Photovoltaic system

Abstract

Photovoltaic system (1"), to which at least one photovoltaic module (3) can be connected, with a converter and interface unit (7) for connecting the photovoltaic module or photovoltaic modules to a power grid or a consumer, wherein the photovoltaic system comprises: - Detector means (10) for detecting a fault operating state that deviates from a normal operating state and at least one characteristic operating parameter of the same and for outputting a corresponding detector signal (SD), - input-side processing and control means (8; 8') connected to the detector means for classifying the detected fault operating state as one of several predetermined fault operating states based on the characteristic operating parameter and for outputting a control signal characteristic of the classified fault operating state from a plurality of control signals (SC; S1; S2) each assigned to a predetermined fault operating state and - Actuator means (4; 4b; 4c) connected on the input side to the processing and control means for effecting a switching process characterized by at least one characteristic switching variable from a plurality of predetermined switching processes of the photovoltaic system, wherein the processing and control means (8; 8') are configured to provide at least one actuator activation signal (S1) as the first control signal and one shutdown signal (S2) as the second control signal, and to output a third control signal that prevents shutdown, and wherein the actuator means (4; 4b; 4c) are designed to activate for a predetermined delay time after the first control signal (S1) is omitted and to subsequently switch off the respective affected photovoltaic module (3) after this time has elapsed without receiving a further, third control signal in response to the first control signal (S1) or to switch off the system component immediately in response to the second control signal (S2).

Description

[0001] The invention relates to a photovoltaic system to which at least one photovoltaic module can be connected, and a converter and interface unit for connecting the photovoltaic module or photovoltaic modules to a power grid or a consumer. State of the art

[0002] Photovoltaic systems are designed to generate electrical energy from solar radiation. Typically, in these systems, individual photovoltaic modules convert the solar radiation into direct current (DC), which is then converted into alternating current (AC) either directly at the module (in a microinverter) or at a central point (in a string or central inverter). The AC is usually fed either into the household electrical system for direct on-site consumption or, alternatively, into the public power grid, as in... Fig. Figure 1 is shown schematically. Accordingly, a photovoltaic system 1 comprises several photovoltaic modules 3, which are connected in series to an inverter 7 via a direct current line 5. The inverter's (alternating current) output side has a connection 7a to a public power grid.

[0003] To implement the aforementioned functions, the system components require a range of support functions. For example, inverters, microinverters, and DC-DC converters are typically capable of performing system and self-diagnostic functions. This plays an important role in both the installation and maintenance of photovoltaic systems. Another function that has gained importance in recent years due to legal initiatives is the "power cut" safety function.

[0004] The reason for this function is that the direct current generated in a photovoltaic system has a design- and technology-dependent voltage level that is present at almost its full level at the modules even at low irradiance levels. Typical voltage levels for crystalline silicon modules are 30-40 V, while for other technologies the voltage levels are usually even higher (up to 100 V). The now common practice of connecting several modules to form a string involves connecting the modules in series, which keeps the current constant but significantly increases the voltage compared to the voltage of a single module. In practice, maximum string voltages of 600-1000 V are typically encountered; there are also considerations to further increase the maximum string voltage (up to 1500 V).

[0005] During installation, maintenance, and emergency response operations, such as in building fires and floods, photovoltaic systems pose a risk due to the aforementioned voltages, especially if the system is damaged by mechanical or thermal stress. In recent years, numerous technical solutions have been proposed to prevent such problems, particularly through electrical circuits integrated into the PV system at the module or string level. US Patent 2011 / 0172842A1 discloses a system in which a centrally located control unit within a photovoltaic system, upon receiving a shutdown command, sends a shutdown signal via a dedicated communication channel to control circuits located locally on the photovoltaic modules of the system.These circuits typically serve to put the system into a power-free state, either by short-circuiting or by opening the electrical connection, or possibly a combination of both. Individual PV modules or entire strings are taken out of service until operation is permissible for safety reasons. US Patent 2009 / 0207543A1 discloses a fault detection system in which a control circuit can detect or receive a signal indicating a fault condition in a photovoltaic source and, in response to the detection or signaling of the fault condition, prevents the output of electrical power from the photovoltaic source. Often, when operation is permissible, the modules receive an explicit enable or release signal, which then activates power generation by the modules.For example, WO 2010 / 078 303 A2 discloses a system for switching off electrical power from a photovoltaic module, in which a signal generator sends an enable signal to a shutdown circuit connected to the photovoltaic module and the output of electrical power from the photovoltaic module is prevented by the shutdown circuit when the enable signal is absent.

[0006] A corresponding system shows Fig. 2, in which the photovoltaic system is designated by number 1, the photovoltaic modules by number 3, the connecting cable to an inverter by number 5', and the (modified) inverter by number 7'. Each photovoltaic module 3 is assigned an on / off switch 3a, which can be controlled by a signal generator 7b' integrated with the inverter 7' using release signal pulses 9. Without an incoming release signal, the module terminals are short-circuited by an electronic circuit, so that the module is de-energized. When a release signal is received at the module, the short-circuit switch opens, and the module can produce electricity normally. As a technical alternative, the supply lines to the module can also be interrupted; in this case, a switch (installed in the current path for this purpose) would have to be closed when the release signal is applied.

[0007] The PowerCut system has two generic operating modes. In the first, the modules or strings are switched off without any further intervention and must be switched on by the aforementioned release signal (transmitted, for example, via DC line or radio). This variant is inherently safer than the second, in which the default state is the switched-on state and an explicit switch-off is required. A third option is to switch "bistably" between the aforementioned states; however, just as with the second variant, this poses a higher safety risk if the signal transmission path is interrupted before a shutdown can occur.

[0008] The signal to activate or deactivate the PV system or individual strings typically comes from a central point. For example, a signal generator can be integrated into the inverter, or a standalone signal generator can be installed in the string. The first option shows Fig. 3A, in which the system components are based on Fig. 1 and Fig. 2 are designated and each photovoltaic module is directly coupled to a module-based actuator 4 and to the inverter 7 to a processing and control stage 8. Fig. Figure 3B shows the second variant, the difference from the first variant being that a processing and control stage 8' separate from the inverter 7 is provided in the connecting line 5 for controlling the actuators 4.

[0009] Various system functions, such as power cut, module monitoring, and power optimization, require energy for their relevant switching and control processes. Currently, two primary energy sources are used: direct power supply from the modules themselves (i.e., via direct current) or external power supply via the AC grid, if available. The second option has the advantage that the power supply also functions at night or during periods of very low irradiance, when the modules themselves do not generate enough energy. However, this concept presents problems in some situations. One such problem arises with the aforementioned power cut safety function. Energy is required to deactivate the modules, but this cannot be supplied by the modules themselves, since deactivation has not yet occurred.

[0010] Another technical problem to be solved involves the interactions between the various system functions, particularly the "PowerCut" function, and other functions that are typically implemented in PV systems. These interactions lead to technical contradictions, as explained in more detail below. In the context of "PowerCut," the following functions and requirements are particularly relevant: • - Emergency power cut-off: In the event of fire or flooding, the PV system should shut down as quickly as possible. A key trigger for this is the loss of the building's AC power supply, as firefighters typically attempt to de-energize the entire building before entering during rescue operations. However, brief, unintentional disturbances in the power grid lasting only a few milliseconds should ideally not trigger a shutdown. • - Arc detection and shutdown: If signs of arcing are detected in the system, e.g., at the inverter, the corresponding modules or string should be shut down as quickly as possible to avoid the risk of damage or fire. Ideally, the shutdown time should be as short as possible, lasting only a few milliseconds. • Fault Ride-Through: If a PV system's connection to the power grid fails or major grid disturbances occur, PV systems should, in principle, stop feeding electricity into the grid. However, sometimes only very short-term disturbances occur. If large PV systems were to stop feeding electricity into the grid immediately, the destabilization could intensify, and small disturbances could escalate. Therefore, grid operators' feed-in guidelines often stipulate that, for larger systems, the feed-in from PV systems must be maintained for a few seconds after grid disturbances to avoid the aforementioned domino effect (so-called fault ride-through or dynamic grid stabilization). • - Flashing the modules (measuring the current-voltage characteristic curve): According to current testing procedures, current-voltage characteristic curves are recorded when modules are shipped and certified; that is, the module's full voltage range is scanned. Recording such a curve typically takes around 50 ms. However, if a module's voltage falls below a value required for the operation of module-based electronics, a proper measurement of the module may no longer be possible.

[0011] In summary, the aforementioned functions place very different demands on the PowerCut with regard to switch-off times and response, for example, in the event of a power outage. While arc detection requires the fastest possible switch-off, flashing and fault ride-through require a system with the slowest possible response time. Disclosure of the invention

[0012] The invention provides a photovoltaic system with the features of claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

[0013] The invention includes the concept of equipping the photovoltaic system in such a way that it can recognize certain typical fault conditions or anomalous operating conditions and, in response, autonomously execute a differentiated shutdown process. A further concept involves providing detector means for detecting a fault operating condition that deviates from a normal operating condition, as well as at least one characteristic operating parameter thereof, and actuator means for initiating a switching process characterized by at least one characteristic switching parameter from a plurality of predetermined switching processes of the photovoltaic system.Furthermore, the invention includes the concept of providing processing and control means connected to the detector means at the input side for classifying the detected fault operating state as one of several predetermined fault operating states based on the characteristic operating parameter and for outputting a control signal characteristic of the classified fault operating state. This control signal is selected from a plurality of control signals, each assigned to a predetermined fault operating state.

[0014] Furthermore, the invention includes the consideration of resolving the aforementioned energy supply problems by using a suitable energy source while simultaneously minimizing the necessary modifications to the existing photovoltaic system. The invention also includes the concept of integrating at least one self-sufficient short-term energy storage system into the system for this purpose.

[0015] In one embodiment of the invention, the processing and control means are provided in or associated with the converter unit, and the actuator means are associated with the photovoltaic module or modules. In a further embodiment, which can be combined with the aforementioned embodiment or implemented independently, the detector means are at least partially provided in or associated with the converter unit. However, at least a portion of the detector means can also be arranged in the photovoltaic modules or each assigned to one of them.

[0016] Functionally, the proposed photovoltaic arrangement is designed in such a way that the actuators for implementing a power-cut function are configured in different versions, each characterized by a distinctive switching parameter. Specifically, each actuator has at least one on / off switch energized by the control signal.

[0017] From a functional perspective, it is still preferred that the detector means are designed for the specific detection of at least the formation of an electric arc within the system and a shutdown of the system's or the consumer's mains connection, in particular a shutdown exceeding a predetermined time period.

[0018] In further advantageous embodiments of the invention, the short-term energy storage device comprises a capacitor or supercapacitor, or an intrinsic capacitance of the converter unit or the photovoltaic module, a rechargeable electrochemical element, or an inductor. In principle, non-rechargeable electrochemical elements (batteries) can also be used instead of rechargeable batteries, and the term "short-term energy storage device" is intended to characterize the usable storage elements only insofar as they can supply the components essential for the implementation of the invention with energy for at least a relatively short operating period during which no grid connection is available and the system does not generate electricity. It is understood, however, that this also includes energy storage devices with a larger storage capacity (e.g., for bridging a larger number of interruption periods).

[0019] In a suitable configuration, the processing and control means comprise a comparator unit with multiple outputs or a multi-valued output, connected on one side to the detector means and on the other side to an error operating state memory. Each output is connected to one of the areas of the control signal memory, or each output value can be addressed to an area of ​​a control signal memory, such that when responding to the output or output value of the comparator unit, the control signal characteristic of the classified operating state is selected and output.

[0020] In a further suitable embodiment, which can be combined with the aforementioned embodiment, the processing and control means are configured to provide at least one actuator activation signal as the first control signal and a shutdown signal as the second control signal, as well as to output a third control signal that prevents shutdown. The actuator means are configured accordingly to activate the respective system component, in particular a photovoltaic module, for a predetermined delay time and then to shut it down after this time has elapsed without receiving a further, third control signal in response to the first control signal, or to shut down the system component immediately in response to the second control signal. Drawings

[0021] The invention is explained in more detail below using an exemplary embodiment with reference to the accompanying schematic drawings. These show: Fig. 1. A schematic representation of the basic structure of a photovoltaic system, Fig. 2. A schematic representation of the basic structure of a photovoltaic system with a representation of an additional function. Fig. 3A and Fig. 3B Schematic representations of the basic structure of a photovoltaic system with a processing and control unit and the actuators assigned to the photovoltaic modules, Fig. 4A and Fig. 4B Schematic representations of the basic structure of a photovoltaic system with a processing and control unit and actuators assigned to the photovoltaic modules according to an embodiment of the invention, Fig. 5A to Fig. 5D schematic section views of an embodiment of the photovoltaic system according to the invention to illustrate selected operating states and Fig. 6 a more detailed description of the structure of the processing and control means as well as the actuator means according to an embodiment of the invention. Embodiments of the invention

[0022] Fig. 4A and Fig. 4B show in of Fig. 3A and Fig. Figure 3B, derived from the illustrations where the reference numeral 1" is chosen for the photovoltaic arrangement and the designations of the system components are otherwise retained, shows an inventive embodiment of the system with short-term energy storage devices for supplying energy to the system components essential to the invention. These are first short-term energy storage devices 4a assigned to the photovoltaic modules 4 and a second short-term energy storage device 8a assigned to the processing and control unit 8 or 8'. In technical implementation, these can be, for example, capacitors, supercapacitors, inductors, or accumulators. If the control unit is installed in the inverter, existing but previously unused storage devices, such as the inverter input capacitance, can alternatively be used.

[0023] The principle outlined above will be discussed below in the context of a system where a control signal is generated at one point and a switching actuator is present at a second point. Whether the latter is implemented at the string or module level is irrelevant to the fundamental design.

[0024] A key element of the invention is the detection of the aforementioned operating states and a corresponding logic for their evaluation. Rapid shutdown is advantageous in the case of arcing. Several methods have been proposed for such detection, for example, identifying a characteristic arc spectrum in the DC line. The information from the detected arc should be available to the control unit as quickly as possible, which is easily achieved, for example, by combining both functions in a single unit.

[0025] The second scenario, occurring on a timescale of 50-100 ms, involves flashing modules and bridging short disturbances in the PV system. In this case, logic in the shutdown electronics, preferably supplemented by a suitably sized energy storage system, can ensure that the shutdown only occurs after the critical time window.

[0026] Since different shutdown procedures are required in the two scenarios, the communication in the system is adapted so that two clearly distinguishable signals can be sent to the shutdown electronics: a release signal S1 ( Fig. 5A / Fig. 5B) and a shutdown signal S2 ( Fig. 5C / Fig. 5D). The first option activates the electronics for a longer period (e.g., 50-100 ms), even without the signal needing to continue. Only when no further signal is received does the electronics switch off. The shutdown signal, on the other hand, deactivates the electronics as immediately as possible, possibly with a specific time interval during which reactivation is not possible.

[0027] Fig. 5A and Fig. Figures 5B show the system behavior after sending the enable signal S1 to a module-based shutdown actuator 4b, 4c, which is present until time t0 and then disappears. Despite the disappearance of the enable signal, the Fig. Figure 5B schematically depicts the active operating state being maintained for a time interval Δt until a predetermined time t1. Only then is the photovoltaic module 3 switched off with a short shutdown time tA.

[0028] Fig. 5C and Fig. Figure 5D shows the system behavior in the case where, after sending the enable signal S1 at time t0, the shutdown signal S2 is immediately sent for a (again short) shutdown time tA. Immediately after receiving the shutdown signal S2, the module is switched off until time t2 by triggering the switches 4b and 4c assigned to the photovoltaic module 3. This occurs regardless of whether another signal (not shown in the figures) is received later, indicating that the module 3 is being enabled – whereas in the implementation variant according to Fig. 5A / Fig. 5B the input of an activation signal within the time interval Δt would inhibit the shutdown process.

[0029] For technical implementation, a range of standard methods are available, such as frequency division multiplexing (like using a pilot tone method with two different frequencies), time division multiplexing, or code division multiplexing. Optionally, different transfer channels can also be used, which would likely entail additional infrastructure requirements.

[0030] A specific requirement mentioned above is the fault ride-through scenario, in which operation should be maintained for several seconds even during prolonged grid disturbances. Regular inverters or accessory systems should be able to detect a deviation from the regular grid operating conditions and thus define a point at which operation should be maintained (possibly combined with a defined shutdown procedure). This can be used to signal the processing and control unit (control unit) to maintain its enable signal over the critical period, even if the external power supply via the grid is no longer available. If the control unit can only be powered via the AC grid (and not via the DC side), a sufficiently large energy storage system must be provided.Only then is an explicit activation signal sent, or alternatively, the activation signal is no longer sent.

[0031] In cases where a shutdown should be triggered not only by a loss of AC power but also by other factors, the proposed concept can be easily extended. Examples of such triggers would be the connection of a manual emergency stop switch or a connection to a larger fire alarm control panel. In this case, it would be advantageous to send the explicit shutdown signal to the system immediately upon receipt of the trigger signal, analogous to arc flash detection. A similar approach applies if, for example, faults in the system are detected in inverters or accessory components (very sudden voltage drops, ground faults, leakage currents, etc.).

[0032] Fig. Figure 6 shows, as a functional block diagram, essential elements of the processing and control unit 8 of a photovoltaic system 1" according to the invention in conjunction with an operating status detector 10 (which is located in Fig. 4A and Fig. 4B (not shown) and actuator means 4. The functional components shown are not necessarily separate hardware components in practical implementation, but can be at least partially embedded in the converter unit or inverter on the one hand or the photovoltaic module on the other and implemented in software.

[0033] The detectors 10 detect a fault operating state that deviates from the normal operating state of the system or a module, as well as at least one characteristic operating parameter thereof, and output a corresponding detector signal Sd to the processing and control unit 8, which is then forwarded to a comparator unit 8b. In this unit, the detector signal Sd is compared with characteristic signals stored in a fault operating state memory 8c, corresponding to typical fault operating states. Depending on the comparison result, a selection signal (not separately designated) is output at one of several outputs of the comparator unit 8b, which addresses one of several areas of a control signal memory 8d. Each of these areas contains a control signal or a combination of control signals that controls a specifically predetermined actuation sequence of the actuators 4 of the photovoltaic system.A corresponding output signal SC from the control signal memory 8d passes through a delay stage 8e, in which a time delay can be applied to the control signal or one of several control signals, which is also stored in the control signal memory 8d. Finally, the control signal (or control signal combination) SC reaches the actuators as an output signal from the processing and control unit 8, specifically at the point in . Fig. 5A to Fig. The actuator shown in Figure 5D controls both switches 4b and 4c according to the predetermined control signal type and waveform. As mentioned above, the actuator typically also includes a (not shown) timer element, which delays the shutdown upon receiving a specific control signal SC (namely, the enable signal explained above).

[0034] Further developments and embodiments of the method and device described here only as examples arise within the framework of professional practice.

Claims

[1] Photovoltaic system (1"), to which at least one photovoltaic module (3) can be connected, with a converter and interface unit (7) for connecting the photovoltaic module or photovoltaic modules to a power grid or a consumer, wherein the photovoltaic system comprises: - Detector means (10) for detecting a fault operating state that deviates from a normal operating state and at least one characteristic operating parameter of the same and for outputting a corresponding detector signal (SD), - input-side processing and control means (8; 8') connected to the detector means for classifying the detected fault operating state as one of several predetermined fault operating states based on the characteristic operating parameter and for outputting a control signal characteristic of the classified fault operating state from a plurality of control signals (SC; S1; S2) each assigned to a predetermined fault operating state and - Actuator means (4; 4b; 4c) connected on the input side to the processing and control means for effecting a switching process characterized by at least one characteristic switching variable from a plurality of predetermined switching processes of the photovoltaic system, wherein the processing and control means (8; 8') are configured to provide at least one actuator activation signal (S1) as the first control signal and one shutdown signal (S2) as the second control signal, and to output a third control signal that prevents shutdown, and wherein the actuator means (4; 4b; 4c) are designed to activate for a predetermined delay time after the first control signal (S1) is omitted and to subsequently switch off the respective affected photovoltaic module (3) after this time has elapsed without receiving a further, third control signal in response to the first control signal (S1) or to switch off the system component immediately in response to the second control signal (S2). [2] Photovoltaic system according to claim 1, wherein the processing and control means (8) are provided in or assigned to the converter unit and the actuator means (4) are assigned to the or each photovoltaic module. [3] Photovoltaic system according to claim 1 or 2, wherein the detector means (10) are at least partially provided in or associated with the converter unit. [4] Photovoltaic system according to one of the preceding claims, wherein the processing and control means and / or the actuator means comprise a short-term energy storage device (4a; 8a) to ensure functionality in the event of an interruption of operation of the photovoltaic system, wherein the or each short-term energy storage device (4a; 8a) comprises a capacitor or supercapacitor or an intrinsic capacitance of the converter unit or of the photovoltaic module, in particular a rechargeable electrochemical element or an inductor. [5] Photovoltaic arrangement according to one of the preceding claims, wherein the actuator means (4; 4b; 4c) for realizing a power cut function are designed in different embodiments, each characterized by a characteristic switching variable. [6] Photovoltaic system according to one of the preceding claims, wherein the actuator means (4; 4b; 4c) each have at least one on / off switch supplied with the control signal. [7] Photovoltaic system according to one of the preceding claims, wherein the processing and control means (8; 8') comprise a comparator unit (8b) with multiple outputs or a multi-valued output, which is connected on the one hand to the detector means and on the other hand to a fault operating state memory (8c), wherein each output with each output value is addressable to an area of ​​a control signal memory (8d) or one of the areas of the control signal memory is connected, such that in response to the output or output value of the comparator unit, the control signal (SC) characteristic of the classified operating state is selected and output. [8] Photovoltaic system according to one of the preceding claims, wherein the detector means (10) are designed for the specific detection of at least the formation of an arc within the system and a shutdown of the grid connection of the system or the consumer, in particular a shutdown exceeding a predetermined time period.

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