http://hdl.handle.net/10397/898 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5703 Title: Application of linear switched reluctance actuator in active suspension systems<br/><br/>Authors: Zhang, Zhu<br/><br/>Abstract: Electromagnetic active suspension system is attracting more and more attention due to recent advances in motor design, power electronics and modern control method. Compared to the hydraulic active suspension system, it is more energy-efficient, and has a faster dynamic response. In this thesis, a novel configuration of linear switched reluctance actuator (LSRA) is proposed for the application in active suspension system. The robust construction, low manufacturing and maintenance cost, less thermal problem, good fault tolerance capability and high reliability in harsh environments make LSRA attractive alternative to permanent magnet actuator. In order to determine the requirements on actuator design, the effects of suspension parameters on system characteristics are analyzed by the frequency response Bode plots method. A Linear Quadratic Regulator (LQR) controller is developed and simulated with the quarter-vehicle model to obtain the optimal force requirement on LSRA. By considering the requirements and constraints, a novel configuration of LSRA that comprises of four double-sided modules is proposed. The whole design procedure, ranging from the determination of basic actuator parameters to the calculation of flux linkage and force characteristics, is demonstrated in this thesis. The accuracy of the analytical design is then verified by the finite element method (FEM). Besides, the longitudinal and transversal end effects of double-sided LSRA are evaluated by analyzing the sensitivities of translator position and excitation current.; To improve the performance of designed actuator, a multi-objective optimization method to obtain higher average force, reduced force ripple and higher force density is proposed in this thesis. Some practical constraints are taken into consideration in the optimization procedure. The effects of stator and translator pole width on the three optimization criteria and the actuator volume are analyzed. Based on the optimized specification, a prototype of the proposed LSRA was fabricated. The flux linkage and force characteristics were measured to verify the theoretical design. Finally, an improved direct instantaneous force control (DIFC) scheme for four-quadrant operation of the proposed LSRA is developed. The controller incorporates adaptive force distribution function (FDF), instantaneous force estimation, hysteresis force controller and on-line determination of switching positions. By introducing the on-line estimated force of outgoing phase to FDF, the force demand of incoming phase is adaptively adjusted. Hence, the force ripple can be minimized over a wider range of switching positions. On the other hand, the operational efficiency is improved by on-line optimizing the switching positions according to the force demand. The simulation and experimental results demonstrate the effectiveness of the proposed control scheme.<br/><br/>Description: xx, 151 leaves : ill. (some col.) ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P EE 2012 ZhangZ Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10397/5702 Title: Application of SVC and STATCOM to improve stability of AC/DC hybrid power systems and to suppress subsynchronous oscillation<br/><br/>Authors: Lin, Yong<br/><br/>Abstract: As the power systems continue to grow in size, large interregional AC/DC hybrid grids come into being, ultrahigh-voltage long-distance power transmission lines and ultra-large-capacity generation units are gradually put into operation, and the series capacitor compensators and High Voltage Direct Current (hereinafter referred to as HVDC) systems are adopted to improve the power system stability and transmission capability. Therefore the subsynchronous resonance/oscillation problems and the stability problems in the large-scale AC/DC hybrid power systems resulting from these factors will necessarily become the problems in the secure operation of the grids that can't be ignored. With the implementation of the "Transmission of Power from the West to the East" program, it is of obvious engineering application value to research the stability of AC/DC hybrid grids and the technologies of suppressing subsynchronous oscillations of the power system. This dissertation, in accordance with the applications of the SVC and STATCOM in the large complicated AC/DC hybrid grids, proposes novel control design theories and methods, and tests these theories and methods through calculation analyses and simulation experiments. The SVCs and STATCOMs designed according to these theories and methods have been successfully applied to the 210Mvar SVC at 500kV Wuzhou Substation in China Southern Power Grid, the four sets of SSR-DSs in Guohua Jinjie Power Plant, the 240Mvar SVCs at Chuxiong Converter Station of the Yunnan-Guangdong ±800kV ultrahigh-voltage DC power transmission project in China Southern Power Grid, and the ±200Mvar STATCOMs at 500kV Dongguan Substation in China Southern Power Grid. This dissertation contributes to the research and engineering practice of the SVC mainly in the following aspects: (1) Calculates the static voltage stability and transient voltage stability of China Southern Power Grid through simulation experiments, especially researches the transient voltage stability in the cases of abrupt load increases and the faults in tie lines, builds the models for the motor loads at the receiving-end system, calculates and analyses the impact of the proportions of dynamic loads and the abrupt load increases on the stability, simulates the dynamic processes in time of AC/DC faults in the AC/DC hybrid grids, and researches the impact of bipolar block faults in the DC power transmission systems in the cases of different load models on the stability and calculates the reactive power requirements. (2) Introduces the engineering design and calculation methods of the capacity of the SVC used to enhance the system voltage, calculates the voltage fluctuations at the 500kV side of Wuzhou Substation when the SVCs are put into operation and the swing curves of the maximum relative angles among the generator units in the system when the SVCs are in/out of operation, tests the necessity of installing the SVC accordingly, and chooses the capacity of the SVC at Wuzhou Substation according to the comparisons of the stability calculation results in the cases of typical faults. (3) Brings forward the design method of the additional damping controller of the SVC to suppress the low-frequency oscillations, and conducts analysis and verification through time-domain simulation experiments, whose results prove that this design approach is effective, providing ground for the design of the SVC used for suppressing the subsynchronous oscillations of the power systems. The Prony analysis is introduced to get the controlled system model for the SVC damping controller tuning. The most detailed and widely used SVC control system and control strategies for the supplementary controller design and parameters tuning is modeled.; (4) Takes the SVCs at Wuzhou Substation as an example, conducts simulation experiments with the RTDS simulator in connection with the real SVC controller in accordance with the IEEE 30-bus systems and tests the concrete results of the SVC used for improving the steady and transient stability and for suppressing low-frequency oscillations of the power system. (5) Proposes the scheme of suppressing subsynchronous resonance/oscillation with the SVC, introduces the concrete system structure design, presents the implementation of the algorithm of introducing the subsynchronous frequency components in the process of fundamental-frequency susceptance regulations, and on the basis of the actual project at the Guohua Jinjie Power Plant and with the methods combining off-line calculation, dynamic simulation and field test, conducts comprehensive and in-depth calculation and analysis of the subsynchronous oscillations resulting from the series compensator at Jinjie Power Plant, and the four sets of SSR-DSs designed successfully accordingly have been put them into operation. (6) Introduces the roles that the SVC plays in ameliorating the stability of the power systems containing HVDC systems, analyses the cause of reactive power oscillations in the context of two sets of SVCs in parallel operation, proposes a novel composite control structure that enables shunt 2 self-governed SVCs to achieve balanced outputs in steady states and transient states and eliminated oscillations, and tests the real SVC controller through the simulation experiments with the RTDS simulator. The SVCs at Chuxiong Converter Station of the Yunnan-Guangdong ±800kV ultrahigh-voltage DC power transmission project were designed based on this structure, and the field operation results are good. This novel composite control structure also tackle the difficult problems of current-averaging in large power electronics devices of the FACTS equipment, and the 200Mvar STATCOMs at Dongguan, the STATCOM of the largest capacity worldwide, designed based on this structure have been in operation. (7) Researches the STATCOM in providing reactive voltage support for the grid, builds the mathematical model for the cascaded STATCOM, proposes the principle and implementation of the decoupled control of the STATCOM, builds the simulation model of the STATCOM, and tests the effectiveness of the control system designed according to the decoupled control principle under normal and abnormal conditions through time-domain simulation experiments. The 200Mvar STATCOMs designed on the basis of this principle and algorithm are the STATCOMs with the highest voltage level of direct connection worldwide. The works of this thesis can be also adopted to improve performance for distributed generation system such as wind farm which is sensitive to oscillation and demands dynamic reactive power support.<br/><br/>Description: xxx, 315 p. : ill. ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P EE 2012 Lin Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10397/5701 Title: Finite element analysis with embedded global optimization method for optimal design of electric devices<br/><br/>Authors: Chen, Ningning<br/><br/>Abstract: In this project, three-dimensional (3D) Finite element method (FEM) embedded global optimization method is applied to obtain optimal design electric devices. FEM with nodal basis function and edge basis function are used to analysis magnetic field and the eddy current problem in electric devices. Time step FEM with slave master technique, circuit coupling technique is applied to simulate the performance of electric motor. Global optimization method including Genetic algorithm (GA), simulated annealing (SA), taboo search (TA) and particle swarm optimization (PSO) are coupled with FEM program to find the parameters of the optimal design. Parameter extraction technique is applied to extract the mass parameters of electric motor to accelerate the computation speed of optimization process. Moving least square (MLS) based surface response model is applied to reduce the optimization time. The coupled FEM with optimization method is applied to optimize the performance of surface mounted PM motor, magnetic gear and an axial flux magnetic motor. In the thesis, the following work has been done: (1) 2D and 3D FEM program for eddy current have been implemented and couple with optimization method. (2) A two-grid FEM has been studied for reducing the 3-D FEM computation time to reduce the computation time of nonlinear problems. TEAM Workshop problem 13 is used to test the two-grid method and the results obtained using the two-grid algorithm are compared with those using conventional methods. Since the two-grid method requires less computing time, it can be effectively applied to study large-scale nonlinear problems. (3) Particle swam optimization (PSO) optimal algorithm and genetic algorithm (GA) have been implemented for optimization computation. A surrogate based on moving least squares (MLS) method has been developed to approximate the expected fitness evaluations, which would replace many times of FEA computation and would save much computation time. FEM with embedded GA has been applied to optimize the shape design of permanent magnet (PM) in motors to reduce the cogging torque. (4) Moving mesh FEM has been proposed for coupling FEM with optimization method. (5) The state of art programming method with object oriented programming technique for FEM is introduce to faculae the complexity of programming. The major contributions of the thesis are reflected in the following aspects: It proposes a novel moving mesh method to handle the mesh re-generation in the optimization step; Two-grid method is introduced to reduce the computational time of the nonlinear Maxwell system with nonlinear materials, and an effective interpolation of the FE solution from coarse grid to non-nested fine grid is proposed. 3D nodal and edge FEMs are implemented to analyze the eddy current problem involved in electric devices, and coupled with some global optimization process to design optimal electric devices. The FEM with global optimization method is applied to optimize the performance of PM motors and magnetic gears. Slave master technique is extended for 3D FEM computations to handle the non-conforming meshed on the interface between the moving and static parts of the devices. Time step FEM along with the slave master technique and circuit coupling technique is used to simulate the performance of the electric motors.<br/><br/>Description: xii, 131 leaves : ill. ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P EE 2012 Chen Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10397/5526 Title: Field analysis and high frequency conversion for multi-coils induction heating appliances<br/><br/>Authors: Meng, Lichan<br/><br/>Abstract: Today, induction heating is becoming a viable alternative to conventional cooking methods by providing a quiet, safe and low radiation cooking environment. Nevertheless, the commonly used single coil induction heater suffers from the problems of localized thermal distribution and fast aging of the induction pan. The design of multi-coils induction heater outperforms the conventional single coil products by enhancing power capability and providing uniform thermal distribution. The objective of this research is to realize a uniform distribution of field patterns in commercial products through systematic and in-depth investigation of the multi-coils technique for induction heating appliances. The thermal impacts of electromagnetic proximity effects in induction cooker with multi-coils are comprehensively studied. An analytical computation method is developed and implemented with different effecting parameters, so as to analyze the thermal impacts of proximity effects and eddy currents distribution in the system. For enhancing heating performance of the induction cooker with Chinese wok, Variable Turn Pitch (VTP) coils are designed and applied to address the localized eddy currents distribution problem of single coil system. Corresponding analytical equations are given to illuminate the design process of the VTP coils. The thermal field distribution on the wok is experimentally validated to be remarkably improved by applying the VTP coils.; To improve electrical efficiency of high-power induction cooker for commercial applications, its control strategies are thoroughly studied. Various control algorithms for the power regulation are studied in detail. In particular, the loss analysis of switches facilitates comparing the obtained results by adopting different control methods. Consequently, an optimized hybrid power regulation strategy is proposed in this research. The experimental results sufficiently verify the validity and reliability of the proposed control strategy. Moreover, induction cookers with distributed multi-coils are proposed and investigated to improve their heating performances. Multi-coils solutions including 7-circle coils, hexagon like 7-coils, and square 9-coils are designed and investigated to replace the traditional single coil design. A switched exciting method for driving the multi-coils is adopted for obtaining optimized performance. The testing results on the prototype verify that the proposed solution is capable of providing more uniform and better thermal distribution. A novel cordless ironing system by implementing multi-coils induction heating techniques is proposed and investigated in this research. The coils solution is thoroughly investigated and determined based on thermal performance analysis. In addition, the inductances characteristics of the coils are studied by analytical computation and Finite Element Method (FEM) analysis, given that the iron is placed above the coils at different locations on the ironing board. The experimental results on the prototype amply prove the theoretical analysis and also confirm the feasibility of the proposed induction iron system. To sum up, this research has accomplished comprehensive analysis and in-depth studies in various aspects including magnetic field, thermal field, control strategies, and practical applications of multi-coils induction heating techniques. The research outcomes provide meaningful theoretical findings as well as feasible application solutions of induction heating appliances with multi-coils.<br/><br/>Description: xxix, 213 leaves : ill. ; 30 cm.; PolyU Library Call No.: [THS] LG51 .H577P EE 2012 Meng Sun, 01 Jan 2012 00:00:00 GMT