电压型PWM整流器控制现状及发展趋势分析
国网陕西省电力公司黄陵县供电分公司 延安 727300
Analysis of Control Status and Development Trend of Voltage Source PWM Rectifier
Huangling Power Branch of State Grid Shanxi Electric Power Company Yanan 727300 China
收稿日期: 2018-05-9 网络出版日期: 2018-10-31
Received: 2018-05-9 Online: 2018-10-31
作者简介 About authors

张 军 男 1973年生,助力工程师,长期从事电力系统基层生产运行工作。
针对微电网及工业领域中目前广泛应用的电压型PWM整流器,首先对其主要原理、双闭环控制结构进行了简要分析,按被控量类型将控制系统分为电流和功率两大类,在此基础上全面阐述了传统、现代及智能控制等方法,最后展望了电压型PWM整流器控制的发展趋势。
关键词:
For the voltage source PWM rectifiers which are increasingly widely used in micro-grids and many industrial fields, the main principles and double closed-loop control structure of the voltage source PWM rectifiers are briefly analyzed. According to the type of controlled quantity, the control system is divided into two categories including current and power, then the traditional, modern and intelligent control methods are comprehensively expounded based on the strategy. Finally the development trend of voltage source PWM rectifier control is expected in the paper.
Keywords:
本文引用格式
张军.
Zhang Jun.
1 引言
传统的整流电路主要由二极管(不控)、晶闸管(相控)等器件构成,普遍存在谐波畸变大、功率因数低及能量损耗大[1]等问题。随着全控型器件IGBT的迅速发展,PWM整流器应运而生,其功率因数校正和谐波抑制效果显著,目前己被广泛用于微电网系统[2]、有源滤波器[3]、无功补偿器[4]、超导储能[5]、交流传动[6]、直流输电[7]及统一潮流控制[8]等方面。按直流侧电源储能方式,PWM整流器可分为电压型整流器(Voltage Source Rectifier,VSR)和电流型整流器(Current Source Rectifier,CSR)等。因VSR结构简单、电能损耗小、动态响应快,目前在PWM整流器研究领域处于主导地位,其控制技术更是研究重点。
VSR的控制一般采用直流电压外环、交流电流内环的双级环路结构,外环的输出作为内环的指令来进行直流电压与交流电流的相互控制[9]。本文按被控量类型对其进行分类,从传统、现代及智能控制三个层面综述VSR的各种控制技术,并对其发展前景进行展望。
2 VSR双闭环控制策略
控制策略一直是诸多VSR研究的重点和热点,主要包括两个控制目标,一是使VSR直流侧输出电压稳定;二是让网侧电流正弦化,且与电压相位同步,达到单位功率因数运行。
3 VSR主要控制方法
3.1 传统控制方法
在设计控制系统时,VSR常被视为线性系统,但其本质属于动态系统,采用非线性控制技术可提高鲁棒性与适应性,故常将成熟的线性控制与非线性理论结合。
滞环电流控制因其原理简单、设计方便等优势被广泛应用于整流器控制中[14],但其没有固定的开关频率,滤波环节的设计相对困难;其后,三角载波比较法[15]的出现固定了开关频率,克服了滞环电流控制的不足,但却存在电流偏差;随后出现了PID控制,大大提高了控制系统的性能[16],目前在控制领域被广泛应用,但参数的整定始终需要反复凑试来确定;比例谐振控制[17]的出现省去了坐标变换环节,直接对交流量进行控制,但控制器的设计依然没有避免繁琐的凑试环节。上述控制方法目前都需要通过计算机数字化方法实现,采样及计算等必然存在延迟,虽然其后预测电流、无差拍、单周、重复、模型预测[18,19,20,21,22]等几种补偿延迟的预测控制技术也相继被提出,但普遍对参数变化敏感,数学精度要求较高。
3.2 现代非线性控制方法
上述基于理想模型的线性控制方法经过了过多的简化处理,控制效果始终有限,故现代非线性控制理论也被应用于PWM整流器控制中。
随着现代控制理论的进一步发展,基于Lyapunov能量函数稳定性理论的控制方法也出现在整流器系统中。起初,文献[28]利用电感、电容储能的定量关系,以及数学模型、空间矢量的约束条件等推导出新算法,解决了大范围稳定问题,但Lyapunov能量函数的建立不唯一,最佳函数难以获取;随后,将控制理论从信号处理转化到能量处理角度的无源控制(Passivity-Based Control,PBC)[29]被提出,它基于欧拉–拉格朗日(Euler-Lagrange,EL)数学模型,通过能量整形和阻尼注入,迫使系统总能量去跟踪预期的能量函数,从而达到闭环控制系统无源的目的,整个设计过程省去了寻找Lyapunov函数的步骤,但在构造存储函数时会对Lagrange的结构造成破坏,影响其稳定性;基于哈密顿系统的PBC控制[30]采用端口受控哈密顿函数模型(Port-Controlled Hamiltonian,PCH)表示系统,利用能量耗散的概念将引入系统变为端口受控的耗散哈密顿系统(Port-Controlled Dissipative Hamiltonian,PCHD),再结合反馈镇定原理来寻找反馈控制,解决了Lagrange结构被破坏的问题,但期望哈密顿函数、互联和阻尼矩阵等变量都缺乏必要的物理意义,计算较复杂,难以实际应用;最终出现的反步控制法[31]以Lyapunov能量函数收敛为目标,将复杂的非线性系统分解成若干个子系统,采用虚拟控制量进行静态补偿,各个子系统间从前往后递推设计,后面的子系统保证前面的子系统达到正定,整个设计保证了系统全局一致的渐近稳定,解决了Lyapunov能量函数的构造性问题,不要求非线性系统满足匹配条件,增大了应用范围,但要求对象数学模型精度高,参数变化也需满足线性化条件,计算量大大增加,实现难度进一步加大。
3.3 智能控制方法
上述传统或现代的控制方法都是在PWM整流器的数学模型基础上,从不同角度综合考虑多种因素并对系统进行控制,控制策略因控制目标侧重点的不同而不同。而对于一些无严格数学描述、缺乏必要物理意义及无规律可循的系统模型,现有的控制方式通常无法直接使用,故新的智能控制方法应运而生。
目前应用最广泛的智能控制方法主要有两种:一种是模糊控制;另一种是神经网络控制。模糊控制模仿人的思维方式,将精确量模糊化,通过推理运算求得输出后,再利用去模糊化获得输出的确定值[32]。它无需依赖被控对象的数学模型,对系统参数的变化适应性强,鲁棒性高,但其设计精度与控制规则的优劣相互制约,具有很大的人为主观因素,难以实现最优控制;基于神经网络的控制是模仿大脑对信息的处理方式,将函数的映射关系分布在网络连接权与节点的函数中,将输入、输出数据设为学习样本,调节每层的连接权值,使输入与输出间的关系可任意逼近期望的非线性动态系统[33]。其自学习能力强、容错性高,但物理意义不够明确,尚无较科学的理论依据,且在控制过程中对数据信号的处理要求较高。
智能控制方法各有其优势及局限,可根据应用场合合理选取。目前,将各智能控制方法优势互补,集成融合为更高智能的方案已成为新趋势,如模糊神经控制[34]法,将模糊控制与神经网络控制结合,取长补短,相互组成更为智能的控制方案,此类控制思想将成为VSR智能控制的大势所趋。
4 VSR控制技术研究展望
随着PWM整流器的广泛应用,其控制技术的研究将不断发展,主要表现在以下几个方面:
(2)CSR控制研究[38]。超导技术的迅速发展,解决了直流侧储能元件为电感的CSR效率问题,其控制电流更为直接,动态响应更为迅速,体积及成本也得到较大改善。因此,CSR 在中等及大功率场合具有更宽阔的应用前景,其控制技术研究也将成为一大热点。
(3)新控制方法研究。随着电力电子、微处理器、计算机等技术的突飞猛进,复杂、繁琐、计算量大的算法已可逐步实现,这给寻找新控制方法及改进传统控制提供了可能;很难仅用一种方案来解决实际应用中出现的众多问题,故将不同类型控制方法 “整合”成为综合控制策略也是一种新趋势,如电网侧利用神经网络控制离线训练一个控制器来代替滞环比较器,不仅保持了滞环控制器的鲁棒性及快速性,还可限制开关器件的通断频率[39]。总之,不同方法取长补短,博采众长,优势融合组成更有效的新控制方案是VSR控制技术的一个新方向。
5 结论
本文对电压型PWM整流器控制方法进行了详细阐述,并对其进行科学分类,全面地分析了各种方法的原理及优缺点。在此基础上,针对VSR控制中存在的一些尚未完全解决的问题及不足,对其发展方向作了分析。可预见的是,随着整流行业及数字化技术的不断发展,VSR的应用前景将更为广阔。
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