基于微分几何理论的直流微电网控制策略研究

2019-01-10 01:48:14 现代电子技术2019年1期

韩小雨 李田泽 陈洪涛

关键词: 直流微电网; 非线性控制; 微分几何原理; 鲁棒控制的μ综合方法; Simulink; 控制器

中图分类号: TN710?34; TM73                    文献标识码: A                     文章编号: 1004?373X(2019)01?0129?05

Abstract: The nonlinear droop control is mostly used in microgrid inverter, which makes the microgrid have the function of frequency modulation. However, this kind of frequency modulation as primary frequency modulation can′t modulate the frequency without difference, has the disadvantages in the operation of microgrid system, and is harmful to the stable operation of electric power system. Aiming at the shortcomings of nonlinear control, a simplified equivalent model of DC microgrid is taken as the research object, the traditional microgrid nonlinear control system is transformed into a linear control system, and the differential geometry principle is used to establish the affine nonlinear system of the equivalent model. The μ?synthesis method based on robust control is adopted to establish the rational controller K, and obtain the nonlinear robust controller of the system. The Simulink simulation results show that the dynamic stability of the system is perfect when the external parameters of the system are changed.

Keywords: DC microgrid; nonlinear control; differential geometry principle; μ?synthesis method for robust control; Simulink; controller

0  引  言

传统能源的大量消耗使得新能源的重要性日益凸显,以光伏、风机、燃料电池和微型燃气轮机为代表的新型分布式发电技术的广泛应用引起了研究人员的普遍重视。随着配电网中分布式电源渗透率的迅速增长,其对配电网本身的安全性和稳定性造成了严重影响[1]。微电网作为新能源与配电网的中间媒介,可以有效缓解新能源对配电网造成的冲击[2]。同时微电网本身是由负载、分布式能源、储能装置、电力电子变换器结合在一起的小型分配电系统,既可以与配电网工作在并网模式下,又可以独立工作在孤岛模式下,具有较高的可靠性和稳定性[3]。微电网一般可分为直流微电网与交流微电网。直流微电网因为结构简单,无需对电压的相位和频率进行跟踪,而且不存在涡流损耗和无功补偿等问题,成为电力工业的主要研究方向[4]。

随着电力电子技术的发展,直流微网电力电子化是未来能源发展的趋势之一。分布式电源、本地负载和储能装置都通过整流逆变装置接入直流母线,同时多电子器件之间的相互作用是造成直流微电网系统不稳定的重要原因[4],许多学者对此做了大量研究。文献[5]通过对微源和储能测DC/DC变换器进行小信号建模,研究了负荷功率类型,变流器下垂系数对系统稳定性的影响,不过该方法依然利用传统的近似线性化方法,且前期需要大量的矩阵运算。文献[6]从振荡系统的耦合出发,通过引入源侧变换器电感的多相性,选取合适的耦合系数可以达到抑制振荡的作用,但是该方法局限性太大,而且仍然采用平衡点处近似等效,没有形成一个普遍的解决方案。

本文基于微分几何原理,通过构建恰当的坐标转换,使传统非线性系统转化为线性系统,并且完整保留了系统的非线性特性,得到完全解析表达式的非线性控制规律[7?9],可以对此类问题形成一种普遍的解决方案,易于工程实现。

4  结  论

直流微电网系统内带有大量的恒功率负载和电力电子元器件,给系统本身的稳定运行带来了不利影响。本文利用状态反馈精确线性化的方法对直流微電网的简化等效模型进行建模,得到线性系统的布鲁诺夫斯基标准型,采用鲁棒控制μ方法设计控制器,仿真结果表明外界条件变化时,系统动态性能良好。

注:本文通讯作者为李田泽。

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