Method for operating a power converter by means of a grid-forming controller

Abstract

The invention relates to a method for operating a power converter (10) for exchanging electrical power (PDC,PAC) between a DC unit (11) and an AC grid (13). The DC unit (11) is connected to a DC connection (12) of the power converter (10) and exchanges a DC power (PDC) with the power converter (10) on the basis of a DC voltage (UDC) at the DC connection (12), and the AC grid (13) is connected to an AC connection (14) of the power converter (10) and exchanges an AC power (PAC) with the power converter (10) via the AC connection (14) on the basis of a voltage curve deviation between an AC voltage curve (UAC) generated by a clocked bridge circuit (15) of the power converter (10) and a grid voltage curve (Ugrid). The power converter (10) adjusts the AC voltage curve (UAC) on the basis of an AC power control value (PAC,set) by means of a grid-forming AC controller (20) and varies the AC power (PAC) by means of an adjustable induced power response for network events. The induced power response comprises a dynamic AC power deviation between the AC power (PAC) and a power setpoint value. The method is characterized in that the induced power response to a network event is adjusted using an asymmetry characteristic curve (50, 51, 52, 53). The asymmetry characteristic curve (50, 51, 52, 53) specifies different increases of a parameter (p) of the AC controller (20) and / or a DC controller (30) as a function of the sign of a deviation (p-plim) of the parameter (p) from a parameter limit value (plim), wherein the parameter (p) comprises in particular a DC voltage difference (ΔUDC) between the DC voltage (UDC) and a DC setpoint voltage (UDC,set) and / or an AC power difference (ΔPAC) between the AC power (PAC) and the AC power control value (PAC,set). The invention further relates to a power converter and to an energy supply

Description

[0001] 23-248-P-WO - 1 - submitted version

[0002] METHOD FOR OPERATING A POWER CONVERTER WITH A NETWORK-FORMING CONTROL

[0003] TECHNICAL AREA

[0004] The application relates to a method for operating a power converter for exchanging electrical power between a DC unit and an AC network, a power converter with a network-forming AC control system, and a power supply system.

[0005] STATE OF THE ART

[0006] Conventional power plants, particularly thermal power plants and hydroelectric power plants, comprise grid-synchronously rotating flywheels of the synchronous generators or turbines and the respective drive train. These power plants exchange electrical power with an alternating current (AC) grid, with the entire flywheel mass of the plants being electromechanically active and contributing significantly to the stabilization of the AC grid. In particular, the inertia of the respective flywheel mass, due to the rotational energy stored within it, causes inertia (also called inertia) in the rotating voltage space vector of the conventional power plants relative to the voltage space vector in the AC grid.As a result, in the event of phase jumps and / or frequency changes of the voltage space vector in the AC network, an instantaneous change in the power supply systems takes place, which is caused in particular by inductive effects and a phase angle difference between the voltage space vector of the flywheel and the voltage space vector of the network voltage.

[0007] In this respect, a conventional power supply system provides a so-called instantaneous reserve and limits the rate of change of the grid frequency of the AC power grid, especially in the event that power imbalances between the supply and outflow of electrical power, i.e. between generation and consumption in the AC power grid, occur relatively quickly, for example due to a fault in a transmission line in the AC power grid.

[0008] The energy exchanged as instantaneous reserve power between the power supply system and the AC grid is drawn from or supplied to the rotating mass of the conventional power supply system by decelerating or accelerating the respective flywheel (23-248-P-WO - 2 - submitted version), whereby the exchanged power and energy are limited by the overall physical properties of the power supply system. The provision of the instantaneous reserve ends as soon as the voltage space vector of the flywheel has synchronized with the voltage space vector of the grid and its rotational frequency has aligned with the grid frequency, i.e., in particular as soon as any drift of the grid frequency has stopped, for example, after the power imbalance has been eliminated by further frequency control mechanisms or a grid self-regulation effect.

[0009] Energy supply systems that exchange electrical power with the AC grid via power electronic converters, such as photovoltaic systems, wind turbines, or grid-connected energy storage systems, generally lack rotating masses synchronized with the grid voltage angle. Therefore, from a grid perspective, they lack suitable mechanical inertia, little or no mechanical storage capacity, and low overcurrent capability. The power electronic converters of such energy supply systems, particularly inverters, can be designed specifically for the grid-following exchange of a predetermined electrical power with an existing AC grid and, at best, can support the establishment of an island grid.

[0010] Grid-following power supply means that a power converter, particularly a power converter, synchronizes its AC-side voltage with the existing grid in terms of voltage angle and amplitude. The power converter follows the grid in terms of frequency and voltage as quickly as its control system allows. Furthermore, a power converter with grid-following power supply is current-limiting, as the exchanged power is regulated to a setpoint largely independently of the specific parameters of the grid. Grid-shaping power supply, on the other hand, means that a power converter uses grid-shaping control to generate an AC-side voltage that may differ from the existing grid in terms of voltage angle and amplitude, i.e., in terms of its phase and / or voltage.Therefore, the network-forming exchange of electrical power with an existing network is directly influenced by network characteristics and network events such as network frequency changes or network phase shifts, although the influence of the network-forming power exchange on these network characteristics is very limited. Several voltage-impacting converters with network-forming power exchange can, with suitable coordination or concertation, e.g., by means of a specific design or (higher-level) control, be capable of maintaining or forming a (spatially limited) AC network, e.g., a distribution network. Finally, a network-forming converter is capable of forming a network on its own and maintaining it, whereby the network-forming converter can determine the frequency and voltage, in particular the voltage angle and voltage amplitude, of the network to be formed.However, the network formed by grid-forming power converters is essentially dependent on the performance of the specific power converter and is therefore usually spatially limited, e.g. a local island grid.

[0011] Various types of network events can occur in an AC power grid. In particular, the grid frequency can change with different signs, i.e., increase or decrease. A grid-shaping control system must react autonomously to such network events and, to the best of its ability, make power adjustments with correspondingly different signs to contribute to grid stability.

[0012] From DE 10 2020 119 039 A1, a system with inverters is known that operates with a respective droop control system, allowing for voltage regulation and instantaneous response to grid events by changing the power output. A system controller adjusts parameters of the droop control system, whereby the adjustment includes, in particular, a change in the setpoint frequency or, alternatively, the setpoint power in response to a power change, in order to restore the system's power output to the setpoint grid power after a grid event. This solution makes it possible to precisely set the setpoint grid power at the grid connection point.

[0013] From WO 2023224648 A1, a control system for a PV inverter with a power-frequency droop control is known, which enables, among other things, grid-forming operation in an island grid and grid-forming operation on an AC grid, whereby in grid-forming operation a frequency control value of the power-frequency droop is modified depending on a difference between the actual power and a reference power.

[0014] The EP 2469680 B1 is a PV inverter with droop control, in which the inverter phase angle is determined from a frequency control value that is set depending on the difference between the actual power and a target power. The target power corresponds to the maximum power point (MPP) of the PV generator. The inverter phase angle is additionally corrected with a phase correction value that is set depending on the difference between the DC output voltage and a DC target voltage.

[0015] US Patent 11 316347 B2 discloses a control unit for a so-called virtual synchronous generator, which, in grid-following operation with a PV generator, adjusts its AC power output using a direction-dependent P(df / dt) control. The directionality is adjustable by a power limiting block. 23-248-P-WO - 4 - submitted version

[0016] TASK

[0017] The application is based on the task of demonstrating a method for operating a power converter that improves the network-forming exchange of electrical power between a DC unit and an AC network.

[0018] SOLUTION

[0019] The problem is solved by a method having the features of claim 1, by a power converter having the features of claim 22, and by a power supply system having the features of claim 23. Embodiments are specified in the respective dependent claims.

[0020] DESCRIPTION

[0021] In a patented method for operating a power converter, the power converter is configured to exchange electrical power between a DC unit and an AC network. The DC unit is connected to a DC terminal of the power converter and exchanges DC power with the power converter depending on the DC voltage at the DC terminal. The AC network is connected to an AC terminal of the power converter and exchanges AC power with the power converter depending on the voltage deviation between an AC voltage waveform generated at the AC terminal by a switched-mode bridge circuit of the power converter and a network voltage waveform.

[0022] The power converter uses a network-shaping AC control system to adjust the AC voltage profile based on an AC power setpoint; that is, the power converter is fundamentally in a voltage-regulating operating mode. The AC control system can take into account a power setpoint, which, for example, represents the power to be exchanged between the DC unit and the AC network during steady-state normal operation, particularly when the electrical parameters of the AC network are within a normal range. The AC power setpoint can correspond to the power setpoint or be derived from it within the process, for example, by using the AC power setpoint to adjust the power setpoint during steady-state normal operation.

[0023] In contrast, during network events, the AC power varies with an adjustable induced power response, the induced power response comprising a dynamic AC power deviation between the AC power and the power setpoint, so that, as per 23-248-P-WO - 5 - submitted version, an adjustable control power is induced by a network event and, in particular, an instantaneous reserve power is exchanged with the AC network.

[0024] The patented method is characterized in that the induced power response to a network event is adjusted by means of an asymmetry characteristic. A patented asymmetry characteristic specifies different gains of a parameter of the network-forming AC control and / or of a DC controller connected to the network-forming AC control, depending on the sign of a deviation of the parameter from a parameter limit value. The parameter includes, in particular, a DC voltage difference between the DC voltage and a DC setpoint voltage and / or an AC power difference between the AC power and the AC power setpoint.

[0025] The patented method allows the power converter to react to a grid event in different ways using the asymmetry characteristic, depending on the sign of the grid event and the power response induced by the voltage-regulating operation. The sign of the grid event is reflected in the sign of the parameter, in particular by a grid event causing a deviation of the grid voltage waveform from the AC voltage waveform of the power converter and a grid-shaping change in the AC power, which in turn results in an AC power differential in the AC control and / or a DC voltage differential in the DC controller.The asymmetric amplification of the deviation of at least one of these parameters from its corresponding parameter limit value thus influences the power response occurring during a specific network event, in particular the resulting dynamic AC power deviation between the AC power and the power setpoint. The specific design of the asymmetry characteristic and the parameter limit value allows for particular consideration of the characteristics of the DC unit used, ensuring, for example, that electrical power is actually available for the power response in reaction to potential network events and can be exchanged between the DC unit and the AC network.

[0026] In one embodiment, the parameter limit can specifically have the value zero, so that the asymmetry characteristic exhibits different slopes depending on the sign of the DC voltage difference between the DC voltage and a DC setpoint voltage and / or on the sign of the AC power difference between the AC power and an AC power setpoint. This allows the power response to vary directly depending on the sign of the network event. This is particularly advantageous when a maximally asymmetric response is required, i.e., with fundamentally different magnitudes of AC power deviations in response to network events with different signs, e.g., when a DC unit connected to the power converter (23-248-P-WO - 6 - submitted version) can or should change its power output from the power setpoint essentially only in one direction.

[0027] In an alternative embodiment, the parameter limit can specifically have a non-zero value, so that the asymmetry characteristic exhibits different slopes depending on whether the parameter lies within or beyond the associated parameter limit. This allows the power response to initially occur with the same gain regardless of the sign of the network event, and the parameter is only amplified differently when it exceeds the associated parameter limit. This is particularly advantageous when at least a limited degree of symmetry is required, i.e., with dynamic AC power deviations of identical magnitude in response to network events with opposite signs, e.g.because the DC unit specifically connected to the power converter can change its power output to a certain extent in both directions from the power setpoint, but only up to reaching the parameter limit, i.e. up to a predefinable maximum AC power difference and / or a maximum DC voltage difference caused by the power response.

[0028] Specifically, the DC unit within the framework of the method can comprise a battery, a PV generator, or an electrolyzer. Based on a power setpoint and the associated power exchanged between the DC unit and the AC grid during steady-state normal operation, a battery, for example, can generally exchange a higher or lower DC power and thus support a symmetrical power response, but only as long as a corresponding storage capacity is available in the battery. If the battery is, for example, completely empty or completely full, and / or if the battery has differently limited charging and discharging capacities, operation with the asymmetry characteristic curve according to the application is advantageous.A PV generator inherently exhibits non-linear power behavior and, in steady-state normal operation, can be operated particularly close to the maximum power point (MPP), so that an increase in DC power is only possible to a very limited extent and should be avoided, in particular to prevent instabilities in the control of the power converter; this can be taken into account using the asymmetry characteristic curve according to the application, for example by amplifying a DC voltage difference induced by a grid event between the DC voltage and an MPP voltage of the PV generator as the DC setpoint voltage, depending on the sign of the DC voltage difference.An electrolyzer is regularly operated in steady-state normal operation with a power setpoint that is close to a maximum power of the electrolyzer, so that a dynamic AC power deviation due to a network event is in principle symmetrical in both directions, but only as long as the AC- 23-248-P-WO - 7 - submitted version.

[0029] The power difference must not exceed a corresponding parameter limit, i.e., a maximum permissible power increase. Here, the asymmetry characteristic curve according to the application can be advantageously used, as it has different slopes on either side of the parameter limit and, in particular, prevents escalation, such as an overload of the electrolyzer, and / or a shutdown of the DC unit, when the parameter limit is exceeded in response to a network event.

[0030] In one embodiment of the method, the grid event particularly includes a grid frequency event, wherein the voltage waveform deviation comprises a phase angle difference between an AC phase angle at the AC terminal of the power transformer and a grid voltage phase angle. The AC phase angle at the AC terminal is predetermined by the AC control and set by the bridge circuit of the power transformer. A grid frequency event, such as a grid frequency change or a grid phase shift, causes a change in the phase angle difference, given the initially constant AC voltage waveform, and thus automatically a power response from the power transformer, leading to a change in the parameters AC power difference and / or DC voltage difference.The asymmetry characteristic curve specified in the application results in, in particular, that this parameter change is amplified differently depending on the sign of the change in the phase angle difference, thus enabling an asymmetric power response to mains frequency events with different signs.

[0031] In another embodiment of the method, the AC power setpoint of the network-shaping AC control is specified by the DC controller. The AC power setpoint can depend, in particular, on the DC voltage difference between the DC voltage and the DC setpoint voltage and / or on the DC current difference between a DC current and a DC current setpoint. This allows, for example, the DC controller to influence the AC power using the AC power setpoint in such a way that a deviation of the DC voltage from the DC setpoint voltage is reduced, so that the DC setpoint voltage, and thus any corresponding power setpoint, can be reached and maintained, at least during steady-state normal operation.

[0032] The asymmetry characteristic can include an inertial asymmetry characteristic that is applied in the AC control to the AC power difference between the AC power and the AC power setpoint. Alternatively or additionally, the asymmetry characteristic can include an inertial asymmetry characteristic that is applied in the DC controller to the DC voltage difference between the DC voltage and the DC setpoint. In principle, several entities of asymmetry characteristics can be used in the application procedure, for example, several inertial asymmetry characteristics in the network-shaping AC control and in the DC controller, which, through their interaction, determine an asymmetric inertia of the power response of the power converter to a network event.By using at least one inertial asymmetry characteristic, for example, the provision of asymmetric control power, in particular asymmetric instantaneous reserve power, is made possible, whereby the control power on either side of the parameter limit can comprise a significantly different amount of control energy. For example, a PV generator can be operated at its maximum power point (MPP) by the power converter, in particular by the DC controller, while the power converter simultaneously reacts to grid events in a grid-shaping manner. For this purpose, an AC power deviation from the MPP power of the PV generator towards lower power and / or a DC voltage difference from the MPP voltage of the PV generator towards higher DC voltages can be temporarily permitted by a slight gain of the corresponding parameter.On the other hand, an AG power exceeding the MPP power and / or a DC voltage below the MPP voltage, and thus exceeding the associated parameter limits, can be reliably suppressed by a high gain of the corresponding parameter.

[0033] In embodiments of the method, the slopes of the inertia-asymmetry characteristic curve on either side of the parameter limit for the AC power difference or for the DC voltage difference can differ by at least a factor of 2, preferably at least a factor of 5. This results in different changes in the AC power, both in magnitude and shape, for different signs of the parameter deviation from the parameter limit in the grid-following AC control system, and thus a power response with asymmetric inertia. As a rough guideline, the inertia-asymmetry characteristic curve can be designed such that the resulting power response includes a control power that, depending on the sign of, for example, a grid frequency event, comprises a control energy that differs by at least a factor of 2, preferably at least a factor of 5.

[0034] In one embodiment of the method, the grid-forming AC control includes a droop controller in which an AC phase angle for the AC voltage waveform is determined. For this purpose, a droop reference power or an AC droop difference between the current AC power and the droop reference power is multiplied by a droop factor, the resulting product is added as a frequency offset to a nominal frequency, and the resulting sum is integrated as the target frequency. The resulting phase angle can be adjusted by appropriately timing the bridge circuit of the power converter, so that a corresponding AC voltage waveform is generated at the AC terminal of the power converter. Such a droop controller is also called an f(P) controller and can, in particular, automatically adjust the frequency of the AC voltage waveform to the frequency of the grid. 23-248-P-WO - 9 - submitted version

[0035] voltage waveforms, although depending on the selected droop factor, a significant phase angle difference and a corresponding AC power flow can be associated with a change in mains frequency.

[0036] In a further embodiment of the method, the asymmetry characteristic can include a droop asymmetry characteristic that is applied in the droop controller to the droop reference power or to the AC droop difference and whose gain varies depending on the sign of its deviation from a parameter limit. Alternatively or additionally, the asymmetry characteristic can include an asymmetry droop gain that specifies an asymmetry droop gain depending on a droop power change rate of the droop reference power or the AC droop difference, wherein the asymmetry droop gain is applied in the droop controller to the droop reference power or to the AC droop difference between the current AC power and the droop reference power. In particular, the asymmetry droop gain can have different slopes depending on the sign of the droop power change rate.The slope of the asymmetry droop gain can be zero for the first sign of the droop power change rate and greater than zero, preferably greater than 1, for the other sign of the droop power change rate.

[0037] The droop asymmetry characteristic and the asymmetry droop gain allow, for example, the setting of the grid-shaping AC control so that the setpoint frequency is adjusted at different rates to the changing frequency of the grid voltage waveform in response to grid frequency events with different signs of the induced power response. This results in different phase angle differences and correspondingly different dynamic AC power deviations between the AC power and the power setpoint due to grid frequency events with different signs.This difference can be used advantageously, for example, to prevent an increase in the phase angle difference and thus an increase in AC power to a value beyond the MPP power when operating a PV generator at the MPP. This is achieved by having the AC setpoint frequency respond to an increase in AC power with high gain and quickly resynchronize the AC phase angle with the grid voltage phase angle. However, a decrease in the phase angle difference and thus a reduction in AC power due to a corresponding grid frequency event can be permitted by having the AC setpoint frequency respond to a reduction in AC power with relatively low gain, based on the droop asymmetry characteristic. Furthermore, in particular, the application of the asymmetry droop gain as a function of the droop power change rate can provide an asymmetric grid-shaping response to a gradient of the droop (23-248-P-WO - 10 - submitted version).

[0038] reference power or AC droop difference enable, i.e., to design a control power asymmetrically already independent of the position of the droop reference power or the AC droop difference relative to the associated parameter limit.

[0039] In one embodiment of the method, the AC control system incorporates an inertial controller. The inertial controller determines the droop reference power by integrating the AC power difference after applying the inertial asymmetry characteristic and multiplying it by an inertia factor. Integrating the AC power difference over time when determining the droop reference power ensures that the change in phase angle difference associated with a grid frequency event is fed back in such a way that the power response of the grid-shaping control system takes on the character of an instantaneous reserve power. The inertia factor can be dimensioned such that, for example, the power response to a grid frequency change is proportional to the frequency change rate.Furthermore, applying the inertial asymmetry characteristic when determining the droop reference power in the inertial controller enables particularly good adaptation of the grid-shaping AC control to the characteristics of the DC unit used. This ensures, for example, that the available power and energy reserves of the DC unit can actually be exchanged between the DC unit and the AC grid for the power response in response to possible grid events, especially if these power and energy reserves are themselves asymmetrical.For example, when operating a PV generator, a stronger counter-reaction of the droop controller can be achieved when the AC power exceeds the MPP power and / or the DC voltage drops below the MPP voltage due to a grid frequency event, compared to a reduction in AC power that would otherwise be inconsequential. This is because applying the inertial asymmetry characteristic to the AC power difference results in a greater increase in the droop reference power or the AC droop difference for a negative AC power difference than for a positive one. This allows, in particular, the creation of a negative instantaneous reserve while simultaneously effectively suppressing a positive instantaneous reserve.Conversely, when operating an electrolyzer at its rated DC power, a positive instantaneous reserve can be generated and supported by reducing the electrolysis power, while simultaneously a negative instantaneous reserve can be effectively suppressed by increasing the electrolysis power beyond the rated power. When operating a battery as a DC unit, the instantaneous reserve can be selected asymmetrically depending on the state of charge.

[0040] In one embodiment of the method, the AC power setpoint in the DC controller is determined by measuring the DC voltage difference between the DC voltage and the DC setpoint. (23-248-P-WO - 11 - submitted version)

[0041] The voltage is integrated after applying the inertia-asymmetry characteristic and multiplied by an inertia factor, with the AC power setpoint thus determined being used, in particular, as a droop reference power. The AC power setpoint determined in the DC controller can additionally include a proportional component, which is formed as the product of the DC voltage difference and a DC proportional factor, where the DC proportional factor preferably differs depending on the sign of the DC voltage difference. Integrating the DC voltage difference over time when determining the AC power setpoint for the grid-shaping AC control ensures, in particular, that the change in DC voltage associated with the power response to a grid frequency event is reduced by the change in the AC power setpoint being reduced by the change in the phase angle difference associated with a grid frequency event.By applying the inertial asymmetry characteristic to the DC voltage difference, this feedback can also be designed asymmetrically by amplifying DC voltage differences with opposite signs differently and correspondingly adjusting them at different speeds. This allows, for example, the realization of an asymmetric instantaneous reserve or, in combination with other entities of asymmetry characteristics, the refinement of the grid-shaping AC control, particularly to optimally utilize the potentially asymmetrically available power and energy reserves of the DC unit used for grid shaping.

[0042] In further embodiments of the method, the power converter can include a DC current controller which, depending on the connected DC unit, performs, in particular, battery current control, MPPT control, and / or electrolysis current control. The DC current controller can be connected upstream of the power converter's DC controller, so that the DC controller receives the target DC voltage from the DC current controller.

[0043] In the case of a PV generator as a DC unit, the DC current controller preferably implements MPPT control to set and monitor the maximum power point (MPP) of the PV generator. For this purpose, the DC current controller can incrementally change the DC setpoint voltage to maximize the DC power of a connected PV generator, with the direction of the change in the DC setpoint voltage depending on the direction of the change in the DC power of the PV generator at previously set DC setpoint voltages. The respective DC setpoint voltage is then preferably taken into account via the DC controller or directly by the AC control system and is set, in particular, during steady-state normal operation in the absence of grid events, so that the MPP power indirectly serves as the power setpoint.In an extended embodiment of the DC current controller, the MPPT control can set an operating point of the PV generator whose DC power deviates from the current MPP power by a fixed or variable amount. This allows a power reserve to be created, which can be used as a corresponding shift of the parameter limit for the AC power difference.

[0044] Similarly, the DC current controller can adjust the DC setpoint voltage for electrolysis current control depending on the DC current to a connected electrolyzer. This allows it to set a predefined DC electrolysis current setpoint as the power setpoint during steady-state normal operation and optionally maintain a power reserve above the DC electrolysis current setpoint, which can be taken into account as the parameter limit for the AC power difference. If a battery is used as the DC unit, the DC current controller can adjust the DC setpoint voltage for battery current control depending on the DC current to the connected battery. This allows it to set a predefined DC battery current setpoint as the power setpoint during steady-state normal operation.At the same time, the application of the asymmetry characteristic in the network-shaping AC control enables in every case an asymmetrically adjustable power response to a network event, in particular an asymmetric instantaneous reserve in the event of a network frequency event with optimal use of the actual, possibly asymmetric, power and energy reserves of the specific DC unit used.

[0045] A power converter according to the patent application for exchanging electrical power between a DC unit and an AC network comprises a DC intermediate circuit, a bridge circuit with controllable semiconductor switches, and a control unit. The power converter, and in particular the control unit of the power converter, is configured to perform network-shaping AC regulation of the AC voltage waveform at an AC terminal of the power converter. The power converter according to the patent application is characterized in that the control unit is configured to execute one of the patent application methods described above.

[0046] A power supply system according to the application comprises a power converter that can be connected to a DC unit via a DC connection and to an AC grid via an AC connection, wherein the power converter is operated using one of the methods described above according to the application. The DC unit can, in particular, comprise a battery, a PV generator, or an electrolyzer. In a specific embodiment of the power supply system, the DC unit comprises a PV generator or an electrolyzer that do not themselves have a dedicated energy storage capability. The power converter can, in particular, be configured to exchange asymmetrical control power with the AC grid in the event of a grid frequency event, the degree of which depends on the sign of the grid frequency event.The power converter preferably includes an energy storage capacity that is at least a factor of 10, preferably at least a factor of 100 smaller than the control energy required in a 23-248-P-WO - 13 - submitted version.

[0047] The system exchanges power for a grid frequency event with a relatively high control power output due to its sign. Preferably, the power generation plant and the power converter, apart from the intermediate circuit capacity of a conventional DC intermediate circuit, do not include any further energy storage devices in the power path. Using the method described in the application, the power supply system is nevertheless capable of performing grid-forming AC control and, in particular, of contributing significantly to grid stabilization of the AC grid by providing control power during grid events.

[0048] BRIEF DESCRIPTION OF THE FIGURES

[0049] The invention will now be further explained and described with reference to exemplary embodiments shown in the figures.

[0050] Fig. 1 shows a first embodiment of the method according to the application.

[0051] Fig. 2 shows a second embodiment of the method according to the application.

[0052] Fig. 3 shows a third embodiment of the method according to the application.

[0053] Fig. 4 shows a fourth embodiment of the method according to the application.

[0054] Fig. 5 shows a fifth embodiment of the method according to the application.

[0055] Fig. 6 shows a sixth embodiment of the method according to the application.

[0056] Fig. 7 shows a seventh embodiment of the method according to the application.

[0057] Fig. 8 shows an eighth embodiment of the method according to the application.

[0058] Fig. 9 shows an exemplary time course of a mains frequency and an AC power when applying the method according to the application.

[0059] The same reference symbols are used in the figures for identical or similar elements. The representations in the figures cannot be to scale.

[0060] FIGURE DESCRIPTION

[0061] Fig. 1 schematically shows a power supply system with a power converter 10, which is configured for the exchange of electrical power PDC, PAC between a DC unit 11 and an AC network 13. The DC unit 10 is connected to a DC terminal 12 of the power converter 10 and exchanges DC power PDC with the power converter 10 depending on a DC voltage UDC at the DC terminal 12. The DC unit 11 can, in particular, comprise a battery, a PV generator, or an electrolyzer. (The AC-23-248-P-WO-14 submitted version)

[0062] Network 13 is connected to an AC terminal 14 of the power converter 10 and exchanges an AC power PAC with the power converter 10 depending on a voltage profile deviation between an AC voltage profile UAC generated by a clocked bridge circuit 15 of the power converter 10 and a mains voltage profile U gr The output is via the AC terminal 14. Optionally, an AC filter 16 is connected between the bridge circuit 15 and the AC terminal 14, across which the voltage waveform deviation is reduced. The DC voltage UDC and / or the AC power PAC can be measured using suitable measuring instruments. It is understood that, within the scope of this application, the quantities voltage, current, and power are interrelated on both the AC and DC sides, so that, in particular, power can be specified as current at a given voltage or vice versa.

[0063] The power transformer 10 includes a grid-forming AC control 20. Using the grid-forming AC control 20, the power transformer 10 adjusts the AC voltage profile UAC as a function of a power setpoint PAC, set. Due to the grid-following AC control 20, the AC power PAC depends on the specific profile of the grid voltage U. gr The AC voltage waveform UAC is relative to the AC voltage waveform. The resulting voltage waveform deviation includes, in particular, a phase angle difference between an AC phase angle 3 set by the bridge circuit 15 and a mains voltage phase angle, where the AC phase angle 3 is determined by the AC control unit 20. By means of the network-shaping AC control unit 20, the AC power PAC varies in response to network events, especially network frequency events such as changes in the network frequency or phase jumps in the mains voltage waveform, with an adjustable power response.

[0064] The power response to network events includes a dynamic AC power deviation between the AC power PAC and a power setpoint, which can, for example, correspond to the AC power setpoint PAC, set. The AC power setpoint PAC, set can also be specified by a DC controller 30 and is particularly dependent on a DC voltage difference AUDC between the DC voltage UDC and a DC setpoint voltage UDC, set and / or on a DC current difference AIDC between a DC current l D c and a DC current setpoint l Dc,set be. In a stationary operation with an AC network 14, whose electrical parameters are within the standard range and are constant, the network-forming AC control 20 of the AC voltage UAC results in an AC power PAC, which essentially corresponds to a power setpoint for the energy supply system, for example an MPP power of a PV generator, an electrolysis power of an electrolyzer or a battery current of a battery as a DC unit 11.

[0065] The power response induced by a network event is set using an asymmetry characteristic 50. The asymmetry characteristic 50 provides different gains of a parameter p of the AC controller 20 and / or a DC controller 30 (see Fig. 2ff) in the version submitted in 23-248-P-WO - 15.

[0066] Dependence on the sign of a deviation p-pum of the parameter p from a parameter limit pi imIn the example shown in Fig. 1, the different gains are implemented as different slopes of the asymmetry characteristic curve 50, which can therefore be implemented, for example, as a simple table and which corresponds to the parameter p, taking into account its distance from the parameter limit pi. im assigns the correspondingly amplified parameter p'.

[0067] The parameter p can, in particular, comprise a DC voltage difference AUDC between the DC voltage UDC and the DC setpoint voltage Uoc.set (see Fig. 2ff) and / or an AC power difference APAC between the AC power PAC and the AC power setpoint PAc.set (see Fig. 3ff). The asymmetrically amplified parameter p' resulting from the application of the asymmetry characteristic 50 to the parameter p can be converted into an AC voltage waveform UAC via further AC control elements 28, which is then passed as a control signal to the bridge circuit 15. The AC voltage waveform UAC can be represented by one or more other values ​​suitable for controlling the bridge circuit 15, for example, the phase angle 3 (see Fig. 2ff).

[0068] Fig. 2 shows a specific embodiment of the patented method in which the AC power setpoint PAc.set is determined in a DC controller 30. A DC voltage difference AUDC is generated between the DC voltage UDC and a DC setpoint voltage Uoc.set, optionally processed by further DC control elements 39, and passed on as the AC power setpoint PAc.set to the grid-shaping AC controller 20. Depending on the power setpoint PAc.set and the AC power PAC, the grid-shaping AC controller 20 sets the AC voltage UAC by controlling the bridge circuit 15 using the phase angle 3, which is determined, for example, by a suitable droop controller.

[0069] Fig. 3 shows a further embodiment of the patented method, in which the DC controller 30 determines the AC power setpoint PAc.set as a function of the voltage difference AUDC and transmits it to the AC controller 20. In the AC controller 20, an AC power difference APAC is generated between the AC power PAC and the AC power setpoint PAc.set. An inertial asymmetry characteristic 51 is applied to the AC power difference APAC, which assigns a modified AC power difference APAC to the AC power difference APAC. The modified AC power difference APAC is amplified differently compared to the AC power difference APAC, depending on the sign of the deviation of the AC power difference APAC from a limit value PAC.I™. In the simplest case, the limit value is PAC.I™ equals zero, so that the AC power difference APAC is multiplied by a constant corresponding to the slope of the inertial asymmetry characteristic 51, where the slope of the inertial asymmetry characteristic 51 differs depending on the sign of the AC power difference APAC. The AC power difference APAC, thus asymmetrically modified, is further modified as 23-248-P-WO - 16 - submitted version.

[0070] AC control elements 28, e.g. a suitable droop controller that determines phase angle 3 and uses this to control the bridge circuit 15.

[0071] Fig. 4 shows a further embodiment of the patented method, in which the DC controller 30 determines the AC power setpoint PAc.set by applying an inertial asymmetry characteristic 51 to the voltage difference AUDC. The inertial asymmetry characteristic 51 amplifies the voltage difference AUDC to varying degrees depending on the sign of the deviation of the voltage difference AUDC from a limit value UDC.I™. In the simplest case, the limit value Uoc.iim is zero, so that the voltage difference AUDC is multiplied by a constant corresponding to the slope of the inertial asymmetry characteristic 51, the slope of which varies depending on the sign of the voltage difference AUDC. The AC power setpoint PAc.set is then determined from the asymmetrically modified voltage difference AUDC via further AC control elements 28.The network-forming AC control 20 sets the AC voltage UAC depending on the AC power setpoint PAc.set and the AC power PAC by controlling the bridge circuit 15 using the phase angle 3.

[0072] Fig. 5 shows a further embodiment of the method according to the application, in which the AC control 20 includes a droop controller 22. In the droop controller 22, the phase angle 3 for the AC voltage UAC is determined as a function of a droop reference power PD, which can correspond to the AC power setpoint PAc.set or be derived from it via further optional AC control elements 29. The droop reference power PD (or an AC droop difference APD between the current AC power PAC and the droop reference power PD, shown here only as an option) is amplified asymmetrically by means of a droop asymmetry characteristic 51, wherein the slope of the droop asymmetry characteristic depends on the sign of the deviation of the droop reference power PD from a limit value P. D ,iim is of different sizes. The resulting asymmetrically modified droop reference power P' D(or AC droop difference AP'D) is multiplied by a droop factor KD, and the resulting product is added as a frequency offset to a nominal frequency. The resulting sum is integrated as the target frequency in an integrator 2n7f to obtain the phase angle 3, which is used to drive the bridge circuit 15.

[0073] Fig. 6 shows a further embodiment of the method according to the application, in which an asymmetry droop gain VAsym is applied to the droop reference power PD in the droop controller 22 (or optionally to the AC droop difference APD, shown here only as an option). The asymmetry droop gain VAsym is specified as a function of a droop power change rate dPo / dt of the droop reference power PD (or the AC droop difference APD) and can be represented as a droop asymmetry characteristic 52. The droop asymmetry characteristic 52 has different slopes depending on the sign of the droop power change rate dPo / dt. In the example shown in Fig. 6, the slope of the asymmetry droop gain VAsym is zero, especially when the droop power rate is positive, i.e., the asymmetry droop gain VAsym is a constant for positive values ​​of the power rate dPo / dt.For a negative sign of the droop power change rate dPo / dt, the slope of the asymmetry droop gain VAsym is approximately two, so that the droop reference power PD (or the AC droop difference APD) is amplified more strongly the faster the droop reference power PD (or the AC droop difference APD) decreases. The resulting asymmetrically modified droop reference power is P'. D (or AC droop difference AP'D) is in turn multiplied by a droop factor KD, the resulting product is added as a frequency offset to a nominal frequency, and the resulting sum is integrated as the target frequency in an integrator 2n7f to obtain the phase angle 3, which is used to drive the bridge circuit 15.

[0074] Fig. 7 shows a further embodiment of the method according to the application, in which the AC control 20 comprises an inertial controller 24 and the droop controller 22. In the inertial controller 24, the droop reference power PD for the droop controller 22 is determined by first applying an inertial asymmetry characteristic 51 to the AC power difference APAC between the AC power PAC and the AC power setpoint PAc.set. The resulting asymmetrically modified AC power difference AP'AC (compare Figure 3) is integrated in an integrator 1 / s and multiplied by an inertia factor Ha. The resulting integral can, in particular, represent the deviation of the AC power PAC from the AC power setpoint PAc.set that has accumulated during a network event and is passed to the droop controller 22 as the droop reference power PD. The droop controller 22 uses the droop reference power PD to determine the phase angle 3, see e.g. Fig. 5.The application of the inertia asymmetry characteristic 51 in combination with the integrator 1 / s in the inertia controller 24 generates a droop reference power that imposes an adjustable asymmetric inertia on the phase angle 3.

[0075] Fig. 8 shows a further embodiment of the patented method in which an inertial asymmetry characteristic 51 is applied to the voltage difference AUDC in the DC controller 30 (compare Fig. 4). The voltage difference AUDC modified in this asymmetrical way is integrated by means of an integrator 1 / s and multiplied by a DC inertia factor HDC. The AC power setpoint PAc.set thus determined is used in the grid-shaping AC control 20 to determine the phase angle 3 (compare, for example, Fig. 7). Optionally, the AC power setpoint PAc.set can additionally include a proportional component, which is formed as the product of the DC voltage difference AUDC and a DC proportional factor KP. Optionally, a further asymmetry characteristic curve 53 23-248-P-WO - 18 - submitted version can be applied to the proportional component, so that the proportional component can also differ depending on the sign of the DC voltage difference AUDC.

[0076] Fig. 9 shows an example of the AC power PAC curve as a function of the mains frequency f. gr id when applying the procedure according to the application in an energy supply system with a PV generator as DC unit 11 , wherein the PV generator is operated at the maximum power point (MPP).

[0077] Initially, the power supply system and the AC network 13 are in a steady-state normal operation, with the network frequency f gr id constant at a nominal frequency f se The time t is reached and the exchanged powers PDC, PAC are identical to the MPP power PMPP, except for operational losses. At time ti, the grid frequency f begins. grThe grid-forming AC control 10 reacts to the grid frequency change with a change in the AC power PAC, which, after a short settling phase, reaches a value that is lower than the MPPP power by a control power, in particular an instantaneous reserve power. Depending on the design of the grid-forming control 20, the control power is proportional to the grid frequency change rate and therefore constant as long as the grid frequency f gr id changes with a constant slope.

[0078] At time t2, the grid frequency f stabilizes. gr The AC power (id) rises to a level higher than the nominal frequency (fset). Simultaneously, the control power is terminated by reducing the AC power (PAC) back to the MPP power (PMPP). Between t2 and ta, the AC network 13 is in a steady state with an increased network frequency (f). grid, where the AC power PAC continues to correspond to the MPP power PMPP. Stabilizing the AC power PAC at a constant grid frequency change rate and restoring the AC power PAC to the original power setpoint after the grid frequency rise has ceased can be achieved in particular by using an inertial controller 24 in the AC control 20 (see Figure 7) and / or an inertial structure of the DC controller 30 (see Figure 8).

[0079] The mains frequency f begins at time ta. grThe grid-forming AC control 10 does not react to the grid frequency change with any change in the AC power PAC; that is, the AC power PAC continues to correspond constantly to the MPP power PMPP of the PV generator. This suppression of a power response during a grid event with a specific sign can be achieved, in particular, by using at least one suitably parameterized asymmetry characteristic 50, especially an inertial asymmetry characteristic 51, in the inertial controller 24 (see Fig. 7) and / or in the DC controller 30 (see Fig. 8), whereby a droop asymmetry characteristic 52 and / or an asymmetry characteristic 53 can optionally be used, for example, to more precisely adjust the transitions at the onset and end of a grid event. 23-248-P-WO - 19 - submitted version

[0080] At time t4, the grid frequency event has ended and the grid frequency corresponds again to the nominal frequency f. set, while the AC power continues to correspond to the MPP power PMPP of the PV generator.

[0081] The behavior of the power supply system is thus maximally asymmetrical with regard to grid events, in that the grid-forming AC control 20 of the power converter 10 only reacts with a change in the AC power PAC in the case of a grid event with a first sign (here: increasing grid frequency between ti and t2), while the AC power is otherwise kept constant at the MPP power, especially in the case of a grid event with a second sign (here: decreasing grid frequency between t3 and t4), which would normally induce an increase in the AC power; this allows the renewably generated power and energy to be used as completely and optimally as possible and, in particular, avoids the need to reduce the AC power below the MPP power PMPP from the outset as a kind of prophylactic measure.

[0082] A similar result, particularly complementary with regard to AC control power, can be achieved, for example, if the power supply system is operated with an electrolyzer as a DC unit 11. In this case, at least one asymmetry characteristic 50 can be used to reduce the DC power PDC drawn from the electrolyzer and thus the AC power PAC in the event of a negative gradient of the grid frequency f. gr to achieve id, while the DC power PDC and correspondingly the AC power PAC increase in the case of a rising grid frequency f gr The ID does not change, or only changes insignificantly.

[0083] When using a battery as a DC unit 11, various asymmetrical power responses to a grid event can be achieved, which, depending on the specific configuration of the asymmetry characteristic(s) 50, can be set somewhere between maximally asymmetrical (compare Fig. 9) and strictly symmetrical. The configuration of the asymmetry characteristic(s) 50 that is chosen can depend on further external factors, such as the battery's state of charge.

[0084] 3-248-P-WO - 20 - submitted version

[0085] REFERENCE MARK LIST

[0086] 10 power converters

[0087] 11 DC units

[0088] 12 DC connector

[0089] 13 Alternating current network (AC network)

[0090] 14 AC outlets

[0091] 15 Bridge circuit

[0092] 16 AC filters

[0093] 20 AC regulation

[0094] 22 Droop controls

[0095] 24 inertial controllers

[0096] 28, 29 AC control elements

[0097] 30 DC regulators

[0098] 39 DC control elements

[0099] 50, 51, 52, 53 Asymmetry characteristic curve

[0100] P Electrical power

[0101] PDC DC power

[0102] PAC AC power

[0103] UDC DC voltage

[0104] UAC, UAC AC voltage curve

[0105] Ugrid mains voltage curve

[0106] P, P' Parameter

[0107] Plim parameter limit

[0108] UDC, set DC set voltage

[0109] AUDC, AU'DC DC voltage difference

[0110] P AC.set AC power setpoint

[0111] APAC, AP'AC AC power difference Δ Phase angle

[0112] PD, P'D Droop reference power

[0113] P D / dt Droop power change rate

[0114] VAsym Asymmetry Droop Gain

[0115] KD Droop factor f Target frequency fset Nominal frequency

[0116] Af frequency offset

[0117] 1 / S, 2TT / f Integrator

[0118] Ha, HDC T inertia factor

[0119] K P DC proportional factor

Claims

23-248-P-WO - 21 - submitted version PATENT CLAIMS 1. A method for operating a power converter (10) for exchanging electrical power (PDC, PAC) between a DC unit (11) and an AC network (13), wherein the DC unit (11) is connected to a DC terminal (12) of the power converter (10) and exchanges DC power (PDC) with the power converter (10) depending on a DC voltage (UDC) at the DC terminal (12), wherein the AC network (13) is connected to an AC terminal (14) of the power converter (10) and exchanges AC power (PAC) with the power converter (10) depending on a voltage waveform deviation between an AC voltage waveform (UAC) generated by a clocked bridge circuit (15) of the power converter (10) and a network voltage waveform (U grid) via the AC connection (14), wherein the power converter (10) adjusts the AC voltage profile (UAC) as a function of an AC power setpoint (PAC, set) by means of a network-shaping AC control (20), wherein the AC power (PAC) varies with an adjustable induced power response during network events, wherein the induced power response comprises a dynamic AC power deviation between the AC power (PAC) and a power setpoint, characterized in that the induced power response to a network event is adjusted by means of an asymmetry characteristic (50, 51, 52, 53), wherein the asymmetry characteristic (50, 51, 52, 53) provides different gains of a parameter (p) of the AC control (20) and / or a DC controller (30) as a function of the sign of a deviation (p-piim) of the parameter (p) from a parameter limit value. (pnm) specifies,where the parameter (p) in particular includes a DC voltage difference (AUDC) between the DC voltage (UDC) and a DC setpoint voltage (UDC, set) and / or an AC power difference (APAC) between the AC power (PAc) and the AC power setpoint (PAC, set).

2. The method of claim 1, wherein the parameter limit (pi) im ) has the value zero, so that the asymmetry characteristic (50,51 ,52,53) has different slopes depending on the sign of the DC voltage difference (AUDC) between the DC voltage (UDC) and the DC set voltage (UDC, set) and / or on the sign of the AC power difference (APAC) between the AC power (PAC) and the AC power setpoint (PAC, set).

3. Method according to claim 1, wherein the parameter limit (pi) im) has a non-zero value, so that the asymmetry characteristic curve (50,51 ,52,53) has different slopes depending on whether the parameter (p) is on this side or on the other side of the associated parameter limit (pi) im ) lies. 23-248-P-WO - 22 - submitted version 4. Method according to any of the preceding claims, wherein the DC unit (11) comprises a battery, a PV generator or an electrolyzer.

5. Method according to one of the preceding claims, wherein the grid event comprises a grid frequency event and the voltage profile deviation comprises a phase angle difference between an AC phase angle (-9) at the AC terminal of the power transformer (10) and a grid voltage phase angle, wherein the AC phase angle (9) at the AC terminal (14) is predetermined by the AC control (20) and set by the bridge circuit (15) of the power transformer (10).

6. Method according to one of the preceding claims, wherein the AC power setpoint (PAC, set) is specified by the DC controller (30) and is in particular dependent on the DC voltage difference (AUDC) between the DC voltage (UDC) and the DC setpoint voltage (UDC, set) and / or on the DC current difference between a DC current and a DC current setpoint.

7. Method according to one of the preceding claims, wherein the asymmetry characteristic (50, 51, 52, 53) comprises an inertial asymmetry characteristic (51) which is applied in the AC control (20) to the AC power difference (APAC) between the AC power (PAC) and the AC power setpoint (PAC, set).

8. Method according to one of the preceding claims, wherein the asymmetry characteristic (50, 51, 52, 53) comprises an inertial asymmetry characteristic (51) which is applied in the DC controller (30) to the DC voltage difference (AUDC) between the DC voltage (UDC) and the DC setpoint voltage (UDC, set).

9. Method according to claim 7 or 8, wherein the slopes of the inertia asymmetry characteristic curve (51) on this side and beyond the parameter limit (pi) im ) for the AC power difference (APAC) or for the DC voltage difference (AUDC) differ by at least a factor of 2, preferably at least a factor of 5.

10. A method according to any of the preceding claims, wherein the AC control (20) comprises a droop controller (22), wherein an AC phase angle (9) for the AC voltage waveform (UAC) is determined in the droop controller (22) by multiplying a droop reference power (PD) or an AC droop difference between the current AC power (PAC) and the droop reference power (PD) by a droop factor (KD), the resulting product being expressed as a frequency offset (Af) to a nominal frequency (f). se t) is added and the resulting sum is integrated as the target frequency (f). 23-248-P-WO - 23 - submitted version 11. Method according to claim 10, wherein the asymmetry characteristic (50, 51, 52, 53) comprises a droop asymmetry characteristic (51) which is applied in the droop controller (22) to the droop reference power (PD) or to the AC droop difference.

12. Method according to claim 10 or 11, wherein the asymmetry characteristic (50, 51, 52, 53) comprises a droop asymmetry characteristic (53) which specifies an asymmetry droop gain (VAsym) as a function of a droop power change rate (dPo / dt) of the droop reference power (PD) or the AC droop difference, wherein the asymmetry droop gain (VAsym) is applied in the droop controller (22) to the droop reference power (PD) or to the AC droop difference between the current AC power (PAC) and the droop reference power (PD).

13. Method according to claim 12, wherein the asymmetry droop gain (VAsym) has different slopes depending on the sign of the droop power change rate (dPo / dt), wherein the slope of the asymmetry droop gain (VAsym) has a value of zero for a first sign of the droop power change rate (dPo / dt) and a value greater than zero, preferably a value greater than 1, for the other sign of the droop power change rate (dPo / dt).

14. Method according to any one of claims 10 to 13, wherein the AC control (20) comprises an inertial controller (24), wherein the droop reference power (PD) in the inertial controller (24) is determined by integrating the AC power difference (AP'AC) after applying the asymmetry characteristic (51) and multiplying it by an inertia factor (Ha).

15. Method according to any one of claims 10 to 13, insofar as related back to claim 6, wherein the AC power setpoint (PAC, set) in the DC controller (30) is determined by integrating the DC voltage difference (AU DC) after applying the inertia asymmetry characteristic (51) and multiplying it by an inertia factor (HDC), wherein the determined AC power setpoint (PAC, set) is used in particular as the droop reference power (PD).

16. Method according to claim 15, wherein the AC power setpoint (PAC, set) determined in the DC controller (30) additionally comprises a proportional component which is formed as the product of the DC voltage difference (AUDC) and a DC proportional factor (KP), wherein the DC proportional factor (KP) preferably differs depending on the sign of the DC voltage difference (AUDC).

17. Method according to one of the preceding claims, wherein the power converter (10) comprises a DC current controller which in particular performs battery current control, MPPT control and / or electrolysis current control. 23-248-P-WO - 24 - submitted version 18. Method according to claim 17, insofar as it relates back to claim 6, wherein the DC controller (30) receives the DC setpoint voltage (Uoc.set) from the DC current controller.

19. Method according to claim 18, wherein the DC current controller for MPPT control incrementally changes the DC setpoint voltage (Uoc.set) to maximize the DC power (PDC) of a connected PV generator, wherein the direction of the change in the DC setpoint voltage (Uoc.set) depends on the direction of the change in the DC power (PDC) of the PV generator at previously set DC setpoint voltages (Uoc.set).

20. Method according to claim 18, wherein the DC current controller for electrolysis current control changes the DC setpoint voltage (Uoc.set) as a function of the DC current to a connected electrolyzer in order to set a predetermined DC electrolysis current setpoint.

21. Method according to claim 18, wherein the DC current regulator for battery current control changes the DC setpoint voltage (Uoc.set) depending on the DC current to a connected battery in order to set a predetermined DC battery current setpoint.

22. Power converter (10) for exchanging electrical power (PDC, PAC) between a DC unit (11) and an AC network (13) comprising a DC intermediate circuit, a bridge circuit (15) with controllable semiconductor switches and a control unit which is configured to perform network-shaping AC control (20) of the AC voltage profile (UAC) at an AC terminal (14) of the power converter (10) according to the method of one of the preceding claims.

23. Power supply system with a power converter (10) which is connected to a DC unit (11) via a DC connection (12) and to an AC network (13) via an AC connection (14), wherein the power converter (10) is operated using a method according to one of claims 1 to 21.

24. Energy supply system according to claim 23, wherein the DC unit (11) comprises a PV generator or an electrolyzer which do not have energy storage capability, wherein the power converter (10) is configured to exchange asymmetric control power with the AC network (13) in the event of a grid frequency event, depending on the sign of the grid frequency event, wherein the power converter (10) comprises an energy storage capacity which is at least a factor of 10, preferably at least a factor of 100 smaller than the control energy that is exchanged in the event of a grid frequency event with a relatively high control power due to its sign.

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