Resonance Mechanism And Suppression Research For Multiple Three Phase Grid-connected-converter System

In recent years, distributed generation based on renewable energy has become an important part of the national energy conservation, emission reduction, and strategy of sustainable development. As distributed generation system and grid connected devices, grid-connected-converter plays a vital role. However, under the condition of weak grid, the LCL filter of three-phase converter may generate resonance unstable problem with line inductance in grid, which frequently leads to system failure, even explosion accident. Therefore, the study of resonance mechanism and suppression strategy of a LCL type grid-connected-converter under distribution network becomes very important for achieving a safe and stable operation of the new energy grid connected system.Firstly, a detailed analysis of resonance mechanism and resonance rule were discussed in this paper, which was based on the open-loop impedance modeling under the condition of multiple grid-connected- converter with LCL filter system.Secondly, the effect of the closed-loop control system on the stability was considered. By establishing the closed-loop Norton equivalent circuit model, a new evaluation method for the stability multi-converter system was proposed, and the relationships between the stability of the multiple grid-connected-converter system and grid impedence, converter closed-loop admittance were evaluated.Furthermore, a control method of proportion resonant(PR) controller and full state feedback control scheme was designed as a single grid-connected converter controller. Full state feedback control was used to adjusting the output admittance of the system. PR controller was used to eliminate the steady-state error, when reducing the parameters entry errors resulted from the introduction of decoupled. MATLAB simulation also verified the effectiveness of the PR controller and full state feedback control for the resonance suppression and network control. Compared with the existing capacitor current feedback control methods, the proposed method in this paper got a better robustness.Finally, in order to facilitate the following experimental research, a new LCL experimental platform with rated capacity of 7.5k W and three phase grid-connected- converter was designed and built up, in which laboratory controller was upgraded, DSP+FPGA based control board was designed. the underlying AD, DA, Protect and PWM hardware drivers based on FPGA Verilog language. C-based DSP control algorithms and RS232 communication algorithm program touch-screen were programed. For the plateform, protection circuits, relays circuit boards, other hardware adapter modules, whole-platform design and debugging were also completed. The proposed scheme studied on the experimental platform, which shown the effectiveness of the resonance suppression.