METHOD FOR PROVIDING REGULATION POWER TO AN AC VOLTAGE NETWORK BY MEANS OF A POWER GENERATION PLANT

Description

TECHNICAL AREA OF INVENTION

[0001] The invention relates to a method for providing control power for an alternating current network by means of an energy generation plant with a photovoltaic generator and an energy storage system. STATE OF THE ART

[0002] In an AC power grid configured as a supra-regional interconnected network, deviations of the grid frequency from the nominal AC frequency can occur due to an imbalance between the electrical power supplied and drawn. This imbalance, and thus the frequency deviation, can be counteracted by appropriately adjusting the power supplied or drawn by devices that can supply electrical power to and / or draw power from the AC grid. In particular, at frequencies above the nominal frequency, the supplied power can be reduced or the drawn power increased, while at frequencies below the nominal frequency, the supplied power can be increased or the drawn power reduced.

[0003] The change in the output of a power generation plant in direct or indirect response to a power imbalance in the electricity grid or a resulting frequency deviation is commonly referred to as balancing power. This balancing power is maintained by dedicated grid operating resources as a control reserve and is called upon for a limited period when needed. The energy supplied during the balancing power call is called balancing energy or control work. In AC grids, such as the European interconnected grid, the provision of this balancing power is typically organized in successive and successive stages with different operating modes.

[0004] The first control stage, known as instantaneous control or instantaneous reserve, serves to limit the frequency change rate. In current power grids, instantaneous reserve is implemented more as a grid characteristic than as active control, and is caused by devices that change their output in direct and immediate response to a frequency change. In particular, rotating masses of generators or motors, due to their inertia, produce an instantaneous reserve power that directly counteracts the power imbalance and limits the frequency change rate.

[0005] In the second control stage, the so-called primary control, which serves to maintain frequency and comes into play in the event of a sustained frequency deviation, devices are used that adjust their power output according to a characteristic curve, depending on the deviation of the grid frequency from the nominal frequency. In the third stage, the so-called secondary control, a foreseeable or ongoing power imbalance in the AC grid is proactively counteracted by instructing devices from a higher-level control unit to adjust their electrical power output accordingly. The secondary control provides power and energy to restore the grid frequency to the nominal value and replaces the second stage.

[0006] Devices that exchange electrical power between the AC grid and an energy storage system are known from the prior art. Such devices can be configured to provide second-stage control power, i.e., to react to a power imbalance within the framework of primary control and to adjust the power exchange between the AC grid and the energy storage system accordingly in order to counteract the imbalance. Control power plants thus have the task of providing a fixed amount of control power during a fixed period as needed.

[0007] Photovoltaic systems are also known that are generally operated in such a way that the maximum possible power is drawn from the photovoltaic generators and fed into the AC grid. Due to the volatility and poor predictability of PV power, which can fluctuate significantly with changes in irradiance and is not available at all, particularly at night, photovoltaic systems can currently only contribute to stabilizing the AC grid by providing balancing power to a limited extent. WO 2013 / 041534 A2 discloses a device for providing balancing power. DE 10 2015 101738 A1 discloses a method for operating an energy generation plant. TASK OF INVENTION

[0008] The invention is based on the objective of demonstrating a method for providing control power for an AC power grid by means of an energy generation plant with a photovoltaic generator and a storage unit, with which control power for the stabilization of the AC power grid can be provided cost-effectively and efficiently. SOLUTION

[0009] The problem is solved by a method comprising the features of independent claim 1 and an energy generation plant according to claim 11. Preferred embodiments are defined in the dependent claims. DESCRIPTION OF THE INVENTION

[0010] In a process for providing ancillary services to an AC grid for a predetermined future period, using an energy generation plant, the plant comprises a photovoltaic generator and an energy storage system. The energy generation plant exchanges a total electrical power with the AC grid. The total power exchanged is adjusted based on the current maximum PV power, a predefinable base PV power between zero and the maximum PV power, and the provided or requested ancillary services. The ancillary services range includes a maximum positive and a maximum negative ancillary services range, which can be set by the energy generation plant as deviations from the base total power during the predetermined future period and are adjusted upon request.The maximum positive and maximum negative control power preferably have the same amount, so that a symmetrical control power is provided for the specified future period. The procedure comprises the following steps: . Determination of an optimal control power range for the specified future period, taking into account the current maximum PV power and the current state of charge of the energy storage system; if no control power is required: feeding in a baseline power that includes the PV baseline power; if negative control power is required: reducing the PV power relative to the PV baseline power; and if positive control power is required: drawing power from the battery if the requested positive control power is greater than the difference between maximum PV power and PV baseline power.

[0011] The inventive method enables an energy generation plant to be optimally used for providing control power. Negative control power is achieved by reducing the PV output, which can include feeding power back into the photovoltaic generator. This provides negative control power that can always be at least equal to the rated output of the photovoltaic generator (provided there is a sufficiently powerful connection to the AC grid). Simultaneously, positive control power can be optimally provided by the energy storage system. Because the energy storage system does not have to contribute to negative control power, a large portion of its storage capacity can be reserved for providing positive control power.

[0012] The baseline power output can include battery power for charging the energy storage system if the storage system is capable of being charged. This reduces the baseline power output compared to the PV baseline power output, as some of the PV power is used to charge the energy storage system if it is not fully charged. If negative control power is required and the energy storage system is capable of being charged, the battery power can first be increased to charge the energy storage system before the PV power output is reduced compared to the PV baseline power output. This ensures that the environmentally friendly energy generated by the photovoltaic generator is used optimally for charging the energy storage system.

[0013] In one embodiment of the method, the PV base power can correspond to the PV maximum power. The photovoltaic generator can thus be operated optimally and generate the maximum possible energy in an environmentally friendly manner, as long as the PV power is not reduced to lower the overall output of the energy generation plant for the provision of negative control power.

[0014] In an alternative embodiment of the method, the PV base power can be lower than the PV maximum power, with the PV power being increased relative to the PV base power when positive control power is required. If the requested positive control power is greater than the difference between the PV base power and the PV maximum power, supplementary battery power is drawn from the energy storage system so that the total power output includes the requested positive control power.

[0015] In an advantageous embodiment, the PV base power is between 40% and 60% of the PV maximum power. This means that between 60% and 40% of the PV maximum power is available as additional positive control power.

[0016] In the method according to the invention, the requested control power can be determined as a function of a deviation of an instantaneous frequency from a nominal frequency of the AC grid and / or a rate of change of the instantaneous frequency by means of a characteristic curve. The characteristic curve can be designed such that positive control power is requested when the instantaneous frequency is lower than the nominal frequency and / or the rate of change is negative, and that negative control power is requested when the instantaneous frequency is higher than the nominal frequency and / or the rate of change is positive. This allows the power generation plant to react autonomously to power imbalances in the AC grid, which can manifest themselves in particular as deviations of the grid frequency from the nominal frequency.

[0017] In an alternative embodiment, the required control power can be specified to the power generation plant by a higher-level control system. This allows the power generation plant to be controlled as needed, for example by a grid operator, so that a power imbalance is specifically compensated for by the higher-level control system.

[0018] In this context, the term "provision" is to be understood as an assurance that a standard service offered can be discontinued in the future period and will be discontinued if it is actually requested in the future period.

[0019] In one embodiment of the method, a forecast for the maximum PV output during the specified future period, or a ratio of the PV nominal output to the energy storage nominal output, can be taken into account before the future period in which control power is provided. For example, the higher the current and forecasted maximum PV output, the more control power can be offered; conversely, the control power offered can be limited by the PV nominal output if only this is available for providing negative control power, for example at night when the energy storage is fully charged.

[0020] In one embodiment of the method, the baseline power output corresponds to or is proportional to the PV maximum power output, so that any variations in the PV maximum power output lead to corresponding variations in the baseline power output. In this case, requested balancing power can be provided as a deviation from the PV maximum power output that would be fed into the grid without a balancing power request.

[0021] In an alternative embodiment of the method, the baseline power output has a constant value. If no balancing power is requested and the maximum PV output is greater than the baseline power output, the baseline power output then consists exclusively of PV output. Any difference between the current PV output and the constant baseline power output can then be compensated for by exchanging electrical power with the energy storage system. This makes the behavior of the energy generation plant more predictable, as a defined power exchange with the AC grid takes place at all times, which is particularly independent of any short-term changes in the maximum PV output, such as those caused by weather conditions.

[0022] In one embodiment of the method, the photovoltaic generator and the energy storage device can exchange electrical power with each other and / or bidirectionally with the AC grid. Specifically, the energy generation plant can exchange its total electrical power with the AC grid via exactly one common grid connection point. Alternatively, the photovoltaic generator and the energy storage device can exchange their respective electrical power with the AC grid via different, spatially separated grid connection points.

[0023] It is understood that the photovoltaic generator can comprise a large number of sub-generators, which can be connected to the AC grid via a corresponding number of inverters. Similarly, the energy storage system can comprise a large number of batteries, which are connected to the AC grid via a large number of converters. The photovoltaic generator and the energy storage system can be connected to the AC grid in the same or different local grids, or at the same or different grid levels.

[0024] In an advantageous embodiment of the method, a control unit receives current operating data from the photovoltaic generator and the energy storage system and specifies setpoints for the power to be exchanged for the operation of the photovoltaic generator and the energy storage system. The control unit can be part of the energy generation plant, particularly if it is connected to the AC grid via a single common grid connection point, or it can be arranged at a higher level and connected to the photovoltaic generator and the energy storage system via a communication line. Such a control unit can have a uniform interface to a higher-level control system, which, for example, is responsible for the operation of the entire AC grid and thus represents a grid operator.

[0025] The energy generation plant can have at least two energy storage systems, wherein the photovoltaic generator and the first energy storage system provide control power for primary control of the AC grid, while the second energy storage system provides control power for instantaneous control of the AC grid.

[0026] In particular, the second energy storage system can exchange instantaneous control power with the AC grid via a voltage-sampling inverter. Using this method, the power generation plant is able to contribute optimally to both the instantaneous control and the primary control of the AC grid.

[0027] An energy generation plant for providing control power to an AC grid comprises a photovoltaic generator, an energy storage system, and a control unit. In an energy generation plant according to the invention, the control unit is configured to operate the energy generation plant using a method as described above.

[0028] In one embodiment of the energy generation system, the photovoltaic generator and the energy storage device are connected to the AC grid via a common grid connection point. This grid connection point can include a transformer with one grid-side winding and at least two windings for connecting the photovoltaic generator and the energy storage device. Furthermore, the energy generation system can have multiple photovoltaic generators and / or multiple energy storage devices connected to the grid connection point via a common bidirectional inverter. Preferably, the inverter is connected to the photovoltaic generators or the energy storage devices via individual DC-DC converters.By using a common inverter, both the number of devices required and the cabling effort are reduced, whereby the inverter must be designed for a total power output that is less than the sum of the nominal power outputs of the individual inverters in a power generation plant with the photovoltaic generators and the energy storage systems individually assigned inverters.

[0029] Advantageously, such an energy generation plant includes a control unit that is located within the energy generation plant and can communicate directly with the photovoltaic generator and the energy storage system or with their respective controls.

[0030] In an alternative embodiment of the energy generation plant, the control unit is communicatively connected to the photovoltaic generator and the energy storage system or their controls via an indirect connection through a network, wherein the photovoltaic generator and the energy storage system are connected to the AC grid via different, spatially separated grid connection points.

[0031] The energy generation system can comprise several energy storage devices of different designs. Preferably, at least one of the energy storage devices can comprise a lithium-ion battery, which is characterized by a high energy density. Particularly preferably, at least one further energy storage device can comprise a supercapacitor, which has a lower energy density compared to the lithium-ion battery but a higher power density. An energy generation system constructed in this way can provide primary control power via the lithium-ion battery in conjunction with the photovoltaic generator and also contribute to instantaneous control via the supercapacitor.

[0032] In a further embodiment of the invention, a control power range can be defined for a predetermined future period, wherein the control power is provided by a power generation plant with a photovoltaic generator and an energy storage system, and the control power range has a baseline total power, a maximum positive control power, and a maximum negative control power. This embodiment can include the following steps: Determining the total base power as a function of the current maximum PV power of the photovoltaic generator and the state of charge of the energy storage system, determining the maximum positive control power as a function of the state of charge of the energy storage system, determining the maximum negative control power as a function of the maximum PV power and a maximum nominal PV power that can be fed back into the photovoltaic generator.

[0033] The baseline power and the maximum positive control power can be determined in such a way that it is excluded that a request for the maximum positive control power for the specified future period leads to a complete discharge of the energy storage system, whereby the baseline power is determined by a difference less than the current PV maximum power, the difference being greater the more the state of charge of the storage system deviates from a full charge state.

[0034] The invention can be further characterized by the following features: To provide a defined, maximum positive control power that is reliably available at all times, it is advantageous to operate the energy storage system of the power generation plant permanently at full charge. To ensure that the power generation plant achieves maximum negative control power even with a fully charged storage system and at night, energy can be fed back into the photovoltaic generator, whereby the possible feed-in power should be at least equal to the battery capacity. Available PV power is used to charge the storage system whenever possible and to maintain the highest possible state of charge. The invention allows for the full utilization of the energy storage capacity with a storage system that is almost always fully charged and full availability of the maximum positive and negative control power.By integrating the photovoltaic generator into the method according to the invention, a symmetrical control power can be provided that is at least twice as high as could be achieved with a corresponding energy storage device alone. BRIEF DESCRIPTION OF THE FIGURES

[0035] The invention will now be further explained and described with reference to exemplary embodiments shown in the figures. Fig. 1 shows an energy generation plant according to the invention comprising a PV generator, an energy storage device, and a control unit; Fig. 2 shows a first time course of electrical power outputs of the PV generator, the energy storage device, the energy generation plant, and a state of charge of the energy storage device; Fig. 3 shows a second time course of electrical power outputs of the PV generator, the energy storage device, the energy generation plant, and a state of charge of the energy storage device; Fig. 4 shows a second time course of electrical power outputs of the PV generator, the energy storage device, the energy generation plant, and a state of charge of the energy storage device. FIGURE DESCRIPTION

[0036] Fig. 1 Figure 2 shows an energy generation plant with a photovoltaic generator 4 and an energy storage system 5.

[0037] Depending on the current solar irradiance, the photovoltaic generator 4 can generate a maximum power output (P_MPP). An inverter 4a extracts a current PV power output (P_PV) from the photovoltaic generator 4, which can be varied between zero and the maximum power output (P_MPP) by adjusting the voltage at the photovoltaic generator 4. The PV power output (P_PV) can also be negative by feeding electrical power back into the photovoltaic generator 4. Conventional PV modules are easily capable of absorbing power outputs on the order of their nominal power output (P_Peak). The inverter 4a converts the PV power output (P_PV), which is exchanged as direct current (DC) with the photovoltaic generator 4, into alternating current (AC) and transmits the PV power output (P_PV) to an AC grid 1 via a grid connection point 1a.

[0038] The energy storage device 5 is connected to an inverter 5a, which exchanges electrical battery power P_Batt with the energy storage device 5, converts it into alternating current, and exchanges this battery power P_Batt with the AC grid 1 via a grid connection point 1b. The energy storage device 5 typically has a specific storage capacity and a current state of charge (SOC), where the state of charge (SOC) is usually expressed as a percentage of the storage capacity, indicating how much energy is currently stored in the energy storage device. A SOC of zero means that the energy storage device 5 is discharged, and a SOC of 100% indicates that the energy storage device 5 is fully charged.

[0039] The energy generation plant 2 exchanges a total electrical power P_Netz with the AC grid 1. The total power P_Netz consists of the PV power P_PV and the battery power P_Batt and can take on positive or negative values.

[0040] The grid connection points 1a and 1b can be replaced by a single, shared grid connection point, meaning that the power generation plant 2 can exchange its total power with the AC grid 1 via a single, shared grid connection point. A shared grid connection for multiple bidirectional inverters 4a and / or converters 5a can include a transformer comprising one grid-side winding and multiple windings for connecting the equipment of the power generation plant 2. This allows multiple devices involved in exchanging electrical power with the grid to be directly connected to the transformer. The transformer must be designed for a rated power that includes only the rated power of the photovoltaic generator 4 and an overload capacity for (short-term) retrieval of positive control power from the energy storage system 5.

[0041] A control unit 9 is communicatively connected to the photovoltaic generator 4 and the energy storage system 5, or to the inverter 4a and the converter 5a. Via this connection, the control unit 9 receives operating data from the photovoltaic generator 4 and the energy storage system 5. Conversely, the control unit 9 sends setpoint values ​​for the PV power P_PV and the battery power P_Batt to the photovoltaic generator 4 and the energy storage system 5, or to the inverter 4a and the converter 5a (or their respective control devices).

[0042] The photovoltaic system formed by the photovoltaic generator 4 and the inverter 4a can comprise a multitude of subunits, which are not shown in detail here. In particular, it can be a photovoltaic system with a multitude of inverters 4a and a corresponding number of photovoltaic generators 4, which are controlled by a common system controller. Likewise, the energy storage system formed by the energy storage unit 5 and the converter 5a can comprise a multitude of subunits, which are not shown in detail here. In particular, it can be a storage system with a multitude of converters 5a and a corresponding number of energy storage units 5, which are controlled by a common system controller.The energy generation plant 2 can, in particular, comprise several energy storage devices 5 of different types, which are connected to the AC grid 1 via several converters 5a at a common grid connection point 1b. Possible storage types include, in particular, electrochemical storage devices, i.e., lead-acid, lithium-ion, or flow batteries and so-called supercapacitors (supercaps), as well as other energy storage devices suitable for providing ancillary services, such as pumped storage.

[0043] Alternatively or additionally, the energy generation plant 2 can comprise several PV generators 4 and / or energy storage units 5 of different types. Several PV generators 4 and / or energy storage units 5 can be connected to a common inverter via individual DC / DC converters and exchange electrical power bidirectionally with the AC grid 1 via this inverter.

[0044] In energy generation plant 2, the control unit 9 communicates with the respective system controllers of the photovoltaic system and the storage system, exchanging the relevant operating data P_MPP, SOC, and the setpoint values ​​P_PV, P_Batt. Energy storage units 5 of different types within energy generation plant 1 are operated with different parameters. For example, a first energy storage unit 5 with a lithium-ion battery, which has a high energy density, is operated differently than a second energy storage unit 5 with a supercapacitor, which has a comparatively low energy density but a significantly higher power density.

[0045] In principle, the control unit 9 can also be implemented as part of the photovoltaic system or the storage system, allowing the respective operating data to be exchanged directly between the photovoltaic system and the storage system. In particular, the control unit 9 can be combined with the control unit of the inverter 4a and receive the operating data directly from the storage system. This can be advantageous because the inverter 4a, by design, already incorporates rapid measurement of frequency, current, and power, thus enabling a faster response than via a control unit 9 located elsewhere.

[0046] In a specific embodiment of the method, current operating data of the photovoltaic generator, in particular the maximum PV output as well as the current and, if applicable, a planned PV output, and of the energy storage system, in particular the state of charge as well as the current and, if applicable, a planned battery output, can be directly exchanged between the photovoltaic generator and the energy storage system. The corresponding control systems of the photovoltaic generator and the energy storage system are then configured to operate autonomously on the one hand and, on the other hand, to take into account the behavior of the other system in order to provide the control power.

[0047] Additionally, the control unit 9 can obtain information about the current operating state of the AC grid 1. In particular, the control unit can detect or receive the grid frequency f_netz of the AC grid 1, possibly also from the inverter 4a. The grid frequency f_netz is, among other things, an indicator of the power balance in the AC grid 1 and can be used by the control unit 9 to determine the need for control power to be provided by the power generation plant 2, in particular by varying the total power P_netz exchanged between the power generation plant 2 and the AC grid 1 in response to deviations of the grid frequency f_netz from a nominal frequency of the AC grid 1.

[0048] Alternatively or additionally, the control unit 9 can be connected to a higher-level control system and instructed by this system to vary the total exchanged power P_Netz to a predetermined extent and to provide the specified control power. Furthermore, the control unit 9 can be configured to inform a higher-level control system how much control power can be provided by the power generation plant 2 within a specified future period.

[0049] The grid connection points 1a and 1b can be located at a distance from each other, in particular in the same or different local grids or on the same or different grid levels. Communication between the control unit 9 and the equipment of the power generation plant 2, as well as between the control unit 9 and a higher-level control system, can each take place via a direct cable connection or indirectly via a network.

[0050] Fig. 2The upper part shows an exemplary time course of electrical power P of the photovoltaic generator 4 (PV maximum power P_MPP and PV power P_PV), the energy storage system 5 (battery power P_Batt), and the power generation plant 2 (total power P_Grid). The lower part shows a corresponding time course of the state of charge (SOC) of the energy storage system 5. The units on the axes are for illustrative purposes only and should be scaled according to the specific embodiment of the power generation plant 2. For example, time t can be given in minutes and power P in kilowatts or megawatts.

[0051] At time t0, the photovoltaic generator 4 is operated such that the PV power P_PV essentially corresponds to the PV maximum power P_MPP, i.e., the photovoltaic generator 4 produces the maximum possible power P_MPP, which, less any losses, is fed into the grid as PV power P_PV via the inverter 4a. The battery power P_Batt is zero at time t0, so the total power P_Grid of the energy generation plant 2 corresponds to the PV power P_PV (less any losses).

[0052] A variation in the PV maximum power P_MPP, for example due to a change in the irradiance on the photovoltaic generator 4, can be passed through to the AC grid 1 as a variation in the total power P_Netz. Alternatively, the total power P_Netz of the energy generation plant 2 can be kept constant at a base total power P_Netz_0 by adjusting the PV power P_PV to follow the variation in the PV maximum power P_MPP and compensating for the difference between the PV power P_PV and the constant base total power P_Netz_0 by appropriately exchanging battery power P_Batt with the energy storage system 5.

[0053] In the example according to Fig. 1The variation in the maximum PV power P_MPP, and thus also the PV power P_PV, during the period t0 to t1 is compensated for by a counteracting battery power P_Batt, such that the total power P_Netz is kept constant at the baseline total power P_Netz_0. As a result, the state of charge (SOC) of the energy storage system 5 changes only slightly. A constant, guaranteed total power P_Netz for a given period is particularly advantageous for the grid operator's ability to plan and control the operation of the AC grid 1.

[0054] During the period t1 to t2, positive control power is requested from the energy generation plant 2 and provided by increasing the total power P_Grid. This request arises, for example, due to a decrease in the grid frequency, indicating a power deficit in the AC grid 1, or due to an explicit request from a higher-level control system. Since the PV power P_PV already corresponds to the PV maximum power P_MPP and therefore cannot be increased, the increase in the total power P_Grid by the positive control power is achieved by increasing the battery power P_Batt. The state of charge (SOC) of the energy storage system 5 decreases accordingly. During the period t1 to t2, variations in the PV maximum power P_MPP can also be compensated for by corresponding changes in the battery power P_Batt to maintain a constant total power P_Grid. In the example according to Fig. 1The total power P_Netz in the period t1 to t2 corresponds to the sum of the basic total power P_Netz_0 and the requested positive control power.

[0055] At time t2, the state of charge (SOC) of energy storage 5 is close to zero, meaning that no positive control power can be provided beyond time t2. Furthermore, the positive control power requested between t1 and t2 should not have been higher; otherwise, energy storage 5 would have been empty before time t2, and the control power would have been prematurely lost. In other words, the maximum possible positive control power for this period was requested from energy generation plant 2 between t1 and t2.

[0056] During the period t2 to t3, negative control power is requested from the energy generation plant 2 and provided by reducing the total power P_Grid. This request arises, for example, due to an increase in the grid frequency, indicating a power surplus in the AC grid 1, or due to an explicit request from a higher-level control system. The PV power P_PV remains at the PV maximum power P_MPP, and the reduction of the total power P_Grid by the negative control power is achieved by reducing the battery power P_Batt. The total power P_Grid is reduced relative to the PV power P_PV by feeding the battery power P_Batt into the energy storage system 5. The state of charge (SOC) of the energy storage system 5 increases accordingly.Even during the period t2 to t3, variations in the PV maximum power P_MPP can be compensated for by corresponding changes in the battery power P_Batt in order to feed a constant total power P_Grid into the grid. In the example according to... Fig. 1 The total power P_Netz in the period t2 to t3 corresponds to the sum of the basic total power P_Netz_0 and the requested negative control power.

[0057] At time t3, the state of charge (SOC) of energy storage device 5 has returned to its initial value at time t0 or t1. In principle, negative control power can be provided beyond time t3, particularly until the state of charge (SOC) of energy storage device 5 reaches 100% and the energy storage device 5 can no longer absorb any power.

[0058] The behavior according to Fig. 1The system can be optimized to offer symmetrical control power over a future period and to provide it as required. This means, for example, that a decision is made before time t1 to offer a specific level of control power for the period t1 to t2. Since it is not predictable whether this control power will be requested as positive or negative control power during the period t1 to t2, the state of charge (SOC) of energy storage 5 must be approximately 50% at time t1 to be able to deliver maximum symmetrical control power—that is, positive or negative control power of the same amount—for the entire period t1 to t2. With a state of charge (SOC) greater than 50%, less energy is available for negative control power than for positive control power, and vice versa. Therefore, the maximum control power that can be offered is reduced if the state of charge (SOC) at time t1 deviates from 50%.

[0059] Fig. 3The upper part shows another exemplary time course of the electrical power P_MPP, P_PV, P_Batt and P_Netz, and the lower part shows a corresponding time course of the state of charge (SOC).

[0060] At time t0, the PV power P_PV essentially corresponds to the PV maximum power P_MPP and is fed into the grid via inverter 4a. The total power P_Grid of the energy generation plant 2 corresponds to the PV power P_PV, since the battery power P_Batt is zero at time t0. A variation in the PV maximum power P_MPP can be compensated for by corresponding changes in the battery power P_Batt in order to maintain the total power P_PV during the period t0 to t1 at a constant baseline power P_Grid_0. The state of charge (SOC) of the energy storage system 5 varies accordingly. Alternatively (not shown here), a variation in the PV maximum power P_MPP can be passed through to the AC grid 1 as a variation in the total power P_Grid.

[0061] During the period t1 to t2, negative control power is requested from the energy generation plant 2 and provided by reducing the total grid power P_Grid. To achieve this, power P_Batt is initially fed into the energy storage system 5 during the period t1 to t1a until it is fully charged and reaches a state of charge (SOC) of 100%. During the period t1a to t2, the energy storage system 5 can no longer accept any more battery power P_Batt. The total grid power P_Grid is then reduced by the requested negative control power by reducing the PV power P_PV relative to the PV maximum power P_MPP. Since the sum of the base grid power P_Grid_0 and the negative control power is negative during the period t1a to t2, the PV power P_PV also becomes negative by feeding electrical power back into the photovoltaic generator 4. Any variations in the PV maximum power P_MPP have no effect during the period t1a to t2.The state of charge (SOC) of energy storage unit 5 remains at 100%.

[0062] During the period t2 to t3, positive control power is requested from the energy generation plant 2 and provided by increasing the total power P_Grid. The PV power P_PV is adjusted to the PV maximum power P_MPP. The increase in the total power P_Grid by the positive control power compared to the baseline total power P_Grid_0 at time t1 is achieved by increasing the battery power P_Batt, i.e., power is drawn from the energy storage system 5. The state of charge (SOC) of the energy storage system 5 decreases accordingly. Variations in the PV maximum power P_MPP, and thus the PV power P_PV, can be compensated for by corresponding counteracting changes in the battery power P_Batt to keep the total power P_Grid constant.

[0063] At time t3, the state of charge of energy storage unit 5 is approximately 50%, meaning that further positive control power can be provided beyond time t3. Alternatively, twice as much positive control power could have been provided during the period t2 to t3 as was actually provided.

[0064] In one embodiment according to Fig. 3Thus, almost the entire storage capacity of the energy storage system 5 is available for providing positive control power, since the provision of negative control power is, if necessary, achieved entirely by changing the PV power output P_PV. Therefore, the state of charge (SOC) of the energy storage system 5 can advantageously be close to 100% at time t1 to ensure a maximum positive portion of symmetrical control power for the period t1 to t2, while a reserve capacity of the energy storage system 5 can be maintained to compensate for fluctuations in the PV maximum power output P_MPP. The maximum negative portion of the symmetrical control power is limited only by the nominal PV power output P_Peak of the photovoltaic generator 4. Feeding power back into the photovoltaic generator 4 at the level of the PV nominal power output P_Peak is possible at any time, especially at night.

[0065] In comparison to the embodiment according to Fig. 1, in which the energy storage device 5 must be able to realize the required control power both positively and negatively on its own, can in the embodiment according to Fig. 3 With the same energy storage system 5, a larger symmetrical control power can be offered, which can be up to twice as large if the PV nominal power P_Peak corresponds at least to the maximum positive control power that can be offered for a future period, which in turn results from the quotient of the storage capacity of the energy storage system 5 and the duration of the future period.

[0066] Fig. 4 The upper part shows another exemplary time course of the electrical power P_MPP, P_PV, P_Batt and P_Netz, and the lower part shows a corresponding time course of the state of charge (SOC).

[0067] At time t0, the PV power P_PV essentially corresponds to the PV maximum power P_MPP and is fed into the grid via inverter 4a. The state of charge (SOC) of energy storage 5 is below 100%, so energy storage 5 is charged with battery power P_Batt. The total power P_Grid of the energy generation plant 2 corresponds to the PV power P_PV minus the battery power P_Batt. A variation in the PV maximum power P_MPP can be compensated for by corresponding changes in the battery power P_Batt in order to maintain the total power P_PV during the period t0 to t0a at a constant baseline power P_Grid_0.

[0068] At time t0a, the energy storage system 5 is fully charged and can no longer accept any battery power P_Batt. However, the total grid power P_Grid is kept constant by reducing the PV power P_PV to a base PV power P_PV_0, which corresponds to the total base power P_Grid_0 of the energy generation plant 2. Any variations in the PV maximum power P_MPP have no effect between t0a and t1. The state of charge (SOC) of the energy storage system 5 remains at 100%.

[0069] During the period t1 to t2, positive control power is requested from the energy generation plant 2 and provided by increasing the total power P_Grid. The PV power P_PV is set to the PV maximum power P_MPP. If the PV power P_PV, increased in this way compared to the total base power P_Grid_0, is insufficient to provide the requested positive control power, the battery power P_Batt is increased such that the difference between the total power P_Grid (including positive control power) and the PV maximum power P_MPP is drawn from the energy storage system 5. The state of charge (SOC) of the energy storage system 5 decreases accordingly. Variations in the PV maximum power P_MPP, and thus in the PV power P_PV, can be compensated for by corresponding counteracting changes in the battery power P_Batt to keep the total power P_Grid constant.

[0070] At time t2, the state of charge (SOC) of energy storage device 5 has decreased by approximately 25%; this is significantly less than in the equally long periods t1 to t2 in Fig. 2 or t2 to t3 in Fig. 3 , although the same positive control power was provided by the energy generation plant 2. By providing a share of the required positive control power through the photovoltaic generator 4, the energy storage system 5 is effectively relieved of some of its load, and the energy generation plant 2 can supply positive control power for a longer period, or a higher overall positive control power can be achieved by the energy generation plant 2 over a given future period without any changes to the energy storage system 5.

[0071] During the period t2 to t3, negative control power is requested from the energy generation plant 2 and provided by reducing the total grid power P_Grid. To achieve this, battery power P_Batt is initially fed into the energy storage system 5 during the period t2 to t2a. If the resulting reduction in the total grid power P_Grid is insufficient to provide the requested negative control power, for example, because the maximum power that can be fed into the energy storage system 5 is limited, the PV power P_PV is reduced relative to the PV maximum power P_MPP. Feeding the battery power P_Batt into the energy storage system 5 increases the state of charge (SOC) of the energy storage system 5.

[0072] At time t2a, the state of charge (SOC) is 100%, meaning the energy storage system 5 is fully charged and can no longer accept any battery power (P_Batt). The total grid power (P_Netz) is kept constant by further reducing the PV power (P_PV), potentially even making it negative, by feeding electrical power back into the photovoltaic generator 4. The total grid power (P_Netz) thus remains constant from t2a to t3 at a value corresponding to the sum of the baseline power at time t0 or t1 and the requested negative control power. The state of charge (SOC) of the energy storage system 5 remains at 100%.

[0073] The definition of PV base power P_PV_0 according to Fig. 4 can also refer to the embodiments according to Fig. 2 and 3This is transferred by ensuring that the PV base power P_PV_0 corresponds precisely to the PV maximum power P_MPP, which in turn serves, at least indirectly, as the basis for determining the total base power P_Netz_0 of the energy generation plant 2. In the embodiment according to Fig. 4 The PV baseline power P_PV_0 is reduced compared to the PV maximum power. This allows the PV power to be increased when needed, thus contributing to the provision of positive control power by the energy generation plant 2.

[0074] In one embodiment according to Fig. 4The PV base power P_PV_0 can be selected between zero and the PV maximum power P_MPP such that the PV power P_PV can be increased to contribute to positive control power. It proves particularly advantageous to select the PV base power at approximately 40% to 60% of the PV maximum power, so that roughly half of the PV maximum power is available as positive control power and the other half as negative control power. These proportions add to the power already available in the embodiment according to Fig. 2 at least available negative control power by feeding back into the photovoltaic generator 4 and the available positive control power by drawing battery power P_Batt from the energy storage unit 5.

[0075] In one embodiment according to Fig. 4Thus, positive control power can be guaranteed for a given future period, calculated as the storage capacity of energy storage unit 5 at the beginning of the period divided by the duration of the future period plus the difference between the PV base power P_PV_0 and the PV maximum power P_MPP. The guaranteed negative control power for the future period corresponds to the PV nominal power P_Peak plus the PV base power P_PV_0. Compared to the embodiment according to Fig. 3 This means that an even greater symmetrical control power can be offered.

[0076] Fig. 5 Figure 1 shows an embodiment of an energy generation plant 2 with a photovoltaic generator 4 and several energy storage devices 51, 52 of different types. The energy storage device 51 can be configured to operate in cooperation with the photovoltaic generator 4 according to one of the parameters shown in Figure 2. Figures 2-4to behave according to the described procedure, so that the energy generation plant 2 provides control power for the primary and / or secondary control of the AC voltage network 1.

[0077] The additional energy storage device 52 can be designed as a storage device with particularly high power density, in particular as a so-called supercapacitor (SC). This energy storage device 52 can then be operated largely independently of the energy storage device 51 and exchange electrical power P_Moment with the AC grid 1 via the grid connection point 1c. The grid connection point 1c can be separate from the grid connection points 1a and 1b or implemented with them in a common unit, for example, as an individual winding on the system side of a transformer with a common grid-side winding. The transformer must be designed for a rated power that includes only the rated power of the photovoltaic generator 4 and an overload capacity for the short-term retrieval of the instantaneous control power P_Moment from the energy storage device 52.It is understood that a targeted direct or indirect exchange of electrical power between the energy storage device 52 and the photovoltaic generator 4 or the energy storage device can be configured. This is particularly useful for adjusting or restoring the state of charge of the energy storage device 52 to a target value as needed.

[0078] The electrical power P_Moment can be adjusted as a function of the grid frequency using a suitable converter 52a to support the instantaneous control of the AC grid 1. In particular, the electrical power P_Moment can be adjusted as a direct function of the rate of change of the grid frequency to counteract rapid changes in the grid frequency and thus stabilize the AC grid 1. For this purpose, it proves particularly advantageous to operate the converter 52a with a voltage-sensing control system that, for example, emulates the behavior of a synchronous machine (so-called virtual synchronous machine, or VSM). REFERENCE MARK LIST

[0079] 1 AC power grid 1a, 1b Grid connection points 2 Power generation plant 4 Photovoltaic generator 4a Inverter 5 Energy storage 5a Converter 9 Control unit P_MPPPV-Maximum power P_PVPV-Power P_BattBattery power P_MomentInstantaneous reserve power P_GridTotal power f_netzNetzfrequency SOC charging status (state-of-charge) t0, t1,time points

Claims

1. A method for providing balancing power for an AC voltage grid (1) for a predetermined future period of time with a balancing power range by means of an energy generation system (2), wherein the energy generation system (2) comprises a photovoltaic generator (4) and an energy store (5),wherein the energy generation system (2) exchanges a total electrical power (P_Netz) with the AC voltage grid (1), wherein the total power (P_Netz) exchanged is set as a function of a current maximum PV power (P_MPP), a predefinable basic PV power (P_PV _0) between zero and the maximum PV power (P_MPP) and a provided or requested balancing power, wherein the balancing power range has a maximum positive balancing power and a maximum negative balancing power, which can be set as deviations from the total basic power (P_Grid_0) in the predetermined future period of time by the energy generation system (2) and are set on demand wherein the method comprises the following steps: - Determination of an optimal balancing power range for the predetermined future period of time, taking into account the current maximum PV power (P_MPP) and the current state of charge (SOC) of the energy store (5) - if no balancing power is requested: feeding in a total basic power (P_Netz_0), which comprises the basic PV power (P_PV_0); - if negative balancing power is requested: reducing the PV power (P_PV) compared to the basic PV power (P_PV_0); - if positive balancing power is requested: drawing a battery power (P_Batt) from the energy store (5) if the requested positive balancing power is greater than the difference between the maximum PV power (P_MPP) and the basic PV power (P_PV_0).

2. The method as claimed in claim 1, wherein reducing the PV power (P_PV) to provide negative balancing power comprises feeding back into the photovoltaic generator (4).

3. The method as claimed in claim 1 or 2, wherein the total basic power (P_Netz_0) contains a battery power (P_Batt) for charging the energy store (5) if the energy store (5) can be charged and / or wherein the battery power (P_Batt) for charging the energy store (5) is first increased if negative balancing power is requested and the energy store (5) can be charged.

4. The method as claimed in one of claims 1 to 3, wherein the basic PV power (P_PV_0) corresponds to the maximum PV power (P_MPP) or is proportional to it, so that any variations in the maximum PV power (P_MPP) lead to corresponding variations in the total basic power (P_Grid_0).

5. The method as claimed in one of claims 1 to 3, wherein the basic PV power (P_PV_0) is lower than the maximum PV power (P_MPP), and in particular is between 40% and 60% of the maximum PV power (P_MPP), wherein the PV power (P_PV) is increased compared to the basic PV power (P_PV_0) if positive balancing power is requested, and additional drawing of a battery power (P_Batt) from the energy store (5) if the requested positive balancing power is greater than the difference between the basic PV power (P_PV _0) and the maximum PV power (P_MPP), so that the total power (P_Netz) includes the requested positive balancing power.

6. The method as claimed in one of the preceding claims, wherein the requested balancing power is determined as a function of a deviation of an instantaneous frequency (f_netz) from a nominal frequency (f_Nenn) of the AC voltage grid (1) and / or a rate of change of the instantaneous frequency (f_netz) by means of a characteristic curve, wherein positive balancing power is requested if the instantaneous frequency (f_netz) is lower than the nominal frequency (f_Nenn) and / or the rate of change is negative, and wherein negative balancing power is requested when the instantaneous frequency (f_netz) is greater than the nominal frequency (f_Nenn) and / or the rate of change is positive.

7. The method as claimed in one of claims 1 to 5, wherein the requested balancing power is predefined to the energy generation system (2) by a superordinate controller.

8. The method as claimed in one of claims 1 to 7, wherein the total basic power (P_Netz_0) has a constant value, wherein, if no balancing power is requested and / or the maximum PV power (P_MPP) is greater than the total basic power (P_Netz_0), the total basic power (P_Netz_0) exclusively comprises PV power (P_PV), and wherein a difference between the current PV power (P_PV) and the total basic power (P_Netz_0) is then compensated for by exchanging electrical power (P_Batt) with the energy store (5).

9. The method as claimed in one of the preceding claims 1 to 8, wherein the photovoltaic generator (4) and the energy store (5) exchange their respective electrical power (P_PV, P_Batt) with the AC voltage grid (1) via different, physically separated grid connection points (1a, 1b).

10. The method as claimed in one of the preceding claims, wherein the energy generation system (2) has at least two energy stores (51, 52), wherein the photovoltaic generator (4) and the first energy store (51) provide balancing power for primary control of the AC voltage grid (1), wherein the second energy store (52) provides balancing power for instantaneous control of the AC voltage grid (1), wherein the second energy store (52) especially exchanges an instantaneous balancing power (P_Moment) with the AC voltage grid (1) via a voltage-impressing inverter (52a).

11. An energy generation system (2) for providing balancing power for an AC voltage grid (1) with a photovoltaic generator (4), an energy store (5, 51, 52) and a control unit (9), wherein the control unit (9) is set up to operate the energy generation system (2) using a method as claimed in one of the preceding claims.

12. The energy generation system (2) as claimed in claim 11, wherein the photovoltaic generator (4) and the energy store (5, 51, 52) are connected to the AC voltage grid (1) via a common grid connection point.

13. The energy generation system (2) as claimed in one of claims 11 or 12, wherein a plurality of photovoltaic generators (4) and / or a plurality of energy stores (5, 51, 52) are connected to the grid connection point via a common bidirectional inverter, wherein the inverter is preferably connected to the photovoltaic generators (4) or the energy stores (5, 51, 52) via individual direct current converters.

14. The energy generation system (2) as claimed in claim 11, wherein the control unit (9) is communicatively connected via an indirect connection via a network to the photovoltaic generator (4) and the energy store (5, 51, 52), wherein the photovoltaic generator (4) and the energy store (5, 51, 52) are connected to the AC voltage grid (1) via different, physically separated grid connection points.

15. The energy generation system (2) as claimed in one of claims 11 to 14, wherein the energy generation system (2) comprises a plurality of energy stores (5, 51, 52) of different designs, wherein preferably at least one of the energy stores (5, 51, 52) is comprises a lithium-ion accumulator and particularly preferably at least one of the energy stores (5, 51, 52) is comprises a supercapacitor.