A control scheme is described to charge series-connected super capacitors for photovoltaic generation systems. Based on the features of the super capacitors charge, the control scheme consists of three modes, i.e., th...
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A control scheme is described to charge series-connected super capacitors for photovoltaic generation systems. Based on the features of the super capacitors charge, the control scheme consists of three modes, i.e., the constant current charge mode, the constant power charge mode, and the constant voltage charge mode. The shift of three modes can be realized by controlling the duty of IGBT in the Boost-Buck converter system. Meanwhile, the high voltage, which is more suitable for application, can be obtained. Compared with the normal charge method with series-connected current-limiting resistance and the charge method with the constant current charge mode and the constant voltage charge mode, the proposed charging control scheme can shorten the charging time and improve the usage of the electric power generated from the PV arrays. The advantage described above is verified by simulations.
This paper puts forward an auxiliary fuzzy logic controller for the Voltage Source Converter based HVDC transmission system, VSC-HVDC, to improve the stability of the AC/ DC system by damping the oscillation effective...
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This paper puts forward an auxiliary fuzzy logic controller for the Voltage Source Converter based HVDC transmission system, VSC-HVDC, to improve the stability of the AC/ DC system by damping the oscillation effectively after disturbance. The fast control capability of the VSC-HVDC and the process of area mode oscillations are analyzed. No detailed model of the system is required for the design of the proposed control scheme. The controller judges the operation states and the control effect and accordingly adjusts its active power order in an adaptive way by using fuzzy rules, so as to damp out the area mode oscillation. Simulation results on the IEEE 4-generator AC/DC powersystems have shown that the controller can enhance the dynamic stability of interconnected powersystems effectively and is robust to the variation of system operating conditions and oscillation modes.
Thyristor controlled series capacitor (TCSC) used in power transmission line can increase the transportability and the stability of system, and decrease the system loss significantly. At the same time, TCSC brings man...
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Thyristor controlled series capacitor (TCSC) used in power transmission line can increase the transportability and the stability of system, and decrease the system loss significantly. At the same time, TCSC brings many serious problems to transmission lines fault location and protective relaying. This paper analyzes the influence of TCSC to EHV transmission line protection, especially to the high-frequency directional protection. It can be obtained from the analyzing that the addition of TCSC to EHV transmission line would make the high-frequency directional protection unwanted operation or failure to operate. In order to solute the problems TCSC caused, this paper presents a novel transient protection scheme based on wavelet transform (WT). The simulation tests have proved that the analyzing and solution of the appearance of TCSC in EHV transmission line are correct.
This paper proposes a fault classification scheme for transmission lines based on spectrum of fault component. First it analyses the spectrum of fault component, then the characters of power frequency and nature frequ...
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This paper proposes a fault classification scheme for transmission lines based on spectrum of fault component. First it analyses the spectrum of fault component, then the characters of power frequency and nature frequencies in two data windows are used to identify fault type and fault phase respectively. The scheme performance was proven using ATP/EMTP simulations in a 500-kV powersystem considering different fault types and fault locations. The results show that the scheme works quickly and is not impacted by harmonics and the DC offset. It is also not sensitive to sampling rate and fault inception angle.
The IEC 61400-25 standard has defined mapping of power plant information model to Web services. How to ensure the security of Web services-based communication for wind power plants is a unsolved problem. WS-security i...
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The IEC 61400-25 standard has defined mapping of power plant information model to Web services. How to ensure the security of Web services-based communication for wind power plants is a unsolved problem. WS-security is a standard used to deal with the security requirement in application of Web services, while username/password and X.509 certificates are security tokens most commonly used in electric power utility. We propose a security mechanism that deal with the requirements of authentication, integrity, non-reputation, and confidentiality across the communication process based on WS-security and the two security token. The security mechanism is implemented by extension of SOAP message, design of security agent, and the related security message processing algorithm. An instance is modeling based on IEC 61400-25 to demonstrate the security enhanced remote control of wind power plants. The result support the usefulness of the security mechanism for Web Services-based wind power plants communication.
When faults occur in transmission lines, the high frequency signals are caused by fault generated traveling waves and the spectrum is a series of harmonic in frequency domain. This paper utilizes lumped and distribute...
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When faults occur in transmission lines, the high frequency signals are caused by fault generated traveling waves and the spectrum is a series of harmonic in frequency domain. This paper utilizes lumped and distributed parameter models to express transmission lines respectively, analyzes the character of nature frequencies. Different influencing factors including different fault conditions, source impedance, bus capacitance, series compensated capacitance and shunt reactor are discussed in this paper. The results have been proven by ATP procedure in a typical 500- Kv power transmission line.
With the start of trial operation of direct purchasing electricity for large consumers in China, the method on how to price electricity is of vital theoretical and practical significance. Hedonic electricity pricing m...
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In the extra high voltage (EHV) transmission system, the transient single-phase to ground faults are the most frequent to occur. Even after the opening of breakers in the two sides of the fault line, an induced curren...
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In the extra high voltage (EHV) transmission system, the transient single-phase to ground faults are the most frequent to occur. Even after the opening of breakers in the two sides of the fault line, an induced current still exists in the arc because of the electrostatic and the electromagnetic coupling from the other two sound phases. Along with the enhancement of the voltage grade, the influence of the secondary arc becomes more and more, and may probably lead to the failure of the reclosing if the secondary arc is not extinguished promptly. In this paper, the dynamic secondary arc model (including recovery voltage and the secondary arc current) in single-phase asymmetric breaking is established based on the distribution parameters of EHV long-line. The method of twice-mode transformation is adopted to calculate the steady-state value of the secondary arc current and recovery voltage. Furthermore, the affects of different overhead line models on the secondary arc current are also analyzed through the real time digital simulation.
With the rapid development of electric electronic technology, non-linear loads, large capacity converters, etc. increase mostly, which brings about the serious problems such as harmonics. Thus, the traditional power t...
With the rapid development of electric electronic technology, non-linear loads, large capacity converters, etc. increase mostly, which brings about the serious problems such as harmonics. Thus, the traditional power theory based on the average is unable to meet with the practical require. In this paper, the power definition in the sinusoidal and non-sinusoidal circuit is discussed and the waveform similarity between voltage and current is analyzed due to the criterion of minimum mean square deviation. Furthermore, the relationships among the waveform similarity factor, displacement power factor and real power factor are also discussed. The results show that power components are well analyzed in use of waveform similarity under the conditions of non-sinusoidal. At the same time, waveform similarity provides a simple but effective method for the calculation of power factor.
This paper discussed the characteristics of power disturbances, and then proposed new classifying method. Disturbances are classified into two main categories, ldquocontinuous typerdquo and ldquoevent typerdquo. Conti...
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This paper discussed the characteristics of power disturbances, and then proposed new classifying method. Disturbances are classified into two main categories, ldquocontinuous typerdquo and ldquoevent typerdquo. Continuous type disturbances typically include voltage deviation, power frequency deviation, unbalance, flicker and harmonics. Event type disturbances (ETD) include voltage sags (including short duration interruptions), outages, and transients. Based on the classification of power disturbances and traditional distribution reliability indices (SAIDI, CAIDI, SAIFI, CAIFI, and ASAI), Voltage sag indices coordinate interruption events indices were proposed: 1) SASDI and CASDI, 2) SASFI and CASFI. The comprehensive index ASAI*, a corrected ASAI, was defined based on SAIDI and SASDI coordinate of the economic losses of customers impacted by event type disturbances. The assessment model of ETD was proposed. The model represents the defined indices, the calculating procedure, the phase aggregation, and the time aggregation, which are four basic factors to rightly assessment power quality. A case study was used to testify the comprehensive method was reasonable and feasible.
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