Inverter circuit and electromotive drive system

Abstract

The present invention relates to an inverter circuit for driving a single-phase or polyphase electric machine for an electric drive system, in particular a dual-rotor motor preferably for or in a motor vehicle, comprising a first and a second supply connection via which the inverter circuit is connectable to a DC voltage source, comprising a load output for coupling to the electric machine, and comprising a controllable inverter which is arranged between the supply connections and the load output and which has a plurality of power switches that are interconnected in order to convert a DC voltage received on the supply side into an AC voltage for driving an electric machine, wherein at least one power switch has a plurality of individual switches which are arranged in parallel with one another and have associated thermal fuses, and the thermal fuses are each arranged in the load path of the respectively associated individual switch. The present invention also relates to an electromotive drive device.

Description

[0001] Inverter circuit and electric motor drive system

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an inverter circuit for controlling a single-phase or multi-phase electrical machine and an electric motor drive system.

[0004] TECHNICAL BACKGROUND

[0005] Electric motor drives have long been used in motor vehicles for a wide variety of applications, such as actuators for window regulators, seat adjustments, parking brakes, sunroofs, doors, trunk lids, and the like. Modern motor vehicles increasingly use electrically powered drives or drive systems—among other things, for sustainability reasons and to avoid CC>2 emissions. Such drive systems include, for example, one or more electrical machines, such as synchronous or asynchronous machines, which are powered by a multi-phase alternating voltage using so-called inverters.

[0006] An inverter, also called an inverter or rotary converter, is an electrical circuit that converts direct current into alternating current. Such inverters and their applications are well known in a wide variety of circuit variants, so there is no need to discuss their general circuit design and functionality in detail here.

[0007] Especially for inverters for high-current applications, such as those used to power motor vehicles, special safety mechanisms are required, especially in the event of a dysfunctional inverter. One widely used safety measure, for example, is the use of an active short circuit of the supply voltage. However, this requires a comparatively complex inverter topology, possibly with redundant circuit elements and / or cost-intensive magnets. Since an active short circuit is usually associated with very high currents that may be problematic for the motor vehicle, it must be specially protected, which in turn entails additional expense.

[0008] Alternatively, a freewheel with a relay (battery contactor) between the inverter and the DC voltage source (battery) is often used for the safety mechanism. In the event of a fault, the relay actively disconnects the freewheel. However, with the battery contactor closed, this can also result in quite high DC currents and, consequently, a high braking torque in the event of uncontrolled regenerative operation of the electric motor.

[0009] The present invention relates, among other things, to so-called double-rotor motors, also referred to as double-rotor, multiple-rotor, or dual-rotor motors for short. These are electrical machines with a stator and two rotors connected to one another in a rotationally fixed manner. Compared to conventional electrical machines with only one rotor, these double-rotor motors can increase both the torque density and the efficiency of electrical drives. The design and operation of such double-rotor motors, as well as their inverter circuits, are described, for example, in German patent DE 10 2021 003941 B4 and German patent DE 10 2021 003942 B4.

[0010] Due to their low inductance and high magnetic flux, such double-rotor motors have a low short-circuit strength, which means that the active short circuit described above is not really suitable as a safety mechanism.

[0011] Against this background, freewheeling with a relay between the inverter and the DC voltage source often represents the only viable safety mechanism at present, although the disadvantages described above must then be accepted.

[0012] This is a situation that needs to be improved.

[0013] SUMMARY OF THE INVENTION

[0014] The present invention is based on the object of providing an improved and in particular a simplified safety concept for protecting an inverter circuit.

[0015] According to the invention, this object is achieved by an inverter circuit having the features of patent claim 1 and / or by an electric motor drive system having the features of patent claim 20.

[0016] Accordingly, it is provided that:

[0017] - An inverter circuit for controlling a single-phase or multi-phase electrical machine for an electrical drive system, in particular a double-rotor motor, preferably for or in a motor vehicle, with a first and second supply connection, via which the inverter circuit can be connected to a DC voltage source, with a load output for coupling the electrical machine, with a controllable inverter arranged between the supply connections and the load output, which has a plurality of power switches which are interconnected in such a way as to convert a DC voltage received on the supply side into an AC voltage for driving an electrical machine, wherein at least one power switch has a plurality of individual switches arranged in parallel with one another with associated thermal fuses,whereby the thermal fuses are each arranged in the load path of the individual switch assigned to them.,

[0018] - An electric drive system, preferably in or for a motor vehicle, with an electric machine, which is preferably designed as a synchronous machine, with a DC voltage source, in particular an accumulator, and with an inverter circuit according to the invention, which is connected on the supply side to the DC voltage source and via its load output to the electric machine.

[0019] The idea underlying the present invention is to provide a safety concept for protecting the inverter circuit for an electric motor drive that can be implemented using comparatively simple means. To this end, the invention initially provides for the power switch(es) of the inverter of the inverter circuit to be implemented with several individual switches arranged in parallel, each of which is assigned corresponding thermal fuses. The individual switches are designed to be as similar as possible, and preferably identical, with regard to their current-carrying capacity and line resistance in their load paths.

[0020] Each of these individual switches with thermal fuse acts as a thermal protection device as follows: A load current flowing through a circuit breaker on the load side is typically distributed evenly between the load paths of the individual switches and therefore also by the associated thermal fuses. If an individual switch is defective and / or the load current through the individual switch is too high, the current density in the associated thermal fuse increases, which, for example, leads to a sudden increase in temperature due to the resistance there. This causes the thermal fuse to melt and interrupt the load circuit of this individual switch, thereby switching off the entire circuit breaker.

[0021] In contrast to known solutions, in the event of a fault in the drive system, freewheeling or idle operation is used as a safe state according to the invention instead of an active short circuit. During freewheeling or idle operation, all power switches of the converter are switched off, so that the current in the electrical machine drops to zero. In this state, the voltage induced by the still rotating electrical machine is rectified via the half-bridge freewheeling diodes and charges the intermediate circuit capacitor with the rectified voltage. In order to protect the vehicle's high-voltage network from this induced voltage and the associated uncontrolled feedback current, in a further development a circuit breaker can be connected, preferably in the supply line connected to the positive supply connection.A suitable electromagnetic design of the electrical machine can ensure that the induced voltage remains below the breakdown voltage over the entire operating range.

[0022] This safe state according to the invention covers all relevant applications without causing dangerous voltage in the drive system or braking torque at the vehicle's wheels. Switching to freewheeling is possible from all possible operating states covered by the drive unit, including operation at maximum speed and / or with very high regenerative power.

[0023] Further advantages of the safety concept according to the invention are the absence of transient overcurrents that could damage the magnets of the double rotor motor, (almost) no braking torques and very low drag losses over the entire speed range.

[0024] Advantageous embodiments and further developments emerge from the further subclaims and from the description with reference to the figures of the drawing.

[0025] In one embodiment, at least one of the thermal fuses is designed as a melting fuse. A melting fuse is an overcurrent protection device that interrupts the circuit by melting a fusible element if the current exceeds a certain value for a sufficiently long period of time.

[0026] In a particularly preferred development, at least one fuse is designed as a PCB conductor track or a part thereof. The PCB conductor track designed as a fuse is designed in such a way that, when a predetermined load current passes through the associated individual switch, the PCB conductor track or a part thereof melts, thereby also switching off the inverter. The predetermined load current refers to the current that flows through the individual switch when it is short-circuited and which is also sufficiently large to melt the PCB conductor track at this point and thus interrupt it. According to a preferred embodiment, the thermal fuse is designed as a thinned material, in particular as a tapered portion of a PCB conductor track on a corresponding printed circuit board. The above-mentioned design of the predetermined load current can be set very easily via the material thinning.

[0027] In an alternative or additional preferred embodiment, the thermal fuse can also be formed using materials with different electrical resistances. For example, the material in the area of ​​the thermal fuse can have a (significantly) higher electrical resistance than outside of it.

[0028] Typically, at least one and preferably each power switch of the inverter has a plurality of individual switches arranged in parallel (with respect to their load paths) with thermal fuses assigned to each of these individual switches. Preferably, each power switch has the same number of parallel individual switches with thermal fuses assigned to each of these. Preferably, at least three individual switches and particularly preferably at least six individual switches are connected in parallel in one power switch.

[0029] According to a further, particularly preferred aspect of the invention, at least one controllable disconnector is provided. The at least one controllable disconnector is arranged between at least one of the supply connections and the load output, for example in the positive and / or negative supply line to the inverter of the inverter circuit. The disconnector could also be integrated into the inverter. The controllable disconnector can be controlled in such a way as to disconnect the electrical machine from the DC voltage source and thus to protect the inverter circuit or its inverter in the event of a malfunction of the electrical machine, for example against an uncontrolled high reverse current or an overvoltage.

[0030] The circuit breaker preferably has a power transistor, preferably a power transistor with an integrated anti-parallel diode. For example, the circuit breaker can be designed as a power MOSFET, which is arranged, for example, in the positive supply branch. An anti-parallel diode is understood to be a diode that is connected in parallel to the load path of the respective power transistor and is also conductively connected from source to drain or emitter to collector of the power transistor. For example, the anti-parallel diode can be formed by the body diode of the power transistor designed as a MOSFET.

[0031] Preferably, a first diagnostic circuit is provided which is designed to diagnose a malfunction of an electrical machine connected to the load output of the inverter circuit. In the event of a diagnosed malfunction of the electrical machine, the first diagnostic circuit controls the isolating switch to an open state. By isolating the inverter or the inverter circuit from the DC voltage supply, the inverter or the inverter circuit is controlled by decoupling into a safe state. A malfunction can, for example, be a state in which such a high load current is supplied to the electrical machine that the inverter circuit generating this load current could be damaged or there would be a risk of overheating. A malfunction could also be a state that could have negative effects on the DC voltage source.Preferably, a second diagnostic device is further provided which is coupled to the circuit breaker and is designed to diagnose the proper functioning of the circuit breaker. The second diagnostic device is further designed to generate a diagnostic signal which contains information about the diagnosed state of the circuit breaker. In this context, “diagnosing” is understood to mean observing, monitoring and / or checking proper functioning. Diagnosing proper functioning can take place at regular intervals, continuously during operation of the electrical machine, at predetermined times, such as each time the electrical machine is restarted, or for example at a predetermined power consumption. Other times would also be conceivable.

[0032] Preferably, a control device coupled to the second diagnostic device is provided. The control device is designed to evaluate the diagnostic signal and, if the diagnosed state of the circuit breaker exceeds a predetermined threshold, to initiate a protective measure. This protective measure can, for example, be the opening of the circuit breaker. However, it can sometimes also be the case that the circuit breaker is defective and can therefore no longer be closed and / or opened or can no longer be controlled. As a protective measure, a more or less slow shutdown of the downstream inverter into a safe state can therefore also be provided, preferably combined with forwarding of the diagnostic signal, e.g. to a corresponding higher-level location. The circuit breaker is not generally used, but should only be actuated if there is a danger to the inverter orthe inverter circuit exists. The predefined threshold is therefore set in such a way that if it is exceeded there is a danger to the inverter or the inverter circuit. This is preferably done by opening the isolating switch, which disconnects the inverter from the DC voltage supply. Alternatively, an alarm signal can be issued or corresponding information can be sent to a higher-level, external vehicle control device if the diagnosed state of the isolating switch exceeds a predefined threshold. Diagnosis can be carried out online, i.e. via an internal vehicle control device, or offline, i.e. via an external vehicle control device.

[0033] The circuit breaker is preferably designed such that the rectified induced voltage at maximum speed of the electrical machine is below the breakdown voltage of the inverter. The breakdown voltage is generally determined by the circuit topology of the inverter and, in particular, by the number, type, and interconnection of the various electrical components of the inverter.

[0034] In a particularly preferred embodiment, the inverter is designed as a fully or at least partially integrated circuit. The isolating switch can be integrated into the integrated inverter. This allows for a circuit that is simplified in terms of manufacturing and thus more cost-effective.

[0035] In a particularly preferred development, at least one freewheeling diode is provided, which is arranged on the supply side between the first and second supply terminals. This freewheeling diode offers further protection for the inverter, i.e., an overcurrent at the inverter input that could endanger the inverter can be diverted via the freewheeling diode. The isolating switch is preferably integrated into the freewheeling diode. Using its single semiconductor component, a dual protection function can thus be provided in a very cost-effective manner.

[0036] In a preferred embodiment, the circuit breakers or their individual switches with thermal fuse can be controlled independently of a disconnector.

[0037] Preferably, the isolating switch and / or the power switches—and thus also their individual switches—are designed as power MOSFETs, so-called power MOSFETs. However, other field-effect transistors, bipolar transistors, thyristors, relays, IGBTs, and the like, each capable of switching the correspondingly high load currents, would also be conceivable. The isolating switches or the power transistors are preferably constructed on the basis of silicon (Si) technology or silicon carbide (SiC) technology, since particularly switching-resistant transistors can be produced using this technology.

[0038] Preferably, a three- or multi-stage inverter is provided.

[0039] The inverter particularly preferably has a number of driver stages corresponding to the number of phases. Each driver stage has at least one and preferably at least two controllable power switches. In the case of two power switches per driver stage, one of these is designed as a high-side switch and the other as a low-side switch, with their load paths connected in series. The center tap between the high-side switch and the low-side switch is in each case coupled to the load output. This load output carries one phase of the load current for driving the electrical machine when the electrical machine is in operation.

[0040] The above embodiments and developments can be combined with one another as desired, where appropriate. Further possible embodiments, developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with reference to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

[0041] TABLE OF CONTENTS OF THE DRAWING

[0042] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawings. In the drawings:

[0043] Fig. 1 is a schematic cross-sectional view of an electrical machine designed as a double rotor motor;

[0044] Fig. 2 is a block diagram of an electric drive system according to the invention;

[0045] Fig. 3 shows a first example of an inverter circuit according to the invention;

[0046] Fig. 4-4B shows a second example of an inverter circuit according to the invention;

[0047] Fig. 5 shows a third example of an inverter circuit according to the invention. The accompanying drawings are intended to provide a further understanding of embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the aforementioned advantages will be apparent from reference to the drawings. The elements of the drawings are not necessarily shown to scale.

[0048] In the figures of the drawing, identical, functionally identical and acting elements, features and components are provided with the same reference symbols unless otherwise stated.

[0049] DESCRIPTION OF EMBODIMENTS

[0050] Fig. 1 shows a schematic cross-sectional view of an electrical machine designed as a double rotor motor.

[0051] The electrical machine designated here by reference numeral 10 is preferably designed as a three-phase synchronous machine or synchronous motor. An aspect that is essential to the invention, but not absolutely necessary, is the fact that the double-rotor motor is also constructed from solid flux-conducting material, i.e., they are not laminated. The flux-conducting material preferably consists of solid iron or a corresponding solid iron alloy. It is also preferred if the electrical machine 10 is a wheel hub motor for an electrically operated motor vehicle. However, other applications would also be conceivable and advantageous.

[0052] The dual-rotor motor 10 comprises the outer rotor 11 and the inner rotor 12. The stator 13 is arranged between the two rotors 11, 12 in a manner known per se. The stator 13 can preferably, but not necessarily, be a yokeless stator 13. The inner rotor 12 is tubular, although a solid, full-volume design of the inner rotor 12 would also be conceivable.

[0053] In the example shown, two opposite-pole magnets 14, 15 are placed between the outer rotor 11 and the stator 13 on the inner surface of the outer rotor 11 in the outer air gap 16. It would be conceivable and advantageous if the magnets 14, 15 were embedded in pocket-shaped recesses provided specifically for this purpose in the outer rotor 11. However, it would also be conceivable if the magnets 14, 15 were spaced from the outer rotor 11, i.e. not attached directly to its inner surface. The flux lines between the north and south poles of the opposite-pole magnets 14, 15 run here in the core material of the outer rotor 11.

[0054] In the example shown, two opposing-pole magnets 18, 19 are also mounted between the inner rotor 12 and the stator 13 on the inner surface of the inner rotor 12 in the inner air gap 17. Here, too, the magnets 18, 19 can be embedded in corresponding pockets of the inner rotor 12 or spaced apart from the inner rotor 12. The flux lines between the north and south poles of the opposing-pole magnets 18, 19 run in the core material of the inner rotor 12.

[0055] Fig. 2 shows a block diagram of an electric drive system according to the invention.

[0056] The electric drive system according to the invention, designated here by reference numeral 20, is preferably—but not necessarily—intended for use in a motor vehicle. The electric drive system 20 according to the invention comprises a DC voltage source 21, an inverter circuit 22 according to the invention with an inverter 23, and a single- or multi-phase electric machine 10, designed, for example, as a double-rotor motor, as shown in Fig. 1.

[0057] The electrical machine 10 is connected on the input side to the inverter circuit 22, which drives the electrical machine 10. The inverter circuit 22 has two supply connections 24, 25, via which the inverter circuit 22 can be connected to the DC voltage source 21, for example a vehicle battery or a corresponding accumulator. A first supply potential V11, for example a positive supply potential, can be tapped off at the first supply connection 24. A second supply potential V12, for example a negative supply potential or a reference potential, can be tapped off at the second supply connection 25. A DC supply voltage VDC=V11—V12 is therefore present between the supply connections 24, 25.

[0058] At a load output 26 of the inverter circuit 22 or its inverter 23, a multi-phase load current IL, for example, can be tapped, via which the various phases of the electrical machine 10, which can be connected via the load output 26, are driven.

[0059] The inverter circuit 22 can, for example, be designed as a three-stage or multi-stage inverter circuit 12. The inverter circuit 22 has an inverter 23, usually referred to as an inverter 23. The inverter 23 is designed to convert the direct voltage VDC received on the supply side into an alternating voltage. The inverter 23 is preferably designed as a multi-phase inverter 23, wherein the number of phases of the inverter 23 typically corresponds to the number of phases of the electrical machine 10. The electrical machine 10 is driven via the phase currents IL provided by the inverter 23 at the load output 26. The electrical machine 10 is preferably, but not necessarily, a synchronous machine. In this case, the inverter circuit 22 preferably includes a three-phase inverter 23.

[0060] Furthermore, a control circuit 28 is provided which is coupled to a control terminal 29 of the inverter circuit 22 and which is designed to control the function of the inverter circuit 22 or its inverter 23 via a control signal.

[0061] In the control circuit 28, an overcurrent detection device can also be provided, which is designed to detect an overcurrent, for example, in the switches of the inverter 23.

[0062] According to the invention, the inverter circuit 22 is equipped with a safety concept 27, which is shown in Fig. 2 merely as a schematic functional block 27. This safety concept 27, its function, its configurations, and variants are described in detail below with reference to Figs. 3 to 5.

[0063] Fig. 3 shows a first embodiment of an inverter circuit according to the invention.

[0064] In the example shown in Fig. 3, a controllable isolating switch 30 is arranged between the supply connection 24 and the inverter 23 of the inverter circuit 22. The controllable isolating switch 30, which is a component of the safety concept 27 according to the invention, is designed to disconnect the electrical connection between the inverter 23 and the DC voltage source as required. For this purpose, the isolating switch 30 is connected with its load path between the supply connection 24 and the inverter 23. If the control connection of the isolating switch 30 is controlled by means of a suitable control signal S2, the load path can be interrupted.

[0065] To control the isolating switch 30, a further control circuit 31 is provided, which is shown only schematically in Fig. 3 and is typically not a component of the inverter circuit 22. Preferably, the further control circuit 31 is a component of the control circuit 28 for controlling the inverter 23 of the inverter circuit 22, although a separate, for example external, control circuit 31 would also be conceivable.

[0066] Fig. 4 shows a second embodiment of an inverter circuit according to the invention.

[0067] In Fig. 4, the inverter 23 of the inverter circuit 22 is designed as a three-phase inverter 23. The three-phase inverter 23 has a separate driver stage 40a-40c for each phase of the output-side load current, each of which is arranged between a first supply path with the first supply potential V11 and a second supply path with the second supply potential V12. The three driver stages 40a-40c each have a half-bridge consisting of two power switches T1-T6. A center tap 41a-41c of a respective driver stage 40a-40c is connected to the load output 26.

[0068] The half-bridge of the first driver stage 40a comprises a power switch TI designed as a high-side switch and a power switch T4 designed as a low-side switch, with the center tap 41a between its load paths connected or coupled to the load output 26. The other two driver stages 40b, 40c are designed analogously.

[0069] In the example of Fig. 4, the above-mentioned safety concept 27 is also implemented in the inverter 23. This safety concept includes two safety elements, which are explained below using a detail for the power switch TI in Fig. 4A.

[0070] According to a first safety feature, the circuit breaker TI does not consist of a single switch. Rather, the circuit breaker TI has a plurality of individual switches Tla-Tle, in the example shown, five individual switches Tla-Tle that are as identical as possible. These individual switches Tla-Tle are arranged in parallel. This ensures that the phase current through the circuit breaker TI is evenly distributed among the individual switches Tla-Tle, so that each individual switch Tla-Tle has to switch a correspondingly lower phase current overall.

[0071] The remaining circuit breakers T2-T6 are designed analogously.

[0072] According to a second safety element, each of the individual switches Tla-Tle of a respective circuit breaker T1-T6 is also assigned a thermal fuse 42a-42e. The assigned thermal fuses 42a-42e are arranged in a load path of the respective individual switch Tla-Tle assigned to them. These thermal fuses 42a-42e can be part of a conductor track 43 connected to the circuit breaker T1, for example a conductor track which is supplied with the first supply potential Vll. The thermal fuses 42a-42e branch off from the common conductor track 43 as supply line sections 43a-43e and thus connect a respective load connection of an individual switch Tla-Tle to the common conductor track 43. The conductor track 43 and thus also the supply line sections 43a-43e connected to it can be made of copper or a copper alloy. Aluminum, silver or alloys of the aforementioned materials would also be conceivable.The conductor track 43 or supply line sections 43a-43e can be coupled to a heat sink for cooling or can be directly water-cooled.

[0073] Fig. 4B shows an example of a possible design for such a thermal fuse 42e. The thermal fuse 42e is accordingly preferably implemented by a (material) thinning 44e in the supply line section 43e for the individual switch Tie. The thinning 44e is selected according to the phase current to be protected. The thinning 44e forms a thermal resistance in the current-carrying path and is dimensioned such that, above a breakdown current predetermined by the width 45e of the thinning, the temperature increases abruptly and, as a result, the supply line section 43e abruptly melts in the region of the thinning 44e. This interrupts the current flow in the respective individual switch Tie.

[0074] The power switch TI and thus also its individual switches are designed using MOS technology, i.e., all individual switches Tla-Tle are, for example, MOSFETs. The MOSFETs are preferably manufactured using SiC technology, but can also be manufactured using conventional silicon or GaAs technology.

[0075] The functionality of the security concept described in Fig. 4 to Fig. 4B is explained in more detail below.

[0076] A low-resistance fault of an individual MOSFET switch Tla-Tle in one of the half-bridges 40a-40c causes an asymmetrical short circuit, which immediately leads to very high peak currents in the short-circuited MOSFET. Without a safety concept, this could lead to thermal damage and possibly to undefined consequential damage in the inverter 23. In addition, the high losses cause a pulsating braking torque in the electrical machine driven by the inverter 23, which can impair the safety and driving stability of the vehicle. Switching to freewheeling does not reduce these currents, since the body diodes of the still intact individual MOSFET switches Tla-Tle would maintain the current flow.

[0077] The inventive inverter circuit 22 with safety concept 27 solves this problem by introducing a thermal fuse in each individual MOSFET switch Tla-Tle of a half-bridge power switch T1-T6. Each of these individual MOSFET switches Tla-Tle carries, for example, 80 A - 120 A in normal operation. A short-circuited individual MOSFET switch Tla-Tle would therefore carry a current 20-30 times higher than in normal operation. Since the current density on the thinning 44e on the conductor lead 43e is already very high in normal operation (typically >400 A / mm 2 ), the current density in short-circuit operation thus reaches much higher currents of typically >10,000 A / mm 2. During this fault operation, the temperature in the area of ​​the thinning 44e increases abruptly (typically in the range of >1.5 million K / s). This causes the material of the thinning 44e to melt within a very short time (typically <1 msec). In combination with overcurrent detection and the associated rapid shutdown of all remaining individual MOSFET switches Tla-Tle controlled by the control circuit, this ensures safe behavior of the drive unit. Existing freewheeling paths in parallel and complementary MOSFETs can prevent the occurrence of any arcs during shutdown. The electrical resistance introduced by the thinning 44e is not particularly relevant in normal operation, typically <0.1 mOhm.

[0078] Fig. 5 shows a third embodiment of an inverter circuit according to the invention.

[0079] The inverter circuit 22 here has an inverter 23, as shown, for example, in Fig. 4-4B.

[0080] Furthermore, an input-side EMC filter 50 is provided, which is arranged between the supply connections 24, 25 and the inverter 23. The EMC filter 50 with its differential mode inductance LDM, the common-mode inductances LCM1, LCM2 and the capacitors CX, CY is important for the safety concept in that it stores a certain amount of energy that influences the shutdown process. In addition, active and passive discharge circuits can be integrated (not shown in Fig. 5) in order to reduce the intermediate circuit voltage to safe values ​​in a short time. The intermediate circuit capacitor CDC is also connected between the EMC filter 50 and the inverter 23.

[0081] In addition to the thermal fuses in the circuit breakers T1-T6 of the half-bridges 40a-40c of the inverter 23, an additional safety concept 27 is implemented here.

[0082] To avoid the high currents and field strengths associated with an active short circuit, freewheeling is used as a safe state. This is made possible by supplementing the inverter circuit 22 with an additional isolating switch 30 designed as a MOSFET and an additional intermediate circuit freewheeling diode DDC. During normal operation, the isolating switch 30 is closed and has no influence on the operation of the inverter 23. In the event of faults in the electrical machine 10, all power switches T1-T6 of the half-bridges 40a-40e are switched off. At the same time, the isolating switch 30 is also switched to the open state. This prevents energy from being transferred back from the electrical machine 10 to the DC voltage source 21. In this no-load operation, the electrical machine 10 does not generate any braking torque and therefore no current flows. However, there are some special features to be observed in this operating mode:

[0083] - The induced voltage of the electrical machine 10 is rectified via the body diodes of the MOSFET power switches TI - T6 and charges the intermediate circuit to the rectified value of the induced voltage.

[0084] - In the field weakening range, the d-axis current disappears and the terminal voltage rises to the induced open-circuit voltage of the given speed, which may be higher than the battery voltage of the DC voltage source 21. However, the isolating switch 30 does not allow any energy transfer to the vehicle, so that the voltage-free state in the vehicle is ensured even when the electric machine 10 is rotating.

[0085] - The inductive energy stored in the windings of the electric machine 10 must be transferred to the intermediate circuit capacitor CDC without exceeding the maximum breakdown voltage of the intermediate circuit capacitor CDC and inverter 23.

[0086] - The isolating switch 30 can switch off high feedback currents, e.g., in the event of a short circuit in the vehicle's high-voltage network. After switching off, the inductive energy stored in the supply voltage leads and the EMC filter 50 must be dissipated in the intermediate circuit freewheeling diode DDC.

[0087] - In generator operation, the overvoltage protection of the inverter 23 must ensure that the device switches off as quickly as possible in order to prevent an excessive voltage increase in the intermediate circuit.

[0088] - The active discharge circuit must withstand the maximum rectified induced voltage and ensure continuous operation, even when the electric machine 10 is idle for an extended period. Appropriate thermal protection strategies are also implemented without compromising the safety of the discharge circuit.

[0089] The term "arranged in parallel" in power switches and power transistors refers to their controlled load paths, which are arranged in parallel. A controlled load path refers to the current-carrying load path or the load path or the output current path. In the case of a bipolar transistor, the controlled load path is the connection between its emitter and collector, and in the case of a field-effect controlled transistor, the controlled load path is the connection between its drain and source. The control terminal in such transistors is called the base or gate. In the case of a multi-phase inverter, the controlled load path refers to the high-current path that carries the phase current.

[0090] Although the present invention has been fully described above with reference to preferred embodiments, it is not limited thereto but can be modified in many ways.

[0091] 10 electric machine

[0092] 11 outer rotor

[0093] 12 inner rotor

[0094] 13 Stator

[0095] 14 Magnet

[0096] 15 Magnet

[0097] 16 outer air gap

[0098] 17 inner air gap

[0099] 18 Magnet

[0100] 19 Magnet

[0101] 20 electric drive system

[0102] 21 DC voltage source

[0103] 22 Inverter circuit

[0104] 23 inverters

[0105] 24 (first) supply connection

[0106] 25 (second) supply connection

[0107] 26 Load output

[0108] 27 Security concept

[0109] 28 St your circuit

[0110] 29 Steue ran End

[0111] 30 disconnect switches

[0112] 31 St your circuit

[0113] 40a 40c driver stages

[0114] 41a 41c Center taps

[0115] 42a 42e thermal fuses

[0116] 43 Conductor track

[0117] 43a 43e Supply line sections

[0118] 44th thinning

[0119] 45e Width 50 EMC— Filter

[0120] CX, CY capacitors

[0121] CDC intermediate circuit capacitor DDC intermediate circuit freewheeling diode

[0122] IL phase current

[0123] LDM Differential mode inductance

[0124] LCM1 , LCM2 common mode inductors

[0125] SI control signal S2 control signal

[0126] T1-T6 circuit breakers

[0127] Tla-Tle single switch

[0128] VI 1 first supply potential, positive supply potential V12 second, negative supply potential, reference potential

[0129] VDC DC supply voltage

Claims

PATENT CLAIMS 1. An inverter circuit for controlling a single-phase or multi-phase electric machine for an electric drive system, in particular a double-rotor motor, preferably for or in a motor vehicle, comprising a first and second supply connection via which the inverter circuit can be connected to a DC voltage source, a load output for coupling the electric machine, a controllable inverter arranged between the supply connections and the load output, which inverter has a plurality of power switches interconnected to convert a DC voltage received on the supply side into an AC voltage for driving an electric machine, at least one power switch having a plurality of individual switches arranged in parallel with associated thermal fuses,whereby the thermal fuses are each arranged in the load path of the individual switch assigned to them., 2. Inverter circuit according to claim 1, characterized in that at least one of the thermal fuses is designed as a fuse.

3. Inverter circuit according to claim 2, characterized in that that at least one fuse is designed as a PCB conductor track, which is designed to switch off the individual switch at a predetermined load current by melting the PCB conductor track.

4. Inverter circuit according to one of the preceding claims, characterized in that the thermal fuse is designed as a material thinning, in particular as a taper of a PCB conductor track.

5. Inverter circuit according to one of the preceding claims, characterized in that the thermal fuse is formed by using materials with different electrical resistance.

6. Inverter circuit according to one of the preceding claims, characterized in that each of the power switches of the inverter has a plurality of individual switches arranged in parallel with each other, each with thermal fuses assigned to it, preferably at least three individual switches and particularly preferably at least six individual switches.

7. Inverter circuit according to one of the preceding claims, characterized in that at least one controllable isolating switch is provided, which is arranged between at least one of the supply connections and the load output and which can be controlled in such a way as to disconnect the electrical machine from the DC voltage source.

8. Inverter circuit according to claim 7, characterized in that the isolating switch has a power transistor, preferably a power transistor with an integrated anti-parallel diode.

9. Inverter circuit according to one of claims 7 or 8, characterized in that a first diagnostic circuit is provided which is designed to diagnose a malfunction of an electrical machine connected to the load output and, in the event of a diagnosed malfunction, to control the circuit breaker into an open state.

10. Inverter circuit according to one of claims 7 to 9, characterized in that a second diagnostic device coupled to the circuit breaker is provided, which is designed to diagnose the proper function of the circuit breaker and to generate a diagnostic signal which contains information about the diagnosed state of the circuit breaker.

11. Inverter circuit according to claim 10, characterized in that a control device coupled to the second diagnostic device is provided, which control device is designed to evaluate the diagnostic signal and, if the diagnosed state of the circuit breaker exceeds a predetermined threshold, to initiate a protective measure and / or to control the inverter into a safe state.

12. Inverter circuit according to one of claims 7 to 11, characterized in that the isolating switch is designed such that the rectified induced voltage at maximum speed of the electrical machine is below the breakdown voltage of the inverter.

13. Inverter circuit according to one of claims 7 to 12, characterized in that the inverter is designed as an integrated circuit, wherein the isolating switch is in particular integrated into the integrated inverter.

14. Inverter circuit according to one of the preceding claims, characterized in that at least one freewheeling diode is provided, which is arranged on the supply side between the first and second supply terminal.

15. Inverter circuit according to one of claims 7 to 14, characterized in that the isolating switch is integrated in the freewheeling diode.

16. Inverter circuit according to one of the preceding claims, characterized in that the circuit breakers with thermal fuse can be controlled independently of a disconnector.

17. Inverter circuit according to one of the preceding claims, characterized that the isolating switch and / or the power transistors are designed as power MOSFETs, in particular as Si MOSFETs or as SiC MOSFETs.

18. Inverter circuit according to one of the preceding claims, characterized in that a three- or multi-stage inverter is provided.

19. Inverter circuit according to one of the preceding claims, characterized in that the inverter has a number of driver stages corresponding to the number of phases, each of which has at least one controllable power switch.

20. An electric drive system, preferably in or for a motor vehicle, comprising an electric machine, preferably designed as a synchronous machine, a DC voltage source, in particular an accumulator, and an inverter circuit according to one of claims 1 to 19, which is connected on the supply side to the DC voltage source and via its load output to the electric machine.

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