DUAL-MOTOR UNIT FOR A FLYWHEEL ENERGY STORAGE SYSTEM WITH A NONLINEAR OVERALL POWER CHARACTERISTIC CURVE

Abstract

Disclosed is a dual motor unit for a flywheel mass accumulator, with at least two electric machines coupled to a common rotary body; wherein the electric machines have different power characteristics and the dual motor unit is adapted to provide a total operating power in an operating speed range (Ω) by an interaction of the electric machines. The power characteristic (P.sub.max) is non-linearly dependent on a rotational speed (ω) of the common rotary body.

Claims

1-13. (canceled)

14. A double motor unit for a flywheel mass accumulator, with at least two electric machines coupled to a common rotary body; wherein the electric machines each have power characteristics different from one another; and the dual motor unit is designed to provide a total operating power in an operating speed range (Ω) by an interaction of the electric machines, wherein the total operating power is determined by a total power characteristic (P.sub.max) resulting from the different power characteristics of the electric machines, and the total power characteristic (P.sub.max) is non-linearly dependent on a rotational speed (ω) of the common rotary body.

15. The Double motor unit according to claim 14, wherein a difference in the respective maximum powers which are produced by the electric machines at an identical rotational speed (ω) is less than 70% of the maximum power of the more powerful electric machine.

16. The dual motor unit according to claim 14, wherein the operating speed range (ω) is predetermined by a minimum speed (ω.sub.min) greater than zero and a maximum speed (ω.sub.max) greater than the minimum speed (ω.sub.min) and comprises more than 30% of a total speed range of the dual motor unit.

17. The dual motor unit according to claim 14, which is adapted to adjust a set total operating power by individually setting a respective operating point for the electric machines, wherein the setting of the operating point comprises setting a moment-determining current and a field-determining current.

18. The dual motor unit according to claim 17, wherein the double motor unit is designed to set the respective operating points of the different electric machines such that the sum of the electric losses in the electric machines is minimal at the set total operating power.

19. The dual motor unit according to claim 14, wherein the power characteristics (Pa, Pb) of the electric machines are predetermined in such a way that a substantially constant maximum power results in the operating speed range according to the overall power characteristic (P.sub.max).

20. The dual motor unit according to claim 14, wherein at least one electric machine is designed in such a way that its torque falls monotonically in a predetermined speed range with increasing speed (ω).

21. The dual motor unit according to claim 14, wherein at least one electric machine is designed such that its torque is at least substantially constant with increasing speed (ω).

22. The dual motor unit according to claim 14, wherein according to the total power characteristic (Pmax) the maximum power of the dual motor unit is achieved at a speed which is below the maximum speed of the operating speed range.

23. The dual motor unit according to claim 14, wherein at least one further electric machine is coupled to the common rotary body, wherein all electric machines have mutually different power characteristics (Pa, Pb); and the dual motor unit is designed to provide the total operating power in the operating speed range (Ω) by interaction of all electric machines, which is predetermined by a total power characteristic (P.sub.max) resulting from the different power characteristics (Pa, Pb) of all electric machines, and the total power characteristic (P.sub.max) is non-linearly dependent on the speed (ω) of the common rotary body.

24. A flywheel mass accumulator with a dual motor unit according to claim 14.

25. A method for controlling a dual-motor unit in a flywheel mass accumulator, the dual-motor unit having a common rotary body coupled to a flywheel mass of the flywheel mass accumulator or a common rotary body comprising the flywheel mass, and having at least two electric machines coupled to the common rotary body, and the electric machines each having mutually different power characteristics (Pa, Pb) with operating the electric machines during ongoing operation of the dual motor unit in accordance with respective individual power specifications in such a way that the electric machines in interaction produce a total operating power which is predetermined by a total power characteristic (P.sub.max) resulting from the different power characteristics (Pa, Pb) of the electric machines (3a, 3b) and which is non-linearly dependent on a rotational speed (ω) of the common rotary body.

26. The method according to claim 25, wherein the electrical machines, when operating in interaction, provide the total operating power with maximum efficiency.

Description

[0044] Advantageous embodiments are explained in more detail with reference to the following figures. The figures show:

[0045] FIG. 1 an exemplary embodiment of a dual motor unit for a flywheel mass accumulator;

[0046] FIG. 2 exemplary first torque characteristics of individual electrical machines including the resulting overall performance curve; and

[0047] FIG. 3 exemplary second torque characteristics of individual electrical machines including the resulting total power characteristic.

[0048] In the various figures, the same or functionally identical components are given the same reference signs.

[0049] FIG. 1 shows a sectional view of an exemplary dual motor unit for a flywheel mass storage system. The dual motor unit 1 has two electric machines 3a, 3b coupled to a common rotary body 2. The electric machines 3a, 3b each have a stator 4a, 4b and a rotor 5a, 5b, which rotate about the common axis of rotation A during operation. In this case, the electric machines 3a, 3b are coupled to the common rotary body 2 with their external rotors 5a, 5b, so that the rotational speed of the two electric machines 3a, 3b is always identical during operation of the dual motor unit 1.

[0050] As explained, for example, in the following figures, the electric machines 3a, 3b each have different power characteristics Pa, Pb. Moreover, the dual motor unit 1 is designed to produce a total operating power in an operating speed range S) through interaction of the electric machines 3a, 3b, which is specified by a total power characteristic P.sub.max resulting from the different power characteristics Pa, Pb of the electric machines 3a, 3b, and the total power curve P.sub.max is not linearly dependent on the (rotational) speed ω of the common rotary body 2.

[0051] In FIG. 2, two exemplary torque characteristics Ma, Mb for two different electric machines are shown in their dependence on the speed co of the common rotary body. The torque Ma of the first electric machine 3a is constant over the speed ω, which leads to a power P that increases linearly with the speed co and thus to a linear power characteristic Pa. The second electric machine 3b is characterized by the torque characteristic Mb, which is also constant below a limit speed ω.sub.f, but drops sharply above it, for example exponentially with increasing speed ω, due to field weakening. The resulting power characteristic Pb is also shown in FIG. 2. Accordingly, the power P of the second electric machine 3b also increases linearly following the power characteristic Pb up to the cutoff frequency wf and remains constant above the cutoff frequency ω.sub.f.

[0052] The interaction of the two electric machines 3a, 3b then results in the total power characteristic P.sub.max shown on the right in FIG. 2. With the total power characteristic Pmax, a linear operating power P.sub.in is achieved for the operating speed range Ω, which extends from a minimum speed Ω.sub.min, which is identical to the limit speed ω.sub.f, to a maximum speed ω.sub.max. Thereby, the power characteristic Pa of the first electric machine 3a is plotted in the same graph for comparison to show that this alone cannot provide the desired operating power P.sub.in. The alternative of a more powerful first electric machine 3a, which has a linear power characteristic and already produces the desired power P.sub.in at the speed ω.sub.min, is drawn in for illustration by the power characteristic P.sub.alt. It is clear that at higher speeds co of the operating speed range ω, for example at ω.sub.max the current in such an alternative first electric machine would have to be very greatly reduced for a linear power curve, which entails large losses. By combining the two electric machines 3a, 3b and the overall power characteristic P.sub.max thus achieved, this effect is significantly reduced, in the present example approximately halved.

[0053] An alternative design of the two electric machines 3a, 3b is exemplarily shown in FIG. 3. There again, the two torque characteristics Ma, Mb of the first and second electric machines 3a, 3b are shown over the speed ω including the resulting power characteristics Pa, Pb. In the example now shown, at least one, in this case even both torque characteristics Ma, Mb are monotonically decreasing. The first torque characteristic Ma falls linearly with the speed ω, which leads to a power characteristic Pa, which rises monotonically with increasing speed, but flattens out with increasing speed ω, i.e. rises less steeply as described by a logarithmic function, for example. The torque characteristic Mb of the second electric machine 3b also falls linearly up to a cutoff frequency ω.sub.f, but thereafter falls sharply similar to the example shown in FIG. 2 due to field weakening, so that the resulting power characteristic Pb rises monotonically only up to a certain frequency ω.sub.p, but falls monotonically above the speed ω.sub.p. Here, the speed ω.sub.p is larger than the speed ω.sub.f.

[0054] A combination of the two electric machines now results in the total power curve P.sub.max shown on the right in FIG. 3. Again, the individual power characteristic Pa of the first electric machine 3a is also drawn in for illustration purposes. This shows that the desired linear operating power P.sub.in could not be efficiently achieved with the first electric machine 3a alone. Thereby, the total power characteristic P.sub.max reaches its maximum value at a speed ω.sub.Peak. This speed ω.sub.peak is greater than the speed ω.sub.p at which the power characteristic Pb of the second electric machine 3b reaches its maximum value. Overall, the interaction of the two electric machines 3a, 3b with the respective torque characteristics Ma, Mb and the power characteristics Pa, Pb thus results in an overall power characteristic P.sub.max which is very flat in the operating speed range Ω and can therefore be used efficiently for a linear operating power in the entire operating speed range a Ω. In the present case, the value of the total power characteristic P.sub.max for the limits of the operating speed range Ω, ω.sub.min and ω.sub.max, corresponds to the value of the desired operating power P.sub.lin for operating speed range Ω. This ensures that the deviation of the maximum value of the total power characteristic P.sub.max at speed ω.sub.peak deviates only minimally from the desired operating power P.sub.in. For example, the corresponding deviation d can be less than 25% or even less than 15%. In the example shown in FIG. 3, it is about 10% of the desired operating power P.sub.in. This also allows the other components to be optimally adapted to the operating power P.sub.in to be provided, so that cooling power, electrical losses and the like are also optimized, so that overall the efficiency of the dual motor unit 1 and thus of an associated flywheel mass storage unit is optimized.