Method for operating a DC / DC converter for supplying an electrolysis device with electrical operating energy and DC / DC converter

Description

[0001] The invention relates to a method for operating a DC controller to supply an electrolysis device with electrical operating energy.

[0002] Hydrogen production via electrolysis requires direct currents of several thousand amperes, but direct voltages in the range of only 100 to 1400 volts.

[0003] For this purpose, electrolysis plants are supplied with direct current (DC) as operating energy by connecting to a medium-voltage AC power grid. The controlled rectifiers used are line-commutated rectifiers (thyristors) and therefore, by their very nature, must always be connected to an AC power grid.

[0004] However, there is also a need to supply electrolysis facilities within smaller island grids with electrical capacities of up to 10 MW with electrical operating energy in the form of direct current from solar cells or wind power.

[0005] From DE 10 2012 201269 A1, a circuit arrangement and a method for selectively controlling an AC motor or a DC motor powered by a DC voltage source are known. The circuit arrangement comprises two converter modules with the same number of half-bridges and a number of bridge chokes corresponding to the number of half-bridges in a converter module, as well as a control unit for controlling the half-bridges of the converter modules. The converter modules are operated as an inverter for controlling an AC motor and as a DC-DC converter for controlling a DC motor.

[0006] From DE 10 2017 217948 A1, a drive device is known which has a first half-bridge with a first phase connection, a second half-bridge with a second phase connection, a third half-bridge with a third phase connection, and a fourth half-bridge with a fourth phase connection, wherein the first phase connection is connected to the second phase connection via a first current-compensated choke which has a first motor winding-side connection, and wherein the third phase connection is connected to the fourth phase connection via a second current-compensated choke which has a second motor winding-side connection. The half-bridges are driven offset within a half-cycle.

[0007] International patent application WO 2016 / 091300 A1 describes a DC controller comprising four transistors that feeds an electrolysis hydrogen storage system. The transistors are controlled by pulse-width modulation.

[0008] WO 2019 / 043136 A1 discloses a DC / DC converter comprising several power switches with chokes connected at their outputs. The power switches are controlled by a control unit using predictive pulse pattern control.

[0009] Therefore, there is a need to show ways in which, for example, a direct connection to a low-voltage direct current network can be achieved to supply an electrolysis plant with electrical operating energy.

[0010] The object of the invention is solved by a method for operating a DC chopper for supplying an electrolysis device with electrical operating energy, in which, in one step, at least four controllable semiconductor switching elements in an H-bridge arrangement with downstream suction chokes are controlled with a predetermined control signal sequence for the direct conversion of an electrical input DC voltage into an electrical output DC voltage, wherein at least two DC voltage converter units, each with four controllable semiconductor switching elements in an H-bridge arrangement with downstream suction chokes, are used, comprising the step: detecting a number of the DC voltage converter units, and adapting the control signal sequence to the detected number of DC voltage converter units.

[0011] The controllable semiconductor switching elements can, for example, be bipolar transistors designed as IGBTs (insulated-gate bipolar transistors). This means that the controllable semiconductor switching elements can not only be triggered like thyristors, but also switched to a blocking state by a corresponding control signal, independent of a zero crossing. Thus, the DC-DC converter can be designed as a self-commutated DC-DC converter. In this case, the DC-DC converter is designed for direct conversion; that is, the input DC voltage is not converted to an AC voltage, followed by transformation and subsequent rectification, for example, in an intermediate circuit.

[0012] This allows corresponding transformer losses to be avoided by directly connecting an electrolysis unit to a low-voltage direct current network.

[0013] A modular DC chopper is used, which can be adapted to the specific load by adding or removing DC-DC converter units. In other words, the DC chopper can be considered a modular, multilevel DC chopper. Before commissioning, or during an initialization phase, the number of DC-DC converter units is automatically determined, for example, by a control unit of the DC chopper, and a correspondingly adapted control signal sequence is provided.

[0014] According to another embodiment, the step of adapting the control signal sequence to the detected number of DC-DC converter units includes adapting a clock frequency of the control signal sequence to the detected number of DC-DC converter units.

[0015] Adjusting the clock frequency can involve reducing it. For example, if two DC-DC converter units are detected, the output clock frequency for operating a single DC-DC converter unit is halved. Conversely, if four DC-DC converter units are detected, the output clock frequency is reduced to a quarter. Similarly, with eight DC-DC converter units, the output clock frequency is reduced to an eighth. Generally, switching losses would increase with a larger number of DC-DC converter units in parallel circuits. However, this can be counteracted by reducing the clock frequencies, so that energy efficiency can at least be kept constant or even improved.

[0016] According to a further embodiment, the step of adapting the control signal sequence to the detected number of DC-DC converter units includes providing a control signal sequence for the time-shifted control of the controllable semiconductor switching elements of the at least the DC-DC converter units. That is, when a controllable semiconductor switching element of a DC-DC converter unit is in a conducting state due to control, the controllable semiconductor switching elements of the other DC-DC converter units are in an electrically blocking state. Thus, for example, by doubling the clock frequency via staggered clocking of the half-bridges connected to the DC-DC converter units, in conjunction with the two voltage divider-acting choke halves, the ripple current can be further reduced.

[0017] Furthermore, the invention includes a computer program product designed to execute the method, a DC-DC converter for supplying an electrolysis device with electrical operating energy, and a control unit for such a DC-DC converter. The control unit for a DC-DC converter is designed and configured such that, when the DC-DC converter is activated, it determines the control signal sequence in such a way that the first inductor and the second inductor are energized with the same electrical current.

[0018] The invention will now be explained with the aid of a drawing. The drawing shows: Figure 1 Schematic representation of the components of a DC converter. Figure 2 further details of the schematic representation of the Figure 1 shown DC converter. Figure 3 further details of the schematic representation of the Figure 1 shown DC converter. Figure 4 in schematic representation a combination of the in the Figures 1 to 3 The DC converter shown has a rectifier. Figure 5 a schematic representation of the procedure for operating the, in particular in Figure 2 shown DC converter.

[0019] It will initially be on Figure 1 Reference made to.

[0020] The figure shows an electrical network 2, which in the present embodiment is designed as a low-voltage direct current network.

[0021] In this embodiment, network 2 is configured as a small island grid with an electrical output of up to 10 MW. In this embodiment, the DC voltage in electrical network 2 is 1500 V.

[0022] Network 2 is supplied with electrical energy from solar cells or wind power. An electrolysis unit 6 (also called an electrolyzer) is connected to Network 2 as a consumer.

[0023] The electrolysis device 6 is designed to bring about a chemical reaction, i.e., a chemical transformation, using the electric current supplied by the network 2. In the present embodiment, water electrolysis, i.e., the decomposition of water into hydrogen and oxygen, is carried out.

[0024] Water electrolysis requires direct electric currents with current strengths of several thousand amperes, but direct electric voltages in the range of 100 to 1400 volts.

[0025] For this purpose, the electrical voltage and current of network 2 are converted accordingly. A DC-DC converter 4 is provided between network 2 and the electrolysis unit 6 for the direct conversion.

[0026] A DC-DC converter (also DC-DC converter, DC-DC converter) is an electrical circuit that converts an electrical DC voltage supplied at the input into an electrical DC voltage with a higher, lower or inverted voltage level.

[0027] In the present embodiment, the DC-DC converter 4 is configured as a self-commutated and modular multilevel DC-DC converter. In this embodiment, the DC-DC converter 4 comprises four DC-DC converter units 8a, 8b, 8c, 8d. In contrast to the present embodiment, the number n of DC-DC converter units 8a, 8b, 8c, 8d can also be different. In particular, it can be provided that the DC-DC converter 4 is modularly adaptable to a load by adding or removing one or more DC-DC converter units 8a, 8b, 8c, 8d.

[0028] In the present embodiment, the four DC voltage converter units 8a, 8b, 8c, 8d are each identically constructed.

[0029] It is further referred to Figure 2 The structure of the DC voltage converter unit 8a is explained.

[0030] In the present embodiment, the DC voltage converter unit 8a has on the input side a diode 10, a capacitor 12, a first fuse 14a and a second fuse 14b.

[0031] Furthermore, the DC voltage converter unit 8a in the present embodiment has a first controllable semiconductor switching element 16a, a second controllable semiconductor switching element 16b, a third controllable semiconductor switching element 16c and a fourth controllable semiconductor switching element 16d.

[0032] The first controllable semiconductor switching element 16a, the second controllable semiconductor switching element 16b, the third controllable semiconductor switching element 16c and the fourth controllable semiconductor switching element 16d are arranged in a bridge-like manner in an H-bridge, wherein the first controllable semiconductor switching element 16a and the third controllable semiconductor switching element 16c form a first bridge branch and the second controllable semiconductor switching element 16b and the fourth controllable semiconductor switching element 16d form a second bridge branch of the bridge circuit.

[0033] In the present embodiment, the first controllable semiconductor switching element 16a, the second controllable semiconductor switching element 16b, the third controllable semiconductor switching element 16c, and the fourth controllable semiconductor switching element 16d each comprise a bipolar transistor with an insulating gate electrode. That is, they are each configured as an IGBT (insulated-gate bipolar transistor), whose collector defines the input of the switching unit and whose emitter defines the output of the switching unit. In the present embodiment, each controllable semiconductor switching element 16a, 16b, 16c, 16d is associated with a freewheeling diode.

[0034] On the output side, the DC-DC converter unit 8a has a first inductor 18a and a second inductor 18b. The first inductor 18a and the second inductor 18b are magnetically coupled in opposite directions, meaning that their respective magnetizations cancel each other out. The use of inductors 18a and 18b advantageously allows for the limitation of current ripple in an electric current.

[0035] A control unit 24 of the DC-DC converter 4 is configured to provide, during operation, a control signal sequence ASF for controlling the controllable semiconductor switching elements 16a, 16b, 16c, 16d in order to effect a direct conversion of an electrical input DC voltage into an electrical output DC voltage. The control signal sequence ASF is determined by the control unit 24 such that the first choke 18a and the second choke 18b are energized by the same electrical current.

[0036] Since the electric currents in the respective arms of the suction chokes 18a, 18b generate opposing, mutually canceling magnetic fields, the two suction chokes 18a, 18b are designed such that the series inductance between two DC-DC converter units 8a, 8b, 8c, 8d is large enough to adequately limit any cross-current flowing between the two DC-DC converter units 8a, 8b, 8c, 8d. Furthermore, it is possible to reduce this cross-current to a minimum by modifying the pulse generation to prevent saturation of the choke core. Because the electric currents in the arms of the respective suction chokes 18a, 18b generate opposing, mutually canceling magnetic fields, the core is not magnetized, or only slightly magnetized, by the load current, allowing it to be dimensioned relatively small.

[0037] For these and the other tasks and / or functions described below, the control unit may in particular have 24 hardware and / or software components.

[0038] It will now also be applied to Figure 3 Reference made to.

[0039] The four identically constructed DC voltage converter units 8a, 8b, 8c, 8d are shown.

[0040] The first DC-DC converter unit 8a and the second DC-DC converter unit 8b are magnetically coupled on their output sides by a third choke 18c and a fourth choke 18d. Similarly, the third DC-DC converter unit 8c and the fourth DC-DC converter unit 8d are magnetically coupled on their output sides in a first plane.

[0041] Furthermore, in the present embodiment, the respective third suction throttles 18c and fourth suction throttle 18d are magnetically coupled on the output side in a second plane analogously by a fifth suction throttle 18e and a sixth suction throttle 18e in a third plane.

[0042] In the present embodiment, the respective third suction throttles 18c and fourth suction throttle 18d of the second level as well as the fifth suction throttle 18e and the sixth suction throttle 18e of the third level are also magnetically coupled in opposite directions, i.e. the respective magnetizations of the respective suction throttles 18c, 18d, 18e, 18f compensate each other.

[0043] Analogous to the previous embodiment according to Figure 1During operation, the control unit 24 of the DC voltage converter 4 provides a control signal sequence ASF for controlling the controllable semiconductor switching elements 16a, 16b, 16c, 16d in order to effect a direct conversion of an electrical input DC voltage into an electrical output DC voltage.

[0044] In the present embodiment, the control unit 24 is configured to determine the number n of DC-DC converter units 8a, 8b, 8c, 8d in advance, i.e., before its commissioning or during its commissioning during an initialization phase. Furthermore, in the present embodiment, the control unit 24 is configured to adapt the control signal sequence ASF to the detected number n of DC-DC converter units 8a, 8b, 8c, 8d.

[0045] In the present embodiment, the adaptation of the control signal sequence ASF involves adjusting the clock frequency f of the control signal sequence ASF to the detected number n of DC-DC converter units 8a, 8b, 8c, 8d. In this embodiment, the output clock frequency is reduced accordingly by the detected number n of DC-DC converter units 8a, 8b, 8c, 8d.

[0046] Therefore, if two DC-DC converter units 8a, 8b are detected, the output clock frequency is halved in the present embodiment to determine the clock frequency f. If – as in the present embodiment – ​​four DC-DC converter units 8a, 8b, 8c, 8d are detected, the output clock frequency is reduced to one-quarter to determine the clock frequency f. Similarly, if, for example, the number n is eight, the output clock frequency is reduced to one-eighth to determine the clock frequency f.

[0047] In the present embodiment, each of the two half-bridges of the DC-DC converter units 8a, 8b, 8c, 8d is clocked at a clock frequency f of, for example, 2 kHz. Due to the parallel connection via the respective chokes 18a, 18b, the output of each DC-DC converter unit 8a, 8b, 8c, 8d is twice the clock frequency f of one half-bridge, i.e., a frequency of 4 kHz. Through the respective interconnection with the respective chokes 18c, 18d, a further doubled frequency of 8 kHz appears at the output. Through the further interconnection with the chokes 18e, 18f, a further doubled frequency of 16 kHz appears at the output.

[0048] In other words, each stage of the throttling mechanism, with throttling elements 18, 18b, 18c, 18d, and 18e, 18f respectively, doubles the clock frequency f. In the present embodiment, the output clock frequency is reduced to one-quarter. This reduction in the output clock frequency reduces the switching losses in the DC-DC converter units 8a, 8b, 8c, 8d. Thus, switching losses can be reduced or even compensated for by additional DC-DC converter units 8a, 8b, 8c, 8d.

[0049] Furthermore, in the present embodiment, the control unit 24 is designed to adapt the control signal sequence ASF in such a way that the DC voltage converter units 8a, 8b, 8c, 8d are controlled with a time offset.

[0050] In the present embodiment, each of the two half-bridges of the DC voltage converter units 8a, 8b, 8c, 8d is controlled by clocking the two respective half-bridges of the DC voltage converter units 8a, 8b, 8c, 8d at 180° intervals.

[0051] In the present embodiment, the control unit 24 provides a control signal sequence ASF with its own carrier signal for controlling the respective half-bridges of the DC voltage converter units 8a, 8b, 8c, 8d.

[0052] In order for each suction throttle stage with the suction throttles 18, 18b or 18c, 18d or 18e, 18f to cause a doubling of the clock frequency f, in the present embodiment the first half-bridge with the controllable semiconductor switching elements 16a, 16c of the first DC voltage converter unit 8a is controlled with switching points at 0°, while the second half-bridge with the controllable semiconductor switching elements 16b, 16d of the first of the DC voltage converter unit 8a is controlled with switching points at 180°.

[0053] Furthermore, in the present embodiment, the first half-bridge with the controllable semiconductor switching elements 16a, 16c of the second DC voltage converter unit 8b is controlled analogously with switching points at 90°, while the second half-bridge with the controllable semiconductor switching elements 16b, 16d of the second DC voltage converter unit 8b is controlled with switching points at 270°.

[0054] Furthermore, in the present embodiment, the first half-bridge with the controllable semiconductor switching elements 16a, 16c of the third DC voltage converter unit 8c is controlled analogously with switching points at 45°, while the second half-bridge with the controllable semiconductor switching elements 16b, 16d of the third DC voltage converter unit 8c is controlled with switching points at 225°.

[0055] Finally, in the present embodiment, the first half-bridge with the controllable semiconductor switching elements 16a, 16c of the fourth DC voltage converter unit 8d is controlled analogously with switching points at 135°, while the second half-bridge with the controllable semiconductor switching elements 16b, 16d of the fourth DC voltage converter unit 8d is controlled with switching points at 315°.

[0056] It can also be provided that the clock frequency f remains constant regardless of the number n of the DC-DC converter units 8a, 8b, 8c, 8d. That is, the DC-DC converter units 8a, 8b, 8c, 8d are simply controlled with a time offset. This also increases energy efficiency and allows for the estimation of degradation effects caused by ripple currents at the electrolysis unit 6.

[0057] This allows the ripple voltage of the output voltage to be significantly reduced, e.g. to a residual ripple in the range of 3% to 5%.

[0058] In the present embodiment, each of the DC-DC converter units 8a, 8b, 8c, 8d provides a DC output current of 2000 A at a DC voltage of 1350 V. Thus, with the four DC-DC converter units 8a, 8b, 8c, 8d in this embodiment, a total current of 8000 A can be provided. Adjustment to a required total current can be achieved by adding or removing DC-DC converter units 8a, 8b, 8c, 8d, whereby the control unit 24 automatically determines the number n of DC-DC converter units 8a, 8b, 8c, 8d and adjusts the control signal sequence ASF accordingly.

[0059] It will now also be applied to Figure 4 Reference made to.

[0060] In the present embodiment, the electrical network 2 is designed as an alternating current network, e.g. as a three-phase network.

[0061] Therefore, a transformer 20, designed as a three-phase transformer in the present embodiment, and a rectifier 22 are provided between the network 2 and the DC voltage converter 4.

[0062] By interposing the transformer 20 and the rectifier 22, the DC voltage converter 4 can also be electrically connected to an AC network or a three-phase network.

[0063] It will also be added to Figure 5 Reference made to.

[0064] The diagram shows a procedure for operating the system in Figure 1 system 2 shown.

[0065] In a first step S1, the control unit 24 detects, e.g. during commissioning or during its commissioning during an initialization phase, the number n of the DC voltage converter units 8a, 8b, 8c, 8d.

[0066] In a further step S2, the control unit 24 adapts the control signal sequence ASF to the detected number n of the DC voltage converter units 8a, 8b, 8c, 8d.

[0067] For this purpose, in the present embodiment, the control unit 24 adjusts the clock frequency of the control signal sequence ASF to the detected number n of the DC voltage converter units 8a, 8b, 8c, 8d and modifies the control signal sequence ASF such that the controllable semiconductor switching elements 16a, 16b, 16c, 16d of the at least four DC voltage converter units 8a, 8b, 8c, 8d are controlled with a time offset.

[0068] With the control signal sequence ASF determined in this way, the controllable semiconductor switching elements 16a, 16b, 16c, 16d of the respective DC voltage converter units 8a, 8b, 8c, 8d are then controlled during operation in order to effect the direct conversion of an electrical input DC voltage into an electrical output DC voltage.

[0069] In contrast to the present embodiment, the sequence of steps can also be different. Furthermore, several steps can be executed simultaneously. Individual steps can also be omitted or skipped.

[0070] For example, transformer losses can be avoided by directly connecting an electrolysis unit to a low-voltage direct current network.

Claims

1. Method for operating a DC chopper for supplying electrical operating power to an electrolysis device (6), wherein, in one step (S3), at least four actuatable semiconductor switching elements (16a, 16b, 16c, 16d) in an H-bridge arrangement are actuated by a predetermined actuation signal sequence (ASF) for the direct conversion of an electrical DC input voltage into an electrical DC output voltage, characterized in that at least two DC voltage converter units (8a, 8b, 8c, 8d) are used, each having four actuatable semiconductor switching elements (16a, 16b, 16c, 16d) in an H-bridge arrangement with interphase transformers (18a, 18b, 18c, 18d, 18e, 18f) connected downstream, comprising the following steps: (S1) detection of a number (n) of DC voltage converter units (8a, 8b, 8c, 8d), and (S2) adaptation of the actuation signal sequence (ASF) to the detected number (n) of DC voltage converter units (8a, 8b, 8c, 8d).

2. Method according to Claim 1, wherein step (S2) for the adaptation of the actuation signal sequence (ASF) to the detected number (n) of DC voltage converter units (8a, 8b, 8c, 8d) comprises an adaptation of a clock frequency of the actuation signal sequence (ASF) to the detected number (n) of DC voltage converter units (8a, 8b, 8c, 8d).

3. Method according to Claim 1 or 2, wherein step (S2) for the adaptation of the actuation signal sequence (ASF) to the detected number (n) of DC voltage converter units (8a, 8b, 8c, 8d) comprises the delivery of an actuation signal sequence (ASF) for the temporally staggered actuation of the actuatable semiconductor switching elements (16a, 16b, 16c, 16d), at least of the DC voltage converter units (8a, 8b, 8c, 8d).

4. Computer program product designed for carrying out a method according to any of Claims 1 to 3.

5. DC voltage converter (4) for supplying electrical operating power to an electrolysis device (6), having at least four actuatable semiconductor switching elements (16a, 16b, 16c, 16d) in an H-bridge arrangement, wherein a controller (24) of the DC voltage converter (4) is designed to deliver a predetermined actuation signal sequence (ASF) to the at least four actuatable semiconductor switching elements (16a, 16b, 16c, 16d) for the direct conversion of an electrical DC input voltage into an electrical DC output voltage, characterized in that the DC voltage converter (4) comprises at least two DC voltage converter units (8a, 8b, 8c, 8d) each having four actuatable semiconductor switching elements (16a, 16b, 16c, 16d) in an H-bridge arrangement with interphase transformers (18a, 18b, 18c, 18d, 18e, 18f) connected downstream, wherein the controller (24) of the DC voltage converter (4) is designed to detect a number (n) of DC voltage converter units (8a, 8b, 8c, 8d) and to adapt the actuation signal sequence (ASF) to the detected number (n) of DC voltage converter units (8a, 8b, 8c, 8d).

6. DC voltage converter (4) according to Claim 5, wherein the controller (24) of the DC voltage converter (4) is designed to adapt a clock frequency of the actuation signal sequence (ASF) to the detected number (n) of DC voltage converter units (8a, 8b, 8c, 8d).

7. DC voltage converter (4) according to Claim 5 or 6, wherein the controller (24) of the DC voltage converter (4) is designed to deliver an actuation signal sequence (ASF) for the temporally staggered actuation of the actuatable semiconductor switching elements (16a, 16b, 16c, 16d) of the DC voltage converter units (8a, 8b, 8c, 8d).

8. Controller (24) for a DC voltage converter (4) according to any of Claims 5 to 7, designed in such a way that, upon actuation of the DC voltage converter (4), the actuation signal sequence (ASF) is determined in such a way that a current of equal current strength flows through the first interphase transformer (18a) and the second interphase transformer (18b).