CN112994010B - 一种计及光伏出力波动的交直流混合配电网安全域计算方法 - Google Patents

一种计及光伏出力波动的交直流混合配电网安全域计算方法 Download PDF

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CN112994010B
CN112994010B CN202110110863.4A CN202110110863A CN112994010B CN 112994010 B CN112994010 B CN 112994010B CN 202110110863 A CN202110110863 A CN 202110110863A CN 112994010 B CN112994010 B CN 112994010B
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陈�胜
裴蕾
卫志农
孙国强
臧海祥
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Abstract

本发明提出了一种计及光伏出力波动的交直流混合配电网安全域计算方法,计及了电压约束、后备容量调节约束、馈线容量约束和关键设备出力约束,构建交直流配电网非线性安全域模型。其次,基于交直流配电网非线性优化运行模型,采用折半求解法获得一系列安全边界点。最后,采取凸包络拟合的方法生成可观测的安全域空间。算例结果验证了凸包络拟合法的合理性,同时评估了交直流混合配电网中换流器控制方式、换流器无功补偿和系统各区域负荷增长等因素对安全域大小的影响。

Description

一种计及光伏出力波动的交直流混合配电网安全域计算方法
技术领域
发明涉及一种计及光伏出力波动的交直流混合配电网安全域计算方法,属于交直流混合配电网运行与调度领域。
背景技术
近年来,国家倡导发展清洁能源,推进生态文明建设,进一步实现能源结构优化,新能源产业得到极大的扶持。随着分布式光伏(Photovoltaic,PV)在电网的渗透率越来越高,电动汽车(electric vehicle,EV)等直流负荷的日益增加,传统交流配电网正逐步演变为交直流混合配电网。相比于传统交流配电网,交直流配电网减少了部分换流环节,更有利于于分布式光伏的接入。分布式光伏的大量接入改变了配电网的潮流分布,间歇性光伏出力易导致配电网出现电压越限、潮流反转等问题。因此定量评估交直流混合配电网对光伏出力波动的接纳能力尤为重要。
安全性是配电网规划、优化和控制的关键,分布式光伏出力的不确定性给配电网的安全运行带来很大挑战。当前的研究存在一定的不足,主要包括三个方面。第一,配电网安全域定义为配电网运行中使所有节点均满足正常安全运行约束条件工作点的集合,描述了系统正常安全运行条件下工作点的最大出力范围,便于进行快速安全评估。但当前针对安全域的研究主要侧重交流配电网,而对于交直流配电网安全域模型的研究相对较少。第二,当前安全域的研究采用的主要是直流潮流线性模型,只考虑了馈线容量和主变容量的约束条件,而忽略了电压约束条件。交直流配电网潮流模型为非线性模型,当接入高比例新能源时配电网不确定性增加,容易出现无功补偿不完全充足和网络损耗较大的情况,配电网的安全运行(安全域)有必要计及电压幅值约束。第三,当前的配电网安全域研究未计及分布式光伏的随机性,将会造成运行控制策略过于乐观,或者构建的安全域无法真实刻画配电网的安全运行空间。第四,上述研究较多采用鲁棒优化等方法处理分布式光伏出力随机性带给配电网运行的影响,但是无法确切地评估配电网接纳光伏出力波动的能力,缺乏定量的刻画手段。
综上所述,本发明采用安全域定量刻画交直流混合配电网接纳光伏出力波动的范围,并提出了计及电压约束、后备容量调节约束、馈线容量约束和关键设备出力约束的交直流配电网安全域模型。其次,采取折半求解法获得一系列安全边界点。最后,采用凸包络法构建交直流混合配电网安全域。本发明所提交直流混合配电网安全域旨在为配电网应对间歇性光伏出力波动的能力评估提供参考。
发明内容:
发明目的:本发明所要解决的技术问题是为衡量配电网应对间歇性光伏出力波动的能力而提供一种计及光伏出力波动的交直流混合配电网安全域计算方法。
技术方案:本发明提供以下技术方案:一种计及光伏出力波动的交直流混合配电网安全域计算方法,在计算机中按以下步骤实现:
1)基于光伏出力日前预测值构建交直流混合配电网确定性优化调度模型;
2)根据确定性优化调度模型求解交直流混合配电网基准运行点;
3)考虑光伏的实时波动特性建立交直流配电网实时调整模型;
4)引入松弛变量,采用折半求解的方法获取安全边界点;
5)采用凸包络法拟合安全边界点,生成安全域空间;
6)输出交直流混合配电网光伏出力波动空间的安全域图像。
作为优化,所述步骤1)中:
交流配电网潮流模型为:
Figure BDA0002918908500000021
Figure BDA0002918908500000022
Figure BDA0002918908500000023
Figure BDA0002918908500000024
Figure BDA0002918908500000025
式中:Pij和Qij为支路ij的支路有功功率和无功功率,Pki和Qki为支路ki的支路有功功率和无功功率,Iki和Iij分别为支路ki和ij的支路电流,Uj和Ui为节点j和i的节点电压,
Figure BDA0002918908500000026
Figure BDA0002918908500000027
为注入节点i的有功功率和无功功率,
Figure BDA0002918908500000028
Figure BDA0002918908500000029
分别为交流电网分布式电源节点i有功出力和无功出力,
Figure BDA00029189085000000210
Figure BDA00029189085000000211
分别为节点i的有功负荷和无功负荷,
Figure BDA00029189085000000212
Figure BDA00029189085000000213
为馈线首端节点i有功出力和无功出力,
Figure BDA00029189085000000214
是换流器节点i注入的无功功率,
Figure BDA00029189085000000215
为换流器节点i注入有功功率,M(i)为交流电网中首节点为i的支路的末节点集合,N(i)为交流电网中末节点为i的支路的首节点集合,ΩAN为交流节点的集合,ΩAL为交流支路的集合,Rij和Rki为ij和ki的支路电阻,Xij和Xki为支路ij和ki的电抗。
交流配电网约束条件为:
Figure BDA00029189085000000216
Figure BDA00029189085000000217
Figure BDA00029189085000000218
Figure BDA0002918908500000031
Figure BDA0002918908500000032
式中,
Figure BDA0002918908500000033
Figure BDA0002918908500000034
分别为馈线首端节点i有功出力上下限,
Figure BDA0002918908500000035
Figure BDA0002918908500000036
分别为馈线首端节点i无功出力上下限,Sij,max为交流电网线路ij传输容量,
Figure BDA0002918908500000037
为交流侧光伏节点i有功出力预测值,
Figure BDA0002918908500000038
Figure BDA0002918908500000039
分别为交流侧光伏节点i的有功出力和无功出力,
Figure BDA00029189085000000310
为光伏的功率因数角,Ui,max和Ui,min分别为节点i电压的上下限,Ωsub和ΩADGN分别为馈线首端集合和交流侧光伏节点集合,
Figure BDA00029189085000000311
Figure BDA00029189085000000312
为馈线首端有功功率和无功功率备用调节容量。
直流配电网潮流模型为:
Figure BDA00029189085000000313
Figure BDA00029189085000000314
Figure BDA00029189085000000315
Figure BDA00029189085000000316
式中:X(i)为直流电网中首节点为i的支路的末节点集合,Y(i)为直流电网中末节点为i的支路的首节点集合,ΩDN为直流节点的集合,ΩDL为直流支路的集合,
Figure BDA00029189085000000317
为直流电网分布式光伏节点i有功出力。
直流配电网约束条件为:
Figure BDA00029189085000000318
Figure BDA00029189085000000319
Figure BDA00029189085000000320
式中:Pij,max为直流电网线路传输容量,
Figure BDA00029189085000000321
为直流侧光伏节点i有功出力预测值,
Figure BDA00029189085000000322
为直流侧光伏节点i的有功出力,ΩDDGN为直流侧光伏节点集合。
换流器数学模型为:
Figure BDA00029189085000000323
Figure BDA00029189085000000324
Figure BDA00029189085000000325
Figure BDA00029189085000000326
Figure BDA00029189085000000327
式中:
Figure BDA00029189085000000328
Figure BDA00029189085000000329
为交流支路ki的支路有功和支路无功,Rc和Xc为换流器等效电阻和电抗,
Figure BDA0002918908500000041
Figure BDA0002918908500000042
为换流器节点i注入有功和无功,ΩAVSCL为交流侧换流器支路集合,ΩVSCN为换流器节点集合,
Figure BDA0002918908500000043
为直流支路ji的支路有功,ΩDVSCL为直流侧换流器支路集合,
Figure BDA0002918908500000044
Figure BDA0002918908500000045
分别为VSC节点i无功补偿量的上下限,
Figure BDA0002918908500000046
Figure BDA0002918908500000047
为VSC节点i有功输出的上下限,
Figure BDA0002918908500000048
Figure BDA0002918908500000049
为换流器有功和无功备用调节容量,μ为直流电压利用率,换流器为SPWM调制方式下μ=0.866,M为换流器的调制比,Uc,i为换流器节点i的相电压,Udc,i为换流器节点i输出直流电压。
由于μ=0.866,0≤M≤1,所以式(A-22)可以等效为如下线性约束:
Figure BDA00029189085000000410
作为优化,所述步骤3)中:
针对光伏出力的随机性,需在确定性优化调度模型的基础上计及配网侧的实时调整,保证在光伏出力波动的情况下配电网新的运行点处于安全运行范围内。交直流配电网实时调整模型为:
Figure BDA00029189085000000411
实时调整过程中,
Figure BDA00029189085000000412
为光伏节点i有功出力,
Figure BDA00029189085000000413
为光伏节点i出力原始运行点,
Figure BDA00029189085000000414
为光伏节点i出力波动值,ΩDGN为光伏节点集合,
Figure BDA00029189085000000415
Figure BDA00029189085000000416
为馈线首端节点i原始出力运行点,
Figure BDA00029189085000000417
Figure BDA00029189085000000418
为馈线首端节点i有功和无功出力,
Figure BDA00029189085000000419
Figure BDA00029189085000000420
为换流器节点i有功无功原始出力运行点,
Figure BDA00029189085000000421
Figure BDA00029189085000000422
为换流器节点i有功无功出力;
同时采用同区域内各光伏出力波动量的差值平方和描述光伏出力相关性:
Figure BDA00029189085000000423
式中:
Figure BDA00029189085000000424
为第n台光伏机组出力波动值,δ为描述光伏出力相关性的常数。
作为优化,所述步骤4)中:
通过建立非线性规划模型求取安全边界点,建立如下优化模型:
Figure BDA00029189085000000426
Figure BDA0002918908500000051
时,
Figure BDA0002918908500000052
在安全域内,
Figure BDA0002918908500000053
时,
Figure BDA0002918908500000054
在安全域外,
Figure BDA0002918908500000055
为目标值,x,y为决策变量,ΩDSSR为安全域内的工作点集合,
Figure BDA0002918908500000056
为等式约束,
Figure BDA0002918908500000057
为不等式约束,s+和s-为松弛变量;
由于安全边界点一定在状态空间边界点和原点的连线上,采用折半求解法可求得安全边界点,安全边界点的搜索过程如下:
步骤1:根据后备调节容量约束条件确定光伏出力波动值的最大范围B,取状态空间边界点为交直流配电网的初始安全边界点
Figure BDA0002918908500000058
步骤2:选取一个正数ε,令tl=0,tu=1;
步骤3:求解非线性规划模型(A-26),若
Figure BDA0002918908500000059
输出最终安全边界点
Figure BDA00029189085000000510
迭代结束,否则进行步骤4;
步骤4:令t=0.5×(tl+tu),
Figure BDA00029189085000000511
求解非线性规划模型(A-26),得到最优解t*
Figure BDA00029189085000000512
步骤5:若tu-tl<ε,则迭代结束,输出最终安全边界点
Figure BDA00029189085000000513
否则,若
Figure BDA00029189085000000514
令tl=t*,若
Figure BDA00029189085000000515
令tu=t*,返回步骤4;
上述步骤中,t为比例系数,tu和tl为t的上下界,
Figure BDA00029189085000000516
为初始安全边界点,
Figure BDA00029189085000000517
为最终安全边界点,t*为t的最优解,
Figure BDA00029189085000000518
Figure BDA00029189085000000519
最优解。
作为优化,所述步骤5)中:
交直流配电网安全域定义为配电网运行中满足馈线容量约束条件、电压约束条件和后备调节容量约束条件的光伏出力波动运行点(即光伏实时出力与预测值的差值)的集合。则交直流配电网安全域内的工作点集合表示为:
Figure BDA00029189085000000520
采用凸包络法拟合安全边界点构建安全域空间,其本质为分段线性化拟合,不受拟合点数量的限制,构建高维安全域时仍有较好的拟合精度,凸包络为包含全部安全边界点的最小凸集,定义安全边界点集合为Y,安全边界点的凸包络表达式如下:
Figure BDA00029189085000000521
式中,δi为第i个分段系数,zi为第i个工作点,kz为边界点个数,z为工作点的线性组合。
有益效果:与现有技术相比,本发明的技术方案具有以下有益技术效果:
本发明采用安全域定量刻画交直流混合配电网接纳光伏出力波动的范围,并提出了计及电压约束、后备容量调节约束、馈线容量约束和关键设备出力约束的交直流配电网安全域模型。其次,采取折半求解法获得一系列安全边界点。最后,采用凸包络法构建交直流混合配电网安全域。本发明所提交直流混合配电网安全域有望为配电网应对间歇性光伏出力波动的能力评估提供参考。
附图说明:
图1:本发明方法流程图;
图2:交直流混合配电网算例拓扑结构图;
图3换流器不同无功补偿下的安全域;
图4换流器不同控制方式下配电网安全域;
图5不同区域负荷加重情况下配电网安全域图像。
具体实施方式:
下面结合附图和具体实施例,进一步阐明本发明,应理解这些实施例仅用于说明本发明而不用于限制本发明的范围,在阅读了本发明之后,本领域技术人员对本发明的各种等同形式的修改均落于本申请所附权利要求所限定的范围。
1交直流混合配电网安全域模型
1.1交直流混合配电网确定性优化调度模型
确定性优化调度模型由交流配电网、直流配电网和换流器的模型构成。
对于交直流配电网的确定性优化运行,采取网络损耗最小为目标函数,即
Figure BDA0002918908500000061
式中:Iij为支路ij电流,Rij为支路ij电阻,f为网络损耗。
交流配电网潮流模型为:
Figure BDA0002918908500000062
Figure BDA0002918908500000063
Figure BDA0002918908500000064
Figure BDA0002918908500000065
Figure BDA0002918908500000066
式中:Pij和Qij为支路ij的支路有功功率和无功功率,Pki和Qki为支路ki的支路有功功率和无功功率,Iki和Iij分别为支路ki和ij的支路电流,Uj和Ui为节点j和i的节点电压,
Figure BDA0002918908500000067
Figure BDA0002918908500000068
为注入节点i的有功功率和无功功率,
Figure BDA0002918908500000069
Figure BDA00029189085000000610
分别为交流电网分布式电源节点i有功出力和无功出力,
Figure BDA0002918908500000071
Figure BDA0002918908500000072
分别为节点i的有功负荷和无功负荷,
Figure BDA0002918908500000073
Figure BDA0002918908500000074
为馈线首端节点i有功出力和无功出力,
Figure BDA0002918908500000075
是换流器节点i注入的无功功率,
Figure BDA0002918908500000076
为换流器节点i注入有功功率,M(i)为交流电网中首节点为i的支路的末节点集合,N(i)为交流电网中末节点为i的支路的首节点集合,ΩAN为交流节点的集合,ΩAL为交流支路的集合,Rij和Rki为ij和ki的支路电阻,Xij和Xki为支路ij和ki的电抗;
式(B-2)-(B-4)为交流配电网支路潮流方程,式(B-5)为节点有功功率注入方程,式(B-6)为节点无功功率注入方程。
交流配电网约束条件为:
Figure BDA0002918908500000077
Figure BDA0002918908500000078
Figure BDA0002918908500000079
Figure BDA00029189085000000710
Figure BDA00029189085000000711
式中,
Figure BDA00029189085000000712
Figure BDA00029189085000000713
分别为馈线首端节点i有功出力上下限,
Figure BDA00029189085000000714
Figure BDA00029189085000000715
分别为馈线首端节点i无功出力上下限,
Figure BDA00029189085000000716
为交流电网线路ij传输容量,
Figure BDA00029189085000000717
为交流侧光伏节点i有功出力预测值,
Figure BDA00029189085000000718
Figure BDA00029189085000000719
分别为交流侧光伏节点i的有功出力和无功出力,
Figure BDA00029189085000000720
为光伏的功率因数角,Ui,max和Ui,min分别为节点i电压的上下限,Ωsub和ΩADGN分别为馈线首端集合和交流侧光伏节点集合,
Figure BDA00029189085000000721
Figure BDA00029189085000000722
为馈线首端有功功率和无功功率备用调节容量;
式(B-7)为馈线首端出力约束,式(B-8)为馈线容量约束,式(B-9)-(B-10)为光伏出力约束,式(B-11)为节点电压约束。
直流配电网潮流模型为:
Figure BDA00029189085000000723
Figure BDA00029189085000000724
Figure BDA00029189085000000725
Figure BDA00029189085000000726
式中:X(i)为直流电网中首节点为i的支路的末节点集合,Y(i)为直流电网中末节点为i的支路的首节点集合,ΩDN为直流节点的集合,ΩDL为直流支路的集合,
Figure BDA00029189085000000727
为直流电网分布式光伏节点i有功出力。
式(B-12)-(B-14)为直流流配电网支路潮流方程,式(B-5)为节点有功功率注入方程。
直流配电网约束条件为:
Figure BDA0002918908500000081
Figure BDA0002918908500000082
Figure BDA0002918908500000083
式中:Pij,max为直流电网线路传输容量,
Figure BDA0002918908500000084
为直流侧光伏节点i有功出力预测值,
Figure BDA0002918908500000085
为直流侧光伏节点i的有功出力,ΩDDGN为直流侧光伏节点集合。
式(B-16)为直流电网的馈线约束,式(B-17)为直流侧光伏出力约束,式(B-18)为节点电压约束。
换流器数学模型为:
Figure BDA0002918908500000086
Figure BDA0002918908500000087
Figure BDA0002918908500000088
Figure BDA0002918908500000089
Figure BDA00029189085000000810
式中:
Figure BDA00029189085000000811
Figure BDA00029189085000000812
为交流支路ki的支路有功和支路无功,Rc和Xc为换流器等效电阻和电抗,
Figure BDA00029189085000000813
Figure BDA00029189085000000814
为换流器节点i注入有功和无功,ΩAVSCL为交流侧换流器支路集合,ΩVSCN为换流器节点集合,
Figure BDA00029189085000000815
为直流支路ji的支路有功,ΩDVSCL为直流侧换流器支路集合,
Figure BDA00029189085000000816
Figure BDA00029189085000000817
分别为VSC节点i无功补偿量的上下限,
Figure BDA00029189085000000818
Figure BDA00029189085000000819
为VSC节点i有功输出的上下限,
Figure BDA00029189085000000820
Figure BDA00029189085000000821
为换流器有功和无功备用调节容量,μ为直流电压利用率,换流器为SPWM调制方式下μ=0.866,M为换流器的调制比,Uc,i为换流器节点i的相电压,Udc,i为换流器节点i输出直流电压。
由于μ=0.866,0≤M≤1,所以式(A-22)可以等效为如下线性约束:
Figure BDA00029189085000000822
式(B-19)-(B-20)为VSC潮流方程,式(B-21)和式(B-22)分别为无功补偿约束和VSC容量约束。式(B-23)为换流器两侧电压关系。
1.2交直流混合配电网实时再调度优化模型
针对光伏出力的随机性,在确定性优化调度模型的基础上计及配网侧的实时调整,保证在光伏出力波动的情况下配电网新的运行点处于安全运行范围内。交直流配电网实时调整模型为:
Figure BDA0002918908500000091
实时调整过程中,
Figure BDA0002918908500000092
为光伏节点i有功出力,
Figure BDA0002918908500000093
为光伏节点i出力原始运行点,
Figure BDA0002918908500000094
为光伏节点i出力波动值,ΩDGN为光伏节点集合,
Figure BDA0002918908500000095
Figure BDA0002918908500000096
为馈线首端节点i原始出力运行点,
Figure BDA0002918908500000097
Figure BDA0002918908500000098
为馈线首端节点i有功和无功出力,
Figure BDA0002918908500000099
Figure BDA00029189085000000910
为换流器节点i有功无功原始出力运行点,
Figure BDA00029189085000000911
Figure BDA00029189085000000912
为换流器节点i有功无功出力;
同时采用同区域内各光伏出力波动量的差值平方和描述光伏出力相关性:
Figure BDA00029189085000000913
式中:
Figure BDA00029189085000000914
为第n台光伏机组出力波动值,δ为描述光伏出力相关性的常数。
1.3交直流混合配电网安全域模型
交直流配电网安全域定义为配电网运行中满足馈线容量约束条件、电压约束条件和后备调节容量约束条件的光伏出力波动运行点(即光伏实时出力与预测值的差值)的集合。则交直流配电网安全域内的工作点集合表示为:
Figure BDA00029189085000000915
式中:ΩDSSR为安全域内的工作点集合,
Figure BDA00029189085000000916
为等式约束,
Figure BDA00029189085000000917
为不等式约束。式(B-27)表明安全域内任意光伏出力波动值下的交直流配电网都存在适当的实时再调度策略使其不违反安全约束条件,反之,安全域外光伏出力波动值下的交直流配电网实时再调度模型不可行。安全域刻画了交直流配电网最大可接受光伏出力波动范围,可用于衡量配电网接纳不确定性注入功率的能力。
2安全边界点的求解
通过建立非线性规划模型求取安全边界点,建立如下优化模型:
Figure BDA00029189085000000918
Figure BDA00029189085000000919
Figure BDA00029189085000000920
Figure BDA00029189085000000921
时,
Figure BDA00029189085000000922
在安全域内,
Figure BDA00029189085000000923
时,
Figure BDA00029189085000000924
在安全域外,
Figure BDA00029189085000000925
为目标值,x,y为决策变量,ΩDSSR为安全域内的工作点集合,
Figure BDA00029189085000000926
为等式约束,
Figure BDA0002918908500000101
为不等式约束,s+和s-为松弛变量。
由于安全边界点一定在状态空间边界点和原点的连线上,采用折半求解法可求得安全边界点,安全边界点的搜索过程如下:
步骤1:根据后备调节容量约束条件确定光伏出力波动值的最大范围B,取状态空间边界点为交直流配电网的初始安全边界点
Figure BDA0002918908500000102
步骤2:选取一个正数ε,令tl=0,tu=1;
步骤3:求解非线性规划模型(B-28),若
Figure BDA0002918908500000103
输出最终安全边界点
Figure BDA0002918908500000104
迭代结束,否则进行步骤4;
步骤4:令t=0.5×(tl+tu),
Figure BDA0002918908500000105
求解非线性规划模型(B-28),得到最优解t*
Figure BDA0002918908500000106
步骤5:若tu-tl<ε,则迭代结束,输出最终安全边界点
Figure BDA0002918908500000107
否则,若
Figure BDA0002918908500000108
令tl=t*,若
Figure BDA0002918908500000109
令tu=t*,返回步骤4;
上述步骤中,t为比例系数,tu和tl为t的上下界,
Figure BDA00029189085000001010
为初始安全边界点,
Figure BDA00029189085000001011
为最终安全边界点,t*为t的最优解,
Figure BDA00029189085000001012
Figure BDA00029189085000001013
最优解。
3算例分析
本发明测试算例采用改进的45节点环状交直流配电网系统,配电网拓扑结构如图2所示。交流电网电压等级为10kV,直流电网电压等级为±10kV,馈线首端载流量为3MVA,支路2-5载流量为1.5MVA,其他支路载流量为1MVA,光伏出力预测误差为30%。安全域边界点的求取(式(B-25)-(B-28))采用GAMS软件中的CONOPT求解器。
本发明设计对比了不同换流器无功补偿下交直流混合配电网安全域、换流器不同控制方式下交直流混合配电网安全域和不同区域负荷变化下交直流混合配电网安全域,并且验证了凸包络法拟合精度。对比分析结果如表1与图3-5所示,由该结果可知,换流器在系统无功不足时进行无功补偿,支撑系统电压,提高了配电网接纳光伏出力波动的能力。主从控制模式下的换流器优化了有功与无功控制参数,有效增大了安全域空间。此外,部分地区的安全域空间易受负荷增长的影响,需安装无功补偿设备以适应未来负荷的增长需求。以上计及光伏出力波动的交直流混合配电网安全域模型定量评估了交直流混合配电网应对间歇性光伏出力波动的能力,有望为配电网后续安全运行及规划设计提供参考。
表1凸包络发拟合精度
Figure BDA00029189085000001014

Claims (1)

1.一种计及光伏出力波动的交直流混合配电网安全域计算方法,其特征在于,该方法包括如下步骤:
(1)基于光伏出力日前预测值构建交直流混合配电网确定性优化调度模型;
(2)根据确定性优化调度模型求解交直流混合配电网基准运行点;
(3)考虑光伏的实时波动特性建立交直流配电网实时调整模型;
(4)引入松弛变量,采用折半求解的方法获取安全边界点;
(5)采用凸包络法拟合安全边界点,生成安全域空间;
(6)输出交直流混合配电网光伏出力波动空间的安全域图像;
所述步骤(1)中:
交流配电网潮流模型为:
Figure FDA0003416945650000011
Figure FDA0003416945650000012
Figure FDA0003416945650000013
Figure FDA0003416945650000014
Figure FDA0003416945650000015
式中,Pij和Qij为支路ij的支路有功功率和无功功率,Pki和Qki为支路ki的支路有功功率和无功功率,Iki和Iij分别为支路ki和ij的支路电流,Uj和Ui为节点j和i的节点电压,Pi inj
Figure FDA0003416945650000016
为注入节点i的有功功率和无功功率,Pi ADG
Figure FDA0003416945650000017
分别为交流电网分布式电源节点i有功出力和无功出力,Pi Load
Figure FDA0003416945650000018
分别为节点i的有功负荷和无功负荷,Pi sub
Figure FDA0003416945650000019
为馈线首端节点i有功出力和无功出力,
Figure FDA00034169456500000110
是换流器节点i注入的无功功率,Pi vsc为换流器节点i注入有功功率,M(i)为交流电网中首节点为i的支路的末节点集合,N(i)为交流电网中末节点为i的支路的首节点集合,ΩAN为交流节点的集合,ΩAL为交流支路的集合,Rij和Rki为ij和ki的支路电阻,Xij和Xki为支路ij和ki的电抗;
交流配电网约束条件为:
Figure FDA00034169456500000111
Figure FDA00034169456500000112
Figure FDA00034169456500000113
Figure FDA00034169456500000114
Figure FDA0003416945650000021
式中,
Figure FDA0003416945650000022
Figure FDA0003416945650000023
分别为馈线首端节点i有功出力上下限,
Figure FDA0003416945650000024
Figure FDA0003416945650000025
分别为馈线首端节点i无功出力上下限,Sij,max为交流电网线路ij传输容量,
Figure FDA0003416945650000026
为交流侧光伏节点i有功出力预测值,Pi ADG
Figure FDA0003416945650000027
分别为交流侧光伏节点i的有功出力和无功出力,
Figure FDA0003416945650000028
为光伏的功率因数角,Ui,max和Ui,min分别为节点i电压的上下限,Ωsub和ΩADGN分别为馈线首端集合和交流侧光伏节点集合,
Figure FDA0003416945650000029
Figure FDA00034169456500000210
为馈线首端有功功率和无功功率备用调节容量;
直流配电网潮流模型为:
Figure FDA00034169456500000211
Figure FDA00034169456500000212
Figure FDA00034169456500000213
Figure FDA00034169456500000214
式中:X(i)为直流电网中首节点为i的支路的末节点集合,Y(i)为直流电网中末节点为i的支路的首节点集合,ΩDN为直流节点的集合,ΩDL为直流支路的集合,Pi DDG为直流电网分布式光伏节点i有功出力;
直流配电网约束条件为:
Figure FDA00034169456500000215
Figure FDA00034169456500000216
Figure FDA00034169456500000217
式中:Pij,max为直流电网线路传输容量,
Figure FDA00034169456500000218
为直流侧光伏节点i有功出力预测值,Pi DDG为直流侧光伏节点i的有功出力,ΩDDGN为直流侧光伏节点集合;
换流器数学模型为:
Figure FDA00034169456500000219
Figure FDA00034169456500000220
Figure FDA00034169456500000221
Figure FDA00034169456500000222
Figure FDA00034169456500000223
式中:
Figure FDA00034169456500000224
Figure FDA00034169456500000225
为交流支路ki的支路有功和支路无功,Rc和Xc为换流器等效电阻和电抗,Pi vsc
Figure FDA00034169456500000226
为换流器节点i注入有功和无功,ΩAVSCL为交流侧换流器支路集合,ΩVSCN为换流器节点集合,
Figure FDA0003416945650000031
为直流支路ji的支路有功,ΩDVSCL为直流侧换流器支路集合,
Figure FDA0003416945650000032
Figure FDA0003416945650000033
分别为VSC节点i无功补偿量的上下限,
Figure FDA0003416945650000034
Figure FDA0003416945650000035
为VSC节点i有功输出的上下限,
Figure FDA0003416945650000036
Figure FDA0003416945650000037
为换流器有功和无功备用调节容量,μ为直流电压利用率,换流器为SPWM调制方式下μ=0.866,M为换流器的调制比,Uc,i为换流器节点i的相电压,Udc,i为换流器节点i输出直流电压;
μ=0.866,0≤M≤1,式(A-22)等效为如下线性约束:
Figure FDA0003416945650000038
所述步骤(3)中:
针对光伏出力的随机性,在确定性优化调度模型的基础上计及配网侧的实时调整,保证在光伏出力波动的情况下配电网新的运行点处于安全运行范围内,交直流配电网实时调整模型为:
Figure FDA0003416945650000039
实时调整过程中,Pi DG为光伏节点i有功出力,
Figure FDA00034169456500000310
为光伏节点i出力原始运行点,ΔPi DG为光伏节点i出力波动值,ΩDGN为光伏节点集合,
Figure FDA00034169456500000311
Figure FDA00034169456500000312
为馈线首端节点i原始出力运行点,Pi sub
Figure FDA00034169456500000313
为馈线首端节点i有功和无功出力,
Figure FDA00034169456500000314
Figure FDA00034169456500000315
为换流器节点i有功无功原始出力运行点,Pi vsc
Figure FDA00034169456500000316
为换流器节点i有功无功出力;
同时采用同区域内各光伏出力波动量的差值平方和描述光伏出力相关性:
Figure FDA00034169456500000317
式中:
Figure FDA00034169456500000318
为第n台光伏机组出力波动值,δ为描述光伏出力相关性的常数;
所述步骤(4)中:
通过建立非线性规划模型求取安全边界点,建立如下优化模型:
Figure FDA00034169456500000319
当r(x,y,ΔPi DG)=0时,ΔPi DG在安全域内,r(x,y,ΔPi DG)>0时,ΔPi DG在安全域外,r(x,y,ΔPi DG)为目标值,x,y为优化变量,包括电压幅值、线路电流线路功率、馈线首段出力及换流器节点功率,ΩDSSR为安全域内的运行点集合,h(x,y,ΔPi DG)为等式约束,g(x,y,ΔPi DG)为不等式约束,s+和s-为松弛变量;
由于安全边界点一定在状态空间边界点和原点的连线上,采用折半求解法可求得安全边界点,安全边界点的搜索过程如下:
步骤1:根据后备调节容量约束条件确定光伏出力波动值的最大范围B,取状态空间边界点为交直流配电网的初始安全边界点
Figure FDA0003416945650000041
步骤2:选取一个正数ε,令tl=0,tu=1;
步骤3:求解非线性规划模型(A-26),若r*(x,y,ΔPi DG)=0,输出最终安全边界点
Figure FDA0003416945650000042
迭代结束,否则进行步骤4;
步骤4:令t=0.5×(tl+tu),
Figure FDA0003416945650000043
求解非线性规划模型(A-26),得到最优解t*和r*(x,y,ΔPi DG);
步骤5:若tu-tl<ε,则迭代结束,输出最终安全边界点
Figure FDA0003416945650000044
否则,若r*(x,y,ΔPi DG)=0,令tl=t*,若r*(x,y,ΔPi DG)>0,令tu=t*,返回步骤4;
上述步骤中,t为比例系数,tu和tl为t的上下界,
Figure FDA0003416945650000045
为初始安全边界点,
Figure FDA0003416945650000046
为最终安全边界点,t*为t的最优解,r*(x,y,ΔPi DG)为r(x,y,ΔPi DG)最优解;
所述步骤(5)中:
交直流配电网安全域定义为配电网运行中满足馈线容量约束条件、电压约束条件和后备调节容量约束条件的光伏出力波动运行点的集合,即光伏实时出力与预测值的差值的集合,则交直流配电网安全域内工作点集合表示为:
ΩDSSR={ΔPi DG|h(x,y,ΔPi DG)=0,g(x,y,ΔPi DG)≤0} (A-27)
采用凸包络法拟合安全边界点构建安全域空间,其本质为分段线性化拟合,不受拟合点数量的限制,构建高维安全域时仍有较好的拟合精度,凸包络为包含全部安全边界点的最小凸集,定义安全边界点集合为Y,安全边界点的凸包络表达式如下:
Figure FDA0003416945650000047
式中,δi为凸包络中第i个分段系数,zi为第i个工作点,kz为边界点个数,z为工作点的线性组合。
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