RELIABLE ELECTRIC BRAKE FOR A SYNCHRONOUS ENGINE

Abstract

A method for controlling a braking torque of a drive system and for braking a vehicle includes in a first state connecting phase connections of a synchronous machine to one another by a changeover apparatus and short circuiting the phase connections such that a first braking torque develops at the synchronous machine. In a second state the phase connections are connected to one another by the changeover apparatus and to a resistance, such that a second braking torque develops at the synchronous machine. The changeover apparatus periodically switches between the first and second states at a switching frequency of 10 Hz or higher to produce a pre-settable braking torque at the synchronous machine, with the changeover between the first state and the second state being controlled by a timing element in an unregulated manner.

Claims

1.-16. (canceled)

17. A method for reliably controlling a braking torque of a drive system and for braking a vehicle, said method comprising: in a first state connecting phase connections of a synchronous machine to one another by a changeover apparatus and short circuiting the phase connections, such that a first braking torque develops at the synchronous machine; in a second state connecting the phase connections to one another by the changeover apparatus and to a resistance, such that a second braking torque develops at the synchronous machine; periodically switching between the first state and the second state by the changeover apparatus at a switching frequency of 10 Hz or higher for producing a pre-settable braking torque on average over time of the first and second braking torques at the synchronous machine; and controlling by a timing element in an unregulated manner the switching between the first state and the second state.

18. The method of claim 17, wherein the vehicle is constructed in the form of a rail vehicle.

19. The method of claim 17, wherein the short circuiting is adopted for a fixed number of oscillation periods.

20. The method of claim 17, further comprising checking voltages and currents at the phase connections for achieving the pre-settable braking torque at the synchronous machine to enhance reliability of a brake.

21. The method of claim 17, further comprising activating a mechanical brake when a pre-set rotary speed of the drive system or a pre-set velocity of the vehicle is undershot.

22. The method of claim 17, further comprising: rectifying currents of the phase connections for developing the second braking torque; and feeding the currents to the resistance following the rectifying.

23. The method of claim 17, further comprising interrupting a current through the resistance via a switch for changing a resistance value effective for generating the second braking torque, such that the second braking torque changes.

24. The method of claim 23, further comprising: forming the changeover apparatus by a self-commutated power converter including on a direct current side an electrical parallel connection of an intermediate circuit capacitor, a series connection of the resistance, the switch and a semiconductor power switch; in a first state of the self-commutated power converter controlling the semiconductor power switch for short circuiting the phase connections; and in a second state of the self-commutated power converter not controlling the semiconductor power switch for connecting the phase connections to the resistance via freewheeling diodes.

25. A drive system for reliably controlling a braking torque and for braking a vehicle, comprising: a synchronous machine including phase connections; a changeover apparatus electrically connected to the phase connections, said changeover apparatus having a first state in which the phase connections are short circuited, and a second state in which the phase connections are connected to a resistance at the synchronous machine; and a timing element configured to control periodically switching between the first state and the second state at a switching frequency of 10 Hz or higher in an unregulated manner.

26. The drive system of claim 25, wherein the phase connections are each connected via a said resistance to a star point in the second state of the changeover apparatus.

27. The drive system of claim 25, wherein the changeover apparatus is formed by a self-commutated power converter, said self-commutated power converter being connected to the phase connections on an alternating current side, said self-commutated power converter including on a direct current side an intermediate circuit, said resistance being arranged in a series connection with a switch, with the series connection being arranged electrically in parallel with the intermediate circuit.

28. The drive system of claim 25, wherein the changeover apparatus is formed by a self-commuted power converter, said self-commuted power converter including on a direct current side an electrical parallel connection of an intermediate circuit capacitor, a series connection of the resistance, the switch and a semiconductor power switch, wherein the semiconductor power switch is controlled for short circuiting the phase connections in the first state and the semiconductor switch is not controlled for connecting the phase connections to the resistance via freewheeling diodes in the second state.

29. A vehicle, comprising a drive system for reliably controlling a braking torque and for braking the vehicle, said drive system comprising a synchronous machine including phase connections, a changeover apparatus electrically connected to the phase connections, said changeover apparatus having a first state in which the phase connections are short circuited, and a second state in which the phase connections are connected to a resistance, and a timing element configured to control periodically switching between the first state and the second state at a switching frequency of 10 Hz or higher in an unregulated manner.

30. The vehicle of claim 29 constructed in the form of a rail vehicle.

31. The vehicle of claim 29, wherein the changeover apparatus is formed by a self-commutated power converter, said self-commutated power converter being connected to the phase connections on an alternating current side, said self-commutated power converter including on a direct current side an intermediate circuit, said resistance being arranged in a series connection with a switch, wherein the series connection is arranged electrically in parallel with the intermediate circuit of the self-commutated power converter.

32. The vehicle of claim 29, wherein the changeover apparatus is formed by a self-commuted power converter, said self-commuted power converter including on a direct current side an electrical parallel connection of an intermediate circuit capacitor, a series connection of the resistance, the switch and a semiconductor power switch, wherein the semiconductor power switch is controlled for short circuiting the phase connections in the first state and the semiconductor switch is not controlled for connecting the phase connections to the resistance via freewheeling diodes in the second state.

Description

[0026] The invention will now be described and explained in greater detail making reference to the exemplary embodiments illustrated in the drawings, in which:

[0027] FIG. 1, FIG. 2 are examples of the shape of the braking torque over velocity for two different resistance values,

[0028] FIG. 3 is the exemplary shape of two braking torques,

[0029] FIG. 4 is a first exemplary embodiment of the invention,

[0030] FIG. 5 is a second exemplary embodiment of the invention, and

[0031] FIG. 6 is a further exemplary embodiment with a self-commutated power converter as the changeover apparatus.

[0032] FIG. 1 shows the shape of the braking torque M.sub.Br against rotary speed in the event that the phase connections 20 are each electrically connected to a resistance 4 with a value R.sub.1. For a second resistance 4 with a value R.sub.2, where R.sub.2<R.sub.1, the shape is shown in FIG. 2. It is clearly apparent that the maximum of the achievable braking torque M.sub.Br for relatively small resistances 4 occurs at lower velocities. At a rotary speed of zero, regardless of the resistance value, no braking torque M.sub.Br is achievable at the synchronous machine 2. In order to be able to apply a braking torque to the drive system also at standstill, a further brake, for example, a mechanical brake must be provided in the drive system 1.

[0033] FIG. 3 shows the shape of a first braking torque M.sub.Br1 where this arises in that the phase connections 20 of the synchronous machine 2 are short circuited, and the shape of a second braking torque M.sub.Br2 wherein the phase connections 20 are connected to one another via at least one resistance 4. The region that lies between the two curves can be used by the method for reliably controlling the braking torque M.sub.Br such that a braking torque M.sub.Br is generated at the synchronous machine 2. The region above the second braking torque, at least the part which lies to the right of the maximum of the second braking torque M.sub.Br2, can be generated at the synchronous machine 2 if the changeover apparatus 3 has a switch 5 which temporarily interrupts the current flow through the resistance 4. With this interruption, the effective resistance at the phase connections 20 can be increased, which leads to a prolongation of the maximum toward higher rotary speeds.

[0034] FIG. 4 shows a first exemplary embodiment of the invention. The drive system 1 herein has a synchronous machine 2, in particular a permanent field synchronous machine 2 and a changeover apparatus 3 which are electrically connected to one another via the phase connections 20. The changeover apparatus 3 comprises a changeover apparatus switch 31. In an upper position of the changeover apparatus switch 31, as shown, this short circuits the phase connections 20, whereas in a second position, i.e. in the lower position of the changeover apparatus switch 31, the changeover apparatus switch 31 connects the phase connections 20 of the synchronous machine 2 to one another via a star connection of resistances 4. The star connection is formed by a connection between the switch contacts of the changeover apparatus 31 and a star point 30 wherein the resistance 4 is respectively arranged in each such connection. It has proved to be advantageous to provide the same resistance values for the resistances 4 shown. Thus, the braking torque is constant over a motor rotation. Unpleasant shuddering, for example, in a vehicle or rail vehicle, is thereby prevented.

[0035] In the exemplary embodiment of FIG. 5 a smaller number of resistances 4 suffices as compared with the exemplary embodiment of FIG. 4. For the avoidance of repetition, reference is made to the description relating to FIG. 4 and the reference signs therein. In the exemplary embodiment of FIG. 5 also, an even braking torque over the whole rotation of the synchronous machine 2 is achieved in that in relation to all the phase connections 20, by the rectification, symmetrical conditions are created. The rectification of the currents of the phase connections 20 is carried out by the means 6 for rectification. In this exemplary embodiment, this is realized by a diode bridge. This diode bridge is designated an uncontrolled B6 bridge or B6 diode bridge. This requires no control and can be economically integrated in the changeover apparatus 3.

[0036] FIG. 6 shows an exemplary embodiment, wherein the changeover apparatus is formed by a self-commutated power converter 11. For the avoidance of repetition, reference is made to the description regarding FIGS. 1 to 5 and the reference signs therein. The self-commutated power converter 11 has a braking controller 7, an intermediate circuit capacitor 13 and power semiconductors 14, 15. A braking controller 7 is arranged in the intermediate circuit. This is arranged parallel to the intermediate circuit capacitor 13. The braking controller has a series connection of the resistance 4 and a switch 5. The power semiconductors 14, 15 of the power converter, i.e. the semiconductor power switch 14 and the freewheeling diode 15 assume the role of the changeover apparatus switch 31. If none of the semiconductor power switches is controlled, currents can only flow via the freewheeling diodes 15 of the self-commutated power converter 11. This takes place when the intermediate circuit voltage, i.e. the voltage at the intermediate circuit capacitor 13 is lower than the amplitude of the voltage induced by the synchronous machine 2. If necessary, the voltage of the intermediate circuit capacitor 13 can be lowered by switching on the switch 5 so far that the freewheeling diodes 15 become conductive and a current flows through the resistance 4.

[0037] In this exemplary embodiment, the switch 5 can be configured, for example, as an electronic power switch, as shown, or as a mechanical switch. In one embodiment as an electronic power switch, it can switch at a high frequency. The switching of an electronic power switch is also designated clocking. If a particularly simple construction is striven for, a mechanical switch can be used as the switch 5, for example a contactor. This switch 5 requires no triggering electronics. With this simple triggering, the mechanical switch is suitable, in particular, for safety-relevant equipment such as the reliable braking of a vehicle.

[0038] In the first state of the changeover apparatus 3, the phase connections 20 of the synchronous machine 2 are short circuited. This takes place with the aid of the power semiconductors 14, 15 of the self-commutated power converter 11. In order to create the short circuit, all the phase connections 20 are connected either to the upper or the lower intermediate circuit potential. For this purpose, at least one semiconductor power switch 14 is to be switched on. Based upon the direction of flow of the currents i.sub.1, i.sub.2, i.sub.3 of the phase connections 20, it is decided whether, during the short circuit, the relevant phase current flows through the semiconductor power switch 14 or the freewheeling diodes 15. Then, only the semiconductor power switch 14 is to be controlled, i.e. switched on, so that the short circuit of the phase connections 20 is produced. In order to avoid a selection logic for the triggering of the semiconductor power switch 15, all the upper semiconductor power switches 15 or all the lower semiconductor power switches 15 can be triggered. The upper semiconductor power switches 15 denotes the semiconductor power switches 15 which are connected to the positive intermediate circuit potential. The lower semiconductor power switches 15 are understood to be the semiconductor power switches 15 which are connected to the negative intermediate circuit potential.

[0039] In the second state of the changeover apparatus 3 in which the phase connections of the synchronous machine are connected to the resistance 4, the switch 5 must be continually switched on or clocked. By means of the clocking, i.e. the repeated switching on and off of the switch 5, the resistance 4 effective for the braking torque of the synchronous machine 2 is increased. Thus, the range of the braking torques achievable at the synchronous machine 2 is increased, as shown in FIG. 3. Since the intermediate circuit capacitor 13 is arranged in parallel with the braking controller 7, the switch 5 can be opened in a simple manner, even when the currents are driven through the inductances of the synchronous machine 2, since on switching off the switch 5, a path for these currents through the intermediate capacitor 13 forms. The semiconductor power switches 14 of the self-commutated power converter 11 are not controlled in the second state of the changeover apparatus 3, i.e. these semiconductor power switches 14 are switched off.

[0040] Although the invention has been illustrated and described in detail based on the preferred exemplary embodiments, the invention is not restricted solely to the examples given and other variations can be derived therefrom by a person skilled in the art without departing from the protective scope of the invention.