Liangzhong Yao

China Electric Power Research Institute, Peping, Beijing, China

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Publications (91)31.41 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The transient stability analysis incorporating wind power intermittency and volatility is studied in this study. The wind turbines with doubly fed induction generator (DFIG) and direct-driven permanent magnet synchronous generator (PMSG) are considered, respectively, during analysis. In modelling of DFIG and PMSG, the default GE wind turbine model and the Western Electricity Coordinating Council generic wind turbine model are employed, respectively. Based on the Jensen model, which is applied to describe the wake effect in a wind farm located on flat terrain, an equivalent simplified model of a wind farm is established regarding wind farm layout. On the basis of the built wind farm model, the Monte Carlo simulation technique combined with two evaluation indices, namely angle-based margin index and critical clearing time (CCT) is applied on the IEEE 10-generator-39-bus test system and a real-sized China-Jiangxi power grid as a benchmark to exploit and explore the effects of wind power intermittency and volatility on power system transient stability. The frequency distributions of transient stability evaluation index, CCT, probability of system transient instability and the range of wind speeds causing system transient instability are simulated. In addition, the influence of wake effect on transient stability is discussed as well.
    IET Renewable Power Generation 01/2014; 8(5):509-521. · 1.72 Impact Factor
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    ABSTRACT: SUMMARY With the rapid development of wind power, the variability and uncertainty of wind power have brought new problems and challenges to the secure and stable operation of the power systems. In this paper, based on the deterministic power flow solution, the probability theory and fuzzy sets theory are employed to implement systematic and thorough studies on power system fuzzy power flow solution incorporating uncertainties of wind power from different types of wind turbines squirrel cage induction generator, doubly fed induction generator and permanent magnet synchronous generator. The Weibull distribution with specific parameters is adopted as wind speed probability density model. With the possibility/probability consistency principle, the probability distribution of wind speed can be transformed into the possibility distribution of wind speed. In accordance with the simplified power vs wind speed curve of wind turbine, and with consideration of wake effect of wind farm, the fuzzy modeling for power output of wind farm is then presented. The proposed fuzzy power flow model incorporating wind power variability and uncertainty is linearized further for simplicity. A sensitivity analysis based method is employed to solve the fuzzy power flow involving different power characteristics of wind turbines. Finally, simulations are carried out on a real-sized China's Jiangxi power grid, and some meaningful and important conclusions and comments are drawn based on the simulation results. Copyright © 2014 John Wiley & Sons, Ltd.
    International Transactions on Electrical Energy Systems 01/2014; · 0.63 Impact Factor
  • Zhou Jian, Libao Shi, Liangzhong Yao, Bazargan Masoud
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    ABSTRACT: In recent years, how to effectively assess the electric grid vulnerability in protecting against a malicious attack becomes one of the most challenging cutting-edge issues to be solved in power systems. This paper presents a framework to analyze the vulnerability of electric grid under different attack-defense scenarios based on the knowledge of game theory. Pure strategy and mixed strategy Nash Equilibrium corresponding to the attack-defense contest can be obtained by solving the payoff matrix under different pre-defined attack-defense scenarios. Based on the Nash Equilibrium, the vulnerability rankings of power grid components can be obtained and the vulnerability assessment can be conducted as well as the allocation plan of defense fund.
    2013 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC); 12/2013
  • Yue Zhao, Libao Shi, Liangzhong Yao
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    ABSTRACT: Based on an advanced distributed real-time platform named Real-Time Laboratory (RT-LAB), the impacts of the static synchronous compensator (STATCOM) on wind power system dynamics is studied in this paper. Firstly, a small-scale wind farm model based on squirrel-cage induction generator (SCIG) is built in MATLABTM/Simulink environment. This model is then rebuilt to be suitable for the real-time operation mode in RT-LAB environment in terms of the operating requirements of RT-LAB. The corresponding comparisons of simulation results carried out in RT-LAB and MATLABTM/Simulink environments respectively demonstrate that it is applicable for wind power system to implement real-time simulation in RT-LAB environment. Finally, the STATCOM device is connected to the power grid. And the comparisons of real-time simulation results of the wind power system with and without STATCOM connected illustrate that the integration of STATCOM can improve the voltage stability of the system.
    2013 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC); 12/2013
  • Source
    Liangzhong Yao
    Journal of Modern Power Systems and Clean Energy. 06/2013; 1(1).
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    Guoyi Xu, Lie Xu, Liangzhong Yao
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    ABSTRACT: The ability of an energy storage system to improve the performance of a wind turbine (WT) with a fully rated converter was evaluated, where the energy storage device is embedded in the direct current (dc) link with a bidirectional dc/dc converter. Coordinated dc voltage control design of the line-side converter and the energy storage dc/dc converters was proposed using a common dc voltage measurement for smoothing the output power. A transfer function and Bode diagram were introduced to analyze the system performance with different control parameters. MATLAB/Simulink simulations are presented to demonstrate the effectiveness of the proposed methods. It was found that the proposed methods smooth the power output from the WT to the grid and thus improve the quality of the generated power.
    Journal of Modern Power Systems and Clean Energy. 06/2013; 1(1).
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    ABSTRACT: This paper presents a search strategy to identify the chains of events that may lead to cascading failures in power systems. The genetic algorithm is applied to implement the search strategy in accordance with a proposed combined risk index incorporating severity and probability of contingency information. The system frequency characteristics are taken into account as well during analysis. Finally, the case studies are conducted to demonstrate the validity of the proposed model and method.
    TENCON 2013 - 2013 IEEE Region 10 Conference (31194); 01/2013
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    ABSTRACT: To describe the impact of uncertainties, such as fluctuation of bus loads and intermittent behavior of renewable generations, on the available load supply capability (ALSC) of distribution system accurately and comprehensively, this paper defines a series of meaningful indices for the probabilistic evaluation of ALSC. An efficient simulation method, Latin hypercube sampling-based Monte Carlo simulation (LHS-MCS), combined with step-varied repeated power flow method is proposed to compute the defined indices. Compared with simple random sampling-based Monte Carlo simulation (SRS-MCS), LHS-MCS is found to be more suitable for the probabilistic evaluation of ALSC. It can achieve more accurate and stable ALSC indices under relatively small sample sizes. The calculation speed of LHS-MCS is comparable with that of SRS-MCS under the same sample sizes, and the required CPU time of LHS-MCS is far less than SRS-MCS under the same calculation accuracy. Case studies carried out on the modified Baran & Wu 33-bus and the modified IEEE 123-bus distribution systems verify the feasibility of the defined indices and high performance of the proposed method.
    IEEE Transactions on Power Systems 01/2013; 28(3):3215-3225. · 2.92 Impact Factor
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    ABSTRACT: Conventional voltage vulnerability assessment methods and indices as well as weak area identification are one-sided and inconsistent with each other. Specially most of solutions are deterministic without considering the uncertainties in nature. Based on Super-Efficiency Data Envelopment Analysis (SEDEA) model, a multi-criteria integrated probabilistic voltage vulnerability assessment method is proposed in this paper. Three voltage vulnerability indices are selected for the assessment. Two integrated indices obtained by SEDEA model, Mean Voltage Vulnerability Index (MVVI) and Deviation Voltage Vulnerability Index (DVVI), are used to indicate the mean and deviation degree of bus voltage vulnerability respectively. By performing numerical simulations on IEEE standard test system, it can be concluded that the proposed method and indices are able to identify weak load buses comprehensively, effectively and objectively with random factors taken into account.
    Power and Energy Society General Meeting (PES), 2013 IEEE; 01/2013
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    ABSTRACT: In this paper, a multi-objective units start-up optimization strategy is proposed. In the proposed model, the economic factors during generator start-up are introduced into the conventional units start-up objective function. Furthermore, the system frequency characteristics as well as generator ramp constraints are considered during analysis. The greedy algorithm is employed to solve the proposed model. Finally, the case studies are carried out based on the IEEE 30-bus test system as benchmark to demonstrate the effectiveness and validity of the proposed model and method.
    TENCON 2013 - 2013 IEEE Region 10 Conference (31194); 01/2013
  • Dong Chen, Lie Xu, Liangzhong Yao
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    ABSTRACT: A stability and dynamic assessment method is proposed for converter interfaced DC networks. With the current loop modeled as a 1st order delay, an actively controlled DC terminal converter and its control can be modeled as a virtual impedance in S-domain. Terminal transfer functions can therefore be obtained using Thevenin's equivalent. Based on the modeling method, a case study concerning voltage variation suppression in a multi-terminal DC network is performed using root locus and open-loop margin analysis. The accuracy of the developed DC network model and its effectiveness for assessing system stability and dynamic performance is validated using circuit simulation in time domain.
    IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society; 01/2012
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    ABSTRACT: This paper proposes a novel integration of wind farm energy storage (ES) systems within microgrids. The main feature of the method is that the voltage and frequency control of the microgrid is shared by the wind generators through droop characteristics. Therefore, the control structure is suitable when the wind generators supply significant part of the load. The paper modifies the standard droop method in order to force the generators to share the load according to their available wind power and not just the generator rating. The paper focuses on islanded microgrid application; however, the method is applicable when there is a controlled connection to the main grid via a power converter, and also for HVDC connection. The proposed control methods are derived for doubly-fed induction generators (DFIGs) and validated using PSCAD/EMTDC simulations. The ride-through in case of a 3-phase fault on the local grid will also be simulated.
    IEEE Transactions on Smart Grid 01/2012; 3(2):728-737.
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    ABSTRACT: This paper presents a solution of optimal power flow (OPF) incorporating wind power. A paradigm for modeling the cost of wind-generated electricity from a wind farm is proposed. Based on the Weibull wind speed distribution and wind turbine model represented by function approximation, the frequency distribution of wind farm power output to be the basis for modeling wind generation cost is established via applying Monte Carlo simulation. The proposed wind generation cost model consists of the opportunity cost of wind power shortage and the opportunity cost of wind power surplus, which reflect the cost of dispatching additional reserve capacity and the cost of environmental benefit loss, respectively, and it is integrated into the conventional OPF program. Furthermore, the small signal stability constraints are considered simultaneously as well during optimization. A self-adaptive evolutionary programming method is employed to solve the OPF with wind power involved. A case study is conducted based on the IEEE New England test system (10-Generator-39-Bus) as a benchmark. The simulation results demonstrate the effectiveness and validity of the proposed model and method.
    IEEE Systems Journal 01/2012; 6(2):233-241. · 1.75 Impact Factor
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    ABSTRACT: Empirical mode decomposition (EMD) method is a novel time-frequency analysis tool to analyse non-stationary signals, which decomposes the signal concerned into intrinsic mode functions (IMFs) modulated in terms of both amplitude and frequency. The original version of EMD, however, suffers from an algorithm difficulty to separate two individual components, frequencies of which are within an octave. To improve the frequency resolution, a signal pre-processing method is used to shift the frequencies apart based on signal communication theory. This proposed frequency shift EMD has been successfully applied to extract modal parameters of low frequency oscillations for power systems. In this paper, this method is used to analyse the transient signals (inrush current) in the field of power transformer protection. Comparing with low frequency oscillation signals, these signals include more frequency components with faster dynamics. Numerical simulations are conducted to verify the frequency shift EMD. The results show that this method is adequate for time-varying waveform analysis for power transformer protection, and with the information provided by this frequency shift EMD, more robust protection schemes for power transformer could be proposed.
    Developments in Power Systems Protection, 2012. DPSP 2012. 11th International Conference on; 01/2012
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    ABSTRACT: Based on principle of energy saving generation dispatch(ESGD), both models considering emission trading and generation rights trading are built. To solve the model and increase global optimization search ability, improved PSO is proposed, with adaptively adjustment in inertial factor and particle correction strategy. Shanghai grid and East China grid are adopted as study case respectively. By programming in C++, generation schedule of coal-fired generators in 24-hour-period is achieved. Finally, the programming results verify feasibility of ESGD models and convergence of algorithm.
    Sustainable Power Generation and Supply (SUPERGEN 2012), International Conference on; 01/2012
  • Yue Zhao, Libao Shi, Yixin Ni, Liangzhong Yao
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    ABSTRACT: In this paper, an advanced distributed real-time platform named Real-Time Laboratory (RT-LAB) is introduced to implement the modeling and simulation of a wind farm. First, a simplified wind farm model based on squirrel-cage induction generator (SCIG) is built in MATLAB™/Simulink environment. This model is then transformed to be suitable for the real-time operation mode in RT-LAB environment according to the operating requirements of RT-LAB. Finally, the comparisons of simulation results carried out in RT-LAB and MATLAB™/Simulink environments respectively demonstrate that it is applicable for wind power system to implement real-time simulation in RT-LAB environment.
    Power and Energy Engineering Conference (APPEEC), 2012 Asia-Pacific; 01/2012
  • M. Fazeli, G.M. Asher, C. Klumpner, Liangzhong Yao
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    ABSTRACT: This paper proposes a novel integration of doubly fed induction generator (DFIG)-based wind farms within microgrids. The main and probably the best feature of this method is that the voltage and frequency of the microgrid are controlled by the wind generators through droop characteristics. Therefore, this control structure is quite suitable for cases where the wind generators supply significant part of the load. This paper will adjust the standard droop method in order to force the DFIG to share the load according to their available wind powers, not only their ratings. This paper focuses on microgrid application; however, the method is quite applicable for ac grid and HVdc link connections as well. The proposed control methods are validated using PSCAD/4.2.1 Professional/EMTDC simulations.
    IEEE Transactions on Energy Conversion 10/2011; · 3.35 Impact Factor
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    ABSTRACT: Since wind generation is one of the most mature renewable energy technologies, it will have the greatest share of future renewable energy portfolio. Due to the special characteristics of the wind generation, it requires extensive research to explore the best choice for wind power integration. In light of the practical project experience, this paper explores the feasibility of using HVdc transmission technology, particularly multiterminal HVdc (MTDC), as one of the preferable solutions to solve the grid interconnection issue of wind generation. This paper mainly focuses on the application of the hybrid MTDC to integrate wind farms into the electric power grid. A five-terminal hybrid MTDC model system including a large capacity wind farm is set up in PSCAD/EMTDC, in which the corresponding control strategy is designed. The operation characteristic of the hybrid system is studied, and the proposed control strategy is verified through simulation under various conditions, including wind speed variation and faults on ac side and dc side.
    IEEE Transactions on Industry Applications 05/2011; · 1.67 Impact Factor
  • V. Hamidi, Furong Li, Liangzhong Yao
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    ABSTRACT: Availability of wind energy which differs across locations primarily determines the appropriate location for installing windfarms. However, the grid location of windfarms must always be considered in an attempt to accurately quantify the benefits which can be achieved from windfarms during their lifetime operation to the supply network. The value of wind power is significantly affected by their penetration and concentration, and is further affected by their location within a network. This is because the location and penetration level of wind generation will result in a significant impact on power-flow distribution across the network. The objective of this paper is to measure the impact of grid location of windfarms on economic and operational parameters of a power system in the lifetime of a windfarm project. This paper first develops an assessment tool to quantify the economic and operational impact of wind power in the grid. This is followed by developing different scenarios in which different penetrations of wind power are installed at different locations in the grid, and it shows how the value of wind power is affected by location and network constraints.
    IEEE Transactions on Power Delivery 05/2011; · 1.52 Impact Factor
  • Source
    Libao Shi, Zheng Xu, Chen Wang, Liangzhong Yao, Yixin Ni
    From Turbine to Wind Farms - Technical Requirements and Spin-Off Products, 04/2011; , ISBN: 978-953-307-237-1

Publication Stats

431 Citations
31.41 Total Impact Points

Institutions

  • 2013–2014
    • China Electric Power Research Institute
      Peping, Beijing, China
  • 2011
    • Huazhong University of Science and Technology
      Wu-han-shih, Hubei, China
  • 2010
    • AREVA
      Lutetia Parisorum, Île-de-France, France
  • 1998–2010
    • Tsinghua University
      • • Graduate School at Shenzhen
      • • Institute of Nuclear and New Energy Technology
      Beijing, Beijing Shi, China
  • 2009
    • The University of Hong Kong
      • Department of Electrical and Electronic Engineering
      Hong Kong, Hong Kong
    • Shanghai Jiao Tong University
      • Department of Electrical Engineering
      Shanghai, Shanghai Shi, China
  • 2008–2009
    • University of Bath
      • Department of Electronic and Electrical Engineering
      Bath, ENG, United Kingdom
    • University of Birmingham
      • School of Electronic, Electrical and Computer Engineering
      Birmingham, ENG, United Kingdom
    • University of Strathclyde
      • Department of Electronic and Electrical Engineering (EEE)
      Glasgow, SCT, United Kingdom
  • 2006–2008
    • University of Nottingham
      • Department of Electrical and Electronic Engineering
      Nottingham, ENG, United Kingdom
    • Queen's University Belfast
      • School of Electronics, Electrical Engineering and Computer Science
      Belfast, NIR, United Kingdom
  • 2007
    • The University of Warwick
      • School of Engineering
      Warwick, ENG, United Kingdom