Current rectifier circuit and current rectifier

Description

[0001] The invention relates to a power converter circuit, an inverter and other devices and methods.

[0002] US 8 618 753 B2 discloses an inverter in which a measuring shunt is arranged in each phase branch.

[0003] JP 6 398 704 B2 and US 8 947 838 B2 each disclose an inverter in which a Y capacitor is connected in parallel to an intermediate circuit capacitor.

[0004] EP 3 631 927 A1 discloses a remote power supply unit for providing direct current to a remote power receiver in a direct current system. A residual current protection circuit comprises a first switch that opens a positive voltage rail and a second switch that opens a negative voltage rail. A first current sensor measures a first residual current between the first switch and the remote power receiver while the first switch is closed and the second switch is open. A second current sensor measures a second residual current between the second switch and the remote power receiver while the second switch is closed and the first switch is open. A controller detects a residual current event when the first residual current or the second residual current is above a residual current threshold.

[0005] DE 11 2014 002 853 T5 discloses an insulation detector for precisely detecting or measuring an insulation resistance of a load or a device with respect to a housing or ground with a simple structure.

[0006] EP 3 165 491 A1 discloses an elevator system and a method for monitoring electrical safety in an elevator system. A monitoring circuit is configured to detect a ground fault in the main circuit.

[0007] CN 1 332 211 C discloses a method for detecting earth faults in a DC power supply system and a detection circuit.

[0008] US 2001 / 0 048 310 A1 discloses a circuit that detects motor insulation deterioration by measuring a common-mode leakage current in the ground wire. A small current transformer detects the common-mode leakage current flowing in the ground wire of the motor control circuit. From the measured current, a pulse-width modulated signal with a duty cycle that varies depending on the magnitude of the common-mode leakage current is generated via several intermediate stations. This output signal is input directly to a microcontroller or a digital signal processor to calculate and determine the extent of motor insulation deterioration.

[0009] It is the object of the invention to propose measures to improve the measurability of small fault currents in circuits supplied by power converters.

[0010] The problem is solved by the subject matter of the independent claims. Preferred developments are the subject matter of the dependent claims.

[0011] The invention provides a power converter circuit for an inverter, wherein the power converter circuit has a current measuring circuit described below and at least one switching device, wherein the switching device is connected between the supply rails and has an electrical output.

[0012] The current measuring circuit comprises a positive supply rail, a negative supply rail, a reference potential rail and a current measuring device, wherein the current measuring device is connected to each supply rail and to the reference potential rail and is designed to measure an electrical fault current between one of the supply rails and the reference potential rail.

[0013] It is preferred that the current measuring device contains at least one current measuring arrangement which is connected either to the positive or to the negative supply rail and to the reference potential rail, wherein the current measuring arrangement contains a current sensor and a measuring capacitor connected in series therewith.

[0014] It is preferred that the current sensor is connected to one of the supply rails and to the measuring capacitor, wherein the measuring capacitor is connected to the current sensor and to the reference potential rail.

[0015] It is preferred that the current measuring device comprises a first current measuring arrangement and a second current measuring arrangement, wherein the first current measuring arrangement is connected to the positive supply rail and the second current measuring arrangement is connected to the negative supply rail or vice versa, wherein each current measuring arrangement is connected to the reference potential rail and comprises a current sensor and a measuring capacitor connected in series therewith.

[0016] It is preferred that the measuring capacitor is configured as a Y capacitor.

[0017] It is preferred that the current measuring device includes a comparator which is designed and connected to detect an overcurrent through the current measuring arrangement.

[0018] It is preferred that the current measuring device contains a comparator for each current sensor, wherein a comparator is connected to each current sensor.

[0019] It is preferred that the current measuring device includes a circuit for measuring the current value, preferably an A / D converter, which is connected to convert an analogue fault current flowing through the current measuring arrangement into a digital fault current signal which is indicative of the magnitude of the fault current.

[0020] Preferably, the current measuring circuit comprises an intermediate circuit capacitor connected between the positive and negative supply rails.

[0021] It is preferred that the intermediate circuit capacitor is effectively connected in series with the current measuring device or each current measuring arrangement.

[0022] It is preferred that the intermediate circuit capacitor is arranged closer to the switching device than any current measuring arrangement.

[0023] The invention provides an inverter comprising a preferred power converter circuit.

[0024] The invention provides a current measuring method for detecting a fault current generated due to an insulation fault in a circuit connected to a power converter by measuring a current flowing through a capacitor connected between a supply rail of the power converter and a reference potential rail of the power converter during a switching operation of the power converter, wherein an insulation fault is assumed if a current flow through the measuring capacitor is measured during the switching operation which exceeds a predetermined threshold value.

[0025] The power converter is configured as an inverter, wherein the current flowing through the measuring capacitor is measured during the positive half-wave and / or during the negative half-wave, wherein an insulation fault is assumed if, during one of the switching operations, a current flow through the measuring capacitor is measured which exceeds a predetermined threshold value.

[0026] The invention was made in the technical field of power electronic systems. Their product safety and fault detection capability play a central role. Applications in the electrification of aircraft powertrains, in particular, require reliable fault detection.

[0027] One fault mechanism is the so-called AC fault, in which, for example, one phase of a multiphase inverter or motor suffers an insulation fault, which can lead to a malfunction of the drive train or the entire system. These systems are therefore designed to be as fail-safe as possible.

[0028] According to the ideas presented here, a new method for AC fault detection is proposed which is easier to implement and more reliable.

[0029] Currently known methods are essentially based on measuring the current on each phase of the inverter / motor and calculating the sum of all three phases. The result of this summation should be close to zero in a symmetrical AC system.

[0030] One difficulty is that the load currents can often be orders of magnitude higher than the fault currents that can arise due to asymmetries caused by insulation faults. Therefore, it has so far been difficult to detect small deviations that could indicate an incipient insulation problem.

[0031] To monitor for insulation deterioration, separate insulation monitoring systems are typically used. Since these systems are designed to be as insensitive to mains noise as possible, they usually have a long time constant. The response time is therefore comparatively slow, even in the case of higher fault currents.

[0032] Another limitation is that the insulation monitoring systems mentioned can currently only be applied to symmetrical systems.

[0033] The ideas presented here enable faster and more reliable AC fault detection. Furthermore, implementation is simpler. The proposals can be used in virtually any AC system to detect insulation faults in the phase branches. The detection circuit is also simpler than with conventional methods.

[0034] In common measurement methods (e.g., symmetrical three-phase systems), the currents in all three phases L1, L2, and L3 are measured separately (for feedback). The sum IL = IL1 + IL2 + IL3 of all currents in the phase branches is then calculated. In an ideal symmetrical system, IL = 0 if no insulation fault occurs. In the case of an AC fault, IL ≠ 0.

[0035] In real-world applications, IL ranges from a few milliamperes up to nominal current values, so detecting small values ​​can be difficult if the measurement is designed for normal operating points. Furthermore, most systems are not 100% symmetrical.

[0036] Instead, a different method is proposed that does not use the sum of the phase currents for detection. Instead, an additional current sensor—e.g., a shunt resistor—is connected in series with a Y capacitor. In ideal operation, the current through the Y capacitor is zero. However, if an AC fault occurs, the system becomes unbalanced, and a current flows through the Y capacitor back into the DC link capacitor.

[0037] This current can be detected by a current sensor (e.g. shunt resistor) and used as a reference for fault detection.

[0038] The current is measured within a narrow range, allowing it to be measured more accurately than before. The current measurement is based on a non-floating (DC) potential. A simple comparator circuit can be used.

[0039] Alternatively or additionally, an A / D converter (ADC) can also be used for the measurement.

[0040] Examples of embodiments are explained in more detail below using the attached schematic drawings. They show: Fig. 1 an example of a circuit with an AC fault.

[0041] It is referred to below Fig. 1Referring to FIG. 1, which shows an embodiment of an electrical circuit 10, the electrical circuit 10 includes a supply 12 that includes a voltage source 14. The voltage source 14 is preferably a DC voltage source. The supply 12 provides a positive supply rail 16, a negative supply rail 18, and a reference potential rail 20. The reference potential rail 20 is at a reference potential. The reference potential can be ground. The reference potential is preferably midway between the potentials of the positive and negative supply rails 16, 18.

[0042] Furthermore, the supply 12 may include an output capacitor 22. The output capacitor 22 is connected between the positive supply rail 16 and the negative supply rail 18.

[0043] The supply 12 can have a capacitance 24 between its lines and a housing connected to reference potential. The capacitance 24 is modeled here as a capacitor. The capacitance 24 can—but does not have to—be designed as a component of the supply. The supply 12 is shown here merely to better explain its functionality and can have a variety of designs that are known as such.

[0044] The circuit 10 comprises an inverter 26. The inverter 26 contains at least one phase branch 28 with a switching device 30. The switching device 30 comprises two power switches that can be operated in push-pull mode: a first power switch 31 and a second power switch 32. The switching device 30 further comprises an output busbar 34. The output busbar 34 is arranged between the two power switches 32.

[0045] The inverter 26 further includes an intermediate circuit capacitor 36 which is connected between the positive supply rail 16 and the negative supply rail 18 and is preferably arranged near or immediately adjacent to the switching device 30.

[0046] The inverter 26 also includes a current measuring circuit 38. The current measuring circuit 38 is connected to the two supply rails 16, 18 and the reference potential rail 20. The current measuring circuit 38 includes a current measuring device 39 designed to measure a current.

[0047] The current measuring device 39 comprises a first current measuring arrangement 40 and a second current measuring arrangement 42. The first current measuring arrangement 40 is connected to the positive supply rail 16 and to the reference potential rail 20. The second current measuring device 42 is connected to the negative supply rail 18 and to the reference potential rail 20.

[0048] Each current measuring arrangement 40, 42 contains a current sensor 44 and a measuring capacitor 46 connected in series therewith. The current sensor 44 is connected to the respective supply rail 16, 18, while the measuring capacitor 46 is connected to the reference potential rail 20.

[0049] The measuring capacitors 46 of each current measuring arrangement 40, 42 are connected as Y capacitors between the supply rails 16, 18 and the reference potential rail 20. Depending on the case, the measuring capacitors 46 can also be part of a suppression capacitor set.

[0050] Current sensor 44 may include a shunt resistor for current measurement. The shunt resistor is connected in series with measuring capacitor 46. Current sensor 44 may additionally include a comparator connected to the shunt resistor for measuring an overcurrent in the respective current measuring arrangement 40, 42. Optionally, current sensor 44 may include an A / D converter for precisely quantifying the overcurrent.

[0051] It is assumed below that the circuit 10 has an AC insulation fault 48, which allows an undesired current flow and is modeled here by a resistor 50. However, other types of AC insulation faults 48 can also be detected. The AC insulation fault 48 can occur, for example, in a supply system to one or more terminal devices or in the terminal devices themselves. A fault current is detected as follows: When the circuit breaker 31 is switched on, the positive pole of the voltage source 14 is pushed to reference potential, for example ground, by the AC insulation fault 48. When the circuit breaker 32 is switched on, the negative pole of the voltage source 14 is pushed to reference potential, here ground, by the AC insulation fault 50.

[0052] This change in the supply voltage with respect to the reference potential causes a charge carrier flow through each measuring capacitor 46. This measuring current is then used to determine the AC insulation fault 48.

[0053] Unlike conventional devices and methods, the measures described here also allow for the detection of AC insulation faults that result in only low fault current values. This enables early detection. Furthermore, by directly measuring the current of the measuring capacitors, the measuring current can be decoupled from the actual load current, allowing simpler, faster, and more accurate measurements.

[0054] In order to enable early detection of AC insulation faults (48) and to permit simpler, faster, and more accurate measurement of small currents in inverters (26), a current measuring circuit (38) for a power converter (26) is proposed. The current measuring circuit (38) has a positive supply rail (16), a negative supply rail (18), a reference potential rail (20), and a current measuring device (39) containing a Y capacitor (46) and a current sensor (44) connected in series therewith. The at least one Y capacitor (46) can decouple the load current from the measuring current, so that even small fault currents can be reliably detected by the current sensor (44), even at high load currents. List of reference symbols

[0055] 10Circuit 12Supply 14Voltage source 16Positive supply rail 18Negative supply rail 20Reference potential rail 22Output capacitor 24Capacitance 26Inverter 28Phase branch 30Switching device 31First circuit breaker 32Second circuit breaker 34Output rail 36Intermediate link capacitor 38Current measuring circuit 39Current measuring device 40First current measuring arrangement 42Second current measuring arrangement 44Current sensor 46Measuring capacitor 48AC insulation fault 50Resistance

Claims

1. A converter circuit for an inverter (26), the converter circuit comprising a current measuring circuit (38) and at least one switching device (30), the current measuring circuit (38) comprising a positive supply rail (16), a negative supply rail (18), a reference potential rail (20) and a current measuring device (39), the switching device (30) being connected between the supply rails (16, 18) and having an output rail (34), the current measuring device (39) being connected to each supply rail (16, 18) and to the reference potential rail (20), 18) and has an output rail (34), wherein the current measuring device (39) is connected to each supply rail (16, 18) and to the reference potential rail (20), wherein the current measuring device (39) is designed to measure an electrical fault current between one of the supply rails (16, 18) and the reference potential rail (20) in each case.

2. Converter circuit according to claim 1, characterised in that the current measuring device (39) contains at least one current measuring arrangement (40, 42) which is connected either to the positive or to the negative supply rail (16, 18) and to the reference potential rail (20), the current measuring arrangement (40, 42) containing a current sensor (44) and a measuring capacitor (46) connected in series therewith.

3. Converter circuit according to claim 2, characterised in that the current sensor (44) is connected to one of the supply rails (16, 18) and to the measuring capacitor (46), the measuring capacitor (46) being connected to the current sensor (44) and to the reference potential rail (20).

4. Converter circuit according to claim 2 or 3, characterised in that the current measuring device (39) contains a comparator which is designed and connected to detect an overcurrent through the current measuring arrangement (40, 42).

5. Converter circuit according to one of claims 2 to 4, characterised in that the current measuring device (39) includes a circuit for measuring the current value which is connected to convert an analogue fault current flowing through the current measuring arrangement (40, 42) into a digital fault current signal which is indicative of the magnitude of the fault current.

6. Converter circuit according to one of the preceding claims, characterised by an intermediate circuit capacitor (36) which is connected between the positive and the negative supply rail (16, 18).

7. Converter circuit according to claim 6, characterised in that the DC link capacitor (36) is arranged closer to the switching device (30) than any current measuring arrangement (40, 42).

8. inverter (26) comprising a converter circuit according to one of the preceding claims9. A current measuring method for detecting a fault current generated due to an AC insulation fault (48) in a circuit (10) connected to a power converter by measuring a current flowing through a measuring capacitor (46) connected between a supply rail (16, 18) of the power converter and a reference potential rail (20) of the power converter (26), wherein an AC insulation fault (48) is assumed when a current flow through the measuring capacitor (46) is measured during a switching operation, which exceeds a predetermined threshold value, wherein the power converter is configured as an inverter (26), wherein the current flowing through the measuring capacitor (46) is measured during the positive half-wave and / or during the negative half-wave, wherein an AC isolation error (48) is assumed if a current flow through the measuring capacitor (46) which exceeds a predetermined threshold value is measured during one of the switching operations.