【作者】 倪馨馨；

【导师】 姚文熙； 王正仕； 陈辉明；

【作者基本信息】 浙江大学 ， 电气工程， 2012， 硕士

【摘要】 随着分布式供电、新能源发电和电动汽车系统等的不断发展,级联成为电力电子变换器越来越常见的连接方式,级联系统所特有的非线性特性、动态和稳定性问题也随之成为研究的热点。电力电子变换器一般都是闭环调节控制,当作为负载变换器时在输入端便会表现出恒功率负载特性。如果没有合理的控制方案,恒功率负载的时变负阻抗特性将可能引起前级变换器的输出不稳定甚至振荡问题。电力电子变换器是典型的开关非线性系统,基于传统控制理论的线性化控制方案从本质上讲不是最佳的控制方案,且在平衡点进行线性化处理的系统小信号模型也无法解决大信号扰动带来的一系列问题。故基于非线性控制理论的非线性控制方法成为近年来的研究热点。本文将非线性控制理论应用到级联系统前级直流变换器的建模与控制中,得到非线性控制策略,提高了系统的控制性能。以Boost变换器与逆变器组成的级联系统为例,首先分析了后级逆变器作为负载对前级Boost变换器的影响：闭环控制的逆变器平均功率恒定,具有时变负阻抗特性,严重影响了Boost变换器的闭环控制的稳定性和输出动态特性。其次,选取新的状态变量,利用状态空间平均法对级联系统进行建模,得到系统的仿射非线性模型。理论证明该模型符合精确线性化的两个条件,级联系统经过状态反馈精确线性化变换为一个线性可控系统。最后分别利用经典控制理论中典型二阶系统的特性和最优控制理论的线性二次型最优控制的方法求得被转换后的线性可控系统的最优控制解,从而得到最终的非线性控制策略。两种控制策略均用Matlab仿真工具进行验证。仿真结果表明,两种方法确定的非线性控制策略均可使系统达到理想的目标。故状态反馈精确线性化技术可以实现对Boost变换器带逆变器负载的控制,在电源及负载大范围变化时,能够保证系统的稳定运行,具有大信号稳定特性。更多还原

【Abstract】 Distributed power architectures comprised of power electronic converters are becoming increasing common in recent years. Tightly regulated closed-loop converters exhibit instantaneous constant-power-load (CPL) characteristics. Without appropriate controls, the negative impedance characteristics of CPL may lead to significant oscillations in the output voltage of feeder converters and impact power quality and system stability. And because of the nonlinearity of converters, classical linear control methods, which are often used to design controllers, have stability limitations. This paper introduced nonlinear control theory into modeling and control design of interconnecting converters to ensure large-signal stability.Take a Boost converter operating with an inverter as an example, the nonlinear characteristics, dynamics, and stability problems are analyzed firstly. Tightly-regulated inverters, which have negative impedance characteristics at the input terminals, might seriously impact the dynamics and stability of the Boost converter.Then, this paper presents an exact linearization technique for DC-DC converters feeding inverters. An affine nonlinear model of a Boost converter operating with an inverter has been set up by introducing control aims into system state equations. Exact state feedback linearization is proved to be easily performed on this model. A nonlinear feedback can be found to cancel the nonlinearity of the interconnecting system.Finally the classical control theory and the optimal control method are respectively used to deduce the control law of the transformed linear system and nonlinear controllers derived can approximately linearize the system. The controllers are exemplified and validated by a Matlab Simulation model. Simulation results illustrate that the output voltage of the boost converter feeding an inverter has a large-signal stability characteristic. It is conclude that state feedback exact linearization ensures cascaded systems operating steadily.更多还原