DE102014103993A1 - Method and device for detecting and signaling a contact fault within a photovoltaic module - Google Patents

Abstract

The invention relates to a method for detecting and signaling a contact fault within a PV module (11) of a PV generator (10), wherein the PV module (11) has at least two submodules (12) connected in series, to each of which Bypass diode (13) is connected in parallel, to which a current through the PV module (11) can commute current. The method comprises the following steps: - performing an impedance measurement on the PV generator (10) at a first operating point of the PV generator (10), which lies within an uncommutated operating point range (I), to determine at least one impedance value (| Z |) of the PV generator (10); - comparing the at least one determined impedance value (| Z |) with a reference impedance value (| ZR |) of the PV generator (10); and - detecting and signaling a contact fault within the PV module (11) of the PV generator (10) as a function of a result of the comparison of the measured impedance value (| Z |) at the first operating point with the reference impedance value (| ZR |). The invention further relates to a device for detecting and signaling a contact fault within a PV module (11) of a PV generator (10) with an impedance measuring device (40) and an adjustment unit for the operating point of the PV generator (10).

Description

The invention relates to a method for detecting and signaling a contact fault within a photovoltaic module of a photovoltaic generator, wherein the photovoltaic module has at least two submodules connected in series, to each of which a bypass diode is connected in parallel, to which a current flowing through the photovoltaic module can commute.

Defective electrical contacts in photovoltaic generators, hereinafter referred to as PV generators for short, can heat up during operation of a PV generator due to the power loss resulting from the defective contact and cause fires. In addition, the yield of recovered electrical energy is reduced by defective contacts, so that the photovoltaic system (PV system) is operated less effectively.

To be able to detect defective contacts as possible during operation of the PV system is from the document DE 10 2006 052 295 B3 a method and a circuit arrangement for monitoring a PV generator by means of an impedance measurement known. In this method, an impedance spectrum, that is to say a dependence of an impedance of the photovoltaic generator on a frequency, is preferably measured during the night hours, and conclusions about possible contact errors are made of changes in the impedance spectrum.

A similar process is from the document WO 2011/0144649 A1 in which a measured impedance of a PV generator is compared with a calculated impedance curve of a modulated PV generator. From an adaptation of the modulated to the measured impedance curve, electrical parameters of the PV generator, in particular a contact resistance, can be determined. An increased contact resistance indicates contact failure.

In another method, an operating point of the PV generator is monitored for a sudden, such as sudden change. Such a sudden change of the operating point, e.g. detected in a change of the photovoltaic voltage and / or the photovoltaic current, also suggests contact problems.

PV generators are usually formed by one or more photovoltaic modules (PV modules). A PV generator often includes series connection of several PV modules, a so-called string. In order to prevent the case of shading of a portion of the modules or a part of a module resulting high negative voltages and thus high power losses on the affected module parts, the PV modules are usually provided with so-called bypass diodes. These become conductive as soon as one of the voltages resulting from the photovoltaic effect (PV voltage) is applied to the opposite voltage on the module or module part. Frequently, the modules are internally composed of a series connection of several, at least two, usually three, submodules, each of the submodules having its own bypass diode connected in parallel. In the case of partial shading, only the submodules affected by the shading are bridged by the conductive bypass diode of a PV module. The current flow through the PV generator leads through the respectively assigned bypass diode for the affected submodules. Otherwise, all PV modules or submodules not affected by the shading still contribute to power generation. The bypass diodes mentioned are not only active in the event of shading, but also when a contact error occurs within a PV module and this contact error within a PV module causes a higher voltage, which is opposite to the PV voltage, than the respective one from the contact error provides affected submodule as PV voltage (neglecting the forward voltage of the bypass diode).

In the known methods for detecting a contact fault of a PV generator, the bypass diodes can cause the region in which the contact fault occurs, due to a commutated to the bypass diode current is not in the power path of the PV generator and thus the Measurements made for the detection of contact error is not accessible.

It is therefore an object of the present invention to provide a method and apparatus for detecting and signaling a contact fault that also reliably detects a contact fault occurring within a PV module.

This object is achieved by a method and a device having the respective features of the independent claims. Advantageous embodiments and further developments are the subject of the dependent claims.

An inventive method of the aforementioned type comprises the following steps: An impedance measurement is performed on the PV generator in a first operating point of the PV generator, wherein the first operating point is within an uncommutated operating point range. The impedance measurement determines at least one impedance value of the PV generator. The at least one determined impedance value is compared with a reference impedance value of the PV generator and a contact error within the PV module of the PV generator is detected and signaled depending on a result of the comparison of the measured impedance value in the first operating point with the reference impedance value.

According to the invention, the choice of the operating point ensures that a PV current flowing through the PV generator actually flows through the possible contact fault location and is not commutated to an associated bypass diode. A commutated to a bypass diode PV current would mask the contact error and preclude a reliable detection of the contact error. A localized within a PV module contact error can be detected so sure.

In the context of the application is to be understood as a non-commutated operating point range, a range of the operating point of the PV generator in which all submodules of a PV module and thus none of parallel to a possible contact error arranged bypass diodes is energized. Conversely, a commutated operating point range is to be understood as meaning a region of the operating point of the PV generator in which the PV current is commutated, at least for one of the submodules, to the bypass diode arranged parallel to a possible contact error.

The operating point of the PV generator can be approached specifically as part of the uncommutated operating point computation by selecting a PV voltage that lies below the open circuit voltage of the PV generator by an amount that is less than the open circuit voltage of one of the submodules of the PV array. Generator is. Alternatively, a PV current smaller than a certain limit current can be set. As a third possibility, the choice of a voltage of the PV generator is given above an impedance jump in the transition between the commutated and the commutated operating point range. Conversely, analogously, an operating point in the commutated operating point range can also be approached in a targeted manner by selecting a voltage which lies below the open-circuit voltage of the PV generator by an amount which is greater than the open-circuit voltage of one of the submodules or by setting a PV current that is larger than the said limit current. As a third possibility, the choice of a voltage of the PV generator below the impedance jump in the transition between the uncommutated and the commutated operating point range is given.

In an advantageous embodiment of the method, a reference impedance measurement is performed on the PV generator or an identical PV generator for determining the at least one reference impedance value of the PV generator in a reference operating point of the PV generator or the identical PV generator , If the reference impedance measurement is performed on the PV generator itself, it may, in one embodiment, be performed within the uncommutated operating point range, if this occurs earlier, when there is no contact fault. Alternatively, it may preferably be carried out in an operating point of the PV generator which is remote from the idling distance, in particular in a commutated operating point range, during operation of the PV generator. It is exploited that, depending on the choice of the operating point, the contact fault point is energized or not. Thus, the reference impedance value can also be determined on the faulty PV generator.

In a further advantageous refinement of the method, the reference impedance measurement and the impedance measurement are each performed at at least two different frequencies, wherein the reference impedance value and the impedance value are each formed from a combination of individual measured values at the different frequencies. The combination is preferably a sum weighted by weighting factors. Also preferably, the reference impedance value and / or the impedance value can be determined as an integral parameter by integrating impedance values over a frequency range. The inclusion of multiple measurements in determining the reference impedance value and / or the impedance value increases the accuracy with which the respective impedance value can be determined. Disturbances that could distort a result at a single measurement frequency become less relevant by taking into account results at other frequencies.

In a further advantageous embodiment of the method, a contact error is detected and signaled when the measured impedance value is greater than the reference impedance value. Contact errors are associated with increased DC resistance, which is also reflected in the impedance. Generally, the contact error is preferably detected and signaled when a difference in the impedance of the PV generator in the first operating point compared to the reference operating state is greater than a first limit value. A connector break as a special case of a contact fault can then be detected and signaled when the difference of the impedance of the PV generator in the first operating point compared to the reference operating state is greater than a second limit, which in turn is greater than the first limit. The method additionally allows a distinction of the cause of the error in this embodiment.

In a further advantageous embodiment of the method, the following additional steps are provided. A further impedance measurement is carried out on the PV generators in a second, in particular in the commutated operating point range, operating point of the PV generator during operation of the PV generator for determining at least one further impedance value of the PV generator. It is then determined whether a comparison of the further impedance value with the reference impedance value indicates an increase in the impedance of the PV generator at the second operating point compared to the reference operating state. If the comparison indicates such a rise, a contact error within an external wiring of the PV generator is detected and possibly signaled. These steps provide an additional check as to whether an error is actually within one of the PV modules of the PV generator. If this check fails, ie if the reference impedance value is above a defined limit value in relation to the impedance value even in the second operating point, it is concluded that the increase in the impedance value does not originate within the PV module but externally, for example, in the external cabling.

In a further advantageous refinement of the method, the impedance measurement or the reference impedance measurement is respectively performed on PV subgenerators of the PV generator connected in parallel to one another. Impedance values can thus be determined separately for the PV subgenerators. A contact error detection and signaling is thus possible at the level of each PV sub-generators, whereby a contact error can be located at the level of the PV sub-generators.

A device according to the invention for detecting and signaling a contact fault within a PV module of a PV generator has an impedance measuring device and an adjustment unit for the operating point of the PV generator, wherein the device is configured to perform one of the aforementioned methods.

Preferably, the device comprises at least one coupling means for an AC test signal in the PV generator, and at least one decoupling means for decoupling an AC signal from the PV generator. More preferably, the device is suitable for detecting and signaling a contact fault within a PV module of a PV generator having two or more PV sub-generators connected in parallel, the device comprising means for carrying out impedance measurements of the individual PV sub-generators. The device then particularly preferably has a decoupling means for decoupling an AC voltage signal from each of the PV subgenerators.

This results in each case the advantages described in connection with the method.

In a further advantageous embodiment of the device, at least the setting unit for the operating point of the PV generator is arranged in an inverter for a PV system. Inverters often already have an adjustment unit for the operating point of the PV generator, which is used for finding and setting an optimal operating point. This adjustment unit can be used in the context of carrying out the method according to the invention. The apparatus required for the realization of the operating point setting in the method according to the invention can thus be minimized.

The invention will be explained in more detail by means of embodiments with reference to figures. The figures show:

1a a block diagram of a PV system with a device for detecting and signaling a contact fault;

1b a schematic diagram showing the internal structure of a PV module;

2 a schematic equivalent circuit diagram of a PV module with an internal contact error;

3a schematic current-voltage characteristics of a PV module with and without internal contact error;

3b a schematic impedance curve of a PV module with an internal contact error;

4 a flowchart of a method for detecting and signaling a contact fault; and

5 a block diagram of another PV system with a device for detecting and signaling a contact fault.

1a shows a PV system in a block diagram. The PV system has a PV generator 10 on that via DC lines with an inverter 20 connected, in turn, the AC side with a power grid 30 is coupled. An example is the inverter 20 for three-phase supply to the power grid 30 designed. It is understood, in alternative embodiments, also a different number of phases in which the inverter 20 into the power grid 30 fed, is possible. In the 1a only the essential elements of the PV system are shown. On the AC side of the inverter 20 For example, switching devices, not shown, (eg isolators), filters (eg, sinusoidal filters), network monitoring devices and / or transformers may be provided. Similarly, DC side in the connection between the PV generator 10 and the inverter 20 not shown here elements such as safety devices or switching devices, for example, load disconnector, DC contactors, etc., to be arranged.

The PV generator 10 is formed in this illustrated example as a string, that is, as a series connection of a plurality of PV modules. Exemplary are in the 1 for the PV generator 10 two PV modules 11 shown in series.

In 1b is the internal structure of one of the PV modules 11 also reproduced in a schematic diagram. The PV module 11 has three submodules in this example 12 on, which in turn are connected in series. To each of the submodules 12 is a bypass diode 13 connected in parallel, which in case of shading and / or contact problems within a submodule 12 becomes conductive, allowing one through the PV module 11 flowing current to the corresponding bypass diode 13 corresponding to the shadowed and / or contact-defective submodule 12 is assigned, commutated.

Furthermore, the PV system has a device 40 for performing and evaluating impedance measurements and detecting and signaling contact faults in the PV array 10 on. The device 40 includes a coupling agent 41 via which an AC test signal is applied to one of the two DC lines between the PV generator 10 and the inverter 20 can be applied. In the embodiment of 1 is the coupling agent 41 a transformer which is looped with a secondary winding in the DC line and a primary winding with a signal generator 42 connected is. Furthermore, the PV generator 10 a decoupling agent 43 assigned, which is also configured in the embodiment as a transformer. The decoupling agent 43 is with a primary winding each with the PV modules 11 of the PV generator 10 series-connected. A secondary winding of the decoupling agent 43 is with a signal amplifier 44 connected.

Furthermore, a control device 45 provided, on the one hand the signal generator 42 controls and on the other hand, an output signal of the signal amplifier 44 for further processing. The control device 45 also has a signal output 46 at which a detected contact error is signaled. The signal output 46 can, as shown, in an advantageous embodiment with the inverter 20 be coupled to warning devices of the inverter 20 to use for signaling the contact error. Alternatively or additionally, the signal output 46 also be paired with an external device. In an advantageous embodiment, the device 40 also completely or partially in the inverter 20 be integrated. This relates in particular to the control device 45 and the signal generator 42 , if necessary, but also the coupling agent 41 and / or the signal amplifier 44 into the inverter 20 be integrated.

For impedance measurement, one of the signal generator 42 generated AC signal via the coupling means 41 fed into the DC circuit of the PV system. The injected signal superimposes a direct current that may be flowing in the DC circuit. That in the PV generator 10 flowing AC signal is from the decoupling means 43 disconnected from the signal amplifier 44 reinforced and for evaluation to the controller 45 forwarded.

To measure an impedance curve, ie the dependence of the impedance on the frequency of a signal, for example, the signal generator 42 output a signal whose frequency is varied over time. That of the signal amplifier 44 output signal is correlated with the alternating current flowing in the DC circuit and becomes dependent on the frequency of the signal generator 42 evaluated, for example, in terms of amplitude level. For this purpose, the signal amplifier 44 a rectifying amplifier which directly detects and propagates a signal amplitude or a DC equivalent of the signal. Assuming that the voltage of the injected signal is constant in the DC circuit, the measured amplitude level characterizes the magnitude of the impedance. Alternatively, to determine the impedance in the DC circuit, the magnitude of AC and AC current can be determined, and from the ratio of the two quantities, the impedance can be calculated.

In an alternative embodiment, it is possible that the signal generator 42 emit a wideband noise signal containing frequency components of a plurality of frequencies. To determine the frequency-dependent impedance is then by means of a in the evaluation 45 or in the signal amplifier 44 existing tunable bandpass filter has a signal amplitude within the PV generator 10 detected as a function of the filter frequency while the filter frequency is varied.

In a further alternative embodiment, it is also possible that once at the beginning of a contact fault detection, an impedance curve of the PV generator 10 is measured. From this characteristic parameters of the impedance curve are then determined, for example a resonance frequency and an amount of the impedance minimum. Subsequently, it is analyzed by further continuous measurements, whether - and possibly in which direction - these characteristic parameters of the impedance curve change over time. For these continuous measurements, therefore, a complete run of a predefined frequency spectrum is no longer required. Rather, it can be determined quickly and simply by means of fewer frequency interpolation points in the vicinity of the originally determined resonant frequency, whether - and optionally in which direction - a change of these characteristic parameters of the impedance curve has taken place.

In the illustrated embodiment, the coupling means 41 the test signal inductively impressed and by the decoupling means 43 an alternating current within the PV generator 10 measured. It is understood that, alternatively, the test signal can also be capacitively coupled. The decoupling agent 43 can also be alternatively and / or additionally formed as a voltage-measuring elements.

The principles underlying the method according to the invention are first based on the 2 to 4 explained in more detail. 2 shows in a similar way as 1b a block diagram of a PV module 11 , At the in 2 shown PV module is the submodule shown in the figure below 12 a contact error, which is symbolized via a resistor R as an equivalent circuit diagram. 3a shows schematic current / voltage characteristics, hereinafter also referred to as I / U characteristics of the PV module 11 of the 2 in a diagram. For this purpose, a through the PV module is on the vertical axis of the diagram 11 flowing current I as a function of the PV module 11 provided voltage U (also called PV voltage U) shown.

In 3a is a first I / U characteristic shown in dashed lines 50 a PV module 11 reproduced without contact error. In the block diagram of 2 that would correspond to a resistance R = 0. The I / U characteristic 50 shows a typical curve for a non-shaded PV module, wherein in the limiting case of small currents, a PV open-circuit voltage of size 3 · U ₀ sets. The voltage U ₀ denotes the open circuit voltage of each of the three submodules here 12 , As the voltage U decreases, it rises through the PV module 11 flowing current I up to a short-circuit current value I ₀ .

A second characteristic 51 in 4a indicates the contact failure case where the value of the resistance R is significantly greater than 0. For small voltage values, the characteristic curve runs 51 almost coincident to the characteristic 50 , in particular the same short-circuit current I _{0 is} reached. As the PV voltage increases, the characteristic traverses 51 then a range in which the current I with increasing PV voltage U first slow, then steeper drops. Similar to the characteristic 50 while falling exponentially to the current 0 at the voltage 3 · U ₀ , the characteristic falls 51 exponentially against a value of I = 0 at a voltage 2 · U ₀ . For PV voltages U between 2 · U ₀ and 3 · U ₀ , the current I linearly drops from a value near 0 at the PV voltage 2 · U ₀ to 0 at the PV voltage 3 · U ₀ . The voltage drop is determined by the ohmic law from the size of the resistance value of the contact error.

The voltage range between 2 · U ₀ and 3 · U ₀ is in the 3a as a first area I. The voltage range smaller than 2 · U ₀ is characterized as a second region II.

2 shows by means of current paths, why the characteristic 51 in the first and second region I, II has such a different course. The current path denoted by I is present in the first region I, the current path denoted by II in the second region II. In the first region I, the voltage drop across the resistor R is smaller than that of the submodule 12 provided voltage. Accordingly, the associated bypass diode blocks 13 and the current I flows through the resistor R and the three submodules 12 ,

If, on the other hand, a voltage drops across the resistor R which is greater than the submodule affected by the contact error 12 provided voltage, is the associated bypass diode 13 conductive and the PV current in the PV module 11 commutates to this bypass diode 13 , This situation is in the second area II as indicated by the corresponding current path II in 2 is shown. The second area II is therefore also referred to in the context of the application as a commutated area, since the current on at least one of the bypass diodes 13 is commuted and the contact error location is bypassed. The first region I is also referred to as the uncommutated region I, since at one operating point of the PV module 11 in this non-commutated operating point I the contact error is energized, ie on the current path through the PV module 11 lies.

It is noted that in the 3a the uncommitted area I and commutated area II depending on the PV module 11 provided PV voltage U are shown. As well the uncommutated area I or the commutated area II can also be displayed depending on the current. In this case, the commutated region II lies above a limiting current I _G and the uncommutated region I below the limiting current I _G. The height of the limiting current I _G is approximately given by the quotient U ₀ / R.

In 3b is an absolute value of an ideal value | Z | of the PV module depending on the PV voltage U shown. The PV voltage U is indicated on the same horizontal axis as in the 3a , The impedance value | Z | is given by way of example at a specific, not defined frequency of the AC voltage. A characteristic feature of the illustrated curve is a significant jump, here an increase to an impedance value | Z | _G , the magnitude of the impedance | Z | at the transition from the commutated area II to the uncommutated area I. The impedance value | Z | G is a measure of the resistance R.

In a method according to the application, a first operating point of the PV generator is selected such that it lies within the uncommutated operating point range I. At this first operating point of the PV generator, at least one impedance value of the PV generator is determined and compared with a reference impedance value. Depending on the result of the comparison, a contact error is detected and signaled.

According to the above statements, an adjustment for the operating point, the control device 45 may include and / or also part of the inverter 20 can be an operating point of the PV generator 10 targeted approach as part of the uncommutated operating point I compute by a voltage is selected, which is an amount below the open circuit voltage of the PV generator 10 which is smaller than the open circuit voltage U _{0 of} a submodule 12 is or by setting a module current I which is smaller than the limiting current I _G. The third option is to choose a PV generator voltage 10 given above the impedance jump at the transition between the uncommutated and the commutated operating point range. Analogously, an operating point in the commutated operating point range II can be targeted by selecting a voltage that is lower by an amount below the open circuit voltage of the PV generator 10 which is greater than the open circuit voltage U _{0 of} a submodule 12 is or by a module current I is set, which is greater than the limiting current I _G. The third option is to choose a PV generator voltage 10 given below the impedance jump at the transition between the commutated and the commutated operating point range.

An embodiment of a method according to the application is in 4 in a flowchart shown in more detail. The method can be used, for example, with the in 1 shown PV system and will be described with reference to this embodiment and using the reference numerals given there below.

In a first step S1, a first operating point of the PV generator is set in the uncommutated first operating point range I. To set the operating point, for example, by the controller 45 in 1 a corresponding signal via a control line, eg a communication connection, to the inverter 20 output, which has a corresponding operating point on the PV generator 10 established. Such a first operating point can be set, for example, by specifying a high, PV voltage U, which is in the range of the open circuit voltage of the PV generator. Likewise, if from the inverter 20 a control of the working point on the PV current I takes place, a going to zero PV power can be specified.

In a next step S2 becomes an impedance value Z of the PV generator 10 measured. An underlying impedance measurement may be at one or more predetermined frequencies or by varying the frequency for a particular frequency range. Regardless of whether impedance values at discrete frequencies or an impedance characteristic in a (quasi) continuous frequency range is determined, an average impedance value can be determined therefrom. Impedances are usually complex quantities, without limitation, it is assumed below that an absolute value | Z | the determined impedance value Z is based on the further evaluation. However, an evaluation can also be based on the real and / or imaginary part of a measured impedance value.

In a next step S3, a difference between the measured first impedance value | Z | and a reference impedance value or, in turn, its magnitude | Z _R | calculated. The reference impedance value | Z _R | may for example be taken from a previously performed impedance measurement, which was carried out at a time in which the PV generator was faultless and had no contact problem. The reference impedance value can also be taken from a measurement made at an operating point of the PV generator from the commutated operating point range II.

In a next step S4, the difference of the impedance values ΔZ determined in step S3 is compared with a first limit value ΔZ ₁ . If the measured difference ΔZ is not greater than the first threshold ΔZ ₁ , the process branches to a step S5, in which a waiting time is waited before the process is performed again with the step S1. During the waiting time the PV generator becomes 10 preferably operated to generate electrical energy at its optimum operating point. If the waiting time is too short, the efficiency of the PV system drops, because during the execution of the diagnostic steps S1 to S4, the PV generator is not operated at its optimum operating point. If the waiting time in step S5 is too long, the diagnosis may under certain circumstances be carried out too rarely in order to protect against consequential damage to a contact fault that has not been detected in good time. Preferably, a waiting time is set in step S5, which represents a compromise between the different requirements.

If it has been detected in step S4 that the difference ΔZ is greater than the first limit value ΔZ ₁ , the method branches to a step S6, in which a contact fault is detected and signaled. In a first embodiment of the method, this can be ended with the detection and signaling of the contact error in step S6. If necessary, the inverter can 20 be instructed to dwell in the first operating point, in order to avoid overheating of the contact fault range by the low current flow at this operating point.

Optionally, the two in 4 dashed blocks individually or successively in addition to be traversed. In a first block with steps S7 to S9, a distinction can be made between different probable types of contact error. In a second block with the steps S10 to S14, it can be made plausible that an error actually exists within one of the PV modules of the PV generator and not externally in the wiring between the modules or between the PV generator and the inverter.

In a first step S7 of the first block, the measured difference ΔZ of the impedance values is compared with a second limit value ΔZ ₂ . This second limit value ΔZ ₂ is greater than the first limit value ΔZ ₁ . If the difference .DELTA.Z is greater than this second limit value .DELTA.Z _2, the process branches to a step S8 in which a type of contact failure, a possible connector demolition within a PV module 11 is shown. The background is that a contact error associated with such large impedance values is due to a complete interruption within the PV module, which is likely to indicate a release of a cell connector.

If it is determined in the step S7 that the difference ΔZ is not larger than the second threshold ΔZ ₂ , the process branches to a step S9 in which an unspecified high-resistance contact fault is displayed. After executing either of steps S8 or S9, the first optional block is completed.

In the second optional block, which can be run from step S6 or after completion of the first optional block, a second operating point of the PV generator is in step S10 10 set in the commutated second operating point II (see. 3a ) of the PV generator.

If the contact fault detected in step S6 is actually within a PV module 11 is the contact error range when operating the PV generator in the commutated area II by commutation of the PV power to the contact error range associated bypass diode 13 (see. 2 ) bypassed. The contact error range would thus no longer be contained in the current path.

In a next step S11, analogously to step S2, the impedance value | Z | measured again. From this measured value, in turn, the difference ΔZ to the reference value is determined analogously to step S3 and compared in a subsequent step S12 with the first limit value ΔZ ₁ . If the difference .DELTA.Z the measured impedance value with the reference impedance value is not greater than the first threshold .DELTA.Z ₁ in this case, this indicates that a very high probability of contact failure actually within the PV module 11 present. In the measurement in step S11, the contact error was made by commutating the PV power to the bypass diode 13 masked.

If, on the other hand, it is determined in step S12 that the difference ΔZ of the impedance values is greater than the first limit value ΔZ ₁ in this second operating point of the PV generator as well, this indicates an error in the wiring of the PV modules 11 between each other or the wiring between the PV generator 10 and the inverter 2 which does not cause a commutation of the PV current to a bypass diode 13 leads.

5 shows a further embodiment of a suitable for carrying out the method PV system. The same reference numerals in this figure denote the same or equivalent elements as in FIG 1 ,

From the basic structure corresponds to the in 5 represented PV system of in 1 shown, to the description of which reference is hereby made. Unlike the in 1 shown Embodiment, the PV generator of the PV system includes the 5 a parallel connection of two PV subgenerators 10a and 10b , Each of these PV subgenerators 10a . 10b is in the example given as a string, that is, a series connection of a plurality of PV modules 11a respectively. 11b educated.

Each of the subgenerators 10a . 10b is a decoupling agent 43a respectively. 43b associated, in turn, as the decoupling means 43 in the embodiment of 1 is designed as a transformer. The decoupling agent 43a . 43b are with a primary winding each with the PV modules 11a respectively. 11b the PV subgenerators 10a respectively. 10b series-connected. A respective secondary angle of the decoupling means 43a . 43b is with a respective separate signal amplifier 44a . 44b connected. The outputs of the signal amplifier 44a . 44b be from the controller 45 accepted and further processed. As in the embodiment of 1 is a coupling agent 41 with assigned signal generator 42 available.

In the 5 The arrangement shown allows impedance values within the PV subgenerators 10a and 10b by evaluation of the corresponding signals of the signal amplifier 44a respectively. 44b to determine independently of each other.

This in 4 illustrated method can be separated according to different runs for the PV subgenerator 10a or the PV subgenerator 10b be performed. Contact error detection and signaling is thus at the level of the individual PV subgenerators 10a . 10b possible, creating a contact error at the level of PV subgenerators 10a . 10b can be located.

The illustrated number of two PV subgenerators 10a . 10b in the embodiment of 5 is purely exemplary and not restrictive. This in 5 The measuring principle of the impedance measurement within a single PV subgenerator shown can also be transferred to a larger number of PV subgenerators within a PV generator.

LIST OF REFERENCE NUMBERS

10

PV generator

10a, 10b

PV Array

11, 11a, 11b

PV module

12, 12a, 12b

submodule

13

Bypass diode

20

inverter

30

Power grid

40

Device for detecting and signaling a contact fault

41

coupling means

42

signal generator

43, 43a, 43b

decoupling

44, 44a, 44b

signal amplifier

45

control device

46

signal output

50, 51, 52

curve

I

uncommitted operating point range

II

commutated operating point range

I

PV electricity

U

PV voltage

U ₀

 Open circuit voltage of a submodule

| Z |

impedance value

| ZR |

Reference impedance value

.DELTA.Z

 difference

ΔZ ₁

 first limit

ΔZ ₂

 second limit

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006052295 B3 [0003]
• WO 2011/0144649 A1 [0004]

Claims (17)

Method for detecting and signaling a contact fault within a PV module ( 11 ) of a PV generator ( 10 ), the PV module ( 11 ) at least two submodules connected in series ( 12 ), to each of which a bypass diode ( 13 ) is connected in parallel to the one through the PV module ( 11 ) can commute current, with the following steps: - Performing an impedance measurement on the PV generator ( 10 ) in a first operating point of the PV generator ( 10 ), which lies within an uncommutated operating point range (I), for determining at least one impedance value (| Z |) of the PV generator ( 10 ); Comparing the at least one determined impedance value (| Z |) with a reference impedance value (| Z _R |) of the PV generator ( 10 ); and - detecting and signaling a contact failure within the PV module ( 11 ) of the PV generator ( 10 ) depending on a result of the comparison of the measured impedance value (| Z |) in the first operating point with the reference impedance value (| Z _R |). Method according to Claim 1, in which a reference impedance measurement on the PV generator ( 10 ) or an identical PV generator for determining the at least one reference impedance value (| Z _R |) of the PV generator ( 10 ) in a reference operating point of the PV generator ( 10 ) or the identical PV generator. Method according to Claim 2, in which the reference impedance measurement on the PV generator ( 10 ) is performed within the uncommutated operating point range (I) at an earlier time when there is no contact error. Method according to Claim 2, in which the reference impedance measurement on the PV generator ( 10 ) in an idle remote, in particular in a commutated operating point range (II) lying operating point of the PV generator ( 10 ) during operation of the PV generator ( 10 ) is carried out. Method according to one of claims 2 to 4, wherein the reference impedance measurement and the impedance measurement are each performed at at least two different frequencies, wherein the reference impedance value (| Z _R |) and the impedance value (| Z |) each of a combination individual measured values at the different frequencies is formed.  The method of claim 5, wherein the combination is a weighted weighted sum.  Method according to Claim 5, in which the impedance value (| Z |) is determined as an integral characteristic by integration of impedance values over a frequency range. Method according to one of claims 1 to 7, wherein a contact fault is detected and signaled when the measured impedance value (| Z |) is greater than the reference impedance value (| Z _R |). Method according to Claim 8, in which the contact error is detected and signaled when a difference (ΔZ) in the impedance of the PV generator ( 10 ) in the first operating point compared to the reference operating state is greater than a first limit value (ΔZ ₁ ). Method according to Claim 9, in which a connector break is detected as a special case of a contact fault and signaled when the difference (ΔZ) in the impedance of the PV generator ( 10 ) in the first operating point compared to the reference operating state is greater than a second limit value (.DELTA.Z ₂ ), which in turn is greater than the first limit value (.DELTA.Z ₁ ). Method according to one of claims 1 to 10, which additionally comprises the following steps: - carrying out a further impedance measurement on the PV generator ( 10 ) in a second, in particular in the commutated operating point range (II) lying operating point of the PV generator ( 10 ) during operation of the PV generator ( 10 ) for determining at least one further impedance value of the PV generator ( 10 ); Determining whether a comparison of the further impedance value with the reference impedance value causes an increase in the impedance of the PV generator ( 10 ) in the second operating point relative to the reference operating state; and signaling a contact fault within an external wiring of the PV generator ( 10 ), if the comparison indicated such an increase. Method according to one of claims 1 to 11, wherein the impedance measurement or the reference impedance measurement respectively at mutually parallel PV partial generators ( 10a . 10b ) of the PV generator ( 10 ) is carried out. Device for detecting and signaling a contact fault within a PV module ( 11 ) of a PV generator ( 10 ), comprising an impedance measuring device ( 40 ) and an adjustment unit for the operating point of the PV generator ( 10 ), wherein the device is adapted to perform a method according to one of claims 1 to 11. Apparatus according to claim 12, comprising at least one coupling-in means ( 41 ) for a AC test signal into the PV generator ( 10 ), and at least one decoupling agent ( 43 . 43a . 43b ) for coupling an AC signal from the PV generator ( 10 ). Apparatus according to claim 12 or 13 for detecting and signaling a contact fault within a PV module ( 11 ) of a PV generator ( 10 ), two or more PV subgenerators connected in parallel ( 10a . 10b ), wherein the device comprises means for carrying out impedance measurements of the individual PV subgenerators ( 10a . 10b ). Device according to Claim 15, each comprising a decoupling means ( 43a . 43b ) for coupling an AC signal from each PV subgenerator ( 10a . 10b ). Device according to one of claims 13 to 16, wherein at least the setting unit in an inverter ( 20 ) is arranged for a PV system.

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