DE102013202926A1 - Arrangement of photovoltaic module array, has filter arrangement designed such that alternating current harmonics abutting against direct current input of inverter is suppressed and not allowed to pass toward module array - Google Patents

Abstract

The arrangement has an inverter (3) tapping generated direct current (DC) voltage (UDC) from a photovoltaic module array (10). A filter arrangement is connected between the inverter and the photovoltaic module array. The filter arrangement is designed such that alternating current (AC) harmonics abutting against the DC input of the inverter is suppressed and not allowed to pass toward the photovoltaic module array. The filter arrangement includes a capacitor, which is electrically connected to DC supply lines extending to the inverter from the photovoltaic module array.

Description

The present invention relates to the suppression of AC harmonics on photovoltaic modules.

In the field of photovoltaic is known to connect several photovoltaic modules in series and interconnect several such modules rows to a photovoltaic field. The DC voltage U _DC generated at such a photovoltaic field is tapped and converted by an inverter into an AC voltage.

Most inverters are based on the so-called PWM converter principle (pulse width modulation). In the conversion of DC into AC AC harmonics are generated, which also feed back to the DC input of the inverter. In order to mitigate this, capacitors and coils on the DC input side are already installed in some inverters, which indeed attenuate the AC harmonics, but do not sufficiently suppress them.

So far, the inverter has not been considered separately in the production, whether they are used in photovoltaic. In photovoltaics, too, the module manufacturers did not pay attention to the extent to which the inverters used cause a feedback of the AC harmonics generated by the conversion to the modules. Furthermore, the problem of module damage has not yet been sufficiently investigated in order to reduce the degradation of the photovoltaic modules to harmonics generated by the inverter.

It has been shown that in most cases of inverters a DC input side attenuation of the AC harmonics by integrated capacitors and coils is not sufficient to prevent negative effects on the connected solar modules. To adequately dampen the AC harmonics would require the use of more expensive, larger capacitors and coils, which, however, the inverter manufacturers do not obstruct. As in the 1 and 2 shown measurements have been made on photovoltaic inverters, which due to the PWM-based circuit topology of the inverters, at whose DC inputs AC harmonics are applied, which also feed back to the connected photovoltaic modules. Investigations have now shown that these harmonics caused a module degradation and thus it comes to power losses. With today's photovoltaic module lifetimes, this degradation cause needs to be addressed.

Going further in the investigation and analyzing the measured voltage U _DC by means of a Fourier transformation, it can be seen that a wide variety of frequencies are present in this signal. Particularly high frequencies above about 1 kHz are highly detrimental to the photovoltaic modules. Under extreme load conditions, a loss of up to 25% of the original power due to the feedback AC signal of the inverter is to be noted as early as 150 hours of operation.

It is therefore an object of the present invention to provide a long-lasting powerful photovoltaic arrangement of photovoltaic modules with an inverter.

The object of the invention is achieved by an arrangement according to claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

The arrangement according to the invention for suppressing AC harmonics comprises a photovoltaic field which has at least one photovoltaic module and an inverter which picks up the photovoltaic field-generated DC voltage U _DC . In this case, a filter arrangement is interposed between the photovoltaic field and the inverter. In this case, the filter arrangement is designed such that AC harmonics which are applied to the DC input inverters are suppressed so that they can not continue in the direction of the photovoltaic field.

This has the advantage that the photovoltaic modules of the field are not burdened by the fed back AC voltage and also do not degrade prematurely. The AC harmonics generated by the inverter, which also abut on its DC input side and could feed back to the photovoltaic modules, are suppressed by precisely this filter arrangement. Accordingly, this arrangement has the advantage of ensuring a longer-lived and more stable photovoltaic array.

In particular, the filter arrangement can also be comprised by the inverter component or by the photovoltaic field, depending on which manufacturer side undertakes the task. For example, however, the filter arrangement can also be independent of the inverter manufacturing and of the photovoltaic field production and can be specially matched to the combination of photovoltaic field and inverter. For example, the filter arrangement by means of capacitive and / or inductive filter is designed so that it suppresses frequencies from 1 kHz, in particular over 2.5 kHz is particularly effective.

The photovoltaic panel comprises at least one photovoltaic module or at least one row of modules, the row of modules in turn comprising at least one photovoltaic module. In an advantageous embodiment of the arrangement, in each case a plurality of photovoltaic modules are connected in series and a plurality of module rows are combined to form a photovoltaic array. At this photovoltaic field, the entire generated DC voltage is tapped and converted by means of an inverter. Accordingly, voltages can be tapped and converted around 800 V, for example.

For example, the filter arrangement comprises at least one capacitance which is electrically connected to the DC supply lines leading from the photovoltaic array to the inverter. Alternatively or additionally, the filter arrangement comprises at least two inductances which are each electrically connected to one of the DC supply lines which lead from the photovoltaic field to the inverter. In an advantageous embodiment of the invention, the filter arrangement comprises at least two inductors, which are each electrically connected to one of the DC supply lines from the photovoltaic array to the inverter and at least two capacitances which are electrically connected to the DC supply lines, wherein a first capacitor is connected between the photovoltaic field and the inductors and a second capacitance is connected between the inductors and the inverter. These embodiments of the filter arrangement have the advantage that the electrical filters from capacitors or inductors can be adapted separately from the photovoltaic field and independently of the inverter to the combination of photovoltaic field and inverter and can be independently replaced and maintained depending on the life of the components. The use of multiple capacitors can reduce their required size and thus save costs for individual large capacitors.

In addition to suppressing the AC harmonics, there is also the possibility of using the self-capacitance of a photovoltaic module for capacitive filtering. The inherent capacity of the photovoltaic modules results from the structure in which a module is held by a frame whose purpose is the assembly of the module, but which consists of an electrically conductive material and is therefore grounded. Typically, a photovoltaic module is composed of a plurality of photovoltaic cells, which are interconnected via interconnects. Photovoltaic cells and the cell-connecting tracks are embedded, for example, in a polymer. The back of the photovoltaic module is formed for example of a backsheet and the front of the photovoltaic module, for example, from a glass. The photovoltaic cells together with cell connectors and the module frame are two electrically conductive components which are electrically isolated from each other via a polymer and thus constitute a capacitor. Due to the grounding of the frame, the photovoltaic module thus forms a capacitance to ground via the AC leakage currents, in particular high-frequency leakage currents can flow to earth. The grounding of the module frame is realized, for example, via the elevation. These described AC leakage currents not only cause a voltage and therefore power loss of the photovoltaic array, but also contribute significantly to the degradation of the modules. However, the supposedly harmful intrinsic capacity of the photovoltaic modules and their capacitor effect can now be used according to the invention for the protection of the photovoltaic arrangement.

In a particularly advantageous embodiment of the invention, the arrangement comprises at least one photovoltaic module, which is designed as a filter module. In this case, the filter module comprises at least one photovoltaic cell, an electrically conductive grounded module frame, which is designed for mechanical support of the photovoltaic module, a polymer enclosure, a glass cover and a backsheet, and an electrically conductive layer, which is connected to the electrically conductive module frame and thus forms a capacity with the photovoltaic cell. The introduced electrically conductive layer is in this case in particular connected to the module frame such that the electrode surface of the capacitor is enlarged. This has the particular advantage that a filtering of the AC harmonics can be made without requiring a separate filter arrangement between the photovoltaic field and the inverter.

In particular, the arrangement comprises at least two photovoltaic modules, which are designed as filter modules. These are in each case external of series-connected photovoltaic modules of the photovoltaic field and therefore connected directly to the inverter via the DC supply lines. This has the advantage that the outer photovoltaic modules act as a filter and all internal modules in the series circuit are protected against degradation by AC harmonics.

In an advantageous embodiment, the arrangement according to the invention comprises a photovoltaic field, which therefore comprises at least one module row, the module row having at least two outer and at least one inner photovoltaic module, the modules being connected in series. In a photovoltaic field, in particular, a plurality of module rows are interconnected and their entire generated voltage is forwarded to an inverter.

The introduced electrically conductive layer in the photovoltaic module is arranged, for example, between the backsheet and the polymer enclosure. Alternatively, it may also be disposed between the glass cover and the polymer enclosure. For example, it is preferably metallic when attached to the back. In particular, it may be a thin metal layer deposited on the backsheet. If the conductive layer is applied to the front side, transparent conductive oxides, for example, which can be applied directly to the glass cover in known deposition processes, for example, are conceivable. The module frame, for example, is made of aluminum. As the polymer, for example, EVA films are used. The backsheet is, for example, Tedlar. As a conductive layer on the back of metals such as aluminum or copper in question, on the front side in addition to TCOs (Transparent Conductive Oxides) can also be used for example Pedot. In particular, the conductive layer has a thickness of 300 μm or less. So far, the inherent capacity of the modules was basically only a bad capacitor, since the intrinsic capacity was previously an unwanted by-product of the modules in a frame. To improve the filter properties so a photovoltaic module by an additionally inserted electrically conductive layer to a better capacitor and accordingly filter. The filter modules can degrade faster by this additional task as far as their function of photovoltaic power generation is concerned. The edge modules are sacrificed in this case, so to speak.

To adjust the electrical size of the capacitance of the filter modules, e.g. the thickness of the insulating polymer can be varied, or the area of the conductive components, which also includes the interconnects for cell connection.

For example, the width of the cell connectors can also be varied in order to change the capacity of the filter module.

The harmonics generated by inverters are frequency z. In the range of 2.5 kHz and above: f _g ≥ 2.5kHz

For filtering such frequencies in the range of 2.5 kHz, a module capacity C of the filter modules of about 64 MF is needed: → C ≈ 64μF

This is calculated from the formula for a low pass:

Here, the ohmic resistance R of the leads, which of course also depends on the length of the leads, as about R ≈ 1 Ω assumed. The capacitance C of the module includes its area A and the thickness d and the dielectric property ε _{r of} the insulating encapsulation: C = ε ₀ ∈ _r A / d

This is, for example, an EVA encapsulating film having a thickness of 1 mm. In particular, the thickness can also be less than 1 mm. The module area is for example 1.5 m ² .

Embodiments of the present invention will be described by way of example with reference to FIGS 1 to 12 the attached drawing:

1 shows an arrangement of photovoltaic field and inverter,

2 shows a voltage-time diagram, the tapped at the DC input voltage U _DC ,

3 shows a first exemplary embodiment of the filter arrangement,

4 shows a further exemplary embodiment of the filter arrangement,

5 shows a further exemplary embodiment of the filter arrangement,

6 shows a further exemplary embodiment of the filter arrangement,

7 shows a schematic cross section through a photovoltaic module,

8th shows a schematic cross section through a modified example of the filter module photovoltaic module,

9 shows a further exemplary embodiment of a filter module,

10 shows a perspective view of a photovoltaic module,

11 shows a perspective view of a first exemplary embodiment of a photovoltaic module
and

12 shows a further exemplary embodiment of a filter module.

The 1 and 3 to 6 show wiring diagrams of a photovoltaic system, each on the left side of the photovoltaic field 10 is shown. Exemplary for this are three photovoltaic modules 1 shown connected in series, which each have a grounding on the module frame 11 exhibit. To the outer photovoltaic modules 1 close the DC supply lines 32 on which the photovoltaic field 10 with the inverter 3 connect to the right in the figure. While the 1 The state of the art shows by the photovoltaic modules 1 directly to the DC input 31 of the inverter 3 are connected, the show 3 . 4 . 5 and 6 various interconnection schemes for forming a filter 2 against the AC harmonic feedback of the inverter 3 on the modules 1 , The inverter 3 generated AC harmonics are clearly in the voltage-time diagram in 2 recognizable. Without scaling, one first recognizes a voltage U _DC of 800 V, but in detail significant harmonics of about ± 3 V can be seen around the DC voltage. The in 2 shown voltage curve U _DC is, as in 1 shown at the DC input 31 of the inverter 3 tapped.

The 3 shows a filter assembly 2 with a capacitive filter 21 between the first module row of the photovoltaic field 10 and the exchange funnel 3 is switched. 4 shows a filter assembly 2 with inductive filters 22 , In this case, there are two coils 22 in each case in the two DC supply lines 32 from the photovoltaic field 10 to the DC input 31 shown. The 5 shows a combination of capacitive and inductive filters. 6 shows another combination with an additional capacity 21 ,

In the 7 . 8th and 9 is in each case a schematic cross section through a photovoltaic module 1 shown. In all three figures, one first sees the aluminum frame on the right side 110 that covers and holds together all the layers of the photovoltaic module. To the left side of the presentation you have to look at the module 1 around even a lot of solar cells 14 imagine extended. The centrally located photovoltaic cells 14 are via so-called cell connectors 15 , ie traces 15 electrically connected to each other. This whole of photovoltaic cells 14 in a photovoltaic module 1 is in an insulating polymer 13 edged. Such a border 13 or encapsulation can be realized for example by EVA films. The back of the photovoltaic module 1 is through a backsheet 16 realized, which may include, for example, the material Tedlar. The front of the module 1 is in particular a glass cover 12 , The glass cover 12 is for example a hard glass cover.

In the 8th and 9 is shown at which point in the photovoltaic module 1 for example, the electrically conductive layer 17 may be introduced, which is electrically connected to the module frame 110 is connected, and thus represents an increase in the capacitor area. By means of this introduced electrically conductive layer 17 becomes the module 100 to a filter module. The electrically conductive layer 17 can be like in 8th on the backsheet 16 or as in 9 between polymer embedding 13 and glass cover 12 be introduced. The layer 17 on the back, for example, is made of a metal such as aluminum or copper. The insulating layer 17 , which is mounted on the front, must be transparent, ie in particular made of a transparent conductive oxide (TCO) or alternatively also of a conductive polymer such as Pedot. About the thickness d of the polymer encapsulation 13 and the dielectric property ε _{r of} this material also becomes the capacitance C of the filter module 100 affected: C = ε ₀ ∈ _r A / d

In the 10 to 12 are once again the photovoltaic modules 1 shown in another perspective view. The area of a photovoltaic module 1 amounts to eg up to 1.5 m ² . The conductive layer 17 is in particular a layer thickness of 300 microns, preferably, the layer thickness is less than 300 microns.

Claims (11)

Arrangement of a photovoltaic field ( 10 ) with at least one inverter ( 3 ) and a filter arrangement ( 2 ) for suppression of AC harmonics, wherein the photovoltaic field ( 10 ) at least one photovoltaic module ( 1 ) and the inverter ( 3 ) from the photovoltaic field ( 10 ) _DC tapped off _DC , wherein between the photovoltaic field ( 10 ) and the inverter ( 3 ) the filter arrangement ( 2 ) is interposed, wherein the filter arrangement ( 2 ) is designed such that AC harmonics, which at the DC input ( 31 ) of the inverter ( 3 ) are so suppressed that they are not in the direction of the photovoltaic field ( 10 ) can continue. Arrangement according to claim 1, wherein the filter arrangement ( 2 ) at least one capacity ( 21 ) electrically connected to the DC leads ( 32 ) from the photovoltaic field ( 10 ) to the inverter ( 3 ). Arrangement according to one of the preceding claims, wherein the filter arrangement ( 2 at least two inductors ( 22 ), each of which is connected to one of the DC supply lines ( 32 ) from the photovoltaic field ( 10 ) to the inverter ( 3 ) are electrically connected. Arrangement according to one of the preceding claims, wherein the filter arrangement ( 2 ) at least two inductors ( 22 ), each of which is connected to one of the DC supply lines ( 32 ) from the photovoltaic field ( 10 ) to the inverter ( 3 ) are electrically connected and at least one capacity ( 21 ) electrically connected to the DC leads ( 32 ) connected is. Arrangement according to one of the preceding claims, wherein the filter arrangement ( 2 ) at least two inductors ( 22 ), each of which is connected to one of the DC supply lines ( 32 ) from the photovoltaic field ( 10 ) to the inverter ( 3 ) are electrically connected and have at least two capacities ( 21 ) electrically connected to the DC leads ( 32 ), wherein a first capacity ( 21 ) between the photovoltaic panel ( 10 ) and the inductors ( 22 ) and a second capacity ( 21 ) between the inductances ( 22 ) and the inverter ( 3 ) is switched. Arrangement according to claim 1, wherein at least one photovoltaic module ( 1 ) of the photovoltaic field ( 10 ) as a filter module ( 100 ), wherein the filter module ( 100 ) at least - a photovoltaic cell ( 1 ), - an electrically conductive grounded module frame ( 110 ), for the mechanical support of the photovoltaic module ( 1 ), - a polymer enclosure ( 13 ), a glass cover ( 12 ) and a backsheet ( 16 ), and - an electrically conductive layer ( 17 ), which with the electrically conductive module frame ( 110 ) and with the photovoltaic cell ( 1 ) forms a capacity. Arrangement according to claim 6, wherein at least two photovoltaic modules ( 1 ) as filter modules ( 100 ) are configured, which the respective outer of the series-connected photovoltaic modules ( 1 ) of the photovoltaic field ( 10 ) and therefore directly via the DC supply lines ( 32 ) with the inverter ( 3 ) are connected. Arrangement according to claim 6 or 7, wherein the photovoltaic field ( 10 ) comprises at least one module row, the module row comprising at least two outer and one inner photovoltaic module ( 1 ), which are connected in series. Arrangement according to one of claims 6 to 8, wherein the electrically conductive layer ( 17 ) between the backsheet ( 16 ) and the polymer enclosure ( 13 ) is arranged. Arrangement according to one of claims 6 to 8, wherein the electrically conductive layer ( 17 ) between the glass cover ( 12 ) and the polymer enclosure ( 13 ) is arranged. Arrangement according to one of claims 6 to 10, wherein the module frame ( 110 ) for the mechanical mounting of the photovoltaic module ( 1 ) is configured.

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