DE102019212055A1 - Electric drive system with a separately excited synchronous machine - Google Patents

Abstract

An electrical drive system comprising a separately excited synchronous machine, the separately excited synchronous machine having a stator and a rotor (1) assigned to the stator, the stator at least three phase windings and the rotor (1) at least two rotor poles (2, 3) each with a first pole end ( 4) and a second pole end (5) and a control unit, the control unit being designed in such a way that the rotor poles (2, 3) are fed separately from one another with direct or alternating current during operation of the separately excited synchronous machine and the current direction can be variably adjusted is.

Description

Field of the Invention

The present invention relates to an electric drive system comprising an externally excited synchronous machine, the externally excited synchronous machine having a stator and a rotor assigned to the stator, the stator having at least three phase windings and the rotor having at least two rotor poles each having a first pole end and a second pole end and one Control unit.

State of the art

Synchronous electrical machines can be operated as rotating electrical machines both as a motor and as a generator. Corresponding synchronous drives can be used in a wide variety of different technical areas, including automotive engineering. Such a synchronous machine basically has a stator with stator windings, so-called phase windings, which generate a rotating magnetic field in the region of the rotor. Appropriate control of the phase windings causes the magnetic field to rotate. A rotor in the rotating field with magnetic poles, which can be designed either as permanent magnets (permanent magnet-excited synchronous machine) and / or as electrically excited magnets (externally excited synchronous machine), rotates synchronously with the speed of the rotating field generated by the stator.

With at least partial drive of a motor vehicle by means of a motor-driven electrical machine, for example a synchronous machine, there is generally a need to adapt the operating parameters of the electric motor to the driving situation. At low speeds, a high torque should be available so that it can accelerate on steep inclines and approaches, for example. At the same time, the motor vehicle should be able to achieve the highest possible top speed. These requirements, namely a high torque and a high top speed, are opposed, because in order to achieve the highest possible top speed, the electric motor must generate the lowest possible electromagnetic counterforce and in order to generate high torque, the electric motor must generate the highest possible electromagnetic counterforce.

To counteract this conflict, for example, a mechanical gear can be used. However, in addition to the additional space required, this causes additional costs and an increased weight.

In the case of permanently excited electrical machines, the magnetic poles of the rotor are predetermined by the magnets and can only be changed by complex magnetizing currents.

Summary of the invention

It is an object of the invention to improve the prior art, in particular with regard to electrical synchronous machines.

The object is achieved by an electric drive system comprising an externally excited synchronous machine, the externally excited synchronous machine having a stator and a rotor assigned to the stator, the stator having at least three phase windings and the rotor having at least two rotor poles, each with a first pole end and a second pole end and a control unit, the control unit being designed such that during operation of the externally excited synchronous machine, the rotor poles are fed separately from one another with direct current and the current direction can be variably adjusted.

According to the invention, the electric drive system comprises an externally excited synchronous machine and a control unit.

The term “externally excited synchronous machine” is to be understood on the one hand as a synchronous machine whose rotor poles are designed as electrically excited magnets and on the other hand as hybrid versions whose rotor poles are formed from permanent magnets and electrically excited magnets.

According to the present invention, the externally excited synchronous machine has a stator and a rotor assigned to the stator.

According to the invention, the stator has at least three phase windings and the rotor has at least two rotor poles, each with a first pole end and a second pole end.

The control unit is designed in accordance with the present invention in such a way that during operation of the externally excited synchronous machine, the rotor poles are fed separately from one another with direct or alternating current and the current direction can be variably adjusted.

If alternating current is applied to the rotor poles, this can be rectified, for example, by means of a rectifier.

Due to the construction of the electric drive system according to the invention, two separate rotor windings and their control a particularly cost-effective and space-efficient pole-changing, externally excited synchronous machine.

Further developments of the invention are specified in the dependent claims, the description and the accompanying drawings.

The control unit particularly preferably comprises a semiconductor bridge circuit which has a number of half bridges corresponding to the number of rotor poles increased by at least one, the first pole ends of the rotor poles in each case being connected with a half bridge of the control unit for control purposes, and all second pole ends of the rotor poles in star connection with a common half bridge are tax-effective.

Both the currents and the current direction in the rotor poles can preferably be regulated separately from one another via the pulse width of the three half bridges.

In a preferred embodiment variant of the present invention, the electric drive system has a cooling circuit, the cooling circuit being designed such that primarily, i.e. First, the star connection on the common half-bridge branch is cooled.

Figure list

• Fig. zeigt schematisch einen Rotor einer fremderregten Synchronmaschine sowie eine Halbleiterbrückenschaltung einer Steuereinheit.

The invention is described below by way of example with reference to the drawings.

• Fig. Shows schematically a rotor of an externally excited synchronous machine and a semiconductor bridge circuit of a control unit.

Detailed description of the invention

The electric drive system has an externally excited synchronous machine and a control unit.

The externally excited synchronous machine comprises a stator and a rotor assigned to the stator 1 . The externally excited synchronous machine can have an internal rotor 1 , an external rotor 1 or be designed as an axial flow machine.

In the embodiment shown in Fig. The rotor has 1 two rotor poles 2nd , 3rd , namely a first rotor pole 2nd and a second rotor pole 3rd , on. The rotor poles 2nd , 3rd are formed by electrically excited magnets. Each of the two rotor poles 2nd , 3rd has a first pole end 4th and a second pole end 5 on.

The control unit has control electronics and a semiconductor bridge circuit 6 on. The semiconductor bridge circuit shown schematically in FIG 6 is designed as a three-phase full bridge. The full bridge has a first half bridge 7 , a second half bridge 8th and a third half-bridge 9 on. The first half bridge 7 has a first controllable semiconductor element 11 and a second controllable semiconductor element 12th on. The first controllable semiconductor element 11 and the second controllable semiconductor element 12th are connected to each other in series and can be controlled via the control electronics. In the other two half bridges 8th , 9 there are also two controllable semiconductor elements connected in series 11 , 12th . All controllable semiconductor elements 11 , 12th are preferably identical, but can also be designed differently.

The three half bridges 7 , 8th , 9 each have a center tap 13 on. The center tap 13 the first half bridge 7 is with the first pole end 4th of the first rotor pole 2nd connected. The center tap 13 the second half bridge 8th is with the first pole end 4th of the second rotor pole 3rd connected. The center tap 13 the third half-bridge 9 is in star connection 10th with the second pole end 5 of the first rotor pole 2nd and the second pole end 5 of the second rotor pole 3rd connected.

Parallel to the half bridges 7 , 8th , 9 The three-phase full bridge is connected to an intermediate circuit capacitor, which forms an energy store for the intermediate circuit and can be discharged if necessary (not shown).

The first pole ends 4th the rotor poles 2nd , 3rd represent the input side of the respective rotor pole 2nd , 3rd is thus the input side of each rotor pole 2nd , 3rd a half bridge 7 , 8th the semiconductor bridge circuit 6 assigned to the control unit, which is switchable to the individual rotor poles 2nd , 3rd impress a current or a current flow.

During the operation of the separately excited synchronous machine, the two rotor poles can 2nd , 3rd can be fed separately from each other with direct current and the current direction can be variably adjusted. An optional rotor pole changeover is implemented in this way. The current is regulated via pulse width control of the respective half-bridge 7 , 8th , 9 in the respective rotor pole 2nd , 3rd embossed. The setting is made via the selected pulse pattern of the first half bridge 7 and the second half bridge 8th . The pulse pattern of the third Habbrücke 9 is normally selected to 50%, but can be adjusted depending on the operating point. So you can use the pulse width of the three half bridges 7 , 8th , 9 the currents and the current direction in the two rotor poles 2nd , 3rd can be regulated separately.

By changing the current direction (positive or negative) of one of the two rotor poles 2nd , 3rd (In the present exemplary embodiment in FIG. 2 there are two rotor poles 2nd , 3rd , but it can also be several) can be the number of pole pairs of the rotor 1 and thus the electromagnetic counterforce of the externally excited synchronous machine can be changed. The two rotor poles 2nd , 3rd can either be energized in such a way that either one pair of poles (two poles) or two pairs of poles (four poles) result. In the case of one pole pair, the externally excited synchronous machine delivers half the torque, but almost twice the speed (high top speed). In the case of two pole pairs, the separately excited synchronous machine delivers half the speed, but twice the torque (high torque at a constant frequency of the stator current).

For the exemplary embodiment shown in FIG. 1, switching from two pole pairs to one pole pair during the operation of the synchronous machine thus changes the speed / torque behavior of the synchronous machine. For example, in operating situations with a low speed requirement but a high torque requirement, the number of poles can be switched to two - in this way a high torque is achieved, for example, for starting a motor vehicle. In operating situations with low torque requirements but high speed requirements, the number of pole pairs can be switched to one - this way a high speed is achieved.

Reference list

1

rotor

2nd

First rotor pole

3rd

Second rotor pole

4th

First pole end

5

Second pole end

6

Semiconductor bridge circuit

7

First half bridge

8th

Second half bridge

9

Third half bridge

10th

Star connection

11

First semiconductor element

12th

Second semiconductor element

13

Center tap

Claims (4)

Comprehensive electric drive system - An externally excited synchronous machine, the externally excited synchronous machine having a stator and a rotor (1) assigned to the stator, the stator having at least three phase windings and the rotor (1) at least two rotor poles (2, 3) each having a first pole end (4) and a second pole end (5) and - A control unit, the control unit being designed such that the rotor poles (2, 3) are fed separately from one another with direct or alternating current during operation of the externally excited synchronous machine and the current direction can be variably adjusted. Electric drive system after Claim 1 , characterized in that the control unit comprises a semiconductor bridge circuit (6) which has the number of rotor poles (2, 3) increased by at least one half bridges (7, 8, 9) corresponding to at least one, the first pole ends (4) of the rotor poles ( 2, 3) are each connected to one half bridge (7, 8) for tax purposes and all second pole ends (5) of the rotor poles (2, 3) are connected in star configuration (10) to a common half bridge (9) for control purposes. Electric drive system after Claim 2 , characterized in that both the currents and the current direction in the rotor poles (2, 3) can be regulated separately from one another via the pulse width of the three half bridges (7, 8, 9). Electric drive system after Claim 2 or 3rd , characterized in that the electrical drive system has a cooling circuit, the cooling circuit being designed such that primarily, namely first, the star connection (10) of the second pole ends (5) is cooled on the common half-bridge (9).

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