Energy generation plant and operating method

Abstract

In an operating method for an energy generation plant (1), the input side of which is connected to a solar generator (2) via a clockable electromechanical switch (3) of the energy generation plant (1), the output side of the energy generation plant (1) being connected to a grid (9) via a grid isolating switch (4), wherein an inverter (7) of the energy generation plant (1) converts the current of the solar generator (2) supplied via a DC bus (13) for feeding into the grid (9), and wherein a supercap storage device (5) is connected to the DC bus (13) via a fuse (10), having a trip current lower than the short-circuit current of the solar generator (2), and an isolating switch (6) , the isolating switch (6) is first of all closed when the grid isolating switch (4) is open and the clockable switch (3) is open, then the clockable switch (3) is clocked with a clock pattern, which excludes tripping of the fuse (10), until a voltage of the DC bus (13) and a voltage of the supercap storage device (5) have been balanced, and then it is closed. The grid isolating switch (6) can then be closed and a current of the solar generator (2) converted by the inverter (7) can be fed into the grid (9). A corresponding energy generation plant (1) is also described.

Description

[0001] Energy generation plant and operating procedures

[0002] Description

[0003] The invention relates to an energy generation plant and an operating method for an energy generation plant.

[0004] As part of the energy transition, energy generation plants are increasingly tasked with counteracting short-term deviations in grid parameters, such as frequency or voltage, in a manner comparable to power plants, whose contribution to energy generation is steadily decreasing. This task can include providing so-called instantaneous reserve, i.e., an operating mode of the energy generation plant's inverter that stabilizes grid parameters without requiring active activation. Instead, the inverter independently recognizes and implements measures to counteract deviations, such as providing reactive and / or active power.

[0005] To accomplish this task, a power generation plant must be able to provide and absorb very high power outputs at short notice. Therefore, energy storage systems must be integrated into the power generation plant to accommodate the corresponding amount of energy required for such short-term power peaks. The DC link capacitors typically used in the inverters of power generation plants do not have sufficient storage capacity for this purpose. One solution would be to add supercapacitor storage devices to the DC link capacitors, matching the required storage capacity. Ideally, these supercapacitors would be connected directly in parallel to the DC link during operation, thus stabilizing the DC link voltage even during high power peaks.

[0006] For the smooth operation of the power generation plant, it is essential to ensure that the voltage of such supercapacitor storage devices is above, or at least sufficiently close to, the grid peak voltage when the mains disconnect switch is closed. Otherwise, an uncontrolled equalizing current would flow from the grid into the DC link containing the parallel-connected supercapacitor storage device after the mains disconnect switch closes. This equalizing current would damage or destroy the freewheeling diodes of an inverter bridge located between the mains disconnect switch and the supercapacitor storage device, unless it is prevented by the tripping of a suitably positioned and sized fuse. This would shut down the power generation plant until the fuse is replaced or reset during maintenance.However, the fuse would also be triggered by these dimensioning requirements if the solar generator were connected to the DC bus without a timer during commissioning when the supercapacitor storage was not charged or not sufficiently charged, since in this case the current generated by the solar generator would flow into the supercapacitor storage via the fuse for too long a period of time.

[0007] Therefore, prior art uses charging circuits to precharge a supercapacitor from the mains in a controlled manner, particularly with a charging current defined by suitable current-limiting components. For example, US 2023 / 0299681 A1 discloses a start-up circuit for an LED driver with a boost converter, in which a clocked semiconductor switch is used to precharge an output capacitance from the mains.

[0008] Accordingly, the purpose of this invention is to demonstrate an energy generation plant that can be reliably put into operation without a charging circuit for pre-charging the supercapacitor storage from the grid.

[0009] This problem is solved by an operating method with the features of claim 1. An energy generation plant according to claim 7 includes a control system for carrying out this operating method. Preferred embodiments of the invention are claimed in the dependent claims.

[0010] According to the invention, an operating method for an energy generation plant, which is connected on the input side to a solar generator via a clockable electromechanical switch of the energy generation plant, wherein the energy generation plant is connected on the output side to a grid via a grid disconnect switch, wherein an inverter of the energy generation plant converts the current supplied by the solar generator via a DC bus for feeding into the grid, and wherein a supercapacitor storage device is connected to the DC bus via a fuse with a tripping value that is lower than the short-circuit current of the solar generator, preferably less than half this value, and a disconnect switch, comprises the following steps:

[0011] First, with the mains disconnect switch and the clocked switch open, the disconnect switch is closed, connecting the supercapacitor to the DC bus. Then, with the disconnect switch closed, the clocked switch is closed in a clocked pattern. This clock pattern is chosen to prevent the fuse from tripping. This method takes advantage of the characteristic inertia of fuses, meaning they can withstand currents exceeding their specified tripping current for a specified period, potentially even several times higher, without the fuse tripping. The clock pattern is applied until the voltages on the DC bus and the supercapacitor are equalized.

[0012] By using an electromechanical switch—as opposed to, for example, semiconductor switches—it is ensured that a current interruption caused by the switch opening does not lead to a voltage spike, due to an explicitly designed or parasitic inductance, that could damage or destroy the switch. At the same time, the intrinsically limited maximum short-circuit current of the solar generator allows for sufficiently long switch closure times without the fuse tripping. The permissible closure times can range from a few tenths of a second to several seconds, for example, 5 seconds or even up to 30 seconds.

[0013] The clock pattern can be a static pattern with fixed durations for the closing and opening phases. However, it is also conceivable that the durations of the closing and opening phases vary, for example, to account for changes in current flow during successive closing phases. The lower the current flow during a closing phase, the longer the closing phase can last and / or the shorter the subsequent opening phase can last. These durations can be determined based on a measured current flowing through the fuse into the supercapacitor or a measured temperature of the fuse, or they can be taken from a sequence table with varying durations for the closing and opening phases.In particular, during timed closing, an open phase can be carried out between closing phases with such a duration that a measured or estimated temperature of the fuse falls below a predetermined maximum temperature value.

[0014] Once the voltage between the DC bus and the supercapacitor storage has equalized, the switch is permanently closed, thus permanently connecting the solar generator to the DC bus. The AC disconnect switch is then closed, and the solar generator's power, converted by the inverter, is fed into the grid.

[0015] In an advantageous embodiment, the clockable switch is permanently closed when a voltage difference between the DC bus and the supercapacitor falls below a predetermined limit, which serves as a criterion for voltage equalization.

[0016] In a further advantageous embodiment, the power generation plant provides instantaneous reserve power to the grid after the network disconnect switch closes. The power generation plant can determine the provided instantaneous reserve power by measuring the capacitor voltage and the grid peak voltage. The voltage difference between these voltages is calculated using the formula E = (Uc 2 -Uk 2)*C / 2 is suitable for displaying the available instantaneous reserve energy to the higher-level control system, indicating the minimum amount of energy that can be provided in the event of a frequency event. In addition to or instead of the active power reserve, the system can also provide reactive power if a voltage change occurs in the grid. In this respect, the system operates similarly to a STATCOM. The reactive power control range is linearly dependent on Uc-llk. Other grid services provided by the energy generation plant, particularly for grid stabilization, are also conceivable and can be commissioned by a higher-level control system.

[0017] In another aspect of the operating procedure, the switch is permanently opened before the disconnect switch is opened during a shutdown of the power generation plant. This prevents unwanted discharge of the supercapacitor storage and allows the power generation plant to be restarted more quickly later. Typically, the energy storage system loses approximately 2% to 5% of its charge per night.

[0018] Another aspect of the invention relates to a power generation system that has an input connection for connecting to a solar generator, wherein the input connection is connected to a DC bus of the power generation system via a clocked electromechanical switch. Furthermore, the power generation system comprises a supercapacitor connected to the DC bus via an inertia-controlled fuse, preferably a thermally triggered fuse, with a tripping value that is lower than the short-circuit current and preferably less than half the short-circuit current of the solar generator, and via a disconnect switch, and an inverter connected to the DC bus on the DC side and to a grid on the AC side via a mains disconnect switch. In this case, thermal fuses can be subjected to the short-circuit current of the solar generator, optionally a multiple of the fuse's tripping value, for several seconds without tripping.At the same time, however, in the event of a grid-side equalizing current, which flows when the DC bus voltage is below the value of the grid peak voltage of the connected grid, they trigger quickly enough to protect the freewheeling diodes of the inverter bridge from damage or destruction.

[0019] In an advantageous embodiment of the invention, the tripping current of the fuse can be selected such that the short-circuit current of the solar generator, under maximum possible irradiance and low temperature, is between four and eight times the tripping current. This prevents the fuse from tripping during the closing phase of the pulsed switch, since sufficiently short closing phases, for example less than 100 ms, can be achieved with commercially available switches. In one embodiment, the shortest duration of the closing phase is 500 ms and the subsequent opening phase is 70 s, thus ensuring sufficient cooling of the fuse before the subsequent closing phase.

[0020] The control system for the energy generation plant is designed and set up to carry out the operating procedure described above.

[0021] The inverter is preferably set up to provide instantaneous reserve and reactive power to stabilize the grid and can, for example, but not necessarily exclusively, also take on the function of a STATCOM.

[0022] In an advantageous embodiment of the power generation system, the connection between the DC bus and the supercapacitor storage system includes an inductor. This inductor serves to shield the supercapacitor storage system from higher-frequency fluctuations in the DC bus voltage, which can be caused, for example, by the operation of the inverter's converter bridge and which could damage the supercapacitor storage system. This also enables or improves power line communication over the DC bus. Alternatively, the inductor can also be part of the DC bus itself, and in particular, located between the inverter and the supercapacitor storage system.

[0023] A nominal tripping current for the fuse is determined by the operating parameters of the power generation plant, such as the rated power of the power generation plant's inverter, and is preferably less than half the short-circuit current of the solar generator. This protects the supercapacitor storage device from a short-circuit event on the DC bus, including the case where the DC bus voltage falls below the peak voltage of the connected grid during power generation plant operation. However, due to these sizing requirements, the fuse would also trip if the solar generator were connected to the DC bus without a timer during startup while the supercapacitor storage device is not charged or insufficiently charged, as the solar generator's short-circuit current would then flow through the fuse into the supercapacitor storage device for an excessively long period.

[0024] In an advantageous embodiment, the supercapacitor storage system of the power generation plant comprises two sub-storage units, each connected to the DC bus via a separate fuse and a separate disconnect switch. This division into sub-storage units allows for the desired scaling of the amount of energy available in the supercapacitor storage system and the maximum extractable peak power. Simultaneously or alternatively, this allows the use of fuses with a lower tripping current than would be possible without the division into sub-storage units. The invention is illustrated below with reference to figures, of which

[0025] Fig. 1 shows a first embodiment of an energy generation plant according to the invention,

[0026] Fig. 2 shows a second embodiment of an energy generation plant according to the invention and

[0027] Fig. 3 shows a flowchart of the operating process according to the invention.

[0028] Fig. 1 shows a first embodiment of an energy generation plant 1 according to the invention. The energy generation plant 1 has an inverter 7, which is connected to a grid 9 via a mains disconnect switch 4. On the DC side, the inverter 7 is connected to a DC bus 13, to which a solar generator 2 is connected via a clockable electromechanical switch s. A supercapacitor 5 is also connected to the DC bus 13 via a fuse 10 and a disconnect switch 6. The connection of the supercapacitor 5 to the DC bus 13 can additionally include a choke 11 to shield the supercapacitor 5 from higher-frequency interference voltages.

[0029] Optionally, a second, dashed-line sub-storage unit 12 can be connected in parallel to the supercapacitor 5 on the DC bus 13, which also includes a fuse, a disconnect switch, and optionally a choke. Further parallel sub-storage units can, of course, be provided.

[0030] In a second embodiment shown in Fig. 2, the choke 11 for shielding the supercapacitor(s) 5 from higher-frequency interference voltages in the DC bus is arranged in a section facing the inverter 7. In this way, the shielding of all supercapacitors 5 can be achieved jointly via a single shielding choke.

[0031] The disconnect switch 6, the momentary switch 3, and the mains disconnect switch 4 are controlled by a control unit 8 of the power generation plant 1, which can also control the inverter 7. An electromechanical switch controlled by the inverter 7 for disconnecting the solar generator is regularly required by standards anyway to enable galvanic isolation of the solar generator from the rest of the power generation plant 1.

[0032] To commission a power generation plant, a method according to the invention, shown as a flowchart in Fig. 3, is carried out, in particular by means of the control unit 8 of the power generation plant 1. In a first step S1, with the mains disconnect switch and the clockable switch open, the disconnect switch is closed so that the supercapacitor is connected to the DC bus. Subsequently, in a second step S2, with the disconnect switch closed, the clockable switch is closed in a clock pattern determined by the control unit. The clock pattern is applied until an equilibrium has been reached between a DC bus voltage and a voltage of the supercapacitor. Subsequently, in a third step S3, the clockable switch is permanently closed so that the solar generator is also permanently connected to the DC bus.In a fourth step, S4, the AC disconnect switch is closed, and the electricity from the solar generator, converted by the inverter, is fed into the grid. Commissioning is then complete, and in a fifth step, S5, the system can remain in operation until a signal is given to decommission the energy generation system.

[0033] To decommission, in a sixth step S6 the clockable switch is first permanently opened, before in a seventh step S7 the disconnect switch is opened as part of decommissioning the energy generation plant.

[0034] Reference symbol list

[0035] 1 Energy generation plant

[0036] 2 solar generators

[0037] 3-position switch

[0038] 4 mains disconnect switches

[0039] 5 Supercap

[0040] 6 disconnect switches

[0041] 7 inverters

[0042] 8 Control

[0043] 9 network

[0044] 10 fuse

[0045] 11 Throttle

[0046] 12 sub-memories

[0047] 13 DC bus

[0048] S1 - S7 Step

Claims

Patent claims:

1. Operating method for an energy generation plant (1) which is connected on the input side via a clockable electromechanical switch (3) of the energy generation plant (1) to a solar generator (2), wherein the energy generation plant (1) is connected on the output side via a network disconnect switch (4) to a network (9), wherein an inverter (7) of the energy generation plant (1) converts the current supplied by the solar generator (2) via a DC bus (13) for feeding into the network (9), and wherein a supercapacitor storage device (5) is connected to the DC bus (13) via a fuse (10) with a tripping current that is lower than the short-circuit current of the solar generator (2) and via a disconnect switch (6), comprising: - with the mains disconnect switch (4) open and the pulse switch (3) open, closing the disconnect switch (6), - with the disconnect switch (6) closed, the clockable switch (3) is closed in a clock pattern that prevents the fuse (10) from tripping until an equalization has occurred between a voltage of the DC bus (13) and a voltage of the supercapacitor (5), and - then permanently closing the programmable switch (3) and closing the mains disconnect switch (6) and feeding current from the solar generator (2) converted by the inverter (7) into the mains (9).

2. Operating method according to claim 1, wherein the clockable switch (3) is permanently closed when a voltage difference between DC bus (13) and supercap storage (5) falls below a predetermined limit value.

3. Operating method according to one of the preceding claims, wherein the clock pattern is determined by measuring the current flowing through the fuse (10).

4. Operating method according to one of the preceding claims, wherein the energy generation plant (1) provides instantaneous reserve for the network (9) after closing the network disconnect switch (4).

5. Operating method according to one of the preceding claims, wherein, during the clocked closing, an open phase of such duration is carried out between closing phases that the temperature of the fuse (10) falls below a predetermined maximum temperature value.

6. Operating method according to one of the preceding claims, wherein the programmable switch (3) is permanently opened before the disconnect switch (6) is opened as part of a shutdown of the power generation plant (1).

7. Energy generation plant (1), comprising: - an input terminal for connecting to a solar generator (2), wherein the input terminal is connected via a clockable electromechanical switch (3) to a DC bus (13) of the power generation plant (1), - a supercapacitor storage device (5) connected to the DC bus (13) via a fuse (10) and a disconnect switch (6), and - an inverter (7) connected on the DC side to the DC bus (13) and on the AC side to a network (9) via a mains disconnect switch (4), characterized in that a short-circuit current of the solar generator (2) is higher than a tripping value of the fuse (10) and the energy generation plant (1) has a control system (8) which is provided and configured to carry out an operating procedure according to one of the preceding claims.

8. Energy generation plant (1) according to claim 7, wherein the inverter (7) is configured to provide instantaneous reserve for stabilizing the grid (9).

9. Energy generation plant (1) according to claim 7 or 8, wherein the connection between inverter (7) and supercap storage (5) further comprises a choke (11).

10. Energy generation plant (1) according to claim 9, wherein the choke is arranged in a section of the DC bus (13) facing the inverter (7).

11. Energy generation plant (1) according to one of claims 7 to 10, wherein a tripping value of the fuse (10) is less than half of the maximum short-circuit current of the solar generator (2), in particular between one quarter and one eighth of this value.

12. Energy generation plant (1) according to one of claims 7 to 11, wherein the fuse (10) is a thermally triggered fuse.

13. Energy generation plant (1) according to one of claims 7 to 12, wherein the supercap storage (5) comprises two sub-storage units (12) which are each connected to the DC bus (13) via a separate fuse (10) and a separate disconnect switch (6).

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