GB2424523A - Electronically commutated electrical machine - Google Patents
Electronically commutated electrical machine Download PDFInfo
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- GB2424523A GB2424523A GB0505749A GB0505749A GB2424523A GB 2424523 A GB2424523 A GB 2424523A GB 0505749 A GB0505749 A GB 0505749A GB 0505749 A GB0505749 A GB 0505749A GB 2424523 A GB2424523 A GB 2424523A
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- electronic
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- commutator
- electrical machine
- electronic commutator
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/006—Controlling linear motors
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/16—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring
- H02P25/18—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring with arrangements for switching the windings, e.g. with mechanical switches or relays
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc Machiner (AREA)
Abstract
The present invention relates to an electrical machine such as a brushless dc rotating or linear machine, for example. The electrical machine includes a first electronic commutator and a first stator winding including a number of coils linked by the same number of points of common coupling, each point of common coupling being connected to the first electronic commutator. The electrical machine also includes a second electronic commutator and a second stator winding including a number of coils linked by the same number of points of common coupling, each point of common coupling being connected to the second electronic commutator. The dc terminals DC1, DC2 of the first and second electronic commutators can be connected together in a series, parallel or series-parallel arrangement - circuits B,C,D.
Description
TITLE
Electrical machine topologies
DESCRIPTION
Technical Field
The present invention relates to electrical machine topologies, and in particular to topologies for rotating and linear machines (such as dc brushless rotating and linear machines, for example) that employ electronic commutation.
Background Art
A brushless dc rotating machine typically includes a rotor surrounded by a wound stator, An electronic switching circuit is used to control the commutation of current in the stator winding based on the angular position of the rotor. The rotor provides a rotating magnetic field and this can be generated by permanent magnets, conventional windings with a slip ring or brushless excitation power supply, or superconducting windings with a suitable excitation power supply.
A brushless dc linear machine typically includes a moving member and an adjacent or surrounding wound stator. An electronic switching circuit is used to control the commutation of current in the stator winding based on the linear position of the moving member. The moving member provides a moving magnetic field and this can be generated by permanent magnets, conventional windings with a slip ring or brushless excitation power supply, or superconducting windings with a suitable power excitation supply. Whereas the motion of a rotating machine is usually continuous, this cannot be so in a linear machine, hence a linear machine could be used in applications that inherently benefit from reciprocating motion, for example wave power generators.
British Patent Application 2117580 discloses a hrushles ic otating machine that employs an electronic switching circuit. Tlic electronic switching circuit essentially replicates a conventional brush and commutator topology for an industry-standard lap wound stator where the brushes are replaced by thyristors and the commutator segments are replaced by a point of common coupling between associated pairs of thyristors. One thyristor in each thyristor pair has its anode connected to a first dc terminal, while the other thyristor in that pair has its cathode connected to a second dc terminal. A stator winding with n series connected coils has n nodes that intercept the n points of common coupling in the electronic switching circuit. This is illustrated in Figure 1 for the case where n = 8.
It can seen from Figure 1 that a first coil Cl is connected to a second coil C2 and to a first pair of thyristor switches SI a and SI b by means of a first point of common coupling PCC 1. The anode of thyristor Si a is connected to a first dc terminal DC 1 by means of a first ring "Ring 1" and the cathode of thyristor Sib is connected to a second dc terminal DC2 by means of a second ring "Ring 2". The second coil C2 is connected to a third winding C3 and to a second pair of thyristor switches S2a and S2b by a second point of common coupling PCC2. The anode of thyristor S2a is connected to the first dc terminal DC 1 by means of the first ring "Ring 1" and the cathode of thyristor S2b is connected to the second dc terminal DC2 by means of the second ring "Ring 2". The remaining coils are connected to the first dc terminal DC1 and the second dc terminal DC2 in a corresponding manner.
The thyristor pairs are commutated by the back emf (i.e. the electromotive force induced in the stator windings) of the brushless dc rotating machine and by the application of gate pulses that are synchronised with the angular position of the rotor.
At low rotor speeds this back emf can be insufficient for the commutation of the thyristors and an external commutation circuit of the dc line type is employed. This external commutation circuit is also synchronised to the angular position of the rotor and hence to the gating of the thyristor pairs.
The brushiess dc rotating machine of British Patent Application 2117580 suffers from the following disadvantages: (i) the terminal voltage between the dc terminals DC1 and DC2 is limited by the forward and reverse blocking voltage ratings of available thyristor switching devices; (ii) the synchronisation of the gating of the thyristor pairs to the angular position of the rotor is difficult to implement and is prone to electromagnetic interference; and (iii) the gating synchronisation of the thyristor pairs and the subsequent commutation process is not capable of precisely adapting to the load conditions of the machine.
Summary of the Invention
The present invention does not suffer from the disadvantages mentioned above and provides an electrical machine comprising: a first electronic commutator having two dc terminals; a first stator winding including a number of coils linked by the same number of points of common coupling, each point of common coupling being connected to the first electronic commutator; a second electronic commutator having two dc terminals; and a second stator winding including a number of coils linked by the same number of points of common coupling, each point of common coupling being connected to the second electronic commutator; and wherein at least one of the dc terminals of the first electronic commutator is connected to at least one of the dc terminals of the second electronic commutator.
It will be understood that the electrical machine is not limited to just two stator windings and that additional stator windings and associated electronic commutators can be provided. The dc terminals of the electronic commutators can be connected together in a series, parallel or series-parallel arrangement to achieve the optimum dc terminal voltage and current lbr a particular application.
If the first and second electronic commutators are to be connected together in a series arrangement then one dc terminal of the first electronic commutator and one dc terminal of the second electronic commutator are connected together in series. The other dc terminal of the first electronic commutator and the other dc terminal of the second electronic commutator (that is the unconnected dc terminals of the first and second electronic commutators, respectively) can then be connected to a dc supply network.
On the other hand, if the dc terminals of the first electronic commutators and the dc terminals of the second electronic commutator are to be connected together in parallel then one of the dc terminals of the first electronic commutator is connected to one of the dc terminals of the second electronic commutator, and the other of the dc terminals of the first electronic commutator is connected to the other of the dc terminals of the second electronic commutator. Both pairs of connected dc terminals of the first and second electronic commutators can then be connected to a dc supply network.
The electrical machine may further comprise: a third electronic commutator having two dc terminals; and a third stator winding including a number of coils linked together by the same number of points of common coupling, each point of common coupling being connected to the third electronic commutator.
In this case, one dc terminal of the third electronic commutator can be connected to the dc terminal of the second electronic commutator that is not already connected to a dc terminal of the first electronic commutator. The other dc terminal of the first electronic commutator and the other dc terminal of the third electronic commutator (that is the unconnected dc terminals of the first and third electronic commutators, respectively) can then be connected to a dc supply network. If additional stator windings and electronic commutators are provided then it will be understood that the unconnected dc terminal of the third electronic commutator can be connected to a dc terminal of another electronic commutator, and so on.
The electrical machine may also further comprise: a third electronic commutator having two dc terminals; a third stator winding including a number of coils linked together by the same number of points of common coupling, each point of common coupling being connected to the third electronic commutator; a fourth electronic commutator having two dc terminals; and a fourth stator winding including a number of coils linked together by the same number of points of common coupling, each point of common coupling being connected to the fourth electronic commutator.
In this case, the dc terminals of the third electronic commutator and the dc terminals of the fourth electronic commutator can be connected together in parallel, and one of the pairs of connected dc terminals of the first and second electronic commutators and one of the pairs of connected dc terminals of the third and fourth electronic commutators can be connected together in series.
The other pair of connected dc terminals of the first and second electronic commutators and the other pair of connected dc terminals of the third and fourth electronic commutators (that is the pair of connected dc terminals of the first and second electronic commutators that are not already connected to the pair of connected dc terminals of the third and fourth electronic commutators) can then be connected to a dc supply network.
In each case, the connection to the dc supply network can be made directly or by means of a passive filter or a supply-side power converter apparatus.
Each of the points of common coupling of the first stator winding is preferably connected to one of dc terminals of the first electronic commutator by a first power electronic switching device and to the other of the dc terminals of the first electronic commutator by a second power electronic switching device, and each of the points of common coupling of the second stator winding is preferably connected to one of dc terminals of the second electronic commutator by a first power electronic switching device and to the other of the dc terminals of the second electronic commutator by a second power electronic switching device. The same is also true for any additional stator windings and associated electronic commutators if they are provided.
The first power electronic switching devices connected to the points of common coupling of the first stator winding can be thyristors or diodes having their anodes connected to said one of the dc terminals of the first electronic commutator and the second power electronic switching devices connected to the points of conmion coupling of the first stator winding can be thyristors or diodes having their cathodes connected to said other of the dc terminals of the first electronic commutator.
Similarly, the first power electronic switching devices connected to the points of common coupling of the second stator winding can be thyristors or diodes having their anodes connected to said one of the dc terminals of the second electronic commutator and the second power electronic switching devices connected to the points of common coupling of the second stator winding can be thyristors or diodes having their cathodes connected to said other of the dc terminals of the second electronic commutator.
The electrical machine preferably includes a controller for regulating the first and second electrical commutators (and any additional electrical commutators where appropriate). The controller can use coil voltages in the first and second stator windings to synchronise the first and second electrical commutators with the electrical machine.
The electrical machine can be a rotating machine having a rotor and a stator. In this case, the controller can also use the angular position of the rotor to synchronise the first and second electronic commutators with the electrical machine. The stator preferably incorporates the first and second stator windings, which circumferentially overlap.
If the electronic commutators are connected together in a series arrangement then identical currents will flow in all slots in a given stator pole face, thereby maximising the air-gap shear stress for a given flux density. The rotor will usually have p poles, either generated electro-magnetically using conventional or superconducting windings, or by permanent magnets. The magnetic flux in the air gap between the pole faces can have a sinusoidal circumferential distribution, or have a profile with a fundamental plus odd order harmonics, in order to further maximise the air gap shear stress.
The stator will usually incorporate p12 stator windings each having its own electronic commutator. Commutation of current is achieved through a combination of the switching action of the power electronic switching devices in the electronic commutators and the emf generated within the stator windings by the interaction with the rotor flux and the inductance of the individual coils. As with a conventional dc machine having a lap wound stator, brushgear and a commutator, the dc terminal voltage of each electronic commutator is equal to the maximum terminal to terminal voltage across the associated stator winding and the terminal current is the sum of the two opposing currents in the associated stator winding.
The electrical machine can also be a linear machine having a moving member and a linear stator assembly incorporating the first and second rotor windings. The linear machine may be incorporated in a wave generator where it will be used in a generating application to provide power from the reciprocating movement of ocean waves.
The moving member is preferably provided with a source of excitation. Such as permanent magnets, for example. The moving member can be longer or shorter than the linear stator assembly.
Drawings Figure 1 is a schematic diagram showing a prior art stator winding and associated electronic commutator that replicates a conventional brush and commutator topology for an industry-standard lap wound stator where the brushes are replaced by thyristors and the commutator segments are replaced by a point of common coupling between associated pairs of thyristors; Figure 2 is a schematic diagram showing some typical stator winding/commutator circuits that can be used in an electrical machine according to the present invention; Figure 3 is a schematic diagram showing the dc terminal voltage and current relationships when the stator winding/commutator circuits of Figure 2 are operated in an inverting mode; Figure 4 is a schematic diagram showing the dc terminal voltage and current relationships when the stator winding/commutator circuits of Figure 2 are operated in a rectifying mode; Figure 5 is a schematic showing a typical full pitch coil having three turns that forms part of a stator winding that is used in a brushless dc rotating machine according to the present invention; Figure 6 is a schematic showing three adjacent stator poles of a stator that is used in a brushless dc rotating machine according to the present invention; Figure 7 is a schematic showing a stator winding having fourteen individual coils and fourteen points of common coupling that is used in a brushless dc rotating machine according the present invention; Figure 8 is a schematic showing an electronic commutator that is used to supply the current to the stator winding of Figure 7; Figure 9 is a schematic showing a complete stator this is used in a brushless dc rotating machine according to the present invention; Figure 10 is a schematic showing how an electronic commutator of Figure 8 is connected to each of the stator windings of Figure 7; Figure 11 is a schematic showing an example of a control architecture for controlling a brushless dc rotating machine according to the present invention; Figure 12 is a schematic showing a first embodiment of a brushless dc linear generator according to the present invention, having a permanent magnet-excited moving member that is significantly longer than each of the stator windings of the stator assembly; and Figure 13 is a schematic showing a second embodiment of a brushless dc linear generator according to the present invention, having a permanent magnet-excited moving member that is significantly shorter than each of the stator windings of the stator assembly.
The present invention uses two or more stator windings (preferably socalled polygonal or lap stator windings), each having its own electronic commutator or electronic switching device. The combination of a single stator winding and associated commutator is referred to below as a "stator winding/commutator circuit".
The dc terminals of the respective electronic commutators can be connected together in series, parallel or a combined series-parallel arrangement. The use of an even number of stator winding/commutator circuits facilitates the construction of parallel and series-parallel connected arrangements where the voltage and current ratings of the individual stator windings are balanced. Similarly, the use of an odd number of stator winding/commutator circuits facilitates the construction of series connected arrangements where the voltage and current ratings of the individual stator windings are balanced. The balancing of the voltage and current ratings is important because it ensures that any particular arrangement will have electromagnetic symmetry.
Figure 2 illustrates some possible stator winding/commutator circuit arrangements.
For reasons of clarity, the stator winding/commutator circuit of Figure 1 has been simplified to the circuit labelled "Circuit A". It will therefore be readily appreciated that "Circuit B" represents an arrangement with three stator winding/commutator circuits in series, "Circuit C" represents an arrangement with two stator winding/commutator circuits in parallel, and "Circuit D" represents an arrangement with two stator winding/commutator circuits in parallel and in series with two further stator winding/commutator circuits in parallel. Each of the stator winding/commutator circuits includes a stator winding having n series connected coils and n points of common coupling. Each point of common coupling is connected to first and second rings by a pair of diodes or thyristors as described above.
The electronic commutators of "Circuit C" and "Circuit D" are connected together in parallel and industry-standard means must be employed to ensure that the currents in the parallel branches are sufficiently well balanced, for example, by employing carefully controlled impedances and flux linkages. The total current at the dc terminals of "Circuit C" and "Circuit D" is the sum of the currents in the parallel connected branches. On the other hand, the electronic commutators of "Circuit B" are connected together in series so all of the currents are inherently identical and the total voltage at the dc terminals is the sum of the individual terminal voltages. More particularly, in "Circuit B" a first stator winding/commutator circuit has a pair of terminals DCI a/DC2a, a second stator winding/commutator circuit has a pair of terminals DC 1 b/DC2b and a third stator winding/commutator circuit has a pair of terminals DCI c/DC2c. For stator winding/commutator circuits that are connected together in series, the connection must be series-additive to be beneficial. Therefore, it will be appreciated that terminal DC2a of the first stator winding/commutator circuit must he connected to terminal DCI b of the second stator winding/commutator circuit, terminal DC2b of the second stator winding/commutator circuit must be connected to terminal DCI c of the third stator winding/commutator circuit and (for the general case) so on down the series string. The total voltage is therefore the voltage across terminals DCI a and DC2c.
In "Circuit C" a first stator winding/commutator circuit has a pair of terminals DCI d/DC2d and a second stator winding/commutator circuit has a pair of terminals DC 1 e/DC2e. Terminals DCI d and DCI e are connected together and terminals DC2d and DC2e are also connected together. The total current is therefore the sum of the currents in the interconnection of terminals DC1d and DCIe on the one hand, and the interconnection of terminals DC2d and DC2e on the other.
Finally, in "Circuit D" a first stator winding/commutator circuit has a pair of terminals DC I f/DC2f, a second stator winding/commutator circuit has a pair of terminals DC 1 g/DC2g, a third stator winding/commutator circuit has a pair of terminals DCI h/DC2h and a fourth stator winding/commutator circuit has a pair of terminals DCI i/DC2i. The first and second stator winding/commutator circuits are parallel connected such that terminals DC 1 f and DCI g are connected together and terminals DC2f and DC2g are also connected together. Similarly, the third and fourth stator winding/commutator circuits are parallel connected such that terminals DCIh and -Il- DCI i are connected together and terminals DC2h and DC2i are also connected together. However, the two pairs of parallel connected stator winding/cormnutator circuits are also connected together in series such that terminals DC2f and DC2g are connected to terminals DCIh and DC ii. The total current is therefore the sum of the currents in the interconnection of terminals DC if and DC 1 g on the one hand, and the interconnection of terminals DC2h and DC2i on the other, and the total voltage is the voltage across terminals DC if and DC2h, or DC 1 g and DC2i.
In each case mentioned above, the polarity of the terminals labelled DC1# have the same polarity with respect to the terminals labelled DC2#. This is particularly important for stator winding/commutator circuits that are connected together in parallel because otherwise large circulating currents would flow.
It will therefore be readily appreciated that larger numbers of stator winding/commutator circuits may be connected together to create series, parallel and series-parallel arrangements using the principles described above.
Figure 3 shows the dc terminal voltage and current relationships when the stator winding/commutator circuits of "Circuit A", "Circuit B", "Circuit C" and "Circuit D" of Figure 2 are operated in an inverting mode (that is when the associated brushless dc rotating or linear machine is used for motoring applications). Figure 4 shows the dc terminal voltage and current relationships when the stator winding/commutator circuits of "Circuit A", "Circuit B", "Circuit C" and "Circuit D" of Figure 2 are operated in a rectifying mode (that is when the associated brushless de rotating or linear machine is used for generating applications).
A particularly preferred arrangement of stator winding/commutator circuits for a brushless dc rotating machine will now be explained with reference to Figures 5 to 11.
The chording of the individual coils of each stator winding will depend on the application of the brushless dc rotating machine and will be a compromise. Full pitch coils will provide increased power rating but only at the expense of increased end - 12- winding size. Full pitch coils depart from a first point of common coupling into a first slot, returning in a second and equivalent slot in the adjacent stator pole and finally terminate at a second and adjacent point of common coupling. Each coil in such a stator winding will consist of a single turn, or an integer number of turns, chosen to achieve the desired terminal voltage characteristics. Multiple turn coils pass through the first and second slots are many times as required. By way of example, Figure 5 shows a typical full pitch coil having three turns.
In a brushless dc rotating machine having p stator poles, there will be p12 full pitch coils and p12 electronic commutators. Each stator winding of a machine having n slots per stator pole will consist of 2n coils connected in series, using 2n points of common coupling with the electronic commutators. Figure 6 shows three adjacent stator poles for the case where n = 7 and where full pitch coils are used. The middle pole "Pole 2" is fully populated with coils according the industry-standard two-layer arrangement. Of course, a concentric arrangement could also be used. For reasons of clarity, the adjacent poles ("Pole 1" and "Pole 3") are shown partly populated with coils. More particularly, the top pole "Pole 1" (the uppermost on the page) is shown populated with a top layer (the black lines) while the bottom pole "Pole 3" (the lowermost on the page) is shown populated with a bottom layer (the grey lines).
Figure 7 shows a stator winding having fourteen individual coils (labelled 1 to 14) and fourteen points of common coupling (labelled A to N). According to convention, when the brushless dc rotating machine is used for motoring applications, current is supplied to the positive dc terminal of the electronic commutator by external means.
The current is then routed by the electronic commutator to any point in the stator winding where it splits into two paths. One path flows according to convention away from that point in the stator winding in one direction around the stator winding and the other path flows away from that point in the stator winding in the opposite direction to exit at the opposite point. For example, if current is supplied at point A then one path will flow through coils I to 7 and the other path flows through coils 14 to 8 to exit at point H. Likewise, according to convention, when the brushless dc rotating machine is used for generating applications, current is supplied by the - 13- positive dc terminal of the electronic commutator to external means. The phasing relationship between the supply point and the voltages in the individual coils 1 to 14 allows the machine to operate either as a motor or a generator. Current balance in the two halves of the stator winding is subject to the design issues mentioned above.
The electronic commutator used to supply the current to the stator winding is shown in Figure 8. It includes twenty-eight power electronic switching devices, fourteen of which are connected to a first dc terminal and the other fourteen are connected to a second dc terminal. The fourteen points of common coupling A to N are connected to the interconnecting points between associated pairs of power electronic switching devices. The nature and operation of the power electronic switching devices is described in more detail below.
Figure 9 shows the stator of the brushless dc rotating machine. The stator has ten poles (that is the case where p = 10) that are divided into five segments. The segments occupy inner and outer layers of a cylindrical arrangement that extends along the axis of the machine. The segments therefore overlap with each other in a circumferential maimer. As shown in Figure 9, each pole pair of the stator occupies three adjacent circumferentially displaced poles. This is described above with reference to Figure 6. However, it should be noted that the circumferential axis of Figure 9 is equivalent to the vertical linear axis of Figure 6. It should also be noted that the disposition of the coils in Figure 6 is as viewed through the air gap, from the centre of the machine whose stator is outside its rotor. In Figure 6, according to industry-standard winding terminology, the term "bottom" is used to describe the limbs of coils that are furthest towards the "bottom" of the slots in the stator. When the stator is outside the rotor, the "bottom" limbs described in Figure 6 appear as the outer circular layer in Figure 9. Thus, the pole numbers shown in Figures 6 and 9 are identical.
An electronic commutator "EC" is connected to each of the five stator windings as shown in Figure 10. The dc terminals of the commutators are connected together in series, thereby ensuring that all of the stator windings have the same total current.
- 14 - The total number of stator slots is pn and the total number of power electronic switching devices is 2pn. Accordingly, in the preferred arrangement shown in Figures to 11 where p 10 and n = 7 it will be readily understood that the total number of stator poles pn = 70 and the total number of power electronic switching devices 2pn 140.
The operation of the electronic commutators will now be described. If the brushless dc rotating machine is used for motoring applications (that is in an inverting mode) then conventional thyristors may be used as the power electronic switching devices.
In this case the commutation process will be generally as describedBritish Patent Application 2117580. This is because the series interconnection of the multiple electronic commutators actually has a minimal impact on the commutation process itself. However, alternative power electronic switching devices and operating modes are possible.
The brushless dc rotating machine can also be used for generating applications (that is in a rectifying mode) using thyristors or diodes and natural commutation. The commutation process is still largely as described in British Patent Application 2117580 but the available turn-off time for the power electronic switching devices is greater than when the machine is operating in an inverting mode. When diodes are used then the dc terminal voltage of the machine can only be controlled by varying the rotor excitation. This means that the dc terminal voltage will be approximately proportional to the speed of rotation of the rotor under conditions of constant excitation. The effect of armature reaction will be the same as that in a conventional un-compensated dc machine with brushes, that is the dc terminal voltage will reduce when load current flows in the dc terminals of the machine. It is not practical to incorporate a direct equivalent to compensating poles in such a machine. However, thyristors may be used in the place of diodes and these can be phase controlled to regulate the dc terminal voltage in an appropriate manner. The thyristors can be phase controlled in both rectifying and inverting modes. Gating synchronisation of the thyristors can be performed by a controller such as a high performance digital controller with effective noise immunity with respect to the electromagnetic interference that will typically be generated within and nearby the machine and its electronic commutation system. Before the gating synchronisation can start, it is usually necessary to wait until the machine has commenced rotation and sufficient terminal voltage has been developed for it to be reliably sensed by the controller.
Only a small number of coil voltages need to be sensed by the controller in order to determine the angular position of the rotor. However, when the brushless dc rotating machine is stationary, or is operating at very low speed, absolute and incremental encoders, respectively, may be employed in order to determine the angular position of the rotor. A control architecture that is suitable for both motoring and generating applications is shown in Figure 11.
The control architecture of Figure 11 is generally reliant on additional supply-side power conversion equipment for some control and protection functions. However, some applications may be satisfied by means of a passive filter connection to a dc supply network or power grid. The supply-side power converter 20 has little impact on the control principles employed in the electronically commutated machine and it will not be described in detail. A common controller is preferably used to control the operation of the supply-side power converter and the commutation of the brushless dc machine as long as both power conversion systems (that is the supply-side power converter and the electronic commutation system or machine-side power converter) are co-located or located sufficiently close to one another to facilitate viable interfaces between the controller and the two power converters. A brushless dc rotating machine 2, which may be a motor or a generator, is shown in Figure 11 having five connections with an associated electronic commutator 4. This simplification has been made for reasons of clarity and it will be readily appreciated that the exact number of stator windings, power electronic switching devices and associated electronic commutators is not critical to the discussion of the control architecture.
A controller 6 includes a rotor position estimator 8, a commutation controller 10 and top level regulators 12. The rotor position estimator 8 supplies estimate of the angular position of the rotor to the commutation controller 10 based on input signals from an encoder 14 and input signals indicative of the terminal voltage. The commutation controller 10 also receives feedback signals indicative of the stator current supplied to the electronic commutator 4. The commutation controller 10 uses these inputs signals to determine the safe timing and spatial limits, and the synchronisation signals for the generation of a thyristor firing sequence. The top level regulators 12 determine the requirement to adjust the timing of the thyristor firing relative to the coil voltages in the stator winding, in response to application demands 22 and feedback signals from dc link current and voltage transducers 16 and 18. The thyristor firing sequence is therefore synchronised to the coil voltages in such a way that the safe commutation of the thyristors is ensured, while at the same time matching the dc terminal power flow to the requirements of the application. For example, the timing of the thyristor firing can be adjusted to regulate the dc terminal voltage of a brushless dc generator to a constant level. The voltage regulation could be achieved during variable speed operation of the generator having fixed rotor excitation provided by permanent magnets of High Temperature Superconducting (HTS) field coils powered by a power supply with limited forcing voltage.
The preferred arrangement of stator winding/commutator circuits described above can also be adapted for use with linear machines, which have a moving member or reaction plate in place of a rotor. The stator windings of a linear machine and their electromagnetic relationship with the moving member will be subject to discontinuitjes at all stator and moving member ends. The linear machine can employ a two-layer winding, but it will be readily apparent that these discontinuities will result in slots at both ends of the stator being part populated.
A linear machine stator may be wound exactly as for the brushless dc machine shown in Figure 9, but where the stator of a rotating machine can be visualised as a continuous loop occupying stator poles I to 9 and with the segment 5 acting as a joining piece, the linear machine might be visualised as poles 1 to 9 of the rotating machine straightened out (or in other words, unwrapped). In the linear machine, the joining segment 5 would be absent. Note that in this arrangement only one of the two layers in each of the poles would be populated and packing pieces must be fitted in - 17- the top half of the slots in one pole and in the bottom half of the slots in the other pole.
A linear machine having this arrangement will produce an air gap shear stress and off load terminal voltage according to the same electromagnetic principles that govern rotating machine behaviour. In a linear machine, the air gap stress results in the generation of a force between the moving member and the stator whereas in a rotating machine this force translates as a torque that is dependant upon the mean air gap radius. Similarly, the linear machine develops an emf that is proportional to the velocity of the moving member, whereas the rotating machine develops an emf that is proportional to the peripheral velocity of the rotor and this translates to angular velocity. These comparisons between linear and rotating machine terminology are valid for applications with fixed excitation and constant flux linkage. In the case of the linear machine, the excitation and flux linkage suffer discontinuity when moving member displacement is sufficient to cause the stator and moving member ends to pass one another.
The control architecture for a linear motor is comparable to that for a rotating machine, within the region between the previously described discontinuities.
However, it is necessary to adapt the control to suit the inherent discontinuities if the working displacement of the moving member is sufficient to pass the points of discontinuity. A precise moving member position estimator and knowledge of the non-linearity of the linear machine would be needed.
The control architecture for a linear generator is far less complicated if diodes are used in the electronic commutators because there is no need to generate a thyristor firing sequence and the commutation process is inherently reliable. If thyristors are used then the discontinuity must be accommodated. However, the requirements for thyristor commutation are far less stringent when the electronic commutators are operating in a rectifying mode.
Where appropriate, for example when the cost of excitation equipment is sufficiently low, a long moving member can be used in conjunction with a short stator assembly.
Such an arrangement is shown in Figure 12, where a brushless dc linear generator has a permanent magnet-excited moving member 28 that is significantly longer than each of the slator windings 26 of the stator assembly. A stator assembly having two stator windings 26 is shown but it will be readily appreciated that three or more stator windings can be used. Each of the stator windings has an associated electronic commutator 24 and these are connected together in series. This arrangement achieves economies in the materials and components used in the stationary parts of the linear generator. The electronic commutators 24 have been implemented using diodes but alternative power electronic switching devices can be used. It will be noted that the stator windings 26 are depicted as a simple linear array but in practice the stator windings will overlap as previously described.
Figure 13 shows an alternative arrangement that might be appropriate if the cost of the excitation equipment is high. In this case, the brushless dc linear generator has a relatively short permanent magnet-excited moving member 34 and a long stator assembly. The stator assembly has two stator windings 32 and the associated electronic commutators 30 are connected together in parallel. Of course, more stator windings 32 can be added and different power electronic switching devices can be used. The stator windings 32 will also overlap as previously described.
In both of the arrangements shown in Figures 12 and 13 the magnetic circuit must make a transition from a small air gap to a very long air gap. However, in the arrangement of Figure 12 these discontinuities arise at the ends of the stator windings 26 whereas in the arrangement of Figure 13 they arise at the ends of the moving member 34, As a result of the discontinuity in the magnetic circuit, one of more stator windings at one or both ends of the stator assembly may produce a lower terminal voltage than those stator windings towards the centre of the stator assembly.
One benefit of the present invention is that only those stator windings that produce useful power output carry current and the efficiency of the overall system is therefore increased and the leakage reactance is reduced.
The brushless dc linear generators shown in Figures 12 and 13 are particularly applicable to the extraction of power from sources of reciprocating energy such as
waves, for example.
Claims (24)
1. An electrical machine comprising: a first electronic commutator having two dc terminals; a first stator winding including a number of coils linked by the same number of points of common coupling, each point of common coupling being connected to the first electronic commutator; a second electronic commutator having two dc terminals; and a second stator winding including a number of coils linked by the same number of points of conmion coupling, each point of common coupling being connected to the second electronic commutator; and wherein at least one of the dc terminals of the first electronic commutator is connected to at least one of the dc terminals of the second electronic commutator.
2. An electrical machine according to claim 1, wherein one dc terminal of the first electronic commutator and one dc terminal of the second electronic commutator are connected together in series.
3. An electrical machine according to claim 1, wherein the dc terminals of the first electronic commutators and the dc terminals of the second electronic commutator are connected together in parallel.
4. An electrical machine according to any preceding claim, wherein each of the points of common coupling of the first stator winding is connected to one of dc terminals of the first electronic commutator by a first power electronic switching device and to the other of the dc terminals of the first electronic commutator by a second power electronic switching device, and each of the points of common coupling of the second stator winding is connected to one of dc terminals of the second electronic commutator by a first power electronic switching device and to the other of the dc ternn1aI of the second electronic commutator by a second power cieclionic switching device.
5. An electrical machine according to claim 4, wherein the first power electronic switching devices connected to the points of common coupling of the first stator winding are thyristors having their anodes connected to said one of the dc terminals of the first electronic commutator and the second power electronic switching devices connected to the points of common coupling of the first stator winding are thyristors having their cathodes connected to said other of the dc terminals of the first electronic commutator.
6. An electrical machine according to claim 4 or claim 5, wherein the first power electronic switching devices connected to the points of common coupling of the second stator winding are thyristors having their anodes connected to said one of the dc terminals of the second electronic commutator and the second power electronic switching devices connected to the points of common coupling of the second stator winding are thyristors having their cathodes connected to said other of the dc terminals of the second electronic commutator.
7. An electrical machine according to claim 4, wherein the first power electronic switching devices connected to the points of common coupling of the first stator winding are diodes having their anodes connected to said one of the dc terminals of the lirst electronic commutator and the second power electronic switching devices connected to the points of common coupling of the first stator winding are diodes having their cathodes connected to said other of the dc terminals of the first electronic commutator.
8. An electrical machine according to claim 4 or claim 5, wherein the first power electronic switching devices connected to the points of common coupling of the second stator winding are diodes having their anodes connected to said one of the dc terminals of the second electronic commutator and the second power electronic switching devices connected to the points of common coupling of the second stator winding are diodes having their cathodes connected to said other of the dc terminals of the second electronic commutator.
- 22 -
9. An electrical machine according to claim 1 or claim 2, further comprising: a third electronic commutator having two dc terminals; and a third stator winding including a number of coils linked together by the same number of points of common coupling, each point of common coupling being connected to the third electronic commutator; wherein a dc terminal of the third electronic commutator is connected to the dc terminal of the second electronic commutator that is not connected to a dc terminal of the first electronic commutator.
10. An electrical machine according to claim 3, further comprising: a third electronic commutator having two dc terminals; a third stator winding including a number of coils linked together by the same number of points of common coupling, each point of common coupling being connected to the third electronic commutator; a fourth electronic commutator having two dc terminals; and a fourth stator winding including a number of coils linked together by the same number of points of common coupling, each point of common coupling being connected to the fourth electronic commutator; wherein the dc tenninals of the third electronic commutator and the dc terminals of the fourth electronic commutator are connected together in parallel, and one of the pairs of connected dc terminals of the first and second electronic commutators and one of the pairs of connected dc terminals of the third and fourth electronic commutators are connected together in series.
11 An electrical machine according to claim 1 or claim 2, wherein the other dc terminal of the first electronic commutator and the other dc terminal of the second electronic commutator are connected to a dc supply network, either directly or by means of a passive filter or a supply-side power converter apparatus.
12. An electrical machine according to claim 3, wherein the pair of connected dc terminals of the first and second electronic commutators are connected to a dc supply - 23 - network, either directly or by means of a passive filter or a supply-side power converter apparatus.
13 An electrical machine according to claim 9, wherein the other dc terminal of the first electronic commutator and the other dc terminal of the third electronic commutator are connected to a dc supply network, either directly or by means of a passive filter or a supply-side power converter apparatus.
14. An electronic machine according to claim 10, wherein the other pair of connected dc terminals of the first and second electronic commutators and the other pair of connected dc terminals of the third and fourth electronic commutators are connected to a dc supply network, either directly or by means of a passive filter or a supply-side power converter apparatus.
15. An electrical machine according to any preceding claim, further comprising a controller for regulating the first and second electrical commutators.
16. An electrical machine according to claim 15, wherein the controller uses coil voltages in the first and second stator windings to synchronise the first and second electrical commutators with the electrical machine.
17. An electrical machine according to claim 15 or claim 16, further comprising a rotor and wherein the controller uses the angular position of the rotor to synchronise the first and second electronic commutators with the electrical machine.
18. An electrical machine according to any preceding claim, further comprising a stator incorporating the first and second stator windings and wherein the first and second stator windings circumferentially overlap.
19. An electrical machine according to any of claims 1 to 16, further comprising a moving member and a linear stator assembly incorporating the first and second rotor windings.
- 24 -
20. An electrical machine according to claim 19, wherein the moving member is provided with a source of excitation.
21. An electrical machine according to claim 19 or claim 20, wherein the moving member is shorter than the linear stator assembly.
22. An electrical machine according to claim 19 or claim 20, wherein the moving member is longer than the linear stator assembly.
23. A wave generator incorporating an electrical machine according to any of claims 19to22.
24. An electrical machine substantially as described herein and with reference to Figures2to 13.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0505749A GB2424523A (en) | 2005-03-21 | 2005-03-21 | Electronically commutated electrical machine |
| PCT/GB2006/000486 WO2006100420A1 (en) | 2005-03-21 | 2006-02-13 | Electrical machine topologies |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0505749A GB2424523A (en) | 2005-03-21 | 2005-03-21 | Electronically commutated electrical machine |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0505749D0 GB0505749D0 (en) | 2005-04-27 |
| GB2424523A true GB2424523A (en) | 2006-09-27 |
Family
ID=34531582
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0505749A Withdrawn GB2424523A (en) | 2005-03-21 | 2005-03-21 | Electronically commutated electrical machine |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB2424523A (en) |
| WO (1) | WO2006100420A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2638621B1 (en) | 2010-11-12 | 2017-01-11 | ABB Research Ltd. | A rotating electrical machine and corresponding method |
| DE102011089498A1 (en) * | 2011-12-21 | 2013-06-27 | Wobben Properties Gmbh | Generator of a gearless wind turbine |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3616221A1 (en) * | 1986-05-14 | 1987-11-19 | Mueller Arnold Gmbh Co Kg | Electrical machine |
| JPH09331694A (en) * | 1996-06-10 | 1997-12-22 | Toshiba Corp | Inverter motor |
| US6064172A (en) * | 1997-02-11 | 2000-05-16 | Power Superconductor Applications Corporation | Method and apparatus for detection, classification and reduction of internal electrical faults in alternating current propulsion machinery using synchronous detection scheme |
| JP3605720B2 (en) * | 2000-08-11 | 2004-12-22 | 住友重機械工業株式会社 | Motor control device for injection molding machine |
| US6946750B2 (en) * | 2000-08-14 | 2005-09-20 | Aloys Wobben | Wind power plant having a power generation redundancy system |
| US6633151B2 (en) * | 2001-03-09 | 2003-10-14 | Eltra Systems, Inc. | Electric vehicle drive system |
| DE60221712T2 (en) * | 2002-01-10 | 2008-05-15 | Seabased Ab | WAVE ENERGY UNIT AND THE USE OF A WAVE POWER UNIT FOR GENERATING ELECTRICAL ENERGY, METHOD FOR GENERATING ELECTRICAL ENERGY AND COMPONENT SYSTEM FOR PRODUCING A LINEAR GENERATOR FOR A WAVE POWER UNIT |
| JP2004364352A (en) * | 2003-06-02 | 2004-12-24 | Matsushita Electric Ind Co Ltd | Motor, drive method thereof, and automobile |
-
2005
- 2005-03-21 GB GB0505749A patent/GB2424523A/en not_active Withdrawn
-
2006
- 2006-02-13 WO PCT/GB2006/000486 patent/WO2006100420A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO2006100420A1 (en) | 2006-09-28 |
| GB0505749D0 (en) | 2005-04-27 |
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Owner name: ALSTOM POWER CONVERSION LTD Free format text: FORMER APPLICANT(S): ALSTOM |
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| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |