Compound AC generator

In a compound AC generator having at least one pair of magnetic poles, series field windings wound on the magnetic poles, respectively, and at least one shunt field winding wound on at least one of the pair of magnetic poles in layers with the series field winding wound thereon, the series field winding wound in layers with the shunt field winding is associated with means for blocking the current flow through the series field winding in a direction to increase the magnetic fluxes through the associated magnetic pole thereby to minimize the effects of pulsating field current through the shunt field winding and to stabilize the output of the generator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a compound AC generator and, more 
particularly, to a compound AC generator having a control circuit so 
designed as to prevent the voltage pulsation in a shunt field winding from 
affecting a series field winding. 
2. Description of the Prior Art 
In general, a compound AC generator requires arrangement of its series 
field winding to have (1) a large diameter of the wire, (2) a large number 
of turns, and (3) to be divided into parallel circuits, in order to 
enhance the compensation for drooping of the terminal voltage of the 
generator due to overload. When using such a series field winding, 
however, the space occupied by the series field winding is larger than 
that of the shunt field winding, resulting in necessity of disposing the 
series and shunt field windings on a common magnetic pole. The series 
field winding is wound to be distributed uniformly on magnetic poles in 
order to reduce the resistance of the field winding, to reduce the heat 
evolved and to prevent nonuniform magnetic flux distribution. The shunt 
field winding is connected through a half-wave rectifier to the generator 
to receive a half-wave rectified field current and a flywheel diode is 
connected in parallel to the shunt field winding to prevent interruption 
of the field current during another half-cycle, whereby the shunt field 
winding is supplied with a pulsating field current without interruption, 
resulting in pulsating magnetic flux produced by the shunt field winding. 
This causes an exciting current to flow in a direction to increase the 
magnetic fluxes through the series field winding wound on the same 
magnetic pole in layers with the shunt field winding, resulting in 
variation of the output voltage of the generator. The effects of the 
variation of the output voltage is especially great at a light load and 
its voltage regulation is about 15%, thereby presenting poor performance 
as a power source. 
SUMMARY OF THE INVENTION 
It is, accordingly, an object of the present invention to provide a 
compound AC generator with a possibly small voltage variation and an 
excellent compensation for the terminal voltage dropping appearing during 
an overload. 
Another object of the present invention is to provide a compound AC 
generator as above-mentioned with a simple and practical circuit 
construction. 
The present invention has features in that the variation of the output 
voltage is restricted to a possibly small value without unfavourable 
affect on the voltage dropping compensation characteristic during an 
overload. 
According to the present invention, a compound AC generator having at least 
one pair of magnetic poles, series field windings wound on the magnetic 
poles, respectively, and at least one shunt field winding wound on at 
least one of the magnetic poles and in layers with the shunt field winding 
wound thereon is arranged such that the series field winding, which is in 
layers with the shunt field winding, is associated with means for blocking 
the current flow through the series field winding in a direction to 
increase the magnetic fluxes through the associated magnetic pole, thereby 
to minimize the effects of pulsating voltage developed in the field 
winding and to stabilize the output of the generator. 
These and other more specific objects will be understood from the following 
description with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, reference numeral 1 designates an armature, and 2 a shunt field 
winding which is excited by the current rectified through a combination of 
a diodes 3 and a flywheel diode 4. Reference numerals 5 and 6 denote 
series field windings, respectively, connected in parallel to each other, 
and the connecting points of the parallel circuits are connected to the 
terminal of the armature through a diode bridge 7 constituting a full wave 
rectifier circuit. Reference numerals 8 and 8' designate output terminals 
both coupled with a load 9. Reference numeral 10 designates a diode for 
blocking the current in a direction to increase magnetic fluxes through 
the associated magnetic pole. The arrangement of installed coils mentioned 
above will be described with reference to FIG. 2 in which reference 
numeral 15 is representative of a yoke with magnetic poles 11 and 12 
integral therewith. On one of the magnetic poles 11 is wound a shunt field 
winding 2 in layers with the series field winding 5, while only the series 
field winding 6, which is connected in parallel to the series field 
winding 5, is wound on the other magnetic pole 12. 
It is to be noted here that the series field windings 5 and 6 are wound on 
the corresponding magnetic poles 11 and 12, respectively, in order to 
reduce the whole resistance of the windings and to reduce heat production. 
With such construction, the field current flowing through the shunt field 
winding 2 includes a half-wave rectified current through the diode 3 
during one half-cycle and a current through the flywheel diode 4 during 
another half-cycle. More particularly, the field current takes a form of 
pulsating current, as shown in FIG. 4A. Accordingly, the flux developed by 
the shunt field winding 2 also pulsates, as shown in FIG. 4B. During the 
period of time T.sub.1 in FIG. 4B, the intensity of the magnetic flux 
increases with time and thereby the shunt field winding 5 induces a 
voltage e.sub.a in a direction to prevent the increase of the magnetic 
flux. On the other hand, during the period of time T.sub.2, the intensity 
of the magnetic flux decreases with time thereby to induce in the shunt 
field winding 5 a voltage e.sub.r in a direction to prevent the decrease 
of the magnetic flux. The time T.sub.2 is substantially equal to the time 
T.sub.1 and the rate of variation of the magnetic flux during the time 
T.sub.1 is substantially symmetrical with that during the time T.sub.2. 
Thus, the voltage e.sub.a is substantially equal in amplitude and opposite 
in direction to the voltage e.sub.r, as shown in FIG. 4C. 
The induced voltage e.sub.a produces a current i.sub.a through the series 
field winding 6, as well as a current flowing through the rectifier bridge 
7. The current i.sub.a is given as 
##EQU1## 
where r.sub.5 and r.sub.6 indicate the resistances of the series windings 
5 and 6, respectively and r.sub.7 the resistance of the rectifier bridge 
7. 
The rectifier bridge blocks the current flow therethrough due to the 
induced voltage e.sub.r. However, if the diode 10 were omitted, the 
induced voltage e.sub.r would produce a current i.sub.r flowing through 
the loop of the series field windgs 5 and 6. The current i.sub.r is given 
by 
##EQU2## 
As abovementioned, since e.sub.a = e.sub.r and hence i.sub.r &gt; i.sub.a, the 
resultant current flowing through the series field winding 6 would be 
i.sub.r - i.sub.a and flow in a direction to increase the magnetic flux in 
the series field winding 6. 
The diode 10 is effective to prevent the current flowing through the series 
winding 6 due to the induced voltage e.sub.r. In other words, the diode 10 
is connected in such a direction so to block a current flow which will 
otherwise be produced by the voltage induced in one of the series field 
windings 5 and flow through the other series field winding 6 in a 
direction to increase the magnetic flux in the other series field winding. 
For this reason, when pulsating magnetic flux is developed by the shunt 
field winding 2 and, hence, an alternating electromotive force, or 
voltage, is induced in the series field winding 5 disposed on the same 
magnetic pole, the current flowing through the series field winding 5 
includes only the current i.sub.a, as shown in FIG. 4D, in such a 
direction as to reduce the magnetic flux produced by the series field 
winding 6. Therefore, it is possible to restrict the voltage rise across 
the output terminals at a light load thereby resulting in a considerable 
improvement of the voltage regulation. FIG. 3 shows another embodiment of 
the instant invention. In the figure, series field windings 5 and 6 are 
connected to each other through a diode bridge circuit 10A. With such a 
circuit construction, when the voltage induced in the series field winding 
5 is directed in the direction of e.sub.r, no current flows due to the 
action of the bridge circuit 10A. On the other hand, the voltage induced 
in the series field winding 5 takes a direction designated by e.sub.a, the 
current i.sub.a flows through the bridge circuit 10A while no current 
flows through the series field winding 6 coupled across two connecting 
points B and C since the potentials at the points B and C are equal. As a 
result, the induced voltage in the series field winding 5 has no effects 
to increase the magnetic flux and thus it is possible to prevent the 
voltage rise at a light load. 
Reference is now made to FIG. 5 illustrating an example of the current 
variation of the series field winding with respect to the load current 
change of a 50 Hz, 100 V, and 1.5 KVA AC generator. As seen from the 
figure, the current in the series field winding of the compound wound AC 
generator of the present invention traces a solid line Y.sub.2 whereas 
that of the conventional one a dotted line Y.sub.1. That is, there is 
observed a reduction of the field winding current at a light load. It is 
also seen from the figure that the curve X.sub.1 representing the 
variation of the terminal voltage with change of the load current for the 
conventional generator is improved to a shape of curve X.sub.2 for the 
present invention, and thus the voltage rise across the terminal voltage 
at a light load is restricted. Listed below are measurements of the 
relationship between the terminal voltage vs. the load current. 
______________________________________ 
50% 125% 
No rated Rated rated Voltage 
load load load load regula- 
(0A) (10A) (20A) (25A) tion 
______________________________________ 
Prior 115V 107V 101V 92V 13.9% 
Art 
Present 
inven- 107V 107V 101V 92V 5.9% 
tion 
______________________________________ 
It will be seen from the table that, in an AC generator of the present 
invention, there is no reduction of the output voltage at light road 
without reduction of the output voltage at heavy or overload, or as 
maintaining the characteristics of compensation for the voltage droop at 
heavy or overload. 
As clear from the above description, in the present invention, the current 
block means 10 or 10A is provided to block a current which will otherwise 
be produced by a voltage induced into one of the series field windings due 
to a field current flowing through a shunt field winding which is wound in 
layers with the one series field winding on one of the magnetic poles and 
flow through the other series field winding in a direction to increase the 
magnetic flux in the other series field winding. 
Thus, it will be clear that, if both of the series field windings are wound 
in layers with shunt field windings, respectively, wound on the respective 
magnetic poles, the same effects will be achieved by providing such 
current block means in each of the parallel circuits of the series field 
windings 5 and 6. 
Further, the embodiments of the present invention have been described with 
reference to a compound motor having a pair of magnetic poles, but it will 
be also clear for those skilled in the art that the present invention is 
applicable to a compound motor having two or more pairs of magnetic poles. 
As described above, according to the present invention, it is possible to 
prevent the current during a light load in the series field winding, which 
is provided for compensating for the voltage drooping during heavy or 
overload. The result is that the voltage regulation is considerably 
improved during not only heavy or overload, but also light load, by 
maintaining the voltage drooping compensation characteristic at any load 
condition.