The Brushless Doubly-Fed Machine (BDFM) has recently become an important research topic in the field of variable-speed AC drives. In recent studies, the BDFM has shown significant potential for improving the reliability and performance of AC drive systems, as well as reducing total system cost. While the BDFM offers several advantages over existing AC drives in steady-state operation, it suffers from dynamic instabilities and slow response times, and a feedback control system is necessary. The mathematics of the BDFM are much more complicated than those of a singly-fed machine, and thus traditional control methods can't be applied. In this thesis, a control method known as "Direct Torque Control" has been adapted from that of a singly-fed induction machine and successfully applied to the BDFM. The thesis begins by discussing the background of the BDFM, its open-loop operating characteristics, and some of the control considerations. The reduced-order system differential equations are introduced, and it is noted that they are coupled and nonlinear. Furthermore, all state variables are time-varying (but periodic), even in steady-state operation. In the controller development, it is found that a linear relationship exists between the desired torque/flux-level change and the d-q voltages to be applied to the control winding of the machine via the power-electronic converter. This linear relationship, together with a one-step-ahead predictor to compensate for computational delay, is successfully used to control the speed and efficiency of the machine, for a wide range of speeds and load torques. Numerous open- vs. closed-loop simulations are compared and summarized, and it is found that the performance of the BDFM is greatly improved in the closed-loop, with faster response and reduced oscillation. Further simulations investigating the robustness of the controller are summarized, and it is found that the controller is reasonably insensitive to errors in most of the the static machine parameters. Hardware implementation is briefly discussed but is not complete; laboratory results are not yet available but should be soon. Future controller considerations are then discussed; included among the recommendations are an on-line parameter estimator for use in adaptive control, and a controller for generator applications of the BDFM. / Graduation date: 1993

The loads on the electrical systems of automobiles are projected to increase significantly in the near future. This will result in a requirement for improved efficiency over the present-day car alternators. An alternative scheme proposed at Oregon State University employs a Brushless Doubly-Fed Machine (BDFM) as an alternator. This thesis begins with a study and characterization of the existing car alternator system. The configuration of the proposed scheme is discussed. In the proposed configuration, the power winding of the machine generates the bulk of the power and the control winding provides the excitation. The power winding feeds a power rectifier, which in turn charges the battery in an automobile. The control winding is supplied through an inverter. Issues related to inverter and rectifier design are discussed. A 3-phase pulse width modulated inverter and a bridge rectifier were developed and tested for performance. A PSPICE simulation model for the rectifier was developed and results are compared with laboratory tests. A Voltage Regulator Circuit (VRC) and an Efficiency Maximizer Unit (EMU) for the system are designed and developed. A prototype alternator system is tested and the principle of efficiency maximization is verified. Finally. the comparative performance of the the existing and the proposed system is discussed and some recommendations for further improvements in the prototype system are made. / Graduation date: 1992

A superimposed steering system is the combination of a conventional steering system with an electric motor which is used to alter the steering angle imposed by the driver. The potential benefits are increased agility, automatic compensation for lateral wind forces and decreased braking distance (in combination with an electronic stability program). In this thesis we implement a model and a controller for a superimposed steering system thus achieving the first of these potential benefits. The vehicle model is based on the single-track or bicycle model. Unlike most other publications, the motor model in this thesis goes down to the level of the electrical dynamics of the motor. The model is divided into three main modules (vehicle module, steering module and friction module) as well as several submodules to ensure easy adaptability. The overall control objective consists of increasing vehicle agility by achieving a variable ratio between the steering wheel angle and the actual road wheel angle as a function vehicle velocity. We divide the controller into a torque and a current controller. The actual controller is derived in three steps starting from an analog torque controller as well as an analog current controller then moving to a digital torque controller. In doing so we use the model matching, feedback linearization and state feedback control techniques. The model and the controller are evaluated using the parameters of a small truck and different road scenarios. Finally, the Validation Square technique is applied to assess the validity of the results.

Thesis--M. Sc.(Eng.), University of Hong Kong. / Mimeographed.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 113-117.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 96-99). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 96-99). Also available on the Internet.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Conventional PM machines have fixed PM excitation and can only perform flux-weakening by controlling the d-axis current. This current incurs the power dissipation and reduces the efficiency during flux-weakening operations. Memory machines change this situation by introducing the memory function, namely magnetizing or reversely magnetizing Al-Ni-Co PMs to change the air-gap flux density. This provides another new way to realizing flux-weakening. And the elimination of the flux-weakening d-axis current improves the overall efficiency. But the single-memory machines have lower power density due to the low-energy Al-Ni-Co PMs. By incorporating the memory concept and with the intention of improving the power density, the DC-excited PMBL dual-memory machines have been proposed and implemented, based on two kinds of PMs which are high-coercivity Nd-Fe-B PMs and low-coercivity Al-Ni-Co PMs. The Nd-Fe-B PMs provide a strong magnetic field to excite high air-gap flux density; while the Al-Ni-Co PMs can be forward magnetized to strengthen the magnetic field produced by Nd-Fe-B PMs or can be reversely magnetized to cancel that field. Consequently the air-gap flux density can be controlled within a wide range. A series of design principles on such kind of dual-memory machine are devised for guidance. The key design principles involve how to determine the number of salient poles on the stator and rotor, how to choose the surface areas and thicknesses of the two kind of PM pieces and how to size the rotor dimension. Generally, increase on the proportion of Nd-Fe-B PMs will raise the base field and the load capacity. On the other hand, increment on the proportion of Al-Ni-Co PMs will extend the controllable flux range. Analysis is also carried out on the equivalent magnetic circuit to formulate the magnetizing force exerted on Al-Ni-Co PMs. The machine model is analyzed by using time-stepping FEM (TS-FEM) and co-simulation of FEM software and Matlab Simulink. The dynamic reverse magnetizing processes are simulated and presented in details under different magnetizing current. In addition the effect of adding iron bridges between the two kinds PMs is also evaluated by simulations. Furthermore, the control methods are evaluate by simulations and experiments. The direct torque control (DTC) scheme is adapted to this doubly-salient dual-memory machine and a torque estimator is proposed to facilitate the DTC method. Both of the simulation results and the experimental results confirm the validity of the proposed design principles and the effectiveness of the control methods. Eventually, this dual-memory machine is proposed as a pole-changing wind power generator and a pole-changing EV machine. Simulation and experimental results have verified the validity of the pole-changing scheme and the pole-protection scheme. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy