Journal of Shandong University(Engineering Science) ›› 2021, Vol. 51 ›› Issue (5): 53-62.doi: 10.6040/j.issn.1672-3961.0.2020.287

Previous Articles     Next Articles

Review and prospect of renewable energy ramp events

Xueshan HAN(),Xinyi WANG,Ming YANG*(),Yixiao YU   

  1. Key Laboratory of Power System Intelligent Dispatch and Control of Ministry of Education (Shandong University), Jinan 250061, Shandong, China
  • Received:2020-07-13 Online:2021-10-20 Published:2021-09-29
  • Contact: Ming YANG E-mail:xshan@sdu.edu.cn;myang@sdu.edu.cn

Abstract:

This article elaborated the wind and solar power ramp events from the three levels: the definition, prediction method and control strategy. The common definitions of wind and solar ramp were listed, and their advantages and disadvantages were analyzed in turn. It summarized the current mainstream prediction methods of ramp events, which were divided into direct method and indirect method according to whether the power prediction results were used, and the commonly used evaluation indicators were evaluated. It elaborated the current commonly used methods of control strategy, taking energy storage participation as a division, it was divided into finite control strategy without energy storage participation and infinite control strategy with energy storage participation. The current research problems and key research directions in the future were summarized and prospected.

Key words: wind power ramp event, solar power ramp event, ramp forecasting, finite control strategy, energy storage control

CLC Number: 

  • TM71

Fig.1

Ramp event"

Fig.2

Prediction method of ramp events"

Fig.3

Direct prediction of ramp events"

Fig.4

Indirect prediction of ramp events"

Table 1

Judgement for forecast result of ramp events"

类型 事件观测真 事件观测假 总计
事件预测真 TP FP 预测真
事件预测假 FN TN 预测假
总计 观测真 观测假

Fig.5

Stage control of ramp events"

Fig.6

Flow chart of coordination control based on game strategy"

Fig.7

Control model based on prediction-online optimization-feedback"

Fig.8

Control strategy with wind/solar-storage"

1 张东英, 代悦, 张旭, 等. 风电爬坡事件研究综述及展望[J]. 电网技术, 2018, 42 (6): 1783- 1792.
ZHANG Dongying , DAI Yue , ZHANG Xu , et al. Review and prospect of research on wind power ramp events[J]. Power System Technology, 2018, 42 (6): 1783- 1792.
2 TRUEWIND A. AWS Truewind's final report for the Alberta forecasting pilot project[R]. New York: Wind Power Forecasting PILOT Project, 2008.
3 KUSIAK A , ZHENG H , SONG Z . Wind farm power Prediction: A data-mining approach[J]. Wind Energy, 2009, 12 (3): 275- 293.
doi: 10.1002/we.295
4 KAMATH C. Understanding wind ramp events through analysis of historical data[C]//Proceedings of the IEEE PES Transmission and Distribution Conference and Exposition. New Orleans, USA: IEEE, 2010.
5 BOSSAVY A, GIRARD R, KARINIOTAKIS G. Forecasting uncertainty related to ramps of wind power production[C]//Proceedings of the European Wind Energy Conference & Exhibition. Warsaw, Poland: EWEC, 2010.
6 KAMATH C . Using simple statistical analysis of historical data to understand wind ramp events[M]. Livermore, USA: Lawrence Livermore National Security, 2010.
7 李芬, 李春阳, 闫全全, 等. 多时间尺度下光伏出力爬坡事件概率建模与评估研究[J]. 太阳能学报, 2019, 40 (11): 3289- 3298.
LI Fen , LI Chunyang , YAN Quanquan , et al. PV power ramp events probability modeling and assessment in multiple time scales[J]. Acta Energiae Solaris Sinica, 2019, 40 (11): 3289- 3298.
8 ZHENG Haiyang , KUSIAK A . Prediction of wind farm power ramp rates: a data-mining approach[J]. Journal of Solar Energy Engineering, 2009, 131 (3): 31011.
doi: 10.1115/1.3142727
9 KAMATH C. Associating weather conditions with ramp events in wind power generation[C]//2011 IEEE/PES Power Systems Conference and Exposition. Phoenix, USA: IEEE, 2011.
10 朱文立, 张利, 杨明, 等. 考虑日周期性影响的光伏功率爬坡事件非精确概率预测[J]. 电力系统自动化, 2019, 43 (20): 31- 40.
doi: 10.7500/AEPS20190131003
ZHU Wenli , ZHANG Li , YANG Ming , et al. Imprecise probabilistic prediction of photovoltaic power ramp event considering daily periodic effect[J]. Automation of Electric Power System, 2019, 43 (20): 31- 40.
doi: 10.7500/AEPS20190131003
11 SOTO W D , KLEIN S A , BECKMAN W A . Improvement and validation of a model for photovoltaic array performance[J]. Solar Energy, 2006, 80 (1): 78- 88.
doi: 10.1016/j.solener.2005.06.010
12 匡洪海, 王建辉, 张瀚超, 等. 一种新型的风电功率爬坡段识别方法[J]. 电网技术, 2019, 43 (5): 1752- 1759.
KUANG Honghai , WANG Jianhui , ZHANG Hanchao , et al. A novel wind power climbing section identification method[J]. Power System Technology, 2019, 43 (5): 1752- 1759.
13 甘迪, 柯德平, 孙元章, 等. 基于突变理论的风电爬坡多步预测[J]. 现代电力, 2016, 33 (3): 14- 21.
doi: 10.3969/j.issn.1007-2322.2016.03.003
GAN Di , KE Deping , SUN Yuanzhang , et al. Multi-step wind power ramp forecasting based on catastrophe theory[J]. Power System Technology, 2016, 33 (3): 14- 21.
doi: 10.3969/j.issn.1007-2322.2016.03.003
14 唐振浩, 孟庆煜, 曹生现, 等. 基于小波深度置信网络的风电爬坡预测方法[J]. 太阳能学报, 2019, 40 (11): 3213- 3220.
TANG Zhenhao , MENG Qingyu , CAO Shengxian , et al. Wind power ramp prediction algorithm based on wavelet deep belief network[J]. Acta Energiae Solaris Sinica, 2019, 40 (11): 3213- 3220.
15 ARIAS-CASTRO E , KLEISSAL J , LAVE M . A Poisson model for anisotropic solar ramp rate correlations[J]. Solar Energy, 2014, 101, 192- 202.
doi: 10.1016/j.solener.2013.12.028
16 刁浩然, 杨明, 韩学山, 等. 电力设备停运概率的非精确条件估计[J]. 中国电机工程学报, 2016, (19): 5134- 5144.
DIAO Haoran , YANG Ming , HAN Xueshan , et al. Imprecise estimation for conditional outage probabilities of power components[J]. Proceedings of the CSEE, 2016, (19): 5134- 5144.
17 GAN Di , KE Deping . Wind power ramp forecasting based on least-square support vector machine[J]. Applied Mechanics and Materials, 2014, 3044, 162- 166.
18 吴振威, 蒋小平, 马会萌, 等. 多时间尺度的光伏出力波动特性研究[J]. 现代电力, 2014, 31 (1): 58- 61.
doi: 10.3969/j.issn.1007-2322.2014.01.011
WU Zhenwei , JIANG Xiaoping , MA Huimeng , et al. Study on fluctuations characteristics of photovoltaic power output in different time scales[J]. Modern Electric Power, 2014, 31 (1): 58- 61.
doi: 10.3969/j.issn.1007-2322.2014.01.011
19 JIANG Quanyuan , WANG Haijiao . Two-time-scale coordination control for a battery energy storage system to mitigate wind power fluctuations[J]. IEEE Transactions on Energy Conversion, 2013, 28 (1): 52- 61.
doi: 10.1109/TEC.2012.2226463
20 叶林, 路朋, 滕景竹, 等. 考虑风电功率爬坡的功率预测-校正模型[J]. 电力系统自动化, 2019, 43 (6): 49- 56.
YE Lin , LU Peng , TENG Jingzhu , et al. Power prediction-correction model considering wind power ramp[J]. Automation of Electric Power Systems, 2019, 43 (6): 49- 56.
21 CUTLER N , KAY M , JACKA K , et al. Detecting, categorizing and forecasting large ramps in wind farm power output using meteorological observations and WPPT[J]. Wind Energy, 2007, 10 (5): 453- 470.
doi: 10.1002/we.235
22 崔明建, 孙元章, 柯德平. 基于原子稀疏分解和BP神经网络的风电功率爬坡事件预测[J]. 电力系统自动化, 2014, 38 (12): 6- 11.
doi: 10.7500/AEPS20130418003
CUI Mingjian , SUN Yuanzhang , KE Deping . Wind power ramp events forecasting based on atomic sparse decomposition and BP neural networks[J]. Automation of Electric Power Systems, 2014, 38 (12): 6- 11.
doi: 10.7500/AEPS20130418003
23 黄麒元, 王致杰, 杜彬, 等. 基于前置分解组合预测方法的风电功率爬坡预测研究[J]. 可再生能源, 2016, 34 (12): 1847- 1852.
HUANG Qiyuan , WANG Zhijie , DU Bin , et al. Wind power ramp forecasting based on the front decomposition combination forecast method[J]. Renewable Energy Resources, 2016, 34 (12): 1847- 1852.
24 欧阳庭辉, 查晓明, 秦亮, 等. 基于相似性修正的风电功率爬坡事件预测方法[J]. 中国电机工程学报, 2017, 37 (2): 572- 580.
OUYANG Tinghui , ZHA Xiaoming , QIN Liang , et al. Wind power ramp events forecast method based on similarity correction[J]. Proceedings of the CSEE, 2017, 37 (2): 572- 580.
25 王建辉. 风电场短期功率预测及爬坡识别方法研究[D]. 株洲: 湖南工业大学, 2019.
WANG Jianhi. Research on short-term power forecasting and slope climbing recognition method of wind farm[D]. Zhuzhou: Hunan University of Technology, 2019.
26 崔明建, 孙元章, 柯德平. 考虑电网侧频率偏差的风电功率爬坡事件预测研究[J]. 电力系统自动化, 2014, 38 (5): 8- 13.
CUI Mingjian , SUN Yuanzhang , KE Deping . Prediction method for wind power ramp events considering frequency deviation of power grid side[J]. Automation of Electric Power Systems, 2014, 38 (5): 8- 13.
27 李春, 卫志农, 孙国强, 等. 基于DFIG频率模型的风电功率爬坡事件预测方法[J]. 电网技术, 2016, 40 (3): 840- 846.
LI Chun , WEI Zhinong , SUN Guoqiang , et al. Wind power ramp prediction based on DFIG frequency model[J]. Power System Technology, 2016, 40 (3): 840- 846.
28 王勃, 汪步惟, 杨明, 等. 风电爬坡事件的非精确条件概率预测[J]. 山东大学学报(工学版), 2020, 50 (1): 82- 94.
WANG Bo , WANG Buwei , YANG Ming , et al. Imprecise conditional probability prediction of wind power ramp events[J]. Journal of Shandong University(Engineering Science), 2020, 50 (1): 82- 94.
29 郝正航, 余贻鑫, 曾沅. 改善电力系统阻尼特性的双馈风电机组控制策略[J]. 电力系统自动化, 2011, 35 (15): 25- 29.
HAO Zhenghang , YU Yixin , ZENG Yuan . A control strategy for increasing power system damping with wind turbine-driven doubly-fed induction generator[J]. Automation of Electric Power Systems, 2011, 35 (15): 25- 29.
30 廖勇, 何金波, 姚骏, 等. 基于变桨距和转矩动态控制的直驱永磁同步风力发电机功率平滑控制[J]. 中国电机工程学报, 2009, 29 (18): 71- 77.
doi: 10.3321/j.issn:0258-8013.2009.18.012
LIAO Yong , HE Jinbo , YAO Jun , et al. Power smoothing control strategy of direct-driven permanent magnet synchronous generator for wind turbine with pitch angle control and torque dynamic control[J]. Proceedings of the CSEE, 2009, 29 (18): 71- 77.
doi: 10.3321/j.issn:0258-8013.2009.18.012
31 乔颖, 鲁宗相. 考虑电网约束的风电场自动有功控制[J]. 电力系统自动化, 2009, 33 (22): 88- 93.
QIAO Ying , LU Zongxiang . Wind farms active power control considering constraints of power grids[J]. Automation of Electric Power Systems, 2009, 33 (22): 88- 93.
32 张昭遂, 孙元章, 李国杰, 等. 超速与变桨协调的双馈风电机组频率控制[J]. 电力系统自动化, 2011, 35 (17): 20- 25.
ZHANG Zhaosui , SUN Yuanzhang , LI Guojie , et al. Frequency regulation by doubly fed induction generator wind turbines based on coordinated over speed control and pitch control[J]. Automation of Electric Power Systems, 2011, 35 (17): 20- 25.
33 戚永志, 刘玉田. 风电高风险爬坡有限度控制[J]. 中国电机工程学报, 2013, 33 (13): 69- 75.
QI Yongzhi , LIU Yutian . Wind power high risk ramp limited control[J]. Proceedings of the CSEE, 2013, 33 (13): 69- 75.
34 KHODAYAR ME , SHAHIDEHPOUR M . Stochastic price-based coordination of intrahour wind energy and storage in a generation company[J]. IEEE Transactions on Sustainable Energy, 2013, 4 (3): 554- 562.
doi: 10.1109/TSTE.2012.2228284
35 梅生伟, 郭文涛, 王莹莹, 等. 一类电力系统鲁棒优化问题的博弈模型及应用实例[J]. 中国电机工程学报, 2013, 33 (19): 47- 56.
MEI Shengwei , GUO Wentao , WANG Yingying , et al. A game model for robust optimization of power systems and its application[J]. Proceedings of the CSEE, 2013, 33 (19): 47- 56.
36 戚永志, 刘玉田. 基于竞争博弈的风电爬坡协同控制策略[J]. 中国电机工程学报, 2014, 34 (25): 4341- 4349.
QI Yongzhi , LIU Yutian . Wind power ramping cooperative control strategy based on competitive games[J]. Proceedings of the CSEE, 2014, 34 (25): 4341- 4349.
37 夏雪, 戚永志, 刘玉田. 风机爬坡功率的有限度控制策略[J]. 电力系统自动化, 2014, 38 (20): 26- 32.
doi: 10.7500/AEPS20130608010
XIA Xue , QI Yongzhi , LIU Yutian . Limited control strategy of wind power ramp events[J]. Automation of Electric Power Systems, 2014, 38 (20): 26- 32.
doi: 10.7500/AEPS20130608010
38 崔阳. 计及载荷优化的风机爬坡控制研究[D]. 济南: 山东大学, 2015.
CUI Yang. Wind turbinr ramping control considering load optimization[D]. Jinan: Shandong University, 2015.
39 YOSHIMOTO K, NANAHARA T, KOSHIMIZU G. New control method for regulating state-of-charge of a battery in hybrid wind power/battery energy storage system[C]//Proceedings of IEEE Power Systems Conference & Exposition. Atlanta, USA: IEEE, 2006.
40 王伟, 薛金花, 叶季蕾, 等. 基于SOC调控的用于抑制光伏波动的电池储能优化控制方法[J]. 电力系统保护与控制, 2014, 42 (2): 75- 80.
WANG Wei , XUE Jinhua , YE Jilei , et al. An optimization control design of battery energy storage based on SOC for leveling off the PV power fluctuation[J]. Power System Protection and Control, 2014, 42 (2): 75- 80.
41 鲍雪娜, 张建成, 徐明, 等. 基于混合储能的并网光伏电站有功分级控制策略[J]. 电力系统自动化, 2013, 37 (1): 115- 121.
BAO Xuena , ZHANG Jiancheng , XU Ming , et al. Active power hierarchical control strategy of interconnected photovoltaic station based on hybrid energy storage[J]. Automation of Electric Power Systems, 2013, 37 (1): 115- 121.
42 JIANG Quanyuan , HONG Haisheng . Wavelet-based capacity configuration and coordinated control of hybrid energy storage system for smoothing out wind power fluctuations[J]. IEEE Transactions on Power Systems, 2013, 28 (2): 1363- 1372.
doi: 10.1109/TPWRS.2012.2212252
43 吴振威, 蒋小平, 马会萌, 等. 用于混合储能平抑光伏波动的小波包-模糊控制[J]. 中国电机工程学报, 2014, 34 (3): 317- 324.
WU Zhenwei , JIANG Xiaoping , MA Huimeng , et al. Wavelet packet-fuzzy control of hybrid energy storage systems for PV power smoothing[J]. Proceedings of the CSEE, 2014, 34 (3): 317- 324.
44 田立亭, 李建林, 程林. 基于概率预测的储能系统辅助风电场爬坡率控制[J]. 高电压技术, 2015, 41 (10): 3233- 3239.
TIAN Liting , LI Jianlin , CHENG Lin . Wind farm ramp rate control using energy storage based on probability prediction[J]. High Voltage Engineering, 2015, 41 (10): 3233- 3239.
45 付爱慧. 高渗透率光伏电网储能容量规划与优化控制研究[D]. 济南: 山东大学, 2018.
FU Aihui. Research on capacity planning and optimal control of BESS in a high photovoltaic penetration power grid[D]. Jinan: Shandong University, 2018.
46 ALAM M J E , MUTTAQI K M , SUTANTO D . A novel approach for ramp-rate control of solar PV using energy storage to mitigate output fluctuations caused by cloud passing[J]. IEEE Transactions on Energy Conversion, 2014, 29 (2): 507- 518.
doi: 10.1109/TEC.2014.2304951
47 黄麒元, 王致杰, 杜彬, 等. 基于前置分解组合预测方法的风电功率爬坡预测研究[J]. 可再生能源, 2016, 34 (12): 1847- 1852.
HUANG Qiyuan , WANG Zhijie , DU Bin , et al. Research on wind power grade ability prediction based on pre-decomposition combined forecasting[J]. Renewable Energy, 2016, 34 (12): 1847- 1852.
[1] Xiaoyan QI,Hengjie LIU,Qiuhua HOU,Xiaoyu LIU,Yanchao TAN,Liancheng WANG. Short-term load forecasting of iron and steel industry area based on combination model of SVM and LSTM [J]. Journal of Shandong University(Engineering Science), 2021, 51(4): 91-98.
[2] Xiaoming LIU,Yini CONG,Wenbo LI,Yutian LIU. Comprehensive decision-making method for large-scale photovoltaic system integrated to receiving-end power grid [J]. Journal of Shandong University(Engineering Science), 2019, 49(4): 115-122.
[3] Meng LIU,Taoyang XU,Changgang LI,Yue WU,Zhi WANG,Fangfang SHI,Jianjun SU,Guohui ZHANG,Kuan LI. Optimization of emergency load shedding of receiving-end power grid based on Particle Swarm Optimization [J]. Journal of Shandong University(Engineering Science), 2019, 49(1): 120-128.
[4] CONG Yini, CAO Zenggong, MU Hong, WANG Chunyi, LIU Yutian. Scheme analysis on GW-scale coastal mud flat PV system connected to power grid [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2017, 47(6): 77-82.
[5] LI Sun, WANG Chao, ZHANG Guilin, XU Zhigen, CHENG Tao, WANG Yiyuan, WANG Ruiqi. Short-term power load forecasting based on support vector regression [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2017, 47(6): 52-56.
[6] JI Xingquan, HAN Guozheng, LI Kejun, FU Rongrong, ZHU Yanghe. Application of improved K-means clustering algorithm based on density in distribution network block partitioning [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2016, 46(4): 41-46.
[7] ZHAO Kang, WANG Chunyi, YANG Dong, LIU Yutian. Short circuit current limiting optimization of ultra-high voltage receiving-end power grid [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2016, 46(4): 117-124.
[8] YU Songqing, HOU Chenghao, SUN Yingtao. Power demand forecasting in Shandong province with system dynamics [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2015, 45(6): 91-98.
[9] WANG Ming. Fault line selection method of distribution network based on the relative change rate in dominant bands [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2015, 45(4): 25-30.
[10] GAO Hong-Xia, XU Meng-Ming, LI Ge-Jun, TAN Shen-Yu. A new detecting method for the voltage sag source in a distribution system [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2009, 39(5): 115-119.
[11] LI Li,LIU Yu-tian . Out-of-step splitting scheme based on coherency identification and self-adaptive power system separation criteria [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2007, 37(6): 49-53 .
[12] NIU Xin-sheng,YE Hua,WANG Liang . SVC influences on the Shandong power system and the optimal locations [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2007, 37(4): 68-72 .
[13] JI Tao,GAO Xu/sup>,SUN Tong-jing,XUE Yong-duan/sup>,XU Bing-yin/sup> . Characteristic analysis of fault generated traveling waves in 10 Kv automatic blocking and continuous power transmission lines [J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2006, 36(2): 111-116 .
[14] SUN Donglei, ZHAO Long, QIN Jingtao, HAN Xueshan, YANG Ming, WANG Mingqiang. Bi-level planning of transmission network with solar-storage combination system based on learning theory [J]. Journal of Shandong University(Engineering Science), 2020, 50(4): 90-97.
[15] GE Weichun, LI Zhao, ZHAO Dong, LI Zhenyu, YE Qing, FU Yu, YU Na. Comprehensive benefits analysis of power supply side of regional power grid with electrode-type electric boiler [J]. Journal of Shandong University(Engineering Science), 2020, 50(5): 90-98.
Viewed
Full text


Abstract

Cited

  Shared   
  Discussed   
[1] WANG Su-yu,<\sup>,AI Xing<\sup>,ZHAO Jun<\sup>,LI Zuo-li<\sup>,LIU Zeng-wen<\sup> . Milling force prediction model for highspeed end milling 3Cr2Mo steel[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2006, 36(1): 1 -5 .
[2] ZHANG Yong-hua,WANG An-ling,LIU Fu-ping . The reflected phase angle of low frequent inhomogeneous[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2006, 36(2): 22 -25 .
[3] LI Kan . Empolder and implement of the embedded weld control system[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2008, 38(4): 37 -41 .
[4] SHI Lai-shun,WAN Zhong-yi . Synthesis and performance evaluation of a novel betaine-type asphalt emulsifier[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2008, 38(4): 112 -115 .
[5] KONG Xiang-zhen,LIU Yan-jun,WANG Yong,ZHAO Xiu-hua . Compensation and simulation for the deadband of the pneumatic proportional valve[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2006, 36(1): 99 -102 .
[6] LAI Xiang . The global domain of attraction for a kind of MKdV equations[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2006, 36(1): 87 -92 .
[7] YU Jia yuan1, TIAN Jin ting1, ZHU Qiang zhong2. Computational intelligence and its application in psychology[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2009, 39(1): 1 -5 .
[8] LI Liang, LUO Qiming, CHEN Enhong. Graph-based ranking model for object-level search
[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2009, 39(1): 15 -21 .
[9] CHEN Rui, LI Hongwei, TIAN Jing. The relationship between the number of magnetic poles and the bearing capacity of radial magnetic bearing[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2018, 48(2): 81 -85 .
[10] WANG Bo,WANG Ning-sheng . Automatic generation and combinatory optimization of disassembly sequence for mechanical-electric assembly[J]. JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE), 2006, 36(2): 52 -57 .