WO2018042226A1

WO2018042226A1 - Electric generator and electric power generation system

Info

Publication number: WO2018042226A1
Application number: PCT/IB2016/055197
Authority: WO
Inventors: Tawanda MUNJERI
Original assignee: Munjeri Tawanda
Priority date: 2016-08-31
Filing date: 2016-08-31
Publication date: 2018-03-08

Abstract

An electric generator (23) for an electric power generation system includes a rotor (24) and a stator (25). A stationary ferromagnetic member (28) is positioned between the stator (25) and the rotor (24) to form a first air gap (27) and a second air gap (26) respectively. The stationary ferromagnetic member (28) is appropriately positioned such that an electromotive force is statically induced in the stator windings (253). Furthermore, to utilize a single magnetic flux to simultaneously generate an electromotive force and produce reluctance torque so that torque requirement from the prime mover is reduced thereby increasing efficiency. The generator (23) can be configured for either angular operation or linear operation and is operable as a single phase or multi phase generator. Furthermore an electric generation system (20) comprising such a generator (23) is provided.

Description

Electric generator and electric power generation system

The present invention relates to an electric generator as well as to an electric power generation system comprising an electric generator.

A conventional electric power generation system 10 in accordance with the prior art shown in fig .1 comprises a prime mover 12, and a generator 13. The generator 13 comprises a stator 15, and a rotor 14 separated by an air gap 16. As will be understood by those skilled in the art, the prime mover 12 transforms primary energy into mechanical energy. The electric generator 13 transforms the mechanical energy from the prime mover 12 to electrical energy. The market and society continues to demand increasing efficiency in the transformation process. To that end great efforts have been made to reduce losses in the transformation process. However there is still potential for improvement.

Technical Problem

The objective of the present invention is to provide an improved electric generator. It is also another objective of the present invention to provide an electric generator which improves the efficiency of the electrical power generation system. It is a further objective of the present invention to provide an electric power generation system comprising aforementioned electric generator.

Solution to Problem

In accordance with the present invention, there is provided an electric generator, comprising a stator having a plurality of poles, and further having at least one phase winding wound thereon for outputting electrical power, a member movable relative to the stator, said member having a magnetic field generating device for generating a magnetic flux, the member further having a plurality of salient poles, at least one stationary ferromagnetic member, each of the at least one ferromagnetic member having a first end and a second end, each of the said at least one ferromagnetic member positioned between the rotor and the stator such that in alignment the first end of each of the at least one ferromagnetic member is disposed adjacent to a respective pole of the plurality of stator poles to form a first air gap therebetween and the second end of each of the at least one ferromagnetic member is disposed adjacent to at least one pole of said plurality of member poles to form a second air gap therebetween.

In accordance with the present invention, there is further provided an electric power generation system comprising an electric generator as described above

Advantageous Effects of Invention

Advantageously, the stationary ferromagnetic member is appropriately positioned between the rotor and the stator such that electromotive force is statically induced electromotive force in the stator windings. Furthermore, to utilise a single magnetic field source for simultaneously generating an electromotive force and producing reluctance torque. Reluctance torque so produced reduces toque requirement from the prime mover thereby increasing efficiency.

Further benefits and advantages of the present invention will become apparent after careful reading of the detailed description with the appropriate reference to the accompanying drawings.

The accompanying drawings are presented in the cause of providing a description of the principles and conceptual aspects of the present invention. In this regard the accompanying drawings are not necessarily drawn to scale or to illustrate inconsequential minutia beyond what is needed for fundamental understanding of the present disclosure. In the accompanying drawings:

is a block diagram of a prior art electric power generation system;

is a block diagram of an electric power generation system in accordance with the preferred embodiment of the present invention;

is a cross-sectional view of an electrical generator in accordance with the preferred embodiment of the present invention;

is a graphical presentation of flux linkage characteristics at different rotor position in accordance with the preferred embodiment of the present invention;

is a graphical presentation of the torque at different rotor position in accordance with the preferred embodiment of the present invention;

is a graphical presentation of output of a three phase electric generator in accordance with the preferred embodiment of the present invention.

shows an electric generator in accordance with another preferred embodiment of the present invention.

Referring to drawings and initially to fig.3, an electric generator 23 in accordance with the preferred embodiment of the present invention comprises an electric generator 23 configured for angular operation, more particularly radial operation. The electric generator 23 comprises a rotor 24 manufactured from a magnetically permeable material such as iron. The rotor has a plurality of salient poles 241a and 241b which are disposed around and project radially outward from an axis of rotation 29, the poles 241a and 241b having thereon field winding 242 for generating a magnetic field 30 when the windings 242 are supplied with direct current.

The generator 23 has a stator 25 which is manufactured from magnetically permeable material having a back iron 251 and further having a plurality of poles 252a, 252b and 252c. The poles 252a, 252b and 252c are disposed radially inward toward the rotor 24. At least one phase winding 253 and typically three phase windings A, B and C are wound on the stator 25 for outputting electrical power.

Stationary ferromagnetic members 28a, 28b and 28c respectively are provided for stator poles 252a, 252b and 252c respectively. The stationary ferromagnetic members 28a, 28b and 28c respectively are positioned between stator poles 252a, 252b and 252c respectively and the rotor 24. The ferromagnetic members 28a, 28b and 28c are held stationary by any appropriate means. For example ferromagnetic members are attached to the stator 25 by a non ferrous connector 21(not shown in fig. 3). Each of the stationary ferromagnetic members 28a, 28b and 28c have a first end 281 and second end 282. As shown in fig. 3, stator pole 252a, ferromagnetic member 28a and rotor pole 241a are in alignment such that the first end 281 is disposed adjacent to a stator pole 252a to form a first air gap 27 therebetween, the second end 282 is disposed adjacent to rotor pole 241a to form a second air gap 26 therebetween.

The machine operation is based on two principles combined by the presence and positioning of the ferromagnetic member, the principle of electromagnetic induction and magnetic variable reluctance principle.

A direct current is applied to the rotor windings 242. The rotor 24 becomes an electromagnetic which generates a magnetic field 30 exhibiting flux, which is conducted through a magnetic circuit 31. Magnetism is induced in the stationary ferromagnetic members 28a, 28b and 28c by the rotor magnetic field 30 so that the stationary ferromagnetic members 28a, 28b and 28c become magnets. Specifically, the second ends 282 of the ferromagnetic members are magnetized with opposite polarity of the adjacent rotor pole 241a and 241b.

The effect of the positioning of the stationary ferromagnetic members 28a, 28b and 28c and the effect of their magnetism is as follows. First, an electromagnetic force of attraction is generated between rotor poles 241a and 241b and the stationary ferromagnetic members 28a, 28b and 28c. Second, a reluctance torque is generated on the rotor 24 as the poles of the rotor 241a and 241b are attracted to position that minimizes the magnetic reluctance of the circuit where the rotor poles 241a and 241b are aligned with the ferromagnetic member. Third, the ferromagnetic members 28a, 28b and 28c respectively directly become the source of magnetic field to the stator poles 252a, 252b and 252c respectively.

For example rotor pole 241b is attracted to stator pole 252c to minimize the magnetic reluctance generating a torque on the rotor 24. At the same time, magnetic flux 30 through stator pole 252c increases to its maximum as the rotor pole 241b moves into alignment, and because the stator windings C are wound on the magnetic path 30, electromotive force is statically induced in the stator windings C since the source of the magnetic field is directly the ferromagnetic member.

On the contrary, rotor pole 241a is in alignment with stator pole 252a. The rotor pole 241a is driven by a torque to bring it out of alignment and to a position of maximum reluctance position y. At the same time, the magnetic flux 30 through stator pole 252a decreases as the rotor pole 241a moves to y, accordingly, electromotive force is statically induced in the stator windings A due to the variation of magnetic flux.

Fig. 4 shows the flux variation through a stator pole with rotor position. The rotor position is plotted on the x-axis and the flux linkage on the y-axis. Alignment of stator pole 252a, and ferromagnetic member 28a and rotor pole is shown graphically by position 33. The period when the flux is increasing 37 corresponds to the period when the rotor pole 241b is moving into alignment with stator pole 252c and the period when the flux is decreasing 38 corresponds to the period when the rotor pole 241a is moving away alignment position to position of maximum reluctance y represented by position 34.

Fig.5 shows torque variation with rotor position. The rotor position is plotted on the x-axis and the torque on the y- axis. Position 39 is the position of alignment between the stator, ferromagnetic member and the rotor. The period when the torque is increasing 42 corresponds to the period the rotor pole 241b is moving to its minimum reluctance position y. A reluctance torque is generated. The period when the torque is decreasing 43 correspond to the period when the rotor pole 241a is moving out of alignment with stator pole 252a. A braking torque is generated. A torque at least equal to the braking torque is applied to move the rotor 24.

Movement of rotor pole 241b to its minimum reluctance position y with respect to stator pole 252c, and accordingly production of reluctance torque corresponds with the period when phase current is increasing in the stator windings 252c while at the same time movement of the rotor pole 241a to its maximum reluctance position y, and accordingly production of braking torque corresponds to the period when phase current is decreasing in the stator windings 252a. Referring to fig.6, at point 46 the rotor experiences a reluctance torque due to phase A and B and a braking torque due to phase C. The torque from the three phases is additive. Similarly, at point 47 the rotor experiences a reluctance torque due to phase B and phase C and a braking torque due to phase A.

Performance characteristics are as follows. The back electromotive force can be positive or negative depending on whether the rotor pole is moving into alignment or out of alignment so exciting current needs to be adjusted accordingly during operation. In multiphase systems the positive and negative back electromotive force from some phases may cancel out since they are in the same rotor windings. There is mutual inductance between the stator magnetic flux and the flux from the ferromagnetic member, hence the exciting current and/or velocity of the rotor needs to be adjusted accordingly during operation to maintain constant output.

Although angular operation has been explained, more particularly radial operation, it is obvious that the electric generator in accordance with the present invention can be adapted for axial operation.

Referring to fig.5, an electric generator 50 in accordance with another preferred embodiment of the present invention comprises an electric generator 50 configured for linear operation. The electric generator 50 comprises a stator 55 made from magnetically permeable material and rigidly affixed on the plain on which it sits. The stator carries single phase winding 551 for outputting electrical energy.

The electric generator comprises a translator 54 which functions analogously to the rotor 24 in the angular configuration. The translator 54 can have permanent magnets attached to it or it can be a magnet. For example the translator 54 is a permanent magnet.

The ferromagnetic member 58 is rigidly affixed to the plain on which it sits and positioned between the translator 54 and the stator 55. The ferromagnetic member having a first end 581and a second end 582, the first end 581 disposed adjacent to the stator pole 552a and the second end 582 disposed adjacent to the translator pole 541a.

The electric generator 50 operates in a manner identical to the operation previously described for angular operation, except that it is single phase and the movement is linear rather than angular. Disadvantageously, a single phase is unable to utilise reluctance torque from other phase.

As in the case of angular configuration, the translator 54 tends to move to position e where magnetic reluctance is minimized. The stationary ferromagnetic member 58 becomes a magnet and the translator 54 is attracted to the ferromagnetic member 58 to minimize reluctance generating a reluctance torque on the translator. At the same time, the magnetic flux through the stator increases generating a statically induced electromotive force in the stator windings 551. A force is applied to move the translator 54 away from e to a position of maximum reluctance d, and at the same time an electromotive force is statically induced in the stator windings 551.

Accordingly, the stationary ferromagnetic member is appropriately positioned between the rotor and the stator such that electromotive force is statically induced in the stator windings. Furthermore, to utilise a single magnetic field source for simultaneously generating an electromotive force and producing reluctance torque. Reluctance torque so produced reduces toque requirement from the prime mover thereby increasing efficiency.

Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many possible modifications and variations can be made without departing from the scope of the present invention. It is therefore contemplated that the appended claim or claims will cover such modifications and variations that fall within the true scope of the invention.

Claims

An electric generator, comprising:
a stator having a plurality of poles, and further having at least one phase winding wound thereon for outputting electrical power;
a member movable relative to the stator, said member having a magnetic field generating device for generating a magnetic flux, the member further having a plurality of salient poles; and
at least one stationary ferromagnetic member, each of the at least one stationary ferromagnetic member having a first end and a second end, said each of the at least one stationary ferromagnetic member positioned between the member and the stator such that in alignment the first end of each of the at least one stationary ferromagnetic member is disposed adjacent to a respective pole of the plurality of stator poles to form a first air gap therebetween and the second end of each of the at least one stationary ferromagnetic member is disposed adjacent to at least one pole of said plurality of member poles to form a second air gap therebetween.
The electric generator according to claim 1, wherein said member is a rotor, and further wherein said rotor, said at least one stationary ferromagnetic member and said stator are configured for angular operation and wherein said movement relative to the stator is angular.
The electric generator according to claim 1, wherein said member is a translator and further wherein said translator, said at least one stationary ferromagnetic member and stator are configured for linear operation and said movement relative to the stator is linear.
An electric power generation system, comprising:
a prime mover;
an electric generator according to any of the preceding claims.