Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
Th;s invent;on relates to a rectifier asse~bly for use on the rotor
of a synchronous machine such as a brushless alternating current generator
or a brushless synchronous motor.
A synchronous machine, such as a brushless alternating current
generator, has an exciter generator comprising a DC stator field with an AC
armature on the rotor. An example of such a machine is provided by Sones
et al U.S. Patent No. 3,059,168. A rectifier on the rotor rectlfies AC
from the exciter for the main generator DC field winding which is also
located on the rotor. The main AC armature is on the stator and the AC
voltage is available therefrom. The rectifier typically uses individual
semiconductor diode rectifiers mounted in a housing on the rotor shaft.
Several disadvantages are encountered when employing individual
semiconductor diode rectifiers. For example, mounting complexity is
encountered due to the physical stresses from the rotational"6" forces at
speeds up to 20,0~0 RPM, which are used in aircraft generators and motors.
Also, since the casing of the semiconductor d;ode rectifier is usually the
anode or the cathode of the device, the rectifier must be insulated from
the mounting base if the moun~ing base is conductive. Moreover,
reliability of the rectifier is degraded due to the complexity of the
entire rectifier assembly. Also, effective cooling of the semiconductor
diode rectlfier is difficult to obtain since there is a high thermal
resistance between the outer casing of the semiconductor diode assembly and
the wafer within. Thus, even if the rectifier assembly is immersed in a
cooling medium, inefficient cooling results. -
Considering these drawbacks, I have developed a rectifier assembly ~ ;
for a synchronous machine which is easily mounted to the housing, insulated
from the mounting base, capable of wl~hstanding centrifugal force created
at normal operating speeds and is efficiently cooled. The assembly can be
connected as either a half wave or a full wave rectifier.
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1 SUMMARY 9F THE INVENTION
_
A plurality of semiconductor wafers forming either a half wave or a
full wave rectifier are conta;ned within a rectifier assembly attached
directly to an inner section of a housing mounted on a shaft of a
synchronous machine. In one embodiment, the assembly is provided wlth
inlets and outlets for the passage of a cooling medium. The cooling medium
traverses the surface of the semiconductor wafers to provide high
efficiency heat removal. In another embodiment, the cooling medium
traverses the face of a heat sink on which the wafers are mounted.
It is a feature of the present invention to provide a rectifier
assembly which permits the cooling medium to traverse the surface of the
semiconductor wafers within the rectifier assembly.
Another feature of the present invention is to provide a rectifier
assembly having a heat sink wherein the cooling medium traverses the heat
sink to remove heat.
Yet another feature of the present invention is to provide a
rectifier assembly which is efficiently cooled and capable of withstanding
high centrifugal forces and has a high reliability.
Other features of the invention will become apparent when
considering the specification and the drawings in which:
DRAWIN~S
Fig. 1 is a cross-sectional view of a brushless alternating current
generating system having a rectifier assembly of the present invention;
Fig. 2 is a schematic diagram of a full wave rectifier for
converting three-phase AC to DC;
Fig. 3 is a half wave rectifier for converting three-phase AC to DC;
Fig. 4 is an end view of the brushless alternating current
generating system of Fig. 1 taken through the line 4-4;
Fig. 5 is a perspective view of one of the three casings which
house the semiconductor wafer in the rectifier assembly; and
Fig. 6 is a perspective view of an alternative construction of the
rectifier assembly.
67B
1 DESCRIPTION OF PREFERRED EMBODIMENT
Referring to Fig. 1, brushless alternating current generating
system 10 is shown. Although the invention will be described for use in
conjunction with a synchronous generator, it also may be used with a
synchronous motor. The generating system 10 includes rotatable shaft 12
driven by an external source (not shown) to produce an AC output from
terminals 14. The system may provide a single phase or a polyphase voltage
supply. As shaft 12 rotates, AC armature 16, wound around an annular
housing 18, provides a polyphase excitation power source for the system as
AC armature 16 cuts through the DC exciter field established by DC windings
20. The AC from armature 16 ls rectified by rectifier assembly 22 which is
located in an inner section 24 of annular housing 18. Rectifier assembly
22 iS connected to provide either a half wave or a full wave rectifier and
is coupled to DC field winding 26 by leads (not shown) from the terminals,
as terminal 30.
DC field windings 26 are secured to shaft 12 and spaced apart from
housing 18 by spacer 32. As shaft 12 rotates, current provided DC field
winding 26 establishes a DC field which cuts through AC output windings
34. The AC output windings 34 provide the single phase or polyphase supply
and are connected to terminals
14. Housing 36 is provided with a cooling medium, as oil or air. Suitable
inlet and outlet ports (not shown) to and from the generator assure
adequate cooling of the alternating current generating system 10 during
operation in the well known manner. Also, each end of shaft 12 is provided
with suitable bearings, as bearings 38, to enhance rotation.
An electrical schematic of a full wave rectifier is shown in Fig. 2
as having three pairs of diodes 40, 42 and 44. An electrical schematic of
a half wave rectifier having diodes 46, 48 and 50 is shown in Fig. 3. As
will be explained in greater detail below, either the full wave or the hal~
wave rectifier is contained by rectifier assembly 22, and in either case,
the DC voltage output therefrom is provided to DC windings 26.
Referring to Fig. 4, rectifier assembly 22 is shown and includes
three individual casings 52, 54 and 56 symmetrically disposed about shaft
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1 ~ in inner sec~ion 24 of annular housing 18. Each casing contains diode
pair 40, 42 and 44, respectively. The leads from the diodes of each casing
may be interconnected to form the full wave rectifier of Fig. 2.
Referring to Fig. 5, the construction of casing 52 of rectifier
assembly 22 will now be described. The discussion relating to the
construction of casing 52 equally applies to similarly constructed casings
54 and 56. Cover 53 of casing 52 is mounted on a conductive shell 58.
Diode wafers, such as semiconductor wafers 60 and 62, are mechanically and
electrically attached to conductive shell 58. Specifically, the flat
~0 planar anode surface of diode wafer 60 is attached to shell 58 and the flat
planar cathode surface of diode wafer 62 is attached to shell 58. High
temperature solder or an adhesive which is electrically conductive may be
used to attach the wafers to the shell. The conductive shell 58 provides a
common terminal between wafers 60 and 62 of diode pair 40 for applying
phase A of the AC voltage input (Fig. 2). Since cover 53 is in mechanical
contact with shell 58, terminal 64 mounted on cover 53 is used for providing
the conductive shell 58 with the polyphase AC source. Leads 66 and 68 are
secured to the upper surface of wafers 60 and 62, respectively, to connect
the diodes to terminals 70 and 72 which are mounted on, but electrically
insulated from, cover 53. A coating compatible with the cooling material
may be apptied over the chips to isolate them from contaminants present in
the cooling medium.
Casing 52 is electrically insulated from the annular housing 18 by
insulative pad 59 and is attached to housing 18 by screws 74 and 76.
Insulative washers 78 and 80 electrically insulate the screws from cover
53. Cover 53 is spaced apart from the inner wall 84 of the base plate by a
distance d to form an arcuate inlet. Nonconductive coolant material, as
air or lubricating oil, blowing in a direction generally parallel with the
shaft 12, enters the inner cavity of casing 52 between inner wall 84 and
cover 53. An example of how hydraulic lubricating oil can be used to cool
the various components of a high speed aircraft-type generator is provided
in Baits U.S. Patent No. 3,576,143. The flow of the coolant material is
provided directly across the surface of wafers 60 and 62 or across the
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67B
1 r,otective coating. Because the coolant is in direct contact with the
semiconductor material itself, particularly efficient heat removal is
attained, thereby allowing the rectifier diodes to operate at substantially
lower temperatures and thus increasing the life and reliability of the
wafers. Slots 86 in cover 53 provide an outlet for the coolant material
and since the rotor and hence the cover are rotating, centrifugal force
will cause the coolant to flow over the diodes 60 and 62 and out of the
casing 52. As shown in Fig. 1, housing 18 may be provided with channels 88
to enhance coolant flow through the entire housing if desired.
Referring to Fig. 6, an alternative construction of the rectifier
assembly is shown. Nonconductive plate 90 forms the base of assembly 92.
Plate 90 has a large center hole 94 which accommodates shaft 12, and six
small holes, as hole 96, for cooling, as will be explained below.
Diode triplet assemblies 98 and 100 are secured to the
nonconductive base plate 90. Each triplet assembly has three diodes
secured to the upper surface of conductive heat sinks 102 and 104,
respectively. Conductors ~not shown) are secured to each individual diode
wafer of the triplet assembly and to protrusions 106 and 108 on triplet
assemblies 98 and 100. The other ends of the conductors are coupled to
terminals 110, 112, 114, 116 and 118, which are mounted on nonconductive
cover 120. The connection of the conductors with the wafers and the
protrusions 106 and 108 correspond to the connections shown in the
schematic diagram of Fig. 2. The assembly is encapsulated in epoxy or
other suitable material, retaining cover 120 over base plate 90.
The construction of diode triplet assembly 98 will now be
described. Wafers 122, 124 and 126 are electrically and mechanically
attached to conductive heat sink 102. Eaçh of the wafers represents
one-half of the diode pair 40, 42 and 44, respectively, as best shown in
Fig. 2. The flat planar cathode surface of each of the wafers 122, 124 and
126 is attached to conductive heat sink 102. Positive DC potential is
therefore available from the outwardly extending protrusion 106.
The construction of diode triplet assembly 100 will now be
described. Wafers 128 and 130 and a third diode (not shown) are
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1 lectrically and mechanically attached to conductive heat sink 104. Each
of the wafers represents one-half of the diode pair 40, 42 and 44,
respectively, as best shown in Fig. 2. The flat planar anode surface of
each of the wafers 128 and 130 and the third diode is attached to the
inductive heat sink 104. Negative DC potential is therefore available from
outwardly extending protrusion 108.
Assembly 92 is rigidly attached to the annular housing 18 of AC
armature 16 of the generating system 10 by an adhesive. If housing 18 is
provided with suitable passsageways or openings for cooling medium,
efficient heat removal occurs when the cooling material traverses the rear
side of heat sinks 102 and 104 through the six holes, as hole 96.
The above explanation specifically relates to rectifier assemblies
providing full wave rectification. A half wave rectifier, as shown in Fig.
3, could be constructed by providing casings 52, 54 and 56 with a single
diode wafer representing diodes 46, 48 and 50 (as shown in Fig. 2).
Similarly, if a half wave rectifier is employed in the assembly shown in
F;g. 6, only one diode triplet would be employed. In such a case,
rotational balance must be maintained during the operation of the generator.
Finally, although the use of silicone wafers is preferred, diode
wafers constructed of other semiconductive materials may also be used.
3o
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