Patent Application
20170133916
This application is a continuation application, under 35 U.S.C. §111(a), of international application No. PCT/JP2015/070375, filed Jul. 16, 2015, which claims priority to Japanese patent application No. 2014-150442, filed Jul. 24, 2014, Japanese patent application No. 2014-150684, filed Jul. 24, 2014, and Japanese patent application No. 2014-163438, filed Aug. 11, 2014, the disclosure of which are incorporated by reference in their entirety into this application.
Field of the Invention
The present invention relates to a permanent-magnet-less power generator used as a small-sized wind power generator or a power generator using flowing water, for example.
Description of Related Art
Examples of power generators that generate power by rotation include induction power generators and synchronous power generators. Although an induction power generator does not need to excite the windings of the rotor thereof, the induction power generator needs to perform system interconnection and needs to be rotated at a high rotational speed, and thus is not suited for a small-sized power generator. Accordingly, for small-sized wind power generators, etc., synchronous power generators are often used.
However, an ordinary synchronous power generator uses a permanent magnet to generate a magnetic field. Since rare metal which is a component of a permanent magnet is expensive, the total price of such a power generator is high. Furthermore, in synchronous power generators, cogging is generated at a time of starting, and starting torque becomes large due to the cogging torque. Thus, synchronous power generators are not suited for power generators such as small-sized wind power generators which generate power using a small amount of nature power. Some synchronous power generators are separately excited by using electromagnets instead of permanent magnets. However, such a power generator requires a configuration for supplying power from the outside to the electromagnet, and the configuration becomes complicated due to an external power source.
A self-excitation type synchronous power generator has been proposed which solves these problems and does not need a permanent magnet or power supply from the outside (Patent Document 1). The power generator increases current flowing through a field winding, by self-excitation using the residual magnetism of a core, and thereby generates a magnetic flux required for power generation, without requiring any expensive permanent magnet or any external power source for excitation.
In addition, as a power generator which solves the above problems, a reluctance power generator has been proposed which uses reluctance (magnetic resistance), has an output winding and a field winding wound around a stator core, and has a rotor without a coil, wherein a ferrite magnet for magnetically short-circuiting between salient poles of the stator is provided (Patent Document 2).
[Patent Document 1] JP Laid-open Patent Publication No. 2006-149148
[Patent Document 2] JP Laid-open Patent Publication No. 2011-259633
The self-excitation type power generator of Patent Document 1 has the aforementioned great advantages. However, when power generation is stopped or the power generator is disassembled, the residual magnetism of the power generator core is weakened. When the residual magnetism of the power generator core is weak, a magnetic force required for initial excitation is insufficient, and thus, power generation is not started, or the rotational speed for starting power generation needs to become high to some extent. Therefore, in a power generating system such as wind power generation or power generation using flowing water, in which a stop time period is generated or power needs to be generated at a low speed, the self-excitation type power generator cannot provide sufficient reliability of starting power generation.
The power generator of Patent Document 2 achieves the reliability of starting power generation at a restart of rotation after stop of rotation. However, reluctance power generators have been rarely put into practical use, and there are some worries about the practical use thereof.
An object of the present invention is to provide a power generator that does not require a permanent magnet for generating a magnetic flux to obtain an ordinary generation power and does not require power supply for separate excitation from the outside, and that can reliably start power generation by restart of rotation after stop of rotation.
A power generator according to the present invention includes: an output iron core having an output winding wound therearound; and a field iron core having a main field winding and an auxiliary field winding wound therearound. The power generator is of a self-excitation type in which one of the output iron core and the field iron core serves as a stator and the other serves as a rotor, the main field winding is connected to a first rectifying element, the auxiliary field winding is connected to a second rectifying element, and power is generated by relative rotation of the stator and the rotor.
The power generator is provided with an initial excitation unit configured to apply, to one or both of the output iron core and the field iron core, a magnetic force to a degree required for initial excitation in power generation.
With this configuration, since the power generator is a self-excitation type which performs excitation using the auxiliary field winding, power generation can be performed without requiring a permanent magnet for power generation or an external power source for supplying power for separate excitation from the outside. Since no permanent magnet is used, no cogging torque is generated, and thus, the rotor can be rotated with small torque. Since the power generator is a self-excitation type but is provided with the initial excitation unit, power generation can be reliably started even after stop of rotation or disassembly for maintenance, and further even when the rotational speed is low.
Although the initial excitation unit is provided, an extremely small magnetic force is enough for initial excitation because a magnetic flux increases with rotation in a self-excitation power generator. Accordingly, simple means is enough as the initial excitation unit, whether the initial excitation unit is magnetization unit described below or a permanent magnet.
In one embodiment of the present invention, a magnetization unit may be provided which magnetizes one or both of the output iron core and the field iron core. The term “magnetize” means performing magnetization such that residual magnetism is generated after a magnetization process is completed.
An extremely small magnetic force is enough for initial excitation because a magnetic flux increases with rotation in a self-excitation power generator, as described above. Accordingly, the magnetization unit only needs to perform magnetization to a degree enabling generation of a magnetic force required for initial excitation in power generation. Thus, the magnetization unit may be much smaller than external power sources for separately-excited type power generators.
The magnetization unit may be configured to apply magnetization current to any of the output winding, the main field winding, and the auxiliary field winding. As a result of applying current of a certain magnitude or more to a winding, magnetization can be performed on the cores. When the magnetization unit is configured to apply magnetization current to a winding, the magnetization unit may have a simple configuration.
The magnetization current may be direct current, or may be pulse current. When the magnetization current is direct current, the magnetization unit may have a simpler configuration. If the magnetization current is pulse current, strong current required for magnetization can be easily applied temporarily, or the magnitude of magnetization current can be easily adjusted.
The magnetization unit configured to apply magnetization current to the windings, may include: a magnetization power source formed of a secondary battery or a capacitor; and a switching element interposed either between the magnetization power source and the output winding to which the magnetization current is applied, or between the magnetization power source, and the main field winding and the auxiliary field winding to which the magnetization current is applied. With this configuration, the magnetization unit may have a simple configuration.
In one embodiment of the present invention, the initial excitation unit may be an initial excitation magnet in the form of a permanent magnet which is provided in the field iron core and which generates a magnetic force required for initial excitation in power generation.
When the initial excitation unit is an initial excitation magnet formed of a permanent magnet, a circuit as in the magnetization unit is not needed, and the circuit configuration becomes simple. Although the initial excitation magnet is provided, an extremely small magnetic force is enough for initial excitation because a magnetic flux increases with rotation in a self-excitation power generator, as described above. Since the initial excitation magnet is a permanent magnet which generates a magnetic force required for initial excitation, the permanent magnet may be one which generates a magnetic force much weaker than permanent magnets that provide ordinary generation power. Accordingly, expensive rare metal is not needed, an inexpensive material such as a ferrite magnet is enough, a small magnet is enough, and the cogging torque does not become a practical problem.
The power generator is an improved self-excitation type, and thus, can be easily put into practical use, unlike reluctance power generators.
In one embodiment of the present invention, the initial excitation magnet may be embedded in a surface, on a magnetic pole segment of the field iron core, facing the output iron core, or may be embedded between adjacent magnetic pole segments of the field iron core. As a result of the initial excitation magnet being embedded in the surface facing the output iron core or between the magnetic poles in this way, a magnetic force generated by the initial excitation magnet is efficiently used in initial excitation at a start of rotation.
In a case where the field iron core is provided with the initial excitation magnet, the direction of a magnetic flux generated by the initial excitation magnet may be same as the direction of a magnetic flux generated by excitation current flowing through the main field winding.
As a result of making the directions of magnetic fluxes same, a magnetic force generated by the initial excitation magnet is efficiently used in initial excitation at a start of rotation.
According to an embodiment of the present invention, the power generator may be configured as a power generator for wind power generation, in which the rotor is rotationally driven by a wind turbine.
In this way, rotation can be started even with small torque, and power generation can be performed even by low-speed rotation. Thus, in wind power generation in which greatly variable power of nature is used, power can be efficiently generated.
Any combination of at least two constructions, disclosed in the appended claims and/or the specification and/or the accompanying drawings should be construed as included within the scope of the present invention. In particular, any combination of two or more of the appended claims should be equally construed as included within the scope of the present invention.
In any event, the present invention will become more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views, and:
A first embodiment of the present invention is described with reference to
In
The rotor 5 includes a field iron core 8, and main field windings 9 and auxiliary field windings 10 wound around the field iron core 8. The field iron core 8 has a core body 8a formed with a center hole and a plurality of tooth-shaped magnetic pole segments 8b protruding radially outwardly from the outer circumference of the core body 8a and arranged in the circumferential direction of the core body 8a. Three magnetic pole segments 8b are provided for each of the magnetic pole segments 6b of the output iron core 6. The main field windings 9 are each wound over two adjacent magnetic pole segments 8b, 8b. The main field windings 9 each wound over two magnetic pole segments 8b, 8b are connected with each other in series such that different magnetic poles appear on magnetic pole surfaces of a pair of adjacent magnetic poles. The auxiliary field windings 10 are each wound over two adjacent magnetic pole segments 8b, 8b, similarly to the main field windings 9, such that the phase of the auxiliary field windings 10 is shifted from the phase of the main field windings 9 by an amount corresponding to one magnetic pole segment 8b. The auxiliary field windings 10 each wound over two magnetic pole segments 8b, 8b are connected in series such that different magnetic poles appear on magnetic pole surfaces of a pair of two adjacent magnetic poles. As shown in
As shown in
The power generator G is a self-excitation type power generator configured to include the auxiliary field windings 10, and is provided with the magnetization unit 2 serving as an initial excitation unit, as shown in
Magnetization can be performed by causing current of a predetermined magnitude to flow for an extremely short time. The degree of magnetization may be such a degree that residual magnetism required for initial excitation for start of power generation can be obtained. The degree is determined on the basis of the voltage and the magnitude of current depending on the on time of the switching element 13. An operation to open/close the switching element 13 is performed by switching controller 15. For example, the switching controller 15 monitors a signal detected by rotation detector 16 configured to detect rotation of the rotor 5, and upon detection that the rotor 5 in a still state starts to rotate, turns on the switching element 13 for a set time period required for magnetization. When a time during which rotation of the rotor 5 is stopped is short, sufficient residual magnetism remains, and thus, the switching controller 15 may perform control to turn on the switching element 13 in accordance with a set condition of, for example, turning on the switching element 13 only when rotation of the rotor 5 is started after the rotation is stopped for a set time period or longer.
In the embodiment in
Operations according to the first embodiment will be described. Operations in a case where the rotor 5 rotates to generate power are described. Since the first rectifying element 11 is connected in parallel to the main field winding 9, as shown in
The residual magnetism of the output iron core 6 or the field iron core 8 causes current to flow through the main field windings 9. By a magnetic flux, generated by the main field windings 9 due to the current, a magnetic flux interlinking the auxiliary field windings 10 changes so that voltage is generated at the auxiliary field windings 10. With this voltage, the auxiliary field windings 10 supply current via the main field windings 9, and current to flow through the main field windings 9 is increased. When no voltage is induced at the auxiliary field windings 10 and no current is supplied, circulation current flows through the main field windings 9 via the rectifying element 11 to maintain the magnetic flux of the main field windings 9. Current is supplied to the main field windings 9 and a magnetic flux generated by the main field windings 9 is increased, and the magnetic flux interlinking the auxiliary field windings 10 is also increased accordingly. Thus, more current is supplied to the main field windings 9. In this way, current flowing through the main field windings 9 is gradually increased, and a field magnetic flux required for power generation is generated. By the relative movement of the output iron core 6 and the field iron core 8, the interlinkage magnetic flux of the output windings 7 is changed and voltage is generated.
Power is generated during rotation of the rotor 5 as described above. However, when the rotor 5 is stopped for a certain long time, power generation cannot be started because no residual magnetism remains in both the output iron core 6 and the field iron core 8 or the residual magnetism is insufficient. Therefore, in the present embodiment, at a start of rotation after the rotor 5 is stopped, the switching element 13 of the magnetization unit 2 is turned on to cause magnetization current to flow from the magnetization power source 14 to the output windings 7. Thus, the output iron core 6 is magnetized. As described above, since a magnetic flux is gradually increased as rotation is continued, the degree of magnetization may be such a degree that residual magnetism required for initial excitation for starting power generation can be obtained. For this reason, to perform magnetization, current of a predetermined magnitude may be caused to flow for an extremely short time. By the magnetization, power generation is reliably started by a restart of rotation, even after the rotor 5 is stopped for a long time.
In the embodiment illustrated in
According to the power generator G of the aforementioned first embodiment or having the configuration illustrated in
As in the example illustrated in
Alternatively, as shown in
Operations of the power generator G according to the present embodiment are described. Operations of the power generator G during continuous rotation are identical to those in the first embodiment, and the explanation thereof is omitted. In the present embodiment, as in the aforementioned embodiment, power generation is performed during rotation of the rotor 5. However, if the rotor 5 is stopped for a certain long time, power generation cannot be started because no residual magnetism remains in both the output iron core 6 and the field iron core 8 or the residual magnetism is insufficient. Therefore, in the present embodiment, the initial excitation magnets 31 are provided. By magnetic fluxes generated by the initial excitation magnets 31, power generation can be reliably started by restart of rotation even after the rotor 5 is stopped for a long time.
According to the power generator G having this configuration, the following advantages can be obtained. Since the power generator G is a self-excitation type which performs excitation using the auxiliary field windings 10, power generation can be performed without requiring a permanent magnet for power generation or an external power source for supplying power for separate excitation from the outside. Since no permanent magnet for power generation is used, no cogging torque is generated, and thus, the rotor 5 can be rotated with small torque. Although the power generator G is a self-excitation type, since the initial excitation magnets 31 are provided in the field iron core 8, power generation can be reliably started even after stop of rotation or disassembly for maintenance, and further even when the rotational speed is low.
Although the initial excitation magnets 31 are provided, an extremely small magnetic force is enough for initial excitation because a magnetic flux increases with rotation in a self-excitation power generator, as described above. Since the initial excitation magnets 31 are permanent magnets which generate such small magnetic forces required for initial excitation, the permanent magnets may be ones which generate a magnetic force much weaker than permanent magnets that provide ordinary generation power. Accordingly, expensive rare metal is not needed, an inexpensive material such as ferrite magnets is enough, small magnets are enough, and the cogging torque does not become a practical problem. The present embodiment is improvement in a self-excitation type power generator, and thus, can be easily put into practical use, unlike a reluctance power generator.
In the aforementioned embodiments, the output iron core 6 is on the stator 4 side and the field iron core 8 is on the rotor 5 side. However, the field iron core 8 may be on the stator 4 side and the output iron core 6 may be on the rotor 5 side. Further, a bipolar power generator is provided in the aforementioned embodiments. However, a multipolar power generator including four poles, eight poles, or sixteen poles, etc. may be used.
In the aforementioned embodiments, the magnetization unit 2 or the initial excitation magnets 31 are provided as initial excitation unit. Alternatively, as the initial excitation unit, means (not illustrated) may be provided which does not perform magnetization but applies current to any of the windings 7, 8, and 9 only for a predetermined time in the initial stage of rotation, such that a magnetic force required for initial excitation in power generation is generated in one or both of the output iron core 6 and the field iron core 8.
As shown in
As a result of using the power generator G as a power generator for wind power generation in this way, rotation can be started even with small torque, and power generation can be performed even when the rotational speed is low. Thus, in wind power generation using greatly variable power of nature, power can be efficiently generated.
The power generator G according to any one of the aforementioned embodiments can be used for power generation using various energy sources including power generation using flowing water, and power generation using other power of nature, as well as wind power generation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-150442 | Jul 2014 | JP | national |
| 2014-150684 | Jul 2014 | JP | national |
| 2014-163438 | Aug 2014 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2015/070375 | Jul 2015 | US |
| Child | 15412677 | US |
