WO2016124681A1 - Control method and device for the active compensation of power supply- or load dependent fluctuations of the power flow of a power electronic converter system - Google Patents

Abstract

The invention relates to a control method for the active compensation of fluctuations of a power flow of a power electronic converter system, wherein the converter system has a main converter (2) for the transfer of power between a DC port and an output port, as well as a buffer capacity C connected in parallel to the DC port and with a buffer capacity voltage uC, wherein a compensator (4) is connected in parallel to the buffer capacity C, which has a coupling converter (41) and an energy storage means (42), wherein the coupling converter (41) is designed to supply energy to the energy storage means (42) or to remove same. The method involves the following steps: determining an output pout,AC delivered by the main converter at the output port; determining, based on the output pout,AC* delivered by the main converter at the output port, a desired value of an output pK,out* to be discharged or received by the compensator (4) and/or a desired value for an energy storage means current iE* of the compensator (4); actuating the coupling converter (41) such that the output discharged or received by the compensator and/or the energy storage means current follows the corresponding desired value.

Description

 Control method and apparatus for active compensation of mains or load-related fluctuations in the power flow of a power electronic converter system

The invention relates to the field of power electronic converter or converter.

Below are briefly described in sections 1) to 4) examples of power electronic converter (AC / DC, DC / AC, AC / AC and DC / DC converter) with two-port structure, the power flow at a first port of the converter next to a constant proportion of a low-frequency, eg two-fold power frequency alternating component shows. These

Power fluctuation is generally passively filtered by a storage capacitor integrated in the converter structure or a low-pass filter, so that a largely constant power flow occurs at the second port of the converter, or, e.g. one

DC voltage consumers can be supplied with a largely constant voltage. Alternatively, the filtering can also be carried out actively by means of a power electronic unit to be designated generally as a compensator (see Section 5)), in which case the filter characteristic can be predetermined by regulation such that ideally only the constant power flow remains at the second end of the converter. the power fluctuation is completely eliminated by the compensator. The invention is directed to methods and controllers according to the preamble of the corresponding independent claims for controlling such a compensator.

1) AC / DC conversion

 To convert a single-phase AC voltage into a DC voltage today power electronic converters are used, which on the input side (on the input side gate) a sinusoidal current consumption and the output side (on the output side gate) ensure a constant (DC) voltage. Due to the one-phase networks

Sinusstromausnahme characteristic temporal fluctuation of the power output with twice the mains frequency (corresponding to zero crossings of current and / or voltage, switching frequency fluctuations neglected) have this, generally referred to as single-phase pulse rectifier or Power Factor Corrected- (PFC) rectifiers systems on the DC side compelling an energy storage which covers the difference between the constant power delivered by the grid and that consumed by a DC load at a constant voltage. In general, this memory realized by electrolytic capacitors, which, however, have a relatively high volume and a limited life. The large size is mainly due to the fact that the capacitor must be dimensioned so that despite the pulsating power consumption and - the fluctuation of the DC voltage remains limited to a small value, typically a few percent compared to the nominal value. The im

 Capacitor stored in total and the volume directly directing energy is therefore used only to a very small extent for the buffering of the input power fluctuation.

 A situation similar to single-phase pulse rectifier systems exists in three-phase pulse rectifier systems and unbalance of the feeding network. By appropriate control of the input current could be a time constant here

DC side power flow can be achieved, but then occur

low-frequency distortions of the mains current. If sinusoidal mains currents are set, the output power again exhibits a fluctuation at twice the mains frequency. In many cases, the possibility of continued operation of the systems in case of failure of a phase of the network is further required, which is the same conditions as in single-phase pulse rectifier systems in terms of the required size of the DC side energy storage. It should be noted that instead of an electrolytic capacitor, one on the double

Mains frequency tuned LC absorption circuit for buffering the power fluctuation

can be used. Such an arrangement is e.g. used in locomotives in rail technology. However, the function of this system is tied to a fixed network frequency; Furthermore, relatively high voltages occur across the resonant elements. In addition, an inductance is required for the realization of the absorption circuit, which has relatively high losses compared to capacitive elements.

2) DC / AC conversion

If power from the DC voltage side (input-side gate) with sinusoidal current is fed into a single-phase network (output-side gate) or unbalanced three-phase network, ie an inverter function is realized, the same situation applies to the low-frequency difference between input and output power as for a or three-phase pulse rectifier systems given. The case of such a DC / AC conversion is, for example, when connecting a photovoltaic (PV) system to a single-phase network. DC voltage side is here a constant

To ensure power consumption to the PV system in the point of maximum power output (Maximum Power Point, MPP) to keep, on the other hand, however, the network side to generate a doubly power frequency pulsating power or feed by means of a sinusoidal current in the network. The compensation of the input and output side power difference takes place in the simplest case again by a DC voltage side capacitor

Voltage fluctuation by selecting a correspondingly high capacitance value or

Construction volume must be limited to small values to the deviation of the

To limit the operating point of the PV system from the MPP. If the AC side is e.g. To generate reactive power for regulating the mains voltage, the amplitude of the

Power fluctuation and thus the capacitor volume increased again.

 For uninterruptible power supplies (UPS systems), a coupling of a DC voltage source with an AC voltage network is to be made. When

Energy source in this case typically acts as an electrochemical storage, which is to be operated advantageously with a constant current as possible. As a result, on the one hand increases the life and on the other hand higher losses are avoided on longer supply lines between the memory and converter or the supply line can be dimensioned only after the average power consumption. It should be noted that also UPS systems with three-phase output in the supply of asymmetrical load on the DC side power fluctuation with twice the output frequency and thus have a corresponding energy storage requirements.

3) AC / AC conversion

The systems described above for AC / DC or DC / AC conversion can also be combined to form a DC / DC converter system, in which case in addition to the conversion between single-phase AC voltages or three-phase AC voltages, mixed forms, i.e., DC, DC are also used. the coupling of a feeding single-phase network (or

unbalanced three-phase network) with a three-phase load or a three-phase feeding network with a single-phase (or single-ended three-phase) load. It is then to provide a storage capacitor of appropriate capacity in the DC link to the low-frequency component of the difference of on and output torque to compensate for a largely constant DC link voltage.

4) DC / DC conversion

Apart from the above-described power conversion between an AC system and a DC system or between AC voltage systems, a low-frequency difference of input and output power can also occur in DC / DC converter circuits, which may need to be compensated by a storage capacitor. Examples are the feeding of a load with pulsed power peaks from a battery, or the e.g. temporally pulsed fluctuating power generation of an energy harvester which should feed DC loads that tolerate only a small supply voltage fluctuation. It should be noted that the term DC / DC conversion is to be understood very generally here, and also the simplest variant of a DC / DC converter, i. a direct link between positive input and output

Output terminal and the negative input and output terminal includes (input voltage identical to the output voltage).

5) Active power fluctuation filtering by compensator

 As previously described, a storage capacitor can be used to cover a low-frequency component of the difference between input and output power, although the mentioned disadvantage is that a large part of the stored energy is not used to buffer the power fluctuation.

 Advantageously, therefore, the voltage of the storage capacitor is decoupled from the DC voltage to be supported via a DC / DC converter (for example buck or boost converter circuit or a low + boost converter or else a DC / DC converter with potential isolation). It is then permissible for the storage capacitor voltage to fluctuate greatly, because an adaptation to the (constant) DC voltage can always take place via a corresponding duty ratio of the DC / DC converter. Accordingly, the energy content of the storage capacitor can now to a much higher degree for the compensation of low-frequency

Power fluctuation are used; e.g. remain at a discharge of the

Storage capacitor at 50% of the rated voltage only 25% of the original stored

Energy, i. 75% of the nominal energy content is used for power equalization. This allows, instead of electrolytic capacitors foil or ceramic capacitors

to use, which have a significantly higher life. The lower one Capacitance density (capacitance / volume) of these capacitor technologies can be compensated by a correspondingly high fluctuation of the storage capacitor voltage due to the quadratic dependence of the stored energy on the voltage, as opposed to the linear dependence on the capacitance DC voltage despite the additional required Tief- or boost converter a size advantage results.

For further description, the coupled via a DC / DC converter

Storage capacitor generally be referred to as energy storage. When

Embodiment variants of a corresponding DC / DC coupling converter, for simplicity, only a DC / DC buck converter (the current in the buck converter inductance defines directly the current removed from the energy storage) and a DC / DC boost converter (the current in the boost converter inductance directly defines the for the power compensation in the DC voltage supplied current) are considered. These basic variants are also characteristic of more complex converter circuits (for example, with electrical isolation), or the description can be analogously easily transferred to more complex circuits. Overall, a combination of the buck or boost converter and the energy storage can be seen as an active compensator or active filter for a low-frequency component of the difference between the input and output power of the main converter. In addition to the compensator i.a. also a directly on the DC voltage to be supported backup capacitor - im

Further referred to as buffer capacity - to provide, which receives switching-frequency current components and absorbs the remaining due to the real always limited control dynamics of the active compensator remaining power fluctuations.

Concerning. It is important to note that, for DC / DC converters (ie, systems without an AC connection), the compensator should be located favorably at the port where the power fluctuation occurs so that the actual DC / DC conversion is limited to the constant power flow For three-phase AC / AC converters, in addition to coupling the energy store to the DC link, it is also possible to connect to one of the AC ports, in which case an AC / DC coupling converter is to be provided and the power to be supplied by the compensator is fed via appropriate AC currents. In the literature, the structure and basic function of such compensators is generally described, but lacks details to setpoint and control of current drain from the energy storage or power supply to the energy storage and to ensure a mean energy storage voltage, ie a scheme that a steady slow discharge or charge the buffer capacity prevented. Furthermore, the regulation of the actual DC voltage, ie the voltage of the buffer capacity is not treated in conjunction with the compensation of the compensator and it is only a complete and not even partial elimination of the low-frequency power fluctuation considered, which may be pulsating input and output power or may be advantageous or necessary in case of overload or generally minimizing the Kompensatoraufwandes.

The term "low frequency" here denotes frequencies in the range of an AC line voltage or a fundamental frequency of an AC voltage at a port of the converter system. "Low frequency" may thus include frequencies of up to two, five or ten times such a network or fundamental frequency. These are different from "high frequency" frequency ranges, which are in the range of switching frequencies of

electronic switches of the converter system lie.

A possible object of the invention is therefore to provide a method for controlling an active compensator for eliminating low-frequency differences in the input and output power of a converter system, which reduces the capacity of a

Buffer memory of the converter system allowed.

One possible object is to provide a method and a corresponding device which incorporate a regulation of a DC voltage of a converter gate and / or allow specification of a profile of the power to be compensated or the power profile remaining after compensation.

One possible object is to provide a method and a corresponding device which are suitable for use with an AC / DC, DC / AC, AC / AC or DC / DC converter system. At least one of these objects solve a control method and a control device according to the claims.

The control method is used to actively compensate for fluctuations in a power flow of a power electronic converter system,

wherein the converter system comprises a main converter for power transmission between a DC port and an output port, also called an AC port, and a buffer capacitor C connected in parallel with the DC port and having a buffer capacity voltage μC;

wherein parallel to the buffer capacitor C, a compensator is connected, which has a

Coupling converter and having an energy storage device, wherein the coupling converter is adapted to feed energy into the energy storage respectively to remove this. In the procedure, the following steps are performed:

 Determining a power pout, AC supplied by the main converter at the output port;

Determine, based on the power supplied by the main converter at the output port pout, AC *, a setpoint value of a compensator to be delivered by the compensator or

 power to be absorbed pK, out * and / or a setpoint for a

 Energy storage current iE * of the compensator;

 • Activation of the coupling converter so that the power delivered by the compensator and / or the energy storage current follows the corresponding setpoint.

Here, and also in the subsequent variants and exemplary embodiments, the output port is considered as an AC voltage connection by way of example and is also called an AC port. In this case, a voltage at the output port or AC port can in principle have any, that is to say also fluctuating and / or, in the limit, the value zero. Thus, the method is also suitable for use with DC / DC converters.

Output filters on the output port can be designed according to an operating frequency or the operating mode (AC or DC) of the output port.

The determination of the power pout, AC delivered by the main converter at the output port can be done by measurements of quantities such as voltages and currents at the converter and / or by reference values for such quantities. According to one embodiment, to suppress an AC component of the buffer capacitance voltage uC, the following steps are performed:

 Highpass filtering the buffer capacitance voltage uC to determine a variation of the buffer capacitance voltage uC, AC;

 · Processing the variation of the buffer capacity voltage uC, AC in a first

Control element and determining a correction value of the compensator power pK, C * based on an output of this control element;

 • adding this correction value of the compensator power pK, C * to the nominal value of the power pK, out * to be output or absorbed by the compensator before it is further processed.

 This embodiment can be realized in combination with the previously described steps or independently.

According to one embodiment, to control a mean voltage of

Energy Storage performs the following steps:

 Low-pass filtering the energy storage voltage uE to determine an average uEquer of the energy storage voltage uE;

 • forming a difference Du Equer of the mean u Equer of the energy storage voltage uE from a corresponding setpoint uEquer *;

 Processing this difference DuEquer in a second control element and determining a supplementary low-frequency compensator power component pK, Equer * based on an output variable of this control element;

 • Add this compensator power component pK, Equer * to the setpoint of the

 Compensator to be delivered or absorbed power pK, out * before its further processing.

According to one embodiment, the following steps are carried out to regulate the voltage uC at the DC port or the current consumption iinquer from a DC voltage source:

• Specifying a setpoint iinquer * for the DC voltage source

 absorbed current iinquer, or determining this setpoint iinquer * based on a total power requirement of a main converter power component poutquer and a Kompensatorleistungsanteil pK, Equer * and optionally also the

Buffer capacity voltage μC; • Determine, by means of an input current controller, a setpoint for a

 Buffer capacitance voltage average value uCquer *, which corresponds to that from the DC

 Voltage source iinquer leads to its setpoint iinquer *; optionally with a pilot control according to the internal voltage ui of the DC voltage source;

 Determining, by means of a buffer capacitance voltage regulator, a setpoint value for a capacitor current iC * into the buffer capacitance C, which leads the buffer capacitance voltage uC to its desired value uCquer *

 Determining a correction value of the compensator power pK, C * corresponding to this setpoint value for the capacitor current iC *

 • adding this correction value of the compensator power pK, C * to the nominal value of the power pK, out * to be output or absorbed by the compensator before it is further processed. The method according to the invention will be discussed below using the example of a single-phase DC / AC converter (inverter) for power transfer from the DC to the output side or AC side. Furthermore, in the sense of simplicity, only the ratios for as little fluctuation as possible DC voltage, or a time constant

Power flow at the DC port (full coverage of the AC side power swing through the compensator).

Note: By appropriate change of the sign of the currents and

Power flows are the inventive methods simply also on rectifier operation, i. to transmit an inverse power flow direction.

The port of the DC / AC converter (general main converter) to which the compensator is connected is referred to below as the compensator port (interface for the

Compensator connection). For the compensator is a version with

Step-down converter (step-down compensator) and a version with boost converter

(Boost converter compensator) considered.

The DC / AC converter is connected to the DC port through a DC voltage source

Internal resistance is fed and through two bridge branches, whose input voltage through a buffer capacity is formed formed. At the outputs of the bridge branches, a low-pass filter LC is placed against the negative voltage coupons, which the

smoothes discontinuous bridge branch output voltages. The outputs of the two filters directly form the AC output terminals (AC port) to which the AC load is connected. For the further description, both filter stages together are referred to briefly as the output filter.

 For the buck-boost compensator, the coupling converter is formed by a buck converter bridge branch arranged directly on the compensator port or generally one

Kompensatorschaltstufe formed whose output is connected via a buck converter inductance with the energy storage of the compensator. The current taken from the energy store or flowing into the energy store (energy storage current) is thus converted via the switching stage into the current finally delivered or received at the compensator port (see FIG. 1); On the other hand, the switching stage is used to adjust the voltage of the

Energy storage and the compensator port voltage. The Kompensatorausgangsstrom thus shows discontinuous course, which can be smoothed through a filter circuit, which is not discussed here in detail, since the control and regulation of the

Compensator, but not its detailed design of the power unit is the subject of the invention. For the sake of completeness, it should be mentioned that, instead of a bridge branch, it would also be possible to use a full bridge or generally a bidirectional, electrically isolated DC / DC converter with a switching stage located at the compensator port.

 For the boost converter compensator, a boost converter inductor typically branches from the positive terminal of the compensator port and is connected at the other end to a boost converter shift stage, which further connects to the negative terminal of the

Compensator ports is connected. The energy storage is at the output of

Step-up converter switching stage arranged (see Figure 2). Again, this only represents the

Basic arrangement; As described above for the buck converter compensator, further embodiments of higher complexity are also possible here. An important feature of all variants is that the current fed into the compensator port or obtained from the compensator port can be converted via the switching stage into a current drawn from the energy store or flowing into the energy store. If necessary, this discontinuous current can be smoothed by a filter arranged between the switching stage and the energy store. On the other hand, the switching stage is used to adjust the voltage of the energy store and the Kompensatorportspannung. Instead of the bridge branch can without again fundamental influence on the inventive method generally a bidirectional switching stage of higher complexity and possibly be used with integrated potential separation.

Subfunctions of the scheme:

1. Determination of a desired value of the compensator to be delivered or

 power to be absorbed (compensator sport performance) or the

 Energy storage current (see Fig. 3) as a function of the power supplied by the main converter on the AC port and optionally also, defined mainly by the capacitors of the output filter of the main converter capacitive reactive power which represents a fluctuating with two output frequency and thus compensated by compensator power component. This method can be used in conjunction with one of the extensions described below or independently.

2. Control for suppressing an AC component of the voltage of the buffer capacity or the DC port (see Figure 4). This arrangement can be used in addition to subfunction 1) or without subfunction 1) and is based on the basic idea that a smooth voltage at the buffer capacity shows that the temporal fluctuation of the power of the AC port is covered directly by the compensator, whereby the Buffer capacity no further power must be removed or the voltage above the buffer capacity shows a constant value. Via the DC port, i. from the DC voltage source, a constant power is then obtained.

3. Control of the average voltage of the compensation capacitor (see Fig.5). Since only alternating power components are naturally defined on the basis of partial function 1 or 2, an explicit control circuit must be provided for ensuring a corresponding quiescent value of the voltage of the energy store (energy storage quiescent voltage). This Energiespeicherruhespannung is placed in the middle of the energy and not in the middle of the voltage defined by a minimum allowable and a maximum allowable voltage working voltage band of the energy storage, so that the energy storage, starting from the rest voltage until reaching the Maximum voltage can absorb the same amount of energy as he at

 Voltage reduction starting from the rest voltage to deliver the minimum voltage is capable of. This ensures a symmetrical working range for compensating the power swing of the AC port. Note: For a buck-boost compensator of the simplest type, the maximum allowable voltage is given by the buffer capacity voltage and the minimum allowable voltage is zero. Advantageously, however, a safety distance is maintained by both voltage limits. For a boost converter compensator of the simplest type, the minimum allowable voltage is equal to the buffer capacitance voltage, the maximum allowable voltage can be calculated considering the

 Reverse voltage strength of the power semiconductors and the maximum

 Voltage load capacity of the energy storage are set relatively freely.

4. Regulation of the DC (mean) value of the voltage at the DC port or the current consumption from the supplying DC voltage source (which is typically to show a time-constant value). This regulation is necessary since the regulation of the energy storage quiescent voltage according to partial function 3, in particular after load jumps on the AC port, causes a corresponding power output or power consumption of the energy accumulator or compensator, which causes a change in the energy storage

 Buffer capacity voltage results (the buffer capacity is due to the

Arrangement of a compensator typ. Chosen relatively small, which also smaller transient power fluctuations already result in a relatively large variation of the buffer capacity voltage). The regulation according to subfunction 2 now attempts to compensate for this voltage change, for which, however, a power transfer to the energy store would be required. Both regulations therefore counteract each other and a coordination of both control tasks is required. The solution lies in regulating the current consumption from the DC voltage source or not just the AC component of the buffer capacitance voltage (see subfunction 2) but also the DC value, ie the total buffer capacitance voltage.

In the following, the subject invention will be explained in more detail with reference to preferred embodiments, which are illustrated in the accompanying drawings. In the form of circuit diagrams respectively block diagrams they show: 1 shows a converter circuit with an active compensator with a buck converter for active compensation of the voltage of an energy storage of a main converter; FIG. 2 shows a converter circuit with a step-up converter for the same purpose;

3 shows a controller for determining a desired value for an energy storage current of

 compensator;

 4 shows a regulator for suppressing an AC component of a

 Buffering capacity voltage;

FIG. 5 shows a regulator of an average voltage of the energy store of the compensator;

FIG. 6 shows a regulator of an input voltage at a DC port; and

 FIG. 7 shows a controller combining functions of FIGS. 3, 5 and 6.

The methods / functions outlined above are described below

Control technology block diagrams described. As with the conception of the scheme, negligible losses of the converter stages are assumed.

Fig. 1 shows a DC / AC main converter 2 for power transmission between a DC port and an AC port. At the DC port, a voltage supply 1 with an ideal voltage source with voltage uin and an internal resistance is connected by way of example. One

Input current at the DC port is denoted by iin. A load 3 is connected by way of example at the AC port. An output current at the AC port is indicated by iout, an output voltage by uout. The DC / AC main converter 2 has an energy store or buffer capacitor C, connected in parallel with the DC port, with voltage uC, a main converter switching stage 21 and a main converter output filter 22, the outputs of which form the AC port.

Parallel to the buffer capacitor C, an active compensator 4 is connected via a compensator port. This has a coupling converter 41 in order to feed energy in a compensation capacitor or energy storage 42 with voltage uE respectively refer. The coupling converter 41 has a Kompensatorschaltstufe 411 and a coupling inductance 412. In Fig. 1, the coupling converter 41 is designed as a buck converter.

Fig. 2 shows the same elements as Fig. 1, with the difference that the coupling converter 41 is designed as a boost converter. Ad 1. - Determination of a setpoint for energy storage capacity resp. Energy storage power

FIG. 3: The task of the DC / AC main converter 2 is to set an AC voltage according to a setpoint value uout * based on the voltage uC at the DC port on the AC port. For this purpose, μC is converted by means of the main converter switching stage 21 into a pulse-width-modulated voltage and this is smoothed by a single-stage or multistage main converter (LC) output filter 22 (see FIG. 1). The power pout delivered at the AC port is calculated as the product of the measured values uout and iout; As an alternative to uout, the desired value of the output voltage uout * could also be used, since by means of a not described here in more detail

Output voltage control by setting the above mentioned

 Pulse width modulation uout according to the setpoint default uout * can be performed. In order to determine a pendulum power component pout, AC of pout, which has stationary twice the output frequency, a moving average low-pass filter (buckling frequency selected sufficiently far below twice the output frequency) is used for the time being, e.g. determined on a network half-period average poutquer and this then subtracted from pout. To pout, AC * is the, e.g. by temporal differentiation of the one

Output voltage instantaneous value uout (or uout *) associated with stored energy, determined instantaneous power demand of the filter capacitors of the output filter, pout, Q *, added (Note: d / dt (i * C * uout ^A 2) = C * uout * duout / dt)

 The setpoint value of the power supply on the part of the compensator, pK, out * = pout, AC * + pout, Q *, thus formed, is then converted into a desired value of the current iE * to be taken from the energy store 42 for a step-down compensator by division by the voltage of the energy store uE. or the current in the coupling inductance 412 respectively Tiefsetzstellerinduktivität iL, T * converted, which is set by a corresponding control circuit, which influences the timing of Kompensatorschaltstufe 411.

 It should be emphasized that in this case also a limitation (not shown in FIG. 3) of the energy storage current iE * can take place in order to avoid overloading the energy store 42 or the coupling converter 41.

 For a coupling converter 41 as a boost converter (boost converter compensator), pK, out * must be divided by the buffer capacitance voltage uC by the reference value of the

Energy storage current or the setpoint value of the current in the boost converter inductance iL, H * to obtain, which can be adjusted by a current control loop again. It should be noted that the instantaneous blind power requirement of the filter capacitors pout, Q *, eg at low output frequencies or small values of the filter capacitance also

can be disregarded.

 Furthermore, it should be pointed out that the efficiency of the main converter and the coupling converter and of the energy store can be taken into account when determining the desired power values by starting from a loss model of the converter, the setpoint pK, out * by the losses of the respective current flow or power transfer Main converter, coupling converter and energy storage is increased.

 In addition, it should be noted that the determination of pKout * described above on the basis of a block diagram is only intended to represent the fundamental idea of the compensation of both the oscillation component of the output power and the filter capacitor reactive power. The time lapses of the quantities pout, AC * and pout, Q * could alternatively also be derived directly from uout * via frequency doubling and corresponding time shift a and the amplitudes in connection with iout (for pout, AC) based on general

Power flow calculations are determined in single-phase AC systems.

 Finally, the possibility should also be mentioned that pout, AC * only comprises components within an upwardly limited frequency range and not, as in FIG. 3, the entire AC component of pout. The low-pass filtering of pout is then replaced by a band-stop filter.

Ad 2. - Suppression of an AC component of the voltage of the buffering capacity

FIG. 4: The compensator power precontrol described under 1), which leads to pK, out *, can be supplemented by a control loop, which regulates a time fluctuation of the voltage of the buffer capacitor to zero. The buffer capacity is hereby seen as a detector for incomplete compensation of the power pulsation at the inverter input due to the reactive power of the output filter and the fluctuation of the double-frequency power supplied to the load by the compensator, e.g. due to measurement inaccuracies or tolerances of components (capacitors of the output filter) may occur. The remaining after the compensation

Alternating power leads to a fluctuation of the buffer capacitance voltage uC, AC which is detected by high-pass filtering of uC with sufficiently low below twice the mains frequency knee frequency and a target-actual comparison of a Buffer capacity voltage fluctuation control is performed with setpoint zero; the control error is then turned into a by a controller (buffer capacity voltage fluctuation controller)

Correction value of the compensator power pK, C * converted, which is added to the calculated according to the function part 1 setpoint pK, out *, whereby a total setpoint pK, ges * results. Note: pK, C * can be formed directly by the buffer capacitance voltage fluctuation controller or the controller outputs a recharge current setpoint iC, AC * of the buffer capacitance, which is then multiplied by the current buffer capacitance voltage uC to calculate pK, C *, thus achieving the same control target. however, another dynamic behavior of the control results; Furthermore, alternatively, a multiplication of the

Recharging current setpoint iC, AC * with the rated capacity of the buffer capacity voltage available for the respective operating point).

 It should also be noted that the formation of pK, out * according to subfunction 1 can also be omitted altogether, with which pK, C * is identical to the total nominal value pK. The regulation is done so only by means of the sub-function. 2

 As an alternative to determining the temporal fluctuation of the buffer capacitance voltage, the (measured or determined by time derivation of μC) can also be used.

Buffer capacitive current iC are controlled to zero, which would be suppressed by a low-pass filter resulting from the switching mode of operation of the inverter and possibly the compensator switching frequency components. In the block diagram described above, uC would then be to replace AC with iC and omit high pass filtering from uC.

Ad 3. - Regulation of the medium voltage of the energy storage

Fig.5: To control the average voltage of the energy storage, too

Called energy storage quiescent voltage, can mean a value uEquer the

 Energy storage voltage uE be determined by means of a low-pass filter with sufficiently far below the two-fold output frequency kink frequency and can subsequently by means of a target-actual comparison whose deviation DuEquer of a corresponding setpoint uEquer *, for example, defined by the energy center of the allowable fluctuation band of the voltage uE be calculated. DuEquer becomes one

Regulator (energy storage restraint voltage regulator) is supplied, which outputs a Nachladestroms setpoint iEquer *, multiplied by u Equer a supplementary low-frequency

Compensator component pK, Equer * returns uEquer to uEquer *. Note: Instead of multiplication with u Equer, a multiplication with u Equer * can also occur, or the controller can output pKquer * directly.

 It would be obvious to simply add this power component to the total setpoint pK, tot * after subfunction 2. and thus form a total compensator power setpoint. However, this is not possible because e.g. after a load jump on the AC port, a tradable power component pK, Equer * occurs. (A load step also means a momentarily higher power which is correspondingly covered by the partial energy function 1.a us the energy storage and thus leads to a transient change of the energy storage voltage, which also results in a transient output of the energy storage restraint control). The setting of pKEquer * would lead to a transient lowering of the

Buffer capacity voltage lead, which over the

 Buffer capacity voltage fluctuation controller in the request one from which

Energy storage to be covered recharge performance pK, C * would result, which would counteract pK, Equer *. Both controllers would therefore counteract each other, which would potentially give the risk of instability Insta. The

 Energiespeicherruhespannungsregelung is therefore not com bination with the method according to subfunction 2. (Figure 4) but only together with the

 Compensator power precontrol according to subfunction 1. (which defines pK, out *, FIG. 3), resulting in a total compensator power setpoint pK * = pK, out * + pK, Equer * (see FIG. 5). For a simultaneous regulation of

 Buffer capacity voltage fluctuation and energy storage quiescent voltage is one

Modification according to subfunction 4) required.

It should be noted that instead of the linear regulation of the energy storage quiescent voltage u Equer, a non-linear control, e.g. a two-point control of the within the tolerance band defined by the maximum value and minimum value of the energy storage voltage could take place. When exceeding the maximum value or falling below the

In the minimum value, such an energy storage tolerance band voltage controller would then generate a corresponding correction value iEquer * which returns the operationally fluctuating voltage of the energy store to the tolerance band. The width of the

Tolerance band would be advantageous a bhängig of Kompensatorsereinistung pK, out *, ie for smaller power values to choose narrower and the band always energetically to the energy center between minimum and maximum value of the energy storage voltage to lay around to ensure the maximum possibility of a transient energy supply from the memory or a transient power consumption by the memory.

Ad 4. - Regulation of the DC (average) value of the voltage at the DC port or the current consumption from the supplying DC voltage source

Fig. 6: Both the mean value of the output power poutquer and the power value pK, Equer for a possible correction of the mean energy storage voltage to the energy storage rest voltage value by the compensator are to be referred to from the input. The sum of these two powers or their setpoints poutquer * and pK, Equer * is considered to be the total power requirement. It can therefore be a regulator for the out of the DC

Voltage source (equal) current to be implemented iinquer whose setpoint based on the total power demand as iinquer * = (poutquer * + pK, Equer *) / uCquer is determined. In this case, uCquer is formed by low-pass filtering of the buffer capacitance voltage uC; The low-pass kink frequency should be chosen sufficiently low below twice the output frequency. This setpoint value linquer * is then compared with the actual value iin of the input current (alternatively with the low-pass filtered current iinquer) and the control error Diin fed to an input current regulator which sets a nominal value of the internal impedance of the supplying voltage source with internal voltage ui

Voltage drop uZiquer * outputs, taking into account uinquer by

Difference formation, a setpoint for the buffer capacity voltage mean value uCquer * can be determined. Alternatively, the feedforward control by subtraction with uin also omitted, the input current controller then has to output directly uCquer *.

 The setpoint value for the buffer capacitance voltage average value uCquer * is then compared with the actual value uC of the buffer capacitance voltage (here, for example, higher-frequency

Components of uC can also be separated by a low-pass filter with a high bending frequency, or a defined frequency range of uC can be masked out by a band-stop filter). The resulting control deviation DuC is fed to a buffer capacity voltage regulator which outputs a setpoint value of the capacitor current iC * required for the correction of uC in the direction uCquer *. This can be converted by multiplication with uCquer into a nominal value for correction of the compensator power pK, C *. In an alternative embodiment, it is also possible to multiply with the actual value μC, in which case a different control-technical behavior results. Analogous to the subfunction 2. pK, C * is then added with pK, out *, thus forming the total setpoint for the total power pK, ges * to be supplied by the compensator. It should be noted that, the precontrol of pK, ges * can also be omitted by pK, out *, in which case pK, C * directly assumes the function of pKges *.

 It is also important to note that the above described

Structure is also implicitly achieved the elimination of an AC component of the buffer capacitance voltage, since the setpoint value of the buffer capacitance voltage average value uCquer * is compared with the unfiltered buffer capacitance voltage and not with a low-pass filtered voltage. In the control error DuC is thus also a possible fluctuation of uC with twice the output frequency or affects the regulation in the direction of a suppression of such a fluctuation.

If the internal impedance of the DC port feeding source is known, and e.g. purely ohmic characteristic (internal resistance), the setpoint value of iin * can also be set by direct specification of uCquer * as an alternative to an input current regulator, where uCquer * is then chosen such that the voltage drop across the internal resistance Ri is directly a current consumption = iin * (uZiquer * = Ri * iinquer * or uCquer * = uin - iin * Ri; uin denotes the internal voltage of the voltage source supplying the DC port).

It should be noted that by expanding the block diagram according to FIG. 6, it is also possible to achieve a defined fluctuation of the power taken from the supplying voltage source. It may be e.g. with the addition of poutquer * and pK, Equer *

Be supplemented or added to the subtraction of iinquer * and iinquer an alternating current component. It should also be pointed out that a defined fluctuation of the voltage uC can be achieved by adding an alternating component to the subtraction of uinquer and uZiquer *. Finally, iC * can also be specified directly, in which case another method must be provided for ensuring a variation of uC around the energy-voltage center uEquer *. The above-described interventions may be e.g. done by higher-level controller.

Fig. 7 shows a possible combination of individual arrangements described above. It is a part of the controller of FIG. 5 according to subfunction 3. for determining pK, Equer * the Controller upstream of Fig. 6. Furthermore, the setpoint value for the compensation of the compensator power pK, C * determined with the controller from FIG. 6 in accordance with the partial function 1 is added to the setpoint value of the power delivery corresponding to the load pK, out * formed as in FIG Total setpoint value for the total power pK, ges * to be delivered by the compensator

In general, the controllers or control elements used are typically PID controllers, which of course also includes pure P, PI, PD controllers, etc. However, they can also have non-linear and / or time-invariant and / or adaptive elements, etc.

Control structures for a compensator with boost converter are formed in an analogous manner. The following principles apply: Naturally, for the step-up converter, the current iK occurring at the compensator port is directly due to the current in the

Boost converter inductance 412. Instead of the necessary for the buck converter compensation of power at the compensator port, which then with the energy storage voltage uE in a the energy storage 42 entnehmendem, or to be adjusted in the buck converter inductance current iE *, is for the

Boost converter a direct consideration of iK or the setpoint iK * possible, so that different multiplications and divisions in the control algorithm can be omitted; in any case, however, iK * must always be calculated by division by uC or uCquer * from pK, ges *.

Claims

claims 1. A control method for the active compensation of fluctuations in a power flow of a power electronic converter system, wherein the converter system comprises a main converter (2) for power transmission between a DC port and an output port, and a buffer capacitor C connected in parallel to the DC port with a buffer capacity voltage μC; wherein parallel to the buffer capacitor C, a compensator (4) is connected, which has a coupling converter (41) and an energy store (42), wherein the coupling converter (41) is adapted to feed energy into the energy store (42) and to remove this ; and wherein in the method the following steps are performed:  • Determine a power supplied by the main converter at the output port  pout, AC *;  Determining, based on the power supplied by the main converter at the output port pout, AC *, a setpoint value to be output from the compensator (4) or  power to be absorbed pK, out * and / or a setpoint for a  Energy storage current iE * of the compensator (4); and  • Driving the coupling converter (41), so that the output from the compensator (4) or recorded power and / or the energy storage current the  corresponding setpoint follows. 2. Control method according to claim 1, wherein for determining the setpoint value to be output by the compensator or to be included power pK, out *,  • this setpoint is calculated as the difference pout, AC * between an instantaneous value and a time average of the power delivered by the main converter at the output port; and  Optionally calculating an instantaneous power requirement pout, Q * of filter capacitors of an output filter (22) of the main converter (2) and adding it to pout, AC *. 3. Control method according to claim 1 or 2, wherein for determining the setpoint value for the energy storage current iE * In the case that the coupling converter (41) is realized as a step-down converter, this setpoint iE * is divided by dividing the setpoint value of the compensator to be delivered or  absorbed power pK, out * is determined by the voltage of the energy storage uE; and  «In the case that the coupling converter (41) is realized as a boost converter, this setpoint iE * by dividing the set value of the compensator to be delivered or  power to be picked up pK, out * is determined by the buffer capacitance voltage uC. 4. A control method according to any one of claims 1 to 3, wherein for suppressing an AC component of the buffer capacitance voltage μC, the following steps are carried out: Highpass filtering the buffer capacitance voltage uC to determine a variation of the buffer capacitance voltage uC, AC;  Processing the fluctuation of the buffer capacity voltage uC, AC in a first control element and determining a correction value of the compensator power pK, C * based on an output variable of this control element;  • adding this correction value of the compensator power pK, C * to the setpoint value of the power pK, out * to be output by the compensator (4) before its further processing. 5. Control method according to claim 4, wherein in determining the correction value of the compensator power pK, C *  The correction value of the compensator power pK, C * is set equal to the output value of the first control element; or  • the correction value of the compensator power pK, C * is determined as the product of the output value of the first control element with the current buffer capacity voltage uC; or • the correction value of the compensator power pK, C * is determined as the product of the output value of the first control element with a nominal value of the buffer capacitance voltage uC. 6. Control method according to one of claims 1 to 3, wherein for controlling a mean voltage of the energy store (42), the following steps are carried out: Low-pass filtering the energy storage voltage uE to determine an average uEquer of the energy storage voltage uE;  Forming a difference Du Equer of the mean u Equer of the energy storage voltage uE from a corresponding setpoint uEquer *;  Processing this difference DuEquer in a second control element and determining a supplementary low-frequency compensator power component pK, Equer * from an output of that control element;  Adding this compensator power component pK, Equer * to the setpoint value of the power pK, out * to be output by the compensator (4) before its further processing. 7. Control method according to claim 6, wherein in determining the Compensating power component pK, Equer *  The compensator power component pK, Equer * is set equal to the output value of the second control element; or  The compensator power component pK, Equer * is determined as the product of the output variable of the second control element with the mean value uEquer of the energy storage voltage uE; or  • the compensator power component pK, Equer * as product of the output value of the  second control element with the setpoint u Equer * the mean of the  Energy storage voltage uE is determined. 8. Control method according to one of claims 1 to 3, wherein for controlling the voltage uC at the DC port or the current consumption iinquer from a DC voltage source, the following steps are carried out:  • Specifying a setpoint iinquer * for the DC voltage source  absorbed current iinquer, or determining this setpoint iinquer * on the basis of a total power requirement from a main converter power component poutquer and a compensator power component pK, Equer *;  · Determine, by means of an input current controller, a setpoint for a  Buffer capacitance voltage average value uCquer *, which corresponds to that from the DC Voltage source iinquer leads to its setpoint iinquer *; optionally with a pilot control according to the internal voltage ui of the DC voltage source;  Determining, by means of a buffer capacitance voltage regulator, a setpoint value for a capacitor current iC * into the buffer capacitance C, which leads the buffer capacitance voltage uC to its desired value uCquer *  Determining a correction value of the compensator power pK, C * corresponding to this setpoint value for the capacitor current iC *  • adding this correction value of the compensator power pK, C * to the setpoint value of the power pK, out * to be output by the compensator (4) before its further processing. 9. Control method according to one of claims 1 to 3, wherein the following steps are carried out to determine the compensator power component pK, Equer *:  Low-pass filtering the energy storage voltage uE to determine an average uEquer of the energy storage voltage uE;  • forming a difference Du Equer of the mean u Equer of the energy storage voltage uE from a corresponding setpoint uEquer *;  • processing this difference DuEquer in a second control element and determining the compensator power component pK, Equer * from an output of this  Control element. 10. Control method for active compensation of fluctuations of a power flow of a power electronic converter system, wherein the converter system comprises a main converter (2) for power transmission between a DC port and an output port, and a buffer capacitor C connected in parallel to the DC port with a buffer capacity voltage μC; wherein parallel to the buffer capacitor C, a compensator (4) is connected, which has a coupling converter (41) and an energy store (42), wherein the coupling converter (41) is adapted to feed energy into the energy store (42) and to remove this ; and being in the process to suppress an AC component of the buffer capacitance voltage uC, the following steps are performed: Highpass filtering the buffer capacitance voltage uC to determine a variation of the buffer capacitance voltage uC, AC;  Processing the variation of the buffer capacity voltage μC, AC in a first control element and determining a correction value pK, C * based on an output value of this control element;  • Actuation of the coupling converter (41), so that the output from the compensator (4) or recorded power this correction value pK, C * follows. 11. Control device comprising digital and / or analog signal processing means, and which is adapted to realize one of the methods according to one of claims 1-10.