Research On Pitch Control Technology Toward Grid-friendly Wind Turbine

With the enlargement about installed capacity of wind turbines, more and more units have being in operation into power grid. The grid-friendly wind turbines in the grid operation, which aimed to how to adapt to the changes and the needs from grid, became today's research hotspot. Mw-class direct-driven wind power system will become the mainstay of grid-friendly units because of its characteristics with large capacity and high reliability, high efficiency and power output stability, long service life, high potential for grid-connected operation etc. As one key step about power regulation of wind turbines, pitch control's quality directly determines the level of the ability of their grid-connected operation.The MW-class direct-driven wind turbines are selected in this paper as research object and improving the turbines grid-connected ability as the goal. Then A deep research on pitch control and strategies of turbines is appeared. A kind of variable pitch control strategy which supported of low voltage ride through was put forward because of weak grid ability of Mw-class direct-driven wind turbines. On this basis, a kind of design method of software based on multi-level state machine about variable pitch control was proposed because of the existing control system software architecture limitations. In order to verify the correctness of the control target and the effectiveness of the control strategy, this paper used MATLAB to construct simulation model containing Mw-class direct-driven wind generator and power system, and had done many kinds of cases of simulation and analysis. In order to verify the correctness of the software, a comprehensive test platform about variable pitch control software based on embedded system had been designed and realized, and the performance was verified.The specific works in this paper are as follows:The mathematical models of various part of system were established by MATLAB after analyzing the overall structure and characteristics of Mw-class direct-driven wind turbines. Then a simulation analysis about the variation characteristics of parameters of wind turbine has done in the normal operation, which verified the accuracy of model.The targets of pitch control and the basic control strategy under different wind conditions had been researched according to running characteristics of pitch control system about Mw-class direct-driven wind turbine. Specially the variable pitch control strategy which supported of low voltage ride through had been proposed and verified after the research on pitch control objectives under different voltage conditions when in power grid failure, which the turbine should be ensured safety in operation.Because of standalone limitations and sequence control flow defects about the existing pitch control software, the pitch control software design based on multi-level state machine had been proposed in the paper after the analysis about the characteristics of control software in the main control system and the research about the architecture of pitch control system hardware and software, which would enhance software configurable, increase the turbine's ability to deal with external events and improve the unit's grid capacity. In the paper, the state machine of pitch control software had been simulation and verified by using MATLAB State flow tools.About the test problems of pitch control software, the article shows the design and implementation of pitch control software test platform, which had been test and validation with testing method of hardware in the loop at low speed, high-speed, power fault conditions etc. will guide specific significance. It provides guidance for the development of next-generation intelligent pitch system.