Chi-Jui Wu

National Taiwan University of Science and Technology, T’ai-pei, Taipei, Taiwan

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Publications (60)39.72 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: The requirement of high quality electric power supply from utility is a common practice today. Thus, no matter in planning, designing, or system dispatching, it is desired to give un-interrupted electric power to customers. However, when the loading of a distribution system power feeder is too high or the feeder needs to be maintained, the feeder load should be transferred to other feeder. There are two types of feeder load transferring, interrupted and un-interrupted. The un-interrupted type means that the electric power supplied to customers will not be interrupted during feeder load transferring. However, there are several factors to affect the feeder current magnitude during load transferring, such as transformer impedances, primary side power level, and original loading of the feeder. If the current is too high, the feeder protection system will trip the feeder breakers to shut down the power supply system. A novel approach is presented to reduce the feeder current magnitude during load transferring. The phasor measurement units (PMU) will be used to obtain the synchronous voltage magnitude and phase angle of the transformers, of which feeders are transferred. A power conditioner is installed in the secondary side of the transformer. Then the phase angle values from the PMUs will be sent to the power conditioner and the suitable phase shifting will be used to reduce the phase angle difference between the two transformers. The simulation results show the feeder current magnitude will be greatly reduced during load transferring. The power supply reliability is raised.
    Proceedings of the 10th WSEAS international conference on Instrumentation, measurement, circuits and systems; 03/2011
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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: This paper examines and compares the voltage deviation, voltage unbalance, and harmonic distortion of V-V, Scott, and Le Blanc connected transformers by a novel approach. The power quality factors are needed to truly reflect the loading characteristics of these transformers. The computation results of several loading cases and simulation cases demonstrate the differences. The level of voltage unbalance of the V-V connection scheme is substantially worse than that of the Scott and Le Blanc connection schemes in normal operation. So the voltage deviation, voltage unbalance, and harmonic distortion are important indexes of power quality for these transformers.
    04/2010;
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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: This paper proposes a field-programmable gate array (FPGA)-based integrated circuit (IC) for computing apparent powers and power factors of power systems. In a nonsinusoidal and unbalanced three-phase power system, the calculation of apparent powers and power factors has many definitions. Load characteristics of harmonic and unbalance can not be expressed in the traditional apparent power and power factor, which only consider the fundamental and three-phase balanced sinusoidal conditions. This paper utilizes the FPGA chip to develop the platform to implement the calculation methods of apparent powers and power factors. The proposed design scheme is developed using the very high speed integrated-circuit hardware description language (VHDL), which provides high flexibility and technology independence. This paper discussed the effective power and power factor, the arithmetic power and power factor, and the fundamental power and power factor. The design of filters for the computation of fundamental frequency components is given. ModelSim is used at first to simulate the calculation of apparent powers and power factors to ensure the accuracy of timing and function. Research results show that the designed chip can compute accurately the apparent powers and power factors considering the effects of nonsinusoidal and unbalanced conditions.
    WSEAS Transactions on Circuits and Systems 07/2009; 8(7):559-568.
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    ABSTRACT: The application of data compression technique using the normalized embedded zero-tree wavelet (NEZW) coding is presented for the long-duration monitoring of a DC electric arc furnace, where voltage fluctuation and loading fluctuation are critical and stochastic load characteristics. While keep enough stochastic load information, it is desired to reduce data size in long duration recording of voltage and current waveforms. The effects of multi-resolution analysis levels and threshold values in the NEZW coding are investigated. From the calculation results of field measurement data, the NEZW coding almost preserves the values of voltage fluctuation and power quantities. For storage of the field measurement voltage and current waveforms, the NEZW coding can not only greatly reduce data size, but it also can preserve sufficient load information.
    Proceedings of the 8th WSEAS international conference on Instrumentation, measurement, circuits and systems; 05/2009
  • Ping-Heng Ho, Chi-Jui Wu
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    ABSTRACT: The 58.9 km, 161 kU 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. Copyright © 2009 John Wiley & Sons, Ltd.
    European Transactions on Electrical Power 01/2009; · 0.63 Impact Factor
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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;
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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
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    Shu-Chen Wang, Yu-Jen Chen, Chi-Jui Wu
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    ABSTRACT: This paper proposes a field-programmable gate array (FPGA)-based integrated circuit (IC) for measuring voltage flicker using the instantaneous voltage vectors. The proposed design scheme is developed using the very high speed integrated-circuit hardware description language (VHDL). The instantaneous voltage vector module, management module, and quantification modules are developed to construct the entire system. Some novel IP (intellectual property) cores, such as CORDIC and FFT, are used. Then the chip for voltage flicker calculation is designed based on these IP cores and is realized using a signal FPGA (XC3S1500). Some given simulation waveforms and field-measured waveforms with voltage flicker disturbances are adopted to demonstrate that the designed IC can obtain flicker components precisely.
    04/2008;
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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;
  • 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 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; · 3.35 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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    ABSTRACT: In this paper, electromagnetic interferences (EMI) occurred in electric power and telephone lines due to radiation at a frequency of 525 kHz from an aeronautical radio navigation station are presented. The induced voltages measured on those lines caused malfunction or even damage to some electrical devices inside the station. To understand those EMI effects further, an FDTD software package, XFDTD, was applied to evaluate the induced voltages. It was found that the major reasons resulting in interferences were due to longitudinally induced voltages and ground potential rises. They were caused by the radiation from the antenna of the station and current flowing through the ground grids, respectively. In addition, mitigation of EMI was performed to correct those problems by applying separate grounding systems, shielding the telephone, and using underground cables instead of overhead lines near the station. Currently, the whole system, including electric power, navigation and telephone, inside the station operates normally
    IEEE Transactions on Power Delivery 11/2006; · 1.52 Impact Factor
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    ABSTRACT: This paper presents the application to the identification of coherent generators in a power system based on the fuzzy c-means clustering. In view of the conceptual appropriateness and computational simplicity, the fuzzy c-means give a fast and flexible method for clustering analysis. At first, the coherency measures are derived from the time-domain responses of generators to reveal the relations between any pair of generators. Then the coherency measures are used as initial membership matrix in the fuzzy c-means clustering, which can let the clustering procedures converge quickly. An example power system is used to show the effectiveness of this method. The schemes of various number of generator clusters can be procured. The approach in this paper needs less iterative times and can directly begin a clustering procedure for any number of clusters.
    10/2006;
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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