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ABSTRACT: Due to the existence of reverse recovery time of power diodes, the clamp diodes and di/dt-chokes diodes of three-level NPC inverter will enter the reverse recovery region at the same time, and the partial over-circuit phenomena will occur. This problem limits the output power of inverter system and do harm to the devices. To avoid this over-current problem, a new circuit implementation of 6 kV three-level NPC inverter based on three phase individual DC-link is presented. Using this new circuit the partial over-current problem of traditional three-level NPC inverter can be solved. On the other hand, the security, stability and flexibility of three-level NPC inverter control system are much more complicated than traditional two-level system and low-voltage inverter. So the high reliability hardware and software based on layer organization structure has been put forward. This control scheme is realized with only a single FPGA chip and can provide an effective, flexible, and safe solution for high-power three-level NPC inverters. At last, some simulation and experimental results are presented to verify the advantages of the 6 kV three-level NPC inverters.
Communications, Circuits and Systems, 2009. ICCCAS 2009. International Conference on; 08/2009
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ABSTRACT: In this paper, the digital realization theory and key technologies of Multi-Level SPWM scheme implementation for the three-level neutral point clamped (NPC) inverter is presented. The digital asymmetrical regular sampling principle of SPWM is realized with only a single FPGA chip LFEC10 from LATTICE Inc. and the programming language is very high speed integrated circuit hardware description language (VHDL). This full digital circuit can provide an effective, flexible, and safe solution for high-power inverts. At last, some simulation and experimental results have been presented and discussed in this paper.
Communications, Circuits and Systems, 2007. ICCCAS 2007. International Conference on; 08/2007
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ABSTRACT: This paper gives out a detail analysis on the fuzzy zone about the differential protection based on sampled values (the sample differential protection in short). At first it gives a brief introduction about the sample differential protection and illuminates some basic rules about the sequential fulfilled zone R and the repeated fulfilled zone S. Based on the relationship among R S and their medially unfulfilled zone, it unprecedentedly decomposes all the combination values of R S and jV into three cases. Then it gives out the mathematics expressions about the boundaries and fuzzy zone of all three cases. For easily unstanding this paper presents the 3-D illustration about the boundaries and the fuzzy zone. After analyzing it gives out some useful conclusions about how to choose R and S. It also makes some comparisons about the reliability and sensitivity between the two differential protections.
Power System Technology, 2006. PowerCon 2006. International Conference on; 11/2006
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ABSTRACT: In this paper, a new circuit implementation of a multi-level sinusoidal pulse width modulation (SPWM) for three-level neutral point clamped (NPC) inverter is presented. The SPWM control scheme is realized with only a single FPGA chip LFEC10 from LATTICE, Inc. and the programming language is very high speed integrated circuit hardware description language (VHDL). The filed programmable gate array (FPGA) chip is incorporated in a digital signal processor (DSP) TMS320VC33. It receives the commands with specified amplitude, frequency, primary phase, min pulse width and dead time from DSP, and finishes the asymmetrical regular sampling principle of SPWM function independently. This circuit structure can provide an effective, flexible, and safe solution to high-power inverters. The output gating signals of the proposed circuit are used to control the inverters of the drive system of a 6 kV/1000 kW motor. The simulation and experimental results are given to verify the implemented SPWM control system
Universities Power Engineering Conference, 2006. UPEC '06. Proceedings of the 41st International; 10/2006
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ABSTRACT: Technology of short-circuited experiment of the power capacitors is crucial to transmit the energy efficiently with high stability and reliability. Research indicates that the equivalent circuit of the short-circuited experiment of the capacitors can be simplified as R-L-C under-damped loop. Experimental currents belong to pulsed waveforms. The measurement system centered on Rogowski coil is proposed to measure short-circuited currents of the measured capacitors. The operation principle of Rogowski coil is introduced. The proposed simulation model is composed of Rogowski coil, experimental capacitors and powering loop and load. The methods for optimizing coil's parameters are presented. The characteristics of the measurement system are analyzed. Simulation results based on the SIMULINK environment of MATLAB software is presented. The prototype CT centered on the proposed theory and design methods are presented. Simulation and experimental results can verify the validity of the measurement system
Transmission and Distribution Conference and Exhibition: Asia and Pacific, 2005 IEEE/PES; 02/2005
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ABSTRACT: Fault location using traveling wave has been applied in extra-high voltage power grids successfully. Due to its complication and high cost, it is not easy for this technique to be accepted for use in distribution system. A new traveling wave fault location system is developed simply in a cost-effective way for power networks (especially for distribution system) in this paper. Two traveling wave sensors are developed to capture the current traveling wave flowing from the capacitive equipment to earth and the voltage traveling waves in all three phases. The outputs of the sensors are then applied to the trigger and time tagging by using Global Position System (GPS) receiver. The fault position is calculated by the traveling wave arrival times in every power station where only one fault locator is installed. The fault location system is tested in the power system. Testing results show that the fault locator has high precision and robustness.
Industry Applications Conference, 2004. 39th IAS Annual Meeting. Conference Record of the 2004 IEEE; 11/2004
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ABSTRACT: When a genetic algorithm (GA) is used for power distribution network reconfiguration, it is important to improve coding and decoding techniques based on the characteristics of distribution networks in order to enhance the algorithm's efficiency. A loop coding technique is presented; it can efficiently reduce the length of a chromosome by taking out the branches (breakers) that are not included in any loops from the branches included in the chromosome. A new decoding technique is also proposed; it can be used efficiently to solve the objective function. A test computation is presented; it proves these techniques are efficient and practicable, and they can be used in power distribution network reconfigurations.
Universities Power Engineering Conference, 2004. UPEC 2004. 39th International; 10/2004
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ABSTRACT: In this paper the faults of EHV parallel connection reactor are introduced in brief. Then, the paper proposes a novel protection theory of interturn fault based on equivalent inductance, and sets up the computer protection model based on energy loss function. According to the protection model, this paper simulates the interturn fault, external fault, no-load operation fault etc. with EMTP program, the simulated results display that the protection algorithm is effective.
Electric Utility Deregulation, Restructuring and Power Technologies, 2004. (DRPT 2004). Proceedings of the 2004 IEEE International Conference on; 05/2004
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ABSTRACT: Power quality is influenced by neutral grounding methods in distribution systems. Optimization for neutral grounding methods is discussed in the paper. Petersen-coil in parallel with high resistance earthed technique has a better performance in safety and power quality than other neutral point grounding techniques. To improve power quality, a novel method for measurement of zero sequence impedance in distribution systems is presented, Petersen-coil inductance is adjusted to compensate the total capacitance, and the resistor which is in parallel with the Petersen-coil is adjusted to control the over-voltage; some other novel techniques for grounding fault feeder protection based on testing the fault resistance or the energy dissipated in the fault point are also presented. The method of Petersen-coil tuning has been developed. Experimental results show that the optimization for neutral grounding methods and the protections proposed can improve the power quality by reducing the over-voltage, the residual current and the grounding fault duration.
Electric Utility Deregulation, Restructuring and Power Technologies, 2004. (DRPT 2004). Proceedings of the 2004 IEEE International Conference on; 05/2004
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ABSTRACT: Many mining power systems utilize ineffectively grounded sources to restrict the residual current of single-phase earth fault in order to reduce outage and shock hazard. In practice, with the system expansion, topology changing, and insulation aging, the potential residual current and zero-sequence voltage for earth fault vary dynamically and some arcing earth faults can easily cause over-voltage and induce multiple faults. In order to improve the system safety, on-site condition monitoring, safety evaluation, and preventive maintenance for earth fault are proposed in this paper. Some techniques for online parameters measurement based on resonance-measurement principle are presented. Power system operation states are classified into normal secure state, alert state, incipient fault state, and fault state. Some security enhancement methods (preventive action and remedial action) for each state are implemented. The prototype for safety evaluation has been developed and installed in industry power systems for several years.
IEEE Transactions on Industry Applications 12/2003; · 1.66 Impact Factor
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ABSTRACT: This paper presents an adaptive overcurrent relay based on the principle of phase-to-phase differential currents, denominated as I˙<sub>AB</sub>, I˙<sub>BC</sub> and I˙<sub>CA</sub>, to detect phase fault of transmission and distribution line. The characteristics of phase- to-phase differential currents under phase fault condition are analyzed. The trip criterion and coordination principle are described. This relay is adaptive to the type of phase fault, the operating conditions of power system and the disconnection of PT. It can also provide an adaptive backup protection for the secondary-side overcurrent relay of a delta-wye transformer. Comparing with conventional overcurrent relays, this relay has a larger zone of protection and higher sensitivity.
Transmission and Distribution Conference and Exposition, 2003 IEEE PES; 10/2003
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ABSTRACT: The sampled value differential protection is described in this paper. The selections of S, R are investigated and the basic selective rule is to ensure that the restraint effectiveness of the sampled value differential protection be equal or superior to the corresponding phasor differential protection during external faults. The particular fuzzy operating zone of the proposed protection is also discussed and its expressions are presented. In addition, the phasor analyzing method, in which the phasor relationships of input currents of the protected system are used to represent the operating zone, fuzzy operating zone and restraint zone, is proposed to analyze the operating characteristic. The engineering applications and test results are also introduced.
Electrical and Computer Engineering, 2003. IEEE CCECE 2003. Canadian Conference on; 06/2003
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ABSTRACT: In order to get a reasonable simultaneity coefficient rather than one offered by the regulations and the design handbook, a statistical algorithm to computer the simultaneity coefficient based on the real-time data of the practical electrical network is presented in this paper. This algorithm uses the data of the typical consumers' load power from the power measurement system to compute the simultaneity coefficient. This kind of simultaneity coefficient can reflect the characteristic of a practical electrical network. The algorithm of simultaneity coefficient can be applied to power system planning and design, load forecasting and distribution automation.
Power System Technology, 2002. Proceedings. PowerCon 2002. International Conference on; 11/2002
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ABSTRACT: A new technique for long transmission line protection based on the balance of energy principle is described in this paper. It can distinguish between internal and external faults by comparing the net energy fed into the protected line in a short time interval. Energy is calculated by two different methods. The results calculated by EMTP show that under any condition of power system the proposed technique has excellent performance for the earth-fault distance protection under high-resistance earth-fault conditions and a short operation time.
Power System Technology, 2002. Proceedings. PowerCon 2002. International Conference on; 11/2002
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ABSTRACT: In order to avoid the disadvantages of conventional mechanical tap changing system and its influence on power system, a new on-load tap changing system with power electronic elements for power transformers is presented in this paper. The system is composed of main circuit, signal detection and triggering circuit design, choice of the thyristor switching, protecting transformer from overvoltage both in case of switching on and switching off no-load transformer. It possesses the inherent attributes of greater efficiency and less maintenance.
Power System Technology, 2002. Proceedings. PowerCon 2002. International Conference on; 11/2002
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ABSTRACT: In this paper, to solve the problem of communication between different type PLCs (programmable logic controllers) which implement different protocols. Firstly, the protocol conversion thought is laid out. On this basis, a general plant control system protocol converter model is presented. Secondly, the protocol converter is developed as one ActiveX control by the COM (component object model) technology, which gives many advantages to plant control system protocol converter of opening, security, easy update and visual parameter setting and so on. Finally, the protocol converter is used to realize protocol conversion between two different PLC protocols in a project.
Power System Technology, 2002. Proceedings. PowerCon 2002. International Conference on; 11/2002
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ABSTRACT: The performance of electric equipment can be influenced by many factors, so fuzzy logic and expert system methods are being introduced to resolve this problem and a maintenance analysis system based on fuzzy logic is founded. This system is an object-oriented one and the input information is affluent. Through applying information technology to make full use of information, it's possible to realize optimal maintenance of equipments. In this system, data are acquired and processed by local intelligent equipment. With careful consideration, planning and sharing of data, the information for condition monitoring system can be derived. Decision making can he accomplished by software programming. Through this way, the hardware and software configuration of the condition monitoring system can be simplified. And the pressure of data communication and processing in the system can be alleviated. The efficiency of information can be improved, too. An application system for substations is listed.
Transmission and Distribution Conference and Exhibition 2002: Asia Pacific. IEEE/PES; 11/2002
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ABSTRACT: As the main facility, the transformer plays an important role in the security of power system. The effectiveness of the differential relay used for protecting transformer against internal faults is undisputed. The introduction of microprocessor technology enabled multiple protection relays to be integrated into one protection platform, which has advantages when applied to transformer protection. A scheme for large capability transformer is brought forward in this paper, which applies differential protection principles to cooperate with one another, so that it can make a compromise with operating speed and sensitivity at the same time. This paper also provides an insight into the hardware and industry application experience.
Transmission and Distribution Conference and Exhibition 2002: Asia Pacific. IEEE/PES; 11/2002
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ABSTRACT: This paper introduces the new current differential protection based on instantaneous values. Firstly, some theory problems about the novel method are discussed, the operation equation of the protection is presented and its reliability effected by data window is analyzed. The main result obtained is that the width of the data window should be greater than π/2. Then, the paper discusses the special operation character of the novel protection that is called fuzzy zone. Some corresponding conclusions about the above discussion are given. Finally, the paper presents some practical application of the novel protection.
Transmission and Distribution Conference and Exhibition 2002: Asia Pacific. IEEE/PES; 11/2002
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ABSTRACT: Based on the analysis of the characteristics of some stator ground protection schemes, the protection schemes suitable for the generators in Three-Gorges Power Station are presented in this paper. To match the protection requirements of those generators, new protection schemes are suggested. Simulation and experimental results show that the protection schemes suggested in this paper can obtain higher sensitivity and reliability for the generators in Three-Gorges Power Station.
Power System Technology, 2002. Proceedings. PowerCon 2002. International Conference on; 02/2002
