METHOD FOR OPTIMAL USE OF THE RESERVES OF A POWER REFERENCE SYSTEM FOR GRID SUPPORT

Abstract

The invention relates to a method for operating a power converter, wherein the method comprises: providing an overcurrent, the overcurrent being greater than a continuous current of the power converter and lying within the limits of a defined overcurrent profile. The method further comprises the steps (I) before providing the overcurrent, maintaining a reserve, which is formed by at least one distance between at least one power converter parameter and defined parameter limits, and depending on the reserve, one or more preset overcurrent profiles are permissible; (II) providing the overcurrent for a period defined by the respective permissible overcurrent profile, wherein the resulting current is limited to the current limits of the respective permissible overcurrent profile; and (III) after providing the overcurrent, restoring the conditions for providing the overcurrent.

Description

TECHNICAL AREA OF INVENTION The invention relates to a method for the optimized use of the reserves of a power converter system for grid support. Technical field: The invention was developed in the technical field of grid support, in particular by a power converter system with regard to reserves. STATE OF THE ART Systems that maintain reserves for providing, for example, electricity above the permissible level are known. Such systems can provide a one-time increase in electricity. However, this increased electricity is somewhat undefined, and providing it again would take a considerable amount of time. TASK OF INVENTION The invention is based on the objective of demonstrating a method for the optimal use of the reserves of a power converter system for grid support. DESCRIPTION OF THE INVENTION The present application relates to a method for operating a power converter. The method includes the step of providing an overcurrent, wherein the overcurrent is greater than a continuous current of the power converter and lies within the limits of a defined overcurrent profile. Further steps include (I) providing a reserve before supplying the overcurrent, which is formed by at least one distance of at least one converter parameter to defined parameter limits, and depending on the reserve, one or more preset overcurrent profiles are permitted, (II) providing the overcurrent for a period defined by the respective permissible overcurrent profile, whereby the resulting current is limited to the current limits of the respective permissible overcurrent profile, and (III) after supplying the overcurrent, restoring the conditions for supplying the overcurrent. A power converter operated according to the inventive method can, for example, be part of a system tasked with providing grid support services, such as frequency and voltage stabilization, or generating power from sources such as photovoltaic modules for a power grid, supplying loads with electrical power, or storing energy. The power converter can perform various tasks, such as converting a direct current into an alternating current or vice versa, for example, when connected to a long-term energy storage system in which energy is stored or retrieved. The method offers significant advantages. Firstly, providing an overcurrent is beneficial when grid stabilization or grid support functions are required. For example, a drop in grid frequency may necessitate the provision of high active power. Since the voltage is fixed on the grid side, increasing the active power can only be achieved by increasing the supplied current. The method according to the invention allows an overcurrent—that is, a current higher than the continuous current—to be provided without the risk of damaging the power converter, for example, to stabilize the frequency of a supply network. A further advantage is that the ability to provide overcurrent is restored. Should several events occur in rapid succession in the power grid, a converter operated according to the invention can provide the overcurrent for at least one, but presumably for several, events. According to one embodiment, the power converter, which can be operated using the aforementioned method, comprises at least one current conversion stage. This ensures that the provision of overcurrent is possible, since switchable elements, such as semiconductor switches, are required to provide an overcurrent or maintain a specific current. These switchable elements also allow the supplied current to be varied. The method therefore offers the advantage that it can be used without difficulty for systems with multi-stage power converters or current transformers. For example, converters comprising a rectifier and a downstream inverter could be used. According to one embodiment, the provision of the overcurrent is carried out in response to network events, such as changes in voltage angle, voltage frequency, and voltage amplitude, load changes, and switching operations in the power grid. A particular need for an overcurrent arises, for example, when certain network parameters deviate from the norm. For instance, when large loads or similar are connected to a network, the demand for active power fed into the grid may increase. According to a method according to the invention, the active power provided by the converter can be supplied in the form of an overcurrent, thereby increasing grid stability. Other examples of deviations may also necessitate the provision of an overcurrent of varying magnitude. In one embodiment, the converter is a voltage-regulating converter. A voltage-regulating converter, in contrast to a current-regulating converter, is capable of independently regulating a system voltage. In this way, the voltage-regulating converter is suitable for establishing a power grid and, with sufficient current, power, and energy reserves, maintaining and operating it alone or with other voltage sources. A voltage-regulating converter operated using the method according to the invention is therefore capable of shaping a power grid and reacting directly to unforeseen events in this grid with a grid-stabilizing current flow. In one embodiment, the overcurrent is provided instantaneously. The defined provision and control of an instantaneous, i.e., immediate, overcurrent resulting from grid events is a major advantage of the method according to the invention, since a grid event can be counteracted immediately and the grid can be stabilized with highly available current. According to one embodiment, the overcurrent comprises at least one of the following current components: active current component, reactive current component, AC component, DC component, positive-sequence component, negative-sequence component, zero-sequence component, and harmonic / distortion component. Certain events in a network may necessitate responding with different types of overcurrent. For example, when a large load is connected to a network via a transformer, it may be necessary, in addition to the load's active current, to provide a current with a high reactive component to magnetize the transformer. According to one embodiment, the preset overcurrent profile comprises at least two immediately consecutive overcurrent sectors, each with an overcurrent and a respective duration, and the overcurrent of the first overcurrent sector is greater than or equal to the overcurrent of the immediately following overcurrent sector. This embodiment describes how the overcurrent of two successive overcurrent sectors behaves. In this context, it is advantageous if the overcurrent of an overcurrent sector immediately following another overcurrent sector is less than or equal to the current of the preceding overcurrent sector. This prevents damage to a power converter operated according to the invention during overcurrent provision. Furthermore, this embodiment allows an overcurrent to be provided for a longer period. For example, after providing an initial high overcurrent, there may not be sufficient reserve for a further overcurrent of the same magnitude. However, there may be a reserve for a lower overcurrent, which can then be provided.Thus, this embodiment extends the capability of a power converter operated by the method according to the invention to provide an overcurrent. According to one embodiment, the reserve is continuously monitored and an immediately subsequent overcurrent sector of a preset overcurrent profile can be executed depending on the continuously monitored reserve. To determine the magnitude of an overcurrent that can be provided in an overcurrent sector following a previous overcurrent sector, it is necessary to continuously monitor the reserves of the power converter described by the method according to the invention. Continuous monitoring of the power converter's reserves allows it to be determined whether an overcurrent can be provided following a previous overcurrent sector and, if so, how large it is. The power converter's ability to provide an overcurrent is thus maximized or at least increased. According to one embodiment, the immediately successive overcurrent sectors of the permissible overcurrent profile can be executed for a defined duration, depending on the time elapsed after the overcurrent is supplied. Whether an overcurrent can be supplied within an overcurrent sector can be determined either by the reserve of a parameter available in the converter, or, as described in this embodiment, by a specific time period. In this case, for example, a table can indicate that after a certain overcurrent has been supplied, only a specific second overcurrent can be supplied for a certain period, with a higher second overcurrent resulting in an overload of the converter. In this way, an overcurrent that can follow an overcurrent in a previous overcurrent sector can be defined without additional or complex sensors. According to one embodiment, if an immediately subsequent overcurrent sector cannot be implemented, the current is set to or below the continuous current. It is possible that in a given overcurrent profile, the next sector is a non-implementable overcurrent sector. This can occur if the converter's reserve is insufficient to provide this overcurrent sector, or if it has otherwise been determined that the overcurrent in this sector cannot be provided. In this case, the provided current is set to or below a continuous current value. This achieves two advantages. First, current can continue to be provided to a grid or system, thus maintaining grid-serving functionality. Second, the converter's readiness to provide an overcurrent can be quickly restored. According to one embodiment, the reserve comprises: a temperature reserve, which is a distance between the operating temperature of converter or system components and temperature limits; an energy reserve, which is a distance between the available energy in the converter or system and energy limits; a power reserve, which is a distance between the power provided by the converter or system and the maximum power of the converter or system; a current reserve, which is a distance between the current provided by the converter or system and the maximum current of the converter or system; and a voltage reserve, which is a distance between the voltage provided by the converter or system and the maximum voltage of the converter or system. In this embodiment, the reserves provided are characterized by at least one of the converter parameters. In particular, the reserves are determined by hardware limitations. For example, a temperature reserve is assigned to each overcurrent sector. A temperature reserve depends on the temperature of the temperature-critical components both in the converter (especially power semiconductors) and, if applicable, also in the system (e.g., energy storage). The size of the reserve is determined, for example, as a minimum temperature margin to the permissible / defined maximum temperature(s) (temperature condition for providing the overcurrent), depending on the overcurrent to be provided. Another possible reserve is an energy reserve for the instantaneous retrieval of active energy, which is assigned to an overcurrent sector and is characterized by the fact that the energy state on the DC side of the converter system has a minimum energy distance to the maximum and minimum energy state limits (energy availability condition for providing the overcurrent). Another possible reserve is a power reserve, which is assigned to each overcurrent sector and is characterized by the fact that the current has a minimum power margin to the maximum and minimum power limits (power condition for providing the overcurrent). Another possible reserve is a current reserve, which is assigned to each overcurrent sector and is characterized by the fact that the current has a minimum current distance to the maximum and minimum current limits (current condition for providing the overcurrent). Another possible reserve is a voltage reserve, which is assigned to each overcurrent sector and is characterized by the fact that the voltage has a minimum voltage difference to the maximum and minimum voltage limits (voltage condition for providing the overcurrent). Furthermore, it is possible to use hysteresis curves for the reserve instead of fixed values. These allow for greater safety in providing the overcurrent. Likewise, a margin must be maintained between the reserve and the minimum or maximum limits of an operating parameter. For example, if an energy reserve becomes too large, it can lead to an overload of the power converter, with undesirable side effects. According to one embodiment, after the overcurrent is provided, a preset temperature reserve is achieved by limiting the electrical power or current of the converter to a continuous power and / or current, preferably to a preset power or current, or by providing an active cooling system with a cooling capacity higher than the cooling capacity when the continuous current is provided, or by a combination of the foregoing. This embodiment examines the temperature reserve in more detail. In particular, it specifies an exemplary way in which a temperature reserve can be restored after an overcurrent has been applied. According to this embodiment, this can be achieved by limiting the power or current of the converter to a continuous power and / or current. The cooling capacity of a converter is conventionally dimensioned for a continuous power and / or current of the converter, so limiting this leads to a reduction in the converter temperature, thus restoring a temperature reserve. It is also possible to limit the power / current to a lower value than the continuous power / current, so that the temperature reserve is restored even more quickly. This can mean that maximum power is provided while simultaneously maintaining the temperature reserve.Furthermore, an additional active cooling system, which is rarely or never needed during normal operation, can be activated to provide increased cooling capacity and restore the temperature reserve. It is also possible to activate both of the aforementioned options simultaneously. This combination allows for an even faster restoration of the temperature reserve. According to one embodiment, the energy gap for an energy reserve is created before and after the overcurrent is provided by recharging an energy storage device of the converter system, via which electrical active energy is exchanged between the energy storage device and the power grid, with a current and active power that is less than or equal to the continuous current and / or the continuous power of the converter; or recharging the energy storage device of the converter system, via which electrical active energy is exchanged between the energy storage device and a DC source or DC sink, with a current and active power that is less than or equal to the continuous current and / or the continuous power of the converter; or shifting the operating point of the DC source or DC sink.the DC sink to values ​​suitable for maintaining the energy reserve, wherein the resulting current and active power is less than or equal to the continuous current and / or continuous power of the converter, or by a combination of these methods. This embodiment examines the energy reserve in more detail. The energy reserve can be achieved, in particular, by limiting the exchanged power / current between the energy storage device, the power grid, and / or the DC source or DC sink to a continuous power / current level. This prevents the converter from converting too much power, thus ensuring that an energy reserve remains available within the system. According to one embodiment, the voltage difference for a voltage reserve is created before and after the overcurrent is supplied by bringing the electrical voltage of the converter to values ​​which have the voltage difference necessary for reserve purposes from a minimum and a maximum limit. In this embodiment, the voltage reserve is explained in more detail. The voltage reserve can, for example, be based on a DC voltage at the converter's intermediate circuit or on a supplied AC voltage. Furthermore, it is possible for the reserve to be stored in a short-term energy storage device, such as an ultracapacitor or supercapacitor, which is connected to the converter, for example, via a DC-DC converter. A certain voltage level must be maintained as a reserve with respect to the intermediate circuit voltage to ensure sufficient overcurrent is available, since the intermediate circuit voltage drops when the overcurrent is supplied.Furthermore, a reserve must be maintained with regard to the DC link voltage, such that the DC link voltage is not at a maximum value and can still rise safely should a negative overcurrent be supplied, i.e., power be drawn by the converter operated with the method according to the invention. Should the DC link voltage fall below a certain value, the converter may switch off. Likewise, the converter will switch off if the DC link voltage rises above a certain value. Regarding the supplied AC voltage, this embodiment can also provide a reserve. In a voltage-regulating converter, a voltage can be provided that does not correspond to the maximum possible adjustable voltage, but is reduced compared to this maximum voltage. This ensures that, if higher power is required, sufficient reserve is available to increase the supplied AC voltage. According to one embodiment, when restoring the current reserve for a renewed overcurrent, a prioritization can be made between the individual reserves, temperature reserve, energy reserve, power reserve, and voltage reserve, wherein the prioritization depends on the availability of the individual reserves or the prioritization depends on the size of the reserve, with the restoration of the temperature reserve preferably being given a higher priority than the restoration of the other reserves. In this embodiment, temporal prioritization is particularly important. This means that a temperature reserve is preferably restored first, before other reserves are restored. Prioritizing the temperature reserve is advantageous because it depends, for example, on the maximum permissible temperature of the individual components of the power converter and is therefore of high importance for providing an overcurrent. According to one embodiment, a status signal is generated and sent, which reflects the state of the available reserves or the readiness of the power converter to provide the overcurrent. The status signal can be sent to an operator of the plant, the system, or a grid operator, so that the information that an overcurrent can be provided is known. This is particularly useful when the power converter is operated to stabilize grids by providing market-based grid system services. In this way, it is known whether the power converter and other power converters operated using the method according to the invention can contribute to grid stabilization or whether other stabilization methods must be used. According to one embodiment, the transition from the current limit of an overcurrent sector to the current limit of an immediately following overcurrent sector occurs according to an adjustable time constant. The time constant between immediately successive overcurrent sectors can be zero or have a specific time value. "Immediately" means that no other overcurrent sectors exist between the first and the immediately subsequent overcurrent sector. If the time constant is set to zero, meaning that immediately successive overcurrent sectors follow one another without delay, overcurrent can be provided as quickly as possible, corresponding to the overcurrent sectors. In some cases, however, it may be useful to establish an interval without providing an overcurrent between overcurrent sectors. During this interval, for example, the state of a connected power grid can be observed, and if a subsequent overcurrent sector is no longer required, normal operation can be resumed. Alternatively, a subsequent overcurrent sector can be modified.For example, a lower overcurrent than originally planned can be provided. This allows the overcurrent capability to be provided more quickly due to the lower overcurrent and the reduced load on the converter, as reserves are restored more rapidly. Furthermore, an adjustable time constant greater than zero allows for a smoother transition between significantly different current amplitudes in successive overcurrent sectors. While an abrupt change in current amplitude can lead to undesirable side effects, these are reduced with a smooth transition. In summary, a time constant of zero allows for faster provision of more overcurrent, while a time constant greater than zero allows for more targeted provision of overcurrent. According to one embodiment, the defined current limits of the overcurrent sectors can be higher than the continuous operating value of the converter. In this way, a short-term overcurrent can be provided that exceeds the converter's continuous operating capability and consequently counteracts a grid event even more effectively. This is possible because a continuous operating value is calculated, for example, with a safety factor. Alternatively, the conventional limitation of the continuous operating value can be achieved via a component other than the converter bridge, such as the heat dissipation value of a heat sink. However, short-term heat generation exceeding this value can be tolerated. According to the inventive method, a reserve is restored after the overcurrent has been provided, so that only reversible exceedances of permissible continuous operating values ​​are targeted. According to one embodiment, the current limit and duration of immediately successive overcurrent sectors of an overcurrent profile depend on changing SdL market conditions and / or the expected lifetime of the components of the power converter system. The provision of grid support or grid stabilization functionalities may be incentivized through market instruments via the provision of excess current in an overcurrent sector or immediately consecutive overcurrent sectors, and the provision of such functionalities may be monetarily compensated or mandated by regulations. In this case, the provision of excess current in immediately consecutive overcurrent sectors may be aligned with this compensation or regulatory requirements. For example, if compensation is paid only for a small excess current, the excess current may be limited to this amount, even though physical limitations of the power converter or grid events would allow or necessitate a larger excess current. Furthermore, providing an overcurrent, for example due to higher temperature fluctuations in the components, can limit the lifespan of a power converter. Therefore, an overcurrent can be set for overcurrent sectors in such a way that a power converter operated in this manner achieves the expected or required lifespan. According to one embodiment, the power converter parameters are determined either directly or indirectly through measurement, or indirectly calculated from other quantities or using a model. Sensors or observers can be used for this purpose. It is possible to determine the power converter parameters via direct measurements, such as current, or via indirect measurements, such as the temperature rise of individual components. Both methods offer advantages over the other. For example, direct measurement requires little further processing of the measured values. Indirect measurement allows for inferences about values ​​that are not directly measured but are calculated from measured values ​​or obtained using a model, based on a direct measurement of another value. According to one embodiment, the current limiting is achieved by voltage control, in particular via a virtual impedance and / or a pulse width limiting. Current limiting primarily protects against overcurrents and resulting damage to components, thus increasing the safety of electronic systems. One example of this is virtual impedance, which enables effective current limiting. Another example of current limiting, either as a supplement or on its own, is pulse width modulation (PWM). Pulse width modulation limits the time a semiconductor switch is in the conducting state using a pulse-width modulation signal. By alternately switching the semiconductor switch between conducting and non-conducting, the current can be maintained at a specific level. According to one embodiment, the additional electricity provided includes one or more grid system services. The provision of additional power, encompassing one or more grid system services such as short-circuit current, angle-of-change power, and RoCoF (rate of change of frequency) power, offers significant benefits for grid stability and resilience. Short-circuit current supports grid voltage and aids in fault detection and isolation, minimizing the impact of short circuits. Angle-of-change power stabilizes the grid during transient events and prevents generator drift. RoCoF power supports frequency stability during sudden load changes or generator failures, which is particularly important in grids with a low proportion of synchronous generators, which have less inertia. Overall, the integration of these system services improves grid reliability and resilience to disturbances, ensuring stable and safe operation. According to one embodiment, the DC side of the power converter comprises a DC source or DC sink, a short-term energy storage device and / or a long-term energy storage device. Integrating a DC source or sink, a short-term energy storage device (such as ultracapacitors), and / or a long-term energy storage device (such as batteries) on the DC side of the power converter offers numerous advantages. DC sources and DC sinks, which can include PV modules, fuel cells, electrolyzers, and wind turbines in addition to those mentioned above, can be used in the inventive method to provide current, power, and / or energy reserves. For example, providing power via fuel cells as a DC source can replenish reserves that were previously depleted when an overcurrent was supplied. Conversely, short-term energy storage devices can be charged by the power converter at times when reserves are being replenished, ensuring that the reserve is sufficiently large when an overcurrent is subsequently supplied. According to one embodiment, the power converter is designed to carry a temporarily higher current compared to the continuous current. This allows for greater operational flexibility, as short-term load peaks can be handled efficiently without oversizing the entire system. One way to provide overcurrent capability is, for example, to maintain a temperature reserve to ensure that individual components of the power converter do not overheat. According to one embodiment, the power converter system can include an active cooling system for the temperature-critical components in the power converter and / or in the power grid. A power converter system that includes an active cooling system for temperature-sensitive components offers advantages, particularly when supplying a higher current for short periods than the continuous current. Active cooling ensures that the temperature reserve can be restored more quickly, allowing the components to return to their normal operating temperature range faster, which further improves operational readiness and component lifespan. Overall, such a cooling system increases the power converter's performance and stability, which is especially beneficial in applications with variable load requirements. BRIEF DESCRIPTION OF THE FIGURES The invention will now be further explained and described with reference to exemplary embodiments illustrated in the figures. Fig. 1 shows an exemplary sequence of an overcurrent supply according to the method according to the invention, Fig. 2 shows another exemplary sequence of an overcurrent supply according to the method according to the invention, Fig. 3 shows a flowchart of the method according to the invention, Fig. 4 shows a flowchart according to an embodiment of the method according to the invention, and Fig. 5 shows a flowchart according to an embodiment of the method according to the invention. FIGURE DESCRIPTION Fig. 1 shows an example of an overcurrent supply process. First, a current with ήR as its amplitude is supplied by a power converter operated according to the inventive method. It should be noted that the supplied current with ήR as its amplitude allows the supply of an overcurrent in the form of an overcurrent profile; in other words, a reserve is large enough to supply an overcurrent according to an overcurrent profile. On the horizontal time axis, a grid event occurs at t0, which is detected by a power converter or a higher-level control system. In response to this detection, an overcurrent of magnitude ή1 is supplied between t0 and t1, i.e., in the time interval T1, whereby the supply of a specific overcurrent in a time interval is also referred to as an overcurrent sector.At time t1, the overcurrent event has either ended or there is no longer a reserve available to provide the overcurrent, so the system reverts to providing the initial îR. ​​Subsequently, according to the invention, the reserve is restored by providing the îR. Fig. 2 shows an example of another overcurrent supply process. First, a current with ήR as its amplitude is supplied by a power converter operated according to the inventive method. It should be noted that the supplied current with ήR as its amplitude allows for the provision of an overcurrent in the form of an overcurrent profile; in other words, a reserve is large enough to provide an overcurrent according to an overcurrent profile. On the horizontal time axis, a grid event occurs at t0, which is detected by a power converter or a higher-level control system. In response to this detection, an overcurrent of magnitude ή1 is supplied between t0 and t1, i.e., in the time interval T1. In contrast to the process shown in Fig. 1, the grid event does not end at t1, and the reserve for providing an overcurrent is not exhausted.The converter now provides an overcurrent with a current amplitude of î2 in an overcurrent sector immediately following the first overcurrent sector during the time interval T2, i.e., in the interval between t1 and t2. The same occurs in the overcurrent sector immediately following the second overcurrent sector during the time interval T3, with an overcurrent of amplitude î3 provided. After the third overcurrent sector, the reserve is exhausted, so no further overcurrent can be provided. The current provided in the time interval TN is now set to a continuous current with current amplitude îNo and will be provided as long as the grid event persists or until, for example, other instructions are sent to the converter. Fig. 3 shows a flowchart of the method according to the invention. In step S10, a reserve is maintained, such as a temperature reserve for the individual components of a power converter. In step S20, it is then checked whether a grid event has occurred or whether an overcurrent is being or has been provided as a result of a grid event. If no grid event requiring the provision of an overcurrent has occurred, the method returns to step S10 (S20:-). However, if a grid event requiring the provision of an overcurrent has occurred (S20:+), the method continues with step S30. An overcurrent, according to an overcurrent profile that can be determined by the grid event, is provided in the form of an overcurrent sector, whereby the duration and amplitude of the provided overcurrent can be determined by the grid event, a preset, or the available reserve.Once the overcurrent has been provided downstream of the overcurrent sector, the procedure returns to step S10. Fig. 4 shows a flowchart of the method according to one embodiment of the invention. In step S10, a reserve is maintained, such as a temperature reserve for the individual components of a power converter. Then, in step S20, it is checked whether a grid event has occurred or whether an overcurrent is being or has been provided as a result of a grid event. If no grid event has occurred or whether an overcurrent has been provided as a result of a grid event requiring the provision of an overcurrent, the method returns to step S10 (S20:-). However, if a grid event has occurred or an overcurrent has been provided as a result of a grid event requiring the provision of an overcurrent (S20:+), the method continues with step S31.An overcurrent according to an overcurrent profile, which can be based on the grid event, is provided in the form of an overcurrent sector, whereby the duration and amplitude of the provided overcurrent can be based on the grid event, a preset, or the available reserve. Once the overcurrent has been provided after the overcurrent sector, the procedure continues with step S40. In step S40, it is checked whether the reserve has been exhausted, i.e., whether no further overcurrent can be provided without, for example, irreversibly damaging the converter, or whether the grid event has ended. If this is the case (S40:-), the procedure returns to S10 and the reserve is restored and maintained. If this is not the case, the procedure proceeds to step S50 and provides an overcurrent after a subsequent overcurrent sector. After this second overcurrent sector has elapsed, the procedure returns to step S40 and the same test is performed. Figure 5 shows a flowchart of the method according to one embodiment of the invention. It differs from the method shown in Figure 4 in step S41. In step S41, it is checked whether the reserve has been exhausted, i.e., whether no more overcurrent can be provided without, for example, irreversibly damaging the converter or the grid event ending. If the reserve is exhausted and the grid event has ended (S41:-), the method returns to S10, and the reserve is restored and maintained. If the grid event has not ended but the reserve is exhausted (S41:+-), the method continues with step S60, in which the maximum permissible continuous current of the inverter is provided until the grid event ends. If neither of these conditions is met (S41:+), the method continues with step S50, and an overcurrent is provided after a subsequent overcurrent sector.After this second overcurrent sector has elapsed, the procedure returns to step S40 and the same test is performed. REFERENCE MARK LIST S10-S60 steps

Claims

Method for operating a power converter, wherein the method comprises: providing an overcurrent, wherein the overcurrent is greater than a continuous current of the power converter and is within the limits of a defined overcurrent profile, wherein (I) prior to providing the overcurrent, maintaining a reserve (S10), which is formed by at least one distance of at least one power converter parameter to defined parameter limits, and depending on the reserve, one or more preset overcurrent profiles are permissible, (II) providing (S30) the overcurrent for a period defined by the respective permissible overcurrent profile, wherein the resulting current is limited to the current limits of the respective permissible overcurrent profile, and (III) after providing the overcurrent (S10), restoring the conditions for providing the overcurrent. Method according to claim 1, wherein the power converter comprises at least one power conversion stage. Method according to claim 1 or 2, wherein the provision of the overcurrent is carried out as a result of network events (S20), such as changes in voltage angle, voltage frequency and voltage amplitude, load changes, switching operations in the power network. Method according to one of the preceding claims, wherein the power converter is a voltage-regulating power converter. Method according to one of the preceding claims, wherein the overcurrent is provided instantaneously. Method according to one of the preceding claims, wherein the overcurrent comprises at least one of the current components, active current component, reactive current component, alternating current component, direct current component, positive-sequence component, negative-sequence component, zero-sequence component and harmonic / distortion component. Method according to one of the preceding claims, wherein the preset overcurrent profile comprises at least two immediately consecutive overcurrent sectors with respective overcurrent and respective duration, and the overcurrent of the first overcurrent sector is greater than or equal to the overcurrent of the immediately following overcurrent sector. Method according to one of the preceding claims, wherein the reserve is continuously monitored and an immediately subsequent overcurrent sector of a preset overcurrent profile can be executed depending on the continuously monitored reserve. Method according to one of the preceding claims, wherein the immediately successive overcurrent sectors of the permissible overcurrent profile can be executed for the respective defined duration depending on the time progressing after the overcurrent has been provided. Method according to one of the preceding claims, wherein, if an immediately subsequent overcurrent sector is not feasible, the current is set to or below the continuous current. A method according to any of the preceding claims, wherein the reserve comprises: a temperature reserve, which is a distance between the operating temperature of converter or system components and temperature limits; an energy reserve, which is a distance between the available energy in the converter or system and energy limits; a power reserve, which is a distance between the provided power of the converter or system and the maximum power of the converter or system; a current reserve, which is a distance between the provided current of the converter or system and the maximum current of the converter or system; a voltage reserve, which is a distance between the provided voltage of the converter or system and the maximum voltage of the converter or system. A method according to any of the preceding claims, wherein, after the overcurrent is provided, a preset temperature reserve is achieved by limiting the electrical power or current of the converter to a continuous power and / or current, preferably to a preset power or current, or by providing an active cooling system with a cooling capacity higher than the cooling capacity when the continuous current is provided, or by a combination of the foregoing. A method according to one of the preceding claims, wherein the energy gap for an energy reserve is created before and after the provision of the overcurrent, by recharging an energy storage device of the converter system, via the converter an electrical active energy is exchanged between the energy storage device and the power grid, with a current and an active power that is less than or equal to the continuous current and / or the continuous power of the converter, or by recharging the energy storage device of the converter system, via the converter an electrical active energy is exchanged between the energy storage device and a DC source or DC sink, with a current and an active power that is less than or equal to the continuous current and / or the continuous power of the converter, or by shifting the operating point of the DC source or DC sink.the DC sink to values ​​suitable for maintaining the energy reserve, wherein the resulting current and the resulting active power are less than or equal to the continuous current and / or the continuous power of the converter, or by a combination of these methods. Method according to one of the preceding claims, wherein before and after the provision of the overcurrent the voltage difference for a voltage reserve is brought about by bringing the electrical voltage of the converter to values ​​which have the voltage difference necessary for reserve purposes from a minimum and a maximum limit. Method according to one of the preceding claims, wherein, when restoring the current reserve for a renewed overcurrent, prioritization can be (temporally) performed between the individual reserves, temperature reserve, energy reserve, power reserve, and voltage reserve, wherein the prioritization depends on the availability of the individual reserves or the prioritization depends on the level of the reserve, wherein preferably the restoration of the temperature reserve is prioritized higher than the restoration of the other reserves. Method according to one of the preceding claims, wherein a status signal is generated and sent which reflects the state of the available reserves or the readiness of the power converter to provide the overcurrent. Method according to one of the preceding claims, wherein the transition of the current limit of an overcurrent sector to the current limit of an immediately subsequent overcurrent sector takes place according to an adjustable time constant. Method according to one of the preceding claims, wherein the defined current limits of the overcurrent sectors may be above the continuous operating value of the power converter. Method according to one of the preceding claims, wherein the current limit and duration of immediately successive overcurrent sectors of an overcurrent profile depend on changed system service market conditions and / or the expected lifetime of the components of the power converter system. Method according to one of the preceding claims, wherein the determination of the converter parameters is carried out either directly or indirectly by measurement or indirectly calculated from other quantities or based on a model. Method according to one of the preceding claims, wherein the current limiting is achieved by voltage control, in particular via a virtual impedance and / or a pulse width limiting. Method according to one of the preceding claims, wherein the provided additional power comprises one or more system services. Method according to one of the preceding claims, wherein the DC side of the power converter comprises a DC source or DC sink, a short-term energy storage device and / or a long-term energy storage device. Method according to one of the preceding claims, wherein the current converter is configured to carry a temporarily higher current compared to the continuous current. Method according to one of the preceding claims, wherein the power converter system may include an active cooling system for the temperature-critical components in the power converter and / or in the power grid. Method according to one of the preceding claims, recording the number of overcurrent events in order to deactivate the overcurrent as required or when a maximum permissible number is exceeded, in order to protect the components.

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