’s phase is achieved combining with the nature of the filter. The pulse generator module of the current source multiple inverter is designed through writing S function.Finally, the simulation model of the whole system is set up in MATLAB/SIMULINK environment. The simulation model is run respectively with different power factors. The grid-connected current waveform and the grid voltage waveform are got. The FFT analysis of grid-connected current is carried out. The results show the current source multiple PV grid-connected inverter can achieve connection to the grid in different power factors condition. The feasibility of this control strategy of the current source multiple PV grid-connected inverter based on phase-shifted control method is tested.