PV energy generation installation with central inverter

Abstract

The application describes a PV energy generation installation having a central inverter unit (20) for attachment to a PV generator, the PV generator comprising a plurality of PV main strings (PVn) connected in parallel, each connected on the input side with the central inverter unit (20) via a DC line. According to the invention, a monitoring unit (21. N) is assigned to each pair of DC lines assigned to a PV main string (PVn), said monitoring unit comprising a differential current measuring device (8. N), a disconnect switch (9.n) and a monitoring control device (17. N), which is designed to switch the disconnect switch (9.n) and open the PV main string (PV.n) after a differential current threshold value IS, Diff is exceeded. In addition, a ground monitoring device (GFDI) (22) is arranged between one pole of the intermediate circuit (7) and a ground connection (13), which ground monitoring device comprises a ground current measuring device (10), a circuit breaking element (11) and a control device (12), the control device (12) being designed to detect a ground fault by exceeding a ground current threshold value IS after detecting the ground fault. If the earth fault still exists after the end of a defined delay time T, the circuit breaking element (11) is triggered after the delay time T. The invention further relates to a method for fault current monitoring of a facility of this type.

Description

Technical Field

[0001] This invention relates to a PV energy generation facility with a central inverter unit including a DC / AC converter that can both feed energy into and extract energy from an AC power grid. Specifically, the PV energy generation facility can be monitored for potential ground faults, and the facility has circuit-breaking devices for the DC-side energy source, particularly the photovoltaic generator. Furthermore, this invention relates to a method for monitoring fault currents in this type of PV energy generation facility and for disconnecting the DC-side energy source. Background Technology

[0002] PV energy generation facilities are opening up increasingly wider application possibilities within the framework of large-scale facilities. In addition to private residential energy generation (i.e., using inverters to convert DC voltage provided by PV generators into AC grid voltage and supply it to the home grid or feed it into the public power grid), PV power plants at increasingly larger power levels are playing an important role as large-scale power plants in the public electricity supply.

[0003] Here, a PV facility may include a large number of electrical components, particularly a large number of PV modules, distributed in a dispersed manner over a large area. A group of PV modules grouped in series, i.e., connected in series with each other, is also called a PV string. The PV generator of the PV facility may have one or more PV sub-generators or main strings, which are composed of multiple PV strings. These PV strings are connected in parallel with each other via connecting devices (also called combiner boxes), and, if necessary, individually via separate DC / DC converters to a common DC voltage intermediate loop (DC intermediate loop) of the PV inverter, or, depending on the application, to other power converter units (e.g., DC / DC converters). Each PV sub-generator may have one or more PV strings interconnected in parallel with each other. Due to structural reasons, the PV modules of a PV facility always have capacitance relative to their environment, especially relative to their normally grounded supports. This capacitance is not mandatory for the function of the PV facility, but is unavoidably generated by the mechanical structure of the PV modules. Therefore, this capacitance is often referred to as "parasitic capacitance" or "derived capacitance". The parasitic capacitance of a PV facility typically increases with the size of the PV generator associated with that facility; therefore, powerful PV generators also have correspondingly large parasitic capacitances. Furthermore, parasitic capacitance is related to environmental conditions and is further increased, for example, during rain due to the associated damp surfaces of the PV modules and / or the altered dielectric constant of the air due to increased humidity.

[0004] Due to the parasitic capacitance of the PV module relative to ground potential, there is always a leakage current of more or less relative to ground potential from the PV generator during the normal operation of PV facilities.

[0005] Currently, if a grounded person comes into contact with a component of the PV generator's pilot voltage (e.g., a damaged line) due to a fault (e.g., damaged line insulation), this direct contact typically generates an additional fault current relative to ground potential in an abrupt manner. Since fault currents can be hazardous to humans starting at approximately 30 mA and are fire-related starting at approximately 300 mA, regulations in freely accessible PV installations—but not in enclosed electrical operating areas—require reliable identification of this type of fault current and the implementation of additional measures upon detection, such as shutting down and / or short-circuiting the PV generator, particularly the associated PV sub-generator. Here, two standards are generally required. Firstly, the fault current must not be abrupt, i.e., it must not rise rapidly above a relatively low limit (e.g., 30 mA) to ensure maximum personal protection. Secondly, for fire prevention and facility protection reasons, the total differential current or capacitive leakage current measured through the PV generator's attached lines must not exceed a significantly higher limit of several hundred mA.

[0006] As the rated power of PV facilities increases, the parasitic capacitance of the associated PV generators or PV sub-generators also increases, and consequently, the capacitive leakage current that is always present in the normal operation of PV facilities also increases. However, the threshold value associated with the leakage current (e.g., 300mA) remains constant, and may even decrease further due to stricter regulatory constraints. Therefore, the potential fault current may be significantly smaller compared to the always-present capacitive leakage current of the PV facility. Consequently, fault current detection becomes increasingly complex and expensive due to the low signal-to-noise ratio and the associated need for highly sensitive measurement systems. Therefore, it is desirable, especially in larger PV facilities, to reliably and cost-effectively detect potential fault currents, particularly when the potential fault current is small relative to the capacitive leakage current that is always present in the normal operation of the PV facility.

[0007] The problem is that the parasitic capacitance of the PV field on the central DC intermediate circuit of the power converter unit (such as the central inverter) is so large that a person or animal may be injured by the following large discharge current: when the entire capacitance is recharged through the body of a person or animal in the event of contact with one pole of the PV field due to an insulation fault.

[0008] In the case of particularly large PV fields, parallel connections are implemented by interconnecting individual PV generators into PV strings, and these PV strings are then combined into sub-generators or "main strings" in connection units. The currents from multiple connection units are subsequently combined in a DC pooling unit (e.g., a DC bus or a common DC intermediate loop) and then supplied to the power converter unit (e.g., an inverter or a DC / DC converter). Throughout this process, insulation monitoring is always performed, which includes ground current monitoring and preferably also includes a fault disconnect device (GFDI). Ground Fault Detection and Interruption (Ground fault detection and interruption) so that the PV generator can be monitored and disconnected when needed.

[0009] Standards, such as IEC 63112, stipulate that, starting from a certain power level, PV energy generating facilities must either be operated behind a fence in the electrical operating area, or, if they are generally accessible, be equipped with so-called ground fault monitoring devices and safety shut-off devices that meet the aforementioned standards.

[0010] In the prior art, insulation monitoring is always performed, which includes ground current monitoring and also includes a fault disconnect device (GFDI). Ground Fault Detection and Interruption A ground fault detection and interruption (GFDI) is implemented to monitor the entire PV generator and disconnect it from the central inverter unit when needed. A GFDI is installed here, which triggers according to its triggering characteristics when the trigger current is exceeded. The triggering time depends only on the magnitude of the current generated through the ground fault. Summary of the Invention

[0011] The objective of this invention is to provide a PV energy generation facility that provides improved fault current monitoring even with large electrical power and correspondingly large capacitance of the attached PV generator, and that ensures that large PV energy generation facilities can be operated without the presence of surrounding safety fences.

[0012] This task is accomplished by a PV energy generation facility having the features of independent claim 1 and by a method for monitoring fault current of this type of PV energy generation facility according to claim 16. Advantageous embodiments of the invention are reproduced in claims 2 to 15.

[0013] The energy generation facility according to the present invention includes a central inverter unit and a PV generator for attachment to the central inverter unit. The PV generator comprises multiple PV main strings connected in parallel. Each PV main string is connected to the central inverter unit of the PV energy generation facility on the input side via a DC line and to the AC power grid on the output side via a DC intermediate circuit, a DC / AC converter, an AC circuit breaker, a transformer, and grid connection equipment. Each pair of DC lines associated with a PV main string is equipped with a monitoring unit, which includes a differential current measuring device, a circuit breaker, and a monitoring and control device. The monitoring and control device is configured to detect when a current exceeds a differential current threshold I. S,Diff After the fault is identified, in the reaction time T R The circuit breaker is opened internally to disconnect the PV main string, and a grounding monitoring device is arranged between one pole of the intermediate circuit and the ground connection. This grounding monitoring device includes a grounding current measuring device, a circuit breaker element, and a control device. The control device of the grounding monitoring device is configured to detect when the grounding current exceeds the grounding current threshold I. S If, after a ground fault is detected, the ground fault still exists after a predetermined delay time T, a circuit breaker is triggered after the delay time T. The delay time T is selected to be greater than the response time T. R .

[0014] Monitoring units, assigned to each PV master string for individual monitoring, perform monitoring by differential current measurement of the DC lines of each PV sub-generator. Thus, the differential current measuring device assigned to the sub-generator can detect the difference between the input current flowing into the sub-generator and the return current flowing out of it, which flows to ground through a fault location at the affected sub-generator. This return path is provided by a grounding connection. The described monitoring unit, including the differential current measuring device, circuit breaker, and monitoring control device, is also referred to as RCD ("residual current detection and interruption"). The term RCD is also used synonymously in the following text for the structural group of the monitoring unit.

[0015] The disconnection, achieved through fault identification using a differential current measuring device and via a circuit breaker in the monitoring unit, occurs when the differential current threshold I is exceeded. S,Diff It is then triggered without delay, where "without delay" means that the trigger occurs within reaction time T. RThis occurs within the timeframe, and due to technical limitations, the reaction time cannot be precisely zero. This allows for adaptation to pre-defined specifications regarding permissible fault currents (e.g., in absolute terms or in terms of rapidly changing dynamics), while preventing triggering from occurring with small currents introduced through the parasitic capacitance of a faultless sub-generator.

[0016] This should enable the RCD of only the faulty sub-generator to be triggered and disconnected, while all other fault-free sub-generators can remain connected and function normally.

[0017] However, since the total leakage current of all sub-generators and the grounding current caused by the fault in the faulty sub-generators flow together through the grounding connection and also through the Grounding Monitoring Device (GFDI), these currents will trigger the GFDI or its circuit-breaking element, which will cause the entire PV generator (and all fault-free sub-generators) to be disconnected or safely shut down. The GFDI provides the grounding connection for normal operation.

[0018] For this reason, according to the present invention, the GFDI is provided with a time-delayed trigger. When the measured ground current exceeds a defined ground current threshold I... S At this time, the GFDI control device triggers the circuit breaker element only after a certain delay time T. Here, the circuit breaker element can be configured as a grounding switch. During the time period until the GFDI is triggered, the corresponding monitoring unit of the faulty sub-generator can determine the local fault current through the attached differential current measuring device and trigger the disconnection via the attached circuit breaker without delay. If the only fault is located in the disconnected sub-generator, the grounding current measured by the GFDI normalizes and falls below the grounding current threshold I. S When the fault occurs, the triggering of the circuit breaker (grounding switch) is stopped. If the fault is not only in the disconnected sub-generator, or if the fault occurs in other parts (e.g., due to damage to the housing or cable guide), and therefore the RCD of the sub-generator is not triggered, the circuit breaker (grounding switch) is triggered after the delay time T ends.

[0019] Preferably, the energy generation facility according to the invention is formed by a photovoltaic energy generation facility having multiple PV main strings connected in parallel. These PV main strings are connected to a DC intermediate loop (e.g., the DC current collector or busbar of a central inverter unit) via DC lines. The central inverter unit can be implemented in different ways depending on the application. Thus, the central inverter unit can be formed by a DC / AC central inverter configured to convert energy provided by a DC energy source (i.e., a PV generator) and feed it into the AC grid and / or also extract energy from the AC grid. Here, the inverter can be implemented in a single-stage or multi-stage manner, for example, including additional DC / AC converter stages or DC / DC converter stages. Here, in order to provide a return path and monitoring, a grounding connection must be arranged on the DC side between the monitoring unit of the power converter and the sub-generator on the DC intermediate loop or DC current collector. Here, GFDI and the grounding connection exist on at least one pole of the DC intermediate loop so that the effects according to the invention can occur. Depending on the type of central inverter unit, this can be arranged on the positive terminal, the negative terminal, or the intermediate potential (e.g., on a common midpoint).

[0020] Advantageous configurations of the invention are given in the following description and dependent claims, and their features can be applied individually and in any combination thereof.

[0021] In a preferred embodiment of the PV energy generation facility according to the invention, the delay time T is from 50 ms to 500 ms. Particularly preferably, the duration of the delay time T is selected based on the ground current measured by the ground current measuring device. Therefore, preferably, different ranges of measured ground current values ​​can be associated with different delay times T. Correspondingly, different ground current thresholds I can be defined. S The ground current thresholds are triggered by different delay times T when the measured ground current exceeds the threshold value. Advantageously, this is achieved when the ground current threshold is only slightly above the minimum ground current threshold value I. S,MIN In the case of a measured ground current, a longer duration of the delay time T is set. This duration can be, for example, in the range of minutes. In the case of a higher measured ground current, or when it exceeds another higher ground current threshold I... S In such cases, it is advantageous to choose a shorter delay time T to reduce or avoid damage to the facility due to accidental current flow. Here, the grounding current threshold I... S The precise dimensions of the delay time T must be designed individually to fit the specific circumstances of the PV facility.

[0022] In a particularly preferred embodiment of the PV facility according to the invention, a maximum grounding current threshold I is defined.S,MAX When the maximum ground current threshold is exceeded, the delay time T is set to zero. Therefore, a response to a severe fault can be made without delay, even if the facility requires a complete shutdown regardless of the fault, to protect it. Preferably, the maximum ground current threshold I... S,MAX It can be higher than 30A in order to enable compliant operation in terms of security technology.

[0023] In a preferred embodiment of the PV facility according to the invention, the unique ground current threshold I S Or, in the case of multiple ground current thresholds, the minimum ground current threshold I of the ground monitoring device. S,MIN The value must be greater than or equal to 1A. The delay time T is triggered only from this value.

[0024] To monitor each sub-generator, it is advantageous to have a differential current threshold I in the auxiliary monitoring unit. S,Diff Less than or equal to 300mA. This complies with international fire safety regulations. Another advantage is the ability to adjust the differential current threshold I according to IEC 62109-2 or IEC 63112 standards for sudden changes in the range of 30 to 150mA. S,Diff Monitoring is required. Specific requirements for this are contained in the relevant standards under the keyword "sudden change," and these standards can be considered publicly available in their respective valid versions.

[0025] Typically, the measured differential current I Diff Differential current threshold I S,Diff Less than the measured (total) grounding current I E Grounding current threshold I S Because the sum of all leakage currents of each sub-generator is included in the grounding current I monitored by the grounding monitoring equipment. E In the measurement, the monitoring unit of each main string / sub-generator only observes the differential current I between the current flowing into and out of the sub-generator. Diff The differential current is independent of the magnitude of the total current and even approaches zero in ideal conditions (in the absence of parasitic outflow).

[0026] In a preferred embodiment, the grounding monitoring device has an overcurrent protection device. Particularly preferably, the overcurrent protection device includes a damping resistor. In this way, damage to components of the grounding monitoring device that could be caused by increased current flow occurring during the duration of the delay time T can be avoided.

[0027] In another preferred embodiment, the damping resistor is less than the total resistance of the PV generator, preferably less than 10% of the total resistance of the PV generator, and particularly preferably less than 1%. This advantageously ensures that the damping resistor exerts only a negligible effect on the total resistance of the PV facility and thus avoids interference. Furthermore, the effect on the modulation of the central inverter is reduced.

[0028] To ensure the PV energy generation facility described above operates in a compliant manner, a fuse connected in series with the GFDI is provided for redundancy. To protect this fuse, the damping resistor, acting as an overcurrent protection device, is related to the desired delay time T. The energy input to the fuse increases exponentially with the current. For example, with the same load on the components of the GFDI that draw current, a 12-ohm damping resistor can achieve a delay time T four times longer than a 6-ohm damping resistor.

[0029] In one implementation, the central inverter unit is advantageously configured to operate with a stable modulation that does not apply a clock frequency common-mode voltage to ground to the AC voltage. By avoiding the clock frequency common-mode voltage, feedback to the measured leakage current of the sub-generators is avoided, thus improving measurement accuracy.

[0030] In a preferred embodiment, the monitoring unit is arranged on a DC line, which is located inside the housing of the central inverter unit and is therefore part of the central inverter unit.

[0031] In an alternative implementation, the monitoring unit is part of a connection device assigned to each main string, which connects multiple PV strings into a single main string. This connection device (also referred to as a combiner box) is located outside the housing of the central inverter unit. This decentralized arrangement is particularly advantageous for large equipment with a large number of main strings, or for simplified capacity expansion or the replaceability of individual components.

[0032] Another aspect of the invention relates to a method for monitoring fault current in a PV energy generation facility described above, the PV energy generation facility having a central inverter unit, a monitoring unit, and a ground monitoring device (GFDI), the monitoring unit being associated with each pair of DC lines associated with a PV main string (PVn), and the ground monitoring device being arranged between one pole of the intermediate circuit of the central inverter unit and the ground connection.

[0033] The monitoring unit includes a differential current measuring device, a circuit breaker, and a monitoring and control device. The monitoring and control device continuously monitors the differential current I using the differential current measuring device. Diff Among them, by exceeding the differential current threshold I S,Diff A differential current fault was detected.

[0034] Grounding monitoring equipment includes a grounding current measuring device, a circuit breaker, and a control device. The control device monitors the grounding current I using the grounding current measuring device. E Among them, by exceeding the grounding current threshold I S A grounding fault was identified, among which... - After a ground fault is identified by the ground monitoring device, the triggering delay of its associated circuit breaker element is limited to a delay time T. - After detecting a differential current fault, the monitoring and control device of the monitoring unit reacts within a time T. R Internal switching to open the circuit breaker, and - The grounding monitoring device will only trigger the circuit breaker if the grounding fault persists after a defined delay time T, wherein the delay time T is selected to be greater than the response time T of the monitoring unit. R .

[0035] Advantageous extensions of the invention are derived from the claims, description, and drawings. The advantages of features and combinations of features mentioned in the description are merely exemplary and may work alternatively or cumulatively without being obligatory to obtain these advantages from embodiments according to the invention. Without altering the subject matter of the appended claims, the following applies to the disclosure of the original application and patent: other features can be derived from the drawings—particularly the relative arrangement and effective connection of the components. Combinations of features from different embodiments of the invention or combinations of features from different claims are also likely to deviate from the chosen referential relationship of the claims and are inspired thereto. This also relates to features shown in separate drawings or mentioned in the description of those drawings. These features may also be combined with features from different claims. Features listed in the claims for other embodiments of the invention may also be omitted.

[0036] In the claims and description, the number of features mentioned should be understood to mean that there is exactly one, two, or more of the mentioned number, without necessarily using the adverb "at least". That is, for example, when referring to an element, it should be understood that there is exactly one, two, or more elements. These features may be supplemented by other features, or they may be unique features: the corresponding product is constituted by said features.

[0037] The reference numerals included in the claims are not intended to limit the scope of the subject matter protected by the claims. These reference numerals are used solely for the purpose of making the claims easier to understand. Attached Figure Description

[0038] The invention is illustrated below with reference to the accompanying drawings. The drawings show: Figure 1 One embodiment of the PV energy generation facility according to the present invention is shown; Figure 2 A schematic diagram of a method for monitoring fault current of such a PV energy generation facility according to the present invention is shown. Detailed Implementation

[0039] exist Figure 1 The diagram illustrates one embodiment of a PV energy generation facility according to the present invention. The PV energy generation facility 1 includes a photovoltaic generator as an embodiment for a DC generator, formed by multiple PV main strings PV1, PV2…PVn. Each PV main string PV1 to PVn has multiple PV modules or multiple PV strings connected in series, the PV strings being composed of multiple PV modules. The PV main strings PV1 to PVn are constructed similarly, particularly identically, in terms of the number and type of PV modules. Additionally, the PV main strings PVn are arranged so close to each other that they are subjected to at least similar environmental conditions in terms of incident radiation and temperature. The central inverter unit 20 is exemplary constructed as a so-called multi-string inverter. For this purpose, the multi-string inverter has at least as many DC input terminals for the DC line as the PV main strings PVn present in the facility. Preferably, the DC input terminals are protected by a pair of fuses 36. Each PV main string PVn is connected in parallel to a common DC intermediate circuit 7, for example, via a DC bus. This DC intermediate circuit 7 can also be formed, for example, by a split intermediate circuit with a midpoint. The common DC intermediate circuit 7 is connected to the DC side of the DC / AC converter 5 of the central inverter unit 20. Preferably, a DC circuit breaker 6 is also provided, which can disconnect the entire PV generator from the DC / AC converter 5 and prevent power flow from the PV generator when needed. Figure 1On the AC side of the exemplary three-phase DC / AC converter 5, a similarly three-phase AC power grid 1, such as a medium-voltage grid, is connected via an AC circuit breaker 4, a transformer 3 (especially a medium-voltage transformer), and a grid connection device 2. A single-stage DC / AC converter 5 is shown exemplary. Within the framework of this invention, this single-stage DC / AC converter can also be implemented as a multi-stage converter, for example, with additional DC / DC stages, and can be implemented unidirectionally or bidirectionally. The control unit (not shown) of the central inverter unit 20 operates the switching of the DC / AC converter 5 for the desired voltage conversion. For clarity, other components, such as EMC filters and grid filters, are not shown. The PV facilities, especially the DC intermediate loop 7, are connected to ground potential via a grounding connection 13. Furthermore, electrical disconnection from the AC grid 1 is achieved via the transformer 3.

[0040] To monitor the central inverter unit 20 for ground faults, a ground monitoring device 22, also known as a GFDI ("Ground Fault Monitoring Device"), is installed in the grounding path between one pole of the DC intermediate loop 7 and the grounding connection 13. Ground Fault Detection and Interruption (Ground fault detection and interruption), the ground monitoring equipment includes a ground current measuring device 10, a circuit breaker element 11, and a control device 12. The control device 12 is configured to detect ground current exceeding a ground current threshold I measured by the ground current measuring device 10. S Upon detection of a ground fault, the circuit breaker element 11 is triggered. In particular, the control device 12 of the ground monitoring device 22 is configured to trigger the circuit breaker element 11 only after a defined delay time T.

[0041] Each PV string PV1 to PVn has a parasitic capacitance 14 relative to ground potential, and these parasitic capacitances can be different for each string. Through these parasitic capacitances 14, a leakage current always flows in the direction of ground potential. This leakage current is a capacitive reactive current. The leakage current, along with the parasitic capacitances 14, is related to the environmental conditions of the PV string, such as humidity, temperature, precipitation, or similar factors. The leakage current can vary drastically over time, or even slowly. However, for similar PV strings PV1 to PVn, the leakage current varies in a similar manner.

[0042] In fault conditions, for example when grounding personnel 23 are in one of the PV modules ( Figure 1 When a contact is established between the PV main string (PV1) and ground potential, in addition to the leakage current on the PV string that caused the fault condition, a fault current flows to ground potential through personnel 23.

[0043] To protect personnel 23 from electric shock, it is now necessary to be able to detect sudden changes in current, such as those that could be fatal through the flow of a lethal current through the body of personnel 23. This type of fault current is already lethal at current intensities that may be significantly less than the typical current intensities of harmless capacitive leakage currents. For this reason, according to specifications, this type of PV energy generation facility is only permitted to operate with a (Global Ground Fault Monitoring Device) and within a protected electrical operating range (i.e., typically behind a fence). The fence can be omitted only when the PV string itself is monitored by means of an RCD at the values ​​specified in the specification.

[0044] Therefore, in order to monitor the critical fault current indicating the fault location in the PV string and its parallel circuit, multiple monitoring units 21.1 to 21.n are provided, namely the so-called RCD (“ Residual Current Detection and interruption (Residual current detection and interruption). These monitoring units include differential current measuring devices 8.1 to 8.n, circuit breakers 9.1 to 9.n, and monitoring and control devices 17.1 to 17.n, and are respectively assigned to the PV main strings PV1 to PVn. Using differential current measuring devices 8.1 to 8.n, the differential current I through a pair of DC lines in the PV main strings PV1 to PVn is detected. Diff .exist Figure 1 In the illustrated embodiment, monitoring units 21.1 to 21.n are externally configured, particularly within a connection unit or combiner housing where individual PV modules or PV strings are interconnected to form a PV master string PVn. Further monitoring and safety components may also be arranged within this connection unit or combiner housing. Alternatively, monitoring unit 21.n may be configured as part of the central inverter unit 20, for example, within the housing of the central inverter unit 20, or at the input of each PV master string of the central inverter 20.

[0045] This type of monitoring can only be reliably performed by differential current measuring devices 8.1 to 8.n when a current difference exists on the two monitored lines of a PV main string PV1 to PVn. A return path is required to identify the current flowing through leakage capacitor 14 and, in the event of a fault, through grounding manifold 23. This return path is achieved through grounding connection 13. However, ground fault monitoring is also performed in grounding connection 13, which triggers the disconnection via circuit breaker 11 and thus interrupts grounding connection 13. Furthermore, the entire energy generation facility is shut down, for example, by triggering DC main circuit breaker 6 in the illustrated embodiment. However, this prevents fault monitoring of individual sub-generators. For this reason, the control device 12 of the ground monitoring device 22 is configured to trigger circuit breaker 11 only after a defined delay time T, wherein the delay time T is selected to be greater than the reaction time T of monitoring unit 21.n. R This ensures that during the duration of the delay time T, each monitoring unit 21.1 to 21.n has sufficient time to identify the fault current and, with the aid of its monitoring and control devices 17.1 to 17.n, within their technical response time T R The affected sub-generators PV1 to PVn are disconnected by means of circuit breakers 9.1 to 9.n.

[0046] exist Figure 1 In this example, a ground current fault occurs on the PV main string PV1. Now, a sudden change in common leakage current and / or exceeding of the specified limits can be determined by the differential current measuring device 8.1. This signal is sent to the monitoring and control device 17.1, which then opens the circuit breaker 9.1 and disconnects the faulty sub-generator PV1.

[0047] A damping resistor (not shown) is installed on the grounding monitoring device 20 as an overcurrent protection device, so that the recharging current can flow for a sufficiently long time without damaging the components of the GFDI, while ensuring that the trigger time of the RCD is not less than that required in the event of a dangerous fault current. The damping resistor is designed to be less than the total resistance of the PV generator, preferably less than 10% of the total resistance of the PV generator, and particularly preferably less than 1%. Preferably, the differential current threshold I of the monitoring unit 21.1 is... S,Diff The current is less than or equal to 300 mA, and additionally, sudden changes in the range of 30 to 150 mA are monitored. In this way, the damping resistance has only a very negligible effect on the total resistance of the facility, and therefore also has only a negligible effect on the efficiency of the PV facility.

[0048] exist Figure 2The diagram illustrates a schematic method flow for monitoring fault current in a PV energy generation facility according to the present invention. Here, as the PV energy generation facility is put into operation, continuous fault current monitoring is also initiated by the main control device of the PV energy generation facility (step S0).

[0049] In step S1, the ground current monitoring device 22 continuously monitors the ground current I using its ground current measuring device 10, as described above. E Here, the measured grounding current I... E With ground current threshold I S A comparison is made. Here, this typically refers to multiple ground current thresholds, such as the minimum ground current threshold I. S,MIN and maximum ground current threshold I S,MAX Exceeding the minimum ground current threshold is equivalent to identifying a ground current fault (step S2). The maximum ground current threshold then initiates additional protective measures, as described below. The ground current monitoring device 22 is configured to, after identifying a ground current fault in step S2, that is, at the measured ground current I... E Exceeding the minimum grounding current threshold I S,MIN Then, the circuit breaker element 11 is opened by means of its control device 12, thereby disconnecting the current path. Here, a delay time T is initiated by the control device 12 (step S4), and the circuit breaker element 11 is triggered only after the delay time has ended (step S5). Advantageously, the delay time T can be based on the measured ground current I. E The size is selected based on the monitoring unit's response time T, but it is chosen to be larger than the typical technology-determined response time T of the monitoring unit, which is 21.n. R If, under fault conditions, the measured ground current I in step S3... E The comparison shows that the measured grounding current I E Greater than the maximum grounding current threshold I S,MAX If the delay time T is not used, the circuit breaker element 11 is directly triggered (step 4), or the limited delay time T is set to zero.

[0050] Similar to the grounding current monitoring device 22, in step 1, the differential current I of each main string line is monitored by the monitoring unit 21.n using the differential current measuring device 8.n. Diff If these differential currents exceed the defined differential current threshold I... S,DiffThen, the monitoring and control device 17.n of the relevant monitoring unit 21.n triggers the circuit breaker 9.n and disconnects the relevant main string (step 5). This part of the method flow is only possible during the triggered delay time T, because when the grounding switch (circuit breaker element 11) is triggered, the grounding connection 13 is disconnected and therefore the differential current can no longer be monitored by the monitoring unit due to the lack of a return path. If the grounding current I measured by the grounding current monitoring device 22 is... E If the temperature drops below the threshold caused by the fault, the fault state is canceled, and the delayed triggering of the circuit breaker element 11 (grounding switch) is stopped, allowing the monitoring system to transition back to continuous monitoring (step 1). Nevertheless, a fault notification can be generated in a suitable manner by the facility control device, indicating the fault to the user and enabling the location of the fault in the shut-down sub-generator.

[0051] List of reference numerals 1. AC power grid 2. Power grid connection equipment 3 Transformers 4 AC circuit breakers 5 AC / DC converters 6 DC circuit breakers 7 DC collectors (DC+, DC-) 8.1-8.n Differential Current Measuring Device 9.1-9.n Circuit Breaker 10. Grounding Current Measurement 11. Circuit breaker (grounding switch) 12 GFDI control device 13 Grounding connection 14 Parasitic capacitance 17.1-17.n, 17' Monitoring and control device 20 Central Inverter Units 21.1-21.n Monitoring Unit 22 Grounding monitoring equipment (GFDI) 23 people PV1-PVn sub-generators / PV main string S0 monitoring initialization S1 - S5 Method Steps

Claims

1. A PV energy generation facility, wherein the PV energy generation facility comprises a PV generator and a central inverter unit (20), wherein, The PV generator includes multiple PV main strings (PVn) connected in parallel. Each PV main string is connected to the central inverter unit (20) on the input side via a DC line, and is connected to the AC grid (1) on the output side via the central inverter unit (20)'s DC intermediate circuit (7), DC / AC converter (5), AC circuit breaker (4), transformer (3), and grid access equipment (2). Each pair of DC lines belonging to a PV main string (PVn) is assigned to a monitoring unit (21.n). The monitoring unit includes a differential current measuring device (8.n), a circuit breaker (9.n), and a monitoring and control device (17.n). The monitoring and control device (17.n) is configured to detect when the differential current exceeds the threshold value I. S,Diff Then, at reaction time T R The circuit breaker (9.n) is opened to disconnect the PV main string (PV.n), and a grounding monitoring device (22) is arranged between one pole of the intermediate circuit (7) and the grounding connection (13). The grounding monitoring device (22) includes a grounding current measuring device (10), a circuit breaker element (11), and a control device (12). The control device (12) of the grounding monitoring device (22) is configured to detect when the grounding current exceeds the grounding current threshold I. S If, after a ground fault is detected, the detected ground fault still exists after a predetermined delay time T, the circuit breaker element (11) is triggered after the delay time T, wherein the delay time T is selected to be greater than the reaction time T. R .

2. The PV energy generation facility according to claim 1, wherein, The delay time T is between 50ms and 500ms.

3. The PV energy generation facility according to claim 1 or 2, wherein, The duration of the delay time T is related to the ground current measured by the ground current measuring device (10).

4. The PV energy generation facility according to claim 3, wherein, Multiple grounding current thresholds I are defined. S The grounding current threshold is assigned to different delay times T.

5. The PV energy generation facility according to claim 3, wherein, When the maximum grounding current threshold I is exceeded S,MAX In this case, the delay time T is set to zero.

6. The PV energy generation facility according to any one of the preceding claims, wherein, The unique ground current threshold I S Or, in the case of multiple ground current thresholds, the minimum ground current threshold I of the ground monitoring device (22) S,MIN , greater than or equal to 1A.

7. The PV energy generation facility according to any one of the preceding claims, wherein, The differential current threshold I of the monitoring unit (21.n) S,Diff Less than or equal to 300mA.

8. The PV energy generation facility according to any one of the preceding claims, wherein, The differential current measuring device (8.n) is configured to detect changes in the differential current according to IEC 62109-2 or IEC 63112 standards.

9. The PV energy generation facility according to any one of the preceding claims, wherein, The grounding monitoring device (22) has an overcurrent protection device.

10. The PV energy generation facility according to claim 9, wherein, The overcurrent protection device includes a damping resistor.

11. The PV energy generation facility according to claim 10, wherein, The damping resistor is less than the total resistance of the PV generator, preferably less than 10% of the total resistance of the PV generator, and particularly preferably less than 1%.

12. The PV energy generation facility according to claim 1, wherein, The central inverter unit is configured to operate with a modulation that does not apply a clock-frequency, ground-based common-mode voltage to the AC voltage.

13. The PV energy generation facility according to claim 1, wherein, The monitoring unit (21n) is arranged on the DC input line of the PV main string (PVn), which is arranged inside the housing of the central inverter unit (20) and is therefore part of the central inverter unit (20).

14. The PV energy generation facility according to claim 1, wherein, The monitoring unit (21n) is part of a connection device that is associated with each PV main string (PVn) and connects multiple PV strings into a single PV main string (PVn). The connection device is located outside the housing of the central inverter unit (20).

15. A method for monitoring fault current in a PV energy generation facility according to any one of claims 1 to 15, wherein, The monitoring unit (21.n) includes a differential current measuring device (8.n), a circuit breaker (9.n), and a control device (17.n), wherein the control device (17.n) measures the differential current I using the differential current measuring device (8.n). Diff To monitor differential current faults, where exceeding the differential current threshold I... S,Diff When a differential current fault is detected, the grounding monitoring device (22) includes a grounding current measuring device (10), a circuit breaker (11), and a control device (12). The control device (12) measures the grounding current I using the grounding current measuring device (10). E To monitor ground faults, whereby the ground current exceeds the threshold I. S A grounding fault was identified, among which... - After a ground fault is detected by the ground monitoring device (22), the triggering delay of the circuit breaker element (11) is limited to a delay time T. - After detecting a differential current fault, the monitoring control device (17.n) of the monitoring unit (21.n) reacts within a time T. R Internally open the circuit breaker (9.n), and - The grounding monitoring device (22) triggers the circuit breaker (11) only if the grounding fault persists after the defined delay time T, wherein the delay time T is selected to be greater than the reaction time T of the monitoring unit (21.n). R .

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