| Due to the crisis of traditional energy and the crisis of environment caused by burning fossil fuels, the development of renewable energy is necessary. As the wind power is a clean, pollution-free, safe and reliable renewable energy, it develops very rapidly in recent years. Because the prospect market, the small permanent magnet synchronous generator (PMSG) wind power system application attracts attention widely. While converter is the core technology of wind power system, it plays a critical role in wind power generation system. This paper mainly focuses on grid side converter and its control strategy of the small permanent magnet direct drive wind power system.Firstly, this paper introduces current research and future development trends of the world and China's wind power. Then analyzes the current converter technology of PMSG wind power system. Combined with the characteristics of small PMSG wind power system, a back to back converter topology is applied as the topology structure for the small PMSG wind power system.Secondly, this paper analyzes the research on grid side control strategy detailed. Based on the mathematical model of grid side converter, this paper analyzes the traditional PI control strategy of inner current loop, outer loop voltage. Based on the PI control, the paper adopted the higher-order sliding mode control (SMC) to control the inner current loop, PI control to control the outer voltage loop. The simulation results show that this proposed scheme has better dynamic performance and robustness under the disturbance of gird voltage. Due to hardware lock is not accurately when the grid voltage distortion happened, a three-phase software PLL is used in the paper, the simulation results verified the proposed strategy even if there is a gird voltage amplitude change or a gird voltage distortion.For the fault of the grid voltage dip, this paper analyzes the commonly used low voltage ride through(LVRT) technology of the PMSG wind power system. And a detailed analysis of the LVRT method of a crowbar protection circuit with resistance is illustrated. Furthermore, the parameter selection principles and control strategy of resistance is analyzed. And the simulation model of the LVRT method of a crowbar protection circuit with resistance is build in MATLAB/Simulink, then the effectiveness of this method is verified.The hardware circuit and software process of the small PMSG wind power system grid side converter is designed in this paper. For hardware, the grid side converter main circuit, sensing circuit, isolation circuit, protection circuit and the auxiliary power supply circuit is designed. For the software, the process of the entire grid control algorithm is illustrated. And a more detailed illustration about PWM interruption subroutine, AD sensing interruption subroutine, and fault protection interruption subroutine are given. And the algorithm analysis and software design process are listed for each of them.Finally, the test platform for the small PMSG wind power system grid side converter is build based on TMS320F2812. And experimental waveform was detailed analyzed. Experimental result shows that the correctness of the grid-connected control strategy. |
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