EP1941335A1

EP1941335A1 - Active network filter

Info

Publication number: EP1941335A1
Application number: EP06791724A
Authority: EP
Inventors: Alfred Punzet; Viet Luu Hong
Original assignee: Bosch Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 2005-09-03
Filing date: 2006-08-30
Publication date: 2008-07-09
Also published as: DE102005041927A1; WO2007025726A1; JP2009507457A; US20080239770A1; DE102005041927B4

Abstract

The invention relates to a supply device (13) which feeds a consumer (7) with power by means of a supply network (12). Said supply device (13) fulfils both the function of a power supply and the function of a network filter, an optimum working point to be adjustable in terms of the operating modes as supplier/active filter, according to the required energy reserves. This is achieved by means of an active phase effect filter, a harmonic wave detection means (3) determining a compensating power dependent on the network harmonic wave power, and a control device component (5) whose action is adapted to the compensating power requirement being provided for the determination of an amplification factor (6). The compensating power is supplied to the current inverter according to the utilisation of the current inverter (1) and the amplification factor (6).

Description

Active line filter

The invention relates to a supply device according to the independent claims, wherein by means of a supply network consumers are supplied with power and the influences of non-linear loads are compensated for the supply network. In the prior art arrangements with inverters are known which as

Supply device for providing electrical power for a

DC link can work. Furthermore, inverter arrangements are known which are able to compensate harmonic currents on the network. The

Invention describes in detail the parallel supply and compensation by a

Arrangement, which can act as a supply device and active filter.

An active line filter basically consists of an inverter or PWM converter in, for example, 3-phase design with IGBT bridge, which is capable of delivering electrical power into a DC voltage intermediate circuit, or - picking up power. The resulting currents can have active and reactive components. The inverter is usually by means of a mains choke comprehensive

Network interface connected to the actual supply network and thus switched between load and network.

In addition, non-linear loads can be connected to the supply network. A simple diode rectifier bridge may already represent such a non-linear load. But even a more complex structure, such as a drive system with electrical loads, causes nonlinear distortions. The non-linear load leads to a network load with harmonic-rich currents. These currents disturb the network balance and create currents in the center conductor. This can lead to problems with parallel connected devices. Depending on the location of the action, these problems are manifested differently by line overloads, voltage drops at the center conductor, component overload due to the harmonics (transformers, capacitors), malfunctions due to the non-sinusoidal network.

In the prior art devices are known which restore such missing network balances. Such devices are known as "Active Line Filters". For example, JP 9258839 shows a relevant active filter which makes it possible to adjust the degree of compensation of the non-linear components by means of an adjustable K-factor. To determine the compensation current, individual harmonics are filtered out via an FFT (Fast Fourier Transformation). The K-factor is used for energy-saving adjustment of the filter and has no other function.

It is the object of the invention to improve an input mentioned supply device such that, depending on the required energy reserves with respect to the network balance optimal operating point with respect to the operating modes as a provider and filter is adjustable.

The invention solves the problem by an active system interference filter with an inverter, a control device and a harmonic detection means, the harmonic detection means determines a dependent on the harmonic power compensation power (pc, qc) and a respect of the compensation power demand adaptive acting control device component for determining a gain factor is included the compensation power is supplied to the inverter in accordance with the load of the inverter and / or the gain factor.

The above-mentioned and inventively modified active filter is preferably connected to a 3-phase network by means of a network filter. The line filter effects a supply-side filtering to reduce the switching frequency generated by the PWM stage of the inverter and superimposed on the line frequency.

The power unit of the inverter includes a PWM IGBT power amplifier with DC intermediate circuit including DC link capacitor. As a rule, a DC load is connected on the DC link side. The inverter represents the utility for this load.

In general, it should be noted that the supply network can also have more or less than 3 phases. The invention is thus by no means limited to use on a 3-phase supply network. A control device is understood to be a unit which comprises components for operating the inverter, in particular components for controlling, controlling and regulating the power output. In turn, all performance characteristics of the inverter can be stored in the control device. These may include, but are not limited to, permissible maximum current Imax, allowable maximum voltage Umax, inverter thermal characteristic, degree of instantaneous load / load, maximum power output, etc. The controller may also include the harmonic detection means and the adaptive controller component.

A harmonic detection means is understood to mean a device which is capable of mathematically detecting the proportion of non-linear distortions in the current and / or voltage profile of a supply network and thus also the active power component or the reactive power component in the supply network.

An adaptively acting control device component is understood to mean a device which determines a compensation factor by means of which the quality of the active filtering can be set as a function of the required and the available energy (current performance of the inverter and / or state of the DC intermediate circuit). As a result of this measure, a lower filter quality can be set in favor of an increased power requirement of a DC load connected to the inverter. Between the two operating modes "supply" and "filter" can thus produce a virtually continuous transition.

The term "in accordance with the capacity utilization of the inverter" is to be understood as a regulation of the compensation power dependent on the instantaneous degree of utilization / degree of load of the inverter as a supplier.

The active filter according to the invention therefore has two possible modes of operation. A first mode as a line filter to compensate for nonlinear distortions and a second

Operating mode as utility ^' for a load connected on the DC link side.

Both modes may be active in parallel or alternatively at different intensities.

Due to the fact that the required compensation performance in accordance with the

Utilization of the inverter and the adaptively determined gain factor is transformed into a compensation current setpoint, the degree of compensation is adjustable and individually adjustable. Thus, at the same time, the operating mode of the mains feedback filter is possible as a voltage supply device (supplier) or filter depending on the harmonics generated by a non-linear load. Thus, both the function of a power supply and the function of a network filter is met, wherein depending on the required energy reserves, an optimal operating point with respect to the modes of supply / filter is adjustable.

Particularly preferably, the compensating power and possibly additionally the power requirement Pdc of a DC load connected to the inverter is taken into account at the input of a current transformer and transformed by means of the current transformer into compensation current nominal values (1 ^* q, 1 ^* d). The transformation of the powers into currents taking place in this processing stage has the advantage that the magnitudes on which the amplification factor acts and also the output of the voltage regulator are independent of the mains voltage level. It can be counted up to this point at the performance level.

The DC voltage U _D c is a DC link voltage generated by the inverter to which a load to be fed with DC voltage is usually connected. By thus taking into account the connectable load, it is possible to prioritize one of the operating modes of the inverter (supplier and / or filter), so that a load-dependent mode selection results from it. If, for example, large non-linearities are to be compensated, the filter mode should be given priority, provided that there is still enough power available to supply additional loads.

Very particular preference is the current feedback filter according to the invention comprises a current control, in particular a Pl-current control with dead-beat behavior. The advantage of using the dead-beat behavior over the pure Pl behavior is the faster setting of the currents and thus a more accurate adjustment of the compensated current waveform.

Advantageously, an active network feedback filter according to the invention comprises a

Voltage regulator, whose input-side control difference from an am

DC voltage output of the inverter applied DC voltage and a DC voltage reference is formed and wherein the output of the voltage regulator corresponds to an active power setpoint. The regulator may be a PI voltage regulator. Thus, it is easy to determine a DC-side power setpoint from the DC link voltage.

Preferably, the harmonic detection means comprises a mains AC voltage and mains AC currents and transforms them by means of the Clarke transformation in accordance with the active power / reactive power theory (PQ theory) in compensating power setpoint values pc, qc that can be represented in the dq coordinate system. The input value of the harmonic detection means may be a 3-phase supply network current or a 3-phase supply voltage of the supply network to which a non-linear load is connected and whose harmonic components are to be compensated. The calculated correction results in sum with the harmonic mains power supply at the grid feed point a sinusoidal active power. It is thus created a way to capture the power to be compensated mathematically efficient and reproducible.

Particularly preferably, the adaptively acting control device component comprises a control circuit for calculating the amplification factor, wherein the amplification factor acts as a control member and controls the proportion of the compensation power. The quality with which a compensation is carried out depends, among other things, on the performance of the control loop.

Most preferably, the compensation in its intensity between a state without compensation (device in the supplier operation) and a state of maximum possible compensation (supply in the filter mode) or a lying within the aforementioned state range sub-range virtually infinitely regulate. The network reaction filter according to the invention can thus be infinitely regulated between the two operating modes filter and supply depending on load conditions.

Advantageously, the amplification factor is determined in dependence on the square of the inverter maximum current and the square of the Kpmpensationsstromsollwerte based on the following decision ^{ε =} y _m ^~ ^ d ⁺ * ^q))> 0 - Due to the vectorial calculation and considering the total vector lengths by the elevation of the currents in the second power is avoided exceeding the inverter maximum current. For further optimization purposes of the behavior of the arrangement in real operation, additional influencing factors, in particular the thermal behavior of the inverter, are taken into account in the calculation of the amplification factor and advantageously the amplification factor is determined as a function of a load which can be connected to the inverter, so that during the filter operation a base load compensation and / or or a peak load compensation for this load is feasible.

In accordance with the size of the nonlinear network load is thus definable whether and / or with what intensity a power of the harmonics power compensation occurs. Depending on the type of network, the specifications of the energy supplier or the guidelines of the connected consumers can be reacted flexibly.

A further possibility to solve the problem is that an input mentioned active network feedback filter, in particular with the properties described above, as a slave to a master in the form of a central control device (9) can be assigned and a

Input and / or output is connected to the connection with the master, said means of the

Input a compensation power setpoint is receivable. The active one

Network feedback filter would thus operate autonomously or centrally controlled in a network of active network feedback filters.

The output is used to transmit static and / or dynamic device data of the inverter to the central control device, there to calculate the appropriate for the inverter and individual compensation power components. By means of the output, inverter-specific data, in particular data relating to the performance and / or utilization / load of the inverter and the DC voltage intermediate power Pdc, to the. Master transferable.

Furthermore, the invention comprises a central control device, which can be assigned as master to a slave in the form of an active network retroactive filter according to the invention and an input and / or output for connection to a slave is included, wherein by means of the output compensation power setpoints are transferable. A control device can thus control several active line filters. Advantageously, inverter-specific data, in particular data relating to the performance and / or utilization / loading of the inverter, can be received by the slave by means of the input. There are then performance-dependent individual calculations possible, which can be repeated cyclically.

The central control device particularly preferably comprises a harmonic detection means, which determines a compensation power dependent on the harmonic power and comprises an adaptive control device component for determining an amplification factor, the compensation power serving as the compensation power setpoint in accordance with the load / load of the inverter and the amplification factor , The advantages arise from the versions of the active mains feedback filter with integrated control device.

A supply network according to the invention comprises at least one active network feedback filter according to the invention and / or a central control unit. Reference is made here to the advantages already mentioned.

The non-linear load is preferably a drive system, in particular a drive system with further electrical components. Especially in these systems, due to the use of nonlinear components, nonlinear distortions occur.

LIST OF REFERENCE NUMBERS

inverter

control device

Harmonic detection means a current regulator b current transformer

Adaptive controller

gain

DC load

PI controller

Master controller 0 Non-linear load 1 Network interface 2 Power supply 3 Active mains feedback filter 4 Connection

The invention is explained in more detail below with reference to the examples shown in Figures 1 to 3. Show it:

Figure 1 is a control scheme for an active network feedback filter with peripherals; Figure 2 is a schematic block diagram of a supply network with central control device and a plurality of inventive devices; 3 shows a flowchart for determining the amplification factor.

FIG. 1 shows an inverter 1 with a DC load 7 and a control device 2. The control device 2 comprises in particular a current regulator 4a, a voltage transformer 4b, a harmonic detection means 3, an adaptive controller 5, a PI controller 8 and a gain factor Kc 6. The control device 2 is the measured inverter grid current l _s after passage of the network interface 11, the supply network current I _{L of} the non-linear load and the supply voltage U _N supplied. On the supply network 12, a non-linear load 10 is also connected. I _L represents the distorted current of the nonlinear load 10, and Is represents the inverter output current. I ₈ includes the current difference necessary to form a sinusoidal current I _N TO from the distorted current I _L.

If one controls the inverter 1 in a suitable form by using the current consumption I _{L of} the non-linear load 10 as the measured variable, then one is able to influence the supply network side current at any time so that a more or less sinusoidal mains current I _N occurs , Due to the expansion of the inverter 1 to such a current measurement and the corresponding control algorithms can speak of an active line filter 13. Active also because the filtering is based not only on classic low-pass filters with inductances (L) and capacitances (C).

The active mains feedback filter 13 comprises inter alia a fully functional inverter 1, so that it is possible to switch between the ^' operating modes' filter mode ^' and 'supplier mode ^' by suitable, running in the control device 2 control algorithms or to activate them simultaneously or separately. Basically, the control algorithm calculates the current setpoints for active power and reactive power. These are needed to fully compensate for the effects of a nonlinear load. This compensation capacity is limited by the current limit or the performance of the active filter. The harmonic detection means 3 determines a compensation power dependent on the supply network side harmonic power with the effective component pc and the reactive component qc. The compensating power pc, qc is calculated according to the capacity and / or the load / load of the inverter 1 by means of the gain factor 6 in the form of the adaptive compensation power values p ^* c and q ^* c forwarded, which are transformed by the current transformer 4b taking into account the active power setpoint Pdc in the compensation current setpoints l ^* q, l * d and fed to the adaptive controller 5. A control difference is formed from these compensating current setpoint values l ^* q, l * d and the detected inverter network current I ₃ (taking account of active and reactive components according to Clark-dq transformation) and the corresponding voltage setpoint values Uq and Ud for compensating purposes by means of current regulation 4a to inverter 1 fed. In order to take account of the power requirement of the DC load 7 during filter operation, the compensation current setpoint values l * q, l * d are supplied as a function of the load on the DC supply voltage U _D c, which is applied to the DC voltage output of the inverter 1. In order to include U _D c, a voltage regulator 8 is included whose input-side control difference is formed from one of the DC voltage U _D c and a DC voltage setpoint U ^* _D c and whose output corresponds to the active power setpoint Pdc. To the compensation power setpoint p ^* c, the formed active power setpoint is practically added to Pdc.

The supply system shown in FIG. 2 comprises a supply network 12 and a plurality of active network feedback filters 13 according to the invention with peripherals 10, 11. As is already known from the previous explanations, the active network feedback filter 13 comprises an inverter 1 and a control device 2. The illustrated interruption of the supply network 12 should indicate that a plurality of further active network feedback filters 13 could be connected to the supply network 12. For example, the term "peripheral" includes the network interface 11. A non-linear load 10 and a central control unit (master controller) 9 are also shown. Between the control devices 2 of the active network feedback filter 13 and the master controller 9 bidirectional and / or unidirectional connections 14 are arranged. Thus, the master controller 9 can communicate with the slave controllers 2. By means of this connection 14, it is possible, for example, to transfer compensating power setpoint values p * c, q ^* c from the master controller 9 to the control devices 2. This is then transformed into compensating current setpoints l ^* q, l ^* d by means of a decentralized current transformer 4b comprised by the active mains feedback filter 13. A current regulator 4a uses these compensation current setpoint values Tq ₁ l * d for generating the voltage setpoint values Uq, Ud, which are supplied to the inverter 1 for compensation purposes. Preferably, this current transformation and current regulation takes place in the control device 2 (see FIG. 1).

The master controller 9 in turn can receive and utilize inverter-specific data, in particular data relating to the performance and / or the load / load of the inverter 1, by means of the connection 14. The central control device 9 or the master controller 9 comprises a harmonic detection means 3. This determines the dependent of the harmonic power compensation power pc qc as already described above, wherein in a relative to the compensation power demand adaptively acting control device component 5 determines a gain factor 6 (K _c ) is determined, which determines the required compensation power for the inverter according to the individual capacity or utilization on the basis of the data received by the connection 14 of the inverter.

The non-linear load 10 could be, for example, a drive system, in particular a drive system with further electrical components. It is by no means deducible from FIG. 2 that only a single nonlinear load 10 can be supplied by the supply network. Rather, the non-linear load 10 is representative of parallel and / or series-connected possibly further non-linear loads. The combination of the non-linear loads 10 produces a harmonic pattern specific to this arrangement. This harmonic image is detected by the master controller 9 to affect it specifically.

In summary, using a central control device 9 is a complete or partial and dynamically adjusted compensation of the harmonics of Supply network 12 by means of several inverters 1 possible, the power reserves / utilization / load of the available inverter 1 is taken into account. An application example of this would be, for example, a production island within a production line with multiple drive sets consisting of active mains feedback filters 13, which can operate as a regenerative utility because of the inverter 1, which may be the DC loads to axis inverter and motors. The non-linear loads 10 in this example could consist of supply devices in feed-in technology (rectifier bridges) and connected Achsinrichtern, and other unspecified consumers. Depending on the requirements, the system is therefore equipped in part with supply units in feed-in technology (non-linear load due to rectifier bridge) and in regenerative technology (inverter and thus capable of functioning as a utility or active filter).

The adaptively acting control device component 5 from FIG. 1 (in FIG. 2 from the master controller block 9) comprises a control circuit for calculating the

Amplification factor 6, wherein the gain factor 6 as shown in Figure 1 by means of

Arrow indicated acts as a control member and controls the formation of the control difference at the input of the current transformer 4b required proportion of the compensation powers pc and qc. After multiplication by the amplification factor, the adapted compensation powers p ^* c, q ^* c are available. The compensation current I ^* q, I ^* d can thereby be regulated indirectly by means of the amplification factor 6 in its intensity.

The gain factor 6 is determined as a function of the square of the maximum permissible inverter current (Imax) and the square of the compensation current command values l ^* d, l ^* q based on the following decision ^{ε =} \ ⁱ ^ ^~ i ⁱ d ^{+ i} _q ))> 0 Determination of the amplification factor 6 is shown in FIG. 3.

FIG. 3 shows a flowchart / flowchart for calculating the amplification factor 6 (Kc). This diagram is characterized in that formulaically defined decisions are represented by diamond-shaped symbols and instructions by means of rectangular symbols. The terms "true" and "false" indicate whether an underlying decision (diamond) is satisfied or not. Depending on the result of the comparison, a branch takes place. The term "end" means that the algorithm is left until the next calculation interval. First, however, the variables or terms used in figure are briefly defined.

The adaptive gain K ₀ controls the proportion of calculated compensation power values pc, qc that are used for active network filtering. A factor K ₀ of 0 in this example does not mean active network filtering, a factor of 1 means complete network filtering in this example. Consequently, the gain factor 6 (K ₀ ) should lie in the following range: 0 <K _c ≤ 1. The adaptive

Amplification factor 6 (K ₀ ) is always recalculated depending on the cycle in accordance with the flowchart by means of the control device 5.

K _{c (k)} denotes the current value and Kc _(k -i ₎ the value of the previous calculation.

I ⁴ _C l ₁ l ^* q represent the compensation current desired values calculated taking into account the supply network phase angle φ in the current transformer 4b, which can be represented in an orthogonal dq coordinate system. The input variables of the current transformer p ^* c and q ^* c are already present in the dq system. The consideration of the mains voltage U _N takes place by means of a transformed into an αß system (transformation of a three-phase system with the phases a, b, c in a two-phase system with the phases α, ß) mains voltage U _N. Ua, b, c stands correspondingly for the three phases of the mains voltage U _N. The conversion is carried out by means of the following calculation. For further details on the αβ transformation, reference is made to the relevant specialist literature.

with p = (p ^* c + Pdc) and q = q * c (see the control difference supplied to the current transformer 4b of Figure 1) follows:

Where l ^* d and l ^* q are finally calculated to:

l ^* d = iα ^* cos φ + iβ * sin φ l ^* q = -iα ^* sin φ + iβ ^* cos φ

The currently possible maximum current l _{max of} the inverter applies to the vectorial sum of the currents in the dq direction. By definition, the d component corresponds to the active component. The currently possible maximum current of the converter | 2 _max (vectorial addition) is provided by an external source and in the simplest case can be a fixed value. Another possibility would be the provision of a thermal model of the PWM power amplifier.

By comparing | 2 _max with the compensation current setpoints I ^* ^ l ^* q, it is determined how much the inverter is operating at full capacity. By using the current utilization, a strategy can be derived as to how the inverter should behave for the next time intervals.

The current reserve ε for active filtering is calculated from the geometric subtraction of the currents l _max and 1 ^* ^ l ^* q -

In the currently described embodiment, the gain factor (6) K _{0 is} calculated by means of a discrete proportional controller. The proportional gain λ serves to adjust the loop gain.

In the event that the current power reserve ε> 0, ie it can be provided power for the operating mode "Active network filtering", the controller is turned on and the adaptive gain K _{c is} increased. When the limit of K _c = 1 is reached, it is limited to this value.

In the event that the current reserve ε <0, ie it can not provide power for the operating mode "Active network filtering", the controller is deactivated and the adaptive gain factor (6) reduces K ₀ . When the lower limit of K ₀ = 0 is reached, it is limited to this value.

In the limiting case K ₀ = 0, the compensation current setpoints are set to zero. The current share from the voltage regulation for Upjc ^is not affected by this. Only at K ₀ = 0 an additional calculation is therefore provided, in which the current setpoint values l ^* d, l * q are proportionately limited from the normal supply control. Since the individual vector lengths are determinative, this limitation must be carried out vectorially.

Since the proportion of intermediate circuit power P _{dc is} not multiplied by the gain factor K ₀ , the provision of active power and thus the operating mode of the entire device as a supplier always takes precedence over the operating mode as an active supply network filter.

This creates the problem that even with no active power requirement through active filtering, the PWM output stage can already be thermally utilized. The currently possible maximum current of the converter l ² _max would be due to the thermal load, and thus the filter capacity. At a beginning now

Active power request, the compensation current setpoints would have to be lowered. The current released for the required active power would then possibly no longer be sufficient due to the thermally induced reduction of l ² _max. To cover this case as well, the currently possible maximum current of the converter l ² _{max can} be reduced by the current l ² _{dcma vorher} to be defined previously become. The height of l ² _dC ma _x can be pre-determined for the respective application, depending on the expected load or capacity of the inverter. Thus, an active power reserve can always be occupied in advance, which can not be undershot by the thermal load in the filter mode.

By appropriate conversion of the limiting algorithm (FIG. 3) and arrangement of the factor K ₀ in the region of P _dc , the operating principle can be reversed. Thus, it would be possible to prioritize operation as an active filter, of course at the expense of providing energy as a utility. It is also possible in the calculation of the gain factor 6 (K _c ) additional influencing factors, in particular to take into account the already mentioned thermal behavior. Basically, these factors attack the default value l ² _max .

It would also be possible to design the control device component 5 such that it is always optimally filtered up to a freely definable nonlinear load variable 10. This would mean that the inverter 1 always works with a basic load due to the compensation of non-linear distortions in the supply network 12 as a filter and supply unit on the supply network 12. Rarer peak loads would then be partially compensated. On the other hand, one can imagine that especially at low non-linear loads on the supply network 12, the compensation is completely omitted in order to compensate only at high, non-linear peak loads. Such an arrangement could be realized by a specially designed control characteristic. Depending on the curve shape of the control curve s, p ^* c, q ^* c results from s (pc, qc) x pc.qc. In the picture, pc '= pc ^* and qc' = qc ^* .

The control characteristic may be inserted after the harmonic detection means 3 and acts as an additional non-linear gain factor.

Claims

claims:

1. Active network feedback filter with an inverter (1), a control device (2) and a harmonic detection means (3), characterized in that the harmonic detection means (3) determines a power of the harmonic power compensation (pc, qc) and adaptive with respect to the compensation power requirement acting control component (5) for determining a gain factor (6) is included, wherein the compensation power (pc, qc) according to the load of the inverter (1) and / or the gain factor (6) is supplied to the inverter (1).

2. Active mains feedback filter according to claim 1, wherein the compensation power (pc, qc) by means of * a current transformer (4b) is transformed into a compensation current setpoint (l ^* q, l ^* d).

3. Active mains feedback filter according to claim 2, wherein the load of a DC voltage output of the inverter (i) measurable DC voltage (U _D c) by means of an active power setpoint (P _dc ) in the current transformation (4b) is taken into account.

4. Active mains feedback filter according to one of the preceding claims, wherein a current control (4a) is included, preferably a current control (4a) with PI and dead-beat behavior.

5. Active mains feedback filter according to one of the preceding claims, wherein a voltage regulator (8) is included, wherein its input-side control difference from a DC output (U _D c) of the inverter (1) applied DC voltage (U _D c) and a DC voltage setpoint (U ^* _D c) is formed and wherein the output of the voltage regulator (8) corresponds to an active power setpoint (Pdc).

6. Active network feedback filter according to one of the preceding claims, wherein the harmonic detection means (3) detects at least one AC line voltage (U _N ) and / or a load alternating current (I _L ) and transformed by means of the Clarke transformation and in accordance with the active power / reactive power theory (PQ- Theory) determines the compensation power nominal values (pc, qc) that can be represented in the dq coordinate system.

An active network feedback filter as claimed in any one of the preceding claims, wherein the adaptive controller component (5) comprises a loop for calculating the gain (6).

8. Active network feedback filter according to one of the preceding claims, wherein the compensation power (pc, qc) is adjustable in intensity.

The active mains feedback filter of any one of the preceding claims, wherein the gain factor (6) is based on the square of the inverter maximum current (Imax = imax) and the square of the compensation current command values (l ^* d = i ^* d, l ^* q = i ^* q) is determined on the following decision ^{ε =} y _τm ^~ (ßd ^{+ i} q))> 0.

10. Active mains feedback filter according to one of the preceding claims, wherein in the calculation of the gain factor (6) additional influencing factors, in particular the thermal behavior of the inverter (1), are taken into account.

11. Active mains feedback filter according to one of the preceding claims, wherein the amplification factor (6) depending on a load (7) connectable to the inverter (1) is determined, so that during the filter operation simultaneously a base load compensation and / or peak load compensation for the supply network (12 ) is feasible.

12. Active network feedback filter according to one of the preceding claims, wherein according to the size of a network (12) connected to the non-linear network load (10) can be defined, with which intensity compensates.

13. Active network feedback filter, in particular according to one of claims 1 to 12, characterized in that this as a slave master in the form of a central control device (9) can be assigned and an input and / or output to the connection (14) with the master (9 ), wherein by means of the input a compensation power setpoint (p ^* c, q ^* c) can be received.

14. Active network feedback filter according to claim 13, wherein by means of the output inverter-specific data, in particular data relating to the performance and / or utilization / load of the inverter, to the master (9) are transferable.

15. Central control device, characterized in that this as a master (9) a slave in the form of an active network feedback filter (13) according to claim 13 or 14 can be assigned and an input and / or output to the connection (14) with the slave (13) is included, wherein by means of the output a compensation power setpoint (p * c, q ^* c) is transferable.

16. Central control device according to claim 15, wherein by means of the input inverter-specific data, in particular data relating to the performance and / or utilization / load of the inverter, from the slave (13) are receivable.

17. Central control device according to claim 15, wherein the latter comprises a harmonic detection means (3), which determines a compensation power (pc, qc) dependent on the harmonic power of the harmonic generator and an adaptive control device component (5) for determining an amplification factor (6) ), wherein the compensation power in accordance with the load / load of the inverter (1) and the gain factor (6) as a compensation power setpoint (p ^* c, q ^* c) is used.

18 supply network, characterized in that this comprises an active line filter (13) according to ^' one of the preceding claims 1 to 14 and / or a central control device (9) according to one of claims 15 to 17.

19. Supply network according to claim 18, wherein a non-linear load (10) is a drive system, in particular a drive system with further electrical components.