Filter units and inverters

Abstract

A filter unit (1), wherein the filter unit (1) is arranged to be connected between an inverter (2) and an electric motor (3), wherein the filter unit (1) comprises: - a plurality of phase connection terminals (Ue, Ve, We) for connecting to corresponding phase connection terminals (2a, 2b, 2c) of the inverter (2), - a first intermediate circuit connection terminal (ZK+) for connecting to a first intermediate circuit connection terminal (2d) of the inverter (2) and a second intermediate circuit connection terminal (ZK-) for connecting to a second intermediate circuit connection terminal (2e) of the inverter (2), - a plurality of current connection terminals (Ue, Ve, We) for connecting to corresponding connection terminals (3a, 3b, 3c) of the electric motor (3). Motor connection terminals (Ua, Va, Wa), a plurality of filter elements (L1, L2, L3) for reducing the voltage rise rate at the motor connection terminals (Ua, Va, Wa) of the filter unit (2), wherein the corresponding filter elements (L1, L2, L3) are looped between the corresponding phase connection terminals (Ue, Ve, We) of the filter unit (1) and the corresponding motor connection terminals (Ua, Va, Wa) of the filter (2), and a coupling unit (4) which capacitively couples the filter elements (L1, L2, L3) with the first intermediate circuit connection terminal (ZK+) and the second intermediate circuit connection terminal (ZK‑) of the filter unit (1).

Description

Technical Field

[0001] The invention relates to a filter unit and a frequency converter having such a filter unit. Background Art

[0002] The switching speeds of modern power semiconductors for inverters are becoming ever higher. At the same time, if one wants to use maximum switching speeds of 10-14 kV / μs for standard IGBTs, a level of development has been reached where electric motors with special insulation are required. This can result in the available switching power of the IGBT no longer being fully utilized and the switching speeds becoming slower.

[0003] When using SiC transistors, switching speeds exceeding 100 kV / μs are expected in the future, which will inevitably necessitate additional restrictions on the voltage rise speed.

[0004] In order to limit the voltage rise rate to an acceptable level (eg <1 kV / μs), so-called du / dt filters are known from the prior art, which are connected between the output of the inverter and the electric motor. Summary of the invention

[0005] The object of the present invention is to provide a filter unit, for example in the form of a du / dt filter, and a frequency converter which have lower losses and / or a smaller overall volume and / or a lower weight than filter units of the prior art.

[0006] The invention achieves this object by means of a filter unit proposed according to the invention and a frequency converter proposed according to the invention.

[0007] The filter unit according to the invention is provided to be connected or looped in between, in particular, a conventional inverter and an electric motor.

[0008] The filter unit has a plurality of phase connections for connection to corresponding phase connections of the inverter. The filter unit may, for example, have exactly three phase connections. The filter unit also has a first intermediate circuit connection for connection to a first intermediate circuit connection of the inverter. The inverter may output, for example, a positive intermediate circuit potential at the first intermediate circuit connection.

[0009] The filter unit further has a second intermediate circuit connection for connection to a second intermediate circuit connection of the inverter. The inverter can output, for example, a negative intermediate circuit potential at the second intermediate circuit connection.

[0010] The potential difference between the positive and negative intermediate circuit potential can represent, for example, the intermediate circuit voltage.

[0011] The filter unit also has a plurality of motor connections for connection to corresponding connections of the electric motor. The filter unit can, for example, have exactly three motor connections for electrical connection to associated phase connections of the electric motor.

[0012] The filter unit also has a plurality of filter elements. The filter unit can have, for example, exactly three filter elements. The filter elements can be, for example, inductively effective components in the form of chokes.

[0013] The corresponding filter elements are looped in between the corresponding phase connection of the filter unit and the corresponding motor connection of the filter unit. For example, the first filter element is looped in between the first phase connection and the first motor connection, the second filter element is looped in between the second phase connection and the second motor connection, and the third filter element is looped in between the third phase connection and the third motor connection.

[0014] The filter unit furthermore has a coupling unit which capacitively couples the filter element to the first intermediate circuit connection and to the second intermediate circuit connection of the filter unit.

[0015] A filter element connected to the capacitively effective coupling unit reduces the rate of voltage rise at the motor connection of the filter unit.

[0016] According to one embodiment, the coupling unit has a plurality of capacitors. The coupling unit may have, for example, six capacitors. When a cable connection is used, the capacitance of the cable connection may have a considerable additional capacitance and thus additionally reduce the voltage rise rate. This may have an influence on the dimensioning of the number of capacitors. In the case of sufficient capacitance of the cable connection, the plurality of capacitors may be completely omitted.

[0017] For example, a first capacitor may be looped in between the first motor connection terminal and the first intermediate circuit connection terminal, a second capacitor may be looped in between the second motor connection terminal and the first intermediate circuit connection terminal, a third capacitor may be looped in between the third motor connection terminal and the first intermediate circuit connection terminal, a fourth capacitor may be looped in between the first motor connection terminal and the second intermediate circuit connection terminal, a fifth capacitor may be looped in between the second motor connection terminal and the second intermediate circuit connection terminal, and a sixth capacitor may be looped in between the sixth motor connection terminal and the second intermediate circuit connection terminal.

[0018] According to one embodiment, the capacitor is a ceramic capacitor.

[0019] According to one embodiment, the coupling unit has a voltage clamping unit which limits the difference between the respective potential at the motor connection and the potential at the first intermediate circuit connection to a predetermined first potential difference. The voltage clamping unit can also limit the difference between the respective potential at the motor connection and the potential at the second intermediate circuit connection to a predetermined second potential difference. The first and second potential differences can be the same or different. The first and second potential differences can be, for example, approximately 30 V in value.

[0020] According to one embodiment, the coupling unit has an active feedback unit which transfers energy from the voltage clamping unit into an intermediate circuit of an inverter which is connected to the first intermediate circuit terminal and to the second intermediate circuit terminal.

[0021] According to one specific embodiment, the feedback unit has at least one buck converter.

[0022] According to one specific embodiment, the feedback unit has at least one flyback converter.

[0023] According to one embodiment, the voltage clamping unit has a first voltage clamping subunit that limits the difference between the respective potential at the motor connection and the potential at the first intermediate circuit connection to a predetermined first potential difference. The voltage clamping unit also has a second voltage clamping subunit that limits the difference between the respective potential at the motor connection and the potential at the second intermediate circuit connection to a predetermined second potential difference.

[0024] According to one embodiment, the feedback unit has a first feedback subunit, which transmits energy from the first voltage clamping subunit to the intermediate circuit of the inverter, which is connected to the first intermediate circuit connection terminal and the second intermediate circuit connection terminal. Correspondingly, the feedback unit has a second feedback subunit, which transmits energy from the second voltage clamping subunit to the intermediate circuit of the inverter, which is connected to the first intermediate circuit connection terminal and the second intermediate circuit connection terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention is described in detail below with reference to the accompanying drawings.

[0026] Figure 1 shows a drive system having an inverter, a filter unit according to the invention and an electric motor,

[0027] Figure 2 Shows Figure 1 A first embodiment of the feedback unit of the filter unit is shown in,

[0028] Figure 3 Shows Figure 1 Another embodiment of the feedback unit of the filter unit is shown in

[0029] Figure 4 Shows Figure 1 An exemplary output voltage profile of the filter unit is shown in FIG. DETAILED DESCRIPTION

[0030] Figure 1 The drive system is shown having a frequency converter 6 and a conventional electric motor 3 which is driven by means of the frequency converter 6 .

[0031] The frequency converter 6 has a conventional inverter 2 and, downstream of the inverter 2 , a filter unit 1 according to the invention which forms a du / dt filter.

[0032] The inverter 2 (also called converter) converts a DC voltage into an AC voltage or converts a DC current into an AC current. For this purpose, the inverter can conventionally have, for example, a plurality of controllable inverter bridges, which are applied with an intermediate circuit voltage and controlled according to the output voltage to be generated. For the rest, reference is also made to the relevant professional literature.

[0033] The filter unit 1 is connected between the inverter 2 and the motor 3 .

[0034] The filter unit 1 has three phase connection terminals Ue, Ve, We for connecting to corresponding phase connection terminals 2 a, 2 b, 2 c of the inverter 2 .

[0035] The filter unit 1 furthermore has a first intermediate circuit connection ZK+ for connection to a first intermediate circuit connection 2 d of the inverter 2 and a second intermediate circuit connection ZK− for connection to a second intermediate circuit connection 2 e of the inverter 2 .

[0036] The filter unit 1 also has three motor connections Ua, Va, Wa for connection to corresponding phase branch connections 3a, 3b, 3c of the motor 3.

[0037] The filter unit 1 furthermore has three filter elements L1 , L2 , L3 in the form of chokes or coils for reducing the rate of rise of the voltage at the motor connections Ua, Va, Wa of the filter unit 1 .

[0038] The first coil L1 is looped between the first phase connection terminal Ue and the first motor connection terminal Ua, the second coil L2 is looped between the second phase connection terminal Ve and the second motor connection terminal Va, and the third coil L3 is looped between the third phase connection terminal We and the third motor connection terminal Wa.

[0039] The filter unit 1 furthermore has a coupling unit 4 which capacitively couples the coils L1 , L2 , L3 on their motor connection side in each case to a first intermediate circuit connection ZK+ and a second intermediate circuit connection ZK−.

[0040] The coupling unit 4 has six capacitors C1 to C6 which are implemented as ceramic capacitors. The capacitor C1 is looped between the connection of the coil L1 coupled to the first motor connection Ua and the first intermediate circuit connection ZK+, the capacitor C2 is looped between the connection of the coil L2 coupled to the second motor connection Va and the first intermediate circuit connection ZK+, the capacitor C3 is looped between the connection of the coil L3 coupled to the third motor connection Wa and the first intermediate circuit connection ZK+, the capacitor C4 is looped between the connection of the coil L1 coupled to the first motor connection Ua and the second intermediate circuit connection ZK-, the capacitor C5 is looped between the connection of the coil L2 coupled to the second motor connection Va and the second intermediate circuit connection ZK-, and the capacitor C6 is looped between the connection of the coil L3 coupled to the third motor connection Wa and the second intermediate circuit connection ZK-.

[0041] The coupling unit 4 has a voltage clamping unit, which has a first voltage clamping subunit 5a and a second voltage clamping subunit 5b, which limits the difference between the corresponding potentials at the motor connections Ua, Va, Wa and the potential at the first intermediate circuit connection ZK+ to a predetermined first potential difference of approximately 30V, and limits the difference between the corresponding potentials at the motor connections Ua, Va, Wa and the potential at the second intermediate circuit connection ZK- to a predetermined second potential difference of approximately 30V.

[0042] The first voltage clamping subunit 5a limits the difference between the corresponding potential at the motor connection terminals Ua, Va, Wa and the potential at the first intermediate circuit connection terminal ZK+ to a predetermined first potential difference, and the second voltage clamping subunit 5b limits the corresponding potential at the motor connection terminals Ua, Va, Wa and the potential at the second intermediate circuit connection terminal ZK- to a predetermined second potential difference.

[0043] The first voltage clamping subunit 5a has diodes D1, D2, D3, D7, capacitor C7 and resistor R1 in the circuit shown. Diode D1 is electrically connected to the following connection end of coil L1 on the anode side, which is electrically connected to the first motor connection Ua. Diode D2 is electrically connected to the following connection end of coil L2 on the anode side, which is electrically connected to the second motor connection Va. Diode D3 is electrically connected to the following connection end of coil L3 on the anode side, which is electrically connected to the third motor connection Wa. On the cathode side, diodes D1 to D3 are electrically connected to each other. Resistor R1 is looped in between the cathodes of diodes D1 to D3 and the connection ZK+. Diode D7 is electrically connected with its anode to the cathodes of diodes D1 to D3, and with its cathode to the output KK1 of the first voltage clamping subunit 5a. Capacitor C7 is looped in between the output KK1 of the first voltage clamping subunit 5a and the connection ZK+.

[0044] The second voltage clamping subunit 5b has diodes D4, D5, D6, D8, capacitor C8 and resistor R2 in the circuit shown. Diode D4 is electrically connected to the following connection end of coil L1 on the cathode side, which is electrically connected to the first motor connection Ua. Diode D5 is electrically connected to the following connection end of coil L2 on the cathode side, which is electrically connected to the second motor connection Va. Diode D6 is electrically connected to the following connection end of coil L3 on the cathode side, which is electrically connected to the third motor connection Wa. On the anode side, diodes D4 to D6 are electrically connected to each other. Resistor R2 is looped in between the anodes of diodes D4 to D6 and the connection ZK-. Diode D8 is electrically connected with its cathode to the anodes of diodes D4 to D6, and with its anode to the output KK2 of the second voltage clamping subunit 5b. Capacitor C8 is looped in between the output KK2 of the second voltage clamping subunit 5b and the connection ZK-.

[0045] The coupling unit 4 also has a feedback unit having a first feedback subunit RS1 and a second feedback subunit RS2 , which transmits energy from the voltage clamping subunits 5 a , 5 b into the intermediate circuit of the inverter 2 .

[0046] The first feedback subunit RS1 transfers energy from the first voltage clamping subunit 5 a into the intermediate circuit of the inverter 2 , and the second feedback subunit RS2 transfers energy from the second voltage clamping subunit 5 b into the intermediate circuit of the inverter 2 .

[0047] Figure 2 A first embodiment of a feedback unit is shown, the feedback unit comprising Figure 11 and 2. The feedback subunits RS1 and RS2 of the filter unit 1 shown in FIG. The feedback subunits RS1 and RS2 are respectively configured as potential-connected step-down converters. The feedback subunit RS1 has a capacitor C9, a field effect transistor M1, a diode D9, and a coil L4 in the circuit shown. Correspondingly, the feedback subunit RS2 has a capacitor C10, a field effect transistor M2, a diode D10, and a coil L5 in the circuit shown.

[0048] Figure 3 Another embodiment of the feedback unit is shown. The feedback unit comprises Figure 1 1 and 2. The feedback subunits RS1 and RS2 of the filter unit 1 shown in FIG. The feedback subunits RS1 and RS2 are respectively configured as flyback converters. The feedback subunit RS1 has a capacitor C9, a transformer Tr1, a field effect transistor M1, and a diode D9 in the circuit shown. Correspondingly, the feedback subunit RS2 has a capacitor C10, a transformer Tr2, a field effect transistor M2, and a diode D10 in the circuit shown.

[0049] Figure 4 Compared with the idealized output voltage variation curve Ua′ without using the filter unit 1, Figure 1 An exemplary output voltage profile Ua of the filter unit 1 is shown in FIG.

[0050] Capacitors C1 to C6 are preferably designed as ceramic capacitors which, due to the voltage dependence of the capacitance, are derived to ZK+ and ZK-. This results in an approximately constant capacitance with respect to the voltage.

[0051] If the capacitors C1 to C6 are each clamped to ZK+ and ZK−, then an oscillating circuit, for example, consisting of L1 , C1 in parallel with C4 is effective for the corresponding switching process.

[0052] As an oscillating circuit, for example, coil L1 and capacitor C1 in parallel with C4, i.e. Lf and 2xCf, work effectively in phase U. The inductance on the motor side is much greater than Lf and can therefore be neglected. The cable capacitance increases the effect of Cf and additionally acts as a filter capacitor, wherein Cy in the return path is still effective in the frequency converter 2.

[0053] In a specific embodiment not shown, the capacitor banks C1 to C3 or C4 to C6 can be omitted. The remaining capacitors should then preferably be designed as film capacitors so that the capacitance value is independent of the voltage.

[0054] like Figure 4As shown in , the to-and-fro oscillation process would rise to approximately double the ZK voltage Vzk in the case of free oscillation, but would be clamped by diodes D1 to D6 to a value above or below the ZK voltage, for example Vclamp, which is 30 V, for example.

[0055] Due to the abrupt clamping and parasitic elements, an oscillation around the clamping voltage will result. The resistors R1 and R2 dampen this oscillation, and the losses are relatively small.

[0056] The filter unit 1 according to the present invention has the following advantages:

[0057] - Relief of capacitive loads on the power semiconductors in inverter 2, such as cable capacitance (loss reduction)

[0058] - The maximum switching speed of the semiconductor switches in the inverter that can be used

[0059] - A relatively compact design is possible, whereby the active filter unit 1 can be integrated into the frequency converter

[0060] - Low loss in active filter unit 1

[0061] - Improved EMV characteristics

[0062] - Reduce leakage current on the motor side

[0063] - The parameters of the active filter units (du / dt, clamping voltage, damping) can be dimensioned independently of each other.

[0064] According to the invention, the outputs of the filter elements or coils L1 to L3 are capacitively coupled to the intermediate circuit ZK+, ZK- by means of capacitors C1 to C6. The use of low-inductance ceramic capacitors is advantageous here, since this achieves favorable EMC properties.

[0065] Together with the relatively small, low-loss individual inductors L1 to L3, a high-quality oscillating circuit is obtained which, although it causes a limitation in the voltage rise rate, will lead to excessively high oscillating voltages at the terminals Ua, Va, Wa. These overvoltages are limited in the two voltage clamping subunits 5a and 5b by means of diodes D1 to D6 and capacitors C7 and C8 to a voltage above ZK+, for example 30 V, and below ZK-, for example 30 V. As a result, the energy additionally stored in the inductors L1 to L3 during the switching edges is released to the two voltage clamping subunits 5a and 5b.

[0066] In order to prevent the voltage in the two voltage clamping subunits 5a and 5b from rising, the two feedback subunits RS1 and RS2 ideally keep the respective voltages across C9 and C10 to a constant value of, for example, 30 V, independently of the load. The feedback subunits RS1 and RS2 can be implemented, for example, according to Figure 2 The step-down converter is connected to the potential of the Figure 3 Variants with a flyback converter have the advantage that they can be designed identically on the primary side and that, moreover, the semiconductors can be operated at a more favorable operating point than solutions with a potential-connected buck converter.

[0067] The filter unit 1 according to the invention can be integrated into the frequency converter 6 itself due to its implementation. This would not be possible with du / dt filters of conventional technology due to the structural volume, weight and electrical losses. The filter unit 1 can be arranged, for example, on a printed circuit board of the frequency converter 6, on which the power semiconductors of the inverter 2 are also arranged. This is also meaningful for EMC reasons, since the return paths to ZK+ and ZK- should have the smallest possible inductance.

[0068] The motor 3 can be connected directly, i.e. in the shortest route, to the motor connections Ua, Va, Wa. Alternatively, for example in a switch cabinet or in the case of a wall-mounted device, a cable connection, for example a shielded one, can be provided between the motor connections Ua, Va, Wa and the motor. When a cable connection is used, the capacitance of the possibly shielded cable connection can have a considerable additional capacitance and thus additionally reduce the voltage rise rate. This can affect the design of the filter unit 1, in particular the size determination of the capacitors C1 to C8.

Claims

1. A filter unit (1), wherein the filter unit (1) is arranged to be connected between an inverter (2) and a motor (3), wherein the filter unit (1) has: - a plurality of phase connection terminals (Ue, Ve, We) for connection to corresponding phase connection terminals (2a, 2b, 2c) of an inverter (2), - a first intermediate circuit connection (ZK+) for connection to a first intermediate circuit connection (2d) of the inverter (2) and a second intermediate circuit connection (ZK-) for connection to a second intermediate circuit connection (2e) of the inverter (2), - a plurality of motor connection terminals (Ua, Va, Wa) for connecting to corresponding connection terminals (3a, 3b, 3c) of the electric motor (3), - a plurality of filter elements (L1, L2, L3), wherein the respective filter element (L1, L2, L3) is looped in between the respective phase connection (Ue, Ve, We) of the filter unit (1) and the respective motor connection (Ua, Va, Wa) of the filter unit (1), and - a coupling unit (4) which capacitively couples the filter elements (L1, L2, L3) to a first intermediate circuit connection (ZK+) and a second intermediate circuit connection (ZK-) of the filter unit (1), The coupling unit (4) has a voltage clamping unit (5a, 5b) which limits the difference between the respective potential at the motor connection (Ua, Va, Wa) and the potential at the first intermediate circuit connection (ZK+) to a predetermined first potential difference and limits the difference between the respective potential at the motor connection (Ua, Va, Wa) and the potential at the second intermediate circuit connection (ZK-) to a predetermined second potential difference.

2. The filter unit (1) according to claim 1, characterized in that - The coupling unit (4) has a plurality of capacitors (C1 to C6).

3. The filter unit (1) according to claim 2, characterized in that - The capacitors (C1 to C6) are ceramic capacitors.

4. The filter unit (1) according to claim 1, characterized in that The coupling unit (4) has a feedback unit (RS1, RS2) which transfers energy from the voltage clamping unit (5a, 5b) into an intermediate circuit of an inverter (2), which is connected to a first intermediate circuit terminal (ZK+) and a second intermediate circuit terminal (ZK-).

5. The filter unit (1) according to claim 4, characterized in that - The feedback unit (RS1, RS2) has at least one buck converter.

6. The filter unit (1) according to claim 4 or 5, characterized in that - The feedback unit (RS1, RS2) has at least one flyback converter.

7. The filter unit (1) according to any one of claims 1 to 5, characterized in that - Voltage clamp unit with: - a first voltage clamping subunit (5a) which limits the difference between the respective potential at the motor connection (Ua, Va, Wa) and the potential at the first intermediate circuit connection (ZK+) to a predetermined first potential difference, and A second voltage clamping subunit (5b) which limits the difference between the respective potential at the motor connections (Ua, Va, Wa) and the potential at the second intermediate circuit connection (ZK-) to a predefined second potential difference.

8. The filter unit (1) according to claim 7, characterized in that - The feedback unit has: - a first feedback subunit (RS1) which transfers energy from the first voltage clamping subunit (5a) into an intermediate circuit of an inverter (2) which is connected to a first intermediate circuit connection terminal (ZK+) and a second intermediate circuit connection terminal (ZK-), and - a second feedback subunit (RS2) which transfers energy from the second voltage clamping subunit (5b) into an intermediate circuit of an inverter (2) which is connected to a first intermediate circuit connection (ZK+) and a second intermediate circuit connection.

9. Frequency converter (6), having: - Inverter (2), and - A filter unit (1) according to any of the preceding claims 1 to 8.

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