电气工程学报, 2015, 10(6): 27-32 doi:

理论研究

双级矩阵变换器–统一潮流控制器预测控制策略研究

邓文浪, 余帅, 郭有贵, 刘和, 黄斯瑶

湘潭大学信息工程学院 湘潭 411105

Predictive Control Study on Unified Power Flow Controller Based on Two Stage Matrix Converter

Deng Wenlang, Yu Shuai, Guo Yougui, Liu He, Huang Siyao

Xiangtan University Xiangtan 411105 China

责任编辑: 郭丽军

收稿日期: 2015-01-19   网络出版日期: 2015-06-25

基金资助: 国家自然科学基金资助项目.  51277156

Received: 2015-01-19   Online: 2015-06-25

作者简介 About authors

邓文浪 女 1970年生,博士,教授,博士生导师,研究方向为电力电子变换和控制技术、矩阵变换器及其应用。

余 帅 男 1988年生,硕士研究生,研究方向为新型功率变换器及其控制技术、新能源发电技术。

摘要

双级矩阵变换器（TSMC）由于其优良的电气性能,在统一潮流控制器（UPFC）中具有较大的应用价值。本文首先分析了TSMC的双空间矢量调制策略（DSVM）,建立了TSMC-UPFC串联侧的预测模型,在此基础上提出了基于TSMC-UPFC串联侧电流预测控制策略。仿真研究表明,本文提出的控制策略对线路潮流具有很好的调节效果,可以快速、精确地跟踪参考值,超调量小,具有较好的动静态性能。

关键词： 统一潮流控制器 ; 双级矩阵变换器 ; 空间矢量调制 ; 预测控制

Abstract

Two stage matrix converter (TSMC) because of its excellent electrical performance, in unified power flow controller (UPFC) has great application value. This paper analyzes the space vector modulation strategy of two TSMC and predictive model was established on TSMC-UPFC series side, on the basis of the series side predictive current control strategy based on TSMC-UPFC is proposed. Simulation results show that the control strategy proposed in this paper has good adjustment effect on line flow, can quickly and accurately track the reference value, small overshoot, and has better dynamic and static performance.

Keywords： Unified power flow controller ; two stage matrix convertor ; space vector modulation ; predictive control

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本文引用格式

邓文浪, 余帅, 郭有贵, 刘和, 黄斯瑶. 双级矩阵变换器–统一潮流控制器预测控制策略研究. 电气工程学报[J], 2015, 10(6): 27-32 doi:

Deng Wenlang. Predictive Control Study on Unified Power Flow Controller Based on Two Stage Matrix Converter. Journal of Electrical Engineering[J], 2015, 10(6): 27-32 doi:

1 引言

统一潮流控制器（Unified Power Flow Controller,UPFC）是一种灵活、快捷且多功能的新一代柔性交流输电装置[1],综合了FACTS设备的多种灵活控制手段,包括电压电流调节、串联补偿及潮流控制等功能[2],其中快速、独立地控制输电线路中有功功率和无功功率潮流是UPFC一大特点,从而通过控制线路的潮流分布有效地提高了电力系统的可靠性、稳定性及灵活性[3,4]。

双级矩阵变换器（Two-Stage Matrix Converter,TSMC）是最近几年在（Conventional Matrix Converter,CMC）基础上发展起来的一种新型拓扑结构的矩阵变换器。TSMC具有结构简单、结构紧凑、能量可双向流动、可产生正弦输入电流和输出电压及输入功率因数角可调等优点,无须采用CMC复杂的4步换流法。由于上述优点,TSMC在UPFC中具有较大的应用价值[5]。

文献[6,7,8]提出的基于CMC的潮流控制策略均基于常规的PI闭环控制,控制效果一般,解耦效果不太好,响应比较慢。文献[9]中对基于CMC的UPFC展开研究,通过分析其标量模型提出了一种单环解耦控制策略,但精度不够高。文献[10]对基于CMC的UPFC采用了包含滑模控制的直接功率控制策略,但是控制策略较复杂。文献[11]构建三环控制系统：功率环、电压环和电流环,令电流跟踪电压的变化,使得系统的动、静态性能和稳定性得到了一定提升,但是由于采用过多环节,控制策略复杂。

预测控制处理复杂非线性、时变性和不确定性系统,建模方便,具有控制精度高、算法简单、对模型要求低等优点,能提高系统的鲁棒性,具有较好的动态控制效果。本文将预测算法引入TSMC-UPFC控制系统中,首先分析了TSMC的双空间矢量调制策略,接着建立了TSMC逆变级的预测模型,在此基数上提出了TSMC-UPFC串联侧逆变级的电流预测控制策略,最后建立了仿真模型对控制策略进行验证。仿真结果表明：所提控制策略有效地提高了TSMC-UPFC系统潮流控制的动静态性能,从而验证了所提控制策略的有效性[12]。

2 TSMC-UPFC电路结构及原理

TSMC-UPFC基本电路结构如图1所示,TSMC由整流级和逆变级两级变换电路构成,中间无滤波元件。TSMC整流级经并联变压器与电网连接,逆变级经串联变压器与电网连接。并联侧整流级为串联逆变级提供直流电压,提供其所需要的有功功率。串联侧逆变级通过调节串接在线路上的电压幅值,改变线路的有功功率和无功功率的流动,以达到控制潮流的目的[4]。

图1

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图1   基于TSMC的统一潮流控制器

Fig.1   Structure of UPFC based on TSMC


3 TSMC调制策略

UPFC中,TSMC整流级主要作用是给逆变级提供直流电压,为了防止逆变级开关上、下直通事故,要求整流级输出电压极性保持为正。

可以把输入三相电压的每一个周期都划分为六个区间,如图2所示。使每一个区间都有具有相同的特点：其中有一相的电压绝对值最大,另外两相电压的极性与之相反。

图2

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图2   六个区间的区分

Fig.2   Six intervals


将每个PWM调制周期分为两个部分,并分别在这两段时间内,将对应的两个极性为正且绝对值最大的线电压由直流侧输出,构成线电压的两个相电压瞬时比值即为每个线电压占空比。以第二区间为例,两个线电压分别为ubc、uac,对应的占空比计算公式为

在TSMC整流级在一个PWM周期内输出两级电压,以第二区间为例,一个PWM周期内整流级输出的电压在两时间段分别为ubc、uac,且开关频率大大高于输入电压频率,因此在一个PWM周期内的两个线电压可以看成常量,逆变级可以看作是在两时间段分别由ubc、uac供电的电压源逆变器。

而逆变级的6个开关可合成6个有效空间矢量和2个零矢量,可以组成8种不同开关状态如图3所示。括号内数字依次表示A、B、C三相桥臂上下开关的导通和关断情况,l表示与直流p点相连的开关处于导通状态,0表示与直流n点相连的开关处于导通状态[13]。

图3

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图3   逆变级空间矢量调制

Fig.3   The space vector modulation of inverter


设VJ为某一瞬间的输出线电压空间矢量,它落在六边形空间矢量中的某个区域内,其相对应两有效空间矢量为VM和VN,则VJ可由矢量VM和VN合成,其关系式为

式中,m0是逆变级的调制系数;θ是VJ和VM的夹角;dN、dM、d0分别是VM、VN、V0（零电压矢量）的占空比。在进行整流级零电流换流的情况下,可以将各时间段的开始和结尾部分时间分配给逆变级的零电压矢量,则TSMC在一个PWM周期内整流级和逆变级开关的协调控制如图4所示。

图4

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图4   两个时间段直流电压和开关矢量

Fig.4   The DC voltage in two portions and switchingvector sequence


4 TSMC串联侧逆变级的电流预测控制策略

4.1 线路潮流控制原理

在两相静止坐标下,根据瞬时功率理论,主线路上的有功功率和无功功率为

式中,u1α和u1β是线路母线电压值u1在静止坐标系下的α和β分量;i1α和i1β是线路电流值i1在静止坐标系下的α和β分量;po和qo分别是线路有功功率和无功功率。

考虑到母线电流和串联逆变器电流的关系,有

式中,n1和n2分别是串联变压器的一次侧和二次侧的电压比。

从而由式（4）和式（5）的关系可以得到

则由式（6）反变换可得

设给定有功功率和无功功率的参考值为po*和qo*,式（7）可得参考电流表达式为

由式（8）可知,通过控制TSMC逆变级输出侧电流（串联变压器二次电流）,从而改变一次侧的节点电压,可以实现对线路潮流进行控制。根据式（8）和给定潮流（线路参考有功功率和无功功率）可以求得逆变级参考电流。

4.2 预测电流控制策略

由KVL定理可得TSMC输出端的电压方程为

式中,u2表示网侧输入电压;us表示逆变级输出电压;i2表示逆变级输出电流;R和L分别表示逆变级输出侧滤波电路的电阻和电感。在αβ坐标系下,式（9）可以表示为

设采样周期为Ts,式（10）经离散化,得

本文采用无差拍预测电流控制[14,15,16],即在两相静止坐标系下,对TSMC的逆变级进行预测控制。将式（11）转化为

式中,i2α(k + 1)和i2β(k + 1)分别指第k + 1次采样周期时输入电流的采样值,这里分别用给定值i*2α和i*2β来代替,可得

u*sα和u*sβ作为空间矢量脉宽调制算法（SVPWM）的参考给定,由式（8）可得线路潮流给定值po*和qo*。控制框图如图5所示。图5中,Po*和Qo*分别表示有功功率和无功功率的参考值,us表示TSMC逆变级的输出电压,u2表示滤波后逆变级输出电压,u1表示主线路的检测电压,i2表示经过滤波后的TSMC逆变级输出电流,i1为主线路电流。通过逆变级电流预测控制得到线路目标输出功率。

图5

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图5   控制框图

Fig.5   The control diagram


TSMC与主电路并联的整流级采用空间矢量调制,把输入相电压作为调制信号,为逆变级提供直流电压,提供其所需要的有功功率。

5 仿真分析

利用Matlab/Simulink搭建TSMC-UPFC的系统模型。主要仿真参数如下：系统电网相电压为10kV,电网角频率为50Hz;线路中等效电阻为0.5Ω,电感为1mH;UPFC的并联部分（整流级）接入电网的并联变压器为Yd接法,一次、二次侧电压比为2.5∶1;UPFC的串联部分（逆变级）接入电网的串联变压器为Yd接法,一次、二次侧电压比为6∶8;输出滤波器的电感为1mH,电路等效电阻为0.03Ω。设定功率基准值为10MW。

（1）0~0.1s潮流给定为Pref = 0.1(pu),Qref = 0,0.1s潮流给定为Pref = 0.2（pu）,Qref = 0,仿真结果如图6和图7所示。

图6

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图6   线路有功功率和无功功率波形

Fig.6   The power waveforms of line


图7

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图7   线路A 相电压电流波形

Fig.7   Voltage and current waveforms of A phase


由图6可以看出,在0.1s之前,系统实际有功功率和无功功率值按照参考值准确输出,且波形较好。0.1s时有功功率参考值突变,无功功率参考值保持为0时,实际检测到的有功功率快速响应,暂态过程中有功超调量较小,且对无功功率影响很小,说明解耦效果较好。图7为在给定潮流情况下检测到的线路A相电压电流波形,从该图可以看到,0~0.1s时间段内电压电流波形正弦,相位保持一致。在0.1s有功功率变化后,电压电流波形依旧保持良好,无功功率保持为0。

（2）0~0.1s潮流给定为Pref = 0.15(pu), Qref =0,0.1s潮流给定改为Pref = 0.3(pu), Qref = 0.1(pu),仿真结果如图8和图9所示。

图8

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图8   线路有功功率和无功功率波形

Fig.8   The power waveforms of line


图9

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图9   线路A 相电压电流波形

Fig.9   Voltage and current waveforms of A phase


由图8可以看出,有功功率和无功功率同时变化时,相互不干扰,解耦性能好。图9为该条件下的线路A相电压电流波形。

（3）设置：0.05s之前,给定有功功率参考值为0.1(pu),无功功率为0。0.1s开始给定有功功率为0.2(pu),无功功率参考值保持为0。本文在上述条件下进行了电流环分别采用PI控制和预测控制的仿真实验。图10为电流环采用PI控制时线路潮流变化图。从图10可以看出,PI控制响应时间慢,有功超调量较大。图11为采用预测控制系统仿真波形,与PI控制相比,有功功率超调量很小、响应快速、波形平稳,有功功率和无功功率之间相互影响非常小,具有更好的动静态性能。

图10

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图10   采用PI 控制的系统有功功率和无功功率波形

Fig.10   Waveforms of power waveforms under PI control


图11

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图11   采用预测控制的系统有功功率和无功功率波形

Fig.11   Waveforms of power under predictive control


6 结论

本文分析了TSMC双空间矢量调制策略,建立了UPFC中TSMC逆变级的数学模型,在此基础上提出了UPFC串联侧的TSMC逆变级的电流预测控制策略。该控制方法使得有功功率和无功功率独立控制,较好地实现了解耦,系统具有较好的动静态性能,且控制简单灵活,便于数字化实现。

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三相Boost并网逆变器工作在直流输入电压小于电网电压峰值的场合，具有输入电压调节范围宽的优良特性，适合用于燃料电池、光电池等可再生能源系统的单级并网发电。提出一种三相Boost并网逆变器网侧电流的离散时间预测控制。该方法在每一个采样周期内，利用逆变器输出电流的离散时间模型和逆变器产生的7种电流空间矢量，预测逆变器下一个采样周期的网侧电流，并以该电流与理想网侧电流的误差最小作为优选指标，确定下一个采样周期的开关信号。该方法不需要传统Boost逆变器控制中的任何调制策略，方法简单，实现容易。实验结果表明，采用离散时间预测控制的三相Boost逆变器并网系统具有优良的并网性能。

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