Research On Control Technology Of Small And Medium-sized Grid-connected Wind Power Generation

Energy crisis has accelerated the human pace of studying and developing new energy sources. As a resource-rich, clean, and renewable resource, wind power has been widely concerned all around the world, grid connected wind power generation technology has become a hot research at home and abroad. Due to its small footprint, without energy storage devices, low cost, flexible controlling way, small and medium in-grid wind power system has become one of the most active research directions of the wind power generation. The core of grid connected wind power generation is the grid-connected inverter whose performance will directly influence generating efficiency of the grid-connected generation system. Taking the small and medium grid-connected inverters as the research object, this paper will study their topology structure, controlling method, digital phase-locking and etc.First, compare and analyze several regular kinds of operation modes of grid-connected wind power generation systems, and choose permanent-magnet direct-drive grid-connected mode which is fit for small and medium grid –connection with high efficiency, simple structure and low cost. Permanent magnet motor coupling with blower directly can eliminate the gearbox, reduce maintenance costs, it can also run in a wide range of wind speeds, which will improve the utilization of wind powder. Intermittent and randomness of the wind speed will result in the frequent changing of the output voltage of the wind generator. Use the closed-loop booster circuit at the preceding stage of the inverter can achieve the effect of stabilizing voltage so as to reduce the difficulty of the inverter design. Based on the above analysis, this paper will present the topological structure of the single-phase grid-connected wind power system, introduce its working principle and the functions of the various component units of the grid-connected system, so as to provide theoretical preparation for the selection of scientific and reasonable controlling scheme.Secondly, study the controlling strategy of the inverter. This paper adopts the controlling methods of inputting voltage and outputting current modes to analyze the direct controlling methods of two kinds of currents: hysteresis controlling, and triangle wave comparison controlling. This paper adopts the triangular wave comparison method to establish the mathematical model of the current closed loop controlling system. It can be found that the feedforward controlling can effectively reduce the disturbance of the network voltage on the system. Compare and analyze the traditional PI controller, the structural model and the characteristics of the right PR controller, adopt a kind of recombined control strategy which is based on feedforward controlling and right PR controlling, and set up the model of grid-connected controlling system with Matlab/simulink. The simulation results show that compared with the methods of feedforward controlling and PI controlling, the improved right PR controlling method can improve the stability of the system performanceFinally, make a detailed analysis and design on the filter of alternating current side and the direct current side. By analyzing the mathematical model of AC side filter, the harmonic wave inhibition effects of undamped LCL filter with the capacitor branch series resistance is pretty good. On the basis of the theoretical research, design the hardware and software systems of grid connected inverter device for 3 kw small grid connected wind power system which is based on TMS320F2812.