Brushless high-frequency alternator and excitation method for DC, single-phase and multi-phase AC power-frequency generation
A method is disclosed for arranging and exciting the stator, rotor and various windings of a multi-stage brushless high frequency alternator so that the resulting multiple high frequency sub-phase armature winding outputs can be rectified and commutated into desired phases of power-frequency alternating current (AC) electrical output, including single-phase, split-phase, three-phase and other multiple phase output. Power frequency currents in field windings control output amplitude, output frequency, and output phase. If desired, DC power output can be accommodated as zero power-frequency operation. Devices incorporating this arrangement are suitable of generating fixed frequency electrical power while accommodating variable speed rotation of a generator shaft and offer multiple advantages over existing techniques. The capability to generate speed independent electric power allows natural power sources such as windmills and hydro-power stations to be efficiently coupled to fixed frequency power grids.
1. A brushless high-frequency alternator device for use in the generation of fixed power-frequency electrical power from an external source of rotary mechanical power into n desired power-frequency output line voltages, L 1 , L 2 . . . Ln, wherein n is any positive integer greater than zero, and wherein each of the output line voltages has a power-frequency time-varying sinusoidal amplitude, and wherein the various output line voltages are phase displaced one from another as required, the device comprising:
(a) a shaft;
(b) a rotor coaxial to, and arranged to turn with, rotation of said shaft when coupled thereto;
(c) a stator having an inner circumference and arranged coaxial to, and separated from, said rotor by a radial air gap;
(d) a plurality of field coils located on said stator, said field coils arranged for excitation by electrical currents such that the inner circumference of said stator is divided into one or more sets of said integer n discrete circumferential sectors, each sector having a field modulated level of net magnetic excitation (mmf) therein, said mmf being substantially uniform across said sector, and said field coils further arranged so that the mmf in each of the said integer n sectors within each of the one or more sets corresponds to the instantaneous phase and amplitude of a corresponding one of the output line voltages L 1 , L 2 , . . . Ln;
(e) a plurality of high-frequency windings for each of said sectors arranged so that rotation of said rotor generates multiple phases of high-frequency alternating electrical output which are amplitude modulated by the mmf within each of said sectors and also arranged so that the electrical output of each of the multiple high-frequency phases is phase displaced with respect to the electrical outputs of others of the multiple high-frequency phases so as to be suitable for rectification into an amplitude modulated rectified output corresponding in phase and amplitude to one of the output line voltages; and
(f) means to couple said shaft to the external source of rotary mechanical power.
2. The device of claim 1 wherein said integer n is 1 and the output is single phase.
3. The device of claim 1 wherein said integer n is 2 and the output is split phase, wherein the output level for either phase may be arbitrarily adjusted.
4. The device of claim 1 wherein said power-frequency is 0 Hz and the desired output is DC in nature.
5. The device of claim 1 wherein said rotor and said stator are constructed of low loss magnetic material.
6. The device of claim 1 having more than one set of said integer n discrete sectors, the device further comprising means for interconnecting together the electrical outputs of each of the high-frequency phases from corresponding ones of the different sectors to form interconnected electrical outputs of each of the multiple high-frequency phases prior to rectification thereof into the amplitude modulated rectified outputs corresponding in phase and amplitude to the respective output line voltages.
7. The device of claim 1 wherein the level of mmf for each of the sectors is time varying and uniform across the sector.
8. The device of claim 1 further comprising means to hold said shaft and said stator in relative concentric and axial position with respect to one another, and bearing means arranged to allow said rotor to rotate relative to said stator.
9. The device of claim 1 further comprising first interconnection means for electrically attaching said field coils to an external source of excitation, and second interconnection means for electrically attaching said high-frequency windings to an external rectifier.