【作者】 耿强；

【导师】 夏长亮；

【作者基本信息】 天津大学 ， 电机与电器， 2012， 博士

【摘要】 直驱式永磁风力发电系统因具有能量转换效率高、可靠性高、抗电网干扰能力较强等优点,成为继双馈风力发电系统之后风电技术领域的重要发展方向。本文以一种较为常见Boost斩波型直驱式永磁风力发电系统为研究对象,重点研究了全功率变换器的运行特性,并提出了相应的控制策略。永磁同步发电机和电机侧Boost斩波型变换器属于强非线性系统,采用普通的PI控制器难以在正常运行范围内保证系统性能,且非线性系统PI控制器参数难于整定。针对其非线性特性,在适当简化的基础上,采用分区间建模的方法,以功率器件开关信号占空比为输入变量,发电机转速为输出变量,建立了发电机与变换器整体二阶仿射非线性模型;引入微分几何理论,利用反馈线性化方法,在单区间内将非线性系统转换为线性系统;根据线性系统设计闭环转速控制器,并利用线性二次型最优控制方法对发电机转速进行控制。经仿真验证,基于该控制器的系统具有良好的稳态和动态性能。在发电机与变换器二阶模型基础上,将发电机角位置作为状态变量,分区间建立了三阶仿射非线性模型,重新构造输出函数,以发电机角位置作为输出变量,实现了单区间内系统完全输入-输出反馈线性化;根据输出变量与发电机转速的数学关系,设计闭环转速控制器,并利用时间与绝对误差乘积积分指标对控制器参数进行了整定。经仿真和实验验证,基于该控制器的系统能够在较大范围内快速跟踪参考转速的变化,具有较好的稳态和动态性能,对电机侧Boost斩波型变换器控制策略的设计具有一定的参考价值。根据网侧变换器数学模型,以瞬时功率理论为基础,详细分析了电网电压平衡和不平衡情况下电网瞬时功率表现形式,给出了瞬时功率直流分量和交流分量解析表达式;基于该表达式,利用误差反馈控制原理,针对不同情况,设计了未含不平衡算法的恒频直接功率控制策略和含不平衡算法的恒频直接功率控制策略;基于这两种控制策略的系统具有动态响应快,交流侧滤波器参数易于设计等优点。经仿真和实验验证,电网电压平衡时,基于两种控制策略的系统均能满足电网要求,具有良好的稳态和动态性能;电网电压不平衡时,含不平衡算法的恒频直接功率控制策略可有效地抑制瞬时有功功率波动,减小交流侧电流谐波污染,改善系统性能。更多还原

【Abstract】 The direct driven permanent magnet synchronous generator (PMSG)-based wind energy conversion system (WECS), which has the advantages of high efficiency and reliability and high ability to reject the grid disturbances, is a main type of WECS as well as the doubly fed induction generator (DFIG)-based WECS. The boost-chopper converter followed by a three-phase full-wave converter is a common topology of the full-power AC-DC-AC converter in the PMSG-based WECS, whose performance is analyzed in this paper. Then novel control strategies are purposed.The PMSG and the boost-chopper generator side converter form a nonlinear system. Therefore it is difficult for the system to maintain good dynamic performance within normal operating range under control of the ordinary proportional-integral (PI) controller. Besides, the parameters of the PI controller used in the nonlinear system are always difficult to be tuned. Consequently, a piecewise 2nd-order affine nonlinear mathematical model for the whole system including the generator and the generator side converter is built based on certain assumptions, whose input variable and output variable are the duty ratio of the switching signal for the power device and the speed of the generator respectively. Subsequently the nonlinear mathematical model is transformed into a linear one within every single interval by the input-output feedback linearization (IOFL) method based on the differential geometry theory. In addition, a closed loop speed controller is designed on the basis of the optimal control theory. Simulation results verify the good steady and dynamic performance of the system using the proposed controller within normal operating range.A more precise piecewise 3rd-order affine nonlinear mathematical model is built whose state variables are namely the angle of the generator, the speed of the generator and the current of DC-link inductor respectively. Among then, the angle of the generator is selected as the output variable for complete input-output feedback linearization within every single interval. Then a closed loop controller is designed according to the relationship between the output variable and the speed of the generator considering the integral of time multiplied by the absolute error (ITAE). Finally, simulation and experimental results prove that the system has good steady and dynamic performance with the proposed strategy, such as its rapid step response, through which some drawbacks of the ordinary PI controller are overcome. Also, the proposed strategy can be referred to for the generator side controller design of the direct driven PMSG-based WECS with the boost-chopper converter.According to the instantaneous power theory and the mathematical model of the grid side converter, the analytical equations of DC and AC components of the instantaneous power are given under balanced and unbalanced grid voltages respectively. Then two constant switching frequency direct power control (CSF-DPC) strategies are designed using the feedback control theory. One of them contains unbalanced algorithm while the other does not. The two controllers have the advantages of fixed switching frequency and good dynamic performance. At last, simulation and experimental results demonstrate that the two controllers have good steady and dynamic performance under the balanced grid voltages and the controller containing unbalanced algorithm can effectively improve the performance of the system under the unbalanced grid voltages by reducing input current harmonics and the fluctuations of the instantaneous active power.更多还原