Advanced Materials Research Vols. 1070-1072

Abstract: Load-commutated inverters (LCIs) are the key starting device of wound-field synchronous motor. By detecting the rotor position and inputting a variable frequent current to the stator windings, the LCI can drive the motor from standstill to a given speed. Thus, rotor position detecting method comes to be the key techniques, but at the ultra-low speed period, the motor’s terminal voltage is too low to accurately sampling and is vulnerable to the interference, which brings risks to the variable frequency driving. In this paper, through analyzing the principles of LCIs and synchronous machine, a constant frequency electrical angle control methods is introduced to solve the difficulty of detecting the rotor position in the low speed period. A 98MW synchronous machine driven with an 18MW LCI are experimented in MATLAB and RTDS systems, the results show that the proposed control strategy can realize soft-start of the wound-field synchronous motor without detecting rotor’s position.

Abstract: In order to adapt the grid test study of distributed generation system, a multifunctional variable voltage and variable frequency power supply is proposed. The power supply could work in four quadrant operations, so that energy generated by distributed systems could flow into grid. The fundamental voltage and harmonic voltage are controlled respectively: multiple feedback loop control scheme is applied in fundamental mode and effective value feedback control scheme is applied in harmonic mode. The DSP and FPGA platform are used for implementing the system control and the experimental results show that the performance of the simulator is good and has high stability.

Abstract: This paper presents a method based improved particle swarm optimization optimizing PI control parameters. When the load changes, parallel active power filter, in the traditional PI control strategies, can not well control DC voltage fluctuations leading the deterioration of its dynamic performance. This paper proposes the improved particle swarm algorithm by increasing symbolic function of inertia weight parameter in particle swarm algorithm, and changing position of the random number in the speed update equation. The improved particle swarm algorithm can avoid "premature" or fall into local optimal solution, so it could get a more accurate solution set. Using improved particle swarm algorithm to solve PI controller optimization objective function, to get a more accurate PI control parameters. Simulation and experimental results show that mutations in the case load, the overshooting of an capacitor DC voltage compare with the traditional PI control reduces 5.5%, compared with Particle Swarm Optimization reduces 1.5%. Based on the simulation analyses and experimental results, it has been proved that this method can realize a comprehensive optimization.

Abstract: In order to overcome the large amounts of energy waste in the process of power battery discharge, the two-level grid-connected discharge inverter system of power battery based on LLC is designed. It is composed of LLC resonant full-bridge DC/DC and inverter. The DC-bus voltage is changed and the discharge current is stabilized by adjusting the frequency of the LLC resonant full-bridge DC/DC. The dual-loop control is applied in the inverter system. The stabilization of DC-bus voltage is achieved in the external voltage loop, while the grid-connected is implemented by controlling the grid-connected current in the inner current loop. A prototype is manufactured. The experiment results indicate that it has the characteristics of low harmonic current, high power factor and constant current discharge, and then proves that the inverter system is effective.

Abstract: The operational principle and topology of multi-level current source converter as well as its main advantages are introduced. According to the characteristics of SVG (Static Var Generator), a model of multi-level current source SVG is built up and simulated with PSCAD/EMTDC. The influences of model parameters on the performance of SVG are discussed in the form of dynamic and steady waveforms of system voltage and current. Simulation results display the feasibility of proposed control strategy and the excellent performance of multi-level current source SVG.

Abstract: Compared with the conventional transformer, high temperature superconducting (HTS) transformer can effectively improve the efficiency of the system. The current lead of HTS transformer is a main part that leads to leak out heat, and its thermal leakage loss greatly influents the performance of cryogenic system. So it is important to design and optimize the current lead. In this paper, the current lead of a 50MVA HTS transformer is designed, depended on the calculated conclusion of temperature field with FEM method, the optimization of the current lead is carried out to decrease heat losses.

Abstract: Giant magnetostrictive material (GMM) has the characteristics of big magneto-mechanical coupling coefficient, enormous strain and broad frequency response, which is widely used in audio and ultrasonic technology, ultra precision machining, testing technology, fluid control, vibration control and all kinds of sensors in recent years. This paper introduces some of the good qualities of GMM, compared with electromagnetic and piezoelectric materials, which are used extensively for bone conduction hearing device at present; a bow type giant magnetostrictive bone conduction pronunciation vibrator with simple structure and reliable performance is designed; the paper focuses on establishing the vibrator model and the simulation of ANSYS electromagnetics model; the radial magnetic field distribution is also analyzed. All the work provides reference for structure optimization and the selection of coupling materials for the vibrator.

Abstract: When Micro-grid (MG) is accessed into large scale of wind turbines, whose anti-peak-adjusting characteristic will increases difficulty of economic and safe operation about MG. The ability to participate in the system peak-adjustment of micro-turbine will be greatly limited, as the CHP run as “heat-load-based” mode and the electric power outputting depends on heat load demand. So that, installing heat boiler to absorb surplus wind power in the anti-peak-adjusting periods, and to combine with CHP supplying heat energy will decoupling “heat-load-based” constraint, and then the flexible schedulability of MG will be improved. The minimum operating cost of MG is regarded as optimizing object, Genetic Algorithm is used to optimize operational status of each unit in MG, then the heat and electricity comprehensive optimization is realized.

Abstract: In order to optimize the big data management of smart grid construction, analyze and process the extreme weather grid measuring point data of grid operation data which is abundant and discrete with mathematics. Considering of the continuous changing characteristics of weather in effective field of surface, buffer and expand the influential range of grid measuring point, then merge the same data, embellish the data with B-spline curve, store the spatial coordinates in enterprise-class grid resource centre, publish in map with unified service, and show the visual graphical distribution of extreme weather through OGC protocol, realize the visualization of grid resource.

Abstract: Reducing environmental pollution and achieving economic operation have become focus of the research about micro-grid (MG). The minimum operating cost and the minimum pollution emission cost are taken as optimizing objects, and the multi-object optimizing model of MG is established. The membership function is used to process multi-objective function, then the conversion of multi-object to single object is achieved. Genetic Algorithm is used to optimize the operating state of each unit, then the best operation mode is formed.