Chi-Jui Wu

National Taiwan University of Science and Technology, Taipei, Taipei, Taiwan

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Publications (37)10.02 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The main purpose of this paper is to study the application of fuzzy modeling to the analysis of load characteristics in a power system. A fuzzy model is a set of fuzzy IF-THEN rules for describing system behavior. The method of fuzzy modeling is suitable for the analysis of load characteristic due to the nonlinear load curve. The Sugeno type fuzzy model is adapted in this paper. The fuzzy load model is capable of providing both quantitative and qualitative description for the customer under study and hence will be helpful to the task of analyzing load characteristic. Based on the fuzzy load model, we calculate the peak value, load factor, and consumption of the load curve to analyze the load characteristics. The effects of the fuzzy load model parameters on the load characteristics and load management strategies are also investigated.
    SICE Annual Conference (SICE), 2012 Proceedings of; 01/2012
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    ABSTRACT: This paper is to study the power system dynamic performance and the direct identification of coherent synchronous generators using fuzzy c-means clustering to the Taiwan power system (Taipower). The main purpose of this paper is to analyze dynamic performance of Taipower system and evaluate the influence of low frequency oscillation. And the application of fuzzy clustering approach is used to identify the coherent synchronous generators. The coherency measures are derived from the time-domain responses of generators in order to reveal the relations between any pair of generators. Then they are used as initial element values of the membership matrix in the clustering procedures. The paper is investigated to envelope an effective evaluation of dynamic performance and the characteristic of dynamic stability and is demonstrated to show the effectiveness of this clustering approach.
    SICE Annual Conference (SICE), 2011 Proceedings of; 01/2011
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    ABSTRACT: The N3 power plant of Taipower is located in the southern tip of Taiwan and connected to the power pool by four out-linking 345-kV overhead transmission circuits. There are two 951-MW generators. Each generator occupied 11% of the system peak load in 1985 when the generator was in commercial operation. Since Tai-power is an isolated system, at the N-2 conditions, those generators were reduced to 75% loading to protect the power system. By the way, to avoid damage of negative sequence current (NSC), the limits of the N3 power plant are stricter than those in the IEEE Standard. However, in 2010, the capacity ratio of each gen-erator in the plant to the system peak load has been reduced to 3% only. To increase the economic benefit of those generators, it is required to reassess the operation limits of NSC. EMTP was used to calculate the lev-els of NSC from the out-linking transmission circuits. From the results of this study, the effects of NSC could be ignored when the four out-linking circuits are in N-0, N-1, and N-2 conditions. The generators can be operated in full loading under these conditions. The modifications to the NSC limits of the N3 power plant are also suggested.
    01/2010;
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    ABSTRACT: Voltage instability of power system comes from increasing load rapidly, and causes bus voltage to drop. When voltage is out of control and it can be voltage collapse. This paper presents the fuzzy modeling approach to the description QV curve of power system for analysis of voltage stability. The QV curve can identify voltage stability limit, and it determine robustness of power system. The fuzzy system model is basically a collection of fuzzy IF-THEN rules that are combined via fuzzy reasoning for describing the features of a system under study. The method of fuzzy modeling has been proven to be well-suited for modeling nonlinear industrial processes described by input-output data. In view of the nonlinear characteristic of the QV curve, the method of fuzzy modeling is employed for representing the curve. Based on the Sugeno-type fuzzy model, various models with different numbers of modeling rules are used to describing the QV curve. It is found that such fuzzy model offers both quantitative and qualitative descriptions for the QV curve.
    01/2009;
  • Ping-Heng Ho, Chi-Jui Wu
    European Transactions on Electrical Power - EUR TRANS ELECTR POWER. 01/2009;
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    Ping-Heng Ho, Chi-Jui Wu
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    ABSTRACT: The 58.9-km, 161-kV Taiwan PengHu submarine power cable system (T-P-Cable), the first submarine project of the Taiwan Power Company (Taipower) in this level, will be commercially operated in 2012. It is important to analyze the transient behaviors before operation. It is necessary to find the operation strategy to deal with the transients in advance. The EMTP-ATP was used in this paper to analyze (1) the switched over voltage (SOV) in normal operation, (2) the slow front transients (SFT) voltage in fault contingency, (3) the transient inrush current (TIC) in energizing of the no-load transformers and shunt reactors, and (4) the transient recover voltage (TRV) in de-energizing the shunt reactors. The appropriate set of the surge protective device (SPD) to avoid the SOV and SFT has also been investigated. The results show that there is no TIC in energizing the no-load transformers and shunt reactors. The TRV across the current breaker (CB) contactors is higher than the system TRV when the shunt reactors are de-energized without using SPD. There is no re-strike on the CB contactors. The results of this study provide tremendous prior operation experience and advice for the Taipower.
    Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE; 08/2008
  • Chi-Jui Wu, Shu-Chen Wang
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    ABSTRACT: Effective and accurate calculation methods are presented to obtain the voltage flicker components and the 10-Hz equivalent value. By using the indirect demodulation method, the RMS values of a voltage waveform are calculated cycle by cycle to obtain the envelopment. Then the fast Fourier transform (FFT) is used to get the flicker components. The other method uses the instantaneous voltage vectors. After the voltage waveform of a phase is recorded, the discrete Fourier transform can be used to get the system frequency and magnitude. Then the other two phases are assumed perfectly sinusoidal to construct a virtual three-phase system. The instantaneous voltage vectors are calculated from the virtual three-phase voltages. Finally, the FFT is used to obtain the voltage flicker components from instantaneous voltage vectors. Some given waveforms and field measured waveforms of arc furnace loads with voltage flicker disturbances are used to show the goodness of these approaches.
    01/2008;
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    ABSTRACT: This paper is used to investigate a novel decentralized pole placement design of lead-lag power system stabilizers using hybrid differential evolution (HDE). Since only local speed deviations are used as the feedback signals, the decentralized stabilizers could be easily implemented. It wants to place the electromechanical modes within a designated region to have enough damping. Participation factors are used to select the site and number of stabilizers. If all electromechanical modes have been moved to the specified region at the convergent step, the objective function will reach a minimal value. The objective function is chosen to ensure the real parts and damping ratios of electromechanical modes. A test power system is used to reveal the goodness of this method. Several operating points can be considered simultaneously in the determination of stabilizer parameters to let the stabilizers work well under a wider range of operating conditions. The computation time and convergence characteristic of this approach are better, compared to the differential evolution and genetic algorithm. The coherency measures are also proposed to evaluate the relative behaviours between any pair of generators of the system with and without stabilizers.
    01/2008;
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    ABSTRACT: This paper presents a method for combining sequential neural-network approximation and orthogonal arrays (SNAOA) in the planning of large-scale passive harmonic filters. An orthogonal array is first conducted to obtain the initial solution set. The set is then treated as the initial training sample. Next, a back-propagation sequential neural network is trained to simulate the feasible domain for seeking the optimal filter design. The size of the training sample is greatly reduced due to the use of the orthogonal array. In addition, a restart strategy is also incorporated into the SNAOA so that the searching process may have a better opportunity to reach a near global optimum. To illustrate the performance of the SNAOA, a practical harmonic mitigation problem in a chemical plant is studied. The results show that the SNAOA performs better than the original scheme and satisfies the harmonic limitations with respect to the objective of minimizing the total demand distortion of harmonic currents and total harmonic distortion of voltages. Filter loss, reactive power compensation, and the constraints of individual harmonics are also considered. Additional results related to SNAOA are also reported and discussed as well.
    IEEE Transactions on Power Delivery 08/2007; · 1.52 Impact Factor
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    ABSTRACT: This paper describes the useful experiences about dynamic performance improvement of synchronous generators in the Tong-Shiao Generation Station of the Taiwan Power System. This work includes the dynamic performance test, parameter identification, and parameter retuning of static excitation systems (SESs). Since the hardware circuits of SESs had been modified, it caused the detuning of parameters so that the generators did not have enough ability to sustain large voltage fluctuation disturbances. Those SESs were temporarily retuned according to the results from simple field tests. However, step responses of field tests were different from those of computer simulations. Thus, the least-squared-error algorithm has been employed to estimate the parameters of inner-loop regulators in SESs. Finally, the hybrid differential evolution method was used to get suitable parameter values. The SESs of six gas-turbine generators have been retuned again and these have worked well till now. The experiences and results provide useful references.
    IEEE Transactions on Energy Conversion 07/2007; · 2.43 Impact Factor
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    ABSTRACT: This paper is to investigate the application of fuzzy c-means clustering to the direct identification of coherent synchronous generators in power systems. Because of the conceptual appropriateness and computational simplicity, this approach is essentially a fast and flexible method. At first, the coherency measures are derived from the time-domain responses of generators in order to reveal the relations between any pair of generators. And then they are used as initial element values of the membership matrix in the clustering procedures. An application of the proposed method to the Taiwan power (Taipower) system is demonstrated in an attempt to show the effectiveness of this clustering approach. The effects of short circuit fault locations, operating conditions, data sampling interval, and power system stabilizers are also investigated, as well. The results are compared with those obtained from the similarity relation method. And thus it is found that the presented approach needs less computation time and can directly initialize a clustering process for any number of clusters.
    01/2007;
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    Chi-Jui Wu, Yu-Jen Chen
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    ABSTRACT: A novel approach has been presented in this paper to calculate voltage flicker components precisely by using instantaneous voltage vectors. After the voltage waveform of a phase is recorded, the smart discrete Fourier transform can be used to obtain the system frequency and magnitude. Then, the other two phases are assumed perfectly sinusoidal to construct a virtual three-phase system. The instantaneous voltage vectors are calculated from the virtual three-phase voltages. Finally, the fast Fourier transform is used to obtain the voltage flicker components from instantaneous voltage vectors. The flicker components of the other two phases can be calculated by repeating the procedure. The flicker values of three phases are calculated individually and separately. The effects of jump-sampling, harmonics, power frequency shifting, and sampling rates are investigated. The calculation ability of this approach is compared with the traditional indirect demodulation method. Some given waveforms and field measured waveforms of arc furnace loads with voltage flicker disturbances are used to show the goodness of this approach. From the results, this approach could calculate flicker components accurately with short calculation time by using small size data. It also avoids the frequency leakage effect.
    IEEE Transactions on Power Delivery 08/2006; · 1.52 Impact Factor
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    ABSTRACT: This investigation examines and compares the loading characteristics and power factor values of V-V, Scott, and Le Blanc-connected transformers by a novel approach. Four definitions of power factor are compared-three considering harmonics and unbalances and one based only on fundamental components. A proper power factor value is needed to truly reflect the loading characteristics of these specially connected transformers, considering the influences of harmonics and unbalances. The computation results of the five given loading cases and two simulation cases demonstrate that the power factor values of V-V, Scott, and Le Blanc-connected transformers are different, even with the same loading on the load side. Since the V-V connection scheme has an inherent unbalanced structure, its performance in reducing the three-phase unbalance is substantially worse than that of the Scott and Le Blanc connection schemes, which can more effectively transform three-phase powers to two-phase powers. Additionally, a field measurement of the Le Blanc transformer in a substation of the Taiwan Railway System is also used to identify the contents of power factor definitions. The computation results reveal that the effective power factor could be recommended for use in fairly evaluating the load characteristics for specially connected transformers.
    IEEE Transactions on Power Delivery 08/2006; · 1.52 Impact Factor
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    ABSTRACT: This paper presents the application of fuzzy c-means (FCM) clustering in the order reduction of dynamic models for controller design in a power system. Based on the fuzzy c-means algorithm, a method is proposed for clustering the poles and zeros of the original power system model into new clusters from which a reduced-order model can be obtained. Then the reduced-order model is used to design a proportional-integral type power system stabilizer to improve the damping in system oscillation after a system disturbance. The reduced-order model can contain the critical dynamic characteristics of the original model, but let it easier to design the controller. Results from a sample power system are presented to show the validity of the proposed method. The electromechanical mode of the power system can be improved by the designed power system stabilier from pole assignment.
    01/2006;
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    ABSTRACT: This paper presents the fuzzy modeling approach to the description of wind turbine power curve. The fuzzy system model is basically a collection of fuzzy IF-THEN rules that are combined via fuzzy reasoning for describing the features of a system under study. The method of fuzzy modeling has been proven to be well-suited for modeling nonlinear industrial processes described by input-output data. In view of the nonlinear characteristic of wind turbine power curve, the method of fuzzy modeling is employed for representing the curve. Based on the Sugeno-type fuzzy model, various models with different numbers of modeling rules are used to describing the power curve which depicts the turbine output power under various wind speeds. It is found that such fuzzy model offers both quantitative and qualitative descriptions for the wind turbine power curve.
    01/2006;
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    Yung-Sung Chuang, Chi-Jui Wu
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    ABSTRACT: This paper is used to investigate a novel design of lead-lag type power system stabilizers for a multi-machine power system. In the design procedures, the minimum damping constants requirements of all of electromechanical modes can be designated and several typical operating conditions can be considered at the same time. The hybrid differential evolution (HDE) method is used to tune the parameters of power system stabilizers. In the design procedures, a region in the left half complex plane bounded by a line with a given negative real value is given. Thus, at the final step of the HDE, all of electromechanical modes should be moved to or near this region to have a smaller objective function value. In this paper, the objective function is chosen to let the design results have small real parts of electrome-chanical modes. Since the speed deviations are used as the feedback signals of the power system stabilizers, the stabilizers could be implemented easily. Because several operating conditions are con-sidered in the design of stabilizer parameter values, the damping forces are ensured effective in those operating conditions simultaneously. Nonlinear system time domain simulations are used to demonstrate the design results.
    Journal of Marine Science and Technology. 01/2006; 14:84-92.
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    Chi-Jui Wu, Yung-Sung Chuang
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    ABSTRACT: This paper is used to investigate the application of hybrid differential evolution (HDE) method in the design of output feedback power system stabilizers (PSSs) to enhance damping of electromechanical modes. The HDE is useful to get the parameters of PSSs to suppress oscillations of a power system subjected to disturbances. The PSSs have the output feedback configuration, and thus they could be implemented easily. In the design procedure, the objective function is chosen to ensure the real parts of electromechanical modes and/or the damping ratios. The searching for nearly global optimal solutions could be obtained and the computation time is short. The design purposes are to guarantee the damping effects of the entire power system. The effects of system loading are also considered. Nonlinear system time domain simulations are used to demonstrate the design results.
    Power Engineering Society General Meeting, 2005. IEEE; 07/2005
  • Ying-Pin Chang, Chi-Jui Wu
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    ABSTRACT: This paper is used to investigate the optimal multiobjective planning of large-scale passive harmonic filters for a multibus system under abundant harmonic current sources using the hybrid differential evolution (HDE) method. The migrant and accelerating operations embedded in HDE are used to overcome traps of local optimal solutions and problems of time consumption. The design purposes are to minimize the total demand distortion of harmonic currents and total harmonic distortion of voltages at each bus. Filters loss, fundamental reactive power compensation, and constraints of individual harmonics are also considered. The search for the global optimal solution is applied to the harmonic problems in a steel plant, where both ac and dc arc furnaces are used and a static var compensator is installed. Three design schemes are compared to demonstrate the performance of HDE. Finally, expectations of objective function are used to present the effects of filter parameter detuning and furnace loading uncertainty.
    IEEE Transactions on Power Delivery 02/2005; · 1.52 Impact Factor
  • Chi-Jui Wu, Yu-Jen Chen
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    ABSTRACT: An accurate computation algorithm has been presented in this paper to calculate the voltage fluctuation components of three-phase circuits. Three voltage vectors have been used and compared. After the voltage waveforms of three-phase circuits have been recorded, the voltage vectors are calculated. The jump-sampling approach is used to reduce data size for flicker calculation. Finally, the fast Fourier transform is used to obtain the voltage fluctuation components. The effects of harmonics and power frequency shifting are investigated. The calculation ability of this approach is valuable. Some given waveforms with voltage fluctuation disturbances are used to show the goodness of this approach. From the results, this approach is not influenced by harmonics or power frequency shifting, but also has satisfied accuracy. In general, the three-phase voltage fluctuation is equal to radic3 times of the average value of three phases. This approach provides a good method to track voltage fluctuation values of a three-phase system
    01/2005;
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    ABSTRACT: This paper uses field test methods to compare the dynamic stability of three types of excitation systems, static excitation systems, brushless rotating excitation systems, and digital excitation control system, at the Tong-Shiao Generation Station of the Taiwan Power System. Three electric arc furnaces in this area produce continuous disturbance of voltage flicker (voltage fluctuation). The dynamic performances of generators and effects of voltage flicker will be evaluated by a series of field tests and measurements. At first, the field measurement is taken by injecting a small step signal into the reference input of the excitation systems for the generators at no-load. The system responses are examined and compared with the IEEE standard 421.2 recommendation to check the stability conditions. The tests for the generators at on-load are repeated again. Then the outputs of the generators are continuously monitored during the operation of the electric arc furnaces. The dynamic characteristics of the generators with different excitation systems are compared to reveal the effect of voltage flicker.
    Power System Technology, 2004. PowerCon 2004. 2004 International Conference on; 12/2004

Publication Stats

58 Citations
73 Downloads
3k Views
10.02 Total Impact Points

Institutions

  • 2000–2008
    • National Taiwan University of Science and Technology
      • Department of Electrical Engineering
      Taipei, Taipei, Taiwan