Patent Application
20240291386
The invention relates to a method for operating a DC-DC converter for supplying an electrolysis device with electrical operating power.
Hydrogen production by means of electrolysis requires DC currents in excess of several thousand amperes, but a DC voltage in the region of only 100 to 1,400 volts.
To this end, electrolysis devices are supplied with a DC current, by way of operating power, via a connection to a medium-voltage AC grid system. The controlled rectifiers employed for this purpose are line-commutated rectifiers (thyristors) and, by design, must therefore be connected to an AC grid system at all times.
However, there is also a requirement, within smaller separate networks of electrical capacity up to 10 MW, for electrolysis devices to be supplied with electrical operating power in the form of a DC electric current sourced from solar cells or wind energy.
There is consequently a need for the disclosure of means whereby, e.g. for the supply of an electrolysis device with electrical operating power, a direct connection to a low-voltage DC grid system can be achieved.
The object of the invention is fulfilled by a method for operating a DC-DC controller for supplying an electrolysis device with electrical operating power wherein, in one step, at least four actuatable semiconductor switching elements in an H-bridge arrangement with interphase transformers connected down-circuit are actuated by a predetermined actuation signal sequence for the direct conversion of a DC electric input voltage into a DC electric output voltage, wherein at least two DC voltage converter units are employed, each having four actuatable switching elements in an H-bridge arrangement with interphase transformers connected down-circuit, incorporating the following step: detection of a number of DC voltage converter units and adaptation of the actuation signal sequence to the number of DC voltage converter units detected.
The actuatable semiconductor switching elements can be bipolar transistors which are configured e.g. in the form of IGBTs (insulated-gate bipolar transistors). This means that the actuatable semiconductor switching elements can not only be triggered in the manner of a thyristor, but can also be switched to a blocking state by means of a corresponding actuation signal, independently of a zero-crossing. The DC-DC converter can thus be configured as a self-commutating DC-DC converter. The DC-DC converter is thus configured for direct conversion, i.e. there is no inversion of the electrical input DC voltage into an electrical AC voltage, followed by transformation in the form of a subsequent rectification, e.g. in a DC link.
Corresponding transformation losses can thus be reduced by a direct connection of a low-voltage DC grid system to an electrolysis device.
A DC-DC converter of a modular design is thus employed, which can be adapted to the respective load by the addition or removal of DC voltage converter units. In other words, the DC-DC converter can be configured as a multilevel DC-DC converter of modular design. Beforehand, i.e. prior to commissioning or during an initialization phase in the course of commissioning, the number of DC converter units can be determined independently, e.g. by a control device of the DC-DC converter, and a correspondingly adapted actuation signal sequence can be delivered.
According to a further embodiment, the step for the adaptation of the actuation signal sequence to the detected number of DC voltage converter units includes an adaptation of a pulse frequency of the actuation signal sequence to the detected number of DC voltage converter units.
The adaptation can be a reduction of the pulse frequency. In the event that e.g. two DC voltage converter units are detected, an output pulse frequency for the operation of a single DC voltage converter unit is divided by half. Conversely, in the event that e.g. four DC voltage converter units have been detected, the output pulse frequency is reduced to one quarter. Correspondingly, e.g. in the case of eight DC voltage converter units, the output pulse frequency is reduced to one eighth. In principle, as a result of the greater number of DC voltage converter units connected in parallel, switching losses would be expected to increase. However, this can be counteracted by the reduced pulse frequency, such that energy efficiency at least remains constant, or can even be improved.
According to a further embodiment, the step for the adaptation of the actuation signal sequence to the detected number of DC voltage converter units includes the delivery of an actuation signal sequence for the temporally staggered actuation of actuatable semiconductor switching elements, at least of the DC voltage converter units. This means that, if one actuatable semiconductor switching element of a DC voltage converter unit is in a conducting state, further to actuation, the actuatable semiconductor switching elements of the remaining DC voltage converter units assume an electrically non-conducting state. Thus, e.g. by a doubling of the pulse frequency, associated with the staggered pulsing of DC voltage converter units which are interconnected in the half-bridges, in combination with the two halves of the interphase transformers, which function as voltage dividers, a reduction in the ripple current is further achieved.
The invention further includes a computer program product, which is configured to execute the method, a DC voltage converter for the supply of operating power to an electrolysis device, and a control device for a DC voltage converter of this type. The control device for a DC voltage converter is configured and designed such that, upon the actuation of the DC voltage converter, it determines the actuation signal sequence such that a current of equal strength flows through the first interphase transformer and the second interphase transformer.
The invention is described hereinafter with reference to a drawing. In the drawing:
Reference will firstly be made to
An electrical grid 2 is represented which, in an exemplary embodiment, is configured in the form of a low-voltage DC grid system.
In an exemplary embodiment, the grid 2 is configured as a small separate network with an electrical capacity of up to 10 MW. In an exemplary embodiment, the DC electric voltage in the electrical grid 2 is 1,500 V.
The grid 2 is supplied with electrical energy generated from solar cells or wind power. By way of a load, an electrolysis device 6 (also described as an electrolyzer) is connected to the grid 2.
The electrolysis device 6 is configured, using electric current supplied by the gird 2, to initiate a chemical reaction, i.e. a material conversion. In an exemplary embodiment, the electrolysis of water is executed, i.e. a breakdown of water into hydrogen and oxygen.
The electrolysis of water requires DC electric currents with current strengths of several thousand amperes, but DC electric voltages within the range of 100 to 1,400 volts only.
To this end, the electric voltage and the electric current strength 2 in grid are converted accordingly. For direct conversion, a DC voltage converter 4 is provided between the grid 2 and the electrolysis device 6.
A DC voltage converter 4 (also described as a DC chopper converter or a DC-DC converter) is understood as an electric circuit which converts a DC electric voltage which is infed at the input thereof into a DC electric voltage with a higher, lower or inverted voltage level.
In an exemplary embodiment, the DC voltage converter 4 is configured as a self-commutating multilevel DC-DC converter of modular design. In an exemplary embodiment, the DC voltage converter 4 includes four DC voltage converter units 8a, 8b, 8c, 8d. By way of deviation from an exemplary embodiment, the number n of DC voltage converter units 8a, 8b, 8c, 8d can also be different. In particular, it can be provided the DC voltage converter 4 is adaptable to a load, in a modular manner, by the addition or removal of one or more DC voltage converter units 8a, 8b, 8c, 8d.
In an exemplary embodiment, the four DC voltage converters 8a, 8b, 8c, 8d are of a respectively identical design.
The layout of the DC voltage converter unit 8a is further described with reference to
In an exemplary embodiment, the DC voltage converter unit 8a, on the input side, includes a diode 10, a capacitor 12, a first fuse 14a and a second fuse 14b.
In an exemplary embodiment, the DC voltage converter unit 8a further includes a first actuatable semiconductor switching element 16a, a second actuatable semiconductor switching element 16b, a third actuatable semiconductor switching element 16c, and a fourth actuatable semiconductor switching element 16d.
The first actuatable semiconductor switching element 16a, the second actuatable semiconductor switching element 16b, the third actuatable semiconductor switching element 16c and the fourth actuatable semiconductor switching element 16d are arranged, in the manner of a bridge circuit, in an H-bridge, wherein the first actuatable semiconductor switching element 16a and the third actuatable semiconductor switching element 16c form a first bridge arm, and the second actuatable semiconductor switching element 16b and the fourth actuatable semiconductor switching element 16d form a second bridge arm of the bridge circuit.
In an exemplary embodiment, the first actuatable semiconductor switching element 16a, the second actuatable semiconductor switching element 16b, the third actuatable semiconductor switching element 16c and the fourth actuatable semiconductor switching element 16d each include a bipolar transistor having an insulated-gate electrode. This means that the latter are respectively configured as IGBTs (insulated-gate bipolar transistors), the collector of which defines the input of the switching unit and the emitter of which defines the output of the switching unit. In an exemplary embodiment, one freewheeling diode is respectively assigned to each of the actuatable semiconductor switching elements 16a, 16b, 16c, 16d.
On the output side, the DC voltage converter unit 8a includes a first interphase transformer 18a and a second interphase transformer 18b. The first interphase transformer 18a and the second interphase transformer 18b are magnetically coupled in opposition, i.e. the respective magnetizations of the first interphase transformer 18a and the second interphase transformer 18b mutually compensate each other. The use of interphase transformers 18a, 18b advantageously permits a limitation of ripple in an electric current.
A control device 24 of the DC voltage converter 4 is configured, in operation, to deliver an actuation signal sequence ASF for the actuation of the actuatable semiconductor switching elements 16a, 16b, 16c, 16d, in order to execute a direct conversion of a DC electric input voltage into a DC electric output voltage. The actuation signal sequence ASF is determined by the control device 24 such that a current of equal current strength flows through the first interphase transformer 18a and the second interphase transformer 18b.
As electric currents in the respective arms of the interphase transformers 18a, 18b generate opposing magnetic fields, which cancel each other out, the two interphase transformers 18a, 18b are configured such that the longitudinal inductance between two DC voltage converter units 8a, 8b, 8c, 8d is sufficiently large to provide adequate limitation of any electric crossover current from one DC voltage converter unit 8a, 8b, 8c, 8d to another. It is further possible for this electric crossover current to be reduced to a minimum by means of interventions in pulse generation, in order to prevent any saturation of the reactor core. As electric currents in the arms of the respective interphase transformers 18a, 18b generated opposing magnetic fields, which cancel each other out, the core is thus not magnetized by the load current, or is only magnetized to a limited extent, such that it can be configured with relatively small dimensions.
For this and further operations and/or functions described hereinafter, in particular, the control device 24 can include hardware and/or software components.
Reference will now be additionally made to
Four DC voltage converter units 8a, 8b, 8c, 8d of respectively identical design are represented.
The first DC voltage converter unit 8a and the second DC voltage converter unit 8b, on the output side, are magnetically coupled by a third interphase transformer 18c and a fourth interphase transformer 18d. In an analogous manner, the third DC voltage converter unit 8c and the fourth DC voltage converter unit 8d, on the output side, are magnetically coupled in a first plane.
Moreover, in an exemplary embodiment, the third interphase transformer 18c and the fourth interphase transformer 18d, on the output side, are respectively magnetically coupled in an analogous manner, in a second plane, by a fifth interphase transformer 18e, and by a sixth interphase transformer 18e in a third plane.
In an exemplary embodiment, the respective third interphase transformers and 18c the fourth interphase transformer 18d on the second plane, and the fifth interphase transformer 18e and the sixth interphase transformer 18e on the third plane are also magnetically coupled in opposition, i.e. the respective magnetizations of the respective interphase transformers 18c, 18d, 18e, 18f mutually compensate one another.
In an analogous manner to the preceding exemplary embodiment according to
In an exemplary embodiment, the control device 24 is configured beforehand, i.e. prior to the commissioning thereof or during an initialization phase in the course of the commissioning thereof, to determine the number n of DC voltage converter units 8a, 8b, 8c, 8d. Moreover, according to an exemplary embodiment, the control device 24 is configured to adapt the actuation signal sequence ASF to the number n of DC voltage converter units 8a, 8b, 8c, 8d identified.
In an exemplary embodiment, adaptation of the actuation signal sequence ASF includes an adaptation of a pulse frequency f of the actuation signal sequence ASF to the detected number n of DC voltage converter units 8a, 8b, 8c, 8d. In an exemplary embodiment, an output pulse frequency is reduced in accordance with the detected number n of DC voltage converter units 8a, 8b, 8c, 8d.
Accordingly, if two DC voltage converter units 8a, 8b have been detected, in an exemplary embodiment, the output pulse frequency is halved, in order to determine the pulse frequency f. In the event that—as per an exemplary embodiment—four DC voltage converter units 8a, 8b, 8c, 8d have been detected, the output pulse frequency is reduced to one quarter, in order to determine the pulse frequency f. Correspondingly, e.g. in the event that the number n is equal to eight, the output pulse frequency is reduced to one eighth, in order to determine the pulse frequency f.
In an exemplary embodiment, in operation, each of the two half-bridges of the DC voltage converter units 8a, 8b, 8c, 8d is pulsed with a pulse frequency f of e.g. 2 kHz. At the output of the respective DC voltage converter unit 8a, 8b, 8c, 8d, in accordance with the parallel connection via the respective interphase transformers 18a, 18b on the output side, double the pulse frequency f of one half-bridge, i.e. a frequency of 4 kHz. As a result of the respective interconnection with the respective interphase transformers 18c, 18d, in an analogous manner, a redoubled frequency of 8 kHz is present on the output side. By means of the further interconnection with the interphase transformers 18e, 18f, in an analogous manner, a further redoubled frequency of 16 kHz is present on the output side.
In other words, each interface transformer stage, comprising the interphase transformers 18, 18b or 18c, 18d or 18e, 18f, executes a doubling of the frequency value of the pulse frequency f. In an exemplary embodiment, the output pulse frequency is reduced to one quarter. This reduction of the output pulse frequency reduces switching losses in the DC voltage converter units 8a, 8b, 8c, 8d. Switching losses can thus be reduced or compensated by means of additional DC voltage converter units 8a, 8b, 8c, 8d.
Moreover, in an exemplary embodiment, the control device 24 is configured to adapt the actuation signal sequence ASF such that the DC voltage converter units 8a, 8b, 8c, 8d are actuated in a temporally staggered manner.
In operation, in an exemplary embodiment, each of the two half-bridges of the DC voltage converter units 8a, 8b, 8c, 8d is actuated by a pulse which is offset through 180° on the two respective half-bridges of the DC voltage converter units 8a, 8b, 8c, 8d.
In an exemplary embodiment, the control device 24 delivers an actuation signal sequence ASF with a dedicated carrier signal for the actuation of the respective half-bridges of the DC voltage converter units 8a, 8b, 8c, 8d.
In order to permit each interphase transformer stage, comprising the interphase transformers 18, 18b, or 18c, 18d, or 18e, 18f, to execute a doubling of the frequency value of the pulse frequency f, in an exemplary embodiment, the first half-bridge comprising the actuatable semiconductor switching elements 16a, 16c of the first DC voltage converter unit 8a is actuated with switching points at 0°, whereas the second half-bridge comprising the actuatable semiconductor switching elements 16b, 16d of the first DC voltage converter unit 8a is actuated with switching points at 180°.
Additionally, in an exemplary embodiment, in an analogous manner, the first half-bridge comprising the actuatable semiconductor switching elements 16a, 16c of the second DC voltage converter unit 8b is actuated with switching points at 90°, whereas the second half-bridge comprising the actuatable semiconductor switching elements 16b, 16d of the second DC voltage converter unit 8b is actuated with switching points at 270°.
Moreover, in an exemplary embodiment, in an analogous manner, first the half-bridge comprising the actuatable semiconductor switching elements 16a, 16c of the third DC voltage converter unit 8c is actuated with switching points at 45°, whereas the second half-bridge comprising the actuatable semiconductor switching elements 16b, 16d of the third DC voltage converter unit 8c is actuated with switching points at 225°.
Finally, in an exemplary embodiment, in an analogous manner, the first half-bridge comprising the actuatable semiconductor switching elements 16a, 16c of the fourth DC voltage converter unit 8d is actuated with switching points at 135°, whereas the second half-bridge comprising the actuatable semiconductor switching elements 16b, 16d of the fourth DC voltage converter unit 8d is actuated with switching points at 315°.
It can also be provided that the pulse frequency f remains the same, independently of the number n of DC voltage converter units 8a, 8b, 8c, 8d. This means that only a temporally staggered actuation of the DC voltage converter units 8a, 8b, 8c, 8d is executed. Accordingly, energy efficiency can be increased and, additionally, degradation effects associated with ripple currents on the electrolysis device 6 can be evaluated. Any voltage ripple in the output voltage can thus be significantly reduced, e.g. to a residual ripple, which lies within the range of 3%to 5%.
In an exemplary embodiment, each of the DC voltage converter units 8a, 8b, 8c, 8d delivers a DC electric output voltage with a current strength of 2,000 A, at a DC electric voltage of 1,350 V. Thus, by means of the four DC voltage converter units 8a, 8b, 8c, 8d in an exemplary embodiment, an overall electric current strength of 8,000 A can be delivered. An adaptation to the overall current strength required ca be achieved by the addition or removal of DC voltage converter units 8a, 8b, 8c, 8d, wherein the control device 24 independently determines the number n of DC voltage converter units 8a, 8b, 8c, 8d and adapts the actuation signal sequence ASF accordingly.
Reference will now be additionally made to
In an exemplary embodiment, the electrical grid 2 is configured as an AC grid system, e.g. as a three-phase AC grid system.
Consequently, between the grid 2 and the DC voltage converter 4, a transformer 20 which, in an exemplary embodiment, is configured in the form of a three-phase AC transformer and a rectifier 22 are provided.
By the interposition of the transformer 20 and the rectifier 22, the DC voltage converter 4 can thus also be electrically connected to an AC grid system or to a three-phase AC grid system.
Reference is additionally made to
A process sequence is represented for the operation of the system 2 illustrated in
In a first step S1, the control device 24, e.g. during commissioning or during an initialization phase in the course of commissioning, detects the number n of DC voltage converter units 8a, 8b, 8c, 8d.
In a further step S2, the control device 24 adapts the actuation signal sequence ASF to the detected number n of DC voltage converter units 8a, 8b, 8c, 8d.
To this end, in an exemplary embodiment, the control device 24 adjusts the pulse frequency of the actuation signal sequence ASF to the detected number n of DC voltage converter units 8a, 8b, 8c, 8d and modifies the actuation signal sequence ASF such that the actuatable semiconductor switching elements 16a, 16b, 16c, 16d of the at least four DC voltage converter units 8a, 8b, 8c, 8d are actuated in a temporally staggered manner.
By means of the actuation signal sequence ASF thus determined, in operation, the actuatable semiconductor switching elements 16a, 16b, 16c, 16d of the respective DC voltage converter units 8a, 8b, 8c, 8d are then actuated in order to execute the direct conversion of a DC electric input voltage into a DC electric output voltage.
By way of deviation from an exemplary embodiment, the sequence of steps can also be different. Moreover, a plurality of steps can also be executed simultaneously or in combination. Moreover, individual steps can also be omitted or passed over.
Thus, for example, transformation losses can be prevented by a direct connection of a low-voltage DC grid system to an electrolysis device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21174316.6 | May 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/057767 | 3/24/2022 | WO |
