DE102021123422A1 - ACTIVE FEED-IN CONVERTER - Google Patents

Abstract

The application relates to an active feed converter (10) with an AC output (24), a DC output (26) for supplying a connectable DC bus (14) with DC loads (42, 44). The active feed-in converter (10) includes:
- an inverter (16) whose inverter bridge (20) is connected to the DC output (26) via an intermediate circuit (18),
- a first control unit (30) for providing power at the DC output (26) in such a way that the voltage (UDC) present at the DC output (26) remains within a permissible voltage range (ZB),
- a second control unit (32) for providing a power component at the AC output (24) for the benefit of the grid as a function of at least one electrical parameter, determined at the AC output (24), of an AC grid (12) connected to the AC output (24) , wherein a range is specified for the at least one parameter, within which the grid-friendly provision of the power component takes place, wherein the second control unit (32) is set up to vary the range limits of the range depending on a central controlled variable (ZRG), the central The controlled variable (ZRG) is the voltage present at the DC output (26) or the power provided at the DC output (26).
The application also relates to a method for providing power at a DC output (26) of an active feed converter (10).

Description

The application relates to an active feed-in converter for supplying a DC bus and connected DC loads as well as a method for providing power and for providing grid services at the same time. DC refers to direct current or direct voltage.

Active feed-in converters, also known as active frontends (AFE) or active feed-in converters (AFC), are required to convert larger DC loads such as electrolysers or industrial robots, which are connected to the active feed-in converter via a DC bus, from an AC to supply electrical power to the grid. Here, the active feed-in converter fulfills the task of converting as much power between the DC grid and the AC grid that the voltage of the DC grid remains within a permissible range. The active feed-in converter usually regulates the voltage to a nominal voltage of the DC grid.

An AC network or an AC voltage network is referred to as an AC network. The operators of the AC grid, for example public energy suppliers, may be interested in the active feed-in converter also providing grid services at the same time, i.e. working towards the parameters of the AC grid remaining within a permissible range. Such parameters can be, for example, the frequency or the voltage amplitude of the AC network, but also, for example, the voltage amplitude of a harmonic of the network frequency. In this way, additional, previously known network components that are provided for providing the network service can be saved.

The problem here is that the provision of a grid-serviceable power component, which has to be converted by the active feed-in converter in addition to that for supplying the DC bus with power, can under certain circumstances reach or even exceed the performance of the feed-in converter.

The task is therefore to show an active feed-in converter that can take over the function of the additional grid service components and thereby replace them without overloading the feed-in converter.

The object is achieved by an active feed converter with the features of independent patent claim 1 . The object is also achieved by a method having the features of independent claim 8. Advantageous embodiments of the injection converter and the method are specified in the dependent claims.

An active feed-in converter has a DC output for supplying a connectable DC bus with DC loads and an AC output for connection to an AC grid. The active feed-in converter is set up to provide grid services via the AC output. The active feed-in converter also includes an inverter whose inverter bridge is connected to the DC output via an intermediate circuit, and a first control unit for providing power at the DC output in such a way that the voltage present at the DC output remains within a permissible voltage range. The inverter can have a single-stage design, which simplifies the regulation of the inverter, but there can also be a DC converter connected upstream of the inverter. The active feed-in converter also has a second control unit for providing a power component at the AC output for the grid, depending on at least one electrical parameter, determined at the AC output, of an AC grid connected to the AC output. A range is specified for the at least one parameter, within which the power component is made available for the grid. The second control unit is set up to vary the range limits of the range as a function of a central controlled variable, the central controlled variable being the voltage present at the DC output or the power provided at the DC output.

The range for the at least one parameter can also include, for example, two sub-ranges that are separated, for example, by a dead band in which no grid-friendly provision of a power component takes place.

The active feed-in converter is therefore set up to provide network services in the form of network-related measures at the same time as supplying the DC bus via the DC output with electrical power via the AC output. The grid services have a power component at the AC output. Grid-friendly measures are activated within the limits of "normal operation" of an active feed-in converter. "Normal operation" occurs, for example, when the voltage present at the DC output is within the permissible voltage range and there is still sufficient power reserve to provide the grid-related measures. This can be the case, for example, if the power of the feed-in converter is within a corresponding power band, such as - P _AC -nom * 0.9 < P _AC < P _AC -nom * 0.9. Except As a result, no network services are provided during this "normal operation".

Furthermore, a normal range can be defined around the nominal DC voltage, in which the respective network-related measures work to their full extent. This corresponds to the provision of grid-related measures in a corresponding power range of the active feed-in converter, since the DC voltage is regulated via the AC active power or the AC active current. A nominal DC voltage can be U _N =650V, for example. The active range of the grid-supportive measure can be, for example, U _N +/-10%.

Outside the normal range of the voltage present at the DC output, the grid-related function should not be switched off hard, for example, but run linearly until it becomes inactive, depending on the distance from the normal range of the DC voltage. This ensures that the active feed-in converter can meet its primary control goal of DC voltage stability with its full rated power.

In one embodiment of the active feed converter, the second control unit is set up to leave the range limits of the at least one electrical parameter constant within a predetermined normal range of the central controlled variable. Within the range of the at least one electrical parameter, the power component useful for the grid is provided as a function of the at least one electrical parameter. The range for the at least one parameter can also include, for example, two sub-ranges, which are, for example, below a first range limit and above a second range limit, with a dead band extending between the first and second range limits, in which no grid-serviceable power component is provided .

In one embodiment of the active feed-in converter, the second control unit is set up to provide the power component outside the range of the at least one electrical parameter independently of the at least one electrical parameter. In this way, an overload of the feed converter can be avoided.

In one embodiment, the at least one parameter is a voltage amplitude of the connected AC grid, with the provision of the power component serving the purpose of the grid comprising a provision of reactive power as a function of the voltage amplitude. This can correspond to a grid-friendly measure in the form of a Q(U) control, cos(phi) control or a control with a fixed Q specification. For example, provision can be made for the Q(U) control, the cos(phi) control or the control with a fixed Q specification to act within the range for the at least one parameter. In this embodiment in particular, it can be provided that the area in which the power component is provided as a function of the at least one electrical parameter has two (partial) areas. This means that, in particular, the reactive power is provided as a function of the voltage amplitude below the lower range limit of the voltage amplitude and above the upper range limit of the voltage amplitude. For example, a voltage-stabilizing provision of reactive power can be achieved through a Q(U) characteristic outside of the specified AC voltage limits of the AC grid, such as U _AC < U _AC -nom *0.9 and U _AC > U _AC -nom * 1.1 take place. The range for the at least one parameter, in this example U _AC , has two sub-ranges for this example, one below the first range limit, here U _AC -nom *0.9, and a second one above the second range limit, here U _AC nominal *1.1. In between, no reactive power is provided.

In one embodiment, the central controlled variable is the power provided at the DC output, with the range limits of the voltage amplitude being restricted in such a way that a maximum apparent power of the active feed converter is not reached or exceeded.

In one embodiment, the at least one parameter is a frequency, with the grid-friendly provision of the power component comprising a provision of active power as a function of the frequency, with the range limits of the frequency being selected in such a way that a maximum active power of the active feed-in converter is not reached or exceeded. This corresponds to a grid-friendly measure in the form of a frequency-supporting P(f) regulation.

In a further embodiment, the at least one parameter is an amplitude of an AC voltage with a multiple of the frequency of the connected AC network, a so-called harmonic. In this case, the grid-friendly provision of a power component includes generation of an alternating current component in phase opposition to the voltage with the same multiple of the grid frequency with the aim of compensating for or at least reducing the amplitude of the harmonics. In this case, a limitation of the parameter range is required to ensure that a current value provided by the active feed-in converter does not exceed a permissible maximum current. It is conceivable that the active feed-in converter implements several or all of the above-mentioned embodiments for the grid-friendly provision of a power component at the same time and for this purpose several or all of the parameters mentioned are recorded and used to determine the required power components.

In a method for providing power at a DC output of an active feed-in converter with an AC output and an inverter bridge, the DC output for supplying a connectable DC bus with DC loads is connected to the inverter bridge via an intermediate circuit the power at the DC output is provided in such a way that the voltage present at the DC output remains within a permissible voltage range.

At the same time, a power component is provided at the AC output for the benefit of the grid depending on at least one electrical parameter determined at the AC output of an AC network connected to the AC output, with a range being specified for the at least one parameter within which the provision of the The power component takes place, with the range limits being varied as a function of a central controlled variable, the central controlled variable being the voltage present at the DC output or the power provided at the DC output. The range for the at least one parameter can also include, for example, two partial ranges separated by a dead band.

In one embodiment of the method, the range limits are left constant within a specified normal range of the central controlled variable.

In one embodiment of the method, the power component is provided outside of the range independently of the at least one electrical parameter.

• 1 eine Ausführungsform eines aktiven Einspeisewandlers;
• 2 schematisch die DC-Spannung und das Leistungsband des aktiven Einspeisewandlers;
• 3 Arbeitspunkte des aktiven Einspeisewandlers;
• 4 eine erste Kennlinie einer Q(U)-Regelung;
• 5 eine zweite Kennlinie einer Q(U)-Regelung mit Totband und
• 6 schematisch ein Blockschaltbild mit erster und zweiter Regeleinheit zeigen.

In the following, the subject of the application is illustrated using figures, of which

• 1 an embodiment of an active injection converter;
• 2 schematic of the DC voltage and the power band of the active feed-in converter;
• 3 Operating points of the active feed-in converter;
• 4 a first characteristic curve of a Q(U) regulation;
• 5 a second characteristic curve of a Q(U) control with dead band and
• 6 schematically show a block diagram with the first and second control unit.

In 1 1 is a schematic representation of an embodiment of an active feed converter 10 having an AC output 24 and a DC output 26 . A three-phase AC supply network 12 grounded at ground potential PE in the exemplary embodiment shown is connected to the AC output 24 . A connection of the AC output 24 to an ungrounded network is also conceivable. A DC bus 14 is connected to the DC output 26 . The DC bus 14 may include DC loads 42,44. The DC load 42 , for example a battery, can be connected to the DC bus 14 via DC switches 46 . The DC load 44 can be connected to the DC grid 14 via DC switches 48 . The DC load 44 can in particular include one or more consumers, such as a machine, an industrial plant, or an electrolyzer. The DC loads can act as generators or consumers of power in the DC grid, also in a time-varying manner.

The active feed converter 10 has a single-stage inverter with a bridge circuit 20, a control unit 22 and an intermediate circuit 18. The bridge circuit 20 is designed to convert alternating current or alternating voltage into direct current or direct voltage. The bridge circuit 20 is also designed to convert direct current or direct voltage into alternating current or alternating voltage. In the exemplary embodiment shown, the conversion takes place in that a control unit 22 suitably controls semiconductor switches of the bridge circuit 20 . On the DC side, the bridge circuit 20 is connected to the DC output 26 via the intermediate circuit 18 . The DC bus 14 can be supplied with electrical power from the AC grid 12 via the active feed-in converter 10 .

The active feed converter also has a first control unit 30 . The first control unit is set up to provide electrical power at the DC output 26 in such a way that the voltage U _DC present at the DC output 26 remains within a permissible voltage range ZB (see FIG 2 ). In this way, a reliable supply of electrical power to the DC bus 14 can be ensured.

The active feed converter also has a second control unit 32 . The second control unit 32 is set up to provide a power component at the AC output 24 to serve the grid. The power component useful for the grid depends on at least one electrical parameter, determined at the AC output 24 , of the AC grid 12 connected to the AC output 24 . It a range is specified for the at least one parameter within which the network-friendly provision takes place. The second control unit 32 is set up to vary the range limits of the range as a function of a central controlled variable ZRG, the central controlled variable ZRG being the voltage U DC present at the DC output 26 or the voltage U _DC determined by the first control unit 30 for the operation of the DC -Network 14 to be provided power P is.

The first and the second control unit 30, 32 can optionally be designed as a control unit that performs both control tasks at the same time. Optionally, the control unit 22 can also be implemented in the same unit with the first and second control unit 30, 32.

In 2 is an example of a relationship between DC voltage U _DC , plotted on the x-axis, and at the DC output 26 determined by the first control unit 30 of the active feed converter 10 power P to be provided, plotted on the y-axis, which is represented by the positive nominal power P _N on the one hand and negative nominal power - P _N on the other hand is limited. A positive power P corresponds to the feeding of electrical power into the DC network 14. A negative power P corresponds to the removal of electrical power from the DC network 14. A nominal voltage U _N for the DC voltage U _DC is on Normal range NB of the operation of the feed converter 10 is defined. A nominal voltage U _N for the DC bus 14 is. for example at 650V. The permissible voltage range ZB for the DC voltage U _DC is limited by the minimum DC voltage U _DCmin on the one hand and the maximum DC voltage U _DCmax on the other. At the minimum DC voltage U _DCmin, the first control unit 30 determines the negative nominal power -P _N and at the maximum DC voltage U _DCmax the positive nominal power P _N as the power P to be provided. Both the determined power P to be provided and that at the DC -Output 26 applied voltage U _DC can serve as the central controlled variable ZRG.

In 3 a connection between the normal range NB and the permissible range ZB of the central controlled variable ZRG on the one hand, plotted on the x-axis, and the size of the parameter range Δp, plotted on the y-axis, is shown by way of example. The size of the parameter range Δp, within which the grid-friendly provision of a power component at the AC output takes place, is - as shown - dependent on the central controlled variable ZRG. In the 3 a first operating point AP1 is shown, in which the central controlled variable ZRG is in the normal range NB. The size of the parameter range Δp is largest here. The second operating point AP2 is in a transitional area in which the size of the parameter range Δp becomes smaller toward the edge of the permissible range ZB. At the edge of the permissible range ZB of the central controlled variable ZRG there are optional dead ranges Δ in which the power component at the AC output is no longer available to the grid because the associated parameter range is zero there. As a result, the active feed-in converter can more robustly ensure compliance with the permissible voltage range ZB on the DC bus.

In 4 an exemplary first characteristic curve 28 of a Q(U) control is shown. Here, the voltage U _AC at the AC output, plotted on the x-axis, is the parameter on the basis of which the power component - here the reactive power Q, plotted on the y-axis - is made available at the AC output. The size of the parameter range Δp _AP1 at the first working point AP1 is greater than the size of the parameter range Δp _AP2 at the second working point AP2. For example, the working points AP1 and AP2 correspond to those shown in 3 are shown.

For the operating point AP1, the central controlled variable is ZRG 3 in their normal range. If the voltage U _AC is in the parameter range Δp _AP1 , the reactive power Q is provided as a function of the voltage U _AC . If the voltage U _AC is outside the parameter range Ap _AP1 , a constant reactive power Q is provided (the characteristic curve 28 runs parallel to the U _AC axis).

For the operating point AP2, the central controlled variable is ZRG 3 in the transition area. If the voltage U _AC is in the parameter range Δp _AP2 (which is smaller than Δp _AP1 ), the reactive power Q is provided as a function of the voltage U _AC . If the voltage U _AC is outside the parameter range Ap _AP2 , then a constant reactive power Q is provided (the characteristic curve 28 runs parallel to the U _AC axis).

In 5 a second exemplary characteristic curve 28 of a Q(U) control is shown, which differs from the characteristic curve of 4 differs in that the second characteristic has a dead band TB lying within the parameter ranges, in which no reactive power Q is provided. Of course, the central controlled variable ZRG can be controlled via different characteristic curves as shown in 3 define multiple parameter ranges related to different parameters of the connected AC grid, so that different types of grid services can be provided by the active feed-in converter at the same time. The width of the normal range NB and the width of the dead zones D can be chosen to be the same or different for the various parameters.

In 6 the control with the first and second control unit 30, 32 of the active feed converter 10 is shown schematically. The central controlled variable ZRG is present at the input of the first control unit 30 . The first control unit 30 suitably controls the active feed-in converter 10 in order to make a DC power P ₁ available at the DC output 26, as a result of which a corresponding first active power component P ₁ is taken from the AC grid 12 at the AC output 24 (without taking the converter losses into account). At the same time, the size of the parameter range Δp, which influences the characteristic curve 28 of the second control unit 32, is set by the first control unit 30 via the central control variable ZRG.

The second control unit 32 provides a power component for the AC network 12 using the electrical parameters of the AC network 12 connected to the AC output 24 and the characteristic curve 28 determined at the AC output 24 . The power component can, for example, have a second active power component P ₂ or a reactive power component Q or another grid-related power component X, for example an alternating current with a harmonic frequency of the grid frequency of the connected AC grid, or also several or all of the components mentioned. The power component of the second control unit is added to the first active power component P ₁ of the first control unit via an adder and is made available to the AC grid 12 via the AC output 24 by suitably controlling the active feed-in converter.

It can thus be ensured that the active feed-in converter can reliably make DC power available to the DC bus 14 via its DC output 26 . At the same time, functions useful for the grid can be made available via the AC output 24, which may be required or rewarded by the AC grid operator.

Reference List

10

active feed converter

12

AC grid

14

DC bus

16

single stage inverter

18

intermediate circuit

20

inverter bridge

22

control unit

24

AC output

26

DC output

28

curve

30

first control unit

32

second control unit

42

DC load

44

DC load

46

DC switch

48

DC switch

PE

potential earth

ZRG

central control variable

NB

normal range

Eg

permissible voltage range

AP1, AP2

working points

Δp

Size of the parameter area

Q

reactive power

P

active power

U.D.C

DC voltage

Claims (10)

Active feed-in converter (10) with an AC output (24), a DC output (26) for supplying a connectable DC bus (14) with DC loads (42,44), comprising: - an inverter (16), whose inverter bridge (20) is connected to the DC output (26) via an intermediate circuit (18), - a first control unit (30) for providing power at the DC output (26) in such a way that the output at the DC output (26 ) applied voltage (U _DC ) remains within a permissible voltage range (ZB), - a second control unit (32) for providing a power component at the AC output (24) for the grid, depending on at least one electrical component determined at the AC output (24). Parameters of an AC network (12) connected to the AC output (24), a range being specified for the at least one parameter within which the power component is made available to the grid, the second control unit (32) being set up to define the range limits of the rich to vary depending on a central controlled variable (ZRG), the central controlled variable (ZRG) at the DC output (26) applied voltage or at the DC output (26) is provided power. Active feed-in converter claim 1 , wherein the second control unit (32) is set up to within a predetermined normal range (NB) of the central controlled variable (ZRG) to leave the range limits constant. Active feed-in converter claim 1 or 2 , wherein the second control unit (32) is set up to provide the power component outside of the range independently of the at least one electrical parameter. Active feed-in converter according to one of the preceding claims, wherein the at least one parameter is a voltage amplitude, and wherein the grid-friendly provision of the power component comprises a provision of reactive power as a function of the voltage amplitude. Active feed-in converter claim 4 , wherein the central controlled variable (ZRG) is the power provided at the DC output (26), and the range of the voltage amplitude is restricted in such a way that a maximum apparent power of the active feed converter (10) is not exceeded. Active feed-in converter according to one of the preceding claims, wherein the at least one parameter is a frequency, the grid-friendly provision of the power component comprising a provision of active power as a function of the frequency, the range of the frequency being selected in such a way that a maximum active power of the active feed-in converter ( 10) is not exceeded. Active feed-in converter according to one of the preceding claims, in which the inverter has a single-stage design. Method for providing power at a DC output (26) of an active feed-in converter (10) with an AC output (24) and an inverter bridge, the DC output (26) for supplying a connectable DC bus (14). DC loads (42, 44) are connected to the inverter bridge (20) via an intermediate circuit (18), wherein the power at the DC output (26) is provided in such a way that the voltage present at the DC output (26) remains within a permissible voltage range (ZB), and wherein at the AC output (24) a power component is provided as a function of at least one electrical parameter determined at the AC output (24) of an AC network (12) connected to the AC output (24), with a range for the at least one parameter is specified within which the grid-friendly provision of the power component takes place, the range limits being varied as a function of a central controlled variable (ZRG), the central controlled variable (ZRG) being the voltage present at the DC output (26) or the power provided at the DC output (26). procedure after claim 8 , whereby the range limits remain constant within a specified normal range of the central controlled variable (ZRG). procedure after claim 8 or 9 , wherein outside of the range, the power component is provided independently of the at least one electrical parameter.

Images