WO2015000669A1

WO2015000669A1 - Avoiding braking torques in permanent magnet synchronous machines

Info

Publication number: WO2015000669A1
Application number: PCT/EP2014/062172
Authority: WO
Inventors: Bernd Gross
Original assignee: Voith Patent Gmbh
Priority date: 2013-07-04
Filing date: 2014-06-12
Publication date: 2015-01-08
Also published as: DE102013213045A1

Abstract

The description covers a method for controlling a multi-phase output stage of a permanent magnet electric machine (6), wherein the electric machine (6) is used to drive a motor vehicle, wherein the output stage comprises power switch pairs, each having a first power circuit breaker (1) and a second power circuit breaker (2) connected in series, wherein the first power circuit breaker (1) is connected to a direct voltage source U_BAT and the second power circuit breaker (2) is connected to a reference potential GND of the direct voltage source U_BAT, and wherein nodes between the first and second power circuit breakers (1, 2) are connected to respective phase windings U, V, W of the permanent magnet electric machine (6), comprising the steps of: determining whether in unwanted braking torque is acting on the the vehicle as a result of a generator effect of the electric machine (6), and if so: determining a first instant T₂ at which the nearest voltage maximum between two phase windings U, V, W occurs, and at the first instant T₂: short-circuiting the two phase windings U, V, W, determining a second instant T₃ at which the rotor of the electric machine (6) has advanced electrically by 90° after the first instant T₂ and at the second instant T₃: circuit breakering the output stage to a short-circuit mode.

Description

Avoidance of braking torques in permanent-magnet synchronous machines

DESCRIPTION FIELD OF THE INVENTION

The present invention relates to a method for controlling a multi-phase output stage of a permanently excited electric machine, a control unit for a vehicle and a vehicle.

BACKGROUND OF THE INVENTION

In the prior art permanent magnet synchronous machines are known, which are characterized by high performance.

SUMMARY OF THE INVENTION

If a permanent-magnet synchronous machine is used to drive a vehicle and if this vehicle has a high speed and if the closed-loop control of the synchronous machine also fails, an undesired braking torque can result from the feedback of electrical energy (the synchronous machine operates as a generator). Sudden and uncontrolled braking torques of a vehicle driven by a synchronous machine can endanger driving safety and must therefore be prevented or at least limited. Regeneration and thus unwanted braking can be prevented by short-circuiting the Endstuf e / of the inverter of the synchronous machine. As a result, an unwanted increase in the intermediate circuit voltage can also be avoided, so that no overvoltage occurs.

However, short-circuiting can result in transient effects that lead to high transient currents. These transient currents can exceed the limit values of the circuit breakers of the final stage / of the inverter and destroy them or considerably shorten their service life.

It is therefore an object to provide a method which reduces or avoids undesirable braking torques in multiphase electric machines for driving vehicles and nevertheless prevents damage or destruction of the power switch of the inverter of the electric machine.

As a first embodiment of the invention, a method is provided for driving a polyphase output stage of a permanently excited electric machine, wherein the electric machine is provided for driving a vehicle, the output stage comprises power switch pairs each having a first circuit breaker and a respective second circuit breaker connected in series are, wherein the first power switch is connected to a DC voltage and the second power switch is connected to a reference potential of the DC voltage, wherein respective nodes of the first connected to the second power switch with respective phase strands of the permanent magnet machine, comprising the steps of: determining whether an undesirable Braking torque acts on the vehicle due to a generator effect of the electric machine, if so: determining a first time at which the next voltage maximum occurs between two phase strands , at the first time: Short circuiting of the two phase strands, determining a second time at which the rotor of the electric machine is further rotated electrically by 90 ° after the first time and at the second time: transferring the final stage in a short circuit mode. By means of the staggered short-circuit method according to the invention, excessive strand currents can be prevented by transient currents. In this way it can be ensured that currents that are too high are applied to the circuit breakers of the respective final stage / of the inverter of the synchronous machine and destroy them.

As a second embodiment of the invention, a control unit for a vehicle is provided, wherein the control unit is designed to carry out a method according to one of claims 1 to 6.

As a third embodiment of the invention, there is provided a vehicle comprising a control unit according to claim 7. Exemplary embodiments are described in the dependent claims.

According to an exemplary embodiment of the invention, there is provided a method further comprising the step of: determining if an undesirable brake torque is acting on the vehicle due to a generator action of the electric machine by measuring whether a current is flowing from the electric machine.

By determining the current direction can be determined in a simple manner, whether an undesirable braking torque can occur.

In a further embodiment of the invention, a method is provided, wherein in short-circuit mode, all the first power switches are open and all second power switches are closed, or wherein all first power switches are closed and all second power switches are open.

According to another embodiment of the present invention, there is provided a method further comprising the step of: detecting the location of the rotor of the electric machine by a position sensor for determining the first time.

By arranging a position sensor on the rotor of the permanent-magnet synchronous machine, the rotor position can be reliably determined.

According to an exemplary embodiment of the invention, a method is provided, wherein the electric machine comprises three phases. In another embodiment of the invention, a method is provided wherein the power switches are power MOSFETs or IGBTs.

As an idea of the invention can be considered to avoid the generation of transient currents when shorting the phase strands of an electric machine. For this purpose, in a short-circuiting operation according to the invention, not all the phase strands are simultaneously short-circuited, but initially only two phase strands and subsequently the remaining phase strands, resulting in a staggered short-circuit process. Of course, the individual features can also be combined with each other, which can also be partially beneficial effects that go beyond the sum of the individual effects.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention will become apparent from the embodiments illustrated in the drawings. Show it

1 shows an inverter / an output stage for controlling a permanent-magnet synchronous machine,

2 shows conductor voltage profiles Uuv, Uvw, Uwu of a permanently excited synchronous machine with a simultaneous all-phase short circuit, FIG. 3 shows phase current profiles iu, iv, iw of a permanent-magnet synchronous machine with a simultaneous all-phase short circuit, FIG. 4 shows conductor voltage profiles Uuv, Uvw, Uwu of a permanently excited synchronous machine in the case of a staggered short circuit,

FIG. 5 shows phase current curves iu, iv, iw of a permanently excited synchronous machine in the case of a staggered short circuit.

DETAILED DESCRIPTION EXAMPLE

EMBODIMENTS

1 shows an inverter for controlling a permanent-magnet synchronous machine 6 with circuit breakers 1 highside and circuit breakers low side 2 for connecting the line lines U, V, W.

2 shows the three sinusoidal terminal voltages Uuv, Uvw, Uwu at the phase strands U, V, W up to a point in time Ti. From the time Ti, the phase strands U, V, W are short-circuited and the terminal voltages Uuv, Uvw, Uwu are equal to zero.

3 shows the currents iu, iv, iw 7, 8, 9 in the individual phases U, V, W, the phase currents iu, iv, iw 7, 8, 9 being zero by the time Ti. At the time Ti, the phase strands U, V, W are short-circuited and it results from this time Ti a transient, resulting in transient currents. These transient currents lead to overshoots of the resulting phase currents iu, iv, iw 7, 8, 9. The phase currents iu, iv, iw 7, 8, 9 can be so high in the transition phase that the current carrying capacity of the power switches of the inverter is exceeded. As a result, the circuit breakers can be destroyed or their life can be significantly shortened. FIG. 4 shows, analogously to FIG. 2, the three sinusoidal terminal voltages Uuv, Uvw, Uwu at the phase strands U, V, W up to a point in time T ₂ . From the time t _2, two phase conductors U, V, W are shorted together, namely those in which the terminal voltage has a voltage maximum. From the time T ₃ , all phase strings are short-circuited and the terminal voltages Uuv, Uvw, Uwu are equal to zero. The time T ₃ can be defined in particular as the time at which the rotor of the synchronous machine is exactly further rotated 90 ° to T ₂ electrically. 5 shows the phase currents iu, iv, iw 10, 11, 12 in the individual phases U, V, W, the currents iu, iv, iw 10, 11, 12 being zero by time t ₂ . From the time T ₂ to the time T ₃ is a transition phase, in the present invention, two phase strands U, V, W are shorted together. This results in that a phase current i _Us iv, iw 10, 11, 12 remains zero. In particular, it is ensured that the strand currents iu, iv, iw 10, 11, 12 have no elevations. After the time T ₃ , all phase strings are short-circuited, whereby the conventional short-circuit mode is realized.

The short-circuiting can be done by driving the corresponding circuit breaker of the power amplifier, with all high-side or all low-side circuit breakers are short-circuited for an all-phase short circuit.

It should be noted that the term "comprising" does not exclude other elements or method steps, just as the term "a" and "an" does not exclude multiple elements and steps.

The reference numerals used are for convenience of reference only and are not to be considered as limiting, the scope of the invention being indicated by the claims. LIST OF REFERENCE SIGNS

1 circuit breaker highside

2 circuit breakers lowside

3 freewheeling diodes

4 capacitor

5 capacitor

6 permanent magnet synchronous machine

7 first phase current in a short circuit method according to the prior art

8 second strand current in a short circuit method according to the prior art

9 third phase current in a short circuit method according to the prior art

10 first strand current in a short-circuit method according to the invention

11 second strand current in a short-circuit method according to the invention

12 third phase current in a short-circuit method according to the invention

Ti time at which a simultaneous all-phase short circuit is made

T ₂ Time at which a staggered short circuit starts with the short-circuiting of only two phase strings

T3 time at which the staggered short circuit is continued by all-phase short circuit

U first phase strand

V second phase strand

W third phase strand

Claims

1. A method for controlling a polyphase output stage of a permanent-magnet electric machine (6), wherein the electric machine (6) is provided for driving a vehicle, the power amplifier circuit pairs comprises each with a first circuit breaker (1) and in each case a second circuit breaker (2), are connected in series, wherein the first power switch (1) is connected to a DC voltage U _BAT and the second power switch (2) is connected to a reference potential GND of the DC voltage U _BAT , wherein respective nodes of the first with the second power switch (1, 2) are connected to respective phase strings (U, V, W) of the permanent magnet electric machine (6), comprising the steps of:

Determining whether an undesired braking torque acts on the vehicle due to a generator effect of the electric machine (6),

if yes: determining a first time (T ₂ ) to the next

Voltage maximum occurs between two phase strings (U, V, W), at the first instant (T ₂ ): short-circuiting of the two phase strings (U, V, W),

Determining a second time (T ₃ ) at which the rotor of the electric machine (6) is further electrically rotated by 90 ° after the first time (T ₂ ), and

at the second time (T ₃ ): transfer the output stage into a short circuit mode.

2. The method of claim 1, further comprising the step of: determining if an undesirable braking torque is applied to the vehicle due to a generator action of the electric machine (6) by measuring whether a current is flowing from the electric machine (6).

3. The method according to any one of claims 1 or 2, wherein in the short-circuit mode, all first circuit breakers (1) are open and all second circuit breakers (2) are closed or wherein all the first circuit breaker (1) are closed and all the second circuit breaker (2) are opened ,

4. The method according to any preceding claim, further comprising the step of: detecting the position of the rotor of the electric machine (6) by a position sensor for determining the first point in time (T _2).

5. The method according to any one of the preceding claims, wherein the electric machine (6) comprises three phases (U, V, W).

6. The method according to any one of the preceding claims, wherein the power switches (1, 2) are power MOSFETs or IGBTs.

A control unit for a vehicle, wherein the control unit is configured to perform a method according to any one of the preceding claims.

8. vehicle, comprising a control unit according to claim 7.