Dual motor unit for flywheel mass storage with non-linear total power characteristic curve

Abstract

The invention relates to a dual motor unit (1) for a flywheel mass storage, having at least two electric machines (3a, 3b) coupled to a common rotor (2); wherein the electric machines (3a, 3b) each have a power characteristic curve (Pa, Pb) which is different from one another; and the dual motor unit (1) is configured to generate a total operating power in an operating speed range (Ω) by interaction of the electric machines (3a, 3b), wherein the total operating power is predefined by a total power characteristic curve (P max ) resulting from the different power characteristic curves (Pa, Pb) of the electric machines (3a, 3b), and the total power characteristic curve (P max ) depends non-linearly on the rotational speed (ω) of the common rotor (2), in order to improve a known flywheel mass storage such that the flywheel mass storage can receive and output a constant power with improved efficiency in an as large as possible operating speed range (Ω).

Description

TECHNICAL FIELD

[0001] The invention relates to a dual motor unit for a flywheel mass storage, which has at least two electric machines coupled to a common rotor, said electric machines each having a power characteristic curve which differs from one another. BACKGROUND

[0002] Within the scope of the present application, an electric machine can be understood here only as the electric machine itself, that is to say the rotor, the stator with the windings and the directly associated mechanical components, or but also as the rotor, the stator with the windings together with the associated mechanical components plus the frequency converter, the control unit and, if necessary, other components required for the function of the electric machine.

[0003] Typically, an electric machine having a power P has a torque M which is approximately constant over the rotational speed ω, whereby a linear dependency of the power P on the rotational speed ω results, so that the relationship P = M*ω applies. In many applications and also when using electric machines in flywheel mass storages, a constant power P lin is now required in continuous operation, that is to say in the operating range of the application, while at the same time the rotational speed band, the operating rotational speed range Ω, which is available as the operating range, should be as wide as possible, so that the constant power can be called upon over as large an operating rotational speed range as possible.

[0004] The electric machine must therefore have a torque or torque characteristic which enables the constant power P min required in the respective application to be achieved in continuous operation already at a minimum rotational speed ω lin . The result is that the electric machine is thus significantly oversized in the case of a constant power P lin which generates a higher rotational speed, for example in the case of a maximum rotational speed ω max . The maximum possible power in the case of higher rotational speeds is thus not used in an operation in which only a constant power is required in the operating range. The electric machine and other components such as inverters or frequency converters, cables, etc. are thus oversized.

[0005] Various possibilities are known hitherto to deal with the problem. Thus, for example, the current for the electric machine can be limited in the higher rotational speed range of the operating rotational speed range, as has already been shown. This results in the effective power of the electric machine and the inverter not being fully utilized, and the respective components, such as the frequency converter / inverter, are oversized in order to obtain the desired operating power in the lower range of the operating rotational speed range.

[0006] Another possibility is to operate the electric machine in field weakening. By weakening the field in the electric machine an approximately constant power characteristic curve can be achieved, however, high switching losses in the inverter, which can be critical exactly at high rotational speeds in idling, are produced. But idling at high rotational speeds occurs frequently in the operation of a flywheel mass storage.

[0007] Another possibility is to design the electric machine as constant power by specific topological effects. Thus, in special application cases, for example, by exploiting the structurally determined expansion of the rotor air gap at high rotational speeds and specific machine topologies, such as synchronous reluctance, an approximately constant power characteristic can be achieved. The disadvantage of this solution is the extremely complex interplay of a large number of different system components, which is difficult to control. Accordingly, the solution is limited to a few very specific applications.

[0008] From the automotive sector, for example from DE 102011117853 Al and DE 10160481 Al, solutions are known which solve the problem using two electric machines in the powertrain, which are switched by the transmission depending on the operating point of the drive.

[0009] As far as the connection of two electric machines in one device is concerned, this is also known from machine manufacturing for this reason: For example, an externally excited DC machine can be equipped with an additional exciter or excitation winding. In a synchronous machine coupled to the power grid, it is also known to use a second electric machine on the same shaft for accelerating the synchronous machine. Here, the second electric machine only brings about start-up power, which is negligible compared to the operating power in continuous operation. It is also known to use two electric machines on one shaft, wherein one electric machine is designed as a drive and the other electric machine is designed as a generator, in order to thus achieve an effective functional distribution.

[0010] In the field of flywheel mass stores for storing electrical energy by means of a rotating flywheel mass, there are many limiting framework conditions in terms of derivable cooling power, structural space, routing of power cables and many more, which limit or also exclude the use of the described method. Such flywheel mass stores can be used, for example, for stabilizing the supply network voltage. Here, electrical energy can be stored and called up in variable amounts (dynamically) for at least several seconds. Typically, they have a storage capacity of more than 0.03 kWh. Here, individually installable sub-storage units with individual storage capacities in the range of, for example, 0.5 kWh to 200 kWh per sub-storage unit can be part of the storage unit. Correspondingly, within the scope of the present disclosure, a flywheel mass store is typically a stationary flywheel mass store which is loaded and unloaded at the same location (without moving between them). Such flywheel mass stores can be used, for example, for stabilizing the supply network or for intermediate storage of electrical energy, which can then be provided to consumers, for example electric vehicles, preferably with large current strengths. SUMMARY

[0011] It is therefore the task of the present invention to improve the known flywheel mass stores in such a way that the flywheel mass stores can receive and output constant power with improved efficiency over as large a range of operating rotational speeds as possible.

[0012] This task is solved by the subject matter of the independent claims. Advantageous embodiments result from the dependent claims, the description and the figures.

[0013] One aspect relates to a dual-motor unit for a flywheel mass storage, the dual-motor unit having at least two electric machines coupled to a common rotor. Here, the flywheel mass of the flywheel mass storage can be part of the rotor, or the rotor can also be the flywheel mass or part of the flywheel mass. The rotor can also be or comprise a drive shaft, in particular a hollow shaft. The rotor is preferably configured for operation in a vacuumed space and has components such as magnet bearing arrangements. The electric machines can be built-in machines ("outer rotor") or built-out machines ("inner rotor"). In the case of outer rotors, it is particularly advantageous to implement the drive shaft that is a hollow shaft, which is thus coupled to the rotor of the electric machine. The electric machines each have a stator and the associated rotor coupled to the rotor. Here, the electric machines can also have a common stator and / or a common rotor, which reduces the number of required components. This can be achieved, for example, by means of a dedicated winding pattern for the stator and / or the rotor. The respective individual rotors or the common rotor of the electric machines can be integrated into the rotor, i.e. arranged on the drive shaft in particular in axial direction on top of each other and / or on top of the rotor. By coupling via the common rotor, the rotational speeds of the electric machines (and the common rotor) are linearly related to each other, in particular equal, in each operating point of the dual-motor unit, which is referred to in the following as the overall operating point in order to distinguish from the individual operating points of the respective electric machines. Accordingly, different electric machines (as will be explained further below) can be arranged or installed on the same (drive) shaft. Preferably, the different electric machines cannot be mechanically decoupled from each other in the prescribed use here, there is thus no coupling or the like between the different electric machines.

[0014] Here, the electric machines each have different power characteristic curves from each other, which describe the maximum power P of the respective electric machine as a function of the rotational speed ω. The power characteristic curves can thus also be referred to as rotational speed-dependent power characteristic curves. The power characteristic curves thus illustrate the respective maximum power that can be achieved at the maximum current of the electric machine for a certain rotational speed. Here, the power characteristic curves correspond to the respective torque characteristic of the electric machine according to a known relationship, so that the electric machines also have different torque characteristics from each other. The different power characteristic curves are produced here by the specific design of the stator and / or the rotor of the respective electric machine, i.e. the hardware of the electric machine, and by the respective control scheme with which the respective electric machine is operated. Such a control scheme can be stored in the form of software, for example, on a control unit belonging to the electric machine.

[0015] Accordingly, different power characteristic curves of the electric machines can be predefined on the hardware side, for example, by a selected topology of the electric machines, and also on the software side by the control unit of the dual-motor unit. The structural design (the "hardware") can lead to the electric machines, for example, having a power that rises linearly with the rotational speed up to a maximum rotational speed, or entering a field weakening at a predefined limit rotational speed, for example, at half the maximum rotational speed.

[0016] The software-predefined portion of the different power characteristic curves can accordingly be predefined, in particular, also variably. For example, a limit rotational speed ω f (corresponding to which the electric machines do not operate in field weakening below the limit rotational speed and operate in field weakening above the limit rotational speed) can be moved by the control unit within the limit given by the structure for the electric machines. In such a control unit, it is also possible, for example, in the form of a table or a model, to store which of the electric machines of the dual-motor unit has which efficiency or which losses at a given rotational speed with which power.

[0017] Here, the dual-motor unit is configured such that, within a predefined operating rotational speed range, that is to say in a continuous operation characterized by the operating rotational speed range, a settable total operating power is produced by the interaction of the electric machines, which are preferably different. Here, "settable" can also be understood as "adjustable" or "controllable" within the scope of the dual-motor unit. Here, the continuous operation of the dual-motor unit is distinguished from the start-up operation of the dual-motor unit, in which the dual-motor unit and the associated flywheel mass store fulfill their intended purpose. Accordingly, the operating rotational speed range is a rotational speed range within which the dual-motor unit fulfills the intended purpose in the intended use. The different electric machines can therefore be referred to as so-called "regulated" electric machines.

[0018] The interaction of the electric machines here corresponds to the joint action of the electric machines on the rotors, which joint action is realized in at least one total operating point of the dual-motor unit. The joint action of the electric machines is therefore realized continuously over one or more parts of the operating rotational speed range or over the entire operating rotational speed range.

[0019] Here, the total operating power is predefined by a total power characteristic curve which is derived from the different power characteristic curves of the electric machines, and which depends non-linearly on the rotational speed of the common rotor. In short, a total power characteristic curve which depends non-linearly on the rotational speed of the common rotor can be called a "non-linear total power characteristic curve". Accordingly, the total operating power in the total operating point of the dual-motor unit is derived from the sum of the powers in the respective operating points of the electric machines. The operating points can be determined for the electric machines, for example, by the rotational speed and the power of the electric machines, if necessary also by further operating parameters, for example parameters which are specific to the topology and / or parameters which describe the field weakening of the respective electric machine.

[0020] Preferably, all electric machines of the dual-motor unit are designed here such that they always operate with the same function, that is to say all as drive of the rotor or all as generator on the rotor. The first and second rotor are also advantageously located on the common rotor, in particular on the common (hollow) drive shaft.

[0021] Coupling the two electric machines on the common rotor, in particular shaft, has the advantage that the available installation space can be better utilized, and also the cooling capacity and space for the power cables. The use of two electric machines with different power characteristic curves or different torque characteristics from one another enables a non-linear total power characteristic curve. Thereby, it is possible to reduce or completely avoid limiting the current in the higher rotational speed range of the operating rotational speed range. As a result, the components of the frequency converter and the power guide, such as cables, plugs and feedthroughs, can be operated continuously close to the respective design limit in the operating rotational speed range, which in turn reduces the electrical losses and the required installation space and cooling capacity. Since the individual electric machines can also be controlled individually, great flexibility is achieved here over a wide rotational speed range.

[0022] The inverters or frequency converters of the two electric machines are advantageously coordinated explicitly with the operating mode of the respective operating machine, which leads to a high utilization of the power components. The different electric machines therefore preferably have different inverters which are therefore explicitly matched to the operating mode and the topology of the respective operating electric machine.

[0023] In an advantageous embodiment it is provided that the difference of the maximum power that can be generated by the respective electric machine (at at least one, in the case of two electric machines identical, rotational speed) is less than 70%, in particular 50%, preferably 10% of the maximum power of the stronger or strongest electric machine (at the respective rotational speed). Here, at different rotational speeds, different electric machines can be the respective stronger or strongest electric machine. For example, one electric machine (A) can be stronger than the other electric machine (B) at a rotational speed (1), both electric machines are equally strong at another rotational speed (2), and the other electric machine (B) is stronger than the one electric machine (A) at yet another rotational speed (3). The proportion of the maximum power quantified in the above paragraph preferably applies to at least one rotational speed (i.e. one or more rotational speeds) of the operating rotational speed range, particularly preferably to the entire operating rotational speed range. Alternatively, this can also apply to all rotational speeds of the dual-motor unit and thus of the electric machines. Thus, the maximum power of the different electric machines is preferably of the same order of magnitude.

[0024] This has the advantage that a particularly great flexibility is achieved in the interaction of the electric machines, since, in contrast to a solution in which, for example, the second electric machine only generates starting power and thus cannot contribute significantly to the operating power, in the present case a desired total operating power with great variability in the participation of the different electric machines can be achieved. For example, the electric machine that is to generate the majority of the desired total operating power can be freely selected. Thus, for example, in a total operating power of 90 kW 50 kW is generated by the first electric machine and 40 kW by the second electric machine, whereas in a total power of 110 kW 50 kW is generated by the first electric machine and 60 kW by the second electric machine, the main power of the dual-motor unit can thus be generated by different electric machines, for example corresponding to the losses of the electric machines stored in the control unit for different combinations of power and rotational speed. Here, the efficiency of the dual-motor unit is also increased.

[0025] It can also be provided that, in generating the operating power and thus at at least one identical rotational speed, the difference of the efficiency of the electric machines is less than 10%, in particular less than 5%, preferably less than 2%. The proportion of the efficiency quantified here preferably applies to at least one rotational speed (i.e. one or more rotational speeds) of the operating rotational speed range, particularly preferably to the entire operating rotational speed range, or also to all rotational speeds. Advantageously, the efficiency of the respective electric machine is thus of the same order of magnitude in generating the operating power. The dual-motor unit described here thus also differs from the known application of the second electric machine as a starting aid for synchronous electric machines for coupling to the power grid.

[0026] In another advantageous embodiment it is provided that the operating speed range is predefined by a minimum speed which is greater than zero, for example 2000, 10000 or 30000 revolutions per minute, and a maximum speed which is greater than the minimum speed. Here, the operating speed range advantageously comprises more than 30%, in particular more than 50%, of the total speed range of the dual-motor unit. Here, the total speed range of the dual-motor unit can be predefined or limited by the maximum power of the dual-motor unit. This has the advantage that the nonlinear total power characteristic curve is already realized at low speeds and over a large operating range (operating speed range) and thus the efficiency is improved within said range.

[0027] In another particularly advantageous embodiment it is provided that the dual-motor unit is configured to set the regulated total operating power by respectively individually predefining the respective operating point of the electric machines, that is to say to respectively independently of one another set the power of the electric machines. This applies to at least one speed, that is to say one, several or all speeds, of the operating speed range. The setting of the operating point at at least one speed of the operating speed range, preferably at the speed break range of the operating speed range, here comprises the setting of the current which determines the torque (which can also be referred to as the q current) and / or the current which determines the field (which can be referred to as the d current). In particular, the setting of the operating point at said one or more speeds can also comprise the setting of parameters which are specific to the topology of the electric machines.

[0028] It is thereby possible, for example, to have only one of the electric machines operate in field weakening by suitably selecting the respective currents, or for both electric machines to simultaneously operate in field weakening, which can then result in the desired total operating power depending on the design of the electric machines. The different electric machines can thus not only be regulated symmetrically, that is to say, for example, both or all in field weakening or all without field weakening, but also asymmetrically, that is to say, for example, an electric machine without field weakening and an electric machine in field weakening.

[0029] The dual-motor unit is thereby further able to improve in terms of efficiency, since depending on the operating point, that is to say, for example, the speed, one electric machine is able to operate more efficiently than the other electric machine and thus the total efficiency can be optimized as will also be described below. This is exemplarily shown in the following table:

[0030]

[0031] In this example, instead of setting the rated total operating power of 162 kW, as is usual, by producing 90% of the maximum power of the first and second machine respectively as the respective operating power, the rated total operating power here corresponds to 90% of the maximum power of the double-motor unit. Rather, the same rated total operating power of 162 kW is produced, for example, by setting the operating power of the first electric machine to 100% of its maximum power and the operating power of the second electric machine to 77.5% of its maximum power, while at the same time optimally, non-uniformly dividing the total operating power to be produced over the different electric machines. This can be achieved, for example, on the basis of a table stored in the control unit, which stores the respective efficiencies of the individual electric machines for the respective operating point, so that the control unit can here select the combination of individual operating points with the greatest efficiency.

[0032] Correspondingly, it can be provided here that the double-motor unit is configured in such a way that the respective operating points of the different electric machines are set such that the sum of the electrical losses in the electric machines is minimized at the set or required total operating power. This applies in particular to at least one rotational speed, i.e. one, several or all rotational speeds, of the operating rotational speed range. Here, the total efficiency of the double-motor unit is maximized in such a way that the efficiencies or occurring losses of the individual electric machines are balanced against one another. Thereby, for example, a deterioration in efficiency can be consciously tolerated when it is compensated by an increase in the efficiency of the other electric machines. In the example mentioned above, therefore, for example, the efficiency of the second electric machine can decrease by a smaller first amount when the operating power to be produced is reduced to 77.5% of the maximum power, whereas this is more than compensated by an increase in the operating power from 90% to 100% by an increase in the efficiency of the first electric machine.

[0033] In one particularly advantageous embodiment it is provided that the electric machines comprise at least one permanent-excited synchronous electric machine and / or at least one synchronous-reluctance electric machine and / or at least one asynchronous electric machine, in particular two permanent-excited synchronous electric machines or a combination of one permanent-excited synchronous electric machine and a synchronous-reluctance electric machine, or a combination of a permanent-excited synchronous electric machine and an asynchronous electric machine, or a combination of a synchronous-reluctance electric machine and an asynchronous electric machine. The electric machines can also comprise two asynchronous electric machines or two synchronous-reluctance electric machines. Alternatively or additionally, the electric machines can also comprise one or more electric machines which are not included in the specifications mentioned. Preferably, the electric machines are combined here in such a way that the smallest possible drag losses occur at the maximum rotational speed of the operating rotational speed range. The electric machines can therefore have the same or different topologies from one another and therefore correspondingly be based on the same or different functional principles. The possibilities listed have proven to be particularly advantageous in the area of flywheel mass storage here.

[0034] In another advantageous embodiment provision is made for the power characteristic curve of the electric machine to be predefined, in particular also with a corresponding software in the control unit, such that a maximum power is obtained in the operating speed range according to the total power characteristic curve which is substantially constant or constant. Here, a power which deviates by less than 35%, in particular less than 25%, preferably less than 15% from the maximum of the total power characteristic curve in the operating speed range can be regarded as substantially constant. This has the advantage that, with the known tools of the design of the electric machine, a double-motor unit can be provided overall with minimized losses under the interaction of the electric machines which produces a power which is as constant as possible in the predefined application range.

[0035] In another advantageous embodiment provision is made for at least one, i.e. one, several or all electric machines to be designed such that its torque monotonically decreases with increasing rotational speed in a predefined speed range. In particular, the predefined speed range can be a partial range of or include a partial range of the operating speed range. The partial range can include at least 30%, at least 60% or at least 90% of the operating speed range. Here, the partial range can be connected to or include the upper limit of the operating speed range. In particular, the torque can have a maximum between the partial range and the lower limit of the operating speed range in the operating speed range, from which the torque decreases. At the maximum, the torque can increase with the rotational speed. Alternatively, the predefined speed range can also include the entire operating speed range. This has the advantage that in the total power characteristic curve a plateau can be approximated over a wide operating range and thus a constant power is achieved.

[0036] In another advantageous embodiment provision is made for at least one electric machine to be designed such that its torque is at least substantially constant or constant with increasing rotational speed. This applies in particular at least in the operating speed range. "Substantially constant" can be understood here as constant up to a predefined deviation, which can be for example 35%, 25% or 15%. This has the advantage that in the total power characteristic curve a plateau can be approximated over a wide operating range and thus a constant power is achieved.

[0037] In another advantageous embodiment provision is made for the maximum power of the double-motor unit to be achieved according to the total power characteristic curve at a rotational speed which is lower than the maximum rotational speed of the operating speed range. Preferably, the maximum power of the double-motor unit can be achieved at a rotational speed which deviates by more than 10% or more than 25% from the maximum rotational speed of the operating speed range. This has the advantage that for particularly large operating speed ranges a largely constant maximum power of the double-motor unit is obtained.

[0038] In another advantageous embodiment provision is made for the maximum power of the double-motor unit to deviate by at most 35%, in particular by at most 25% or 15%, from the power of the double-motor unit at the maximum rotational speed of the operating rotational speed range in accordance with the total power characteristic curve. The operating rotational speed range is here and also generally so predefined that the value of the total power characteristic curve is identical at the maximum rotational speed and at the minimum rotational speed of the operating rotational speed range. This is advantageous in particular in combination with the last-mentioned embodiment.

[0039] In another advantageous embodiment provision is made for the double-motor unit to have at least one, i.e. one or more, further electric machine coupled to the common rotor, wherein all electric machines have mutually different power characteristic curves. In operation, the rotational speeds of all electric machines are thus always linearly related to one another, preferably identical. Here, the double-motor unit is configured to generate a total operating power in the operating rotational speed range by interaction of all electric machines, which total operating power is predefined by a total power characteristic curve derived from the different power characteristic curves of all respective electric machines, wherein the total power characteristic curve is nonlinearly dependent on the rotational speed of the common rotor. This applies in at least one, i.e. one or more, operating point in the operating rotational speed range, preferably over one or more ranges of the operating rotational speed range, ideally over the entire operating rotational speed range. Here, the interaction can also vary qualitatively, for example the interaction of all electric machines can comprise the interaction of two first electric machines in a first sub-range of the operating rotational speed range, in which at least one further electric machine does not contribute to the total operating power, and the interaction of one of the two first electric machines with at least one further electric machine in another sub-range of the operating rotational speed range different from the first sub-range, wherein the other of the two first electric machines does not contribute to the total operating power. In a third sub-range different from the first and second sub-ranges, for example all electric machines can interact, and in a fourth sub-range different from the other sub-ranges only one electric machine generates the desired total operating power. This has the advantage that the total power characteristic curve can be predefined more precisely, for example a stronger or weaker undulation can be selected in order to match the double-motor unit to the specific requirements of the respective field of application.

[0040] One aspect also relates to a flywheel mass storage with a double-motor unit according to one of the embodiments set forth. Preferably, the flywheel mass storage has a rotor which is arranged in a vacuum chamber in the use specified. The rotor can be supported using a magnet support device.

[0041] A further aspect relates to a method for controlling, as can also be understood as regulating, a dual-motor unit in a flywheel mass storage, wherein the dual-motor unit has a common rotor mechanically coupled to a flywheel mass of the flywheel mass storage or comprising a flywheel mass, which rotor has at least two electric machines mechanically coupled to the common rotor, and which electric machines each have a power characteristic curve different from one another. The control comprises operating the electric machines in a continuous operation of the dual-motor unit in correspondence with respective individual, i.e. individually predefinable, power specification values, such that the electric machines generate a total operating power in interaction, which total operating power is predefinable by a total power characteristic curve derived from the different power characteristic curves of the electric machines, which total power characteristic curve depends non-linearly on a rotational speed of the common rotor.

[0042] It can be provided here, in particular, that the electric machines are operated in interaction such that the total operating power having a maximum efficiency of the electric machines is generated.

[0043] The advantages and advantageous embodiments of the method correspond to the advantages and advantageous embodiments of the dual-motor unit, and vice versa.

[0044] The features and feature combinations mentioned in the description above, also in the general part, and below in the attached claims, as well as the features and feature combinations mentioned in the attached description and / or shown alone in the attached drawings, can be used not only in the respectively indicated combinations, but also in other combinations, without leaving the scope of the present application. Thus, embodiments and feature combinations that do not have all the features of the originally claimed independent claims are to be considered as disclosed and published. Furthermore, embodiments and feature combinations that go beyond or deviate from the feature combinations recited in the cited claims are to be considered as disclosed and published, in particular by the above embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0045] Here, advantageous embodiments are explained in detail by means of the following drawings. In the drawings:

[0046] Figure 1 An exemplary embodiment of a dual-motor unit for a flywheel energy storage is shown;

[0047] Figure 2 An exemplary first torque characteristic of an individual electric machine is shown, including a resulting total power characteristic curve; and

[0048] Figure 3 An exemplary second torque characteristic of an individual electric machine is shown, including a resulting total power characteristic curve. DETAILED DESCRIPTION

[0049] In the different figures, identical or functionally identical components are provided here with identical reference signs.

[0050] Figure 1 A sectional view of an exemplary dual-motor unit for a flywheel mass storage is shown. Here, the dual-motor unit 1 currently has two electric machines 3a, 3b coupled to a common rotor 2. The electric machines 3a, 3b here each have a stator 4a, 4b and a rotor 5a, 5b, which in operation rotate about a common rotational axis A. Here, the electric machines 3a, 3b in the present case are coupled to the common rotor 2 by their outer rotors 5a, 5b, so that the rotational speeds of the two electric machines 3a, 3b are always identical when the dual-motor unit 1 is in operation.

[0051] As is set forth, for example, with the aid of the following figures, the electric machines 3a, 3b here each have a power characteristic curve Pa, Pb that is different from one another. Furthermore, the dual-motor unit 1 is configured to generate a total operating power in an operating rotational speed range Ω by the interaction of the electric machines 3a, 3b, which total operating power is derived from a total power characteristic curve P max that is predefined and that is not linearly dependent on the rotational speed ω of the common rotor 2. max

[0052] In Figure 2 , two exemplary torque characteristics Ma, Mb of two different electric machines are now shown on the left first in relation to the rotational speed ω of the common rotor. The torque Ma of the first electric machine 3a here is constant with respect to the rotational speed ω, which leads to a power P that rises linearly with the rotational speed ω and thus to a linear power characteristic curve Pa. The second electric machine 3b here in the present case is characterized by a torque characteristic Mb that is likewise constant below a limit rotational speed ωf, however, in addition, strongly, for example exponentially, falls with the rising rotational speed ω as a result of field weakening. The resulting power characteristic curve Pb is likewise shown in Figure 2 . Thus, the power P of the second electric machine 3b also increases linearly with the power characteristic curve Pb up to the limit frequency ω f , and remains constant above the limit frequency ωf.

[0053] Thus, in the interaction of the two electric machines 3a, 3b, a total power characteristic curve P Figure 2 is obtained on the right, which is shown. max By the total power characteristic curve P max , a linear operating power P f is achieved for an operating rotational speed range Ω from a minimum rotational speed ω min that is identical to the limit rotational speed ω max to a maximum rotational speed ω lin ​Here, for comparison, the power characteristic curve Pa of the first motor 3a is plotted in the same graph to show that the first motor is only unable to produce the desired operating power P. lin A more powerful alternative to the first motor 3a is presented intuitively through the power characteristic curve P. alt The graph shows that the first motor has a linear power characteristic curve and at a speed ω min The desired power P has already been applied. lin It is evident here that at higher speeds ω within the operating speed range Ω, for example at ω... max In this case, the current in the first alternative motor must be reduced very drastically for the linear power change curve, which results in large losses. The combination of the two motors 3a and 3b and the resulting total power characteristic curve P... max The effect was significantly reduced, approximately halved in this example.

[0054] An alternative design scheme for the two motors 3a and 3b is exemplarily shown in Figure 3 The following is shown. Again, there are shown the two torque characteristics Ma, Mb of the first or second motor 3a, 3b with respect to speed ω, along with the resulting power characteristic curves Pa, Pb. In the example shown here, at least one, and in this case both, torque characteristics Ma, Mb extend monotonically downwards. Here, the first torque characteristic curve Ma decreases linearly with speed ω, which results in the power characteristic curve Pa, which, although monotonically increasing with speed, decreases with increasing speed ω, that is, increases less drastically, as described, for example, by a logarithmic function. The torque characteristic Mb of the second motor 3b extends up to the limiting frequency ω. f It also decreases linearly, but then it is similar to... Figure 2 The example shown in the figure drops sharply due to field attenuation, causing the resulting power characteristic curve Pb to rise only monotonically up to a specific frequency ω. p However, higher than the rotational speed ω p It decreases monotonically. Here, the rotational speed ω p Greater than the rotational speed ω f .

[0055] The interaction between the two motors is now obtained in Figure 3 The total power characteristic curve P shown on the right max Here, for illustration, the various power characteristic curves Pa of the first machine 3a are also plotted. From this, the desired linear operating power P is obtained. lin This cannot be effectively achieved using only the first motor 3a. Here, the total power characteristic curve P... max At rotational speed ω peak It reaches its maximum value under certain conditions. Here, the rotational speed ω peakis greater than the following rotational speed ω p At this rotational speed, the power characteristic curve Pb of the second electric machine 3b reaches its maximum value. Overall, by the joint action of the two electric machines 3a, 3b with the respective torque characteristic curves Ma, Mb or power characteristic curves Pa, Pb, a total power characteristic curve P max is achieved, which extends very gently within the operating rotational speed range Ω and thus can be used effectively for a linear operating power within the entire operating rotational speed range Ω. Here, for the limits of the operating speed range Ω, ω min and ω max , the value of the total power characteristic curve P max corresponds to the value of the desired operating power P lin for the operating speed range Ω. Thereby, it is achieved that the deviation of the maximum value of the total power characteristic curve P max at the rotational speed ω peak deviates only minimally from the desired operating power P lin . The respective deviation d can be, for example, less than 25% or even less than 15%. In the example shown in Figure 3 , the deviation is approximately 10% of the required operating power P lin . Thereby, the other components can also be optimally matched to the operating power P lin to be generated, so that the cooling power, the electrical losses, etc. are also optimized, so that the efficiency of the double-motor unit 1 is overall optimized and thereby the efficiency of the associated flywheel mass storage is optimized.

Claims

1. Double-motor unit (1) for a flywheel energy storage for storing electrical energy by means of a rotating flywheel mass, the double-motor unit having at least two electric machines (3a, 3b) coupled to a common rotor (2); the rotor being part of the flywheel mass or the flywheel mass being part of the rotor, wherein: - the electric machines (3a, 3b) have respectively different power characteristic curves Pa, Pb from each other; and - the double-motor unit (1) is configured to generate a total operating power in an operating speed range Ω by interaction of the electric machines (3a, 3b), wherein the total operating power is predefined by a total power characteristic curve Pmax resulting from the different power characteristic curves Pa, Pb of the electric machines (3a, 3b), wherein the total power characteristic curve Pmax depends non-linearly on the rotational speed ω of the common rotor (2); the operating speed range Ω is predefined by a minimum rotational speed ωmin greater than zero and a maximum rotational speed ωmax greater than the minimum rotational speed ωmin, and the operating speed range Ω comprises more than 30% of the entire speed range of the double-motor unit (1).

2. Double-motor unit (1) according to claim 1, characterized in that the difference of the maximum power that can be generated by the electric machines (3a, 3b) at the same rotational speed ω is less than 70%, 50% or 10% of the maximum power of the stronger electric machine (3a, 3b) respectively.

3. Double-motor unit (1) according to any of the preceding claims, characterized in that the operating speed range Ω is predefined by a minimum rotational speed ωmin greater than 2000 revolutions per minute, greater than 10000 revolutions per minute or greater than 30000 revolutions per minute, and the operating speed range Ω comprises more than 50% of the entire speed range of the double-motor unit (1).

4. Double-motor unit (1) according to any of the preceding claims 1 to 2, characterized in that the double-motor unit (1) is configured to set the set total operating power by respectively individually predefining a respective operating point for the electric machines (3a, 3b), wherein the setting of the operating points comprises setting a torque-determining current and a field-determining current.

5. Double-motor unit (1) according to any of the preceding claims 1 to 2, characterized in that the double-motor unit (1) is configured to set the respective operating points of the different electric machines (3a, 3b) such that the sum of electrical losses in the electric machines (3a, 3b) is minimal at the set total operating power.

6. Double-motor unit (1) according to any of the preceding claims 1 to 2, characterized in that the power characteristic curves Pa, Pb of the electric machines (3a, 3b) are predefined such that a constant maximum power is obtained from the total power characteristic curve Pmax in the operating speed range.

7. Double-motor unit (1) according to any of the preceding claims 1 to 2, characterized in that ​ ​ ​ ​ ​ ​ ​ ​ The at least one electric machine (3a, 3b) is designed such that its torque Ma, Mbmonotonically decreases with increasing rotational speed ω in a predefined rotational speed range, which includes a partial range of the operating rotational speed range, which contains at least 30%, at least 60% or at least 90% of the operating rotational speed range.

8. Double-motor unit (1) according to any of the preceding claims 1 to 2, characterized in that The at least one electric machine (3a, 3b) is designed such that its torque Ma, Mbis at least constant with increasing rotational speed ω, such that the maximum power of the double-motor unit (1) according to the total power characteristic curve Pmaxdeviates by at most 35% from its value at the maximum rotational speed ωmaxof the operating rotational speed range Ω.

9. Double-motor unit (1) according to any of the preceding claims 1 to 2, characterized in that The maximum power of the double-motor unit (1) is achieved according to the total power characteristic curve Pmaxat a rotational speed which is lower than the maximum rotational speed of the operating rotational speed range.

10. Double-motor unit (1) according to any of the preceding claims 1 to 2, characterized in that - at least one further electric machine is coupled to the common rotor (2), wherein - all electric machines (3a, 3b) have mutually different power characteristic curves Pa, Pb; and - the double-motor unit (1) is configured to generate a total operating power in the operating rotational speed range Ω by the interaction of all electric machines (3a, 3b), which is predefined by a total power characteristic curve Pmaxderived from the mutually different power characteristic curves Pa, Pbof the electric machines (3a, 3b), and which depends non-linearly on the rotational speed ω of the common rotor (2).

11. Flywheel energy store with a double-motor unit (1) according to any of the preceding claims.

12. Method for controlling a double-motor unit (1) in a flywheel energy store for storing electrical energy by means of a rotating flywheel mass, wherein the double-motor unit (1) has a rotor (2) which is mechanically coupled to the flywheel energy of the flywheel energy store or comprises the common rotor (2) of the flywheel energy, which has at least two electric machines (3a, 3b) which are mechanically coupled to the common rotor (2), and which have mutually different power characteristic curves Pa, Pb, respectively; the control comprises operating the electric machines (3a, 3b) in the operating rotational speed range Ω corresponding to the respective individual power specification in continuous operation of the double-motor unit (1) such that they generate a total operating power in interaction, which is predefined by a total power characteristic curve Pmaxderived from the mutually different power characteristic curves Pa, Pbof the electric machines (3a, 3b), which depends non-linearly on the rotational speed ω of the common rotor (2); The operating speed range Ω is predefined by a minimum speed ωmin which is greater than zero and a maximum speed ωmax which is greater than the minimum speed ωmin, and the operating speed range Ω comprises more than 30% of the overall speed range of the double motor unit (1).

13. The method of claim 12, wherein, The electric machine produces total operating power at maximum efficiency in interaction while operating.

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