WO2020011329A1

WO2020011329A1 - Drive circuit and method for operating a drive circuit

Info

Publication number: WO2020011329A1
Application number: PCT/EP2018/000349
Authority: WO
Inventors: Martin Weinmann; Albrecht Mayer; Andreas Schmid
Original assignee: Diehl Ako Stiftung & Co. Kg
Priority date: 2018-07-09
Filing date: 2018-07-09
Publication date: 2020-01-16
Also published as: DE112018007817A5

Abstract

The invention relates to a drive circuit (10) for driving an electronically commutated motor (12), having a rectifier (18) with an AC terminal (20) which can be connected to a supply grid (22), an inverter (16) with a motor phase terminal (17) to which the motor phases (U, V, W) of the motor (12) can be connected, and a DC voltage intermediate circuit (14) between the rectifier (18) and the inverter. According to the invention, a fault detection to detect whether an insulation fault (R7a..c) of the drive circuit (10) is present is carried out by directly detecting a fault current (IR7) and/or at least one voltage (UL, UN, UHV, UPFC) within the drive circuit (10) during a phase in which a current flow from the supply grid (22) to the DC voltage intermediate circuit (14) does not occur in the event of a fault-free drive circuit.

Description

Drive circuit and method for operating a drive circuit

The present invention relates to a drive circuit for driving an electronically commutated motor and a method for operating such a drive circuit.

The present invention relates in particular to residual current monitoring for drive circuits in which the motor is fed from a DC voltage intermediate circuit. A fault current is an electrical current that flows to earth or the protective conductor due to an insulation fault via a given fault location. So-called residual current circuit breakers, which are also referred to as Fl switches, are often used to avert dangers related to personal injury from electric shock and fire. The common principle of such residual current circuit breakers is the measurement of the differential current of the current flowing into and out of the domestic power network, for example, in order to switch off the power supply at all poles when a certain limit value of the differential current is exceeded.

The selection of the RCCB essentially depends on the current shape of a fault current that may occur. Depending on the type of residual current that they can detect, there are different types of residual current circuit breakers. As explained in the introduction to EP 3 059 828 A1, type A residual current operated circuit breakers, which can only measure the AC component of the fault current, are mainly used in building installations and require drive circuits for electronically commutated motors, particularly in connection with active power factor correction (PFC) - Regulation of significantly more expensive type B residual current circuit breakers. EP 3 059 828 A1 therefore proposes a device and a method for detecting fault currents in a regulated direct voltage intermediate circuit with active power factor correction, in which the intermediate circuit voltage is actively reduced in the event of a fault current detection, so that the fault current from A type A residual current circuit breaker can be detected. Residual current is detected by measuring the residual current at the AC input of the drive circuit. The disadvantage of this solution is that such a differential current measurement with a required resolution of a few mA is very complex, expensive and prone to failure.

It is the object of the invention to provide an improved residual current monitoring for a drive circuit for driving an electronically commutated motor.

This problem is solved by the teaching of the independent claims. Particularly advantageous refinements and developments of the invention are the subject of the dependent claims.

In the method according to the invention for operating a drive circuit for driving an electronically commutated motor, which has a DC intermediate circuit, which is connected on the input side via a rectifier to an AC connection, which is connected to a supply network, and on the output side is connected to a motor phase connection via an inverter , to which the motor phases of the motor are connected, an error check is carried out according to the invention as to whether there is an insulation fault in the drive circuit by directly detecting a fault current and / or at least one voltage within the drive circuit during a phase in which, in the case of a faultless drive circuit there is no current flow from the supply network to the DC link.

By directly detecting a fault current and / or at least a voltage within the drive circuit, fault currents can be recognized at short notice. If a fault current is detected, the drive circuit can preferably be switched to an operating mode in which the fault currents can also be reliably detected by the fault current circuit breaker (for example of type A) present, or the respective circuit breaker can be controlled by the drive circuit in order to drive the drive circuit disconnect from the supply network. The fault current detection according to the invention takes place very quickly, so that the drive circuit can be disconnected from the supply network within milliseconds, even at low cost Fault protection switches for example of type A can be made. The fault currents can be detected by various inexpensive fault current detection circuits that are integrated in the drive circuit.

The DC voltage intermediate circuit preferably has an intermediate circuit capacitor. The rectifier preferably has a rectifier bridge circuit, preferably with a plurality of rectifier diodes. The inverter preferably has an inverter bridge circuit, preferably with a plurality of power switches (e.g. MOSFETs or IGBTs with diodes connected in anti-parallel). In accordance with the connected EC motor, the inverter is preferably configured in multiple phases.

The invention is not limited to any particular type of engine. The electronically commutated motor can be, for example, a synchronous motor or asynchronous motor, an AC motor, a three-phase motor or the like.

In one embodiment of the invention, the drive circuit between the rectifier and the DC voltage intermediate circuit also has a power factor correction (PFC) filter in a step-up converter topology with a switch. In this case, the error check is preferably carried out when the switch of the PFC filter is closed / switched on, and a fault current is detected by measuring the fault current in a ground connection between the power factor correction filter and the DC link.

The PFC filter in the step-up converter topology can have, for example, a step-up converter with a switch or at least two step-up converters connected in parallel, each with a switch. In the case of the variant of a so-called interleaved PFC filter, the switches of all step-up converters are closed for error checking so that only the fault current flows via the ground connection between the PFC filter and the DC link.

In this embodiment, it can preferably also be recognized where the insulation fault is. In particular, in the case of a fault check in the case of a continuous course of the measured fault current, an insulation fault of the positive pole of the voltage intermediate circuit, in the case of a clocked profile of the measured fault current, an insulation fault of a motor phase of the motor phase connection or the motor, and / or in the case of a multi-stage clocked profile of the measured fault current, an insulation fault of a star point of the motor is detected.

In this embodiment, the measurement of the fault current when the switch is switched on can also preferably be calibrated by means of an additional test current source, which is connected, for example, to the current measuring resistor. This calibration preferably also takes place during a phase in which, in the case of a fault-free drive circuit, there is no current flow from the supply network to the DC voltage intermediate circuit.

In another embodiment of the invention, the drive circuit also has a power factor correction (PFC) filter with a switch between the rectifier and the DC voltage intermediate circuit, the error check being carried out when the power factor correction filter is switched off and at the same time an intermediate circuit voltage across the DC voltage intermediate circuit is greater than the mains voltage of the supply network, so that a current gap is generated in the current flow from the supply network to the DC voltage intermediate circuit. In this case, the detection of at least one voltage comprises detection of a voltage on a neutral conductor connected to the supply network, detection of a voltage on a phase conductor connected to the supply network, detection of the intermediate circuit voltage across the DC voltage intermediate circuit and / or detection of a voltage on a positive pole of the rectifier.

In the two aforementioned embodiments of the invention, when an insulation fault is detected, the switch of the power factor correction filter is preferably opened permanently (or in the case of the interleaved PFC filter, the multiple switches are all opened permanently). In this way, the drive circuit is switched to a passive operating mode in which an inexpensive type A residual current circuit breaker, which is usually used in building installations, can also detect the residual current and thus any insulation faults. Optionally, the two aforementioned embodiments can also be combined with one another in order to further increase the security of the residual current detection.

In another embodiment of the invention, the drive circuit does not have a power factor correction filter or is in passive operation. In this case, the detection of at least one voltage preferably has a detection of a voltage on a neutral conductor connected to the supply network, a detection of a voltage on a phase conductor connected to the supply network and / or a detection of an intermediate circuit voltage across the DC voltage intermediate circuit.

In this embodiment and also in the previous embodiments of the invention, when an insulation fault is detected, a circuit breaker between the AC connection of the drive circuit and the supply network can preferably be controlled by the drive circuit in order to separate the drive circuit or at least the DC link from the supply network. In this way, the safety in the event of insulation faults can be guaranteed regardless of the type of earth leakage circuit breaker used. The circuit breaker can preferably be a residual current circuit breaker (FL switch), a relay or a contactor.

The drive circuit according to the invention for driving an electronically commutated motor has a rectifier with an AC connection that can be connected to a supply network; an inverter with a motor phase connection to which the motor phases of the motor can be connected; a DC link between the rectifier and the inverter; a control device; and at least one fault current detection circuit connected to the control device for the direct detection of a fault current and / or at least one voltage within the drive circuit during a phase in which, in the case of a fault-free drive circuit, there is no current flow from the supply network to the DC voltage intermediate circuit.

With this drive circuit, the same advantages as with the method described above for operating a drive circuit can be achieved. Regarding the pre parts and design variants according to the invention is therefore additionally made to the above explanations in connection with the method according to the invention.

In one embodiment of the invention, a power factor correction (PFC) filter with a switch is connected between the rectifier and the DC voltage intermediate circuit in a step-up converter topology. In this case, the at least one residual current detection circuit preferably has a residual current detection circuit in a ground connection between the power factor correction filter and the DC voltage intermediate circuit; and the control device is preferably configured to close the switch of the power factor correction filter when a fault test is to be carried out with the fault current detection circuit and to measure the fault current with the fault current detection circuit.

The fault currents can be measured with different versions of current sensors, such as Hall probes or current measuring resistors. In a cost-effective embodiment, the fault current detection circuit mentioned preferably has a current measuring resistor in the ground connection between the power factor correction filter and the DC voltage intermediate circuit, so that the fault current measurement can be carried out, for example, using a voltage drop across this current measuring resistor.

In this embodiment, an additional test current source, which is connected to the current measuring resistor of the fault current detection circuit, is preferably provided for calibrating the measurement of the fault current.

In another embodiment of the invention, a power factor correction (PFC) filter with a switch is connected between the rectifier and the DC voltage intermediate circuit. In this case, the at least one residual current detection circuit preferably has a residual current detection circuit for detecting a voltage on a neutral conductor connected to the supply network, a residual current detection circuit for detecting a voltage on a phase conductor connected to the supply network, a residual current detection circuit for detecting an intermediate circuit voltage across the direct voltage intermediate circuit and / or a leakage current detection circuit for detecting a voltage at a positive pole of the rectifier; and the control device is preferably designed to carry out a fault check with the at least one fault current detection circuit when the power factor correction filter is switched off and the intermediate circuit voltage across the direct voltage intermediate circuit is greater than a mains voltage of the supply network, and to detect an insulation fault on the basis of the at least one detected voltage.

Optionally, the two aforementioned embodiments can also be combined with one another in order to further increase the security of the residual current detection.

In yet another embodiment of the invention, the drive circuit has no PFC filter or is in passive operation. In this case, the at least one residual current detection circuit preferably has a residual current detection circuit for detecting a voltage on a neutral conductor connected to the supply network, a residual current detection circuit for detecting a voltage on a phase conductor connected to the supply network and / or a residual current detection circuit for detecting an intermediate circuit voltage across the direct voltage intermediate circuit and the control device is preferably designed to detect an insulation fault on the basis of the at least one detected voltage.

Preferably, the control device can also be designed to control a circuit breaker (e.g. relay, contactor, etc.) connected to the AC connection when an insulation fault is detected in such a way that it disconnects the drive circuit or at least the intermediate voltage circuit from the supply network.

The above and other features and advantages of the invention can be better understood from the following description of preferred, non-limiting exemplary embodiments with reference to the accompanying drawing. They show, partly schematically:

Fig. 1 shows a first embodiment of a drive circuit according to the present

Invention; 2 shows diagrams to illustrate the time profile of a fault current in the event of an insulation fault at a positive pole of the DC link of the drive circuit from FIG. 1;

3 shows diagrams to illustrate the time course of a fault current in the event of an insulation fault in a motor phase of the drive circuit from FIG.

1 ;

4 shows diagrams to illustrate the time profile of a fault current in the event of an insulation fault at a star point of the DC motor of the drive circuit from FIG. 1;

5 shows diagrams to illustrate the time profile of a direct fault current measurement of the drive circuit from FIG. 1;

Fig. 6 diagrams to illustrate the time course of an exemplary

Calibration of the fault current measurement of the drive circuit of Fig. 1;

7 shows a variant according to the invention of the first embodiment of a drive circuit according to the present invention;

Fig. 8 shows a second embodiment of a drive circuit according to the present

Invention;

9 shows diagrams of the time profile of the detected voltages in the drive circuit of FIG. 8 without insulation faults, in operation with an active PFC filter and artificially generated current gap;

10 shows diagrams of the time profile of the detected voltages in the drive circuit of FIG. 8 with an insulation fault at a positive pole of the DC link, in operation with an active PFC filter and artificially generated current gap; Figure 1 1 shows a third embodiment of a drive circuit according to the present invention.

12 shows diagrams of the time profile of the detected voltages in the drive circuit of FIG. 11 without insulation faults; and

13 shows diagrams of the time profile of the detected voltages in the drive circuit from FIG. 11 with an insulation fault at a positive pole of the DC voltage intermediate circuit.

1 to 6, a first embodiment of a drive circuit for an electronically commutated motor and its fault current monitoring are first explained in more detail.

The drive circuit 10 serves to drive an electronic commutated motor 12. In the exemplary embodiment in FIG. 1, it is a three-phase brushless three-phase motor 12 with three motor phases U, V, W, which are connected to one another at a star point SP. The motor 12 is fed from a DC voltage intermediate circuit 14 via an inverter 16. The DC voltage intermediate circuit 14 has an intermediate circuit capacitor C1, and the inverter 16 has, in this exemplary embodiment, a three-phase inverter bridge circuit with a total of six power switches M1 to M6 (e.g. MOSFETs or IGBTs with antiparallel connected diodes) in its half bridges. The three motor phases U, V, W are connected to a motor phase connection 17, which is connected to the three center taps of the half bridges of the inverter 16.

On the input side, the DC voltage intermediate circuit 14 is connected to an AC connection 20 via a rectifier. In this exemplary embodiment, the rectifier 18 has a rectifier bridge circuit with a total of four rectifier diodes D7 to D10. Via the AC connection 20, the drive circuit 10 is connected to a phase conductor L and a neutral conductor N of a supply network 22. The supply network also has a protective earth PE. In this exemplary embodiment, an optional circuit breaker 24 is also connected between the supply network 22 and the AC connection 20 of the drive circuit 10 and can disconnect the drive circuit from the supply network 22 if required. The circuit breaker 24 is, for example, an F1 switch of type A. Alternatively, the circuit breaker 24 can consist of a relay or contactor, which is opened by the drive circuit 10 when an insulation fault R7a..c is detected, to drive circuit 10 or at least to separate the DC voltage intermediate circuit 14 from the supply network 22.

A power factor correction (PFC) filter 26 is also connected between the rectifier 18 and the DC voltage intermediate circuit 14. The PFC filter 26 is configured in a step-up converter topology and contains in particular an inductance L1, a switch M7 and a rectifier diode D1. The switch M7 is driven by a driver circuit 32.

The drive circuit 10 also has a control device 28. The control device (e.g. a microcontroller) 28 controls the power switches M1 to M6 of the inverter 16 via control signals Suvw. In addition, the control device 28 controls the driver circuit 32 via a control signal SA.

In the drive circuit 10 with active power factor correction (PFC) illustrated in FIG. 1, there are different types of insulation faults which lead to a non-gapless DC fault current or clocked fault current which may not be reliably detected by a type A FL switch can. These critical insulation faults relate to insulation faults at the positive pole of the DC link 14 (shown in FIG. 1 as an insulation fault with the resistor R7a), insulation faults in the motor phases U, V, W (shown in FIG. 1 as an insulation fault with the resistor R7b in FIG. 1 as an example) ) and insulation faults in the vicinity of the star point SP of the DC motor 12 (shown in FIG. 1 by way of example as insulation faults with the resistor R7c).

In order to recognize all of these insulation faults R7a, R7b, R7c, the drive circuit 10 has a fault current detection circuit 30. In this exemplary embodiment, this fault current detection circuit 30 contains a current measuring resistor R8 in the ground connection between the PFC filter 26 and the DC voltage intermediate circuit 14. A switch M8 is connected in parallel with this current measuring resistor R8 and is controlled by a driver circuit 34, which in turn is controlled by a control signal SB from the Control device 28 is controlled. The fault current detection circuit 30 detects a voltage drop across the current measuring resistor and passes this via a RC element with a resistor Ri and a capacitor Ci to the control device 28 as a fault current measuring signal SF.

2 to 6, it will now be described how the various insulation faults R7a, R7b, R7c can be detected with the aid of this fault current detection circuit 30. The diagrams in FIG. 2 illustrate an insulation fault R7a at the positive pole of the DC link 14, the diagrams in FIG. 3 illustrate an insulation fault R7b at the motor phase U, the diagrams in FIG. 4 illustrate an insulation fault R7c at the neutral point SP of the DC motor 12, and the 5 illustrates the fault current measurement.

Depending on the switching state of the switch M7 of the PFC filter 26, the fault current flows through the drive circuit 10 in various ways. If the switch M7 is switched off / open, the fault current flows via the diode D1. On the other hand, if the switch M7 is switched on / closed, the fault current flows via the switch M8 and the current measuring resistor R8 to the intermediate circuit capacitor C1. In order to be able to measure the fault current as a voltage drop across the current measuring resistor R8, the switch M7 must accordingly be switched on during the fault current measurement (cf. FIG. 5).

Since the path of the fault current is dependent on the half-wave of the mains voltage, the path of the fault current for the positive and negative half-wave of the mains voltage is considered separately as an example for an insulation fault R7a at the positive pole of the DC link 14.

During the positive half-wave of the mains voltage ULN, the diodes D7 and D10 of the rectifier 18 are conductive, as a result of which the neutral conductor N or the protective ground PE leads tend to be connected to the ground of the DC link 14. The fault current IR7 thus flows back to the intermediate circuit capacitor C1 via the resistor R7a, the mains voltage source 22, the diode D7, the inductance L1, the conductive switch M7 and the current measuring resistor R8. Since the diodes D7 and D10 and the switch M7 are simultaneously conductive, the mains voltage ULN and the voltage Uu across the inductor L1 are approximately the same. During the positive half-wave, the intermediate circuit voltage UHV is thus present across the resistor R7a. In contrast, during the negative half-wave of the mains voltage ULN, the diodes D8 and D9 of the rectifier 18 are conductive, so that the fault current IR ₇ flows back to the intermediate circuit capacitor C1 via the resistor R7, the diode D8, the inductance L1, the conductive switch M7 and the current measuring resistor R8. Since the diodes D8 and D9 and the switch M7 are simultaneously conductive, the mains voltage ULN and the voltage ULI across the inductor L1 are approximately the same size. During the negative half-wave, the difference between the intermediate circuit voltage UHV and the mains voltage ULN is thus present across the resistor R7a. Since the intermediate circuit voltage UHV is always greater than the mains voltage ULN, the voltage UHVPE across the resistor R7a is positive during the entire negative half-wave, the voltage UHVPE across the resistor R7a reaching its minimum at the negative maximum value -U _N etz.max of the mains voltage ULN ,

The curves in the case of an insulation fault R7a at the positive pole of the DC link 14 are shown by way of example in FIG. 2. Since the intermediate circuit voltage UHV is always greater than the instantaneous value of the line voltage ULN, the fault current IR7 flows in a positive direction over the entire period. During the positive half-wave, the negative pole of the DC link 14 is connected to the neutral conductor N or the protective ground PE via the diode D10. For this reason, the voltage UHVPE across the resistor R7a and thus also the fault current IR _{7 are} virtually constant during the positive half-wave. During the negative half-wave, protective earth PE is connected to the negative pole of DC link 14 via mains voltage source 22 and diode D9 of rectifier 18. Accordingly, the voltage UHVPE across the resistor R7a is the difference between the intermediate circuit voltage UHV and the mains voltage ULN. For this reason, the residual current IR _{7 reaches} its minimum at the negative maximum value of the mains voltage. The insulation fault R7a at the positive pole of the DC link 14 can always occur can be detected when the switch M7 is switched on, and the fault current IR ₇ can be detected and measured in the same way during the positive and negative half-wave of the mains voltage ULN.

The curves for an insulation fault R7b of the motor phase U are shown in FIG. 3. In the drive circuit 10 of FIG. 1, the motor phases U, V, W are clocked. A motor phase assumes either the voltage zero (negative pole of the direct voltage intermediate circuit 14) or the intermediate circuit voltage UHV (positive pole of the direct voltage intermediate circuit 14). During the positive half-wave, the negative pole of the DC voltage intermediate circuit 14 is connected to the neutral conductor N or PE via a diode of the rectifier 18. For this reason, the voltage UHVPE across the resistor R7b and thus also the fault current l _R7 during the positive half-wave are either zero (motor phase off) or as large as in the case of an insulation fault on the DC link (motor phase on). During the negative half-wave, protective earth PE is connected to the negative pole of DC link 14 via the mains voltage and a diode of rectifier 18. Accordingly, the voltage UHVPE across the resistor R7b is equal to the difference between the intermediate circuit voltage UHV and the mains voltage ULN. For this reason, the fault current I _R7 only flows in the positive direction during the negative half-wave when the faulty motor phase is switched on and thus assumes the potential of the DC link 14. Only in this case is the difference between the intermediate circuit voltage UHV and the mains voltage ULN always positive. Accordingly, the fault current IR ₇ when the motor phase is switched on is just as large in the negative half-wave as in the case of an insulation fault on the DC link. The insulation fault R7b of a motor phase U, V, W can only be detected if the faulty motor phase is at 1 (potential of the DC link) and switch M7 is switched on at the same time, the fault current IR ₇ during the positive and negative half-wave being the same Way can be recognized.

In contrast to the positive half-wave, a fault current IR _{7 also flows} through the resistor R7b in the negative half-wave when the motor phase U is at 0. However, the direction of flow of the fault current IR ₇ via the current measuring resistor R8 is only positive when the motor phase U is switched on, which is why the fault current IR ₇ can only be measured with the analog-to-digital converter of the control device 28 when the motor phase U is open 1 is. The curves for an insulation fault R7c at the star point SP of the DC motor 12 are shown in FIG. 4. By clocking the three motor phases U, V, W, the voltage USPPE between the star point SP and the protective earth PE and thus also the fault current IR7 assume three different levels. In the positive half-wave of the mains voltage ULN, the fault current IR7 is always greater than or equal to zero. The largest value of the fault current IR7 occurs when all three motor phases U, V, W are switched on at the same time. In the negative half-wave of the mains voltage ULN, the fault current IR7 only flows in the positive direction if all three motor phases U, V, W are switched on at the same time. Only in this case is the voltage USPPE from the star point SP to the protective earth PE always positive. The insulation fault R7c at the star point SP of the DC motor 12 can only be detected in the positive half-wave of the mains voltage ULN if at least one motor phase is at 1 (potential of the DC voltage intermediate circuit) and the switch M7 is switched on at the same time. However, the level of the measured fault current IR7 is only one third (with only one motor phase to 1) or two thirds (with two motor phases to 1) of the maximum fault current, which is measured when all three motor phases U, V, W simultaneously at 1 are. In the negative half-wave of the mains voltage ULN, the fault current IR7 can only be recognized if all motor phases are at 1 (potential of the DC link) and switch M7 is switched on at the same time. Only in this switching state is the voltage from the star point SP to the protective earth PE always positive. In the negative half-wave, a fault current IR7 flows through the current measuring resistor R8 even if only one or two motor phases are at 1 at the same time; however, in these cases, this fault current IR7 flows temporarily with a negative flow direction and therefore cannot be measured by the analog-digital converter of the control device 28.

The curves of the fault current measurement for the insulation faults R7a..c described above of the drive circuit of FIG. 1 are shown in FIG. 5. While the switch M7 is switched on (control signal SA of the driver circuit 32 to 1), the fault current IR7 flows via the current measuring resistor R8 to the negative pole of the intermediate circuit capacitor C1. The fault current IR ₇ can thus be measured as a voltage drop across the current measuring resistor R8 during this time and as a fault current measuring signal SF Control device 28 are directed. To measure the fault current IR ₇ , it is also necessary that the switch M8 of the fault current detection circuit 30 is switched off during the current measurement (control signal SB of the driver circuit 34 to 0), since the fault current IR7 would otherwise flow via the switch M8 and not via the current measuring resistor R8 , The voltage drop across the current measuring resistor R8, which is directly proportional to the fault current IR7, is filtered with an RC element and recorded with an analog-digital converter of the control device 28.

If the fault current IR ₇ exceeds a predetermined maximum value, the switch M7 is permanently switched off / opened by the control device 28 via the driver circuit 32. The drive circuit 10 thus goes into passive operation, in which the intermediate circuit capacitor C1 is only charged via the diode D1 when the instantaneous value of the mains voltage ULN exceeds the intermediate circuit voltage UHV. In the event of an insulation fault R7a..c, this results in a gaping fault current IR ₇ , which is also recognized by a type A fault current circuit breaker 24.

Alternatively, the control device 28 could, in the event of detection of an insulation fault R7a..c in the manner described above, directly control a circuit breaker 24 in the embodiment of a relay or contactor between the AC voltage connection 20 of the drive circuit 10 and the supply network 22 so that it controls the drive circuit 10 or at least the DC voltage intermediate circuit 14 separates from the supply network 22.

As shown in FIG. 1, the drive circuit 10 of this exemplary embodiment preferably also has a test current source 36 which is connected to the current measuring resistor R8 of the residual current detection circuit 30. The test current source 36 can be controlled by the control device 28 with a control signal SC in order to calibrate the fault current measurement described above with the fault current detection circuit 30.

The curve profiles of such a residual current calibration are shown in FIG. 6. With this exemplary residual current calibration, a zero point adjustment of the residual current measurement is carried out. For this purpose, the test current source 36 can be switched on a precise direct current is impressed into the residual current detection circuit 30. At the time of the fault current calibration, the switch M8 of the fault current detection circuit 30 must be switched off (control signal SB of the driver circuit 34 to 0) so that the direct current provided by the test current source 36 flows through the current measuring resistor R8. In addition, the PFC switch M7 must be switched on (control signal SA of the driver circuit 32 to 1) so that the useful current does not flow through the current measuring resistor R8. The impressed direct current, which is switched on by the control device 28 via the control signal SC, leads to a defined voltage drop across the current measuring resistor R8, which is used for the zero point adjustment of the residual current measurement or the residual current measurement signal SF.

FIG. 7 shows a variant according to the invention of the first embodiment of a drive circuit from FIG. 1. The same components and the same parameters are each provided with the same reference symbols as in the first embodiment.

The drive circuit 10 of FIG. 7 differs from the drive circuit 10 of FIG. 1 in particular in the design of the PFC filter 26. As in the embodiment of FIG. 1, the PFC filter 26 is also high in this embodiment variant - Configurator topology designed. In contrast to the PFC filter 26 with a step-up converter shown in FIG. 1, an interleaved PFC filter 26 with two step-up converters connected in parallel is provided in the variant of FIG. 7. The first step-up converter contains an inductor L1 a, a switch M7a and a rectifier diode D1 a and is driven by a first driver circuit 32a. The second step-up converter contains an inductor L1 b, a switch M7b and a rectifier diode D1 b and is driven by a second driver circuit 32b. The two driver circuits 32a, 32b are controlled by the control device 28 via control signals SAa, SAb.

The fault current detection circuit 30 and the fault test for insulation faults R7a, R7b, R7c correspond to those of the embodiment of FIG. 1, the switches M7a, M7b of all step-up converters of the PFC filter 26 having to be switched on in order to carry out the fault test, so that the fault current through the current measuring resistor R8 the leakage current detection circuit 30 flows. For the rest, the embodiment variant of the drive circuit shown in FIG. 7 corresponds to the first exemplary embodiment from FIGS. 1 to 6.

8 to 10, a second embodiment of a drive circuit for an electronically commutated motor and its fault current monitoring will now be explained in more detail. The same components and the same parameters are each provided with the same reference numerals as in the first exemplary embodiment.

As in the first exemplary embodiment, this drive circuit 10 also contains a PFC filter 26 between the rectifier 18 and the DC voltage intermediate circuit 14. The drive circuit 10 of FIG. 8 differs from that of the first exemplary embodiment in particular by the type of fault current detection circuit (s). Instead of the fault current detection circuit 30 with the current measuring resistor R8 in the ground connection between the PFC filter 26 and the DC voltage intermediate circuit 14, with which the fault current I _{R7 is} measured directly within the drive circuit 10, there are a plurality of fault current detection circuits 38a in the drive circuit 10 of the second exemplary embodiment. .d for the direct detection of a voltage within the drive circuit 10, on the basis of which an insulation fault R7a..c can be detected.

In the exemplary embodiment in FIG. 8, there are a first residual current detection circuit 38a for detecting the voltage UN on the neutral conductor N, a second residual current detection circuit 38b for detecting the voltage UL on the phase conductor L, a third residual current detection circuit 38c for detecting the intermediate circuit voltage UHV via the direct voltage intermediate circuit 14 and a fourth residual current detection circuit 38d is provided for detecting the voltage UPFC at the positive pole of the rectifier 18. All four residual current detection circuits 38a .. d are preferably provided in order to increase the security when detecting an insulation fault R7a..c, but optionally only one, two or three of these residual current detection circuits 38a .. d can also be used.

To detect an insulation fault R7a..c, the voltages UN,

UL, UHV and UPFC divided down by means of voltage dividers in order to then the divided down voltages in the control device 28 with the aid of analog-to-digital converters processed. As shown in FIG. 8, the first fault current detection circuit 38a contains a voltage divider R1, R2 between the neutral conductor N and the ground connection GND, the second fault current detection circuit 38b contains a voltage divider R3, R4 between the phase conductor L and the ground connection GND, the third fault current detection circuit 38c a voltage divider R5, R6 between the positive pole of the DC voltage intermediate circuit 14 and the ground connection GND, and the fourth fault current detection circuit 38d contains a voltage divider R9, R10 between the positive pole of the rectifier 18 and the ground connection GND.

In this exemplary embodiment, insulation faults R7a..c can be detected in operation with an active PFC filter 26 by generating an artificial current gap in the mains current i _N e _t z from the supply network 22 to the DC voltage intermediate circuit 14.

The control device 28 uses the control signal SA to the driver circuit 32 (not shown in FIG. 8) with the active PFC filter 26 to ensure that the PFC filter 26 in a phase in which the intermediate circuit voltage UHV across the direct voltage intermediate circuit is greater than that Mains voltage ULN of the supply network 22 and therefore there is no recharging current from the supply network, is temporarily switched off, so that the mains current I _N _t z temporarily becomes zero (see FIGS. 9 and 10).

In the fault-free state of the driving circuit without insulation fault R7a..c the diodes D7 to D10 of the rectifier 18 are conductive only when the AC current I _N etwork equal to zero. During the positive half wave of the mains voltage ULN are not in other gaps the AC power l _ne t the diodes D7 and D10 conducting conducting and during the negative half-cycle, the diodes D8 and D9. Accordingly, the voltage UL on the phase conductor L is equal to the mains voltage during the positive half-wave of the mains voltage ULN and zero during the negative half-wave of the mains voltage ULN. Analogously, the voltage UN on the neutral conductor N is equal to zero during the positive half-wave of the mains voltage ULN and during the negative half-wave of the mains voltage ULN is equal to the mains voltage. In the phases when the mains current I _{N has} a current gap, both the voltage UL on the phase conductor L and the voltage UN on the neutral conductor N are zero. In addition, the voltage UPFC at the positive pole of the bridge rectifier 18 takes the value of the voltage UL at the phase conductor L in the positive half-wave of the line voltage ULN and the voltage UN at in the negative half-wave of the line voltage ULN Neutral conductor N on. The curve profiles described for the fault-free state of the drive circuit 10 are illustrated in FIG. 9.

The curve profiles for the case of an insulation fault R7a at the positive pole of the direct voltage intermediate circuit are illustrated in FIG. 10. During a current gap in the mains current i _N e _t z, the diode D7 is permanently conductive during the positive half-wave of the mains voltage ULN, so that the voltage UL at the phase conductor L is equal to the intermediate circuit voltage UHV during this time. If the line current l _Ne tz is not equal to zero, the diode D10 of the rectifier 18 also conducts in the positive half-wave of the line voltage ULN in addition to the diode D7, which is why the line voltage ULN is present at the phase conductor L during this time. If the mains current l _N e _t z in the negative half-wave of the mains voltage ULN is not equal to zero, the diode D9 conducts and the voltage UL on the phase conductor L becomes zero. When the mains current l _Net z then has a current gap again, the diode D9 blocks and the voltage UL on the phase conductor L again assumes the intermediate circuit voltage UHV. Similarly, it is with the voltage UN at the neutral wire N. When the AC current I _N etwork a current gap, with the voltage UN participates in the neutral conductor N of the intermediate circuit voltage UHV. If the mains current l _Net z is then not equal to zero, the voltage UN at the neutral conductor N becomes zero because of the conductive diode D10. In the negative half-wave of the mains voltage ULN, the neutral conductor N is connected to the DC voltage intermediate circuit 14 via the resistor R7a. Accordingly, the voltage UN of the neutral conductor N in the current gap of the mains current I _Net z assumes the intermediate circuit voltage UHV. If the mains current l _N e _t z is not equal to zero, the diode D9 becomes conductive and the neutral conductor N is connected to ground GND via the supply network 22. Accordingly, the negative mains voltage -ULN is present at the neutral conductor N during this time. If the mains current l _Ne tz then has a current gap again, the diode D9 blocks and the voltage U _N at the neutral conductor N again assumes the intermediate circuit voltage UHV. In addition, during a current gap in the line current l _N e _t z in the positive half-wave of the line voltage ULN, the diode D7 and in the negative half-wave the diode D8 is conductive, so that the voltage UPFC at the positive pole of the rectifier 18 in the positive half-wave is equal to the voltage UL am Phase conductor L and in the negative half-wave of the mains voltage ULN is equal to the voltage UN at the neutral conductor N. Depending on whether there is an insulation fault R7a..c or not, the voltages UL, UN and UPFC assume different courses during the current gaps in the mains current iNetz. These differences in the voltage curves can be evaluated by the control means 28 while the current gaps in the line current I _N etwork in the active operation of the drive circuit 10 is an insulation fault R7a to detect.

Analogously to the first exemplary embodiment, when an insulation fault R7a..c is detected, the switch M7 can be switched off permanently by the control device 28 via the driver circuit 32, so that the drive circuit 10 changes to passive operation, in which the insulation fault R7a..c also, for example, from a type A residual current circuit breaker 24 can be detected. Alternatively, the control device 28 could, in the event of detection of an insulation fault R7a..c in the manner described above, directly control a circuit breaker 24 in the embodiment of a relay or contactor between the AC voltage connection 20 of the drive circuit 10 and the supply network 22 so that it controls the drive circuit 10 or at least the voltage intermediate circuit 14 separates from the supply network 22.

With reference to FIGS. 1 1 to 13, a third embodiment of a drive circuit for an electronically commutated motor and its fault current monitoring will now be explained in more detail. The same components and the same parameters are each provided with the same reference numerals as in the first and second exemplary embodiments.

The drive circuit 10 of FIG. 11 differs from that of the second exemplary embodiment in particular in that no PFC filter 26 is provided. As in the second exemplary embodiment, a plurality of fault current detection circuits 38a .. c are provided for directly detecting a voltage within the drive circuit 10, on the basis of which an insulation fault R7a..c can be detected. In particular, a first fault current detection circuit 38a with a voltage divider R1, R2 for detecting the voltage U _N on the neutral conductor N, a second fault current detection circuit 38b with a voltage divider R3, R4 for detecting the voltage UL on the phase conductor L and a third fault current detection circuit 38c with a voltage divider R5, R6 for detecting the intermediate circuit voltage UHV over the DC voltage intermediate leg 14 provided. All three residual current detection circuits 38a .. c are preferably provided in order to increase the security in detecting an insulation fault R7a..c, but optionally only one or two of these residual current detection circuits 38a .. c can also be used.

Without the PFC filter 26 or in passive operation, the intermediate circuit capacitor C1 is only charged when the instantaneous value of the line voltage ULN exceeds the intermediate circuit voltage UHV. Accordingly, a mains current INetz flows from the supply network 22 to the DC link 14 only when the instantaneous value of the line voltage ULN exceeds the DC link voltage UHV. In the de-energized phases of the mains current, none of the diodes D7 to D10 of the rectifier 18 is conductive, as a result of which the voltages UL on the phase conductor L and UN on the neutral conductor N against ground GND assume sinusoidal curves in the fault-free state of the drive circuit 10, the amplitudes of which occur when the mains current I _{N occurs} are kept at the intermediate circuit voltage UHV or GND by the conductive diodes (cf. FIG. 12).

In the case of an insulation fault R7a, FIG. 13 shows how this can be detected via the changed profile of the voltages UL on the phase conductor and UN on the neutral conductor N. In the positive half-wave of the mains voltage ULN, in the event of an insulation fault R7a at the positive pole of the DC link 14, the diode D7 of the rectifier 18 is polarized, which is why the voltage UL at the phase conductor L assumes the DC link voltage UHV. In the negative half-wave, all diodes D7 to D10 of the rectifier 18 block, as a result of which the voltage UN on the neutral conductor N assumes the intermediate circuit voltage UHV through the connection via the resistor R7a to the direct voltage intermediate circuit 14.

Thus, during the time in which the mains current is zero, the course of the voltages UL, UN can be used to determine whether there is an insulation fault R7a..c. In the event of detection of an insulation fault R7a..c in the manner described above, the control device 28 can also directly control a circuit breaker in the embodiment of a relay or contactor between the AC voltage connection 20 of the drive circuit 10 and the supply network 22 in such a way that it controls the drive circuit 10 or at least separates the voltage intermediate circuit 14 from the supply network 22. The drive circuit 10 of FIG. 11 without a PFC filter 26 is synonymous with a drive circuit 10 in passive operation. The detection of an insulation fault R7a..c described with reference to FIGS. 1 1 to 13 can therefore also be used in the passive operation of a drive circuit 10 with a PFC filter 26 and can also represent an extension of the fault current measurement in active operation. After fault current detection and the associated change from active to passive operation, it can thus be checked whether the insulation fault R7a.c is still present.

REFERENCE NUMBER LIST

10 drive circuit

12 engine

14 DC link

16 inverters

17 Motor phase connection

18 rectifiers, in particular bridge rectifiers

20 AC connection

22 supply network

24 circuit breakers

26 Power factor correction (PFC) filter

28 control device

30 residual current detection circuit

32 driver circuit for M7

32a, b driver circuits for M7a, M7b

34 Driver circuit for M8

36 test power source

38a .. d residual current detection circuits

C1 intermediate circuit capacitor from 14

D1 rectifier diode

D1 a, b rectifier diodes

D7 - D10 rectifier diodes from 18

L1 inductance of 26

L1 a, b inductors of 26

M1 - M6 circuit breakers from 16

M7 switch of 26

M7a, b switch of 26

M8 switch of 30

R7a..c insulation fault resistors

R8 current measuring resistor of 30 R1, R2 voltage divider for UN

R3, R4 voltage divider for UL

R5, R6 voltage divider for UHV

R9, R10 voltage divider for UPFC

Ri, Ci RC link of 30

SP star point of 12

U, V, W phases of 12, 16

L, N phase conductor and neutral conductor

PE protective earth

GND ground connection

SA control signal at driver circuit 32

SAa control signal at driver circuit 32a

SAb control signal at driver circuit 32b

SB control signal at driver circuit 34

SC control signal at test current source 36

SF fault current measurement signal of 30

SFI control signal at circuit breaker 24

Suvw control signal to inverter 16 iNetwork power from the supply network

IR7 insulation fault current

UHV intermediate circuit voltage

UHVPE voltage via insulation fault resistor R7a

UL voltage on phase conductor L

ULI voltage across inductor L1

ULN voltage between the line conductors L and N

UN voltage at neutral conductor N

V Mains mains voltage

UpFC voltage at the positive pole of the rectifier 18

UsPPE voltage between star point SP and protective earth PE

UuPE Voltage between motor phase U and protective earth PE

Claims

1. A method of operating a drive circuit (10) for driving an electronically commutated motor (12), wherein

the drive circuit (10) has a DC voltage intermediate circuit (14) which is connected on the input side via a rectifier (18) to an AC connection (20) which is connected to a supply network (22), and on the output side via an inverter (16) with a motor phase connection (17), to which the motor phases (U, V, W) of the motor (12) are connected,

characterized in that

an error check whether there is an insulation fault (R7a..c) of the drive circuit (10) by directly detecting a fault current (IR ₇ ) and / or at least a voltage (UL, UN, UHV, UPFC) within the drive circuit (10) occurs during a phase in which, in the case of a fault-free drive circuit, there is no current flow from the supply network (22) to the DC voltage intermediate circuit (14).

2. The method of claim 1, wherein

the drive circuit (10) between the rectifier (18) and the DC voltage intermediate circuit (14) furthermore has a power factor correction filter (26) configured in a step-up converter topology with a switch (M7; M7a, M7b), and the error check is carried out when the switch (M7 ; M7a, M7b) of the power factor correction filter (26) is closed,

wherein the detection of a fault current (IRZ) is carried out by measuring the fault current (IR7) in a ground connection (R8) between the power factor correction filter (26) and the DC voltage intermediate circuit (14).

3. The method of claim 2, wherein

in error checking - in the case of a continuous profile of the measured fault current (IRZ), an insulation fault (R7a) of the positive pole of the DC link (14) is detected,

- In the case of a clocked course of the measured fault current (IR), an insulation fault (R7b) of a motor phase (U, V, W) of the motor phase connection (17) or of the DC motor (12) is detected, and / or

- In the case of a multistage clocked course of the measured fault current (IR7), an insulation fault (R7c) of a star point (SP) of the DC motor (12) is detected.

4. The method according to claim 2 or 3, in which

the measurement of the fault current (IR ₇ ) with the switch (M7; M7a, M7b) switched on is calibrated by means of an additional test current source (36).

5. The method of claim 1, wherein

the drive circuit (10) between the rectifier (18) and the DC voltage intermediate circuit (14) further comprises a power factor correction filter (26) with a switch (M7), and

the error check is carried out when the power factor correction filter (26) is switched off and an intermediate circuit voltage (UHV) across the direct voltage intermediate circuit (14) is greater than a mains voltage of the supply network (22), the detection of at least one voltage being a detection of a voltage (UN) on a neutral conductor (N) connected to the supply network (22), detecting a voltage (UL) on a phase conductor (L) connected to the supply network (22), detecting the intermediate circuit voltage (UHV) via the direct voltage intermediate circuit (14) and / or a detection of a voltage (UPFC) at a positive pole of the rectifier (18).

6. The method according to any one of claims 2 to 5, in which

upon detection of an insulation fault (R7a..c) the switch (M7; M7a, M7b) of the power factor correction filter (26) is permanently opened.

7. The method of claim 1, wherein detecting at least one voltage, detecting a voltage (UN) on a neutral conductor (N) connected to the supply network (22), detecting a voltage (UL) on a phase conductor (L) connected to the supply network (22) and / or a Detection of an intermediate circuit voltage (UHV) across the DC intermediate circuit (14).

8. The method according to any one of claims 1 to 7, in which

upon detection of an insulation fault (R7a..c), a circuit breaker (24) between the AC connection (20) of the drive circuit (10) and the supply network (22) is controlled, around the drive circuit (10) or at least the DC voltage intermediate circuit (14) from the supply network (22) to separate.

9. Drive circuit (10) for driving an electronically commutated motor (12), comprising:

a rectifier (18) with an AC connection (20) which can be connected to a supply network (22);

an inverter (16) with a motor phase connection (17) to which the motor phases (U, V, W) of the motor (12) can be connected;

a DC link (14) between the rectifier (18) and the inverter; and

a control device (28),

marked by

at least one fault current detection circuit (30, 38a .. d) connected to the control device (28) for the direct detection of a fault current (IR ₇ ) and / or at least one voltage (UL, UN, UHV, UPFC) within the drive circuit (10) during a Phase in which, in the case of a fault-free drive circuit, there is no current flow from the supply network (22) to the DC link (14).

10. Drive circuit according to claim 9, wherein

a power factor correction filter (26) with a switch (M7; M7a, M7b), configured in a step-up converter topology, is connected between the rectifier (18) and the DC voltage intermediate circuit (14); the at least one residual current detection circuit (30, 38a .. d) has a residual current detection circuit (30) in a ground connection between the power factor correction filter (26) and the DC voltage intermediate circuit (14); and

the control device (28) is designed to close the switch (M7; M7a, M7b) of the power factor correction filter (26) when a fault check is to be carried out with the fault current detection circuit (30), and with the fault current detection circuit (30) the fault current (IR7 ) To eat.

1 1. Drive circuit according to claim 10, which

furthermore has an additional test current source (36), which is connected to the fault current detection circuit (30), for calibrating the measurement of the fault current (IR7).

12. Drive circuit according to claim 9, wherein

a power factor correction filter (26) with a switch (M7) is connected between the rectifier (18) and the DC voltage intermediate circuit (14);

the at least one residual current detection circuit (30, 38a .. d) a residual current detection circuit (38a) for detecting a voltage (UN) on a neutral conductor (N) connected to the supply network (22), a residual current detection circuit (38b) for detecting a voltage (UL) on a phase conductor (L) connected to the supply network (22), a residual current detection circuit (38c) for detecting an intermediate circuit voltage (UHV) across the direct voltage intermediate circuit (14) and / or a residual current detection circuit (38d) for detecting a voltage (UPFC) at a positive pole the rectifier (18); and

the control device (28) is designed to carry out a fault check with the at least one fault current detection circuit (38a .. d) when the power factor correction filter (26) is switched off and the intermediate circuit voltage (UHV) across the direct voltage intermediate circuit (14) is greater than a mains voltage of the supply network (22), and to detect an insulation fault (R7a..c) based on the at least one detected voltage (UL, UN, UHV, UPFC).

13. Drive circuit according to claim 9, wherein the at least one residual current detection circuit (30, 38a .. d) a residual current detection circuit (38a) for detecting a voltage (UN) on a neutral conductor (N) connected to the supply network (22), a residual current detection circuit (38b) for detecting a voltage (UL) on a phase conductor (L) connected to the supply network (22) and / or a fault current detection circuit (38c) for detecting an intermediate circuit voltage (UHV) across the direct voltage intermediate circuit (14); and

the control device (28) is designed to detect an insulation fault (R7a..c) based on the at least one detected voltage (UL, UN, UHV).

14. Drive circuit according to one of claims 9 to 13, in which

the control device (28) is designed to control a circuit breaker (24) connected to the AC connection (20) when an insulation fault (R7a..c) is detected in such a way that it controls the drive circuit (10) or at least the DC voltage intermediate circuit (14) disconnects from the supply network (22).