Method for controlling electrical consumers of an electrical supply grid

Abstract

A method for controlling an electrical consumer is provided. The electrical consumer is coupled to an electricity supply grid using a frequency converter. The electricity supply grid has a line voltage and is characterized by a nominal line voltage. The electricity supply grid is monitored for a grid fault in which the line voltage deviates from the nominal line voltage by at least a first differential voltage. When the grid fault occurs, the electrical consumer remains coupled to the electricity supply grid, and a power consumption of the electrical consumer is changed on the basis of the deviation of the line voltage from the nominal line voltage.

Claims

1. A method for controlling an electrical consumer, comprising: monitoring an electricity supply grid for a grid fault during which a line voltage of the electricity supply grid deviates from a nominal line voltage of the electricity supply grid by at least a first differential voltage, wherein the electrical consumer is coupled to the electricity supply grid using a frequency converter; in response to detecting the grid fault, retaining coupling between the electrical consumer and the electricity supply grid; and changing a power consumption of the electrical consumer based on a deviation of the line voltage from the nominal line voltage, wherein: the frequency converter has a DC voltage intermediate circuit, the DC voltage intermediate circuit has an intermediate circuit voltage, the intermediate circuit voltage depends on the deviation of the line voltage from the nominal line voltage, and at least one power control operation is provided on the basis of the intermediate circuit voltage.

2. The method as claimed in claim 1, wherein: the electrical consumer includes has at least one main consumer having power consumption that is controllable, and at least one auxiliary device having power consumption that is not controllable, and the method comprises: in response to detecting the grid fault, supplying the at least one auxiliary device with electric power using an uninterruptible power supply irrespective of the deviation of the line voltage; and supplying the main consumer with electric power from the electricity supply grid on the basis of the deviation of the line voltage.

3. The method as claimed in claim 1, wherein: the first differential voltage is at least 10% of the nominal line voltage, and/or the method comprises: disconnecting the electrical consumer from the electricity supply grid when the line voltage is below the nominal line voltage by more than a second differential voltage, wherein the second differential voltage is greater than the first differential voltage and is at least 50% of the nominal line voltage.

4. The method as claimed in claim 3, wherein the first differential voltage is at least 20% of the nominal line voltage, and the second differential voltage is at least 70% of the nominal line voltage.

5. The method as claimed in claim 1, wherein: the electrical consumer includes a battery, and the method comprises: in response to detecting the grid fault, causing the battery to feed electric power into the DC voltage intermediate circuit to power the electrical consumer, power at least one auxiliary device, or feed reactive power into the electricity supply grid.

6. The method as claimed in claim 1, wherein when the grid fault occurs, the frequency converter feeds reactive power into the electricity supply grid, and wherein: the reactive power is fed in using a support current, and the support current is limited based on the line voltage, and/or active power for performing the reactive power infeed is: released by the electrical consumer by reducing the power consumption of the electrical consumer, provided by a battery, and/or provided by the electricity supply grid.

7. The method as claimed in claim 1, comprising: performing, by the frequency converter, intermediate circuit control to regulate the intermediate circuit voltage to a predefined intermediate circuit voltage value; determining, by the frequency converter, an available exchange power; and transmitting the available exchange power to the electrical consumer, wherein a communication device is provided for communication between the frequency converter and the electrical consumer.

8. The method as claimed in claim 1, further comprising: storing the power consumption of the electrical consumer prior to the grid fault as a pre-fault value; and setting the power consumption of the electrical consumer to the pre-fault value after the grid fault has ended.

9. The method as claimed in claim 8, wherein setting the power consumption to the pre-fault value after the grid fault has ended includes setting the power consumption based on a curve that is a temporal ramp function having the power consumption changed linearly up to the pre-fault value.

10. The method as claimed in claim 8, wherein an electrical storage unit sets the pre-fault value.

11. The method as claimed in claim 10, wherein when the electrical consumer is a charging station for charging electric vehicles, at least one storage unit of at least one electric vehicle connected to the charging station sets the pre-fault value.

12. The method as claimed in claim 1, wherein the electrical consumer is an electric charging station for charging electric vehicles.

13. The method as claimed in claim 1, wherein the electrical consumer is configured as a support consumer that uses the frequency converter to support the electricity supply grid, wherein the electrical consumer supports the electricity supply grid based on a presence of at least one parallel consumer feeding into the electricity supply grid, and wherein: the support consumer identifies a grid disconnection of the at least one parallel consumer, the support consumer changes the power consumption based on the deviation of the line voltage such that a total power consumption of the at least one parallel consumer and the power consumption of the support consumer change in accordance with a predefined total power change, and/or after the grid fault has ended, the support consumer sets an infeed power such that the total power consumption reaches a sum of pre-fault values of the support consumer and the at least one parallel consumer.

14. The method as claimed in claim 1, wherein the at least one power control operation is from a list including: the power consumption of the electrical consumer is controlled on the basis of the intermediate circuit voltage, the power consumption of the electrical consumer is controlled depending on predefined consumer droop, wherein the predefined consumer droop specifies a linear relationship between the power consumption of the electrical consumer and the intermediate circuit voltage or a range of intermediate circuit voltages including the intermediate circuit voltage, a power consumption or power output of an uninterruptible power supply is controlled on the basis of the intermediate circuit voltage, the power consumption or power output of the uninterruptible power supply is controlled depending on predefined uninterruptible power supply (UPS) droop, wherein the predefined UPS droop specifies a linear relationship between the power consumption or output of the UPS and the intermediate circuit voltage or the range of intermediate circuit voltages including the intermediate circuit voltage, a power consumption or power output of a battery storage unit is controlled on the basis of the intermediate circuit voltage, and the power consumption or power output of the battery storage unit is controlled depending on predefined storage unit droop, wherein the predefined storage unit droop specify specifies a linear relationship between the power consumption or output of the battery unit and the intermediate circuit voltage or the range of intermediate circuit voltages including the intermediate circuit voltage.

15. A charging station for electric vehicles, comprising: a frequency converter configured to couple the charging station to an electricity supply grid having a line voltage and associated with a nominal line voltage; a monitoring controller configured to monitor the electricity supply grid for a grid fault in which the line voltage deviates from the nominal line voltage by at least a first differential voltage; an operating controller configured to control the charging station such that the charging station remains coupled to the electricity supply grid when the grid fault occurs; and a power controller configured to change a power consumption of the charging station based on a deviation of the line voltage from the nominal line voltage, wherein: the frequency converter has a DC voltage intermediate circuit having an intermediate circuit voltage, the intermediate circuit voltage depends on the line voltage, and at least one power control operation is provided on the basis of the intermediate circuit voltage from a list including: the power consumption of the charging station is controlled based on the intermediate circuit voltage, the power consumption of the charging station is controlled based on predefined consumer droop that specifies a linear relationship between the power consumption of the charging station and the intermediate circuit voltage or a range of intermediate circuit voltages including the intermediate circuit voltage, a power consumption or power output of an uninterruptible power supply (UPS) is controlled based on the intermediate circuit voltage, the power consumption or the power output of the uninterruptible power supply is controlled based on predefined UPS droop, wherein the predefined UPS droop specifies a linear relationship between the power consumption or output of the uninterruptible power supply and the intermediate circuit voltage or the range of intermediate circuit voltages including the intermediate circuit voltage, a power consumption or power output of a battery is controlled based on the intermediate circuit voltage, and the power consumption or the power output of the battery is controlled based on predefined battery droop, wherein the predefined battery droop specifies a linear relationship between the power consumption or output of the battery and the intermediate circuit voltage or the range of intermediate circuit voltages including the intermediate circuit voltage.

16. The charging station as claimed in claim 15, wherein: the charging station has at least one main consumer having power consumption that is controllable and at least one auxiliary device having power consumption that is not controllable, the uninterruptible power supply is used and when the grid fault occurs, the at least one auxiliary device is supplied with electric power using the uninterruptible power supply irrespective of the deviation of the line voltage from the nominal line voltage, and the main consumer is supplied with electric power from the electricity supply grid based on the line voltage.

17. The charging station as claimed in claim 15, comprising: the battery configured to, when the grid fault occurs, feed electric power into the DC voltage intermediate circuit to feed reactive power into the electricity supply grid or power at least one of the charging station or at least one auxiliary device.

18. A method for controlling an electrical consumer, comprising: monitoring an electricity supply grid for a grid fault during which a line voltage of the electricity supply grid deviates from a nominal line voltage of the electricity supply grid by at least a first differential voltage, wherein the electrical consumer is coupled to the electricity supply grid using a frequency converter; in response to detecting the grid fault, retaining coupling between the electrical consumer and the electricity supply grid; and changing a power consumption of the electrical consumer based on a deviation of the line voltage from the nominal line voltage, wherein the electrical consumer includes has at least one main consumer having power consumption that is controllable, and at least one auxiliary device having power consumption that is not controllable, and the method comprises: in response to detecting the grid fault, supplying the at least one auxiliary device with electric power using an uninterruptible power supply irrespective of the deviation of the line voltage; and supplying the at least one main consumer with electric power from the electricity supply grid on the basis of the deviation of the line voltage.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention is now explained in more detail below on the basis of embodiments with reference to the accompanying figures.

(2) FIG. 1 shows a schematic illustration of a charging station as electrical consumer.

(3) FIG. 2 shows various droops for intermediate circuit-dependent power control.

(4) FIG. 3 shows characteristic curves for line voltage-dependent power control.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic illustration of a charging station 1. The charging station 1 has a plurality of charging terminals 2, each of which is symbolized as a DC/DC converter. Likewise illustratively, an electric vehicle 4 is connected to each charging terminal 2. It may usually of course be assumed that different electric vehicles are able to be charged, and the use of the same reference signs for the electric vehicles 4 is intended only to indicate that there is no need for a distinction in connection with the explanations of FIG. 1. The charging terminals 2 and the vehicles 4 should in this respect be understood to be essentially illustrative. More than three charging terminals 2 in particular also come into consideration. However, it also comes into consideration for no electric vehicle 4 to be connected to a charging terminal 2 at times.

(6) In order to supply power to the charging terminals 2, provision is made for a frequency converter 6 that converts electric AC voltage from an illustratively shown electricity supply grid 8 into a DC voltage or a DC current that is available to the charging terminals 2 as an input voltage. The frequency converter 6 in this respect has a DC voltage intermediate circuit, which is not shown in detail, but for example the DC voltage symbol that is shown may in this respect also be representative of this DC voltage intermediate circuit. The frequency converter 6 in this case has a DC voltage output 10, which may be connected directly to the DC voltage intermediate circuit. In this respect, current is able to flow from the DC voltage output 10 and thus from the DC voltage intermediate circuit of the frequency converter 6 to the charging terminals 2, wherein it may for this purpose be divided among the individual charging terminals 2.

(7) The frequency converter 6 is provided with an AC voltage input 12, by way of which it is coupled to the electricity supply grid 8 via a grid disconnection switch 14.

(8) A control peripheral 16 (controller) is provided for control purposes and, in this respect, also forms an auxiliary device or contains auxiliary devices. In this respect, this control peripheral 16 may also be referred to as an auxiliary device (AUX).

(9) The control peripheral 16 in this case comprises a monitoring unit 18 (controller), which has a sensor 20 (voltmeter or multimeter), which is illustrated symbolically and is able to detect a line voltage V of the electricity supply grid 8. In this respect, the monitoring unit 18 may monitor the electricity supply grid 8 for a grid fault, specifically depending on the level of the line voltage V. The monitoring unit 18 in this case supplies the results of the monitoring to an operating control unit 22 (controller) and a power control unit 24 (controller). In addition or as an alternative, the monitoring unit 18 may also transmit the detected voltage values V directly to the operating control unit 12 and the power control unit 24.

(10) The operating control unit 22 is intended, inter alia, to drive the grid disconnection switch 14. This is illustrated by a corresponding connecting double-headed arrow between the grid disconnection switch 14 and the operating control unit 22. The double-headed arrow in this case illustrates that information may also be transmitted from the grid disconnection switch, in particular about its switch position, to the operating control unit 22.

(11) The power control unit 24 in particular controls the overall power consumption of the charging station. This takes place in particular via corresponding driving of the frequency converter 6, and may take place on the basis of the line voltage or information about this. By way of example, the intermediate circuit voltage may provide information about the line voltage. In particular when the intermediate circuit voltage is known as well as the control of the converter based on which at a given intermediate circuit voltage power is drawn from the electricity supply grid, the line voltage may be derived directly or indirectly therefrom. The power control unit 24 may also receive this line voltage or information about this from the monitoring unit 18. However, it also comes into consideration for the frequency converter 6 itself to provide voltage detection of the line voltage V and to transmit information about this line voltage V thus detected or the detected line voltage V as such to the power control unit 24. For the frequency converter 6, a graph of controller droop is shown symbolically and provides a power control possibility that depends on the intermediate circuit voltage, which will be described further below. In this case, it would be possible to dispense with using the level of the detected line voltage. According to one embodiment, the level of the line voltage may in this case be incorporated into regulation of the intermediate circuit voltage as information, and such regulation is preferably performed in the frequency converter 6.

(12) The charging station 1 furthermore also has a battery storage unit 26 (battery), which also serves as pre-charging storage unit in this charging station 1. It is basically coupled to the DC voltage output 10 of the frequency converter 6 via a storage unit converter 28. In general, a DC bus 30 may be provided for this purpose, and is connected to the DC voltage output 10 of the frequency converter 6 and thus connects various DC current sub-consumers, such as the charging terminals 2 and the storage unit converter 28.

(13) In addition to the battery storage unit 26, a graph of controller droop is likewise shown illustratively, which is intended to symbolize that the battery storage unit 26 may have implemented intermediate circuit voltage-dependent power control, which will be explained further below. The battery storage unit 26 or its storage unit converter 28 may be driven accordingly for this purpose. Such driving may also be performed for example by the power control unit 24, which is however not shown in FIG. 1 for the sake of clarity.

(14) Provision is furthermore made for an uninterruptible power supply 32 (uninterruptible power supply battery) that is connected to the DC bus 30 and thus to the DC voltage output 10 of the frequency converter 6 via a UPS converter 34. This uninterruptible power supply (UPS) 32 is able to drive auxiliary devices such as the control peripherals 16. The control peripherals 16, specifically in particular the monitoring unit 18, the operating control unit 22 and the power control unit 24, are essentially designed as process computers, and may also be wholly or partially combined in a practical embodiment, and tolerate only a small change in power, meaning that, even in the event of a grid fault, the uninterruptible power supply 32 is able to ensure a power supply to these control peripherals that is as far as possible unchanged.

(15) The UPS may however also be designed and/or used such that it covers only the losses of the converter. It may in this case be provided as an intermediate circuit UPS, which, as shown in FIG. 2, is connected to the intermediate circuit and feeds electric power into same in order to cover losses of the converter.

(16) The uninterruptible power supply 32 may however also supply power to other auxiliary devices that are not illustrated here for the sake of simplicity, such as for example a communication device for transmitting information within the charging station 1 or else to an externally located central unit. A graph of controller droop is also indicated for the uninterruptible power supply 32, which graph symbolizes a power of the uninterruptible power supply as a function of an intermediate circuit voltage as a control relationship and is described in more detail later.

(17) A graph of controller droop is also illustrated for the charging terminals 2, which graph symbolizes the power of the charging terminals 2 as a function of the intermediate circuit voltage, which is likewise described further below.

(18) Another control option consists in specifying the respective maximum charging power able to be provided by the charging terminals 2, either individually or as a total power. This is symbolized by an arrow illustrated in dashed form, which extends from the frequency converter 6 to a charging terminal 2. However, this should be understood symbolically and should not only symbolize control of the one charging terminal illustrated at the top, but rather all of the charging terminals 2 should be able to receive this power limit as similarly as possible. It however also comes into consideration for a total power limit to be transmitted, which the charging terminals 2 divide among themselves.

(19) FIG. 2 shows a plurality of graphs A to D for power control operations as a function of the intermediate circuit voltage of a frequency converter, specifically in particular of the frequency converter 6 of FIG. 1. These graphs, or the characteristic curves contained therein, may also each be referred to as controller droops. The graphs are particularly illustrative with regard to the power amplitude insofar as the individual graphs may have different scales with regard to the power, that is to say may have different amplitudes. The resolution of the intermediate circuit voltage, which is plotted in each case on the abscissa, is however scaled identically for all of the graphs and is also intended in this case to clarify the relationships that exist in this respect between the individual intermediate circuit voltage-dependent power control operations.

(20) Each graph in FIG. 2 has, plotted on its ordinate, the power that the DC voltage intermediate circuit outputs or is able to output or should output. A positive value in this respect means that power is output from the DC voltage intermediate circuit. To where the respective power is output, or from where it is consumed in the case of negative values, then differs between the individual graphs. The absolute power values, in particular the maximum values or minimum values shown in each case, may differ between the individual graphs.

(21) Graph A shows the proposed power behavior of the frequency converter in relation to the electricity supply grid. With the power P, the graph thus shows the power that is output from the DC voltage intermediate circuit to the electricity supply grid, that is to say is fed into the electricity supply grid. Negative power values, which are thus below the abscissa axis, thus indicate the consumption of electric power from the electricity supply grid into the DC voltage intermediate circuit.

(22) The origin of the graph, where the two graph axes thus intersect, indicates a nominal intermediate circuit voltage V.sub.INT with the power value 0. If the intermediate circuit voltage thus has its nominal value, power is neither drawn from the electricity supply grid nor fed into it. If the intermediate circuit voltage V.sub.INT increases up to a first upper intermediate circuit voltage value V.sub.INT1.sup.+, then the power increases linearly to its maximum value P.sub.max. From then on, maximum power is thus fed into the electricity supply grid from the DC voltage intermediate circuit.

(23) If the intermediate circuit voltage V.sub.INT drops, specifically down to the first lower intermediate circuit voltage value V.sub.INT1.sup.−, then the power also drops to its minimum value P.sub.min. The minimum power value P.sub.min may correspond exactly to the negative value of the maximum power value P.sub.max. In general, it comes into consideration for the characteristic curve shown in graph A to be point-symmetrical about the origin, that is to say point-symmetrical about the point of intersection of the two coordinate axes.

(24) Thus, depending on the intermediate circuit voltage, electric power may be drawn from the electricity supply grid or fed into it. The characteristic curve of graph A may be referred to as a droop of the line-side converter.

(25) A power limit P.sub.L is furthermore also shown, which may possibly represent a limit on the power able to be drawn from the electricity supply grid. This limit power P.sub.L may make provision for power not to be drawn from the electricity supply grid up to the maximum value. A power drawn from the electricity supply grid is thereby able to be reduced or then limited, especially for grid support, in order ultimately also to be able to reduce the power drawn by the electrical consumer, in particular in the event of a grid fault.

(26) Graph B then shows a droop of an electrical storage unit, which may optionally be provided for an electrical consumer under consideration. The electrical storage unit is accordingly not called upon if the intermediate circuit voltage is between the first lower and the first upper intermediate circuit voltage value V.sub.INT1.sup.−, V.sub.INT1.sup.+. Outside this range, the power increases linearly until the intermediate circuit voltage has reached the second upper intermediate circuit voltage value V.sub.INT2.sup.+. As the intermediate circuit voltage increases, there is then provision for the electric power to be output from the intermediate circuit to the electrical storage unit, that is to say to be stored in the electrical storage unit. If however the intermediate circuit voltage drops below the first lower intermediate circuit voltage value V.sub.INT1.sup.−, then the power also drops, specifically down to the second lower intermediate circuit voltage value V.sub.INT2.sup.−. The electrical storage unit then accordingly outputs power to the electrical intermediate circuit storage unit, and the electrical intermediate circuit storage unit thus consumes power from the energy storage unit in accordance with the characteristic curve.

(27) In principle, it should be mentioned for all of the graphs in this FIG. 2 that the term droop relates in particular in each case to the linearly rising or falling branches and, in this respect, a linear section is present. In addition, the droops of graphs A to D are also indicated in each case in FIG. 1 for the respective component.

(28) Graph C shows the proposed droop of the electrical consumer, that is to say in particular of the main consumer, which, according to FIG. 1, is all of the charging terminals 2 with the connected electric vehicles 4. The electrical consumer or main consumer essentially has a maximum value over a majority of the voltage range of the intermediate circuit voltage V.sub.INT, and is thus able to receive maximum power from the electrical intermediate circuit. However, if the intermediate circuit voltage still drops further below the second lower intermediate circuit voltage value V.sub.INT2.sup.−, then there is provision for its power to be reduced, specifically for its power, which it draws from the DC voltage intermediate circuit of the frequency converter, to drop linearly until the intermediate circuit voltage has reached the third lower intermediate circuit voltage value V.sub.INT3.sup.−. It is assumed here that the electrical consumer itself in this respect does not generate any power and could return it to the DC voltage intermediate circuit. At least that is the basis of the consideration.

(29) Graph D shows a droop for an uninterruptible power supply UPS. The uninterruptible power supply may in particular be one such as is illustrated as uninterruptible power supply 32 in FIG. 1. It receives its power from the DC voltage intermediate circuit and then supplies power to peripheral devices, in particular including control devices of the consumer or of the charging station, as illustrated for example in FIG. 1.

(30) The graph shows that the uninterruptible power supply UPS feeds power into the DC voltage intermediate circuit only when the intermediate circuit voltage V.sub.INT drops below the third lower intermediate circuit voltage value V.sub.INT3.sup.−. The power then decreases linearly as the intermediate circuit voltage continues to drop. The uninterruptible power supply then feeds power into the DC voltage intermediate circuit.

(31) In addition, it should be noted in particular for graphs B, D and E that slight deviations of the horizontal characteristic curve from the abscissa should not represent an actual deviation, but rather such a representation was chosen only for the sake of clarity in order to be able to visually distinguish the characteristic curve from the abscissa.

(32) Finally, graph E shows an optional chopper that is able to consume power from the DC voltage intermediate circuit by conducting electric current through appropriate heating resistors in order thereby to destroy energy or convert it into heat.

(33) Droops for such a chopper are shown in graph E. It may be identified there that the chopper becomes active only when the intermediate circuit voltage V.sub.INT has reached a very high value, which is referred to here as fourth upper intermediate circuit voltage value V.sub.INT4.sup.+. From then on, the power that the chopper draws from the DC voltage intermediate circuit increases to a maximum value (reached at a fifth upper intermediate circuit voltage value V.sub.INT5.sup.+) as the intermediate circuit voltage V.sub.INT continues to increase.

(34) FIG. 3 shows a graph of a line voltage-dependent active power characteristic curve and a line voltage-dependent reactive power characteristic curve. It is accordingly proposed for the electrical consumer to feed reactive power Q.sub.FRT into the electricity supply grid or draw it therefrom on the basis of the line voltage V.sub.Net. Accordingly, no reactive power Q.sub.FRT is fed in close to the nominal line voltage V.sub.N. The characteristic curve is shown in this region slightly below the coordinate axis, this serving only for improved illustration. In fact, it should be on the coordinate axis in the region close to the nominal line voltage V.sub.N. If the line voltage V.sub.Net increases to such an extent that it exceeds an upper threshold voltage V.sub.max, then the fed-in reactive power Q.sub.FRT increases, in particular linearly as the line voltage continues to increase. Likewise, particularly point-symmetrically about the origin of the coordinate system that is shown, a reactive power Q.sub.FRT is drawn from the electricity supply grid as soon as the line voltage V.sub.Net drops below a lower threshold voltage V.sub.min. In particular, the amount of this drawn reactive power increases linearly as the line voltage continues to drop. The fed-in reactive power Q.sub.FRT is thus negative, and likewise drops concomitantly as the line voltage continues to drop.

(35) At the same time, the active power P.sub.FRT consumed by the electrical consumer, in particular a main consumer, is illustrated. Accordingly, the consumed electric power adopts a maximum value in the region of the dead band of the reactive power infeed, that is to say between the lower voltage threshold value V.sub.min and the upper voltage threshold value V.sub.max. The electrical consumer is in this case in a normal state in which it consumes maximum power in a manner as unchanged as possible. This power value may also be different from the maximum possible power. In particular, the consumer in this case consumes electric power to the extent that it makes sense for it to operate at the time, regardless of the electrical line voltage V.sub.Net. If the line voltage V.sub.Net then rises above the upper threshold value V.sub.max, it is proposed to reduce the drawn active power as the line voltage increases, in particular to reduce it linearly. Toward the end of the characteristic curve, this is shown in dashed form in order to make it clear that, if the voltage deviation of the line voltage is too high, a shutdown may possibly already come in consideration before the active power consumed has dropped to the value 0.

(36) In a quite similar way, the power consumed by the electrical consumer also decreases when the line voltage has dropped below the lower threshold voltage V.sub.min. It is in particular proposed for the power then to decrease linearly as the line voltage continues to drop, in particular such that it is reduced to the value 0.

(37) The voltage range between the lower threshold voltage V.sub.min and the upper threshold voltage V.sub.max may thus also be referred to as dead band region, at least with regard to the reactive power characteristic curve. It may also be assumed here that a grid fault is present and is also detected accordingly as soon as the line voltage is outside this dead band region, that is to say is above the upper threshold voltage V.sub.max or below the lower threshold voltage V.sub.min.

(38) With regard to the consumed power P.sub.FRT, this is therefore not reduced within the dead band region. In principle, however, it also comes into consideration for the region in which power P.sub.FRT is not reduced not to correspond to the dead band region of the reactive power characteristic curve, but rather to be able to be larger or smaller. It preferably ranges from a line voltage value below the lower threshold voltage V.sub.min up to a voltage value above the upper threshold value V.sub.max. It is thereby in particular possible to achieve a situation whereby, initially, an excessively great voltage deviation, which is indicative of a grid fault, is counteracted through a corresponding reactive power infeed or draw. If the deviation of the voltage from the nominal voltage increases further, then it comes into consideration to additionally change the active power on the basis of the line voltage.

(39) It is particularly important here that the electrical consumer takes part in grid support measures. It should also be emphasized here in particular not only that the electrical consumer is able to reduce its consumed power as active power, but also that it is additionally able to control the voltage via a reactive power infeed.

(40) In addition, provision is also made for an uninterruptible power supply UPS that is able to provide a power, in particular is able to feed it into the DC voltage intermediate circuit, when the consumed power P.sub.FRT of the electrical consumer has already reached the value 0. This active power of the uninterruptible power supply P.sub.UPS may be used in particular to provide active power required for generating reactive power. In particular, active power may be required in order to compensate power loss that occurs when reactive power is fed in. Power required for the peripherals, such as control devices (controller) and process computers, may also be provided by the uninterruptible power supply.

(41) According to FIG. 3, the active power P.sub.FRT, when the line voltage drops, attains the value 0 at a second lower threshold voltage V.sub.min2 If the line voltage continues to drop, the reactive power Q.sub.FRT also decreases further, wherein power is required for controlling or supporting this, and therefore the power P.sub.UPS drawn from the DC voltage intermediate circuit by the uninterruptible power supply is likewise further reduced as the line voltage drops further, in particular linearly with the dropping line voltage. However, this means that the active power P.sub.UPS of the uninterruptible power supply, which is fed into the DC voltage intermediate circuit, or is provided in some other way by the uninterruptible power supply, increases.

(42) The uninterruptible power supply may in this case too thus be integrated into the electrical consumer or its control system in a particularly simple and expedient manner such that the proposed support measures are able to be implemented by corresponding reactive power infeed and by corresponding active power reduction by using power from the uninterruptible power supply.

(43) It is known in principle to support the electricity supply grid, which may also be referred to simply as grid, in the event of grid faults by way of modern wind power installations and, in particular, to control the wind power installations through the fault as far as possible without disconnection from the grid, which is also generally referred to as “fault ride-through” (FRT).

(44) It is proposed to prepare electrical consumers, in particular charging stations, to be controlled through a grid fault. In this case, it is preferably proposed to ensure the supply of power to the consumer up to a predetermined residual voltage in the event of a fault, in particular up to a voltage dip of less than 50% of the nominal line voltage, via an intermediate circuit-coupled UPS. It was not hitherto known to ride through a grid fault with dynamic voltage support in pure load operation, that is to say when the electrical consumer does not have an electrical storage unit, since the intermediate circuit is no longer able to be charged sufficiently from the grid in the event of a voltage dip, that is to say is not able to follow the behavior of the grid.

(45) In order nevertheless to ride through a grid fault with an electrical consumer, in particular in the event of an undervoltage, with dynamic grid support, the following aspects are proposed, at least according to one embodiment:

(46) A supply of power to the peripheral, in particular including control devices, has to be provided. A further aspect is to provide a rapid power reduction of the load or, according to one embodiment, at least partial coverage of the power that the load requires or is currently consuming from a storage unit. What is proposed is a rapid increase in load when the voltage recovers, in particular such that a power value following the grid fault is set to a power value prior to the grid fault. It has also been identified and proposed for coverage of converter losses to be able to be provided in the case of dynamic grid support, that is to say in particular in order to be able to perform a dynamic reactive power infeed.

(47) An important part of the inventive idea, at least according to one embodiment, is a grid follower mode in which the load, that is to say the consumer, follows the grid.

(48) To this end, a storage unit or load connected to a DC voltage intermediate circuit, or simply intermediate circuit, may be provided. The load, or the consumer, thus behaves on the basis of the possible voltage-dependent exchange power with the grid. The power that the load draws from the grid is therefore not based on the needs of the load, but rather on the needs of the grid.

(49) To this end, a distinction is drawn between two variants in particular, the first of which provides a frequency converter without an electrical storage unit in the intermediate circuit, which is referred to as load operation. The second variant provides a frequency converter with an electrical storage unit in the intermediate circuit, which is referred to as charging operation.

(50) The following is provided in load operation:

(51) The load receives, from the intermediate circuit, a fault power P.sub.FRT that is limited for riding through the grid fault. The power that the load receives from the intermediate circuit is thus reduced, and it is reduced such that the intermediate circuit voltage does not collapse.

(52) The peripheral is supplied with power from the intermediate circuit by an uninterruptible power supply UPS. The UPS is thus connected to the intermediate circuit and is still able to supply the peripherals even if the intermediate circuit voltage drops.

(53) However, if the intermediate circuit voltage drops below a predetermined value, the load changes its power consumption in accordance with droops, according to which a setpoint power is predefined on the basis of the intermediate circuit voltage.

(54) In the case of low intermediate circuit voltages, particularly if the intermediate circuit voltage drops below a predetermined first lower voltage limit value, it is proposed to limit a dynamic support current on the basis of the residual voltage of the intermediate circuit. This is intended to ensure that the losses that occur are covered as far as possible.

(55) When the residual voltage of the intermediate circuit is very low, if the intermediate circuit voltage drops below a predetermined second lower voltage limit value, no further active power is drawn and grid support continues to be performed only through a reactive power infeed.

(56) To this end, it is proposed to use an uninterruptible power supply coupled to the intermediate circuit, which may also be referred to as an intermediate circuit UPS, and has a small storage unit (battery), as well as a DC/DC converter, in order to be able to feed power into the intermediate circuit. The intermediate circuit UPS is in this case designed to cover only the converter losses during the fault ride-through (FRT).

(57) As an alternative, a variant is proposed which, on the load side, is not exclusively based on a detected voltage, but rather uses communication: To this end, the frequency converter regulates the intermediate circuit voltage and reports to the load a possible exchange active power that the load is able to draw from the intermediate circuit. This may be performed on the basis of the line voltage or when current limits are reached. The possible exchange active power that the load is able to draw from the intermediate circuit therefore depends on the line voltage and the reactive power fed in or drawn. This means that internal communication takes place between the frequency converter and the load.

(58) The following is provided for the charging operation:

(59) First of all, it is made possible for power also to be able to be drawn from a storage unit, which is however preferably provided only for its own use, that is to say as far as possible not for infeed purposes.

(60) The exchange power in the event of a grid fault, which is therefore exchanged between the intermediate circuit and the consumer or the load, in particular a main consumer, may also be negative. In this case, the consumer that has the storage unit feeds back into the intermediate circuit. As far as possible, however, active power is thus not fed into the grid, but reactive power Q may be fed in.

(61) Droops are proposed that predefine a power setpoint value for the exchange power on the basis of the intermediate circuit voltage. These droops are in this case not limited only to the region in which power is output from the intermediate circuit to the load, but they also concern the region in which power is returned from the load to the intermediate circuit. These droops thus concern an intermediate circuit voltage from below to above a nominal intermediate circuit voltage and range in this case from a negative exchange power to a positive exchange power.

(62) The energy storage unit of the intermediate circuit with a current limit may therefore be sufficient to ride through the grid fault, such that an intermediate circuit UPS and/or load reduction are not absolutely necessary.

(63) It is also proposed to achieve a quick restoration of the pre-fault state following the grid fault. To this end, the state prior to the grid fault, specifically in particular the level of the active power drawn from the grid immediately before the grid fault, may for example be stored. Following the grid fault, the power consumption should then as far as possible be set to the previous state prior to the grid fault, specifically in particular via a power ramp via which the power is able to be returned to the pre-fault state, which may also be referred to as ramping back.

(64) It is therefore preferably proposed, in order to set the power consumption to the level of the pre-fault value after the grid fault has ended, for the power consumption to be set via a predefined change curve, in particular via a temporal ramp function with which the power consumption is changed linearly up to the level of the pre-fault value.