Device for actuating separately excited synchronous machine, separately excited synchronous machine and method

Abstract

The invention relates to a device for controlling a separately excited synchronous machine having a slip ring and a brush, comprising a full-bridge circuit having two half-bridges, each of which has an upper branch and a lower branch, and a control unit for controlling the full-bridge circuit, wherein the first half-bridge has at least one diode connected in a reverse-biased manner in the upper branch and at least one transistor in the lower branch, and wherein the second half-bridge has at least one transistor in the upper branch and at least one diode connected in a reverse-biased manner in the lower branch, at least one resistor connected in parallel to a branch having at least one diode connected in a reverse-biased manner, the at least one diode connected in a forward-biased manner being arranged in series with the at least one resistor; the invention discloses a separately excited synchronous machine. The invention further relates to a method for operating the separately excited synchronous machine.

Description

Technical field

[0001] The invention relates to a device for controlling a separately excited synchronous machine, a separately excited synchronous machine having such a device, and a method for operating such a separately excited synchronous machine. Background art

[0002] In a separately excited synchronous machine, the rotor winding is supplied with direct current, and the current is fed in from the outside through slip rings located on the rotor shaft. Then, the current is picked up from the slip rings by brushes and supplied to or led away from the rotor winding. Here, the fixed brushes press against the rotating slip rings with a certain pressure.

[0003] One application area of such a separately excited synchronous machine is, for example, as an electric motor in an electric vehicle. A full-bridge circuit having two half-bridges is used to control the separately excited synchronous machine or the rotor winding, wherein the rotor winding and the slip rings and brushes are arranged in the bridge or the bridge diagonal. Each half-bridge has an upper branch and a lower branch, wherein the first half-bridge has at least one diode connected in a reverse-biased manner in the upper branch and at least one transistor in the lower branch, and the second half-bridge has at least one transistor in the upper branch and at least one diode connected in a reverse-biased manner in the lower branch. Due to the different materials of the slip rings, brushes and rotor winding, decomposition of the slip rings can occur, especially when the slip rings are exposed to moisture. One remedy is to arrange the slip rings in a protected structural space. Another measure is to temporarily energize with a negative current, thereby forming a protective oxide layer on the slip rings, which counteracts the decomposition. In this case, all branches of the two half-bridges must be equipped with transistors. Summary of the invention

[0004] The invention is based on the following technical problem of creating a device for controlling a separately excited synchronous machine, which counteracts the decomposition of the slip rings with less circuit consumption. Another technical problem is to create such a separately excited synchronous machine and to provide a suitable method for operating the separately excited synchronous machine for use.

[0005] The solution to the technical problem results from the device for controlling a separately excited synchronous machine with slip rings and brushes, the separately excited synchronous machine having slip rings and brushes, and the method for operating the separately excited synchronous machine.

[0006] For this purpose, a device for controlling a separately excited synchronous machine with slip rings and brushes has a full-bridge circuit and a control unit for controlling the full-bridge circuit. Here, the full-bridge circuit has two half-bridges, and each of the half-bridges has an upper branch and a lower branch. Additionally, the first half-bridge has at least one diode connected in reverse bias in the upper branch and at least one transistor in the lower branch. Correspondingly, the second half-bridge has at least one transistor in the upper branch and at least one diode connected in reverse bias in the lower branch. Here, for reasons of voltage strength (Spannungsfestigkeit), multiple diodes can be connected in series in the branch with the diode connected in reverse bias, or additional resistors can be present. In the branch with the transistor, for example, two transistors can be arranged in series. In parallel with the respective branch having at least one diode connected in reverse bias, at least one diode connected in forward bias is arranged in series with at least one resistor. Thereby, the negative offset current is guided through the slip ring with a slight circuit-technical effort, and this negative offset current promotes the growth of oxides on the slip ring.

[0007] In one embodiment, the resistor is dimensioned such that the current through the resistor is at least 100 times smaller than the current through the conducting transistor. Thereby, it is achieved that the negative offset current does not generate a torque or does not generate a torque worth mentioning. Additionally, the negative offset current is preferably 1000 to 3000 times smaller than the current through the conducting transistor. For example, the current through the conducting transistor is in the range of 20 A - 25 A, and the negative offset current is in the range of 10 mA - 25 mA.

[0008] In another embodiment, another resistor is arranged in the bridge and is connected in parallel with the rotor winding. In the case of a fault in the rotor winding, this resistor protects the transistor from overvoltage because it ensures the flow of current.

[0009] In another embodiment, another resistor is at least 10 times larger than the ohmic resistance of the rotor winding. Further preferably, this factor is at least 100. Thereby, it is ensured that most of the negative offset current flows through the slip ring.

[0010] In another embodiment, the control unit is assigned a memory in which the rotor angle of the last stationary position in the stationary state of the separately excited synchronous machine is stored, wherein the control unit is configured such that in the stationary state, the current rotor angle is acquired and compared with the stored rotor angle, and wherein if the difference is less than a preset offset, the rotor winding is energized until the difference is at least equal to the preset offset. This is based on the following idea. When the vehicle is stationary, for example during parking or charging, a negative offset current flows intensively through the area of the slip ring where the brush is currently located. This causes local oxide growth. The rotor angle at shutdown is arbitrary and there is no preferred position, so that in general all positions occur with the same frequency. However, if due to chance or other reasons the brush should be again too densely in the position where previous local oxide growth already exists when the vehicle is stationary, the rotor is moved further so as to at least maintain the preset offset. The offset can be, for example, 5° - 10°. The additional movement caused thereby is minimal. However, this ensures that the local oxide growth is more evenly distributed over the circumference of the slip ring.

[0011] In another embodiment, the control unit is configured such that in coasting operation, the phase current in the stator winding of the separately excited synchronous machine is maintained. Thereby, a negative current is induced in the rotor winding, which also causes oxide accumulation.

[0012] This embodiment is an independent, alternative solution, which can also be used alone.

[0013] The separately excited synchronous machine having slip rings and brushes has the above-described means for control.

[0014] Methodologically, in a separately excited synchronous machine in a predetermined operating state, a negative current is generated in the rotor winding to generate oxide growth on the slip ring. For further possible design options, full reference is made to the previous statements regarding the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be explained in more detail below based on preferred embodiments. In the figures:

[0016] Figure 1 A schematic diagram of a device for controlling the rotor winding of a separately excited synchronous machine in a first embodiment is shown,

[0017] Figure 2 A schematic diagram of a device for controlling a separately excited synchronous machine in a second embodiment is shown,

[0018] Figure 3 A schematic diagram of a slip ring on a rotor shaft is shown, and

[0019] Figure 4 A flowchart of a method for controlling a separately excited synchronous machine is shown. Detailed Embodiment

[0020] In Figure 1 a device 1 for controlling a separately excited synchronous machine is schematically shown. The device 1 has a full-bridge circuit 2 and a control unit 3, where a memory 4 is assigned to the control unit 3. The full-bridge circuit 2 has a first half-bridge H1 and a second half-bridge H2. The first half-bridge H1 has an upper branch ZO1 and a lower branch ZU1. In the upper branch ZO1, at least one diode D connected in reverse bias is arranged, and a series circuit composed of a diode D1 connected in forward bias and at least one first resistor R1 is connected in parallel with the diode D. In the lower branch ZU1, at least one first transistor T1 is arranged. Correspondingly, a second transistor T2 is arranged in the upper branch ZO2 of the second half-bridge H2. In the lower branch ZU2, a diode D connected in reverse bias is arranged, and a series circuit composed of a diode D2 connected in forward bias and at least one second resistor R2 is connected in parallel with the diode D. A rotor winding LR is arranged in the bridge or the bridge diagonal, and another resistor R3 is connected in parallel with it. Slip rings and brushes are not shown, and current is fed into the rotor winding LR through them. Here, the positive current direction is symbolically represented by an arrow. When the two transistors T1, T2 are conducting, the positive current flows. A negative offset current continuously flows through the parallel circuit composed of the resistor R1, the diode D1, another resistor R3, the rotor winding LR, the diode D2, and the second resistor R2. Here, the resistors R1, R2 are dimensioned such that the negative offset current is at least 100 times smaller than the positive current flowing when the transistors T1, T2 are conducting. In the stationary state, i.e., when the two transistors T1, T2 are blocked, only the negative offset current flows and causes oxide growth on the slip rings. The transistors T1, T2 are controlled by the control unit 3. Here, at least the rotor angle of the last vehicle stop is stored in the memory 4 If the separately excited synchronous machine should be switched off (brought to a stop state) at this time, the current rotor angle will be read by the control unit 3. For example, a rotor position sensor provides the rotor angle Then the current rotor angle is compared with the stored rotor angle If the difference is less than a preset offset then the rotor winding LR will continue to be energized through the transistors T1, T2 until the difference is greater than Then, the current rotor angle will be used as the new stored in the memory 4 and the parking brake is activated in the case of an electric vehicle.

[0021] In Figure 2 an alternative embodiment is shown, which can also be used in combination with the embodiment according to Figure 1 Here, the same as Figure 1, T1 and T2 are marked with the same reference symbols. In addition, a free-wheeling diode D3 of the transistors T1 and T2 is shown here, which can be an independent component if the transistors T1 and T2 are configured as MOSFETs, but can also be an intrinsic diode of the transistors T1 and T2. In addition, a stator winding LS is schematically shown. Here, in terms of hardware technology, the device 1 is configured in the same way as in the prior art. According to the present invention, during the coasting operation of the separately excited synchronous machine 100, the energization of the rotor winding LR is stopped (T1 and T2 are blocked), while the stator winding LS continues to be energized. Here, the stator winding LS induces a voltage at the rotor winding LR, so that a negative current flows. The direction of the current is symbolically indicated by an arrow. The negative current then flows into the battery through the free-wheeling diode D3 and returns from there through another free-wheeling diode D3. Since the rotor shaft rotates during the coasting operation, the slip ring is loaded with a rotationally symmetrical negative current, resulting in a symmetrical oxide accumulation.

[0022] Figure 3 Schematically shows how two slip rings 10 are arranged on the rotor shaft 11 , wherein fixed brushes 12 collect current and connect to the rotor winding LR. The slip rings 10 are electrically connected to the center tap of the full bridge circuit 2 .

[0023] Figure 4 In a first step S1, the device 1 acquires the externally excited synchronous machine 100 (see also Figure 2 ) should be turned off (e.g. the electric vehicle should be parked). In a second step S2, the current rotor angle is then determined

[0024] In a third step S3, the rotor angle of the last stop state is then read out from the memory 4. Steps S2 and S3 can also be interchanged or performed simultaneously. In the fourth step S4, the two rotor angles are compared. The difference is formed. If the difference is greater than the preset offset Then turn off the separately excited synchronous machine 100 and store the rotor angle (Step S5). Otherwise, the rotor winding LR continues to be energized by the device 1 until the current rotor angle With the stored rotor angle The difference is greater than (Step S6). Then, the current rotor angle Stored as the new stored rotor angle And the separately excited synchronous machine 100 is turned off (step S7).

[0025] Reference Symbols List

[0026] 1 Device

[0027] 2 Full-bridge circuit

[0028] 3 Control unit

[0029] 4 Memory

[0030] 10 Slip ring

[0031] 11 Rotor shaft

[0032] 12 Brush

[0033] 100 Synchronous machine

[0034] T1, T2 transistors

[0035] D Diode

[0036] D1, D2 diodes

[0037] D3 Self-oscillating diode

[0038] R1 First resistor

[0039] R2 Second resistor

[0040] R3 Another resistor

[0041] LR Rotor winding

[0042] LS Stator winding.

Claims

1. A device (1) for controlling a separately excited synchronous machine (100) with a slip ring (10) and a carbon brush (12), wherein, The device (1) has a full-bridge circuit (2) and a control unit (3) for controlling the full-bridge circuit (2), wherein the full-bridge circuit (2) has two half-bridges (H1, H2), and the half-bridges each have an upper branch (ZO1, ZO2) and a lower branch (ZU1, ZU2), wherein the first half-bridge (H1) has at least one diode (D) connected in reverse bias in the upper branch (ZO1) and at least one transistor (T1) in the lower branch (ZU1), and wherein the second half-bridge (H2) has at least one transistor (T2) in the upper branch (ZO2) and at least one diode (D) connected in reverse bias in the lower branch (TU2). It is characterized in that In parallel with the branch having at least one diode (D) connected in reverse bias, at least one diode (D1, D2) connected in forward bias is arranged in series with at least one resistor (R1, R2).

2. The device according to claim 1, characterized in that, The resistors (R1, R2) are dimensioned such that the current through the resistors (R1, R2) is at least 100 times smaller than the current through the conducting transistors (T1, T2).

3. The device according to claim 1 or 2, characterized in that, Another resistor (R3) is arranged in the bridge and is in parallel with the rotor winding (LR).

4. The device according to claim 3, characterized in that The another resistor (R3) is at least 10 times larger than the ohmic resistance of the rotor winding (LR).

5. The device according to any one of the preceding claims, characterized in that The control unit (3) is assigned a memory (4) in which the rotor angle (φ R0 ) of the last rest position when the separately excited synchronous machine (100) is at rest is stored, wherein the control unit (3) is configured such that in the rest state the current rotor angle (φ R1 ) is acquired and compared with the stored rotor angle (φ R0 ), and wherein if the difference is less than a preset offset (Δφ), the rotor winding (LR) is energized until the difference is at least equal to the preset offset (Δφ).

6. The device according to any one of the preceding claims, characterized in that, The control unit (3) is configured such that the phase current in the stator winding (LS) of the separately excited synchronous machine (100) is maintained during coasting operation.

7. A device (1) for controlling a separately excited synchronous machine (100) having a slip ring (10) and a carbon brush (12), wherein, The device (1) has a full-bridge circuit (2) and a control unit (3) for controlling the full-bridge circuit (2), wherein the full-bridge circuit (2) has two half-bridges (H1, H2), and the half-bridges each have an upper branch (ZO1, ZO2) and a lower branch (ZU1, ZU2), wherein the first half-bridge (H1) has at least one diode (D) connected in reverse bias in the upper branch (ZO1) and at least one transistor (T1) in the lower branch (ZU1), and wherein the second half-bridge (H2) has at least one transistor (T2) in the upper branch (ZO2) and at least one diode (D) connected in reverse bias in the lower branch (TU2). It is characterized in that The control unit (3) is configured such that the phase current in the stator winding (LS) of the separately excited synchronous machine (100) is maintained during coasting operation.

8. A separately excited synchronous machine (100) having a slip ring (10) and a carbon brush (12), wherein, The separately excited synchronous machine (100) has a device (1) for control having the features of any one of the preceding claims.

9. A method for operating a separately excited synchronous machine (100) with the features of claim 8, characterized in that, In a preset operating state, a negative current is generated in the rotor winding (LR).

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