Method for operating converter, converter control unit and converter assembly

Abstract

The invention relates to a method for operating a converter having at least one choke which is arranged between an alternating voltage attachment and at least one converter half-bridge, in the at least one converter half-bridge, an actuatable semiconductor switching element is arranged between the first DC voltage attachment and the at least one choke and between the at least one choke and the second DC voltage attachment. The actuatable semiconductor switching element is actuated by means of an actuation signal having an actuation frequency, the actuation frequency being varied as a function of the current intensity of the phase current flowing through the actuatable semiconductor switching element. The invention further relates to a converter control unit for controlling at least one converter half-bridge and to a converter assembly having a converter and a converter control unit. The invention further relates to a computer program and to a storage medium.

Description

Technical Field

[0001] The invention relates to a method for operating a converter as well as a converter control unit, a converter component and a computer program for carrying out the method. Background Art

[0002] For example, electrolysis devices require a powerful DC voltage source. The power source is usually the mains connection, ie the alternating current connection. Such rectifiers can be constructed with thyristors, but this has the disadvantage of high power loss and, due to the low switching frequency, high mains interference.

[0003] If an active B6 bridge based on semiconductor switches (e.g. metal-oxide-semiconductor field-effect transistors (MOSFET) or bipolar transistors with insulated gate electrodes (IGBT)) is used, the amplitude of the output voltage on the DC voltage side can be increased. In this case, an inductor can be used on the grid connection side, which can serve as an energy store for the voltage increase. Summary of the invention

[0004] According to the invention, a method for operating a converter as well as a converter control unit, a converter component and a computer program for carrying out the method are provided. Advantageous embodiments are the subject of the following description.

[0005] The present invention starts from a converter having at least one choke, which is arranged between an AC voltage attachment end and at least one converter half-bridge, wherein in the converter bridge, controllable semiconductor switching elements are respectively arranged between a first DC voltage attachment end and the choke and between the choke and a second DC voltage attachment end.

[0006] When actuating such a half-bridge, for example, by means of a PWM signal, or in general when changing the switching state of a semiconductor switching element, an increase in the frequency of the actuation signal is accompanied by an increase in the switching losses in the semiconductor switching element. Each switching process of the semiconductor switching element can be carried out according to the phase current I Ph , output DC voltage U DC and temperature T is assigned to the switching energy E SW , where the power loss P SW It is derived as follows:

[0007] P SW =E SW (IPh ,U DC ,T)·f PWM (1)

[0008] Here, the switching energy E SW Phase current I Ph The increase of output DC voltage U DC In order to avoid thermal overload of the switching elements, the control frequency can be increased at low phase currents (partial load), thereby reducing the current ripple. Conversely, at higher phase currents (full load), the switching energy E per switching process is SW Increases, so that the activation frequency must be reduced. As a result, a higher current ripple occurs, but the power loss in the controllable switching elements and the heat generation associated therewith are reduced.

[0009] The present invention utilizes this knowledge and proposes to control the controllable switching elements of the converter by means of a control signal, in particular a pulse width modulation signal, PWM signal, which has a control frequency or PWM frequency that is variable depending on the current intensity of the phase current. In this case, the control frequency increases in particular as the current intensity decreases.

[0010] This avoids excessively large dimensions of the (semiconductor) switching elements that can be actuated. And it can save costs. Since the ripple current is independent of the operating point, that is, independent of the amplitude of the phase current, a constant relative phase current can still be achieved without thermally overloading the semiconductor.

[0011] For a converter, for example an active rectifier, the frequency f of the control signal (the control signal is in particular a PWM signal) is determined according to the frequency f PWM (control frequency; switching frequency of the switching element), grid voltage U AC , allowable current ripple ΔI AC And the output DC voltage U DC The inductance L of the (grid) choke can be AC is given as:

[0012]

[0013] Therefore, the inductance is indirectly proportional to the product of the control frequency (PWM frequency) and the current ripple. Therefore, an increase in the control frequency reduces the size of the inductance.

[0014] In at least one embodiment, the control signal has a control frequency of at least 2 kHz or at least 20 kHz or at least 100 kHz, or at most 8 kHz or at most 50 kHz or at most 150 kHz. In particular, the frequency can be varied between one of the mentioned minimum values ​​and one of the mentioned maximum values, respectively, depending on the current intensity.

[0015] By actuating the actuable switching element at an increased actuation frequency, the inductance of the choke can be reduced, whereby the installation space of the converter assembly can be reduced and the costs of the converter assembly can be reduced.

[0016] The invention is advantageous in a range of power electronic devices in which an inductor is used as an energy store, for example a DC voltage-DC voltage converter in buck operation or boost operation, a buck chopper, a boost chopper or a Cuk converter.

[0017] The converter control unit according to the invention is designed, in particular in terms of programming, to carry out the method according to the invention.

[0018] In addition, the present invention relates to a converter component, which has at least one choke, which is arranged between the AC voltage attachment terminal and at least one converter half-bridge, wherein in the converter half-bridge, a semiconductor switching element that can be controlled is respectively arranged between the first DC voltage attachment terminal and the choke and between the choke and the second DC voltage attachment terminal. In addition, the converter component includes a converter control unit, which controls the semiconductor switching element that can be controlled according to an embodiment of the method according to the present invention. In particular, the converter component has three AC voltage attachment terminals, three chokes and three converter half-bridges, wherein the chokes are respectively arranged between the AC voltage attachment terminal and the converter half-bridge, whereby each phase of the AC voltage attachment terminal is equipped with a combination of a choke and a converter half-bridge.

[0019] In at least one embodiment, the semiconductor switching element that can be controlled is implemented as a bipolar transistor (IGBT) with an insulated gate electrode or a field effect transistor or a metal oxide semiconductor field effect transistor (MOSFET). As a result, the semiconductor switching element that can be controlled and thus the entire converter assembly can be realized in a simple and cost-effective manner.

[0020] In at least one embodiment, a capacitor can be additionally arranged downstream of the converter half bridge in parallel with the first and second DC voltage connection terminals, so that the residual ripple of the voltage rectified by the converter can be reduced by means of the capacitor.

[0021] In at least one embodiment, the converter assembly has at least one detector that determines the current intensity of the phase current through at least one semiconductor switching element that can be controlled and outputs the current intensity to the converter control unit. In particular, the converter assembly can have three detectors, by which the current intensity of the phase current on each semiconductor switching element that can be controlled can be determined. According to the current intensity determined by at least one detector, the converter control unit can change the control frequency for controlling the semiconductor switching element that can be controlled, thereby preventing the semiconductor switching element from being damaged while keeping the current ripple as small as possible. As a result, the service life of the semiconductor switching element and the entire converter assembly can be extended, and at the same time the current at the DC voltage attachment end can be smoothed.

[0022] It is advantageous to implement the method according to the invention in the form of a computer program or computer program product with a program code for executing all method steps, because this generates particularly low costs, especially when the controller to be implemented is also used for other tasks and therefore already exists. Finally, a machine-readable storage medium is provided, which has a computer program as described above stored on the storage medium. Suitable storage media or data carriers for providing computer programs are especially magnetic storage, optical storage and electrical storage, such as hard disks, flash memory, EEPROM, DVD, etc. It is also possible to download programs via computer networks (Internet, intranet, etc.). Here, such downloading can be done wired or cabled or wirelessly (e.g., via WLAN networks, 3G, 4G, 5G or 6G connections, etc.).

[0023] Further advantages and embodiments of the invention emerge from the description and the accompanying drawings.

[0024] It is self-evident that the features mentioned above and those yet to be explained below can be used not only in the respectively stated combination but also in other combinations or alone without departing from the scope of the present invention.

[0025] The invention is schematically illustrated in the drawing according to an exemplary embodiment and is described below with reference to the drawing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The schematic diagram shows a converter assembly having a converter which is designed to carry out one specific embodiment of the method. DETAILED DESCRIPTION

[0027] Figure 1The schematic diagram shows a converter assembly 40 which has a converter 10 and a converter control unit 30 and is designed and configured to carry out one specific embodiment of the method.

[0028] The converter 10 has three converter half-bridges 2a, 2b, 2c, wherein each of the three converter half-bridges 2a, 2b, 2c is connected to one of the three AC voltage terminals U, V, W of an AC current network 60, which outputs an AC voltage with an amplitude of 400 V. For example, the converter 10 can be operated as a rectifier so that a DC voltage, for example a DC voltage of 800 V, is applied to the DC voltage terminals B+, B− on the output side, which DC voltage can be used by a load, for example for operating an electrolysis device.

[0029] Between each of the converter half-bridges 2a, 2b, 2c and the AC voltage attachment terminals U, V, W connected to the corresponding converter half-bridge 2a, 2b, 2c, the converter 10 has an inductance in the form of a choke 1a, 1b, 1c, which serves as an energy storage device in boost operation, i.e. in operation of increasing the voltage.

[0030] The converter half bridges 2a, 2b, 2c respectively have two semiconductor switching elements 21, 22 that can be controlled, wherein a first semiconductor switching element 21 that can be controlled is connected between the choke 1a, 1b, 1c and the first DC voltage attachment terminal B+, and a second semiconductor switching element 22 that can be controlled is connected between the choke 1a, 1b, 1c and the second DC voltage attachment terminal B-. Here, the semiconductor switching elements 21, 22 that can be controlled can be constructed by switches 21, 22 and diodes 21b, 22b connected in parallel with the switches 21, 22, wherein the diodes 21b, 22b are constructed in the form of corresponding reverse diodes. For example, the semiconductor switching elements 21, 22 that can be controlled can be constructed as MOSFETs.

[0031] In the rectification operation, the semiconductor switching elements 21, 22 that can be controlled of each converter half bridge 2a, 2b, 2c are alternately controlled, that is, switched to the conduction state. Therefore, if a positive voltage signal is applied to the AC voltage attachment terminals U, V, W of the converter half bridges 2a, 2b, 2c, the current flows between the AC voltage attachment terminals U, V, W and the first DC voltage attachment terminal B+. Here, the current flows through the closed switch 21a and / or through the diode 21b connected in parallel. Correspondingly, when a negative voltage signal is applied to the AC voltage attachment terminals U, V, W, the current between the second DC voltage attachment terminal B- and the AC voltage attachment terminals U, V, W also flows through the closed switch 22a and / or the diode 22b connected in parallel. Thus, the AC voltage on the AC voltage attachment terminals U, V, W can be rectified.

[0032] In this case, the semiconductor switching elements 21, 22 that can be controlled are controlled by the converter control unit 30. The control signal used for this purpose is, for example, a pulse width modulation signal and has a variable control frequency or pulse width modulation frequency, which is in particular at least 2 kHz or at least 20 kHz or at least 100 kHz or at most 8 kHz or at most 50 kHz or at most 150 kHz, which is advantageously controlled by the controllable switching elements 21, 22 as a function of the intensity of the phase current.

[0033] As the output DC voltage and phase current increase, the switching energy E outputted by each switching process on the semiconductor switching elements 21 and 22 that can be controlled is SW Increase. The power loss is calculated according to equation (1) by dividing the switching energy E SW =E multiplied by the control frequency. Since the power loss is converted into heat at the semiconductor switching elements 21 and 22 that can be controlled, the power loss increases greatly at high phase currents and high control frequencies, so that the semiconductor switching elements 21 and 22 that can be controlled may suffer damage, such as overheating. To prevent this, the control frequency can be reduced at high phase currents (full load). Conversely, at low phase currents and the resulting reduced switching energy E SW In this case, the control frequency can be increased without damaging the semiconductor switching elements 21 and 22 that can be controlled.

[0034] In addition, by controlling the controllable semiconductor switching elements 21, 22 at a high control frequency, the inductance of the chokes 1a, 1b, 1c can be reduced, as can be seen from equations (2) and (3), which inductance can be indirectly proportional to the control frequency, whereby the converter component 40 has a smaller structural size on the one hand and the costs for the inductance can be reduced on the other hand.

[0035] To determine the phase current, each converter half bridge 2a, 2b, 2c of the converter 10 can have a detector 23 which measures the phase current through the controllable semiconductor switching elements 21, 22 and outputs it to a converter control unit 30 which adjusts the control frequency as a function of the measured current intensity.

[0036] In addition, a capacitor 50 of the converter 10 can be connected in parallel to the two DC voltage attachment terminals B+, B-. The capacitor 50 serves as a smoothing capacitor, and the voltage signal rectified by the converter half bridges 2a, 2b, 2c is smoothed by the smoothing capacitor, that is, the remaining voltage fluctuations are removed from the voltage signal.

Claims

1. A method for operating a converter (10), the converter having at least one choke (1a, 1b, 1c), the at least one choke being arranged between an AC voltage connection (U, V, W) and at least one converter half-bridge (2a, 2b, 2c), wherein: In the at least one converter half-bridge (2a, 2b, 2c), a semiconductor switching element (21, 22) that can be controlled is respectively arranged between a first DC voltage attachment terminal (B+) and the at least one choke (1a, 1b, 1c) and between the at least one choke (1a, 1b, 1c) and a second DC voltage attachment terminal (B-), The semiconductor switching elements (21, 22) that can be controlled are controlled by means of control signals. Therein, the actuation frequency of the actuation signal is varied as a function of the current intensity of the phase current flowing through the actuable semiconductor switching elements (21, 22).

2. The method according to claim 1, wherein: The control frequency increases as the current intensity decreases.

3. The method according to claim 1 or 2, wherein: The control frequency is at least 2 kHz, or at least 20 kHz, or at least 100 kHz, or at most 8 kHz, or at most 50 kHz, or at most 150 kHz.

4. A method according to any one of the preceding claims, wherein: The actuation signal is a pulse width modulated signal, PWM signal, and the actuation frequency is a pulse width modulation frequency.

5. A converter control unit (30) which is configured to control controllable semiconductor switching elements (21, 22) in at least one converter half-bridge (2a, 2b, 2c) of a converter (10) according to a method according to any of the preceding claims.

6. A converter assembly (40) comprising a converter (10) and a converter control unit (30) according to claim 5, wherein the converter comprises at least one choke (1a, 1b, 1c) which is arranged between an AC voltage connection (U, V, W) and a converter half-bridge (2a, 2b, 2c), wherein: In the converter half-bridge (2a, 2b, 2c), controllable semiconductor switching elements (21, 22) are respectively arranged between the first DC voltage attachment terminal (B+) and the choke (1a, 1b, 1c) and between the choke (1a, 1b, 1c) and the second DC voltage attachment terminal (B-).

7. The converter assembly (40) according to the preceding claim, wherein: The controllable semiconductor switching elements (21, 22) are bipolar transistors or field effect transistors, in particular metal oxide semiconductor field effect transistors, with an insulated gate electrode.

8. The converter assembly (40) according to claim 6 or 7, wherein: The converter (10) further comprises a capacitor (50) which is connected in parallel with the first and second DC voltage connection terminals (B+, B-).

9. The converter assembly (40) according to any one of claims 6 to 8, wherein: The converter assembly (40) has at least one detector (23) which determines the current intensity of the phase current through the controllable switching elements (21, 22) and outputs the current intensity to the converter control unit (30).

10. The converter assembly (40) according to any one of claims 6 to 9, wherein: The converter assembly (40) has three chokes (1a, 1b, 1c), which are respectively arranged between AC voltage attachment terminals (U, V, W) and converter half bridges (2a, 2b, 2c). 11 . A computer program which, when executed on a computing unit, causes the computing unit to carry out all method steps of the method according to claim 1 .

12. A machine-readable storage medium having stored thereon the computer program according to claim 11.

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