Device for protecting an electrical machine

Abstract

An apparatus for protecting an electrical machine in the event of a fault, the electrical machine having six phase terminals includes a monitoring unit for detecting a fault of the electrical machine and a switchover unit for switching the electrical machine from a normal operating state into a short-circuit operating state if a fault of the electrical machine is detected. The switchover unit is designed to short-circuit the six phase terminals of the electrical machine asynchronously in accordance with a predefined pattern.

Claims

1. An apparatus for protecting an electrical machine in case of a fault, wherein the electrical machine has six phase terminals, comprising: a monitoring unit for detecting a fault of the electrical machine; and a switchover unit for switching the electrical machine from a normal operating state into a short circuit operating state should a fault of the electrical machine be detected, wherein the switchover unit is configured to asynchronously short-circuit the six phase terminals of the electrical machine according to a predefined pattern, the apparatus further comprises a memory that is configured to store a plurality of predefined patterns, each of the plurality of predefined patterns is stored in the memory as a lookup table, and the switchover unit is configured to select one of the plurality of predefined patterns as the predefined pattern.

2. The apparatus according to claim 1, wherein the switchover unit is configured to select one of the plurality of predefined patterns on the basis of a current angle of the rotor of the electrical machine.

3. The apparatus according to claim 2, wherein the switchover unit is configured to select one of the plurality of predefined patterns on the basis of a predefined angle tolerance range.

4. The apparatus according to claim 3, wherein the switchover unit is configured to select one of the plurality of predefined patterns on the basis of a desired variant for switching off the electrical machine.

5. The apparatus according to claim 2, wherein the switchover unit is configured to select one of the plurality of predefined patterns on the basis of a desired variant for switching off the electrical machine.

6. The apparatus according to claim 1, wherein the switchover unit is configured to select one of the plurality of predefined patterns on the basis of a desired variant for switching off the electrical machine.

7. The apparatus according to claim 6, wherein the desired variant is an immediate activation of the short circuit operating state or a delayed activation of the short circuit operating state.

8. The apparatus according to claim 1, wherein the predefined pattern defines a delay between a short-circuit of the first, second, third, fourth, fifth, and sixth phase terminal.

9. The apparatus according to claim 1, wherein the switchover unit is configured to select one of the plurality of predefined patterns on the basis of a predefined angle tolerance range.

10. A method for protecting an electrical machine in case of a fault, wherein the electrical machine has six phase terminals, comprising: detecting a fault of the electrical machine; and switching the electrical machine from a normal operating state into a short circuit operating state should a fault of the electrical machine be detected, wherein the six phase terminals of the electrical machine are asynchronously short-circuited according to a predefined pattern, the predefined pattern is selected from a plurality of predefined patterns, and each of the plurality of predefined patterns is stored in a memory as a lookup table.

11. A computer product having a non-transitory computer readable medium having stored thereon program code that, when executed by a computer, causes the computer to: detect a fault of the electrical machine; and switch the electrical machine from a normal operating state into a short circuit operating state should a fault of the electrical machine be detected, wherein the six phase terminals of the electrical machine are asynchronously short-circuited according to a predefined pattern, the predefined pattern is selected from a plurality of predefined patterns, and each of the plurality of predefined patterns is stored in a memory as a lookup table.

12. An apparatus for protecting an electrical machine in case of a fault, wherein the electrical machine has six phase terminals, comprising: a monitoring unit for detecting a fault of the electrical machine; and a switchover unit for switching the electrical machine from a normal operating state into a short circuit operating state should a fault of the electrical machine be detected, wherein the switchover unit is configured to asynchronously short-circuit the six phase terminals of the electrical machine according to a predefined pattern, and the predefined pattern defines a delay between a short-circuit of the first, second, third, fourth, fifth, and sixth phase terminal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic block diagram of an apparatus for protecting an electrical machine in the case of a fault.

(2) FIG. 2 is a schematic block diagram of the apparatus of FIG. 1 in the overall surroundings of the electrical machine.

(3) FIG. 3 is a schematic illustration of the principle of the apparatus of FIG. 1.

(4) FIG. 4 shows exemplary curves of the quadrature-axis and direct-axis phase voltages of the electrical machine.

(5) FIG. 5 is a schematic flow chart of a method for protecting an electrical machine in the case of a fault.

(6) In the figures, equivalent or functionally equivalent elements have been provided with the same reference sign, provided nothing else has been specified.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) FIG. 1 shows an apparatus 10 for protecting an electrical machine 20 in the case of a fault. The electrical machine 20 has six phase terminals u.sub.1, v.sub.1, w.sub.1, u.sub.2, v.sub.2, w.sub.2, as described in more detail in conjunction with FIGS. 2 and 3.

(8) A monitoring unit 11 of the apparatus 10 monitors the electrical machine 20 and detects the occurrence of a fault. If such a fault is detected, the switchover unit 12 switches the electrical machine 20 from a normal operating state into a short circuit operating state. In order to achieve this, the six phase terminals u.sub.1, v.sub.1, w.sub.1, u.sub.2, v.sub.2, w.sub.2 of the electrical machine 20 are asynchronously short-circuited according to a predefined pattern.

(9) The principle of this switchover is now explained in more detail in conjunction with FIGS. 2 and 3.

(10) The monitoring unit 11 transmits a signal indicating operation under emergency conditions to the switchover unit 12.

(11) Following the reception of the signal indicating operation under emergency conditions, the generation of inverter control pulses is switched to a logical operation under emergency conditions, provided by the apparatus 10 in FIG. 1, by the PWM nominal operation module 22.

(12) In the process, the apparatus 10 carries out an optimal switch off strategy by way of the inverter 21 within the meaning of a suppression of transient short-circuit currents. The optimal switch off pattern is selected on the basis of a current electrical rotor angle, an angle tolerance and the selection of a variant following the input of a signal indicating operation under emergency conditions. In the variants, a distinction can be made between the following options:

(13) 1. Immediately carrying out the active short circuit, the switch off pattern being optimized for the suppression of transient short-circuit currents.

(14) 2. Carrying out the active short circuit in one of the plurality of optimal rotor positions, the switch off pattern being optimized for the suppression of transient short-circuit currents.

(15) The generated or selected optimal switch off pattern for the phase u.sub.1{0,1}, v.sub.1{0,1}, w.sub.1{0,1}, u.sub.2{0,1}, v.sub.2{0,1}, w.sub.2{0,1} is multiplied by the required switch off time offsets 24. These offsets or delays are generated in block 23 of FIG. 3.

(16) In the generated inverter control pulses, the time of the short-circuit for two, three or four phases is delayed by the switch off time offset in order to optimally suppress the transient currents during the switching of the active short circuit.

(17) An example for the curves of the quadrature-axis and direct-axis phase voltages U.sub.d1 (1) and U.sub.q1 (2) is shown in FIG. 4, top. In this case, the switching pattern 1, 1, 0, 1, 1, 0 is used. In order to ensure optimal suppression of the transient short-circuit currents, the phases w.sub.1, w.sub.2 were initially short-circuited at optimal rotor angle 4 (U.sub.d1=U.sub.q1=min), followed by the phases u.sub.1, v.sub.1, u.sub.2, v.sub.2. The lower diagram in FIG. 4 shows the rotor angle 3. As is evident, there is one optimum rotor angle 4 per period 0-2π.

(18) FIG. 5 shows a method for protecting an electrical machine 20 in the case of a fault. The method includes the following steps:

(19) A fault of the electrical machine 20 is detected in a first step 301.

(20) Subsequently, in a second step 302, the electrical machine 20 is switched from a normal operating state to a short circuit operating state, wherein the six phase terminals u.sub.1, v.sub.1, w.sub.1, u.sub.2, v.sub.2, w.sub.2 of the electrical machine 20 are asynchronously short-circuited according to a predefined pattern.

(21) The proposed apparatus renders it possible to suppress the transient short-circuit currents by a factor of 1.5 to 2. Since there is no need for approximate dimensioning of the electrical machine and the power electronics, this is accompanied by lower costs and less installation space. Moreover, no additional hardware is required. Additionally, the DC link capacitor can be discharged during the active short circuit.

(22) Although the present invention was described on the basis of exemplary embodiments, it is modifiable in multifaceted ways.

LIST OF REFERENCE SIGNS

(23) 1 U.sub.d 2 U.sub.q 3 Rotor angle 4 Optimal rotor angle 10 Apparatus 11 Monitoring unit 12 Switchover unit 13 Memory 20 Electrical machine 21 Inverter 22 PWM nominal operation 23 Delay generation 24 Delay 301-302 Method steps