Advanced Materials Research Vols. 433-440

Abstract: There is a smoothing reactor and DC filter between the inverter and the direct current line to form a boundary in the HVDC transmission system. Since this boundary presents the stop-band characteristic to the high frequency transient voltage signals, the high-frequency transient voltage signal caused by external faults through boundary will be attenuated and the signals caused by internal faults will be unchanged. In this paper, a new technique in which the combination of the S–transform and support vector machine (SVM) is used to analyze the transient signals, is proposed for distinguishing internal faults from the external faults based on the significantly difference of high-frequency transient voltage on the point of protection.

Abstract: In recently years, the starting becomes the bottleneck problem of development for brushless DC motors without position sensors. One method, ‘Initial Rotor Position Estimation’, based on inductance variation can be used to start the motor with position feedback, but the performance is affected by the process of freewheeling. Therefore, this paper studies on the two freewheeling modes, which are the freewheeling mode through power and the mode not through power, in the universal three-phase bridge in the system of brushless DC motors. Besides, the paper analyzes the influence caused by different freewheeling modes. The analysis results show that the freewheeling mode through power is more suitable for the starting technique than the other one. On the basis above, the simulation carried out in MATLAB/Simulink verifies the validity of the theoretical analysis.

Abstract: This paper introduces a position synchronized control strategy to deal with the synchronous error caused by the external disturbance in dual linear motors servo system. In order to achieve satisfactory results, a new control scheme combing feedforward control, feedback control and cross-coupled control is proposed and makes progress in decreasing the synchronous error which was shown by the experiment.

Abstract: The thermal deformation of ram system in a heavy-duty CNC milling-boring machine tool has a serious effect on its accurateness. This paper analyses quantificationally the temperature field and deformation field of the ram system, and gives the ram’s heat sources, calculating quantity of heat and transferring type of heat. And then a finite element analysis is performed, the analyzing results provide basic theoretical data for thermal error compensation in machine tools.

Abstract: Three phase induction motors are employed in Textile mills, Agriculture and in almost all the machine tools. More than 60% of electrical energy generated being consumed by the induction motors. Hence, even a small contribution in the improvement of the power factor and efficiency will be cost effective. The power factor and efficiency of an induction motor is based on the shaft load and in order to improve the same, multi windings are suggested in the same stator. In multi winding induction machines, when one set of windings is connected to a three phase a supply, a revolving magnetic field of constant magnitude is developed in the air gap which is responsible to work as a conventional induction motor to meet the mechanical load and to develop a three phase EMF in the other winding that works as an Induction Alternator (IA).Double Winding Induction Motor (DWIM) also provides an opportunity to load each winding individually to its rated capacity. A small three phase load or a single phase load may be connected to the second set of winding. The dependency of separate supply for this load is eliminated. Hence, improvement in the efficiency, power factor and energy conservation is made possible in these machines. In order to validate the problem statement, a 3-phase, 3.0 kW, 415 V Double Winding Induction Motor(DWIM), a 3-phase, 3.0 kW, 415 V Double Winding Synchronous Reluctance Motor (DWSyRM), a 3-phase, 2.2 kW, 415 V Three Winding Induction Motor (TWIM) have been designed, fabricated and tested. Two controllers have been designed, one for a DWIM to operate the motor in power balancing and maximum efficiency modes of operation and other to operate TWIM at three different voltage levels depending upon the shaft load. In this paper, detailed comparisons of performances of three multi winding machines are presented.

Abstract: In this paper we proposed a new technique for identifying system stress due to the loading in wide area of power system based on the phasor angle difference behavior. The difference of voltage phasor angle between busses can be transferred in to a simple conversion and trigonometric wave signal during load increasing. Using Discrete Fourier Transform (DFT), the signal will be transformed into the spectral frequency. The proposed technique will analyzed current condition by visualized the level of stress and proximity to voltage stability limit in the system based on the change of spectral frequency . This method also can be used to monitor such loss of generators or transmission line outages. The result shown that the proposed technique is simple, fast and reliable, requiring minimum data measurement and be suitable for Wide Area Monitoring System.

Abstract: This two-part paper deals with the coordination of the control actions in a network of many interacting components, where each component is controlled by independent control agents. As a case study we consider voltage control in large electric power systems, where ever-increasing pressures from the liberalization and globalization of the electricity market has led to partitioning the power system into multiple areas each operated by an independent Transmission System Operator (TSO). Coordination of local control actions taken by those TSOs is a very challenging problem as poorly coordinated operation of TSOs may endanger the power system security by increasing the risk of blackouts. This coordination problem involves many other issues such as communication, abstraction and last but not least optimization. This first part of the paper is devoted to the principals of the coordination control, addressing some of those issues using as a case study the problem of coordination control for avoiding voltage collapse in large-scale multi-area power systems.

Abstract: This two-part paper deals with the coordination of the control actions in a network of many interacting components, where each component is controlled by independent control agents. As a case study we consider voltage control in large electric power systems where ever-increasing pressures from the liberalization and globalization of the electricity market has led to partitioning the power system into multiple areas each operated by an independent Transmission System Operator (TSO). Coordination of local control actions taken by those TSOs is a very challenging problem as poorly coordinated operation of TSOs may endanger the power system security by increasing the risk of blackouts. This second part of the paper presents simulation results on a 12-bus 3-area test system, using the distributed model predictive control paradigm in order to design a coordinating model-based feedback controller. Coordination requires that each agent has some information on what the future evolution of its power flows to and from its neighbors will be. It will be shown that how the communication between agents can avoid voltage collapse in circumstances where classical uncoordinated controllers fail.

Abstract: This paper presents the optimal and sizing of distributed generation (DG) placement in a radial distribution system for loss reduction. The main emphasis of this paper is to identify proper locations for installing DGs in a distribution system to reduce active power loss and improve bus voltages. Nevertheless, proper placement and sizing of DG units are not straightforward to be identified as a number of their positions and capacities need to be determined. It is therefore proposed in this paper to solve a DG placement problem based on a Tabu search algorithm. The objective function of the problem is to minimize the system loss subject to power flow constraints, bus voltage limits, pre specified number of DGs, and their allowable total installed capacity, and only one distributed generator for one installation position. The effectiveness of the methodology is demonstrated by a practical sized distribution system consisting of 69 bus and 48 load points. The results show that the optimal DG placement and sizing can be identified to give the minimum power loss while respecting all the constraints.

Abstract: Voltage sags and swells are the most common types of power quality disturbances. Often, voltage sags and swells caused by electrical fault in the power system. This allows devices that are installed in the power system damage. Therefore, we have generated voltage sags and swells to simulate events that occur in power systems for virtual reality. In this paper, voltage sags and swells generator (SSG) using the principles by d-, q-axis can be arbitrary control of the magnitude and phase of the injection voltage. The simulation results can confirm, the SSG can generate the arbitrary voltage sags/swells with in phase, phase lead or phase lag.