METHOD FOR SUPPLYING A DC LOAD, ENERGY CONVERSION SYSTEM AND ELECTROLYSIS SYSTEM

Abstract

The disclosure is directed to a method for supplying power to a DC load using an energy conversion system that includes first and second rectifiers and a transformer system. Each of the rectifiers contains an AC-DC converter connected to an AC grid via a separate secondary side of the transformer system. The transformer system provides a first AC voltage having a first voltage amplitude .Math..sub.1 on the first secondary side and a second AC voltage having a second voltage amplitude .Math..sub.2 on the second secondary side, wherein a value of the second voltage amplitude .Math..sub.2 exceeds a corresponding value of the first voltage amplitude .Math..sub.1. The method includes operating the first rectifier with a first non-zero power flow P.sub.1 to supply power to the DC load when an input voltage U.sub.DC,load at the input of the DC load falls below a voltage threshold value U.sub.TH: wherein a second power flow P.sub.2 through the second rectifier is suppressed, and operating the second rectifier with a second non-zero power flow P.sub.2 to supply power to the DC load when the input voltage U.sub.DC,load at the input of the DC load reaches or exceeds the voltage threshold value U.sub.TH. The application likewise discloses an energy conversion system for performing the method and an electrolysis system.

Claims

1. A method for supplying power to a DC load by means of an energy conversion system comprising a first rectifier, a second rectifier and a transformer system, wherein each of the first and second rectifiers comprises an AC-DC converter and is connected to a commonly used AC grid via a separate secondary side of the transformer system, wherein the transformer system is configured to provide a first AC voltage having a first voltage amplitude .Math..sub.1 on a first secondary side and a second AC voltage having a second voltage amplitude .Math..sub.2 on a second secondary side, wherein a value of the second voltage amplitude .Math..sub.2 exceeds a corresponding value of the first voltage amplitude .Math..sub.1, comprising: i) operating the first rectifier with a first non-zero power flow P.sub.1 to supply power to the DC load when an input voltage U.sub.DC,load at the input of the DC load falls below a voltage threshold value U.sub.TH, wherein a second power flow P.sub.2 through the second rectifier is suppressed, and ii) operating the second rectifier with a second non-zero power flow P.sub.2 to supply power to the DC load when the input voltage U.sub.DC,load at the input of the DC load reaches or exceeds the voltage threshold value U.sub.TH.

2. The method as claimed in claim 1, wherein the second power flow P.sub.2 through the second rectifier is suppressed by means of an open AC disconnecting circuit between the second secondary side of the transformer system and the AC-DC converter of the second rectifier and/or a DC disconnecting circuit between the AC-DC converter of the second rectifier and the input of the DC load.

3. The method as claimed in claim 1, further comprising suppressing the first power flow P.sub.1 and the second power flow P.sub.2 in an initial state of a startup procedure for supplying power to the DC load using the energy conversion system.

4. The method as claimed in claim 1, further comprising suppressing the first power flow P.sub.1 and the second power flow P.sub.2 in an end state of a shutdown procedure during the power supply to the DC load using the energy conversion system.

5. The method as claimed in claim 1, wherein, in the method, method acts i) and ii) are run through in an order such that method act ii) follows method act i).

6. The method as claimed in claim 1, wherein, in the method, method acts i) and ii) are run through in an order such that method act i) follows method act ii).

7. The method as claimed in claim 1, wherein, in method act ii), a ratio of the first power flow P.sub.1 to the second power flow P.sub.2, P.sub.1/P.sub.2, for supplying power to the DC load is minimized.

8. The method as claimed in claim 1, wherein method acts i) and ii) are run through temporally repeatedly to track a change in the consumption of the DC load or to set a consumption/time profile of the DC load using the control circuit.

9. An energy conversion system for supplying power to a DC load from an AC grid, comprising: a transformer system, that is connectable on a primary side thereof to the AC grid and is configured to provide a first AC voltage having a first voltage amplitude .Math..sub.1 on a first secondary side and a second AC voltage having a second voltage amplitude .Math..sub.2 on a second secondary side, wherein a value of the second voltage amplitude .Math..sub.2 exceeds a corresponding value of the first voltage amplitude .Math..sub.1, a first rectifier connected on an input side thereof to the first secondary side, and a second rectifier connected on an input side thereof to the second secondary side, which rectifiers are each connected on their respective output side and in parallel with one another to an input of the DC load, and a control circuit configured to control the energy conversion system, wherein the control circuit or the control circuit in combination with further components of the energy conversion system is configured to: i) operate the first rectifier with a first non-zero power flow Pi to supply power to the DC load when an input voltage U.sub.DC,load at the input of the DC load falls below a voltage threshold value U.sub.TH, wherein a second power flow P.sub.2 through the second rectifier is suppressed, and ii) operate the second rectifier with a second non-zero power flow P.sub.2 to supply power to the DC load when the input voltage U.sub.DC,load at the input of the DC load reaches or exceeds the voltage threshold value U.sub.TH.

10. The energy conversion system as claimed in claim 9, wherein the transformer system comprises a first transformer comprising a first primary side and the first secondary side coupled inductively thereto, and a second transformer comprising a second primary side that is different than the first primary side, and the second secondary side inductively coupled thereto.

11. The energy conversion system as claimed in claim 9, wherein the transformer system comprises a primary side inductively coupled both to the first secondary side and to the second secondary side.

12. The energy conversion system as claimed in claim 9, wherein the first rectifier and/or the second rectifier is/are configured to provide a bidirectional power flow.

13. The energy conversion system as claimed in claim 9, wherein the first rectifier and/or the second rectifier comprises a single-stage rectifier.

14. The energy conversion system as claimed in claim 9, wherein the energy conversion system comprises a measurement circuit connected to the control circuit, wherein the measurement circuit is configured to detect the input voltage U.sub.DC,load present at the input of the DC load.

15. The energy conversion system as claimed in claim 9, wherein the transformer system comprises a plurality of taps for varying the first amplitude .Math..sub.1 and/or the second amplitude .Math..sub.2 relative to an amplitude .Math..sub.AC of the AC voltage of the AC grid.

16. An electrolysis system comprising an energy conversion system for supplying power to a DC load from an AC grid, the energy conversion system comprising: a transformer system, that is connectable on a primary side thereof to the AC grid and is configured to provide a first AC voltage having a first voltage amplitude .Math..sub.1 on a first secondary side and a second AC voltage having a second voltage amplitude .Math..sub.2 on a second secondary side, wherein a value of the second voltage amplitude .Math..sub.2 exceeds a corresponding value of the first voltage amplitude .Math..sub.1, a first rectifier connected on an input side thereof to the first secondary side, and a second rectifier connected on an input side thereof to the second secondary side, which rectifiers are each connected on their respective output side and in parallel with one another to an input of the DC load, and a control circuit configured to control the energy conversion system, wherein the control circuit or the control circuit in combination with further components of the energy conversion system is configured to: i) operate the first rectifier with a first non-zero power flow P.sub.1 to supply power to the DC load when an input voltage U.sub.DC,load at the input of the DC load falls below a voltage threshold value U.sub.TH, wherein a second power flow P.sub.2 through the second rectifier is suppressed, and ii) operate the second rectifier with a second non-zero power flow P.sub.2 to supply power to the DC load when the input voltage U.sub.DC,load at the input of the DC load reaches or exceeds the voltage threshold value U.sub.TH, and wherein the electrolysis system comprises an electrolyzer as the DC load.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0029] The disclosure is illustrated below with the aid of figures, in which

[0030] FIG. 1 shows an embodiment of an energy conversion system which is connected on the input side to an AC grid and on the output side to a DC load; and

[0031] FIG. 2 a flowchart of the method according to the disclosure in one embodiment.

DETAILED DESCRIPTION

[0032] FIG. 1 illustrates an embodiment of an energy conversion system 1 according to the disclosure, which is connected on the input side to an AC grid 20 and on the output side to an input 32 of a DC load 30. By way of example, in this case the DC load 30 is illustrated as an electrolyzer 31. The energy conversion system 1 contains a transformer system 21, a first rectifier 2.1, a second rectifier 2.2, a control circuit 15 that is configured to control the first rectifier 2.1 and the second rectifier 2.2 and a measurement circuit or device 13, that is connected to the control circuit 15 for the purpose of control and for data interchange. The measurement device 13 is configured to measure an input voltage U.sub.DC,load present at the input 32 of the DC load 30. The transformer system 21 comprises two separately formed transformers 22.1, 22.2, which each have a primary side 23.1, 23.2 and a secondary side 24.1, 24.2. The primary sides 23.1, 23.2 of the transformers 22.1, 22.2 are connected in parallel with one another to the AC grid 20. The first secondary side 24.1 is connected to the AC input 5 (a first AC input) of the first rectifier 2.1, the second secondary side 24.2 is connected to the AC input 5 (a second AC input) of the second rectifier 2.2. The transformer system 21 is configured, via a corresponding turns ratio of the first secondary side 24.1 to the first primary side 23.1, to transform the polyphase AC voltage of the AC grid 20 having the amplitude .Math..sub.AC into a first AC voltage, which is present on the first secondary side 24.1 and has the first amplitude .Math..sub.1 and the same number of phases. Correspondingly, via a turns ratio of the second secondary side 24.2 to the second primary side 23.2, the polyphase AC voltage of the AC grid 20 having the amplitude .Math..sub.AC is transformed into a second AC voltage, which is present on the second secondary side 24.2 and has the second amplitude .Math..sub.2 and the same number of phases. In this embodiment, a value for the second amplitude .Math..sub.2 exceeds a corresponding value for the first amplitude .Math..sub.1. Each of the rectifiers 2.1, 2.2 comprises, between its AC input 5 and its DC output 3, an AC disconnecting circuit 6, a filter circuit 9, an AC-DC converter (comprised of circuitry) 10, an output capacitance 11 connected on the output side to the AC-DC converter and a DC disconnecting circuit 12. The DC disconnecting circuit 12 is configured to connect and disconnect an output of the AC-DC converter 10, i.e. a DC side of the AC-DC converter, to and from the DC output 3 of the rectifier 2.1, 2.2 and therefore to and from the input 32 of the DC load 30. The AC disconnecting circuit 6 is configured to disconnect and connect the respective secondary side 24.1, 24.2 of the transformer system 21 assigned to the rectifier 2.1, 2.2 from and to an input of the AC-DC converter 10, i.e. from and to an AC-side of the AC-DC converter, (through the filter circuit 9 in one embodiment) assigned to the respective rectifier 2.1, 2.2. The AC disconnecting circuit 6 can additionally optionally be configured to limit a current during precharging of the output capacitance 11 of the rectifier 2.1, 2.2. For this purpose, the AC disconnecting circuit 6 contains two parallel current paths each having a switch 8, wherein a series resistor 7 for current limitation is arranged in one of the two current paths. For reasons of clarity, the reference symbols relating to the components of the rectifiers 2.1, 2.2 are only illustrated in the case of the first rectifier 2.1 in FIG. 1.

[0033] In the text which follows, a state is assumed in which each of the rectifiers 2.1, 2.2 is connected to the secondary side 24.1, 24.2 assigned thereto via the closed AC disconnecting circuit 6 of said rectifier, but the corresponding DC disconnecting circuits 12 are still open. In this state, therefore, both the first power flow P.sub.1 through the first rectifier 2.1 and the second power flow P.sub.2 through the second rectifier 2.2 are suppressed. However, the output capacitance 11 is charged in each of the rectifiers 2.1, 2.2 via a current flow from the AC grid 20 and through the freewheeling diodes of the respective AC-DC converter 10 to a corresponding DC voltage U.sub.DC,1, U.sub.DC,2. In one embodiment, a value for the second DC voltage U.sub.DC,2 of the second rectifier 2.2 exceeds a value for the first DC voltage U.sub.DC,1 of the first rectifier 2.1 owing to the different AC voltages present at the inputs 5 of the rectifiers 2.1, 2.2, in particular their amplitudes .Math..sub.1, .Math..sub.2.

[0034] Depending on a power consumption of the DC load 30 and an associated input voltage U.sub.DC,load at the input 32 thereof, the power flows P.sub.1, P.sub.2 through the respective rectifiers 2.1, 2.2 are now suppressed or enabled. Specifically, in the case of a startup procedure, first the first power flow P.sub.1 through the first rectifier 2.1 can be enabled by closing the DC disconnecting circuit 12 of the first rectifier 2.1, while the second power flow P.sub.2 through the second rectifier 2.2 is still suppressed. In one embodiment, the second power flow P.sub.2 through the second rectifier 2.2 is enabled when, e.g. via an increase in the input voltage U.sub.DC,load of the DC load 30, the consumption of said DC load is increased, for example, when the input voltage U.sub.DC,load of the DC load 30 reaches or exceeds a voltage threshold value U.sub.TH. In the case of input voltages U.sub.DC,load of the DC load 30 which are greater than the voltage threshold value U.sub.TH, it is possible, depending on the consumption of the DC load 30 and on rated powers of the rectifiers 2.1, 2.2, for the DC load 30 to be supplied power only by the second power flow P.sub.2 or by a combination of the first power flow P.sub.1 and the second power flow P.sub.2.

[0035] In FIG. 1, the AC grid 20 is illustrated, by way of example, as a three-phase AC grid 20 and therefore also the rectifiers 2.1, 2.2 are illustrated with an input 5 configured with three phases. Likewise, the transformer system 21 is configured to transform the three-phase AC voltage of the AC grid 20 into a three-phase first AC voltage and a three-phase second AC voltage. In the context of the disclosure, however, other numbers of phases are also possible. For example, the AC grid can also be configured as a single-phase AC grid 20, the transformer system 21 as a single-phase transformer system 21 and/or the inputs 5 of the rectifiers 2.1, 2.2 as single-phase inputs 5. As an alternative to this, the AC grid 20, the transformer system 21 and/or the inputs of the rectifiers can also be configured to have a plurality of phases, wherein the number of phases is different than three. Furthermore, it is possible for the rectifiers 2.1, 2.2 to have further components which are not explicitly illustrated in FIG. 1, for example measurement devices for measuring current and/or voltage at the input and/or output of the AC-DC converters 10 or a communications circuit.

[0036] FIG. 2 illustrates a flowchart of an embodiment of the method according to the disclosure, as can be implemented using the energy conversion system 1 from FIG. 1. The method starts with a first act S1, in which an input voltage U.sub.DC,load present at the input 32 of the DC load 30 is detected, for example, via the measurement device 13 and passed on to the control circuit 15. The first act S1 is, however, only optional, which is illustrated in the flowchart via a dashed frame line. Thus, in one embodiment the input voltage U.sub.DC,load can be known to the control circuit 15 by other means, for example, because specific DC voltages U.sub.DC,1, U.sub.DC,2 at the output of the AC-DC converter(s) 10 are preset by the control circuit 15, and at least one of the DC disconnecting circuits 12 is closed. In this case, the first act S1 is not required. In a second act S2, the control circuit 15 compares a value for the detected input voltage U.sub.DC,load with a predefined voltage threshold value U.sub.TH. When the value for the input voltage U.sub.DC,load of the DC load 30 falls below the voltage threshold value U.sub.TH, the method branches to a fifth act S5, in which the first power flow P.sub.1 through the first rectifier 2.1 is enabled, while the second power flow P.sub.2 through the second rectifier 2.2 is suppressed. In this embodiment, the suppression of the second power flow P.sub.2 can take place, for example, by opening the DC disconnecting circuit 12 of the second rectifier 2.2. In this embodiment, the DC load 30 is therefore supplied power by the first power flow P.sub.1 of the first rectifier 2.1. If, on the other hand, the detected input voltage U.sub.DC,load of the DC load 30 is greater than or equal to the voltage threshold value U.sub.TH, the method branches from the second act S2 to a third act S3, in which the second power flow P.sub.2 through the second rectifier 2.2 is enabled, for example, by closing of the corresponding DC disconnecting circuit 12. In a fourth act S4, which follows on from the third act S3, a ratio of the first power flow P.sub.1 to the second power flow P.sub.2 can be minimized in order to operate the energy conversion system 1 overall with as high an efficiency as possible and low power losses. The fourth act S4 is, however, again optional and not absolutely necessary, which is again characterized via a dashed frame line. In the subsequent sixth act S6, a check is performed to ascertain whether a predefined termination condition has been met. If this is not the case, the method jumps back to the first act S1. If, on the other hand, the termination condition is met, the method ends. The sixth act S6 which, depending on which branch is run through in response to the query in the second method act S2, follows on from the fifth act S5 or the fourth act S4, is also an optional method act and is therefore illustrated by dashed lines in the flowchart. In an embodiment in which the sixth act S6 is not provided, the method can jump back to the first act directly after the fifth act S5 or after the fourth act S4.

[0037] In the context of the disclosure, it is possible for a specific consumption or a consumption/time profile of the DC load to be set and tracked by means of the control circuit 15. If, for example, a consumption of the DC load 30 is intended to be increased, the first rectifier 2.1 is driven, via the control circuit 15, to temporarily increase its first DC voltage U.sub.DC,1 present at the output capacitance 11. When the DC disconnecting circuit 12 of the first rectifier 2.1 is closed, this voltage is also present as input voltage U.sub.DC,load at the input 32 of the DC load 30. The same applies accordingly also to the second rectifier 2.2. Thus, when the DC load 30 is supplied power by a combination of the first power flow P.sub.1 and the second power flow P.sub.2 that each are different than 0 W (i.e., non-zero), the second rectifier 2.2 is also driven at the same time as the first rectifier 2.1, via the control circuit 15, with the aim of temporarily increasing its second DC voltage U.sub.DC,2 present at its output capacitance 11. When the DC load 30 is supplied power by a combination of the first power flow P.sub.1 and the second power flow P.sub.2, values for the first DC voltage U.sub.DC,1, the second DC voltage U.sub.DC,2 and the input voltage U.sub.DC,load of the DC load 30 are virtually identical. A variation in the first power flow P.sub.1 relative to the second power flow P.sub.2 of the combination can take place using the control circuit 15 by virtue of the control circuit correspondingly driving the semiconductor switches of the first rectifier 2.1 and the second rectifier 2.2, for example, the semiconductor switches assigned to the AC-DC converters thereof. For example, the values of the DC voltages U.sub.DC,1 U.sub.DC,2 present at the output capacitances 11 of the respective rectifiers 2.1, 2.2 can be varied slightly with respect to one another via the corresponding driving of the semiconductor switches, and thereby establish the variation in the power flows.