Existing wind power plants utilize synchronous or induction generators in addition to gear boxes. In this thesis a direct permanent-magnet drive without a mechanical transmission is introduced. This new type of wind power plant utilizes a permanent-magnet generator with a wide speed range (e.g., 60-120 rpm), a unity-power factor rectifier and an insulated-gate-bipolar transistor (IGBT) inverter. The energy capture of a wind power plant is increased by about 20% by operating the plant at variable speed.; In the first part of the thesis two types of control schemes for permanent-magnet machines with flux weakening are presented for a given rated output power (e.g., 20 kW). For the first scheme, it is shown that when the magnet is located within the rotor yoke (design # 2), a speed range of 1:10 is possible, while when it is mounted on the rotor surface (design # 1), a maximum speed range of 1:4 is achieved. Two designs are also investigated where no flux weakening is applied (design # 3) resulting in low speed range equal to the output voltage range (e.g., 1:2): in the second one (design # 4) flux weakening is controlled via the field orientation of the stator excitation resulting in a speed range of about 1:4.; In the third Chapter design # 3 is investigated at a load of 300 kW. Two designs are also investigated with respect to the magnet demagnetization under short-circuit conditions. The first design (design A) is the same as design # 3 while in the second design (design # B) the magnet is located within the rotor yoke. Assuming that both designs have a constant outer stator diameter, the second design has two degrees of freedom (magnet length and the magnet cross sectional area), while the first one has only one degree of freedom (magnet length). This fact allows the designer to control the synchronous inductance of the second design for a given operating point which is not the case for the first one.; In Chapter 4 an IGBT-based inverter operating at a switching frequency of 5.76 kHz is presented. Opto-couplers are used for isolation of the upper IGBTs which permit a duty ratio of 1 and decrease the IGBT switching losses. The inverter output current as well as the inverter switching frequency are synchronized with that of the power system via a phase-lock loop permitting the control of the output power factor and canceling noninteger harmonics. Thus no power factor correction capacitors are needed. The inverter output stage also acts as an active filter by being able to produce an output current of fundamental (identical to the power system frequency) and harmonic frequency.; In Chapter 5 a unity-power factor, low total harmonic rectifier is utilized to extract maximum real output power from the permanent-magnet generator. Since this type of rectifier utilizes one switch only, a simple control circuit is built to control the input power factor and the output load. (Abstract shortened by UMI.)
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