WO2009106584A1

WO2009106584A1 - Method and circuit arrangement for the operation of a permanently excited synchronous motor, and radiator fan module

Info

Publication number: WO2009106584A1
Application number: PCT/EP2009/052312
Authority: WO
Inventors: Olga Siwak
Original assignee: Brose Fahrzeugteile Gmbh & Co. Kg, Würzburg
Priority date: 2008-02-26
Filing date: 2009-02-26
Publication date: 2009-09-03

Abstract

The invention relates to a method and a circuit arrangement for operating a permanently excited synchronous motor, especially for a radiator fan in a motor vehicle. In said method, the synchronous motor is triggered by an inverter circuit designed as a center-tap connection in such a way that the AC motor is operated in a deceleration mode via the center-tap connection. The invention further relates to a radiator fan module comprising such a circuit arrangement.

Description

description

Method and circuit arrangement for operating a permanently excited synchronous motor and cooling fan module

Technical area

The present invention relates to a method and a circuit arrangement for operating a permanently excited synchronous motor. The present invention further relates to a radiator fan module having such a circuit arrangement.

Background of the invention

In modern motor vehicles, an increasing number of electric motors are used, which are used for a wide variety of adjustment possibilities in the motor vehicle, for example in the comfort area (for example seat adjustment, window lifters, etc.), in the security area {e.g. electric parking brake) and for other vehicle functions {e.g. Radiator fan). For radiator fan applications, among other things, permanent magnet synchronous motors are used.

For operating and driving these synchronous motors, a controlled power circuit is typically used, of which different circuit topologies are provided depending on the application and intended use. For driving a synchronous motor in the automotive sector, a bridge circuit is often used as the power circuit, which bridge circuit can be designed as a full or half bridge in a manner known per se. Preferably, circuit breakers, such as, for example, MOSFETs, JFETs, IGBTs and thyristors, are used here as switching elements, with which very high currents and powers can be switched and which, in addition, can be produced very simply and cost-effectively. Although such a bridge circuit is generally inexpensive, for example, in Using a so-called B4 bridge circuit, which has four controllable switch, cumbersome and not so flexible in the control.

For this reason, there are also alternative applications in which, instead of a bridge circuit, other power circuits are used for driving the synchronous motors using, for example, inverter circuits formed as a center circuit. An inverter is an electrical device that converts a DC voltage into an AC voltage or a DC current into an AC current. The term center circuit designates DC or also inverter circuits in which a transformer is used for the conversion. Such mid-point circuits are used, for example, in the automotive sector for the control of the electric drives of a radiator fan.

A synchronous motor is a synchronous motor in motor operation, in which a magnetizer constantly magnetized (the so-called rotor) is taken synchronously by a moving magnetic rotating field in the surrounding stator. The running synchronous motor has a synchronous to AC voltage movement, the speed is thus linked via the number of pole pairs with the frequency of the AC voltage. The magnetic field in the rotor can be generated by permanent magnets (self-excitation) or electromagnets (external excitation). The present invention relates specifically to permanent magnet synchronous motors. This synchronous motor can be used as an electric motor, which is operated in a motor operation with a direct current, or as a generator, which converts mechanical energy into an alternating current in a so-called regenerative operation.

In addition, the synchronous motor in addition to the aforementioned motor and generator operating modes can also be operated in a braking operation, which is increasingly of particular interest in automotive applications. The brake drive refers to the mode of operation in which the synchronous motor passes from motor operation to regenerative operation and is decelerated. Preferably, during braking, electrical energy is fed back. On the one hand can be intercepted by the return of electrical energy, which is obtained from the rotation of the electric motor, short-term voltage dips in the electrical energy supply. In addition, the braking of the synchronous motor in itself means an additional functionality that z. To comply with a given speed z. B. can be used in a foreign driven operation.

In order to set a braking mode, a negative direct current must be impressed on the synchronous motor with a positive induced emf voltage and vice versa, so that the generated torque of the synchronous motor becomes negative. A negative direct current means that the polarity of the induced voltage across a motor winding must be reversed. In braking mode, this is achieved by driving the synchronous motor by means of the bridge circuit mentioned above by varying the duty cycle of the drive signals for driving the controllable switch of the bridge circuit.

However, the above-mentioned method for setting a brake operation for a permanently excited synchronous motor does not work, if instead of the bridge circuit, a mid-point circuit is used for the control. At present, therefore, there is no possibility to operate a synchronous motor in braking mode by means of a mid-point circuit, so that hitherto either a bridging circuit had to be used as control for a braking operation or it was necessary to dispense with the braking operation of the synchronous motor.

Summary of the invention

The object underlying the present invention is now to improve the operation of a perma nent excited synchronous motor, in particular when used in a radiator fan.

According to the invention, this object is achieved by a method having the features of patent claim 1 and / or by a circuit arrangement having the features of patent claim 7 and / or by a radiator fan module having the features of patent claim 14.

Accordingly, it is provided:

A method of operating a permanent magnet synchronous motor, in particular for a radiator fan of a motor vehicle, wherein the synchronous motor is controlled by an inverter circuit implemented in center-point circuit such that the DC motor is operated via the center-point circuit in a braking operation.

A circuit arrangement for operating a permanently excited synchronous motor, in particular using a method according to the invention, having a drive circuit which provides at least one drive signal with an inverter circuit which is implemented in a center-point circuit and which supplies a DC supply voltage present on the input side or a DC supply current into an AC voltage or one

Converts alternating current, and having controllable by a respective drive signal switch, which switches the converted AC voltage or the AC power to supply outputs such that a can be coupled to the switching outputs synchronous motor in a braking operation is operable.

A radiator fan module for or in a motor vehicle having a radiator fan disposed in a fan housing, with a synchronous motor coupled to drive the radiator fan therewith, with circuitry according to the invention, whose output terminals are connected to the synchronous motor and which is adapted to the synchronous motor to control such that it is braked motor or generator in a braking mode.

The present invention primarily addresses the problem of the operation of a permanent-magnet synchronous motor when driven by a center circuit formed as an inverter circuit. Here, in addition to the usual operating modes of the synchronous motor as a generator or as an engine, an additional braking operation is possible. This allows a significant expansion of this synchronous motor, which is particularly advantageous in automotive applications and especially in the application of the synchronous motor as a drive for a radiator fan. In particular, here the synchronous motor can be used for the conventional driving of the radiator fan. In regenerative operation, electricity can be fed back into the energy supply, which is advantageous, above all, with regard to avoiding short-term voltage dips in the electrical energy supply. In addition, it is now also possible to equip the synchronous motor with a braking functionality, which in addition to the braking functionality also allows a feeding back of energy, especially in generator mode.

Compared to bridge circuits, which previously had to be used for this purpose, the invention makes it possible to use as

Center circuit formed inverter circuit a more flexible and in particular a simpler control of the synchronous motor.

Advantageous embodiments and modifications of the invention will become apparent from the dependent claims and from the description in conjunction with the figures of the drawing.

In a preferred embodiment, the inverter circuit is driven by a pulse width modulated drive signal with a predetermined duty cycle, wherein the duty cycle is preferably adjustable. In a preferred embodiment, a first operating mode is provided, in which the synchronous motor is operated for the braking operation in motor operation.

In a preferred embodiment, a second operating mode is provided, in which the synchronous motor for the braking operation is operated in regenerative operation.

In a preferred embodiment, the duty cycle of the drive signal in the first operating mode is less than or equal to 0.5 and / or the duty cycle of the drive signal in the second operating mode in the range between 0.5 and 1.

In a preferred embodiment, the braking operation of the

Synchronous motor driven such that a generated by the synchronous motor torque is negative by a negative DC current is impressed in the synchronous motor at a voltage applied to the synchronous motor positive induced EMF voltage and / or by a positive DC current applied to a voltage applied to the synchronous motor negative induced EMF voltage is impressed in the synchronous motor.

In a preferred embodiment, a one-or two-phase center circuit is provided for driving a single-phase or two-phase synchronous motor.

In a preferred embodiment, a load path pair with two load paths coupled by a transformer device are provided for each phase of the mid-point circuit, in each of which a transformer winding, an emf voltage source and a load path of a controllable switch are arranged in series.

In a preferred embodiment, the transformer windings of two coupled load paths are coupled together with an opposite sense of winding and are in particular formed by oppositely wound armature windings of the synchronous motor.

In a preferred embodiment, a field-effect controllable power transistor, in particular a MOSFET, which has an integrated free-wheeling diode is provided as a controllable switch.

In a preferred embodiment, the drive circuit has a PWM modulator which is designed to generate at least one PWM-modulated drive signal with a predetermined and preferably adjustable duty cycle.

In a preferred embodiment, a program-controlled device, in particular a microcontroller, is provided which has the drive circuit.

In a preferred embodiment, the circuit arrangement is arranged in a control device within the fan housing.

The above refinements and developments of the invention can also be combined with one another in any suitable manner.

Summary of the figures

The present invention will be explained in more detail with reference to the exemplary embodiments indicated in the schematic figures of the drawing. It shows:

Fig. 1 is a block diagram of a radiator fan assembly according to the invention with a synchronous motor;

2 shows a circuit diagram for explaining a first general exemplary embodiment of a circuit arrangement according to the invention for controlling a synchronous motor; Fig. 3 is a detailed circuit diagram for explaining a second embodiment of a circuit arrangement according to the invention;

4A-4D signal-time diagrams for explaining the function of the circuit arrangement according to the invention;

Fig. 5 is a detailed circuit diagram for explaining a third, preferred embodiment of a circuit arrangement according to the invention.

In the figures of the drawing are identical and functionally identical elements, features and signals - unless otherwise stated - provided with the same reference numerals.

Description of embodiments of the invention

Fig. 1 shows a block diagram of a radiator fan assembly according to the invention with a synchronous motor.

The radiator fan assembly is designated by reference numeral 10 here. The radiator fan arrangement 10 has a permanently excited synchronous motor 11 and a circuit arrangement 12 according to the invention for operating this synchronous motor 11. The synchronous motor 11 is connected via supply terminals 13, 14 with the circuit arrangement 12 according to the invention. This circuit arrangement 12 has a drive circuit 15 and an inverter circuit 16 connected on the control side to the drive circuit 15.

The inverter circuit 16 is connected on the supply side via two supply terminals 17, 18 to a power supply 19. In the present exemplary embodiment, the energy supply 19 is a DC voltage source, which is preferably designed as a rechargeable battery. Thus, a first supply pole is located at the first supply connection 17. Potential, for example, the positive battery potential VBB, while at the second supply terminal 18, a second supply potential, for example, the potential of the reference ground GND is applied. Between these supply terminals 17, 18 thus drops an intermediate _circuit voltage U _2W , via which the inverter circuit 16 is supplied. Control side, the inverter circuit 16 is connected via control terminals 20, 21 to the drive circuit 15.

The drive circuit 15 may, for. B. part of a control unit, which z. B. has a microcontroller, be. Instead of a microcontroller as a controllable device only one processor can be used here. In addition, it would also be conceivable to implement the functionality of the drive circuit 15 by means of a controllable and preferably programmable logic circuit, such as a PLD or FPGA. The power supply of the drive circuit 15 is here, for better clarity, not shown. On the output side, this drive circuit 15 generates control signals S1, S2, which are supplied to the inverter circuit 16 via the control terminals 20, 21. The function of this inverter circuit 16 and thus of the entire radiator fan arrangement 10 will be explained in more detail below with reference to FIGS. 2 to 5.

In the present embodiment, the radiator fan assembly 10 has a modular cooling fan, in which thus a housing 22 is provided, within which the circuit arrangement 12 according to the invention or at least the inverter circuit 16 together with the synchronous motor 11 and driven by this synchronous motor 11 fan (not here shown) are arranged.

Figure 2 shows a circuit diagram for explaining a first generalized embodiment of an inventive

Circuit arrangement according to Figure 1, as it is used to control a synchronous motor 11. FIG. 2 shows only the circuit arrangement 12 here. This circuit arrangement 12 has two load paths 30, 31 arranged parallel to one another. The two load paths 30, 31 are coupled to one another via a transformer 32. The transformer 32 has two windings 33, 34, which are each arranged in different load paths 30, 31 and which have mutually a direction opposite sense of winding. The transformer windings 33, 34 are formed by the armature windings of the synchronous motor 11.

The coupling of the two windings 33, 34 of the transformer 32 is denoted by k, with an ideal coupling k =

I is.

Within a load path 30, 31 an EMF voltage source 35, 36 is provided, which is represented by the function of the synchronous motor 11, and controllable switches 37, 38 which are the respective transformer windings 33, 34 of a load path 30, 31 connected in series. The controllable switches 37, 38 are actuated via the control terminals 20, 21 with respective control signals S1, S2. The two series circuits, which represent the load paths 30, 31, are connected in parallel with each other and between the supply terminals 17, 18, at which the intermediate circuit voltage U _zw drops.

FIG. 2 shows an inverter circuit 16 designed as a mid-point circuit, which has a single-phase circuit typology in the example shown. In addition, here are no parasitic elements, such as z. B. caused by ohmic or inductive effects of the synchronous motor 11, taken into account.

EMF here refers to the electromagnetic coupling in an electric motor and here in the synchronous motor 11. The EMF

Voltage sources 35, 36 denote those in the synchronous motor

II induced voltages and thus represent sinusoidal Voltage sources. Per motor winding of the 1-phase synchronous motor 11 so there is in each case an EMF Spannυngsquelle 35, 36th

FIG. 3 shows a detailed circuit diagram for explaining a second exemplary embodiment of a circuit arrangement according to the invention.

In contrast to the general exemplary embodiment in FIG. 3, parasitic or scattering effects are also taken into account here. For this reason, the load paths 30, 31 each have a leakage inductance 40, 41 and an ohmic resistance component 42, 43. The leakage inductances 40, 41 are z. B. formed by leads and connecting lines of the circuit arrangement 12 according to the invention for synchronous motor 11, whereas the ohmic resistance components 42, 43 are formed by the ohmic resistance of the transformer windings 33, 34. The stray inductances 40, 41 and the ohirischen resistance components 42, 43 are also in series with the transformer windings 33, 34, the EMK-

Voltage sources 35, 36 and the controllable switches 37, 38 connected.

In the example shown, moreover, the controllable switches 37, 38 are designed as field effect-controllable transistors and in particular as MOSFETs 44, 45. In these MOSFETs 44, 45 is parallel to the controlled path of the MOSFET 44, 45, an integrated Bodydiode 46, 47, which acts here as Feilaufdiode arranged.

In FIG. 3, U _L i, U _L 2 denote the voltages falling across the transformer windings 33, 34, Um, U _R2 the voltages dropping across the resistive components, U _EMKIΛ U _E MK2 the induced EMF voltages and U _v i, Ü _V2 the voltages dropped across the controlled paths of the MOSFETs 37, 38. The currents in a respective load path 30, 31 are denoted by Ii or I ₂ . The leakage inductances 40, 41 are negligibly small in comparison to the inductances of the transformer windings 33, 34, so that here too the voltage drop at the leakage inductances 40, 41 is negligibly small and thus not shown here.

For the center circuit 16 shown in FIG. 3, the following relationships apply:

U _Z w = U _L1 + U _R1 + U _EMK1 + U _vl (1)

Uu -Lu _dt M ^ ⁽ 2 ⁾ with M = k-Lu (3)

Here k denotes the coupling factor of the two transformer windings 33, 34 of the transformer 32 and L _L i denotes the inductance of the transformer winding 33.

Assuming that the coupling factor k is about 1, then for the voltages of the energized phase of the center circuit 16 shown in Fig. 3, the following relation holds:

U _L1 + U _R] = U _ZW _{-U EMK1 -U} _V1 (4) with

U _v1 «2- (la) -U _zw (5)

U _L1 + U _R1 «(2a-l) .U _zw _{-U EMK1} (6) with a = - ¹ ElN _/

a denotes here the duty ratio of the drive signals S 1, S 2 for driving the MOSFETs 37, 38, where dendauer the drive signals Sl, S2 and t _EIK the duty cycle is called.

U _L2 + U _R2 "(l-2a) -U _zw + U _EMK1 (8)

A negative total current Ii or I ₂ is therefore only achieved here if an area of the voltage over time, that is to say the so-called voltage time area, of the magnetically coupled phases is likewise negative. Thus:

[(2a-l) -U _zw _{-U EMK1} ] _.a + [(l-2a) .U _zw + U _EMK1 ]. (La) <0 (9)

4a ² ■ U _zw - 2a • (2 • U _zw + U _EMK1 ) + U _zw + U _EMK1 <0 (10)

If the two inequalities (9) and (10) are resolved, the operating points and thus the limits for the duty cycle for an operation of the synchronous motor 11 in generator operation result for given values of the intermediate circuit voltage U _zw and the emf voltage U _EM κ. Due to the particular circuit typology of a midpoint circuit 16, the solutions of the two inequalities (9), (10) will always be Al = 0.5 and 0.5 <A2 <1. If one selects a duty cycle a between these two values Al, A2, then the synchronous motor 11 is operated in regenerative operation. In the case

0 <a <Al (11)

then a braking operation of the synchronous motor can be realized. This happens because a freewheeling current of the controllable switch 37, 38 designed as MOSFET 43, 44 instead of via its integrated body diode 46, 47 flows via the controlled path of the respective MOSFET 44, 45, whereby the synchronous motor 11 is braked by a motor. For the operating point a> A2, however, no braking operation is possible here.

Figures 4A and 4B show signal-time diagrams for explaining the operation of the synchronous motor 11. Figures 4A, 4B show here the phase currents Ii and I ₂ in generator mode or motor operation. For a respective positive emf voltage UEMK> 0.

In this case, Figure 4A shows the waveforms of the currents Ii, I ₂ in generator operation, for an intermediate circuit voltage U _zw = 12V, an emf voltage U _emf = 6V and a duty cycle a = 0.6 according to inequality (9) and (10). On the other hand, FIG. 4B shows the engine operation in which U _zw = 12V, U _EMK = 6V and a - 0.4 are selected.

The hatched areas 50, 51 in FIGS. 4A, 4B mark the respective current-time areas on the positive and negative side and indicate the polarity of the total current. The synchronous motor 11 is operated in the motor mode, if the product of induced voltage U _emf and total current is positive, and the synchronous motor 11 is operated in generator mode, if the product of induced voltage U _emf and total current is negative. The total Ström results from the addition of the two currents I _1, I _2, in which case the corresponding current time surfaces 50, 51 are relevant. The current-time surface 50 denotes the positive current, and the current-time surface 51 denotes the negative current. Depending on which of these two current-time areas 50, 51 is greater, the result is a total current that is either positive (in the case of FIG. 4B) or negative (in the case of FIG. 4A). In FIG. 4A, therefore, a negative total current and a positive induced voltage U _{EMK is} present, indicating a regenerative operation. In FIG. 4B, the induced voltage U _EMK as well as the total current is positive, so that here a motorized operation of the synchronous motor 11 is given.

In FIG. 4A, although current is fed back in regenerative operation, no braking of the synchronous motor takes place here. 4B shows the motor operation of the synchronous motor 11, in which braking takes place. The problem with using a mid-point circuit 16 as a power circuit for controlling the permanently excited synchronous motor 11 is that braking in the block mode of the synchronous motor 11 only works under certain constellations of the emf voltage U _EMK and the intermediate circuit voltage U _zw . For this reason, therefore, an additional PWM drive signal for the freewheeling path of the midpoint circuit 16 must be provided. However, an additional PWM drive signal means an additional expense, which is associated in particular with a higher circuit complexity for the drive circuit 15, especially its microcontroller. In addition, failure to observe a dead time may result in a short-circuit in the mid-point circuit 16. Finally, when the transformer windings 33, 34 are reversed, which is denoted by reference numeral 52 in FIGS. 4A, 4B, a relatively high so-called ripple torque occurs, which manifests itself both in undesirable electromagnetic radiation (EMC). In addition, a high ripple torque is accompanied by unwanted noise development, which is to be avoided as much as possible in automotive applications.

In order to avoid these disadvantages, the switching on of the controllable switches 44, 45 can also be shifted to the negative emf voltage U _EMK . In this case, inequalities (9) and (10) provide the following solutions:

Al = 0.5 (12)

0 <A2 <0.5 (13)

This means that a motorized braking operation is possible for the case a> A2, ie also for a - Al. A reversal of the transformer winding 33, 34 would be eliminated, which is the example in Figure 4D shown. The freewheeling current can then always flow via the integrated freewheeling diode 45, 46 of the respective MOSFET 43, 44, since they never become zero can. A drive signal required specifically for the complementary load path and the associated circuit complexity are therefore not required.

Figures 4C and 4D show the phase currents Ii and Σ ₂ in the case of a regenerative operation or a motor operation in the event of a negative EMF voltage U _EMK - In Figure 4C is the constellation of the phase currents Ii, I ₂ in the generator mode in Case of U _zw ^~ 12V, U _EMK = 6V and a = 0.4 corresponding to inequalities (9) and (10), whereas FIG. 4D shows the constellation of a motor braking operation for U _zw = 12V, U _EMK - 6V and a = 0.6 shows.

5 shows a circuit diagram for explaining a third preferred exemplary embodiment of a circuit arrangement according to the invention.

5 shows a two-phase center circuit, which thus has two transformers 32, 32 ', wherein in each case one of these transformers 32, 32' has two load paths 30, 31; 30 ', 31' are coupled together and in these load paths 30, 31; 30 ', 31' arranged elements are arranged in series with each other. The elements of the two load paths 30 ', 31' of the second transformer 32 'have been designated with an apostrophe for the sake of simplicity. These load paths 30 ', 31' are arranged parallel to one another and likewise between the supply terminals 17, 18.

For the control of the four controllable switches 44, 45; 44 ', 45' are thus a total of four control signals Sl, S2; Sl ¹ , S2 'provided. In this case, the drive signals S2, S2 'form the control signals inverted respectively to the drive signals S1, S1' and can be derived in a very simple way from these drive signals S1, S1 'by simply inverting. The present invention is not limited to the above embodiments, but can be modified in any way, without ^departing from the subject of the present invention ^¬ the invention.

In particular, the present invention is not limited to the specified circuit typology. Rather, instead of a one- or two-phase center circuit {M2, MA) also a more than two-phase center circuit can be used, for. B. a 3-phase (M6) center circuit. The elements of these midpoint circuits can also be varied. In particular, their controllable switches need not necessarily be formed as a MOSFET, although these are preferred. As a controllable switch, for example, any other integrated switch, such as a JFET, IGBT, thyristor, or even a relay can be used.

As a drive circuit in the present example is arranged in a control unit microprocessor advantage. However, it would also be conceivable to use a different drive circuit, such as B. any trained programmable control logic, z. As a PLD or FPGA circuit, or the like.

It goes without saying that the numbers given above, in particular for the coefficients A1, A2, the voltages, currents and duty cycles, are to be understood as merely exemplary. Thus, corresponding different operating points can be provided. Reference sign list

10 radiator fan assembly

11 trained as a permanently excited synchronous motor

AC motor

12 circuit arrangement

13, 14 supply connections

15 drive circuit

16 formed as a center switching inverter circuit

17, 18 supply connections

19 power supply, rechargeable battery,

DC voltage source,

20, 21 control connections 2222 housing (of the radiator fan)

30, 31 load paths

32 transformer

33, 34 (transformer) windings

35, 36 emf voltage sources, sine voltage sources 3377 ,, 3388 controllable switches

40, 41 leakage inductances

42, 43 ohmic resistance components

44, 45 MOSFETs

46, 47 body diodes, freewheeling diodes 5500 positive current time surface

51 negative current time surface

52 UmpolZeitpunkt

GND second supply potential, potential of the supply mass

I i, I ₂ load currents

S l, S2 control signals

UEMKI / UκMK2 induced EMF voltages

ULI, U _L2 Voltage drop across the transformer windings

URI, UR ₂ decreasing at the ohmic resistance components

tensions Uvi _f U _V2 voltages dropping at the controllable switches UZW DC link voltage

VBB, first supply potential, positive battery potential

Claims

claims

1. A method for operating a permanent magnet synchronous ^¬ motor, in particular for a radiator fan of a motor vehicle, in which the synchronous motor is driven by an executed in central-point inverter circuit such that the DC motor is operated via the center-point circuit in a braking operation.

2. Method according to claim 1, since the inverter circuit is driven by a pulse-width-modulated drive signal with a predetermined duty cycle, wherein the duty cycle is preferably adjustable.

3. Method according to one of the preceding claims, characterized in that a first operating mode is provided, in which the synchronous motor is operated for the braking operation during engine operation.

4. Method according to one of the preceding claims, characterized in that a second operating mode is provided in which the

Synchronous motor is operated for braking operation in regenerative operation.

5. Method according to one of claims 3 or 4, characterized in that the duty ratio of the drive signal in the first operating mode is less than or equal to 0.5 and / or that the duty cycle of the drive signal in the second operating mode in the range between 0 , 5 and 1.

6. The method according to any one of claims 3 to 5, characterized in that that in the braking operation, the synchronous motor is driven in such a way that a torque generated by the synchronous motor is negative by impressing a negative direct current into the synchronous motor at a positive induced EMF voltage applied to the synchronous motor and / or by applying a negative induced EMF to the synchronous motor Voltage a positive direct current is impressed into the synchronous motor.

7. Circuit arrangement for operating a permanently excited synchronous motor, in particular using a method according to one of claims 1 to 6,

with a drive circuit which provides at least one drive signal,

with an application in means punk circuit inverter ^¬ circuit which converts an input side DC supply voltage or a DC supply current into an alternating voltage or an alternating current, and having controllable by a respective drive signal switch which switches the converted AC voltage or the alternating current to supply outputs so in that a synchronous motor which can be coupled to the switching outputs can be operated in a braking mode.

8. The circuit arrangement according to claim 7, characterized in that a one- or two-phase center circuit is provided for controlling a single-phase or two-phase synchronous motor.

9. Circuit arrangement according to claim 8, dadu rch ge kenn ze chenn et that each phase of the mid-point circuit, a load path pair are provided with two coupled by a transformer means load paths, in each of which a transformer winding, an emf voltage source and a load path of a controllable switch are arranged in series with each other.

10. The circuit arrangement according to claim 9, characterized ge kenn ze i chnet that the transformer windings of two coupled load paths are coupled to each other with an opposite sense of winding and are formed in particular by oppositely wound armature windings of the synchronous motor.

11. Circuit arrangement according to one of claims 9 or 10, since you r e g e c e e s that e e s that a controllable field effect controllable power transistor, in particular a MOSFET, is provided which has an integrated freewheeling diode.

12. Circuit arrangement according to claim 7, characterized in that the drive circuit has a PWM modulator which is designed to generate at least one PWM-modulated drive signal with a predetermined and preferably adjustable duty cycle.

13. Circuit arrangement according to one of claims 7 to 12, characterized ge kenn ze i chnet that a program-controlled device, in particular a microcontroller, is provided which has the drive circuit.

14. radiator fan module for or in a motor vehicle,

with a radiator fan arranged in a fan housing,

with a synchronous motor coupled to drive the radiator fan therewith, with a circuit arrangement according to one of claims 7 to 13, whose output terminals are connected to the synchronous motor and which is designed to control the synchronous motor such that it is braked motor or generator in a braking operation.

15. Radiator fan module according to claim 14, characterized in that the circuit arrangement is arranged in a control device within the fan housing.