Overcurrent protection circuit

Abstract

The invention relates to an overcurrent protection circuit (40) for a multiphase alternating current with a number of phase currents (IU, IV, IW), comprising a voltage source (42) for providing a supply voltage (UV) with respect to a reference potential (UB), a reference voltage (URef, URef') as threshold value for overcurrent protection, a current meter (44) for picking up the individual phase currents (IU, IV, IW) in the form of measurement signals (IMessU, IMessV, IMessW), a voltage peak detector (50) to which the measurement signals (IMessU, IMessV, IMessW) of the phase currents (IU, IV, IW) are fed and which generates a detector signal (DS) which essentially corresponds to the measurement signal (IMessU, IMessV, IMessW) with the highest voltage value, and a comparator (62) coupled to the supply voltage (UV) and the reference potential (UB), to which the reference voltage (URef') and the detector signal (DS) are applied, and whose output signal (A) is pulled to the reference potential (UB) when the detector signal (DS) is greater than the reference voltage (URef').

Description

[0001] This invention relates to an overcurrent protection circuit for multiphase alternating current having several phase currents. The invention also relates to a motor-driven device having such an overcurrent protection circuit and an electric refrigerant-driven device having such a motor-driven device.

[0002] Motor vehicles typically contain air conditioning systems that regulate the temperature of the vehicle's interior using a refrigerant circuit. These systems generally have a circuit through which the refrigerant is guided. Refrigerants such as R-134a (1,1,1,2-tetrafluoroethane) or R-744 (carbon dioxide) are heated at the evaporator and compressed by a compressor. The refrigerant then releases the absorbed heat via a heat exchanger and is subsequently guided back to the evaporator via a throttle valve.

[0003] For compressor heads of refrigerant compressors driven by electricity or electric motors, brushless motors are typically provided. In particular, brushless motors, as (alternating current) motors, usually have a stator with multi-phase excitation windings or stator windings, which is arranged coaxially with a rotor having one or more permanent magnets. Both the rotor and stator are constructed, for example, as laminated cores, where stator teeth carry the coils of the stator windings in stator slots between them.

[0004] In brushless motors, an inverter typically generates alternating current to feed the stator windings.

[0005] Alternating current (AC) has several phases or phase currents, each with the same amplitude and frequency, but with a phase difference between them. For example, in three-phase AC, the three phase currents have a 120° phase difference between them. When AC is fed into the corresponding motor or stator phase windings, these windings then generate a rotating magnetic field, which is used to rotate the rotor.

[0006] To protect motors from overload, overcurrent protection circuits are often used to monitor their current consumption. Here and below, "overcurrent" is specifically understood as a current flowing through a circuit or a portion thereof that exceeds the maximum permissible or specified current value. Such overcurrents can be caused by faults, overloads, or short circuits, and can lead to damage to the electronic components of the inverter and / or motor.

[0007] For example, such overcurrent protection circuits have an "OR" logic tripping mechanism implemented by monitoring the current of a single phase. To do this, the phase current is acquired, for example, by means of a measuring resistor or shunt resistor, in the form of a measurement signal generated across its terminals. These measurement signals are then amplified, for example, and each is compared to a reference voltage using a comparator. The comparators typically each have an open-drain or open-collector output (Open-Drain or Open-Kollektor output), allowing them to actively pull the comparator output to LOW, but with high impedance (inactive state) in the HIGH state.

[0008] In each case, a reference voltage is applied to the positive (non-inverting) comparator input, while the corresponding measured signal of the phase current is connected to the negative (inverting) comparator input. Therefore, when the reference voltage is greater than the corresponding measured signal, the comparator output is high impedance. If one of the measured signals is greater than the reference voltage, the corresponding comparator output is pulled low.

[0009] These comparator outputs are interconnected via wire-OR logic and connected to the supply voltage (HIGH) via pull-up resistors. Therefore, when one comparator pulls its output to LOW, the common connection is pulled to the reference potential (LOW) regardless of the states of the other comparators. If all comparators are high impedance, the pull-up resistors pull the line to HIGH. Thus, if at least one phase current reaches an unacceptable overcurrent level (characterized by the reference voltage level), the output of the overcurrent protection circuit is pulled to LOW.

[0010] The disadvantage of this overcurrent protection circuit is that it requires a number of comparators corresponding to the number of AC phases. Therefore, this overcurrent protection circuit is relatively space-consuming and requires a large number of components, and it is also difficult to expand to a larger number of phases.

[0011] The object of this invention is to provide a particularly suitable overcurrent protection circuit. In particular, it should be pointed out that an overcurrent protection circuit is compact in structure and easily expandable in terms of the number of phases. Another object of this invention is to provide a particularly suitable electric motor drive device and a particularly suitable electric refrigerant drive device.

[0012] According to the invention, in terms of the overcurrent protection circuit, this objective is achieved by the features of claim 1; in terms of the drive device, this objective is achieved by the features of claim 9; and in terms of the refrigerant drive device, this objective is achieved by the features of claim 10. Advantageous designs and improvements are the subject of the dependent claims (sub-claims). The advantages and designs mentioned in the overcurrent protection circuit can be similarly transferred to the drive device and / or the refrigerant drive device, and vice versa.

[0013] Here and in the following text, the word “and / or” should be understood as meaning that the features associated with the conjunction can coexist or serve as alternatives to each other.

[0014] The overcurrent protection circuit configuration according to the present invention is suitable and adaptable for monitoring the current consumption of a motor-type drive device or a brushless motor with multiphase rotating field windings.

[0015] In this case, the overcurrent protection circuit specifically monitors the AC current supplied to the drive unit or motor. The AC current has several phase currents, at least two phase currents, and particularly three or more phase currents. These phase currents are AC signals that, during normal operation, have the same amplitude and frequency, and are phase-differentiated with each other.

[0016] An overcurrent protection circuit has a reference potential (e.g., ground potential) and a voltage source that generates a supply voltage relative to the reference potential. That is, the overcurrent protection circuit has a low voltage potential (voltage level) as the reference potential, which is hereinafter referred to as LOW level or LOW potential (abbreviation: LOW), and a high voltage potential as the supply voltage, which is hereinafter referred to as HIGH level or HIGH potential (abbreviation: HIGH).

[0017] Overcurrent protection circuits include ammeters for monitoring or acquiring alternating current or single-phase current. In this case, the phase current is specifically detected or measured as a voltage signal (measurement signal). Preferably, the ammeter is implemented as a number of measuring resistors or shunt resistors corresponding to the number of phase currents, each through which the phase current to be detected flows. For example, the voltage generated across the measuring resistor or shunt resistor in each case is directly used as the measurement signal. Alternatively, the voltage generated across the measuring resistor or shunt resistor in each case is first amplified, and this amplified voltage signal is used as the measurement signal.

[0018] The overcurrent protection circuit also has a reference voltage, i.e., a reference potential or reference level, which is defined as a (voltage) threshold for overcurrent protection. The magnitude of the reference voltage level is between HIGH and LOW. The reference voltage is defined as a threshold such that this threshold corresponds to a voltage level that, in the event of an overcurrent, may appear in one of the measured signals derived from the phase current. In other words, if the corresponding measured signal is greater than the reference voltage, an overcurrent occurs in one of the phase currents.

[0019] According to the present invention, the overcurrent protection circuit has a voltage peak detector and a single comparator.

[0020] A voltage peak detector is connected between the ammeter and the comparator. In other words, the measured signal of the phase current is fed into the voltage peak detector, which is set and adapted to generate a voltage signal (detector signal). In this case, the detector signal essentially corresponds to the measured signal with the highest voltage value / voltage level (minus the voltage drop in the voltage peak detector). Therefore, the voltage peak detector performs an OR logic operation on the measured signals with respect to their respective current highest voltage levels.

[0021] The comparator is coupled to the supply voltage (HIGH) and the reference potential (LOW). The comparator has two input terminals and one output terminal. The reference voltage and the detector signal are applied to the two comparator input terminals. Specifically, the reference voltage is fed to the positive (non-inverting) comparator input terminal, and the detector signal is fed to the negative (inverting) comparator input terminal. The output signal of the overcurrent protection circuit is generated at the comparator output terminal, and when the detector signal is greater than the reference voltage, the output signal is pulled to the reference potential. In other words, when the AC current reaches the overcurrent level, the output signal essentially corresponds to the reference potential. This achieves a particularly suitable overcurrent protection circuit. Specifically, in the operation of the overcurrent protection circuit, multi-channel overcurrent protection for a single AC phase or phase current is achieved.

[0022] According to the present invention, the OR logic operation of the measurement signal is essentially implemented by a voltage peak detector, so the comparator then compares only the highest measurement signal with the reference voltage. This eliminates the need for a "wired OR" combination of comparators, thereby reducing the number of comparators required for overcurrent protection to one.

[0023] In an advantageous embodiment, the overcurrent protection circuit includes a voltage divider for generating a reference voltage. The voltage divider is connected to the supply voltage. In particular, the voltage divider is connected between HIGH and LOW. The voltage divider can be, for example, an adjustable potentiometer; however, preferably, the voltage divider is implemented as a series circuit of two (ohmic) resistors.

[0024] In a preferred design, the comparator output is implemented as an open-drain or open-collector output, thereby actively pulling the comparator output to LOW in the event of an overcurrent, but maintaining high impedance (inactive state) in the HIGH state. A pull-up resistor is connected to the comparator output and is connected to the supply voltage (HIGH). Thus, the output signal of the overcurrent protection circuit is HIGH during normal operation and LOW during an overcurrent.

[0025] An additional or further aspect of the invention is that the voltage peak detector is implemented as a number of parallel diodes corresponding to the number of measurement signals, each diode being connected between the ammeter and the comparator, and one of the measurement signals is applied to each of these diodes. These diodes are connected in the forward direction (forward direction) between the corresponding measuring resistor or shunt resistor (or its respective amplifier) ​​and the comparator input. In other words, the corresponding measurement signal is fed into the anode of the corresponding diode. The cathodes of the diodes are interconnected and connected to the comparator input. Preferably, these diodes are implemented with identical structures, such that all measurement signals flow through the same diode.

[0026] This results in a particularly advantageous implementation scheme for the voltage peak detector. In particular, it enables a particularly low-cost overcurrent protection circuit because, compared to the prior art, the comparator is effectively replaced by a low-cost diode.

[0027] Furthermore, for each replaced comparator, a decoupling capacitor is eliminated, thereby further reducing costs and the installation space requirements for overcurrent protection circuitry. In particular, the installation space requirements can be further reduced by using diode arrays (multiple diodes in an integrated circuit), thus enabling additional freedom in arranging overcurrent protection circuitry on the printed circuit board.

[0028] By implementing a voltage peak detector using a diode, the scalability of the overcurrent protection circuit in terms of the number of AC phases is further improved, because adding a further channel (phase) for overcurrent detection only requires an additional diode, rather than a comparator.

[0029] During normal operation, the measured signals have the same voltage amplitude, but differ in phase depending on the phase current. Since the diodes are conducting in the conduction direction (when the applied voltage exceeds the conduction voltage) and blocking in the blocking direction (reverse direction) (when the voltage is negative), the detector signal generated by the cathodes connected together is an OR operation combination of the positive half-waves of all the measured signals.

[0030] If the positive half-wave of the measured signal exceeds the diode's forward voltage, that half-wave will participate in generating the detector signal. When a negative half-wave is applied, the diode will block, and the detector signal will not be affected by that negative half-wave. Therefore, the detector signal is the superposition of all the positive half-waves of the measured signal.

[0031] In the case of overcurrent, if at least one of the phase currents is an overcurrent, the detector signal is still a superposition of the positive half-waves of all measured signals, where the measured signal with the larger amplitude dominates once it becomes positive. If the positive half-wave of the measured signal with the larger amplitude exceeds the diode's forward voltage, then that measured signal has a greater influence on the detector signal than the other measured signals, provided the other measured signals have lower amplitudes.

[0032] Therefore, the detector signal has a voltage level that corresponds to the voltage level of the measurement signal with the largest amplitude (minus the voltage drop across the corresponding diode).

[0033] The voltage drop across a diode varies with temperature and current. To adjust the reference voltage, the tap voltage can be set differently based on temperature and / or current, particularly in the case of an adjustable voltage divider. However, in a suitable improvement, the voltage peak detector has an additional diode connected between the voltage divider and the comparator. This diode is specifically implemented in this case as having the same structure as the other diodes in the voltage peak detector. Therefore, the tap voltage on the voltage divider is reduced by essentially the same voltage drop magnitude as the measured signal. That is, the reference voltage is the tap voltage minus the voltage drop across the diode. This ensures that the adjustment of the reference voltage is structurally simplified and reduces the number of components used.

[0034] In a preferred embodiment, all diodes of the voltage peak detector—the diodes used to measure the signal and optionally those also used for the reference voltage—are arranged such that they have substantially the same operating temperature during the operation of the overcurrent protection circuit. This means that the diodes are arranged as close together as possible so that the voltage drop across the diodes varies with temperature as evenly as possible for all diodes. Preferably, the diodes are arranged in an integrated circuit, such as a diode array. This effectively eliminates the voltage difference caused by the voltage drop across the diodes, thereby providing a reliable and safe overcurrent protection circuit.

[0035] In an advantageous design, the comparator inputs for the reference voltage and the detector signal are each connected to the reference potential via resistors. Resistors, or ohmic resistors, are added to ensure that at least approximately the same current flows through the diodes for the measurement signal and the reference voltage. In other words, the resistors are sized in this case such that as much current as possible flows through the diodes of the peak detector.

[0036] In a suitable design, the comparator is integrated into the microcontroller. Since only a single comparator is required for the overcurrent protection circuit according to the invention, it is possible to use a comparator integrated into the microcontroller. For example, the S32K1 and 32K3 series microcontrollers have at least one built-in comparator. With the overcurrent protection circuit according to the invention, such a built-in or integrated comparator can be used, meaning that discrete comparators are no longer needed.

[0037] The electric motor drive according to the invention comprises: an inverter for generating multiphase alternating current having several phase currents; and a brushless motor fed with the alternating current. The drive also includes an overcurrent protection circuit as described above. This results in a particularly suitable electric motor drive. In particular, the drive has an overcurrent protection circuit that is particularly compact in installation space, reduces the number of components, and is inexpensive, thereby enabling additional degrees of freedom, especially in terms of installation space.

[0038] The electric refrigerant drive device according to the invention is specifically designed and adapted for vehicle air conditioning systems in motor vehicles. In this case, the refrigerant drive device has an electric motor drive device as described above, which has an overcurrent protection circuit according to the invention. The refrigerant drive device is preferably implemented as a refrigerant compressor, such as a scroll compressor or a rolling piston compressor, wherein the drive device drives the compressor mechanism during operation.

[0039] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which are illustrated in a simplified and schematic manner:

[0040] Figure 1 A refrigerant compressor with an electric motor drive, and

[0041] Figure 2 Overcurrent protection circuit for the drive unit.

[0042] In all drawings, corresponding parts and dimensions always use the same reference labels.

[0043] Figure 1 An electric refrigerant drive unit 2, hereinafter also referred to as a refrigerant compressor, is shown for a vehicle air conditioning system for a motor vehicle. The refrigerant drive unit 2 has an electric motor drive unit 4 and a compressor mechanism 6 driven by the drive unit, such as a scroll compressor or a rolling piston compressor.

[0044] The drive unit 4 has, for example, a multiphase, brushless motor 8, which is connected to a power supply (voltage supply) 12 via an inverter 10. In the illustrated embodiment, the motor 8 is implemented as three-phase. However, the motor 8 can have any number of phases.

[0045] In this embodiment, the power source 12 includes an energy storage device 14 inside the vehicle (e.g., in the form of a (motor vehicle) battery) and a (DC) intermediate circuit 16 connected thereto, which at least partially extends into the inverter 10.

[0046] The intermediate circuit 16 is basically composed of a forward conductor 16a and a return conductor 16b, which connect the inverter 10 to the energy storage device 14. The conductors 16a and 16b are at least partially connected to the inverter 10, in which an intermediate circuit capacitor 18 and a bridge circuit 20 are connected between the two conductors.

[0047] In the operation of the refrigerant compressor 2, the input current supplied to the bridge circuit 20 is converted into three-phase alternating current (motor current, output current), having three phase currents IU, IV, and IW, corresponding to the three phases (U, V, W) of the motor 8. The phase currents IU, IV, and IW are directed to the corresponding phases (windings) of the stator of the motor 8 (not shown in detail).

[0048] The phase terminals 22, 24, and 26 of each phase winding are connected to the corresponding bridge module 28 of the bridge circuit 20.

[0049] The phase windings are controlled by a bridge circuit 20. The bridge circuit 20 is implemented with a bridge module 28, specifically a B6 circuit. In this design, during operation, each of the phase windings U, V, and W is pulse-switched at a high switching frequency between a high (DC) voltage level on the input conductor 16a and a low voltage level on the return conductor 16b. The high voltage level in this case is specifically the intermediate circuit voltage UZK of the intermediate circuit 16, while the low voltage level is preferably the reference potential or ground potential UB. This pulse control is implemented as PWM control via a controller 30—such as… Figure 1 As indicated by the middle arrow, it is feasible to control and / or adjust the speed, power, and direction of rotation of the motor 8 or the compressor mechanism 6 using this controller.

[0050] Each bridge module 28 includes two semiconductor switches 32 and 34. One side of the bridge module 28 is connected to the input conductor 16a via a potential connection 36, and thus to the intermediate circuit voltage UZK. On the other side, the bridge module 28 is connected to the return conductor 16b via a second potential connection 38, and thus to the reference potential UB. Via semiconductor switches 32 and 34, the corresponding phase terminals 22, 24, and 26 of phases U, V, and W can be connected either to the intermediate circuit voltage UZK or to the reference potential UB. When semiconductor switch 32 is closed (conducting) and semiconductor switch 34 is open (not conducting, blocking), phase terminals 22, 24, and 26 are potential-connected to the intermediate circuit voltage UZK. Correspondingly, when semiconductor switch 32 is open and semiconductor switch 34 is closed, phases U, V, and W are in contact with the reference potential UB. Therefore, it is feasible to apply two different voltage levels to each phase winding U, V, and W using PWM control.

[0051] An overcurrent protection circuit 40 is connected between phase terminals 22, 24, and 26 and the motor 8. This overcurrent protection circuit monitors whether the current consumption of the motor 8 is excessive. The overcurrent protection circuit 40 is coupled to the controller 30. When an overcurrent is detected in one of the phases, the controller terminates the operation of the refrigerant compressor 2 or the motor 8.

[0052] The following is for reference. Figure 2 The structure and function of the overcurrent protection circuit 40 will be explained in more detail.

[0053] The overcurrent protection circuit 40 is preferably connected to the reference potential UB of the drive device 4. The overcurrent protection circuit 40 has a voltage source 42 for generating a supply voltage UV. The supply voltage UV constitutes a high voltage level (HIGH) for the overcurrent protection circuit 40, and the reference potential UB constitutes a low voltage level (LOW).

[0054] The overcurrent protection circuit 40 includes an ammeter 44 for detecting alternating current. The ammeter 44 in this case has three measuring resistors or shunt resistors 46 connected to one of the phase lines U, V, and W. Depending on the switching states of the (power) semiconductor switches 32 and 34, phase currents IU, IV, and IW flow through the corresponding shunt resistors 46. The voltage drop across the shunt resistors 46 is amplified by their respective amplifiers 48 and analyzed by a voltage peak detector 50 into measurement signals IMessU, IMessV, and IMessW. The voltage peak detector 50 generates a detector signal (detector voltage) DS from the measurement signals IMessU, IMessV, and IMessW.

[0055] Voltage divider 52 is connected in parallel with voltage source 42. Voltage divider 52 is formed by two ohmic resistors 54 and 56 connected in series, wherein the reference voltage (reference signal) URef is taken from between resistors 54 and 56.

[0056] The reference voltage URef and the detector signal DS are connected to one comparator input terminal 58 and 60 of comparator 62, respectively. Comparator 62 is connected to the supply voltage UV and the reference potential UB. One comparator output terminal 64 of comparator 62 is connected to controller 30.

[0057] The comparator output 64 is implemented as an open-drain output, so in the event of an overcurrent, the comparator output 64 is actively pulled to the reference potential UB, but under the supply voltage condition, it is at high impedance (inactive state). Connected to the comparator output 64 is a pull-up resistor 66, which is connected to the supply voltage (UV).

[0058] Comparator 62 is preferably integrated into the microcontroller. For example, comparator 62 may be integrated into the controller 30 that controls the bridge circuit 28. In other words, overcurrent protection circuit 40 may be partially integrated into controller 30.

[0059] exist Figure 2 In the illustrated embodiment, the voltage peak detector 50 is implemented as a diode array with four identical diodes D1, D2, D3, and D4. Diode D1 is connected in the conduction direction between the voltage tap of the voltage divider 52 and the positive comparator input 58. The anode sides of diodes D2, D3, and D4 are each connected to one of the amplifiers in amplifier 48, and their cathode sides are connected together to the negative comparator input 60.

[0060] At point VP1, the connection between comparator input 58 and the cathode of diode D1, resistor 68 is connected to the reference potential UB. Point VP2, the connection between the cathodes of diodes D2, D3, and D4 and comparator input 60, is connected to the reference potential UB via resistor 70. Resistors 68 and 70 are sized such that approximately the same current flows through diodes D1 through D4.

[0061] The reference voltage URef is designed with resistors 54 and 56 such that it substantially corresponds to a voltage level that is output by the associated amplifier 48 in the event of overcurrent. The reduced reference voltage URef' is applied to the comparator input 58 through the voltage drop across diode D1.

[0062] During normal operation, the measurement signals IMessU, IMessV, and IMessW have the same voltage amplitude, but differ in phase according to the phase currents IU, IV, and IW. Since diodes D2, D3, and D4 are conducting in the conduction direction and blocking in the blocking direction, the detector signal DS generated by the connected cathodes is an OR operation combination of the positive half-waves of all measurement signals IMessU, IMessV, and IMessW.

[0063] In the case of overcurrent, if at least one of the phase currents IU, IV, and IW has an overcurrent level, the detector signal DS is still a superposition of the positive half-waves of all measurement signals IMessU, IMessV, and IMessW, where the measurement signals IMessU, IMessV, and IMessW with larger amplitude values ​​dominate once they become positive. Therefore, the detector signal DS has a voltage level corresponding to the voltage level of the measurement signals IMessU, IMessV, and IMessW with the largest amplitude values ​​(minus the voltage drop across the corresponding diodes D2, D3, and D4).

[0064] At comparator output terminal 64, an output signal A of the overcurrent protection circuit 40 is generated. When the detector signal DS is less than the reference voltage URef' (normal operation), this output signal is equal to the supply voltage UV. When the detector signal DS is greater than the reference voltage URef', the output signal is pulled to the reference potential UB. In other words, when the AC current reaches the overcurrent level, the output signal A is essentially equal to the reference potential UB.

[0065] The claimed utility model is not limited to the embodiments described above. Instead, those skilled in the art can derive other variations of the utility model within the scope of the disclosed claims without departing from the subject matter of the claimed utility model. Furthermore, within the scope of the disclosed claims, all individual features described in conjunction with the various embodiments can be combined in other ways without departing from the subject matter of the claimed utility model.

[0066] List of reference numerals

[0067]

Claims

1. An overcurrent protection circuit (40) for multiphase AC power with several phase currents (IU, IV, IW), having - Voltage source (42), which is used to provide a supply voltage (UV) with respect to a reference potential (UB). - Reference voltage (URef, URef'), which serves as a threshold for overcurrent protection. - Ammeter (44), the ammeter being used to acquire the single phase current (IU, IV, IW) in the form of a measurement signal (IMessU, IMessV, IMessW). - A voltage peak detector (50) is fed with the measured signals (IMessU, IMessV, IMessW) of the phase currents (IU, IV, IW), and the voltage peak detector generates a detector signal (DS) that substantially corresponds to the measured signals (IMessU, IMessV, IMessW) having the highest voltage values. - Comparator (62), the comparator is coupled to the supply voltage (UV) and the reference potential (UB), the reference voltage (URef') and the detector signal (DS) are applied to the comparator, and when the detector signal (DS) is greater than the reference voltage (URef'), its output signal (A) is pulled to the reference potential (UB).

2. The overcurrent protection circuit (40) according to claim 1. Its features are, A voltage divider (52) is connected to the supply voltage (UV) to generate the reference voltage (URef, URef').

3. The overcurrent protection circuit (40) according to claim 1 or 2. Its features are, The comparator output (64) is implemented as an open-drain output, and the comparator output (64) is connected to the supply voltage (UV) using a pull-up resistor (66).

4. The overcurrent protection circuit (40) according to any one of claims 1 to 3. Its features are, The voltage peak detector (50) is implemented as a number of parallel diodes (D2, D3, D4) corresponding to the number of the measurement signals (IMessU, IMessV, IMessW), each of which is connected between the ammeter (44) and the comparator (62) and applies one of the measurement signals (IMessU, IMessV, IMessW) to the diode.

5. The overcurrent protection circuit (40) according to claim 4. Its features are, The voltage peak detector (50) has an additional diode (D1) connected between the voltage divider (52) and the comparator (62).

6. The overcurrent protection circuit (40) according to claim 4 or 5. Its features are, All diodes (D1, D2, D3, D4) are arranged in such a way that they have essentially the same operating temperature during operation.

7. The overcurrent protection circuit (40) according to any one of claims 1 to 6. Its features are, The comparator inputs (58, 60) for the reference voltage (URef') and the detector signal (DS) are each connected to the reference potential (UB) via resistors (68, 70).

8. The overcurrent protection circuit (40) according to any one of claims 1 to 7. Its features are, The comparator (62) is integrated into the microcontroller.

9. A motor drive device (4) comprising: an inverter (10) for generating multiphase alternating current having a plurality of phase currents (IU, IV, IW); a motor (8) fed with said alternating current; and an overcurrent protection circuit (40) according to any one of claims 1 to 8.

10. An electric refrigerant drive device (2) for a motor vehicle, comprising an electric motor drive device (4) according to claim 9.

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