Other

Joseph Vithayathil

John J Vithayathil

An AC generator whose field winding (,) on the rotor is excited by AC so that the resultant speed of the rotating field is the algebraic sum of the rotor speed and the speed of the field relative to the rotor itself. This makes it possible to generate AC at a frequency different from that of conventional DC excited generators by the appropriate choice of the frequency of the AC input to the rotor field circuit. It enables the stabilization of the output frequency of the alternator when speed changes occur, by the adjustment of the AC frequency of the rotor input. The AC fed to the rotor is from an auxiliary winding (,) which may be housed on the rotor itself, thereby eliminating the need for any brushes or slip rings. The AC is induced in the auxiliary rotor winding by having an auxiliary winding on the stator (,), distinct from the main stator winding (,). The input to the stator auxiliary winding may be from an inverter (,) whose frequency may be adjustable. By varying the frequency of the inverter output, the frequency of the AC fed to the main rotor field winding may be varied to achieve the desired output frequency of the generator or to stabilize the generator frequency when speed changes occur. Voltage control of the alternator may be implemented by adjustment of the inverter output voltage. The need for a separate exciter machine may be avoided by housing the main and auxiliary winding in the generator itself By the appropriate choice of different pole numbers for the main and auxiliary windings, these two sets of windings can function independently without magnetic coupling, making the machine both exciterless and brushless The restriction on the choice of pole numbers will not apply if the auxiliary windings are housed in a separate exciter machine, in which case it becomes a brushless machine with exciter.

Brushless AC field system for stable frequency variable speed alternators

A three phase AC motor which rotates at the synchronous speed determined by the number of poles of its main stator winding and the frequency of the AC input to it, which does not need any exciter machine or brushes to provide its DC field current, but has an internal, but independently adjustable excitation system to supply its field current. The internal excitation system consists of an auxiliary winding on the stator which is additional to the main power winding, another auxiliary winding on the rotor besides the main DC field winding, a diode rectifier circuit on the rotor from which the DC field current is supplied by rectification of the induced currents in the rotor auxiliary field. The field current adjustment can be made by adjustment of the input to the stator auxiliary winding. This can be done independently by eliminating any magnetic coupling between the main and auxiliary circuits. The elimination of the magnetic coupling between the main and auxiliary circuits is achieved by winding the auxiliary circuits for a suitably chosen pole number which is different from that of the main circuits. An optional damper winding will assist in starting when the machine is operated from a fixed frequency supply and ensure stability during steady state rotation. The machine is suitable for inverter fed adjustable speed drives and for fixed frequency operation. It can function in the motoring and the generating modes.

Brushless exciterless field system for AC synchronous machines

An AC machine system, in which the machine has an auxiliary rotating magnetic field, in addition to the main rotating field, with different speeds of rotation. The auxiliary field serves to induce AC voltages in the rotor windings, even when the machine is rotating at the synchronous speed of the main field. The induced AC is rectified, by having a rectifier circuit on the rotor, and provides DC excitation, to create fixed magnetic poles on the rotor. Thereby the machine functions at the synchronous speed of the main field, without the need for a DC exciting source, external to the rotor circuit. The presence of AC current components in the rotor coils, enable torque production at non-synchronous speeds also. The combination of main and auxiliary rotating fields can be implemented in several ways, such as a stator supply having more than one frequency components, or components of opposite sequence. It can also be done by appropriate design of the stator circuit.

Growing community of inventors

Bryant, AR, United States of America

Joseph Vithayathil