DE102008029574A1 - Electrical drive unit for use in wind power machine i.e. windmill, to adjust rotor blades, has commutator provided for successively connecting supply terminals with potentials, where supply terminals are provided in three-phase motor - Google Patents

Abstract

The unit (1) has a three-phase motor (2) adjusting angle of incidence of rotor blades of a windmill, an alternating current (AC) source (5), a direct current (DC) source (6) and a mechanical commutator (10). The motor has supply terminals (UM, VM, WM) that are controlled by the AC source in a normal operation and controlled by the commutator in a standby operation, where the commutator is supplied with current from the DC source. The DC source has taps (60-63) providing potentials that are different from each other. The commutator successively connects the terminals with the potentials.

Description

The The invention relates to an electric drive unit and a wind turbine with an electric drive unit. In industrial plants become electric drives for moving and positioning of machine elements used. In wind turbines there are drives for adjusting the rotor blades, so that the angle of attack of the rotor blades accordingly adapted to the wind conditions on an ongoing basis. It is known, for such drives to use DC motors, what However, due to the high collector wear of the DC motors is maintenance intensive.

The DE 10 2006 015 511 A1 Proposes to provide an asynchronous motor which is fed in emergency operation via a commutator driven by a DC motor from a mains-independent DC power source.

It has been shown that when the DC source is a high voltage, for example 300 V, it provides to the brush fire in the commutator can come.

It is therefore an object of the invention, an electric drive unit to provide their three-phase motor safely in an emergency operation can be operated by means of a commutator. It is also a task of the invention, a mechanical inverter and a device to provide an alternating current for enable emergency operation of a three-phase motor safe operation.

It is also an object of the invention, a wind turbine with a corresponding provide electrical drive unit.

According to the invention an electric drive unit is provided, which is a three-phase motor, an AC power source, a DC power source and a mechanical power source Commutator has. The three-phase motor has several supply connections on, which can be controlled by the AC power source in normal operation are. The supply connections are in emergency mode controlled by the commutator, wherein the commutator from a DC power source is fed.

The DC power source has a number of n taps, where n> 2. The taps are for providing n, each different, Potentials provided. The commutator is timed at the respective time successively connecting the supply connections the three-phase motor with the n potentials provided. This means, that the commutator timed each of the supply connections connects in succession with the n potentials.

Thereby, that more than two potentials are tapped, it is possible generate the commutator a stepped output voltage allow. As a result, the voltage changes to the Brushes lower and the brush fire is reduced. By directly tapping the potentials from the DC source it requires no electronic circuit, the z. B. at overvoltage can be destroyed because of lightning strike. Especially with wind turbines It is necessary that the emergency operation also after a lightning strike works reliably. That's why it is Providing a mechanical commutator advantageous because this for Generating the alternating voltages no semiconductor devices needed, which can be broken in a lightning strike.

moreover the electric drive unit offers the possibility by means of the commutator a stepped output voltage provide the three-phase motor, so that the signal of the output voltage closer to the sinusoidal shape than the one in the Prior art proposed rectangular waveform. Thereby the three-phase motor runs quieter in emergency mode.

If the DC power source is a series circuit of rechargeable electrical Energy stores contains, this can be advantageous during normal operation of the three-phase motor constantly be kept at their maximum state of charge.

In a preferred embodiment are between the commutator and the three-phase motor isolating contactors, d. H. electromagnetic Switch, provided. Likewise, contactors are in the connection between the AC power source and the AC motor intended. The contactors disconnect the commutator from the three-phase motor in normal operation and connect them in emergency mode. separation Sagittarius are characterized by their insensitivity to interference because of overvoltages, z. Due to lightning strikes, out.

In In one embodiment, the commutator has a fixed one Collector with several electrically conductive areas on each other electrically are isolated. The conductive areas are with the at the taps electrically connected to applied potentials. A movable rotor with electric brushes for contacting the conductive Areas are also part of the mechanical commutator. The senior Areas can be easily connected to the taps, as the Collector stands firm.

Each brush of the rotor is preferably connected to a slip ring from which a chip tion for the three-phase motor can be removed.

It is alternatively also possible, the collector movable and to provide the brushes fixed.

In In a specific embodiment, the conductive areas with the maximum or minimum potential are provided smaller than the conductive areas, coupled with other potentials to prevent it to unwanted states with only two different energized phases comes.

If the DC power source has series-connected energy stores, whose capacity is different the capacities are adjusted so that the capacities for the partial voltages from which much charge is taken becomes larger than the other capacities are.

Especially the drive circuit according to the invention is suitable for wind turbines, in which the setting angle of the rotor blades should be set. Wind turbines are common to surges due to lightning, whereas the drive device should be protected.

The The invention also relates to a mechanical inverter for generating an alternating current from a DC power source, which is a fixed arranged slip ring having a plurality of conductive regions, wherein the conductive regions are electrically isolated from each other. Each of the conductive areas has a connection for connection with a potential provided by the DC power source. A pantograph is provided with at least one brush. The pantograph is arranged so movable that the brush through a movement in succession with the multiple electrical areas is electrically connectable.

Thereby, that the brush and not the slip ring arranged movably is, a plurality of partial voltages from the DC power source for Generation of AC voltage can be tapped, without the number to increase the brushes. This is especially suitable for the cases where for the number m of the brushes and for the number n of taps the DC power source or input terminals of the mechanical inverter: n> m. This will be the number of brushes not determined by the number of partial voltages. It need only as many brushes are provided as there are initial voltages gives. It is desirable to know the number of brushes m, because at each Gleitverbin training from slip ring and Brush cause thermal losses. In addition, must Brushes are replaced after a long time. ever fewer brushes are used, the lower the effort for this maintenance. Accordingly, the structure with fixed, Segmented slip ring particularly advantageous when a high Number of partial voltages is used. Would the segmented Turn slip ring, would have the partial voltages of the DC voltage source be transferred to the segmented slip ring with the help of n slip rings. If the segmented slip ring is fixed, only need the signals of the brushes of the pantograph over M slip rings are removed. This can be the commutator be built easier, easier and space-saving.

In Another embodiment is at least one more Sliding connection with slip ring and brush provided for Connection of brushes of the pantograph with output terminals of the mechanical inverter. With the help of this further sliding connection can the AC removed from the pantograph at fixed terminals be removed. This allows this AC for a variety of uses are used.

The The invention also relates to a device for generating an alternating current from a DC voltage source, the device being a DC source and a mechanical commutator, wherein the commutator is fed from the DC power source. There are several supply connections provided for outputting an alternating current. The DC source has a number n of taps, n> 2, to provide n, each different, potentials on. The commutator is at the respective time sequential Connecting the supply connections with the n potentials intended.

With With the help of this device, an alternating current can be generated Although it is fed by discrete DC voltages, if possible it is fed to sinusoidal form is approached. In addition, the increased Using the mechanical commutator the robustness of the device at lightning strike.

If the DC source contains a series connection of accumulators, The partial voltages can be easily connected to the terminals the accumulators are tapped.

Preferably the commutator contains a fixed collector a plurality of electrically conductive regions that are electrically conductive from each other are isolated. The executive areas are each attached to one of Coupled with the tapping potentials. A movable rotor with electric brushes is used to contact the conductive Areas.

The invention is illustrated in the drawings an embodiment illustrated in more detail.

1 shows an electric drive unit according to the invention for a wind turbine;

2 puts that to a three-phase motor 1 applied voltages;

3 shows the voltages applied to the collector of the commutator;

4 illustrates the resulting field vectors of the three-phase motor in emergency operation;

5 shows a preferred embodiment of the collector of the mechanical commutator of the electric drive unit.

1 shows a schematic representation of the electric drive unit for a wind turbine. It contains a mechanical commutator 10 , a three-phase motor 2 , an AC power source 5 , a DC power source 6 as well as a first isolating contactor 51 and a second contactor 52 , The DC source 6 contains four accumulators B1, B2, B3 and B4, which are connected in series. The accumulators B4, B3, B2 and B1 each have the same capacity and voltage level and in turn may each consist of a series connection of accumulators, for example lithium-ion accumulators.

The first connection of the accumulator 81 is with the crowd 36 while its second terminal is connected to the first terminal of the rechargeable battery B2, which in turn is connected to the first terminal of the rechargeable battery B3. The second connection of the accumulator 63 is with the first connection of the accumulator 64 connected. The DC voltage source 6 has four taps. The first tap 60 is with the first connection of the accumulator 61 connected while the second tap 61 is connected to the second terminal of the accumulator B1. The third tap 62 is connected to the first terminal of the accumulator B4, whose second terminal is connected to the fourth tap 63 connected is.

The Size of the capacities of the accumulators B1, B2 B3 and B4 can alternatively to the expected Charge be adjusted so that the capacity of this Accumulators are different.

At the taps 60 . 61 . 62 and 63 provides the DC source 6 four different potentials available. The potential at the tap 60 corresponds to the ground potential, the potential at the tap 61 provides 0.25 U ₀ , the tap 62 provides the potential 0.75 U ₀ and the third tap provides the potential U ₀ . The potentials are each related to the ground potential. In one embodiment, the potential U _{0 is} normally at 300 V from the ground potential, so that at the taps 62 and 61 Potentials of 225 V and 75 V are provided against the ground potential.

The mechanical commutator 10 has a collector 3 , a brush star 40 , a wave 4 and a slip ring body 43 on. The commutator 10 will also be referred to as inverter in the following 10 designated. The brush star 40 has three brush taps 401 which protrude perpendicularly from the shaft in a star shape, each brush tapping 401 to the other two brush taps 401 each at an angle of 120 °.

At her, the wave 4 opposite, ends have the brush taps 401 to brush 402 on that on the inside of the annular collector 3 to run.

The slip ring body 43 has four insulating areas 24 and three between the insulating areas 24 provided slip rings 25 on. The slip rings 25 are each electrically conductive and each with one of the brushes 402 the brush taps 401 of the brush star 40 connected.

With a rotation of the shaft 4 also rotates the slip ring body 43 as well as the brush star 40 , Each brush conducts 402 the tension that they put on the inside of the collector 3 picks up on one of the slip rings 25 further.

In the figure it is shown that the collector 3 conductive areas 31 and non-executive areas 30 having. The leading areas 31 are each with one of the taps 60 . 61 . 62 and 63 electrically connected so that they are at one of the potentials 0, 0.25 U ₀ , 0.75 U ₀ and U ₀ . The leading areas 31 are separated from each other by the insulating areas 30 electrically isolated.

The stresses on the sliding joints resulting from the slip rings 25 and the brushes U _MWR , V _MWR , W _MWR are tapped. The three-phase motor 2 has three supply connections UM, VM and WM. The AC power source 5 has three outputs UQ, VQ and WQ and outputs a sinusoidal voltage at their outputs UQ, VQ and WQ. These output signals are mutually phase-shifted by 120 °. In normal operation, the second contactor connects 52 the output UQ with the connection UM, the output VQ with the connection VM and the output WQ with the connection WM. Thus, the three-phase motor 2 from the AC power source 5 driven. The AC power source 5 is in turn so controlled that the three-phase motor 2 adjusts the angle of attack of the rotor blades of the wind turbine according to the wind conditions.

In an emergency operation, the three-phase motor 2 no longer from the AC source 5 be controlled. However, the three-phase motor should turn the rotor blades into a safety position, the so-called flag position. The switches of the second isolating contactor 52 are opened and those of the first contactor 51 closed. The three-phase motor 2 will now be from the DC source 6 and the mechanical inverter 10 driven. The DC source 6 contains z. B. a variety of series-connected batteries that are charged regularly in normal operation, so that enough energy is available in emergency mode.

If the three-phase motor is designed as an asynchronous motor, the rotor, consisting of shaft 4 , Brush star 40 and slip ring body 43 , in emergency mode by means of a in the 1 Not shown DC motor rotated. This DC motor is from the DC power source 6 fed. In further embodiments, the DC motor can also be driven by a different electrical energy source. It is also conceivable to transmit rotational energy from the propeller of the wind turbine so that the rotor is rotated.

is the three-phase motor designed as a synchronous motor, is eliminated the DC motor for driving the rotor. Instead The rotor of the commutator is controlled by the synchronous machine to be controlled self-propelled. In this case, the rotor of the commutator and the rotor of the synchronous machine always have the same speed and in a certain, fixed angular position to each other.

The brushes 402 of the brush star 40 be rotated one after the other with the conductive areas 31 of the collector 3 connected. These conductive areas 31 are each at different potentials. The different potentials are chosen so that the brushes U _MWR , V _MWR , W _MWR tapped stair-step voltage waveforms, which approach as possible a sinusoidal shape. This turns the three-phase motor 2 operated with input signals closer to the sine, so it runs smoother. Compared to inverters that only switch between a minimum potential 0 and a maximum potential U ₀ , the voltage swings on the brushes U _MWR , V _MWR and W _{MWR are} reduced, so that the risk of brush fire on these brushes is minimized.

Thus, partial voltages of the uninterruptible power supply are tapped and these on the commutator 10 guided. So only smaller voltages must be switched and the risk of brush fire is reduced. In addition, the output signal of the mechanical inverter 10 better approximated to the signal shape of the sine wave. This is advantageous for the operating behavior of the engine. The partial voltages are accessible without much effort, since the uninterruptible power supply consists of a series connection of individual capacitors or accumulators. In the embodiment shown, four potentials of the DC power source 6 tapped.

The commutator shown 10 has a rotor with brushes 402 and a fixed collector 3 out. In one, in the 1 not shown, embodiment, the brushes are fixed and the collector rotates.

2 shows the curves of the AC voltage source 5 provided voltage UQ, VQ, WQ and tapped by the brushes U _MWR , V _MWR and W _MWR voltages relative to the ground potential 36 , The sinusoidal voltage UQ is drawn as it is from the AC source 5 is provided in normal operation. The square waveform of the voltage provided by the brush U _MWR is also shown with a solid line. From 0 ° to 60 °, this voltage is 0.75 U ₀ , from 60 ° to 120 ° to 0.25 U ₀ , from 120 ° to 180 ° to 0, from 180 ° to 240 ° again to 0.25 U. ₀ , from 240 ° to 300 ° to 0.75 U ₀ and from 300 ° to 360 ° to 1 U ₀ . Since the signal is periodic, it goes from 360 ° again as shown from 0 °.

The sinusoidal signal VQ is shown with a dashed line, as well as the voltage provided by the brush V _MWR , the course of which should approximate the sinusoidal shape. From 0 ° to 60 ° this is from the mechanical inverter 10 provided signal to 0.75 U ₀ , after which it is from 60 ° to 1 U ₀ to 120 °. From 120 ° to 180 ° it is 0.75 U ₀ and takes the same course as that provided by the brush U _MWR signal with a phase shift of 120 °.

The sinewave signal WQ is indicated by a dot-dash line, as well as that of the mechanical inverter 10 provided signal W _MWR .

The signals U _MWR , V _MWR and W _MWR are mutually phase shifted by 120 °.

3 shows the pattern of a rolled collector 3 out 1 , The collector 3 has six leading areas 31 on top of each other by insulating areas 30 are separated. The leading Be rich 31 are each with taps of the DC power source 6 linked so that they are counted from left to right, on the potentials U _0; 0.75 U ₀ ; 0.25 U ₀ ; 0 U ₀ ; 0.25 U ₀ and 0.75 U ₀ are.

In 3 is also a possible position of the brush star 40 and his taps 402 located. The brush 402 for the signal UMWR is with the first, the brush for the signal WMWR is with the third and that for the signal VMWR is with the fifth conductive region 31 connected. Here are the leading areas 31 counted from left to right. Due to the rotational movement, the taps are continuously led to the left, so that in the following the taps on non-conductive areas 30 and then back to senior areas 31 be guided. Then, the tap for the signal WMWR in the second, the tap for the signal VMWR in the fourth and the tap for the signal UMWR in the sixth conductive region 31 are located.

4 shows the rotating, resulting field vector of the three-phase motor, when it matches the staircase output voltages of the mechanical inverter 10 as in 2 is charged. In the pointer representation, the vector U points vertically up or down. The angle between the vector U and the vector V is 120 °, wherein the vector U must be rotated 120 ° clockwise to be congruent with the vector V. In a further rotation by 120 ° to get to the vector W. In the right column is compared against which potentials see the three brush taps on the collector at the same time. If the taps are guided on the three windings of a three-phase motor, the field vectors shown in the middle column result. The left column shows the voltage conditions at the windings of the three-phase motor.

The resulting field vector is drawn with the solid line. 4 shows six phases. It can be seen that the resulting pointer is rotating. The change between the shown pointer representations occurs abruptly.

At the Apply a three-phase ideal sinusoidal signal the vector would rotate continuously. Indeed the signal shown is a pretty good approximation to one continuously rotating field vector.

It can be seen that the potential changes every 60 °. In order to avoid a short-circuit in the potential change, a small area must be used 30 of the collector to be executed at the potential transitions not conductive. If the potential changes occur simultaneously for all phases, there are no unwanted intermediate states with only two energized phases.

In the transition between the energized phases, all three brush taps are briefly at zero. In these short periods, the three-phase motor 2 not energized. However, this has small insulating areas 31 as not critical, because the rotor of the three-phase motor 2 has a sluggishness, so that the engine continues to rotate before it is energized again.

If more than four potentials are tapped and by the commutator 10 to the three-phase motor 2 guided, the field vector during rotation has more discrete angular positions than with only four taps and the rotation of the field vector is more closely approximated to the continuous rotation. From this point of view, the provision of more taps is advantageous. However, this also increases the number of insulating areas 30 , and thus the time in which the three-phase motor is not energized. It must therefore be weighed between the number n of taps and the time in which the motor is not energized, and the number n to be selected accordingly.

It is possible as a three-phase motor 2 to use a three-phase asynchronous machine or a three-phase synchronous machine.

The electric drive unit shown 1 comes in emergency operation without electronic control. This is important because wind turbines are particularly prone to lightning and electronic circuits are destroyed with lightning strike with a relatively high probability.

5 shows a preferred embodiment of the distribution of potentials on the collector 3 , Between the first conductive area 31 and the adjacent insulating areas 30 and between the fourth conductive region 31 and the adjacent insulating areas 30 are each more insulating areas 32 appropriate. This causes the first and the fourth conductive area 31 each slightly narrower than the second, the third, the fifth and the sixth conductive area 31 is.

It aims to prevent it from passing from the conductive areas 31 in the insulating areas 30 to undesirable intermediate states with only two energized phases comes. This can happen, among other things, if due to production fluctuations, the leading areas 31 are different in size.

Would in the example after 3 For example, the tap WMWR already the non-conductive area 30 contact and would be the tap UMWR still at U ₀ and the tap VMWR at 0.25 U ₀ , the resulting field vector would point diagonally down to the right, although at the end of the second phase according to 4 pointing straight down. This means that the field vector abruptly points in a completely different direction and thus steers the motor in a different direction. This is not desirable, so that according to the embodiment of the 5 the first and the fourth conductive area 31 is made narrower by passing between these conductive areas 31 and the respective adjacent insulating regions 30 an additional insulating area 32 is inserted.

If a potential change now takes place, then the brush tap, which starts or leaves the range 0 U ₀ or 1 U ₀ , is already or still in the insulating zone, while the other two taps have not yet left their conducting regions or already their new ones approached leading areas. The resulting field vector is 0.

Undesirable intermediate states are now prevented because the two brush taps, which do not start or leave the region 1 U ₀ or 0 U ₀ , always lead the same potential of 0.75 U ₀ or 0.25 U ₀ . It can not flow between these taps. The resulting field vector is zero.

1

electrical drive unit

2

Three-phase motor

3

collector

4

wave

5

AC power source

6

DC power source

10

mechanical inverter

24

insulating Area

25

slip ring

30

insulating Area

31

senior Area

32

insulating Area

36

Dimensions or ground potential

40

brush star

43

Ring collectors

51

isolation contactor

52

isolation contactor

60

first tap

61

second tap

62

third tap

63

fourth tap

401

Bürstenabgriff

402

brush

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102006015511 A1 [0002]

Claims (26)

Electric drive unit, with a three-phase motor ( 2 ), an AC power source ( 5 ), a DC power source ( 6 ) and a mechanical commutator ( 10 ), whereby the three-phase motor ( 2 ) has a plurality of supply connections (UM, VM, WM) which, in normal operation, are supplied by the AC power source ( 5 ) are controllable and in an emergency operation of the commutator ( 10 ) are controllable, wherein the commutator ( 10 ) from a DC power source ( 6 ), the DC source ( 6 ) a number n taps ( 60 . 61 . 62 . 63 ), n> 2, for providing n, in each case different, potentials (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ) and the commutator ( 10 ) is provided for the time sequentially connecting the supply terminals (UM, VM, WM) with the n potentials (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ). Electric drive unit according to claim 1, characterized in that the direct current source ( 2 ) contains a series circuit of accumulators (B1, B2, B3, B4) and / or capacitors. Electric drive unit according to claim 1 or 2, characterized in that the three-phase motor ( 2 ) is provided for adjusting the angle of attack of rotor blades of a wind turbine. Electric drive unit according to one of claims 1 to 3, characterized in that in the connections between the commutator ( 10 ) and the three-phase motor ( 2 ) Contactors ( 51 ) and in the connections between the AC source ( 5 ) and the three-phase motor ( 2 ) Contactors ( 52 ) are provided. Electric drive unit according to claim 1 to 4, characterized in that the commutator ( 10 ) a fixed collector ( 3 ) with several electrically conductive areas ( 31 ), which are electrically insulated from each other, wherein the conductive regions ( 31 ) are each coupled to one of the potentials applied to the taps (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ), and characterized by a movable rotor ( 4 . 43 . 40 ) with electric brushes ( 402 ) for contacting the conductive areas ( 31 ). Electric drive unit according to claim 5, characterized in that the number of brushes ( 402 ) is three, and the leading areas ( 31 ) coupled to either the minimum or maximum potential are smaller than the conductive regions coupled to other potentials. Electric drive unit according to one of claims 5 or 6, characterized in that slip rings ( 25 ) are provided on the rotor, each brush ( 402 ) with one of the slip rings ( 25 ) connected is. Electric drive unit according to claim 7, characterized in that further brushes (U _MWR , V _MWR , W _MWR ) for contacting the slip rings ( 25 ) for connection to the supply connections (UM, VM, WM) of the three-phase motor ( 3 ) are provided. Electric drive unit according to one of claims 1 to 4, characterized in that the commutator ( 10 ) a movable collector ( 3 ) with several conductive areas ( 31 ), which are electrically insulated from each other, wherein the conductive regions ( 31 ) to one of the taps ( 60 . 61 . 62 . 63 ) are coupled to potentials, and characterized by fixed electric brushes ( 402 ) for contacting the conductive areas ( 31 ). Electric drive unit according to one of claims 1 to 9, characterized in that the direct current source ( 6 ) connected in series energy storage (B1, B2, B3, B4), wherein the capacities of the energy storage devices (B1, B2, B3, B4) are of different sizes. Electric drive unit according to one of the claims 1 to 10, characterized in that: n = 4. Electric drive unit according to claim 5 to 11, characterized by a DC motor for rotating the collector ( 3 ) or the rotor ( 4 . 40 . 43 ). Electric drive unit according to claim 12, characterized in that the DC motor from the DC power source ( 6 ) is fed. Electric drive unit according to one of claims 1 to 10, characterized in that the three-phase motor ( 2 ) is carried out as a synchronous motor and the collector ( 3 ) or the rotor ( 4 ) of the three-phase motor ( 6 ) is driven. Wind power machine with electric drive unit according to one of claims 1 to 14. Mechanical inverter for generating an alternating current from a direct current source ( 6 ), having the following features: a stationary slip ring ( 3 ) with several conductive areas ( 31 ), from each other electrically insulated, each of the conductive areas ( 31 ) each have a connection for connection to one of the DC power source ( 6 ), - a pantograph ( 40 ) with at least one brush ( 402 ), the pantograph ( 40 ) is movably arranged so that the brush ( 402 ) by a movement successively with the plurality of electrical regions ( 31 ) is electrically connected. A mechanical inverter according to claim 16, wherein for the number m of brushes applies: m> 1. A mechanical inverter according to claim 17, wherein the number n of the terminals of the conductive areas ( 31 ): n> m. A device for generating an alternating current from a DC voltage source, comprising: a DC power source ( 6 ), a mechanical commutator ( 10 ), the commutator ( 10 ) from the DC power source ( 6 ) and a plurality of supply terminals (UM, VM, WM) for outputting an alternating current, the direct current source ( 6 ) a number n taps ( 60 . 61 . 62 . 63 ), n> 2, for providing n, in each case different, potentials (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ) and the commutator ( 10 ) is provided for the time sequential connecting the supply terminals with the n potentials (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ). Device according to claim 19, characterized in that the direct current source ( 2 ) contains a series connection of accumulators (B1, B2, B3, 64) and / or capacitors. Device according to claim 19 or 20, characterized in that the commutator ( 10 ) a fixed collector ( 3 ) with several electrically conductive areas ( 31 ), which are electrically insulated from each other, wherein the conductive regions ( 31 ) are each coupled to one of the potentials (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ) applied to the taps, and characterized by a movable rotor ( 4 . 43 . 40 ) with electric brushes ( 402 ) for contacting the conductive areas ( 31 ). Device according to claim 21, characterized in that the number of brushes ( 402 ) is three, and the leading areas ( 31 ) coupled to either the minimum or maximum potential are smaller than the conductive regions coupled to other potentials. Device according to one of claims 19 to 22, characterized in that further slip rings ( 25 ) are provided on the rotor, each brush ( 402 ) with one of the other slip rings ( 25 ) connected is. Device according to claim 19 or 20, characterized in that the commutator ( 10 ) a movable collector ( 3 ) with several electrically conductive areas ( 31 ), which are electrically insulated from each other, wherein the conductive regions ( 31 ) are respectively coupled to one of the potentials (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ) present at the taps, and characterized by fixed electrical brushes ( 402 ) for contacting the conductive areas ( 31 ). Apparatus according to claim 24, characterized in that the potentials to be conducted to the collector (0, 0.25 U ₀ , 0.75 U ₀ , U ₀ ) are transmitted by means of slip rings. Device according to one of claims 19 to 25, characterized in that the commutator ( 10 ) of a particular from the DC power source ( 6 ) powered DC motor is driven.