Frequency converter and system

Abstract

Frequency converter (100), comprising: - a first half-bridge circuit (1) with a center tap (2), wherein the center tap (2) of the first half-bridge circuit (1) is electrically connected to a first output terminal (3) of the frequency converter (100), - a second half-bridge circuit (4) with a center tap (5), wherein the center tap (5) of the second half-bridge circuit (4) is electrically connected to a second output terminal (6) of the frequency converter (100), - a third half-bridge circuit (7) with a center tap (8), wherein the center tap (8) of the third half-bridge circuit (7) is electrically connected to a third output terminal pole (9) of the frequency converter (100), and - a control unit (10) designed to control the first, second and third half-bridge circuits (1, 4, 7), - wherein the frequency converter (100) has a constant current / constant voltage operating mode in which - a first electrical consumer (11, 12) can be connected to the first output terminal (3) and to the third output terminal (9), - a second electrical consumer (13, 14) can be connected to the second output terminal (6) and to the third output terminal (9), and - the control unit (10) is designed to control the first, second and third half-bridge circuits (1, 4, 7) in such a way that a first pulsed voltage (U1) is output between the first output terminal (3) and the third output terminal (9), and a second pulsed voltage (U2) is output between the second output terminal (6) and the third output terminal (9) in such a way that a current (i1) with an adjustable first current intensity is established through the first electrical load (11, 12), and that a current (i2) with an adjustable second current intensity is established through the second electrical load (13, 14), - wherein the control unit (10) in the constant current / constant voltage operating mode is designed to control the third half-bridge circuit (7) such that a negative intermediate circuit potential is output at the third output terminal pole (9), - wherein the frequency converter (100) in the constant current / constant voltage operating mode provides three user-adjustable parameters, namely a frequency of a current vector generated by the frequency converter (100), an amplitude of the current vector generated by the frequency converter (100), and a starting angle of the current vector generated by the frequency converter (100), - wherein the frequency converter (100) has a three-phase operating mode in which the control unit (10) is designed to control the first, the second and the third half-bridge circuit (1, 4, 7) in such a way that alternating voltages with adjustable frequency and amplitude for controlling an electric motor (15) are output between the first output connection pole (3), the second output connection pole (6) and the third output connection pole (9).

Description

[0001] The invention relates to a frequency converter and a system with such a frequency converter.

[0002] JP H10-164 888 A shows a motor control unit in which two electric motors are controlled by means of three half bridges.

[0003] JP 2012-170 276 A teaches that a B6 bridge can be used either to supply one three-phase machine or two direct current machines.

[0004] EP 1 590 883 B1 shows a converter with a B6 bridge, in which switching between the supply of a rotating field machine and a single DC machine can be carried out by operating a switch.

[0005] DE 10 2015 220 854 A1 shows an electrical arrangement for controlling at least two electric motors by means of a B6 bridge.

[0006] DE 10 2011 118 823 A1 discloses a device and a method for charging a traction battery of an electric or hybrid vehicle, in which a half-bridge of a power converter acts as a DC voltage controller.

[0007] The invention is based on the object of providing a frequency converter and a system with a frequency converter that can be used as universally as possible.

[0008] The invention solves this problem by a frequency converter according to claim 1 and a system according to claim 2.

[0009] The frequency converter according to the invention conventionally comprises: a first half-bridge circuit with a center tap, wherein the center tap of the first half-bridge circuit is electrically connected to a first output terminal of the frequency converter; a second half-bridge circuit with a center tap, wherein the center tap of the second half-bridge circuit is electrically connected to a second output terminal of the frequency converter; a third half-bridge circuit with a center tap, wherein the center tap of the third half-bridge circuit is electrically connected to a third output terminal of the frequency converter; and a control unit configured to control the first, second, and third half-bridge circuits. Reference is also made to the relevant specialist literature in this regard.

[0010] The respective half-bridge circuits can conventionally comprise, for example, at least two series-connected semiconductor switching devices, such as IGBTs. The center tap of the respective half-bridge circuits can be a connecting node of the two semiconductor switching devices of the respective half-bridge circuit. In this regard, reference is also made to the relevant specialist literature.

[0011] According to the invention, the frequency converter has a special constant current / constant voltage operating mode, during which a first electrical load can be connected or is connected to the first output terminal and the third output terminal, and a second electrical load can be connected or is connected to the second output terminal and the third output terminal. In the constant current / constant voltage operating mode, the control unit is designed to control the first, second, and third half-bridge circuits or their semiconductor switching means such that a first pulsed voltage is output between the first output terminal and the third output terminal, and a second pulsed voltage is output between the second output terminal and the third output terminal.

[0012] In the constant current / constant voltage operating mode, the control unit is designed to control the third half-bridge circuit in such a way that a temporally constant potential, namely a negative intermediate circuit potential, is output at the third output terminal pole.

[0013] In the constant current / constant voltage operating mode, the control unit is further configured to generate the first pulsed voltage such that a current, in particular a temporally constant current, with an adjustable first current intensity is generated through the first electrical load and / or to generate the second pulsed voltage such that a current, in particular a temporally constant current, with an adjustable second current intensity is generated through the second electrical load. The first current intensity and the second current intensity can be identical or different.

[0014] The frequency converter further features a conventional three-phase operating mode, in which the control unit is configured to control the first, second, and third half-bridge circuits such that alternating voltages with adjustable frequency and amplitude are output between the first output terminal, the second output terminal, and the third output terminal for controlling an electric motor. Reference is also made to the relevant specialist literature in this regard.

[0015] The system according to the invention comprises a first electrical consumer, in particular in the form of an ohmic heating element, and / or a second electrical consumer, in particular in the form of an ohmic heating element, and a frequency converter as described above, wherein the first electrical consumer is connected to the first output terminal pole and to the third output terminal pole of the frequency converter, and the second electrical consumer is connected to the second output terminal pole and to the third output terminal pole of the frequency converter.

[0016] In addition to electric motors, other auxiliary units often need to be operated and controlled. One example is the control of a welding element for sealing plastic film and similar materials. Welding elements are typically supplied with a constant current, the current intensity of which adjusts the temperature of the welding element.

[0017] According to the invention, these auxiliary units can now be controlled using a frequency converter. The frequency converter according to the invention has a special mode in the form of constant current / constant voltage operating mode, by means of which an electrical load can be stimulated with a defined current or a defined voltage and a defined frequency. For this reason, the aforementioned variables are implemented as user-adjustable parameters. The constant current / constant voltage operating mode can be activated, for example, using a command. Using this operating mode and appropriate parameter settings, two independent constant current sources can be implemented using the frequency converter, which can be used, among other things, to control heating elements.

[0018] The frequency converter according to the invention is designed to power a three-phase electrical system and uses conventional systems of equations to describe a three-phase current or voltage system using a two-phase orthogonal system (sine, cosine) or in polar representation (magnitude and angle). These equations are permanently stored in the frequency converter. In this regard, reference is also made to the relevant specialist literature.

[0019] Based on the equation systems stored in the frequency converter, the inventive constant current / constant voltage operating mode can be implemented. The inventive constant current / constant voltage operating mode has three user-adjustable parameters that specify the length of a current vector (i.e., its amplitude), the frequency of the current vector, and an initial position (starting angle) of the current vector. This allows the current to be controlled independently in two phases. The third current is the sum of the other two currents.

[0020] The above-mentioned parameters frequency, amplitude and starting angle can be set, for example, according to the following equations, where the currents i1 and i2 are the setpoints of the two currents through the electrical consumers Frequency: 0 Hz Amplitude: 23i12+i1i2+i22 Starting angle: arctan(i1+2i23i1)

[0021] The invention is described in detail below with reference to the drawing. Fig. 1 schematically shows a circuit diagram of a system with a frequency converter according to the invention and two electrical consumers fed by the frequency converter.

[0022] Fig. 1 shows a schematic circuit diagram of a system 1000 with a frequency converter 100 according to the invention and two electrical consumers 11, 12 and 13, 14 fed by the frequency converter.

[0023] The frequency converter 100 has a first half-bridge circuit 1, which conventionally has two controllable semiconductor switching devices 19 and 20, which are connected in series between a positive intermediate circuit pole DC+ and a negative intermediate circuit pole DC-. The first half-bridge circuit 1 has a center tap 2, which is formed by an electrical connection between the two semiconductor switching devices 19 and 20. The center tap 2 of the first half-bridge circuit 1 is electrically connected to a first output terminal pole 3 of the frequency converter 100.

[0024] The frequency converter 100 further comprises a second half-bridge circuit 4, which conventionally comprises two controllable semiconductor switching means 21 and 22, which are connected in series between the positive intermediate circuit pole DC+ and the negative intermediate circuit pole DC-. The second half-bridge circuit 4 has a center tap 5, which is formed by an electrical connection between the two semiconductor switching means 21 and 22. The center tap 5 of the second half-bridge circuit 4 is electrically connected to a second output terminal pole 6 of the frequency converter 100.

[0025] The frequency converter 100 further comprises a third half-bridge circuit 7, which conventionally comprises two controllable semiconductor switching means 23 and 24, which are connected in series between the positive intermediate circuit pole DC+ and the negative intermediate circuit pole DC-. The third half-bridge circuit 7 has a center tap 8, which is formed by an electrical connection between the two semiconductor switching means 23 and 24. The center tap 8 of the third half-bridge circuit 7 is electrically connected to a third output terminal pole 9 of the frequency converter 100.

[0026] The frequency converter 100 further comprises a control unit 10, for example in the form of a microprocessor, which is designed to control the semiconductor switching means 19 to 24 of the half-bridge circuits 1, 4, 7.

[0027] In the bridge branches 1, 4, 7, shunt resistors 16, 17, 18 are conventionally provided, by means of which the control unit 10 can conventionally realize a current control.

[0028] The first electrical load in the form of an inductor 11 is connected or looped in series with an ohmic resistor 12 between the first output connection terminal 3 and the third output connection terminal 9 of the frequency converter 100. The second electrical load in the form of an inductor 13 is connected or looped in series with an ohmic resistor 14 between the second output connection terminal 6 and the third output connection terminal 9 of the frequency converter 100. The first inductor 11 and the second inductor 13 can, for example, represent parasitic inductances caused, for example, by long connection cables. The first inductor 11 and the second inductor 13 can additionally or alternatively also represent inductive components, for example, coils.

[0029] The control unit 10 is designed to control the semiconductor switching means 19 to 24 of the half-bridge circuits 1, 4, 7 in such a way that a first pulsed voltage U1 is output between the first output terminal 3 and the third output terminal 9, and a second pulsed voltage U2 is output between the second output terminal 6 and the third output terminal 9, in such a way that a current i1 with an adjustable first current intensity is established through the first electrical load 11, 12, and that a current i2 with an adjustable second current intensity is established through the second electrical load 13, 14.

[0030] For this purpose, the frequency converter 100 provides three user-adjustable parameters in constant current / constant voltage mode: the frequency of a current vector generated by the frequency converter 100, the amplitude of the current vector generated by the frequency converter 100, and the starting angle of the current vector generated by the frequency converter 100. For a given current i1 and i2, the parameters are calculated as follows: Frequency: 0 Hz Amplitude: 23i12+i1i2+i22 Starting angle: arctan(i1+2i23i1)

[0031] In addition to the constant current / constant voltage operating mode, the frequency converter 100 has a three-phase operating mode in which the control unit is designed to control the semiconductor switching means 19 to 24 of the half-bridge circuits 1, 4, 7 such that alternating voltages with adjustable frequency and amplitude for controlling an electric motor 15 are output between the first output terminal 3, the second output terminal 6 and the third output terminal 9.

[0032] For this purpose, the electric motor 15 is electrically connected via its phase terminals u, v, w to a corresponding output terminal of the output terminals 3, 6, and 9, respectively. This corresponds to the state of the art and is therefore not described in detail.

Claims

[1] Frequency converter (100), comprising: - a first half-bridge circuit (1) with a center tap (2), wherein the center tap (2) of the first half-bridge circuit (1) is electrically connected to a first output terminal (3) of the frequency converter (100), - a second half-bridge circuit (4) with a center tap (5), wherein the center tap (5) of the second half-bridge circuit (4) is electrically connected to a second output terminal (6) of the frequency converter (100), - a third half-bridge circuit (7) with a center tap (8), wherein the center tap (8) of the third half-bridge circuit (7) is electrically connected to a third output terminal (9) of the frequency converter (100), and - a control unit (10) designed to control the first, second and third half-bridge circuits (1, 4, 7), - wherein the frequency converter (100) has a constant current / constant voltage operating mode in which - a first electrical consumer (11, 12) can be connected to the first output terminal (3) and to the third output terminal (9), - a second electrical consumer (13, 14) can be connected to the second output terminal (6) and to the third output terminal (9), and - the control unit (10) is designed to control the first, second and third half-bridge circuits (1, 4, 7) in such a way that a first pulsed voltage (U1) is output between the first output terminal (3) and the third output terminal (9), and a second pulsed voltage (U2) is output between the second output terminal (6) and the third output terminal (9) in such a way that a current (i1) with an adjustable first current intensity is established through the first electrical load (11, 12), and that a current (i2) with an adjustable second current intensity is established through the second electrical load (13, 14), - wherein the control unit (10) in the constant current / constant voltage operating mode is designed to control the third half-bridge circuit (7) such that a negative intermediate circuit potential is output at the third output terminal pole (9), - wherein the frequency converter (100) in the constant current / constant voltage operating mode provides three user-adjustable parameters, namely a frequency of a current vector generated by the frequency converter (100), an amplitude of the current vector generated by the frequency converter (100), and a starting angle of the current vector generated by the frequency converter (100), - wherein the frequency converter (100) has a three-phase operating mode in which the control unit (10) is designed to control the first, the second and the third half-bridge circuit (1, 4, 7) in such a way that alternating voltages with adjustable frequency and amplitude for controlling an electric motor (15) are output between the first output connection pole (3), the second output connection pole (6) and the third output connection pole (9). [2] System (1000), comprising: - a first electrical consumer (11, 12) and / or - a second electrical consumer (13, 14), and - a frequency converter (100) according to claim 1, wherein the first electrical load (11, 12) is connected to the first output terminal pole (3) and to the third output terminal pole (9) of the frequency converter (100), and the second electrical load (13, 14) is connected to the second output terminal pole (6) and to the third output terminal pole (9) of the frequency converter (100).

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