EP2008358A1

EP2008358A1 - Control system for an electric motor

Info

Publication number: EP2008358A1
Application number: EP07724286A
Authority: EP
Inventors: Lothar Rehm; Thomas Von Raumer
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2006-04-19
Filing date: 2007-04-17
Publication date: 2008-12-31
Also published as: WO2007121889A1; JP5281567B2; US20090099703A1; DE102006018053A1; CN101427456A; CN101427456B; JP2009535001A; US8054014B2

Abstract

The invention relates to a control system for a permanent-field electric motor (1) and corresponding method. When a function computer (3) and/or a monitoring computer (4) recognises an error in the control system, the electric motor (1) is switched off. The aim of the invention is to reduce the braking torque of a switched-off and still rotating electric motor (1). According to the invention said aim is achieved, wherein a three-phase short-circuit of the output stage (2) is carried out to switch off the electric motor (1) when the rotational speed D1 is not below a fixable threshold value GR1 or a voltage U_DC for the output stage (2) exceeds a threshold value Umax and, otherwise, when the rotational speed D1 is below the fixable threshold GRl and a voltage U_DC for the output stage (2) does not exceed a threshold Umax, all breakers (2ol, 2o2, 2o3, 2ul, 2u2, 2u3) in the output stage (2) are opened to switch off the electric motor (1).

Description

Drive system for an electric machine

The invention relates to a drive system for a permanent-magnet electric machine according to claim 1 and a method for controlling a permanent-magnet electric machine according to claim 4.

From DE 102 05 963 Al a method and drive system for driving a permanent-magnet machine is known, wherein each phase of the electric machine is associated with a half-bridge arrangement having a first and a second switching element for power supply via an intermediate circuit. An operating state of a drive system is monitored and compared with a threshold value. When the threshold value is exceeded, a fault condition is detected and a short circuit between the phases of the electrical machine is generated.

Permanent-magnet electric machines are used, for example, as vehicle drive motors which receive electric energy from a power supply in hybrid drive systems. The power supply takes place, for example, by a battery connected via a power converter and a DC link, in electrically powered vehicles by a so-called traction battery or by a generator driven by an internal combustion engine. In the case of permanent-magnet electric machines, the fundamental problem that due to the relative movement between the armature windings and the permanent magnets occurring during operation is that a countervoltage, known as the pole wheel voltage, is induced in the armature windings. This induced voltage increases with increasing speed and can reach and exceed the amount of the supply voltage of the electric machine. Occur in such drive systems with permanent-magnet electric machines errors, such as the failure of a control electronics for making a field weakening or a winding closure, this leads to a return of electrical energy from the electric machine into the power supply. Thereby, a braking torque can be generated that is undesirable for the operation of the electric machine in a vehicle. Even at low speeds such braking torques can be generated, for example, by a triggered by a detected error three-phase short circuit.

The object of the invention is to reduce the braking torque of a switched off and still rotating electric machine.

This object is achieved by a drive system for an electric machine, in which a three-phase short circuit of the output stage by shorting the three upper circuit breaker or the three lower circuit breaker is feasible for switching off the electric machine, if the speed Dl does not fall below a definable limit GRl or one Voltage U_DC of the output stage exceeds a limit Umax. In this case, the switching elements of the output stage are referred to as a circuit breaker. Advantage of the solution according to the invention is that a three-phase short circuit is performed only under such boundary conditions in which no disturbing braking torque can occur. In the case of a three-phase short-circuit of a permanent-magnet electric machine, no appreciable braking torque is generated at higher speeds (in the range above several hundred revolutions per minute). In addition, damage to components such as battery, power converter and its semiconductor devices, avoided.

In one embodiment of the invention, all circuit breakers of the output stage are obviously for switching off the electrical machine when the speed Dl is below the threshold GR and a voltage U_DC of the final stage falls below a limit Umax.

In the case of a three-phase short circuit of a permanent-magnet electric machine, a disturbing braking torque is generated at very low rotational speeds (in the range of a few hundred revolutions per minute). A shutdown of the electric machine by opening all circuit breakers of the power amplifier is, however, feasible at low speeds without disturbing braking torque. This has the advantage that a shutdown of the electric machine without disturbing braking torque can also be performed when the boundary conditions for the implementation of a low-braking torque three-phase short circuit are not present.

Further advantageous embodiments of the invention will become apparent from the dependent claims and with reference to the drawings. Showing:

1 is a schematic circuit diagram of an inventive proper drive system in conjunction with a permanent-magnet electric machine,

Fig. 2 is an exemplary representation of a speed-dependent error response and the associated braking torque.

Fig. 1 shows an electrical machine 1 with an embodiment of a drive system according to the invention.

The electric machine 1 is connected to an output stage 2. The output stage 2 can be designed as a converter or as a power converter. The illustrated output stage 2 has three upper switching elements 2ol, 2o2, 2o3 and three lower switching elements 2ul, 2u2, 2u3. The switching elements are typically designed as a circuit breaker. These switching elements form three half-bridge arrangements, each consisting of two of the switching elements 2ol, 2ul; 2o2, 2u2 and 2o3, 2u3 are formed and each one of the three phases of the electric machine 1 drive.

The output stage 2 is via a, not shown in Fig. 1. Main contactor with a, not shown in Fig. 1, supply device of the electric machine 1 (for example, a battery) connected. The supply device supplies the output stage 2 with a supply voltage U_DC. The supply device can be switched on and off via the main contactor.

The output stage 2 is connected to a logic module 5 and is controlled by this. In addition, the power amplifier 2 information about the supply voltage U_DC and information about a correct implementation of a three-phase short circuit to the logic device 5 on. As well For example, information about correct conversion of an opening of the switching elements 2ol, 2o2, 2o3, 2ul, 2u2 or 2u3 or about a voltage U_CE of a switching element 2ol, 2o2, 2o3, 2ul, 2u2 or 2u3 can be forwarded to the logic module 5.

The logic module 5 is connected to a function computer 3 and a monitoring computer 4 and receives from these data. The function computer 3 and the monitoring computer 4 are also connected to each other and exchange data with each other. In this case, the monitoring computer 4 monitors the error-free operation of the function computer 3.

The function computer 3 receives the information of a speed sensor 6, which preferably detects a speed Dl of the electric machine 1.

In addition, one or more other speed sensors 7 may be provided for detecting one or more rotational speeds D2. For example, the speed of the electric machine 1 can also be detected as the speed D2. Likewise, a speed of a gear connected to the electric machine 1, a wheel speed of a vehicle wheel or another relevant speed can be detected. Preferably, a wheel speed sensor of a vehicle wheel of an electronic stability program is provided as a speed sensor 7.

In FIG. 1, the rotational speed sensor 7 is connected to the function computer 3. About this connection receives the function calculator 3 information of the speed sensor 7 on the detected speed D2. The function computer 3 has an area 8. This area 8 is referred to as the first level in a two-level monitoring system or a three-level monitoring system. In this case, the first level is monitored by a second level and possibly a third level. In the area 8 of the function computer 3, the current Änsteuersignale for controlling the electric machine 1 are calculated. These control signals are passed from the area 8 of the function computer 3 to a switch 10 of the logic module 5.

The switch 10 of the logic module 5 is the drive signals via a control line to a switch 14 of the logic block 5 on. The switch 14 of the logic module 5 outputs the control signals via a control line to a switch 16 of the logic module 5 on. The switch 16 of the logic module 5 is the drive signals via a control line to the power amplifier 2 on. The output stage 2 sets its switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 in accordance with the control signals and controls the electric machine 1 in accordance with the control signals.

The functional computer 3 is connected via a shutdown path to an element 9 of the logic module 5. In this case, a connection is referred to as Abschaltpfad over which either an enable signal or a shutdown signal can be passed.

The monitoring computer 4 is also connected via a Abschaltpfad with the element 9 of the logic device 5.

In a preferred embodiment, the shutdown signal is provided as a voltage-free default state. Will through If no error is transmitted by the function computer 3 or by the monitoring computer 4 to the logic module 5, then the logic component 5 interprets this as the shutdown signal.

The element 9 is formed in the embodiment shown in Fig. 1 as a "logical AND" element

Like all elements of the logic module 5, 9 can be represented as an electronic component, as a structure within a logic module or by means of software. If the "logical AND" 9 receives a release signal both from the function computer 3 and from the monitoring computer 4, then there is an enable signal to the switch

10 continue, otherwise there is a shutdown signal on.

In an alternative embodiment, the element 9 is implemented as a "logical OR" or the like, in which case the element 9 issues a switch-off signal to the switch 10 when it receives a switch-off signal from the function computer 3 or from the monitoring computer 4 or both.

If the switch 10 receives a switch-off signal from the element 9, it switches over and thus interrupts the forwarding of the control signals calculated by region 8 of the function computer 3. Instead of the drive signals of area 8, the drive signals of an element 11 of the logic module 5 are now passed on. In this case, the element 11 is typically a permanent memory in which the drive signals for a three-phase short circuit are permanently stored.

These drive signals of the element 11 are fed via the switch 10 in the control line and passed through switch 14 and switch 16 to the power amplifier 2. The output stage 2 sets its switching elements 2ol, 2o2, 2o3, 2ul,

2u2, 2u3 in accordance with the control signals for a

Three-phase short circuit, thus creating one

Three-phase short circuit of electric machine 1.

In this case, the drive signals may provide a three-phase short circuit of the switching elements 2ol, 2o2, 2o3 or the switching elements 2ul, 2u2, 2u3. It can also be provided to switch to the respective other variant of a three-phase short circuit if information about the operating state of the switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 allow the conclusion that the selected three-phase short circuit can not be performed without errors or has been performed.

The switch 14 is connected to an element 19. The element 19 is a logic that sends a switch-off signal to the switch 14 in the presence of specified input data. In this case, the switch-off signal causes the switch 14 to be switched to a switching state in which it can pass on its associated drive signals for opening all switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 of the output stage 2 for switching off the electrical machine 1.

The element 19 is connected via an element 20 with the speed sensor 6. The element 20 receives from the rotational speed sensor 6 information about the detected by the speed sensor 6 speed Dl. The speed Dl is preferably a speed of the electric machine 1. The element 20 checks whether the speed Dl is below a threshold GRl. In one embodiment, the element 20 provides a signal to the element 19, if that is the case.

In a further development of this embodiment, it is checked whether the speed sensor 6 and the signal transmission of the value work faultlessly for Dl. In Fig. 1, this test is arranged in an element 18. In this case, element 19 evaluates the information supplied by element 20 about the rotational speed D 1 of sensor 6 only when, in addition, element 18 signals to element 19 that rotational speed sensor 6 and the signal transmission of the value for D 1 operate without errors. If this is not the case, then in a further development, a permanently stored speed value can be assumed.

In the embodiment shown in FIG. 1, the element 19 is connected to the function computer 3 via an element 17. The element 17 receives from the function computer 3 a speed information D2 of an additional sensor 7. In this case, the element 17, alternatively to the embodiment shown in FIG. 1, may also be arranged in the function computer 3.

In a further development, the element 17 only transmits a signal to the element 19 when the

Speed information D2 falls below the limit value GR2. In an alternative simplified embodiment, element 19 provides a signal to element 14, if that is the case.

In a further development of this alternative embodiment, the speed information D2 supplied by the additional rotational speed sensor 7 to the function computer 3 is replaced by the rotational speed information D1 supplied by the rotational speed sensor 6 when the functional computer 3 detects a fault of the rotational speed sensor 7 or the data transmission of the rotational speed sensor 7. In this case, according to a preferred embodiment, element 17 only sends a signal to element 19, when the speed information Dl detected in the function calculator 3 falls below the limit value GR1.

In a preferred embodiment, a signal is then transmitted to the element 14 in the element 19 when the elements 17 and 20 each detect a limit underrun and there is no information about an erroneous detection or transmission of the limit below the signals.

The drive signals, which the switch 10 transmits via the control line to the switch 14, are also forwarded to an element 12. Based on the control signals from switch 10, the element 12 detects whether a

Three-phase short circuit should be triggered. The element 12 forwards this information to the function computer 3 and to the element 19 of the logic module 5.

The element 12 is also connected to the output stage 2 and receives from this information about the operating state or the operating state of their switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3. Typically, it is transmitted whether a voltage U_CE of the switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 assumes a permissible value. Based on the information from the power amplifier 2, the element 12 detects whether the power amplifier 2 generates a three-phase short circuit of the electric machine 1. If there is a properly performed three-phase short circuit, element 12 gives this information to the function computer 3 and to an element 19 of the logic module 5.

If there is a faulty three-phase short-circuit, it is provided in one embodiment, the variant of the three-phase short circuit of the short circuit Switching elements 2ol, 2o2, 2o3 to short circuit of the switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 or vice versa to change.

In the embodiment shown in Fig. 1, the element 19 sends a switch-off signal to switch 14, if the element 19 receives the information that the function calculator 3 via the element 17 detects a speed D2 or Dl below its associated limit value GR2 or GRL has and the element 12 has detected a three-phase short circuit of the output stage 2 and no concern of a shutdown signal from element 9 to switch 10. Here, based on the signals present in element 19, it can be assumed that the function computer 3 operates without errors. Therefore, the signal passed through the element 17 can be trusted and, when the limit value GR2 or GR1 is undershot, the switching to open switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 can be initiated by sending a switch-off signal to switch 14 , This behavior can be used to include a shutdown command supplied by an external control device and not based on fault detection of the function computer 3 or the monitoring computer 4 in the method. This makes it possible to trigger a three-phase short circuit or a shutdown of the electric machine by opening all the switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3, depending on a voltage U_DC, even for an external shutdown command.

In the embodiment shown in Fig. 1, the element 19 sends a switch-off signal to switch 14, if the element 19 receives the information that the element 20 has detected the rotational speed Dl as lying below the limit value GRl associated with it and the element 12 has a three-phase short circuit Amplifier 2 and the concern of a Shutdown signal from element 9 to switch 10 has detected. If a switch-off signal from element 9 to switch 10, the data from the function computer 3 and monitoring computer 4 can no longer be trusted. Therefore, in this case, it makes sense not to use the speed signal transmitted by the function computer 3 to the element 17, but instead to rely on the speed signal D 1 transmitted directly from the sensor 6 to the logic module 5.

In this last illustrated case, in addition to the embodiment illustrated in FIG. 1, the element 18 must signal to the element 19 that the sensor 6 operates without errors. If this is not the case, then a permanently stored speed value can be assumed. This also applies to the case where the element 17 has been replaced by the speed D 1 and element 18 detects an error of the sensor 6.

If the switch 14 receives a switch-off signal from the element 19, it switches over and thus interrupts the transfer of the drive signals coming from element 10. Instead of these drive signals now the information of an element 13 of the logic device 5 are passed. In this case, the element 13 is typically a permanent memory in which the control signals for an opening of all switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 of the output stage 2 are permanently stored.

These drive signals of the element 13 are fed via the switch 14 in the control line and passed through switch 16 to the power amplifier 2. The output stage 2 opens its switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 in accordance with the control signals supplied to them operating parameters and thus controls the electric machine 1 at. The information which the switch 14 transmits via the control line to the switch 16 is also forwarded to an element 21. Based on the information from switch 14, the element 21 detects whether all switching elements 2ol, 2o2, 2o3, 2ul, 2u2, 2u3 should be opened. This information is the element 21 to the function computer 3 on.

The output stage 2 transmits information about the voltages U_CE applied to it to an element 22. Element 22 is a comparator which compares the supplied value for voltage U_CE with a value Umax and forwards a turn-off signal to switch 16 when U_CE is greater than Umax.

If the switch 16 of element 22 receives a switch-off signal, it switches over and thus interrupts the transfer of the drive signals coming from element 14. Instead of these drive signals, the drive signals of an element 15 of the logic module 5 are now passed on. In this case, the element 15 is typically a permanent memory in which the drive signals for a three-phase short circuit of the output stage 2 are permanently stored.

FIG. 2 shows by way of example how a speed-dependent error reaction according to the invention affects the braking torque.

2 schematically shows the course of the operating voltage U_DC, the induced voltages U_ind and the induced braking torque M_ind of a device according to the invention, in which the main contactor arranged between the power supply and output stage 2 is closed, ie the output stage 2 is supplied with a constant voltage U_DC. How to In this case, the induced voltage U_ind increases in proportion to the speed.

In the example shown in Fig. 2, the speed detection of Dl operates properly, i. below the speed limit GRl switching off the electric machine 1 by opening all circuit breakers, from the limit speed by three-phase short circuit. Due to the three-phase short circuit, only a low braking torque is induced at higher speeds (> GRl).

At low speeds, as shown in dotted lines, a strong braking torque is generated in the event of a three-phase short circuit. The reason for this is the short-circuit current in the electric machine 1.

If switching off at low speeds (<GR1) via open circuit breakers, the braking torque decreases. In this area, the induced voltage is lower than the supply voltage U_DC. There is therefore no current flow from U_ind to U_DC, which could generate a significant braking torque M_ind. It also follows that the limit value GR1 (and corresponding to the limit value GR2) usefully lies in a speed range in which Uind is less than U_DC.

Furthermore, a voltage limit Umax is provided, beyond which the shutdown of the electric machine 1 is in each case switched to a three-phase short circuit. This represents a protection of the electric machine against too high a supply voltage U_DC. Thus, the electric machine 1 and the output stage 2 are independent of a faulty speed detection one with the power supply off, if necessary, also inductively generated, protected to high supply voltage.

Claims

claims

1. Control system for a permanent-magnet electric machine (1), with

a function computer (3),

a monitoring computer (4),

a programmable logic module (5),

- A speed sensor (6) for detecting a speed Dl of the electric machine (1) and

- A turn-off amplifier (2) with three upper circuit breakers (2ol, 2o2, 2o3) and three lower circuit breakers (2ul, 2u2, 2u3), wherein a shutdown of the electric machine (1) is feasible if the function calculator (3) or the Monitoring computer (4) detects an error, characterized in that for switching off the electric machine (1) a three-phase short circuit of the output stage (2) by shorting the three upper circuit breaker (2ol, 2o2, 2o3) or the three lower circuit breaker (2ul, 2u2, 2u3) is feasible if the speed Dl does not fall below a definable limit value GR1 or a voltage U_DC of the output stage (2) exceeds a limit Umax.

2. Control system according to claim 1, characterized in that for switching off the electric machine (1) all the power switches (2ol, 2o2, 2o3, 2ul, 2u2, 2u3) of the output stage (2) are obviously when the speed Dl below the threshold GRl is and a voltage U_DC the power amplifier (2) does not exceed a limit Umax.

3. Control system according to claim 1 or 2, characterized in that at least one additional rotational speed sensor (7) is provided for detecting a rotational speed D2.

4. A method for controlling a permanent-magnet electric machine (1), in which a shutdown of the electric machine (1) is performed when a function computer (3) an error of the function computer (3) or a monitoring computer (4) an error of the function computer ( 3) or the monitoring computer (4) recognizes, characterized in that

a speed Dl of the electric machine (1) is monitored by a separate logic (5) and compared with a limit value GR1, and

- a three-phase short circuit of the circuit breaker (2ol, 2o2, 2o3) or the circuit breaker (2ul, 2u2 and 2u3) is triggered when the speed Dl is not below the limit GRl.

5. The method according to claim 4, characterized in that a switching of the output stage (2) of a three-phase short circuit to open circuit breaker (2ol, 2o2, 2o3, 2ul, 2u2, 2u3) takes place when the speed Dl of the speed sensor (6) the limit GRl falls below.

6. A method for controlling a permanent-magnet electric machine (1), in which a shutdown of the electric machine (1) is performed when a function computer (3) detects an error not in the function calculator (3), characterized in that

- One of a speed sensor (7) detected speed D2 is monitored by the function calculator (3), and

- a three-phase short circuit of the circuit breaker (2ol, 2o2, 2o3) or the circuit breaker (2ul, 2u2 and 2u3) of the power amplifier (2) is triggered when the speed D2 is not below the limit GR2.

7. The method according to claim 6, characterized in that a switching of the output stage (2) of a three-phase short circuit open circuit breaker (2ol, 2o2, 2o3, 2ul, 2us, 2u3) takes place when the speed D2 of the speed sensor (7) the limit GR2 falls below.

8. The method according to claim 6, characterized in that a switching of the output stage (2) of a three-phase short circuit on open circuit breaker (2ol, 2o2, 2o3, 2ul, 2us, 2u3) takes place when - An evaluation of the speed signal D2 is not possible and

- An evaluation of the speed Dl of the speed sensor (6) in the function computer (3) falls below the

Limit value GRl detects.

9. The method according to any one of claims 4 to 8, characterized in that a switching of the output stage (2)

Three-phase short-circuit takes place when a voltage U_DC of the output stage (2) exceeds a value U_max.

10. The method according to any one of claims 4 to 9, characterized in that the shutdown of the output stage (2) is terminated when the voltage U_DC of the output stage (2) again falls below the value U_max and currently no shutdown is requested.

11. The method according to any one of claims 4 to 10, characterized in that the switching state of the power switches (2ol, 2o2, 2o3, 2ul, 2u2, 2u3) of the output stage (2) from the logic module (5) to the function computer (3) transmitted becomes.

12. The method according to any one of claims 4 to 11, characterized in that a feedback from an element (12) of the logic module (5) to the function computer (3) takes place, whether a three-phase short circuit is requested and performed.

13. The method according to any one of claims 4 to 12, characterized in that when starting the electric machine (1) a Abschaltpfadtest is performed, in which the correct shutdown and the change of the Abschaltpfades is tested at different speeds.