DE102019125296B4 - METHOD OF DETECTING A SHORT CIRCUIT OF A DC LOAD AND RECTIFIER WITH SUCH A METHOD - Google Patents

Abstract

The application relates to a method for detecting a short circuit (33) of a DC load (30), which can be connected to an AC network (20) via a rectifier (1) comprising an AC / DC converter (10). The method comprises the following steps: - setting a source voltage at an output capacitance (4) of the rectifier (1) via a rectified power flow taken from the AC network (20), ) to the input (32) of the DC load (30), further power flow from the AC network (20) into the rectifier (1) and an associated recharging of the output capacitance (4) being suppressed, - detection of an an input (32) of the DC load (30) applied voltage U and / or a current I flowing through the input (32) of the DC load (30) - signaling of a short circuit (33) when the detected voltage U, a time profile of the detected voltage U, the detected current I, a time profile of the detected current I, a combination of the detected voltage U and the detected current I and / or a combination of the time profiles of the detected voltage U and the de Tektierten current I meet at least one predetermined criterion. The application also relates to a rectifier (1) designed to carry out the method.

Description

Technical field of the invention

The invention relates to a method for detecting a short circuit in a DC load which is connected to an alternating voltage (AC) network via a rectifier. The invention additionally relates to a rectifier which is designed and set up to carry out the method according to the invention. The DC load can be an electrolyzer or a rechargeable battery, for example.

State of the art

In the so-called power-to-gas process, electrical energy is converted into a gaseous energy carrier, for example hydrogen. For this purpose, an electrolyser is connected to an alternating voltage (AC) network via a rectifier. In the electrolyser, which operates as a DC load, the electrolysis of water into hydrogen and oxygen takes place via a power flow from the AC network. A reaction speed of the electrolysis is controlled via the power flow through the rectifier. The hydrogen can be processed into another gaseous energy carrier (e.g. methane) or stored directly. The stored hydrogen can be used to generate energy, for example in a fuel cell, or as a starting product in the chemical industry.

In the case of electrolysers that are currently used, outputs of a few MW to approx. 10 MW are implemented. Their working range in the current-voltage diagram is between 0.1 kA and 4 kA or between 0.3 and 1.5 kV. For safety reasons, a short-circuit test at the input of the electrolyzer is required before starting operation. The short-circuit test is conventionally carried out using precharge resistors, which are provided both at an AC input and at a DC output of the rectifier. The precharging resistors have the task of limiting the flow of power from the AC network, in particular in the event of a load-side short circuit, and thus preventing damage to components of the electrolyzer operating as a DC load and / or the rectifier. The precharge resistors must be able to tolerate a relatively high power flow, at least for a short time. For this reason, too, such precharge resistors are relatively expensive. In normal operation of the electrolyzer, however, they are not required, but rather are bridged with low impedance. It is therefore desirable to dispense with such precharge resistors as far as possible.

The font US 6339526 B1 discloses a battery backup system connected to a load through a low voltage disconnect circuit. The low-voltage isolating circuit comprises a low-voltage monitor connected between an input and an output of the low-voltage isolating circuit, as well as an isolating switch controlled by the low-voltage monitor, which is designed to connect the input to the output. The low-voltage isolating circuit furthermore comprises a short-circuit protection circuit which is designed to determine a short circuit in the load and, together with the low-voltage monitor, to prevent the isolating switch from closing as a function of a specific short circuit.

The pamphlet GB 2520121 A discloses a DC power source comprising: a rectifier circuit coupled to an AC power supply and having a DC output, a capacitor filter circuit for smoothing the DC output having a plurality of capacitor arrays connected in series, and a short-circuit detection unit for monitoring a voltage across each of the capacitor arrays. The short-circuit detection unit is designed to generate an error signal depending on the monitored voltages. The direct current source further comprises a regulator which is designed to limit a current through the capacitor filter circuit if the error signal implies that one of the monitored voltages has fallen below a threshold value. The pamphlet US 6339526 B1 discloses an undervoltage interruption circuit having an input and an output comprising: an undervoltage monitor arranged between an input and an output, a disconnector arranged between the input and the output and controlled by the undervoltage monitor, the disconnector being designed to connect the input to the output connect, and a short-circuit protection circuit which is designed to detect a short-circuit of a load connected to the output and, in conjunction with the undervoltage monitor, to prevent the disconnector from closing.

Object of the invention

The invention is based on the object of specifying a method for detecting a short circuit at an input of a DC load which can be connected to an AC network via a rectifier, in particular an actively controllable rectifier. Damage to components of the DC load and / or the rectifier, in particular in the event of an actual short circuit in the DC load, should be excluded as far as possible. The method should be feasible as inexpensively as possible be. It is also an object of the invention to provide a rectifier suitable for the method. Specifically, the rectifier required for the method should also be as inexpensive as possible and, in particular, be designed with as few precharge resistors as possible.

solution

The object of providing a method for detecting a short circuit at the input of a DC load that can be connected to an AC network via a rectifier is achieved according to the invention with a method having the features of independent claim 1. Advantageous embodiments of the method are in the claims 2 to 11 reproduced. The object of indicating a rectifier suitable for carrying out the method is achieved according to the invention with the features of independent claim 12. Advantageous embodiments of the rectifier are in the claims 13th to 16 reproduced.

Description of the invention

• - Einstellen einer Quellspannung an einer Ausgangskapazität des Gleichrichters über einen dem AC-Netz entnommenen gleichgerichteten Leistungsfluss,
• - Verbinden der zuvor auf die Quellspannung eingestellten Ausgangskapazität des Gleichrichters mit dem Eingang der DC-Last, wobei ein weiterer Leistungsfluss aus dem AC-Netz in den Gleichrichter und ein damit verbundenes Wiederaufladen der Ausgangskapazität unterdrückt wird,

• - Detektion einer an einem Eingang der DC-Last anliegenden Spannung U und/oder eines über den Eingang der DC-Last fließenden Stromes I, und
• - Signalisieren eines Kurzschlusses der DC-Last, wenn die detektierte Spannung U, ein Zeitverlauf der detektierten Spannung U, der detektierte Strom I, ein Zeitverlauf des detektierten Stroms I, eine Kombination der detektierten Spannung U und des detektierten Stroms I, und/oder eine Kombination der Zeitverläufe der detektierten Spannung U und des detektierten Stroms I zumindest ein vorgegebenes Kriterium erfüllen.

A method according to the invention is used to detect a short circuit in a DC load which can be connected to an AC network via a rectifier comprising an AC / DC converter. The procedure consists of the following steps:

• - Setting a source voltage at an output capacitance of the rectifier via a rectified power flow taken from the AC network,
• - Connect the output capacitance of the rectifier, which was previously set to the source voltage, to the input of the DC load, further power flow from the AC network into the rectifier and an associated recharging of the output capacitance being suppressed,

• - Detection of a voltage present at an input of the DC load U and / or a current flowing through the input of the DC load I. , and
• - Signaling of a short circuit of the DC load when the detected voltage U , a time course of the detected voltage U , the detected current I. , a time course of the detected current I. , a combination of the detected voltage U and the detected current I. , and / or a combination of the time courses of the detected voltage U and the detected current I. meet at least one predetermined criterion.

The method uses the effect that when and during the connection of the output capacitance to the input of the DC load, a direct (in the sense of continuous) power flow from the AC network via the rectifier into the DC load is suppressed. Rather, the removal of a power flow from the AC network into the rectifier, on the one hand, and the output of a power flow from the rectifier into the DC load, on the other hand, do not take place at the same time, but rather at different times. Specifically, when the source voltage is set at the output capacitance, the rectifier is connected to the AC grid via an AC disconnection unit. The connection results in a power flow from the AC network into the rectifier, but a simultaneous output of a power flow from the rectifier into the DC load is suppressed. Instead, the energy taken from the AC network is initially temporarily stored in the rectifier and only passed on with a time delay, in particular later on to the DC load.

With a single-stage rectifier, the output of the power flow to the DC load can be suppressed by an open DC disconnector. Such a DC disconnector, via which the output capacitance of the rectifier can be connected to or disconnected from the DC load, is usually arranged at the DC output of the corresponding rectifier and is therefore not an additional component. In the case of a two-stage rectifier, the output can a power flow to the DC load can also be suppressed by deactivating a DC / DC converter which is arranged between the AC / DC converter and the DC output of the two-stage rectifier. Only after the power flow has been taken from the AC network and its energy has been temporarily stored in the rectifier, for example in its output capacitance and / or an intermediate circuit capacitance of the rectifier, the rectifier delivers power to the DC load. For this purpose, the output capacitance of the rectifier, which contains at least part of the energy previously drawn from the AC network, is electrically connected to the DC load, for example by closing the DC isolating switch. However, a further flow of power from the AC network into the rectifier, in particular into the output capacitance of the rectifier connected to the DC load, is suppressed. The suppression can take place in that the previously closed AC disconnection unit is opened again and the AC / DC converter of the rectifier is galvanically isolated from the AC network. Alternatively or cumulatively, in the case of a two-stage rectifier, the power flow from the AC network into the output capacitance of the rectifier can, however, also be suppressed via a deactivated DC / DC converter of the rectifier.

The setting of the source voltage at the output capacitance of the rectifier via the power flow taken from the AC network can, but does not necessarily have to take place at the same time as the power flow is drawn from the AC network. As an alternative to this, it is also possible that the setting of the source voltage at the output capacitance and the associated charging of the output capacitance take place with a time delay to the removal of the power flow from the AC network. Specifically, in the case of a two-stage rectifier, for example, a power flow can be drawn from the AC network, which is initially stored in an intermediate circuit capacitance upstream of the output capacitance. The output capacitance can then be set to the source voltage at a later point in time via charge transport from the intermediate circuit capacitance to the output capacitance.

In the method according to the invention, a possibly existing short circuit in the DC load is only detected by means of a limited amount of energy that was previously taken from the AC network and temporarily stored in the rectifier. A suitable choice of the limited amount of energy can prevent damage to components of the rectifier and / or the DC load.

A value of the source voltage at the output capacitance of the rectifier can be selected in such a way that components of the DC load and / or the rectifier are damaged when an amount of energy assigned to the source voltage is transferred to the DC load, in particular in the case of a DC load. Load present short circuit, is excluded.

The detection of the voltage present at the input of the DC load U and the current flowing through the input of the DC load I. can also include a detection of a time course of the respective variables. Detection can be carried out directly on the DC load using a separate measuring unit. As an alternative, however, the detection can also take place via a measuring unit of the rectifier which is already arranged at the DC output of the rectifier. An evaluation of the detected voltage U and / or the detected current I. can also be done by an already existing control unit of the rectifier. In this way, the method can be carried out as inexpensively as possible, since no additional components of the rectifier are required to carry out the method. Since power is drawn from the AC network into the rectifier and power is output from the rectifier to the DC load, there is no need to provide precharge resistors at the DC output of the rectifier. Rather, these are only required at the AC input of the rectifier. Although the method is not limited to a particular type of DC load, the DC load can in particular comprise an electrolyzer.

• - ein Betrag einer zeitlichen Änderung der an dem Eingang der DC-Last anliegenden Spannung dU/dt übersteigt einen der Quellspannung zugeordneten ersten Schwellwert (dU/dt)_TH , und/oder
• - der über den DC-Eingang der DC-Last fließende Strom I übersteigt einen zweiten Schwellwert I_TH , und/oder
• - ein Quotient der an dem Eingang der DC-Last anliegenden Spannung und des über den Eingang der DC-Last fließenden Stroms I unterschreitet einen dritten Schwellwert R_TH . Das Verfahren kann einen Kurzschluss der DC-Last signalisieren, wenn bei der Überprüfung zumindest eines der Kriterien erfüllt wird. Zusätzlich ist es möglich, einen Kurzschluss dann zu signalisieren, wenn mehrere der Kriterien gleichzeitig erfüllt werden. Es liegt im Rahmen der Erfindung, dass die Werte von Spannung U und Strom I mit Zeitstempeln versehen sein können, die den Zeitpunkt ihrer Detektion kennzeichnen. Dies ist insbesondere dann sinnvoll, wenn Zeitverläufe der Spannung U bzw. des Stroms I detektiert und ausgewertet werden. In diesem Fall können zeitgleich oder zumindest zeitnah detektierte Werte von Spannung U und Strom I einander zugeordnet werden. Für eine Signalisierung eines Kurzschlusses der DC-Last ist es ausreichend, wenn das zumindest eine Kriterium lediglich während einer begrenzten Zeitspanne innerhalb des detektierten Zeitverlaufs, und nicht in dem gesamten detektierten Zeitverlauf erfüllt ist.

In an advantageous variant of the method, at least one of the following criteria can be checked to signal a short circuit in the DC load:

• an amount of a change over time in the voltage dU / dt applied to the input of the DC load exceeds a first threshold value assigned to the source voltage (dU / dt) _TH , and or
• - the current flowing through the DC input of the DC load I. exceeds a second threshold value I _TH , and or
• - a quotient of the voltage present at the input of the DC load and the current flowing through the input of the DC load I. falls below a third threshold value R _TH . The method can signal a short circuit in the DC load if at least one of the criteria is met during the check. It is also possible to signal a short circuit if several of the criteria are met at the same time. It is within the scope of the invention that the values of voltage U and electricity I. can be provided with time stamps that identify the time of their detection. This is particularly useful when the voltage changes over time U or the current I. can be detected and evaluated. In this case, voltage values detected at the same time or at least in real time U and electricity I. can be assigned to each other. For signaling a short circuit in the DC load, it is sufficient if the at least one criterion is met only during a limited time span within the detected time profile and not in the entire detected time profile.

In one embodiment of the method, the rectifier is designed as a single-stage rectifier. The output capacitance of the single-stage rectifier can be charged via freewheeling diodes of the AC / DC converter to a source voltage that corresponds to the amplitude of the AC voltage of the AC network. The output capacity is charged when the AC disconnection unit is closed. When connecting the output capacitance to the DC load, on the other hand, the output capacitance can be galvanically isolated from the AC network via an opened AC isolating unit of the rectifier, whereby a further power flow from the AC network into the output capacitance of the single-stage rectifier can be effectively suppressed . In In some cases it may be necessary for the output capacitance of the single-stage rectifier to be set to a source voltage whose value is below an amplitude of the alternating voltage of the AC network. The setting of the output capacitance to the source voltage can include that a voltage of the output capacitance which is initially above the source voltage is reduced to the desired value of the source voltage by dissipating the energy stored in the output capacitance. The energy stored in the output capacitance can be dissipated by pulsing semiconductor switches in the AC / DC converter. Alternatively or cumulatively, however, the dissipation can also be brought about by operating at least one small consumer connected to the output capacitance, for example a fan of the rectifier. So that when the energy is dissipated, another power flow from the AC network into the output capacitance and thus a renewed charging of the output capacitance is suppressed, the output capacitance can be separated from the AC network during the dissipation of the energy stored in it.

In an alternative embodiment of the method, the rectifier can be designed as a multi-stage rectifier and comprise a DC / DC converter connected downstream of the AC / DC converter and an intermediate circuit capacitance arranged between them. In this case, a power flow from the AC network into the output capacitance can be suppressed via an at least temporary deactivation of the DC / DC converter, for example via an open semiconductor switch of the DC / DC converter. In the case of the multi-stage rectifier, the output capacitance can be set to a source voltage via the DC / DC converter connected upstream of the output capacitance, the value of which is below the amplitude of the alternating voltage of the AC network. For this purpose, a limited amount of charge can be taken from the upstream intermediate circuit capacitance by the DC / DC converter and fed to the output capacitance. The limited amount of charge can comprise all or only part of the amount of charge present in the intermediate circuit capacitance. When connecting the output capacitance to the DC load, the further flow of power from the AC network to the rectifier, in particular in its output capacitance, can be suppressed by deactivating the DC / DC converter, e.g. using an open semiconductor switch of the DC / DC converter . Alternatively or cumulatively, it is of course also possible, when connecting the output capacitance to the DC load, to control the further flow of power from the AC network into the rectifier by opening the AC isolating switch 6th , 8th the AC disconnection unit.

Regardless of whether it is a single-stage or multi-stage rectifier, the power flow for setting the source voltage at the output capacitance can be taken from the AC network via a precharge resistor arranged at the AC input of the rectifier. A current in the initially uncharged output capacitance or intermediate circuit capacitance of the rectifier can be effectively limited via the precharge resistor.

• - einen AC/DC-Wandler,
• - eine mit dem DC-Ausgang des Gleichrichters verbundene Ausgangskapazität,
• - eine mit dem AC-Eingang verbundene AC-Trenneinheit und einen mit dem DC-Ausgang verbundenen DC-Trennschalter. Zusätzlich umfasst der Gleichrichter eine Steuerungseinheit zur Ansteuerung des Gleichrichters, die zur Durchführung des erfindungsgemäßen Verfahrens und dessen Ausführungsformen ausgelegt und eingerichtet ist. Es ergeben sich die bereits im Zusammenhang mit dem Verfahren erläuterten Vorteile.

A rectifier according to the invention is designed to convert an alternating voltage into a direct voltage. For this purpose, the rectifier has an AC input for connecting the rectifier to an AC network and a DC output for connecting the rectifier to a DC load. The rectifier also includes

• - an AC / DC converter,
• - an output capacitance connected to the DC output of the rectifier,
• - an AC disconnection unit connected to the AC input and a DC disconnector connected to the DC output. In addition, the rectifier comprises a control unit for controlling the rectifier, which is designed and set up to carry out the method according to the invention and its embodiments. The advantages already explained in connection with the method result.

In one embodiment of the rectifier, the AC disconnection unit comprises a precharge resistor. In particular, the AC disconnection unit is designed to provide a connection of the AC / DC converter of the rectifier to the AC network on the one hand via the precharge resistor and on the other hand in a direct manner, i.e. without the interposition of the precharge resistor. When the AC / DC converter assigned to the rectifier is connected to the AC network, an intermediate connection of the precharge resistor is required in particular when a previously uncharged energy store of the rectifier is charged with a power flow from the AC network. In this case, the power flow into the uncharged energy store is limited to a value at which damage to components of the rectifier is prevented. The energy store can be, for example, the output capacitance of a single-stage rectifier. In a further embodiment, the rectifier can be designed in multiple stages and comprise a DC / DC converter arranged between the AC / DC converter and the output capacitance. In this case, the precharge resistor can also reduce the power flow into a previously uncharged intermediate circuit capacitance Limit the energy storage of the multi-stage rectifier.

Regardless of whether the rectifier is designed as a single-stage or multi-stage, in particular two-stage rectifier, the rectifier, in particular its AC / DC converter, and possibly also its DC / DC converter, can be designed for bidirectional operation with respect to one direction of the power flow and be set up. A bidirectionally operating rectifier is designed in a first operating mode to convert an alternating voltage into a direct voltage. In contrast, it is designed in a second operating mode to operate as an inverter and convert a direct voltage into an alternating voltage. This is particularly advantageous if the rectifier can be connected at its DC output on the one hand to a DC load and on the other hand to a DC power generation system, for example a photovoltaic (PV) system or a fuel cell. A bidirectional rectifier is also useful if the rectifier is connected to a battery on the DC side.

In principle, it is possible for the voltage present at the input of the DC load to be detected U as well as the current flowing through the input of the DC load I. a separate measuring unit is used. In this case, the separate measuring unit can be connected to the rectifier for control purposes in such a way that the measured values of voltage can be forwarded U and / or electricity I. to the control unit of the rectifier is guaranteed. In this case the detection takes place outside the rectifier, the evaluation of the detected voltage values U and / or electricity I. however, within the rectifier, namely in particular by the control unit of the rectifier. In an advantageous embodiment, however, the rectifier itself comprises a measuring unit for detecting a voltage applied to the DC load and / or a current flowing via the input of the DC load. The measuring unit can be a measuring unit which is already present in the rectifier and is designed for a current flowing via the DC output of the rectifier I. and / or a voltage present at the DC output of the rectifier U to detect. As in connection with the 1 and 2 corresponds to the voltage applied to the input of the DC load when the rectifier is normally connected to the DC load U the voltage present at the DC output of the rectifier U . Likewise, in this case (the usual interconnection of the rectifier with the DC load), the current flowing through the input of the DC load corresponds I. also the current flowing through the DC output of the rectifier. The same correspondence applies to the usual interconnection of rectifier and DC load for the voltage applied to the output capacitance as well as for the current flowing from the output capacitance in the direction of the DC output.

In principle, it is possible for the control unit of the rectifier to be designed to control future operation of the rectifier as a function of whether a short circuit or no short circuit was detected on the DC load. Specifically, if the method does not detect a short circuit at the DC load, the control unit can enable normal operation of the rectifier for supplying the DC load from the AC network. For this purpose, the control unit can be designed and set up to establish a low-impedance connection of the rectifier to the AC network on the one hand by closing the AC disconnection unit and also to establish a low-impedance connection of the rectifier to the DC load by closing the DC disconnector. In contrast, if the method detects a short circuit in the DC load, the control unit can control the rectifier in response to the detected short circuit in the DC load in such a way that a permanent power flow from the AC network via the rectifier into the DC Load and thus normal operation of the rectifier for supplying the DC load is prevented. For this purpose, the control unit can be designed and set up to prevent the AC disconnection unit from closing in response to a detected short circuit in the DC load, provided it is still open. If it is a two-stage rectifier, the control unit can optionally also prevent the semiconductor switches of the DC / DC converter from pulsing and thus deactivate the DC / DC converter. If the AC disconnection unit is already closed, for example because a two-stage rectifier prevents power flow through the rectifier via a deactivated DC / DC converter, the control unit can open the AC disconnection unit and thus disconnect the rectifier from the AC Create a network. If the rectifier is already connected to the DC load with low impedance via a closed DC isolating switch, the control unit can open the DC isolating switch in response to a detected short circuit in the DC load, in order to permanently disconnect the rectifier from the DC load to separate.

Figure list

• 1 einen erfindungsgemäßen Gleichrichter zur Verbindung eines AC-Netzes und einer DC-Last in einer ersten Ausführungsform;
• 2 einen erfindungsgemäßen Gleichrichter zur Verbindung eines AC-Netzes und einer DC-Last in einer zweiten Ausführungsform;
• 3 ein Ablaufdiagramm eines erfindungsgemäßen Verfahrens in einer ersten Variante;
• 4 ein Ablaufdiagramm eines erfindungsgemäßen Verfahrens in einer zweiten Variante.

The invention is illustrated below with the aid of figures. From these show

• 1 a rectifier according to the invention for connecting an AC network and a DC load in a first embodiment;
• 2 a rectifier according to the invention for connecting an AC network and a DC load in a second embodiment;
• 3 a flow chart of a method according to the invention in a first variant;
• 4th a flow chart of a method according to the invention in a second variant.

Figure description

In 1 is a rectifier according to the invention 1 shown in a first embodiment. The rectifier 1 is designed to convert an alternating voltage into a direct voltage and for this purpose at its AC input 2 with an alternating voltage (AC) network 20th and at its DC output 3 with an entrance 32 a DC load 30th connected. The AC network is an example 20th as a three-phase AC network and the rectifier 1 as a three-phase rectifier with three phase connections on its AC input 2 illustrated. In the context of the invention, however, it is also possible that the AC network 20th may have a different number of phase conductors, for example two phase conductors or just one phase conductor. The rectifier can also do the same 1 at its AC output 2 have a different number of phase connections. The DC load 30th is in 1 exemplarily as an electrolyzer 31 shown. In the context of the invention, the DC load 30th however, it can also be designed as a DC load other than an electrolyzer. The DC load 30th does not necessarily have to be designed exclusively for power consumption, but can, in particular in the case of a bidirectional rectifier 1 , in addition to the power-consuming operating mode, also have a power-generating operating mode. This is the case, for example, with a DC load designed as a battery 30th the case.

In 1 is the rectifier 1 designed and included as a single-stage rectifier (viewed from the AC grid 20th ) an AC disconnection unit 5 , a sine filter 9 , an AC / DC converter 10 , one between the AC / DC converter 10 and the DC output 3 of the rectifier 1 arranged output capacitance 4th , a DC disconnector 14th and a control unit 15th to control the components of the rectifier 1 . The connections for control and / or communication are in 1 symbolized by arrows shown in dashed lines. The AC disconnection unit 5 includes a precharge resistor 7th a first AC circuit breaker 6th and a second AC breaker 8th . The first AC disconnector 6th is in series with the precharge resistor 7th interconnected. The second AC breaker 8th is parallel to the series connection of the precharge resistor 7th and the first AC disconnector 6th connected. This is how the AC disconnect unit is 5 designed the AC / DC converter 10 and the output capacitance connected to it 4th in a first operating mode via the precharge resistor 7th and in a second operating mode direct or low-impedance and without the interposition of the precharge resistor 7th with the AC grid 20th connect to. The sine filter 9 is designed to withstand high-frequency interference signals due to the pulsing of semiconductor switches in the AC / DC converter 10 are generated in their propagation in the direction of the AC network 20th to dampen. Likewise is the sine filter 9 designed in the AC network 20th of already existing interference signals in their propagation in the direction of the DC output 3 of the rectifier 1 to dampen. The DC disconnector 14th can be single-pole or multi-pole. It can be used to disconnect the DC load 30th be designed during a current flow and therefore have means for arc extinguishing and / or arc suppression. The DC disconnector 14th is designed the output capacitance 4th when closed, low-impedance with the DC load 30th to connect and when open from the DC load 30th to separate. In contrast to the AC disconnection unit 5 is the DC disconnector 14th in particular free of a precharge resistor.

The rectifier 1 furthermore has a measuring unit 13th on that to measure one at the output capacitance 4th applied voltage U and / or one of the output capacitance 4th towards the DC output 3 flowing stream I. , in particular designed and set up by their time courses. The unit of measurement 13th is designed the measured values of voltage U and electricity I. for evaluation to the control unit 15th to hand over. The control unit 15th is at the same time able to get the detected values of voltage U and / or electricity I. according to the method according to the invention for detecting a short circuit 33 the DC load 30th to evaluate. Furthermore, the control unit 15th to be designed and set up the rectifier 1 to be controlled depending on a result of the evaluation. In particular, the control unit 15th be set up in the event of a detected short circuit 33 at the entrance 32 the DC load 30th both the DC disconnector 14th , as well as the AC circuit breaker 6th , 8th the AC disconnection unit 5 to open, provided the respective disconnector 6th , 8th , 14th are not already open. In this way, both a power flow from the AC network 20th into the rectifier 1 as well as a power flow from the rectifier 1 into the DC load 30th sure to be suppressed.

In 2 is a second embodiment of the rectifier according to the invention 1 for supplying a DC load 30th from an AC network 20th shown. The rectifier 1 corresponds in many features to those already in 1 described rectifier 1 , so refer to the description below with regard to the matching characteristics 1 is referred. Therefore, only the differences to the 1 explained in more detail.

In contrast to the embodiment according to FIG 1 is the rectifier 1 in 2 as a multi-stage rectifier 1 executed. It also includes a DC / DC converter for this purpose 12th the input side via a DC link capacitance 11 to the AC / DC converter 10 and on the output side via the output capacitance 4th with the DC output 3 of the rectifier 1 connected is. Via the DC / DC converter 12th becomes the DC link capacitance 11 from the output capacitance 4th decoupled, so that different voltage values can be set on the intermediate circuit capacitance 11 and the output capacitance 4th is possible. With the DC / DC converter 12th can the rectifier 1 also be designed to allow a power flow from the AC network 20th into the output capacitance 4th - as well as via the DC output 3 - even when the AC disconnection unit is closed 5 to prevent. Semiconductor switches of the DC / DC converter can be used for this purpose 12th to be open. The DC / DC converter 12th can also be designed to allow charge transport from the intermediate circuit capacitance 11 into the output capacitance 4th perform so that the output capacitance 4th is adjusted to the desired value of the source voltage by the charge transport.

In principle, the DC / DC converter 12th be designed as a step-up converter, step-down converter or as a combined step-up / step-down converter. With the DC / DC converter 12th it can, depending on the type of rectifier 1 to a unidirectional as well as a bidirectional DC / DC converter 12th act.

In 3 a flowchart of the method according to the invention is shown in a first variant, as is the case in FIG 1 shown rectifier 1 can be carried out. With a view to better traceability, the following description also includes those in 1 listed reference numerals are used.

The procedure for detecting a short circuit 33 starts in a state where the rectifier 1 both due to an open AC disconnection unit 5 from the AC grid 20th , as well as due to an open DC disconnector 14th from the DC load 30th is separated. In a first step S1 becomes the first AC disconnector 6th closed so that the output capacitance 4th via the precharge resistor 7th with the AC grid 20th connected is. The DC disconnector 14th initially remains open. This will be done in a second step S2 the output capacitance 4th through one of the AC grid 20th drawn power flow and via the semiconductor switches of the AC / DC converter 10 assigned freewheeling diodes charged. The AC grid 20th removed and into the initially uncharged output capacitance 4th flowing power flow is through the precharge resistor 7th so limited that damage to components of the rectifier 1 is excluded. During the charging of the output capacity 4th can be a time course of tension U above the output capacitance 4th through the measuring unit 13th to be tracked. During the steps S1 and S2 is the DC disconnector 14th opened, allowing power flow from the rectifier 1 into the DC load 30th is prevented. In a third step S3 becomes the AC disconnection unit 5 , especially their first AC disconnector 6th by the control unit 15th opened, thus further charging the output capacitance 4th from the AC grid 20th is prevented. The opening of the first AC disconnector 6th can take place when the source voltage reaches a value that corresponds to the amplitude of the alternating voltage in the AC network 20th and in which a further charge even when the AC disconnection unit is closed 5 wouldn't happen anyway. The AC disconnection unit 5 however, it can also be opened beforehand and the output capacity is charged 4th stop actively if a lower value of the source voltage is desired. Should be the voltage of the output capacitance 4th when opening the AC disconnection unit 5 are above a desired value of the source voltage, an optional fourth step can take place S4 at which the higher voltage value at the output capacitance 4th is reduced by dissipation to the desired value of the source voltage. The dissipation can be activated by activating the output capacitance 4th connected small consumers, e.g. a fan of the rectifier 1 (in 1 not shown), or by suitable operation of semiconductor switches of the AC / DC converter 10 be brought about. The fourth step, which is only optional S4 is in 3 shown in dashed lines. In a fifth step S5 becomes the output capacitance set to the source voltage 4th by closing the DC isolating switch 14th with the DC load 30th connected. While the output capacitance 4th with the DC load 30th via the closed DC disconnector 14th connected, the AC disconnection unit 5 operated in an open state. This only puts a limited amount of energy on the DC load 30th transfer. The output capacitance that depends on the source voltage 4th The amount of energy stored is calculated so that even in the event of a short circuit 33 the DC load 30th damage to the DC load 30th and / or components of the rectifier 1 is excluded. Through the low-impedance connection of the output capacitance 4th with the DC load 30th a charge is transported from the output capacitance 4th to the DC load. This will be in a sixth step S6 Time courses of the Output capacitance 4th falling voltage U and that of the output capacitance 4th towards the DC output 3 flowing stream I. through the measuring unit 13th detected. How out 1 (and also 2 ), corresponds to the voltage U above the output capacitance 4th when the DC disconnector is closed 14th both one at the DC output 3 of the rectifier 1 applied voltage as well as one at the DC load 30th applied voltage U . It also corresponds to that of the output capacitance 4th towards the DC output 3 flowing stream I. one via the DC output 3 flowing stream I. on the one hand, and one via the entrance 32 the DC load 30th flowing stream I. on the other hand. In a seventh step S7 an evaluation of the detected voltage values takes place U and / or electricity I. or their time courses by the control unit 15th . It is checked whether the detected voltage U , the detected current I. , and / or a combination of the detected voltage U and the detected current I. meet at least one predetermined criterion. In 3 checked as criteria whether a change in voltage dU / dt over time has a first threshold value (dU / dt) _TH exceeds whether the current detected I. a second threshold I _TH exceeds and / or whether the quotient of voltage and current U / I. a third threshold R _TH falls below. When the detected values of voltage U and / or electricity I. When checking none of the criteria, the control unit concludes that the DC load 30th no short circuit 33 having. Correspondingly, in an eighth step S8 the AC disconnection unit 5 , especially their second AC disconnector 8th , through the control unit 15th controlled closed. This will make the AC / DC converter 10 low impedance with the AC network 20th is connected. The DC disconnector 14th is already closed and the rectifier 1 takes controlled by the control unit 15th its normal operation to supply the DC load 30th on. Conversely, if they meet the detected voltage values U and / or electricity I. the control unit closes at least one of the criteria mentioned 15th when checking the detected values of voltage U and electricity I. on one at the DC load 30th present short circuit 33 . A low-impedance connection of the AC / DC converter 10 with the AC grid 20th in this case would have a power flow with a damaging effect on components of the DC load 30th and / or the rectifier 1 result. The process consequently branches into a tenth step S10 , in which the control unit 15th one on the DC load 30th present short circuit 33 signaled and in an eleventh step S11 an opening of all AC disconnectors 6, 8 of the AC disconnection unit 5 as well as the DC disconnector 14th provided that the relevant disconnectors are not already open. The rectifier 1 is thus galvanic from both the AC network 20th , as well as from the DC load 30th Cut. Any power flow through the rectifier 1 , both from the AC network 20th into the rectifier as well as from the rectifier 1 into the DC load 30th , is thus surely suppressed. The short circuit on the DC load 30th can be disposed of safely.

In 4th a flowchart of the method according to the invention is shown in a second variant. The second variant of the procedure can be carried out with the in 2 shown rectifier 1 be performed. The procedure is similar in many steps to that in 3 presented procedure. In the following, only the differences to the one in 3 described process variant shown.

In this case, too, the method starts in a state in which all AC disconnectors 6th , 8th the AC disconnection unit 5 and the DC disconnector 14th are open. In one step S20 becomes the first AC disconnector 6th the AC disconnection unit is closed. As in 3 This describes the AC / DC converter 10 via the precharge resistor 7th with the AC grid 20th connected. About the resulting power flow from the AC grid 20th is in one step S21 first the intermediate circuit capacitance 11 charged to a voltage equal to the amplitude of the alternating voltage in the AC network 20th corresponds to. In one step S22 becomes a source voltage at the output capacitance 4th set. This is done by operating the DC / DC converter appropriately 12th as long as an amount of charge from the intermediate circuit capacitance 11 into the output capacitance 4th transported until the desired value of the source voltage at the output capacitance 4th is reached. The currently at the output capacity 4th applied voltage U about the measuring unit 13th to be watched. After reaching the desired value of the source voltage at the output capacitance 4th becomes the DC / DC converter 12th in one step S23 deactivated, so that a further charge transport from the intermediate circuit capacitance 11 into the output capacitance 4th is prevented. In an optional step S24 opening of the AC disconnection unit 5 , especially the first AC disconnector 6th the AC disconnection unit 5 respectively. The step S24 however, it is only optional and not absolutely necessary, as power flows from the AC network 20th into the output capacitance 4th thanks to the deactivated DC / DC converter 12th is prevented. In 4th is therefore the optional step S24 shown in dashed lines. In a following step S25 finally becomes the output capacitance previously charged to the source voltage 4th by closing the DC isolating switch 14th low impedance with the DC load 30th connected.

The steps S25 to S31 correspond to the steps S6 to S11 who is already in 3 process variant shown. Specifically, the following equations apply: S5 = S25, S6 = S26, S7 = S27, ... S11 = S31. To avoid redundant information, refer to the description of the method variant according to 3 referenced.

List of reference symbols

1

Rectifier

2

AC input

3

DC output

4th

Output capacitance

5

AC disconnection unit

6th

AC disconnector

7th

Precharge resistor

8th

AC disconnector

9

Sine filter

10

AC / DC converter

11

DC link

12th

DC / DC converter

13th

Measuring unit

14th

DC disconnector

15th

Control unit

20th

AC grid

30th

DC load

31

Electrolyzer

32

Entrance

33

Short circuit

U

tension

I.

electricity

(dU / dt) TH

Threshold

ITH

Threshold

RTH

Threshold

S1-S11

Process step

S20-S31

Process step

Claims (16)

Method for detecting a short circuit (33) of a DC load (30), which can be connected to an AC network (20) via a rectifier (1) comprising an AC / DC converter (10), with the following steps: - Setting a source voltage at an output capacitance (4) of the rectifier (1) via a rectified power flow taken from the AC network (20), - Connect the output capacitance (4) of the rectifier (1), previously set to the source voltage, to the input (32) of the DC load (30), with a further power flow from the AC network (20) into the rectifier (1) and an associated recharging of the output capacitance (4) is suppressed, - Detection of a voltage U present at an input (32) of the DC load (30) and / or a current I flowing via the input (32) of the DC load (30), - Signaling of a short circuit (33) of the DC load when the detected voltage U, a time curve of the detected voltage U, the detected current I, a time curve of the detected current I, a combination of the detected voltage U and the detected current I and / or a combination of the time courses of the detected voltage U and the detected current I meet at least one predetermined criterion. Procedure according to Claim 1 , the at least one predetermined criterion comprising at least one of the following criteria: an amount of a change over time in the voltage dU / dt applied to the input (32) of the DC load (30) exceeds a first threshold value (dU / dt assigned to the source voltage ) _TH , and / or - the current I flowing through the input (32) of the DC load exceeds a second threshold value I _TH , and / or - a quotient of the voltage applied to the input (32) of the DC load (30) U and the current I flowing via the input (32) of the DC load (30) falls below a third threshold value R _TH . Procedure according to Claim 1 or 2 , wherein a value of the source voltage is selected so that when an amount of energy assigned to the source voltage is transferred to the DC load (30), in particular in the event of a short circuit (33) of the DC load (30), damage to components of the DC Load (30) and / or the rectifier (1) is excluded. Method according to one of the Claims 1 to 3 , wherein the rectifier (1) is designed as a single-stage rectifier and the further power flow from the AC network (20) into the output capacitance (4) is suppressed in that when the output capacitance (4) is connected to the DC load (30 ) the output capacitance (4) is galvanically isolated from the AC network (20) via an opened AC isolating unit (5). Method according to one of the preceding Claims 1 to 4th , the output capacitance (4) of the single-stage rectifier (1) being charged via free-wheeling diodes of the AC / DC converter (10) to a source voltage which corresponds to the amplitude of the alternating voltage of the AC network (20). Method according to one of the Claims 1 to 3 , the rectifier (1) being a multi-stage Rectifier is designed with a DC / DC converter (12) connected downstream of the AC / DC converter (10) and an intermediate circuit capacitance (11) arranged in between, and wherein when connecting the output capacitance (4) to the DC load (30) the further power flow from the AC network (20) into the rectifier (1) is suppressed via an open semiconductor switch of the DC / DC converter (12). Procedure according to Claim 6 , the output capacitance (4) of the multi-stage rectifier (1) being set to a source voltage via a DC / DC converter (12) connected upstream of the output capacitance (4), the value of which is below the amplitude of the alternating voltage of the AC network (20) lies. Method according to one of the Claims 1 to 5 , wherein the rectifier (1) is designed in one stage and the setting of the output capacitance (4) to the source voltage includes that a voltage of the output capacitance (4) initially above the source voltage by dissipating the energy stored in the output capacitance (4) to the value the source voltage is reduced, and wherein the output capacitance (4) is disconnected from the AC grid (20) during the dissipation. Procedure according to Claim 8 , whereby the dissipation of the energy stored in the output capacitance (4) is brought about by pulsing semiconductor switches of the AC / DC converter (10) or by operating at least one small consumer connected to the output capacitance (4), e.g. a fan. Method according to one of the preceding claims, wherein the power flow for setting the source voltage at the output capacitance (4) is taken from the AC network (20) via a precharge resistor (7). Method according to one of the preceding claims, wherein the DC load (30) comprises an electrolyzer (31). Rectifier (1) for converting an alternating voltage into a direct voltage, with an AC input (2) for connecting the rectifier (1) to an AC network (20) and a DC output (3) for connecting the rectifier (1) with a DC load (30) comprising - an AC / DC converter (10), - an output capacitance (4) connected to the DC output (3) of the rectifier (1), - An AC disconnection unit (5) connected to the AC input (2) and a DC disconnector (14) connected to the DC output (3), and - A control unit (15) for controlling the rectifier (1), which is designed and set up to carry out the method according to one of the preceding claims. Rectifier (1) Claim 12 , characterized in that the AC disconnection unit (5) comprises a precharge resistor (7) and is designed to connect the AC / DC converter (10) assigned to the rectifier (1) to the AC network (20) on the one hand via the Provide precharge resistor (7) and on the other hand in a direct manner and without the interposition of the precharge resistor (7). Rectifier (1) Claim 12 or 13th , characterized in that the rectifier (1), in particular the AC / DC converter (10), is designed and set up with regard to a power flow for bidirectional operation. Rectifier (1) after one of the Claims 12 to 14th , characterized in that the rectifier (1) is designed in several stages and comprises a DC / DC converter (12) arranged between the AC / DC converter (10) and the output capacitance (4). Rectifier (1) after one of the Claims 12 to 15th , characterized in that the control unit (15) of the rectifier (1) is designed and set up, in response to a detected short circuit (33) of the DC load (30), a permanent power flow from the AC network (20) via the To prevent rectifier (1) in the DC load (30) by preventing the AC disconnection unit (5) from closing and / or possibly pulsing of the semiconductor switches of the DC / DC converter (12).

Images