Embodiments of the present invention relate to an electrical machine.
An electrical machine is an electro-mechanical device permitting the conversion of electrical energy into work or into mechanical energy. Alternating current electrical machines consist of a stator and a rotor. The stator consisting of windings generates a rotating field to which the rotor is subjected. The rotor is made either from permanent magnets or from windings. Thanks to this device, the flux of the rotor and the stator can be offset in an optimal manner (in quadrature). This offset creates a torque according to the law of maximum flux (a north pole attracting a south pole), thus leading to the rotation of the rotor.
Therefore, it is desirable to create electrical machines that function in an optimal manner.
It is known from the thesis of Yvan Crévits entitled Characterisation and command of multi-phase engines in reduced power supply mode (thesis of the University of Sciences and technologies in Lille, submitted on July 12, 2010) that an electrical machine can be six-phased with the six phases distributed in two independent stars. The phases of the two stars are usually shifted at π/6. The multi-phase machine resulting from this association is shown schematically in
The multi-phase machine resulting from this association helps to take advantage of the experience obtained in the implementation of three-phase windings. The windings of these machines can be powered independently by full-wave inverters by distributing the currents between the phase groups in such a way to avoid the effects of the mutual induction.
The windings can also be powered by other components. The evolution of the components of power electronics has actually enabled the use of components with high-frequency commutation. These components permit to limit the harmonics in the power supply signals and to control the phase difference between the current and the voltage of the systems. The voltage inverters are one example. The use of voltage inverters permits to achieve low harmonic distortion rates of the power supply, which results in low content of harmonics in the currents. The low content of harmonics permits to limit the losses in the different parts of the machine independently of the losses from the induced current or the losses in the conductors.
The “reduced power supply mode” or the “reduced mode” appears when the integrity of the electrical power supply is doubtful due to problems in the source, the electrical connection to the machine or to an internal defect of the machine. Such a multi-phase machine appears interesting in the use of the reduced mode due to the significant number of independent phases. In effect, the significant number of the phases provides a favourable redundancy to the functioning in reduced mode.
But if during the functioning in reduced mode one branch of the star is damaged, the corresponding phase is not used anymore. Also, if the power supply device is damaged, the corresponding winding does not function anymore. In both cases, this results in energy loss.
Therefore, there is a need for an electrical machine that helps to achieve better performance in reduced mode, namely in the case of the loss of one phase or damage to one branch of the inverter.
For this purpose, an embodiment of the present invention proposes an electrical machine comprising: a set of at least six windings, each comprising two ends, with the windings in a series configuration, voltage supply devices capable of supplying an electrical phase, a control circuit of the voltage supply devices controlling the phase differences between the phases supplied by the power supply devices, each voltage supply device powers one phase with a common end of two windings, with the other end of the two windings powered by one of the two voltage supply devices, which powers one phase, whose phase shift with the phase powered by the voltage supply device is one of the two that are the lowest in absolute value among the phase shifts between the phases powered by the voltage supply devices and the phase powered by the voltage supply device.
According to other embodiments of the present invention, taken separately or in combination: the voltage supply devices are distributed in an arrangement of at least three voltage supply devices; the control circuit comprises of one control unit per arrangement; every control unit is adapted to apply one control law to the voltage supply devices of the arrangement managed by the control unit; the control law is such that the phase shift between the phase powered by a voltage supply device of an arrangement and the phase powered by the voltage supply device having the phase shift that is the closest in the same arrangement is equal to 2π/n, where n is the number of the voltage supply devices of the arrangement; each of the arrangements comprise of an odd number of voltage supply devices; the arrangements comprise of the same number of voltage supply devices; the electrical machine comprises of two arrangements: a first arrangement of at least three voltage supply devices, of which a first voltage supply device of reference powers a first electrical phase of reference, and a second arrangement of at least three voltage supply devices, of which a second voltage supply device of reference powers a second electrical phase of reference, with the reference phase shift between the first and the second electrical phase being different from 0; the reference phase shift is equal to 7E; the machine comprises of, in addition, a stator, with every voltage supply device located in the stator; the voltage supply devices are positioned in the stator in the form of a regular polygon, the voltage supply devices are positioned in the stator in the form of a hexagon, the voltage supply devices are adapted to deliver a sinusoidal electric signal with harmonic distortion rate less than or equal to 5%.
Other characteristics and advantages of the invention will appear after reading the detailed description, which follows from the modes of embodiment of the invention, provided as an example only, and in reference to the drawings which show:
An electrical machine 10, such as the one presented in
The stator comprises of six windings 12, 14, 16, 18, 20 and 22 forming a set 24. The number of the windings 12, 14, 16, 18, 20 and 22 can be more. Each winding 12, 14, 16, 18, 20 and 22 comprises of two ends. Moreover, the windings 12, 14, 16, 18, 20 and 22 are in a series configuration. This means that each winding is connected on both sides to another winding. Thus the winding set 24 forms a closed loop.
In the example in
In addition, the electrical machine 10 comprises voltage supply devices capable to power the phases to the windings 12, 14, 16, 18, 20 and 22, with the voltage supply devices connected to one end of one winding 12, 14, 16, 18, 20 and 22.
The machine 10 comprises thus a first arrangement 38 of at least three voltage supply devices capable to power one electrical phase. According to the example in
In particular, the number of the voltage supply devices in the first arrangement 38 is an odd number. The choice of an odd number of phases for an arrangement contributes to limiting the generated harmonics spatially. This results in a reduction of the amplitude of the oscillations of the torque of the rotor of the machine 10.
The voltage supply devices 40, 42 and 44 are represented diagrammatically by rectangles in a solid line. In particular, they can be voltage inverters.
The voltage supply device 40 is a first voltage supply device of reference powering a first electric phase of reference. The phase powered by the voltage supply device 40 is marked by V11 further on. The phases, which are capable to power the voltage supply devices 42 and 44, are marked by V12 and V13.
The machine 10 also comprises of a second arrangement 46 of at least three voltage supply devices capable of powering one electrical phase. The first arrangement 38 and the second arrangement 46 are not confused. According to the example in
In particular, due to the same grounds as before, the number of the voltage supply devices in the second arrangement 46 is an odd number. In addition, it is independent of the number of the voltage supply devices in the first arrangement 38. Nonetheless, the same number of voltage supply devices in the first and second arrangements 38 and 46 help to obtain an assembly that is easier to implement.
In addition, the voltage supply devices 48, 50 and 52 are represented diagrammatically in
The voltage supply device 48 is a second voltage supply device of reference powering a second electric phase of reference. The phase powered by the voltage supply device 48 is marked by V21 further on. The phase shift of reference between the first and the second electric phase of reference is different from 0. By marking with ΔφREF the phase shift of reference and with φ(V) the function, which associates the phase with a given voltage V, this last relation is interpreted mathematically in the following way:
ΔφREF=φ(V21)−φ(V11)≠0 (relation 1)
With such a relation, the signals V11 and V21 are different.
In a similar manner to the notations introduced for the first arrangement 38, the phases, which are capable of powering the voltage supply devices 50 and 52, are marked, respectively, by V22 and V23.
In the example in
where:
A system of similar relations can be written for the second arrangement 46 in the case when the phase shift between the phase powered by voltage supply device of an arrangement and the phase powered by the voltage supply device having the phase shift that is the closest in the same arrangement, is equal to 2π/3:
where:
The maintaining of the phase shifts Δφ1, Δφ2, Δφ3, Δφ4, Δφ5 and Δφ6 equal to 2π/3 helps to obtain phases in congruence, which helps to obtain the largest possible effective signal in terms of amplitude.
In the case when an arrangement comprises of n voltage supply devices, in order to obtain the largest possible effective signal in terms of amplitude, it is desirable that the phase shift between the phase powered by a voltage supply device of an arrangement and the phase powered by the voltage supply device having the phase shift that is the closest in the same arrangement is equal to 2π/n. This is interpreted mathematically by the following set of relations:
where:
According to the example in
These two units 54 and 64 are part of a control circuit 58 of voltage supply devices. This control circuit 58 controls the phase shifts between the phases powered by the voltage supply devices. Such control permits to obtain an effective signal of large amplitude.
In addition, each voltage supply device of the two arrangements is connected to the two voltage supply devices, for which the phase shift between the phases powered by the voltage supply devices and the phase powered by the voltage supply device is the least in absolute value, via a winding. In other words, a voltage supply device that is to be connected is linked on the one hand to a first voltage supply device via one winding and, on the other hand, to a second voltage supply device via a second winding. The first voltage supply device powers one phase, whose phase shift with the phase of the voltage supply device to be connected is the lowest, while the second voltage supply device powers one phase, whose phase shift with the phase of the voltage supply device to be connected is the lowest, except for the phase shift between the first voltage supply device and the voltage supply device to be connected.
In the particular case in
From the point of view of the voltage supply devices of the second arrangement 46, this is expressed by the following connections: The voltage supply device 48 is connected, on the one hand, to the voltage supply device 42 via the winding 12 and, on the other hand, to the voltage supply device 44 via the winding 22; the voltage supply device 50 is connected, on the one hand, to the voltage supply device 40 via the winding 18 and, on the other hand, to the voltage supply device 44 via the winding 20 and the voltage supply device 52 is connected, on the one hand, to the voltage supply device 40 via the winding 16 and, on the other hand, to the voltage supply device 42 via the winding 14.
In the case when there are more than two voltage supply devices, for which the phase shift between the phases powered by the voltage supply devices and the phase powered by the voltage supply device is the lowest, one advantageous way to select the voltage supply devices, to which the voltage supply device under consideration is connected, is to also take into account the ease of the connection. As an example, a connection with the two voltage supply devices, which are the closest in terms of distance, may be considered.
The preceding description is a description of the machine 10 from the point of view of the voltage supply devices. It is possible to describe the machine 10 also from the point of view of the windings.
According to this point of view, each voltage supply device 40, 42, 44, 48, 50 and 52 powering a phase of a common end of two windings 12, 14, 16, 18, 20 and 22, the other end of the two windings 12, 14, 16, 18, 20 and 22 being powered by one of the two voltage supply devices 40, 42, 44, 48, 50 and 52 powering a phase, whose phase shift with the phase powered by the voltage supply device 40, 42, 44, 48, 50 and 52 is one of the two least in absolute value among the phase shifts between the phases powered by the voltage supply devices and the phase powered by the voltage supply device 40, 42, 44, 48, 50 and 52.
Therefore, the end 26 is powered by the voltage supply device 46; the end 28 by the voltage supply device 42; the end 30 by the voltage supply device 52; the end 32 by the voltage supply device 40; the end 34 by the voltage supply device 50 and the end 36 by the voltage supply device 44.
This description from the point of view of the windings describes the same structure as the one from the point of view of the voltage supply devices, namely the structure in
In addition, according to the example in
Within the framework of normal functioning, all voltage supply devices 40, 42, 44, 48, 50 and 52 power one voltage. The voltage applied to each winding 12, 14, 16, 18, 20 and 22 of the machine is, therefore, the resultant of the voltage of the voltage supply devices. Thus, as an example, the winding 16 is subjected to voltage V11-V23 at its terminals. Each voltage supply device 40, 42, 44, 48, 50 and 52 shows also current in sinusoidal form whose amplitude is controlled by the control device 58.
It will be demonstrated now that the machine 10 illustrated in
The availability of power of the two electrical machines 10 and 100 in
Let us suppose that one voltage supply device is damaged, the voltage supply device 42 in the case in
In reduced mode, the machine 10 illustrated in
This effect is still more reasonable when the phase shift of reference ΔφREF is equal to π.
In reduced mode, in order to limit the parasite effects (oscillation of the torque, limitation of the current . . . ), it is possible, in addition, to adapt the control of the power supply devices. This is more difficult to achieve with current supply.
The power supply of a machine 10 with current pulses is more delicate in reduced mode. In normal functioning, one of the power supply devices shows a positive current, let us suppose that here it is the power supply device 40. This current is separated in two in order to cross the windings of the machine, then another first power supply device shows a negative current. Only two of the power supply devices are used in this case. A commutation (stopping the power supply devices 40 and 48 and providing power supply with the help of the power supply devices 52 and 44, for example) is necessary to pass to the following stage of power supply.
In the case of failure of the power supply system, it is necessary also to stop using the power supply device that is associated with it. It is possible to function with the remaining power supply devices. In this case, in an embodiment, the machine has more windings in order to obtain an operating mode with limited parasitic effects (namely, oscillation of the torque). This is nonetheless difficult and leads to an increase in the cost.
Moreover, the machine 10 helps to preserve the specific features of a multi-phase machine and particularly its higher tolerance to faults than a three-phase machine.
The machine 10 also helps to obtain functioning in electric commutation.
In addition, the electrical machine 10 is beneficial such that it is easy to be obtained starting from a double-star assembly according to the state of the art. In order to pass from the assembly in
In an embodiment, the voltage supply devices 40, 42, 44, 48, 50, 52 are adapted to deliver a sinusoidal electrical signal with harmonic distortion rate less than or equal to 5%.
A sinusoidal electrical signal with harmonic distortion rate less than or equal to 5% is a sinusoidal signal or a quasi-sinusoidal signal. A sinusoidal signal is a signal whose harmonic distortion rate is zero.
Compared to the use of an electrical signal of the square type or of the trapezoidal type, an electrical signal with harmonic distortion rate less than or equal to 5% is advantageous insofar as the electrical machine presents better efficiency (less vibration, less heat build-up, etc.).
This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Number | Date | Country | Kind |
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1250678 | Jan 2012 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/051261 | 1/23/2013 | WO | 00 |