DE102013016018A1 - Avoiding unfavorable operating conditions for PV modules in PV power plants - Google Patents

Abstract

The present invention relates to a PV module containing the plurality of similar PV cells, and which is provided with an additional electronic circuit, which determines the average cell voltage and the average cell power of the active cells in the module and
if the average cell voltage exceeds a voltage threshold and / or if the average active cell power exceeds a power threshold, the module switches to a reduced output mode in which module power and module voltage are reduced in by deactivating a portion of the cells,
and whereby the "reduced output mode" is ended again, if the conditions for this are no longer met.

Description

In order to optimize the profitability of photovoltaic power plants, on the one hand the costs for the photovoltaic modules have to be reduced as far as possible. On the other hand, other costs that determine the cost-effectiveness of a PV power plant and optimize the overall system must also be considered.

• 1. Die Kosten für die Fläche, auf dem der PV-Park gebaut wird.
• 2. Die Kosten für das Gestell auf dem die PV-Module montiert werden einschließlich der Kosten für die Montage der Module auf dem Gestell.
• 3. Die Kosten für das DC-System, das die elektrische Energie von den PV-Modulen sammelt und zu den Wechselrichtern leitet. Hierzu gehören unter anderem auch die Kosten für die Verkabelung, Generator-Anschlusskästen, DC-Sicherungen, Koppelkästen sowie die DC-seitige Überwachungselektronik.
• 4. Die Kosten für MPP-Tracker-System (Maximum Power Point Tracker), das dafür sorgt, dass die Module in einem optimalen elektrischen Arbeitspunkt betrieben werden, wo sie die maximale elektrische Leistung abgeben können.
• 5. Die Kosten für Wechselrichter-System.
• 6. die Kosten für das AC-System mit dem der Solarpark an das Stromnetz angeschlossen wird, inklusiver etwaiger notwendiger Transformatoren, Umspannwerk und die Verbindungsleitung um das Kraftwerk an das Netz anschließen zu können.

These costs include:

• 1. The cost of the area on which the PV park is built.
• 2. The cost of the rack on which the PV modules will be mounted, including the cost of installing the modules on the rack.
• 3. The cost of the DC system, which collects the electrical energy from the PV modules and routes them to the inverters. These include, among other things, the costs for cabling, generator junction boxes, DC fuses, coupling boxes and the DC-side monitoring electronics.
• 4. The cost of Maximum Power Point Tracker (MPP) tracker system, which ensures that the modules are operated at an optimal electrical operating point where they can deliver the maximum electrical power.
• 5. The cost of inverter system.
• 6. the cost of the AC system connecting the solar park to the grid, including any necessary transformers, substation and connecting line to connect the plant to the grid.

This document describes how to optimize the overall PV system cost by using modules that reduce voltage and power under extreme conditions, thereby saving costs on the other PV system subsystems.

The maximum power (P _{max_STC} ) of a photovoltaic module is measured in W _p (Watts peak) and this is usually under STC conditions ("Standard Test Conditions" are: Irradiance 1000 W / m ² with an AM 1.5 spectrum where the temperature of the PV cells is 25 ° C). For example, if the modules are installed at high altitudes (several 1000 m above sea level) and / or near the equator (more AM 1 spectrum than AM 1.5 spectrum) and / or operate at very low temperatures, it may be easy It may happen that the PV modules emit more than the "maximum" power determined under STC conditions under optimum irradiation conditions. If the other system parts are also designed for this, it is therefore possible that a PV power plant with a total module power of 1 MWp under optimal irradiation conditions and at the lowest possible temperature significantly higher electrical power than 1 MW, for example, 1.1 MW emits.

Consequently, the maximum power of a PV module specified in the data sheets is not the actual maximum that a solar module that is relevant for the application and design of PV power plants can put into practical use.

For this reason, another maximum power is to be introduced here for the PV modules, and a distinction must be made between the P _{max_STC} , the maximum power that the module emits under STC conditions, and P _{max_Inst} , the maximum power, that in an individual PV power plant installed module can emit under optimal irradiation conditions. P _{max_STC} is a size that is specific to a module that is independent of the installation site, and that essentially determines the price of a PV module. P _{max_Inst} depends on the installation site and takes into account, among other things, the local irradiation and the orientation of the module.

• – Solarmodule auf Montagegestell unter optimalen Einstahlbedingungen (P_max-Inst),
• – DC-System,
• – MPPT-System,
• – Wechselrichter(-System),
• – AC-System,

In addition to the cost of the modules, which are mainly determined by P _{max_STC} , the total cost of a PV power plant is essentially determined by the peak performance of each subsystem (that is, by the maximum power that the corresponding subsystem can handle). The maximum electrical power which a solar park can feed into the grid is given by the maximum conduction of the weakest link in the chain:

• - solar modules on mounting frame under optimal one-steel conditions (P _max-Inst ),
• - DC system,
• - MPPT system,
• - inverter (system),
• - AC system,

Although not all system _parts are designed for the same power, it is common for the performance of a solar park to specify the sum of maximum power of the PV modules (P _{max_STC} ) under standard conditions, even though in practice this power may not be able to be generated, because not all system parts are designed for this, or the modules are not optimally aligned with the sun, or there is low solar radiation at the installation site.

In order to design a park as cost-effectively as possible for a location, one can therefore vary the ratio of the peak performance of the individual subsystems. In particular, it makes sense that Ratio of the total maximum module power (P _{max_Inst} ) to the maximum power of the remaining components.

When designing, it must be taken into account in particular that the maximum power of the modules (P _{max_Inst} ) is only relatively rarely available, that is to say that only for a small proportion of all operating hours the modules actually _produce a power close to the maximum power (P _max-Inst ).

It does not always make sense to dimension the remaining subsystems of a PV power plant for the relatively small proportion of time in which almost the maximum module power (P _max-actual ) is available. If the entire power plant is designed for maximum module power (P _max-Inst ), the entire performance of the PV power plant can only be used if the sun's position is optimal and weather conditions are optimal. When designing the solar park, it is therefore often expedient if the maximum overall line of all modules of a PV power plant is set higher together than the corresponding maximum power of the other system parts.

However, care must be taken to ensure that the remaining parts of the system are not overloaded, even if the modules are irradiated under optimum irradiation conditions and can deliver the maximum electrical power (P _max-Inst ). Particularly critical here are the DC system, the MPPT system and the inverter system. In this case, care must also be taken to ensure that even under maximum irradiation of the modules, the maximum system voltage of the individual system parts is not exceeded (this voltage is often 1000 V or 1500 V in the systems, but also any other values may occur). Furthermore, it must be ensured that the maximum permissible voltages are not exceeded, even in the event of a fault, and in other conceivable unfavorable operating states. In particular, the case should be considered that the PV modules are not or only slightly loaded in spite of high irradiance, and thus the modules deliver a voltage near the open circuit voltage, well above the voltage under normal operating conditions (this should near the respective MPP voltage) is. To make matters worse, this case also has to be considered for low operating temperatures, bearing in mind that most module types deliver a higher voltage at low temperatures.

Especially for the DC system and the MPPT system, the cost is significantly affected by the maximum system voltage for which the system is designed.

This is especially true if the system voltage relevant for the design is determined by very rarely occurring events (eg module string is unloaded and it is very cold with very high irradiance).

The cost of the overall system can be reduced if the solar module is designed to prevent the occasional high load on the rest of the system by reducing either the voltage delivered and / or the power delivered in these cases.

Although this slightly reduces the performance of the PV power plant (energy generated per year), this disadvantage can be more than compensated by the savings in the other parts of the system, if the overall system is correctly designed.

This will be explained by means of an example:
It is assumed that a PV power plant is to be erected at a location where a solar module that is optimally aligned with the sun is irradiated with up to 1000 W / m ² . In this case (P _{max_STC} ) would be identical to (P _max-Inst ), so that in this example the mentioned difference need not be considered separately. Furthermore, it is assumed that an irradiation intensity of more than 80% of the maximum irradiance (1000 W / m ² ) on the module occurs only very rarely and therefore the example assumed threshold for power limitation at 80% of the maximum irradiance is a reasonable threshold. In individual cases it can certainly turn out that other threshold values make sense, but it can be assumed that meaningful thresholds are almost always in the range of 65 ... 95% or in most cases in the range of 75 ... 90%.

A solar module specified at 250 Wp (P _{max_STC} ) would then _output exactly 250 W under optimal conditions. 20 modules of this type combined into a "string" would then be able to deliver a power of 5 kW with optimal alignment and irradiation. In other words the string has a maximum power of 5 kWp. To avoid overloading, the rest of the system parts would all have to be designed for maximum performance.

By an additional circuit according to the invention in the PV module can be achieved that whenever the solar module with a Irradiance of just over 800 W / m ² (80% of 1000 W / m ² ) is irradiated, and the MPPT system does not otherwise limit the power, the power dissipating the solar panel is reduced. In addition, in conjunction with the MPP tracker algorithm, the power of the entire PV power plant can be limited to the power of the PV power plant at 80% irradiance at irradiances greater than 80% (as an example) of the maximum irradiance.

This makes it easy to dimension the other system parts (DC system, MPPT system, inverter system, AC system) smaller and thus save costs.

To stick to the example with the previously mentioned 5 kWp string, this string in combination with the additional circuit in the PV modules would only have a power of 4 kWp. The remaining parts of the system, which typically cost 20% of the cost, would only have to be designed for a 4kWp power, saving 20% of the cost of the remainder of the system, accounting for 4% of the PV park's total cost.

At the same time, the energy yield of the PV power plant drops by only 2% ... 3% (typical location in Germany with a 20 ° inclination of the module!) Due to the described measures of module-integrated power reduction at high irradiance.

In sum, costs of the order of magnitude of 1 to 2% of the total costs of a PV power plant can be saved in this example by the measures according to the invention, whereby it is assumed that the costs for the measures according to the invention are negligible. If the electricity price is assumed to be variable over time, the monetary advantage can be significantly higher, since one must assume that the electricity price is lower, especially at times of high solar radiation than in the other times.

The invention is based on the object to modify a PV module so that if the PV module in conjunction with the MPPT system would deliver a power above a certain threshold and / or a voltage above a certain threshold, the power and The voltage can be reduced so that lower requirements are placed on other system components of a PV power plant and these can be produced more cheaply and costs can be saved in other areas.

This is inventively achieved in that in a PV module that includes a plurality of similar PV cells includes an electronic circuit that determines the average voltage and the average power of an active PV cell in the module, and provided that the average voltage exceeds a voltage threshold VT and / or if the average power exceeds a power threshold PT, the module switches to a "reduced output mode" in which module power and module voltage are reduced by deactivating a portion of the cells, whereby the "reduced output mode" terminates again if the conditions are no longer met.

Deactivation of a part of the PV cells of a module means that not all cells of the PV module actively contribute to the energy which is derived as electrical energy from the module electrically via the connection lines of the PV module. PV cells within the module can be excluded from active power generation, either by shorting a group of cells by an electronic switch (see FIG. 2 ) or in that the interconnection of the cells within the module is modified by a switch so that a group of cells is no longer integrated into the active circuit of the module (see FIG. 3 ).

As a rule, the cells in the modules are connected in series. If you deactivate some cells in a module of the serial circuit of PV cells, the power and the voltage of the module decrease in the same way. This condition is referred to herein as "reduced output mode". In the "reduced output mode", compared to the "full output mode" (in this state, all cells of the module are active), both the power that can be delivered by the module and the module voltage are reduced by a specific factor RF (0 <RF <1) , The reduction factor RF is the same for voltage and power. The size RF corresponds to the proportion of deactivated cells relative to the total number of cells in the module. The size (1-RF) corresponds to the proportion of activated cells relative to the total number of cells in the module. The module is switched from the "Reduced Output Mode" into the Full Output Mode, if the conditions for the "Reduced Output Mode" no longer exist for a certain time, and / or the average power and voltage of the active cells (this can be done by Hysteresis taken into account) below the switching thresholds at which the module is placed in the "reduced output mode".

In a further development of the invention, the PV module is modified so that additional hazardous states or other out of control conditions (eg overheating of the solar module, nearby fire, wiring problems in the DC system, interrupted connection to the inverter or to other pantographs, lack of a signal, that confirms the correct operation of one or more other parts of the system of the PV power plant) and is then reacted to a substantial or complete shutdown of the power output from the PV module.

Since a PV module according to the invention in conjunction with a sufficiently dimensioned MPPT system at full irradiance (1000 W / m ² ) goes into the "reduced output mode", the module output measured under STC conditions is significantly lower than the calculated sum the maximum power (at STC and MPP) of all individual cells of the module. From this additional benefits may be drawn. This can be the case, for example, if the PV park or the modules incur costs (customs duties, levies, maintenance costs, insurance premiums, etc.) that are based on the module performance measured under STC conditions. It should also be borne in mind that in many applications the modules are almost never irradiated with an irradiance of 1000 W / m ² . These include, for example, systems that are unfavorably aligned with the sun due to their roof pitch (eg on north roofs), or systems on the façade of houses or systems with east-west orientation of the modules. It should also be remembered that the conventional modules will lose power over time. For example, a conventional module at 1000 W / m ² (900 W / m ² ; 800 W / m ² ) irradiance when new will deliver a power of 100 (90%; 80%) of the specified maximum power (P _max-STC ) ,

After 15 years, these values are at 90% (81%, 72%) of the specified maximum power with an assumed power degradation of 10% after 15 years.

If one assumes that the electronics with which the modules are modified has only a negligible aging, the aging-related power losses of the solar module modified according to the invention would be significantly lower than the values estimated above.

The invention will be explained using the example of a PV module with cells of crystalline silicon. These modules usually consist of 48 ... 72 PV cells connected in series on the basis of monocrystalline or polycrystalline silicon wafers.

It is common to contact these wafer cells on the wafer front and on the wafer back front and back at the so-called busbars and the conductive connection ribbon with the next cell or with the J-box (electrical junction box with the the module is electrically connected). Depending on the cell type used, the front of the cell may be the plus or minus pole. Since the cells are usually connected in series, the busbars on the front side of one cell (in the example the negative pole) are connected to the busbars on the back (in the example the plus pole) of the adjoining cell. Typically, cells today have 2 to 4 busbars that serve as power busbars.

Depending on the cell type, the electrical connection of the cells can also be done differently. So there are cells in which both the plus and the negative pole of the cell are connected to the back. Accordingly, the solar module modified according to the invention may have an electrical connection that differs from the cell connection described here, but that is adapted to the cell type.

Very common today are modules in which 6 rows of PV cells are next to each other, with one cell row consisting of 8 ... 12 serially connected PV cells. The cell rows are then connected meandering in the module and thus connected in series.

By way of example, a 72-cell module is assumed, in which 6 cell rows of 12 cells each are connected in series. For each 2 rows of cells (24 cells in the example), a bypass diode is usually installed, which should limit yield losses in the case of interconnection of the module and should prevent under unfavorable operating conditions (interconnection / reverse current) too high a backward Voltage to a PV cell and could damage it (eg as a result of hot spots). In general, a module with 6 rows of cells contains 3 bypass diodes.

When irradiated (STC conditions) and without load, approximately 72 times the no-load voltage of a representative wafer cell V _{OC-STC-Cell is present} at the connection lines of the module. The open-circuit voltage of an irradiated cell is approx. 25% (rough guideline, which depends inter alia on cell type, radiation intensity and temperature) above the MPP voltage (maximum power point voltage - this is the voltage (depending in particular also on the irradiance), at the the cell gives the maximum possible electrical power). Under normal (optimal) operating conditions, the cell voltage should be close to the MPP voltage (V _MPP-Cell ) (this statement regarding the ratio between open circuit and MPP voltage applies not only to the cell (cell voltage) but also to the module ( Module voltage) and a module string (string voltage)).

When designing a PV power plant, it must also be taken into account that the system voltage (for which an upper limit of 1000 V is assumed here by way of example) is also considered to be extreme Conditions (very low temperature and high radiation intensity) remains within the prescribed range.

Assuming the lowest temperature is -30 ° C, the open-circuit voltage of the cell increases approximately 20% (rough value for silicon wafer cells, which can vary depending on the cell type) compared to the no-load voltage at 25 ° C.

Thus, the relevant for the design maximum open circuit voltage is about 1.2 · 1.25 = 1.5 times the normal operating voltage.

This means that at a given maximum system voltage of 1000 V, the system voltage in normal operation at full irradiance is only 1000V / 1.5 ≈ 666V. This example shows that in a PV power plant, the DC system and the MPPT system have to maintain relatively high voltage reserves in order to be able to ensure a safe function even in (very rarely occurring) extreme conditions.

An advantage of the invention is that the necessary voltage reserves shown here can be smaller, since the module can avoid particularly high voltages due to the "reduced output mode". In the following it will be assumed by way of example that in case of exceeding the intended thresholds for module voltage or module power one of 6 cell rows will be switched off and both the module voltage and the module power will be reduced by 1/6 to 5/6. The factor between maximum MPP voltage and system voltage would no longer be 1.5 but only 1.5 · 5/6 = 1.25. This would mean a maximum MPP voltage of 1000V / 1.25 = 800V, which means an increase in MPP voltage of 20% over 666V. This allows higher power to be processed through a given DC system, reducing the specific cost (€ / kWp) accordingly. At the same time as the mean voltage level of the DC system is increased, the relative electrical losses also decrease.

The reduction in voltage associated with the "reduced output mode" should also be effective in particular when, as a result of low electrical load on the module at high irradiance, overvoltages may occur which could damage other subsystems of the PV power plant.

For the voltage-triggered switching to the "reduced output mode", it makes sense to consider the voltage of a representative active cell in the module. The voltage threshold for switching to this must not be too low, so that it does not unnecessarily often lead to power reductions. Thus one can assume for the voltage threshold the cell voltage of a representative active cell at the lowest expected operating temperature at 1000 W / m ² irradiance, which was still subjected to a reserve of 5 ... 15%.

Since the lowest operating temperature at the place of use is not known in module production, it makes sense to determine the voltage threshold as a function of the cell temperature. In this case, the temperature-dependent voltage threshold should be the voltage that a representative active cell delivers at 1000 W / m ² at the current cell temperature under MPP conditions, increased by approximately 5 ... 15% reserve. The cell temperature can roughly be estimated from the ambient temperature (or the temperature of the electronic circuit (chip temperature).

As a trigger for switching to the "reduced output mode", a power threshold is defined in addition to a voltage threshold (power-triggered switching).

For example, this threshold is 80% of the power of a representative active cell under STC conditions. This means that power reduction always starts when a representative active cell in the module delivers more power than the power threshold for it.

The power of a representative active cell is approximately given by the mean of the power of the active cells. This can determine the electronic circuit of module voltage and module current, and the calculated module power is still divided by the number of cells in the active state in the module. The representative cell voltage can also be determined by measuring the voltage across a group of active cells and calculating the mean cell voltage therefrom.

It should be mentioned at this point that, in conjunction with the module according to the invention, the MPPT system should be designed and / or modified such that, in cases where the "reduced output mode" could be switched on due to the high irradiance, the MPPT system adjust the operating point of the module so that the module does not switch to "reduced output mode". For this purpose, the string voltage must be lowered by adapting the load in the MPPT system, and as a result, the module voltage must be lowered to a value which is lower than the maximum power point.

Note that in this case the MPPT system in the inverter does not operate in a mode in which it searches and sets the MPP, but in a mode in which it is the one from the module limited performance. In the ideal case, the power that can be processed by the inverter is exactly the same as the maximum power that can be delivered by the modules without power reduction.

Ideally, this limits the power output of the modules to a value that ensures that the average power (= representative power) of an active cell in the module is just below the power threshold for switching to reduced output mode. lies.

In principle, the limitation of the module's power dissipation would also work by increasing the string voltage from the MPP value and thus reducing the power that the modules deliver to the DC system. Since in a PV power plant several module strings are usually connected in parallel to an MPPT system, it can be due to variations in module performance (eg scattering by manufacturing, pollution, aging, radiation, shading, ...) and the strong dependence of the cell current on the cell voltage in this range of the current-voltage characteristic of the PV cell (voltage higher than MPP voltage) can easily lead to an uneven distribution of currents between each parallel-connected strings. This could result in further problems (eg vibrations of the power limiting control system).

For example, if the irradiance is close to or just above the upper power threshold (in the example, this is to be reached at 833 W / m ² ), it may be that the module is placed in the "reduced output mode" due to exceeding the power threshold. Since it can be assumed that in a PV power plant several module strings are often connected in parallel on an MPPT system, under certain circumstances the current supplied by the module in the "reduced output mode" can decrease very drastically, which then falls well below the performance threshold is. The electronics in the module would then switch back to the "Full Output Mode" and a new period of oscillation could begin.

• – ohne Zeitverzug schnell in den „Reduced Output Mode” geschaltet wird (damit sich Überlastsituationen zuverlässig vermeiden lassen).
• – das Zurückschalten in den „Full Output Mode” nicht sofort erfolgen kann sondern erst wenn die Vorraussetzungen für den „Reduced Output Mode” eine längere Zeit (einige Sek) nicht mehr gegeben sind.
• – die Schwellen für das Leistungsgetriggerte und das Spannungsgetriggerte Umschalten mit einer Hysterese beaufschlagt werden.

In order to avoid such a swinging of the control loop, the electronics which modifies the module according to the invention can still be provided with an algorithm which ensures that

• - Switches quickly into the "Reduced Output Mode" without delay (so that overload situations can be reliably avoided).
• - The switch back to the "Full Output Mode" can not be done immediately but only when the conditions for the "Reduced Output Mode" a longer time (several seconds) are no longer exist.
• - The thresholds for the power-triggered and the voltage-triggered switching with a hysteresis are applied.

For the reasons given above, in the examples described here, it is always assumed that the MPPT system limits the performance by reducing the string voltage to a voltage below the MPP voltage.

The most important operating states of a PV power plant should be summarized here again. By way of example, it is assumed here that at irradiance (based on the module area) of more than 825 W / m ² (slightly less than 5/6 of the STC power), the modules reduce the power output by 1/6, if these are provided by the MPPT system would be retrieved. In addition, MPPT Alternative A assumes that the MPPT system and the inverter system are designed to achieve the maximum workable power at 800 W / m ² irradiance (full output mode modules), and at higher irradiance levels The operating point of the modules is controlled by lowering the string voltage so that the modules deliver no higher power than at 800 W / m ² irradiance. In MPPT alternative B, it is assumed that the MPPT system for the active cells in the module sets the MPP.

1. Irradiance 1000 W / m ² (STC)

Here we measured the performance with an MPPT after alternative B. The module goes into the "reduced output mode" and delivers the power that all cells in the module could deliver together (ie without power limitation) at 833 W / ^m2 (1000 W / ^m2 · 5/6). This power defines the maximum power (P _{max_STC} ) of the module under STC conditions and is defined as 100% relative module power (cf. 7 ).

2. Irradiance 1000 ... 825 W / m ²

The PV cells generate electricity. The MPPT system lowers the power that the modules deliver, giving the modules the same power as 800 W irradiance (Alternative A). The cells in the solar module are not operated in the MPP. One module delivers 96% of the relative module power.

If the module is connected to an alternative B-type MPPT system that does not limit the module power consumption as described, the electronics in the solar module modified according to the invention will increase power generation by 1/6 5/6 reduce. The solar module provides 83 ... 100% of the relative module power. In this case, the active cells of the module are operated in the MPP of a conventionally operating MPPT system (cf. 7 ).

Over the year, higher yield will be achieved with an alternative power A-limited MPPT system than with alternative B.

3. Irradiance 825 ... 800 W / m ² (80% of 1000 W / m ² )

The PV cells generate electricity. The electronics in the modified module according to the invention does not reduce voltage and power. The Alternative MPPT system regulates the power that the modules deliver, giving the modules the same output as 800W irradiance. The cells in the solar module are not operated in the MPP (as in case 1 with 1000 W / m ² irradiance).

Should the module be connected to an MPPT system according to Alternative B, which does not limit the removed module power as described, the electronics in the solar module modified according to the invention will not reduce the power generation. Thus, under these operating conditions theoretically a higher yield than with alternative A can be achieved. It is assumed that this operating state is only correct in a small fraction of the time, which puts the advantage of alternative B into perspective. In addition, this range is susceptible to hunting as previously described.

4. Irradiance 800 ... 0 W / m ² <(80% of 1000 W / m ² )

The PV cells generate electricity. The module works in "Full Output Mode". The Alternative A and Alternative B MPPT systems behave identically and control the operating point of the modules so that the modules deliver maximum power. The relative module output is 0 ... 96%

In the following the invention will be explained by way of example with reference to the accompanying figures. They show:

1 Electrical wiring of a solar module using the example of a typical module with 72 crystalline silicon wafer cells.

2 Electrical wiring of a modified solar module according to the invention in which the voltage and power can be reduced.

3 Electrical wiring of a modified solar module according to the invention in which the voltage and power can be reduced in two stages.

4 Electrical wiring of a modified solar module according to the invention in which two strings are connected in parallel.

5 : Relative module performance of an idealized module according to 1 depending on the radiation intensity

6 : Relative module performance of an idealized module according to 2 or 4 in conjunction with MPPT system according to alternative A

7 : Relative module performance of an idealized module according to 2 respectively. 4 in connection with MPPT system according to Alternative B

8th : Example of the structure of the control electronics 9

LIST OF REFERENCE NUMBERS

1 ... 6

Connections to the described electronics circuit ( 40 ) can be modified with the solar module.

1

Negative pole of the solar module

2

Minus pole of PV cell array

3

first connection for switch ( 8th )

4

second connection for switch ( 8th )

5

Minus pole of voltage measurement of a group of active cells

6

Plus pole of voltage measurement of a group of active cells

7

Current sensor for measuring the current through module or cells

8th

electronic power switch controlled by 9

9

Control electronics

30

Ribbon to the minus connection of the cell field

31

Ribbon to center tap after a cell row (12 cells) of the cell field

32

Ribbon to center tap after 2 cell rows of the cell field

33

Ribbon to center tap after 4 cell rows of the cell field

34

Ribbon for positive connection of the cell field

38

Minus pole of connection box (J-Box)

39

Plus pole of connection box (J-Box)

40

Electronic circuit can be reduced with the power and voltage of the PV module.

41 ... 43

Bypass diodes

50

Connection box for plus and minus

51

Connection box for minus

52

Connection box for plus

81

Resistor for measuring the module current

82

switch

83

AC peak value determination

84

Analog-to-digital converter to determine the module current

85

Analog-to-digital converter to determine the average active cell voltage

86

Central control

87

programmable memory for individual module data

100

solar module

101 ... 236

PV cells; The cells are numbered according to the interconnection; cell 101 is serial with cell 102 connected, 102 is with 103 connected ....

In 1 is the interconnection of a typical crystalline 72-cell Silizum PV module whose busbars are outlined on the front, while the busbars on the back are hidden.

The negative pole of the connection box (J box) is led to the negative pole of the cell field. The cell field consists of 72 cells, each with 2 busbars, the cells are contacted on the front and on the back. The example uses cells whose positive pole lies on the back, while the front of a cell represents the minus pole of the cell. This cell polarity is only to be understood as an example. A person skilled in the art knows how to modify the interconnection if the cells have a different polarity or if the cell type requires a completely different interconnection. In each case for 2 cell rows a bypass diode is available. When meandering the cells of the bypass diode can be connected with minimal effort (including very short leads). A module with 72 cells in 6 rows requires 3 bypass diodes. One bypass diode each is used for two cell rows. The first bypass diode 41 the cells are connected in parallel to the first 24 cells, whereby the tap after 24 cells between cell 124 and 125 With 32 referred to as. The first diode 41 lies between the negative pole of the cell field and the first tap after 24 PV cells. connection 33 is the tap for another two cell rows (24 cells) between cell 148 and cell 149 , Here is the associated bypass diode 42 between connection 32 and 33 , The third bypass diode 43 lies between the tap 33 and the connection 34 , the positive pole of the cell field. The bypass diodes are polarized in such a way that they reverse polarity during normal operation of the module (the module generates current). If due to shading of some cells of the module, the power generation in the cells of the module is not sufficient to generate a positive module voltage by a sufficiently high current, prevent the bypass diodes that the module is poled too negative. The bypass diodes prevent over individual cells to high reverse voltages (negative compared to the normal operation of power generation) occur. Usually, the bypass diodes are in the junction box 50 accommodated.

In 2 shows the module just described with a modification according to the invention. The modifications are in the circuit block 40 summarized. This includes a current sensor 7 , a circuit breaker 8th , and a control electronics 9 , The control electronics can from the voltages between connection 5 and 6 the mean voltage of an active cell is there between connection 5 and 6 a known number of active cells are connected. At the same time with the help of the current sensor 7 the current through the module (equal to the current through each of the serially interconnected active cells) is determined. The current sensor is with connection 2 at the minus pole of the cell field 30 connected and can, for example, by means of a very low-resistance electrical resistance or with the help of the magnetic field generated by the module current and a magnetic sensor or another technique work. The second connection of the current sensor is with 1 is located at the negative terminal of the PV module so that the current sensor measures the current flowing through the module. From the multiplication of cell current and cell voltage, the average power of an active cell in the module can be determined. If the power of an active cell exceeds a certain threshold, the circuit breaker becomes 8th switched so that the outputable by the module power is reduced and thus the module in the "Reduced Output Mode" is. The example uses a module that has an extra tap 31 after one cell row (or 1/6) of all cells, so that the controller reduces both the module power and the module voltage in the "reduced output mode" by 1/6 to 5/6 of the power. These values, like the rest of the construction information, are to be considered as examples. In practice, meaningful values of power reduction are between 5% and 35%.

The module can be switched back again from the "reduced output mode" if the control electronics detects that the threshold values relevant for switching have fallen significantly below (due to the inclusion of a hysteresis). In 2 the power reduction is achieved by having circuit breakers 8th with the connections 3 and 4 on the one hand 30 , the negative pole of the module field and the other tap 31 is connected and shortcuts exactly one row of modules so that only 5/6 of the cells are active.

The power and voltage reduction does not have to be in one stage and does not have to be done by bridging cells. 3 shows a modification in which there are two stages of "reduced output mode". About the switch 8th Alternatively, different taps ( 30 . 31 . 32 ) of the module field to the current sensor and the negative terminal of the solar module. So once the entire cell field, once only 5/6 and once only 4/6 of the cell field are active.

Again, the sizes 4/6 and 5/6 (factor on which the module performance is reduced) can be seen again as an example. In general, reasonable values are in the range 60% ... 95%.

In 4 another embodiment of the invention is explained. Here, a module is shown in which 2 strings of cells are connected in parallel. The strings have a length of 36 cells each, with the first string passing through the cells 101 ... 136 is formed while the second string through the cells 201 ... 236 is formed. The cell area with cells 101 ... 112 of the first string is electrically parallel to the comparable cell area with cell 201 ... 212 the second string switched. The same applies to the cell areas with cells 113 ... 118 ; 119 ... 124 ; 125 ... 136 from the first string with respect to the comparable cell areas 213 ... 218 ; 219 ... 224 ; 225 ... 236 , The module has two separate junction boxes (J-Box) one for plus and one for minus. The two cans are attached to the right and left of the "landscape" oriented module. This simplifies the interconnection of two modules arranged side by side, since only very short connection lines are required for connection to an adjacent module connected in series.

The cells are connected in such a way that one string lies on the lower half of the module surface and the second string lies on the upper half of the module surface. Thus, even if, for example, the lower half of the module is provided, the module can still deliver the energy that is generated in the uncommunicated second string. The lowering of the module voltage and the module power happens in this case by short-circuiting two parallel-connected partial strings with 6 cells connected in series via the taps between cell 118 and 119 (associated with the tap between cell 218 and 219 ) and between cell 124 and 125 (associated with the tap between cell 224 and 225 ) are connected. In this example, the average voltage of an active cell between the minus pole of the cell field and the center tap of the cell field between cell 118 and 119 (associated with the tap between cell 218 and 219 ) Here, the voltage of 18 cells connected in series is measured. The bypass diode 43 for the serially connected cells 118 ... 136 (respectively. 218 .. .236 ) is housed in the junction box for the positive pole. For the cells 101 ... 118 (respectively. 201 .. .218 ) is the bypass diode 41 available in the junction box for the negative pole.

In 5 ... 7 is shown how the relative output power depending on the radiation intensity behaves for different PV modules in connection with different MPP systems. In each case, the Y-axis indicates the output power relative to the output power of the module at 1000 W / m ² . For the sake of simplicity, it is assumed that the cells show a completely linear behavior between radiation intensity and MPP performance.

5 demonstrates the idealized behavior of a typical PV module 1 ,

6 shows the idealized behavior of a PV module according to the invention 2 or 4 in conjunction with an Alternative A MPPT system that limits the module's performance just below the module's switching threshold.

7 shows the idealized behavior of a PV module 2 or 4 in connection with an MPPT system according to alternative B that does not limit the performance. It can be seen that the "reduced output mode" in the module becomes active. In addition, in this example, a hysteresis is installed, from which it can be seen that the module is switched in this example at a Bestahlungsstärke of about 825 W in the "reduced output mode" and at Bestahlungsstärke of less than 810 W back into the "Full Output Mode "is switched.

The following is an exemplary structure of the control electronics 9 roughly described. It is believed that the current through a low-impedance measuring resistor 81 measured with, for example, 3 miliohms. At a current of 10 A (this is slightly more than a typical short-circuit current of a typical crystalline solar cell), there is a relatively small voltage drop of 30 mV that must be evaluated. This can, for example, a switch 82 take place alternately at both terminals of the measuring resistor picks up the potential and its peak to peak voltage in the AC peak determination 83 is determined and then an analog-to-digital converter 84 is supplied. The signal that the analog to digital converter to the central control 87 supplies represents by the measuring resistor 81 flowing electricity! The central control 87 gets at the same time a representative value for the cell voltage of an active cell, which whereby with the help of the analog to digital converter 85 the voltage between the terminals 5 and 6 that with one active area of the cell array are measured. The threshold for the cell voltage (VT) is in block 86 possibly taking into account that this value is dependent on the temperature. The arrows in the signal paths show the direction of the signals to which the cell voltage and cell power and other module parameters represent. It is obvious to a person skilled in the art that there are a number of (also bidirectional) signals for control in addition. To the control electronics is still a block 87 (programmable memory for individual module data), in which operating parameters or parameters for adjustment are stored, which are stored, for example, during initialization. It would be conceivable that here in the final test of the module in the production z. For example, in the vicinity of the flashing (here we determine the individual module performance) individual module parameters and correction values are stored, which compensate for production-related variations of the module and the control electronics. In the central electronics, the signals of the remaining parts are linked and also the other parts are controlled. In particular, the power and voltage power must be calculated (eg by multiplying the signals or by adding the logarithmic signals - the latter is useful if the AD converters have such a logarithmic characteristic) and with the power threshold possibly taking into account the hysteresis are compared. Furthermore controls the central control 87 also the circuit breaker 8th , which can be realized for example by an n-channel MOS transistor. In order to be able to drive this transistor effectively with a sufficiently high voltage at the gate, it can be advantageous to install a voltage converter for it, which boosts the voltage for it! It is advantageous to integrate most of the functions described here into a chip, so that it can be produced cost-effectively.

Due to the fact that in the modified solar module, the current flowing through the module is measured, so there is also a possibility to determine fault conditions of the PV power plant and to respond to it.

In order to increase the safety of a PV power plant (this can also be a small system on a building), it is advantageous if a PV module reduces the voltage to a non-dangerous level in the event of a fault or even shuts off the supply of energy altogether.

For example, can be recognized as an error case, if for several seconds, only a very small current is removed from the modules, although the modules provide sufficient voltage. For this purpose, the current is measured, which emits the solar module. If this current is very low (for example, less than 50 mA) then the module goes into a safe power state. In this safe power state, the module voltage is only a fraction of the actual module voltage (for example, only 100 mV ... 3 V). Even with series-connected modules in systems with a system voltage of up to 1000 V, only safe voltages (eg 30 V) are to be expected in the Safe Power state. This ensures that it can no longer cause personal injury through electric shock. The PV module can be brought out of the "safe power state" if the current that is removed from the module briefly reaches a relatively high value (eg 200 mA). If one uses the modules of the invention in conjunction with a suitable inverter, which includes an additional circuit that can raise the modules from the "safe power state", so you can make a significant contribution to the safety of PV power plants. Without additional signal lines, the inverter can put the modules into the "safe power state" and also bring the modules back out of it.

Alternatively, the control of the safe power state of the modules can also be switched by a temperature sensor (overtemperature or fire) or additional signals. These signals can also be transmitted wirelessly, for example. For example, it is conceivable that the modules deliver power only when a wirelessly transmitted control signal is present or has been sent a short time ago. This control signal may be, for example, a high frequency signal of a certain frequency. Furthermore, it is conceivable that this control signal is sent via WLAN, Bluetooth or ZigBee to the modules.

It is also conceivable that the electronics in the solar module further distributes the control signal to adjacent modules.

• – Speicherung einer Seriennummer des Moduls
• – Speicherung von Moduldaten und Leistungsdaten (P_max, V_OC, Fertigungsdatum, Hersteller Code, Modultyp, ...) des Moduls bei Auslieferung
• – Ermittlung und Speicherung von Betriebsdaten (Temperaturverlauf, Verlauf der Leistungsabgabe, Verlauf des Stroms, Verlauf der Spannung, Integrale erzeugte Energiemenge, Überschreitungen von Spezifikationsgrenzen, ...)
• – Interface zu einfachen (z. B. drahtlosen) Abfrage der gespeicherten Daten
• – Funktion mit der Modul aktiviert werden kann (denkbar ist, dass ein neues oder mehrere Tage nicht verwendetes Modul vollständig deaktiviert wird, und nur durch einen an die Seriennummer gekoppelten geheimen Code aktiviert werden kann. Damit könnte ein Diebstahl von Modulen weniger attraktiv gemacht wer
• – Interface zu einfachen (z. B. drahtlosen) Abfrage der gespeicherten Daten

It makes sense to integrate all additional functions of the PV module cost-effectively into an integrated circuit. This circuit could also be supplemented by additional functions such as:

• - Storage of a serial number of the module
• - Storage of module data and performance data (P _max , V _OC , production date, manufacturer code, module type, ...) of the module at delivery
• - Determination and storage of operating data (temperature history, course of the power output, course of the current, curve of the voltage, integrally generated energy quantity, exceeding of specification limits, ...)
• - Interface to simple (eg wireless) retrieval of the stored data
• - Function with which the module can be activated (it is conceivable that a module that has not been used for a whole day or several days is completely deactivated and can only be activated by a secret code linked to the serial number, thus making theft of modules less attractive
• - Interface to simple (eg wireless) retrieval of the stored data

Due to the fact that an integrated circuit is built into the module anyway, the functions mentioned can be realized in a particularly cost-effective manner.

Claims (5)

PV module, which includes a plurality of similar PV cells, and which is provided with an additional electronic circuit, which determines the average cell voltage and the average cell power of the active cells in the module and if the average cell voltage exceeds a voltage threshold and / or if the average active cell power exceeds a power threshold, the module switches to a reduced output mode in which module power and module voltage are reduced by deactivating a portion of the cells, and whereby the "reduced output mode" is ended again, if the conditions for this are no longer met. PV module according to claim 1, characterized in that in the module in the "reduced output mode" between 65% and 95% of the cells of the module are in the active state. PV module according to claim 1 or 2, characterized in that the power threshold of an active cell, in which the module in the "reduced output mode" switches is 65 to 95% of the power that generates the cell under STC conditions. PV module according to claim 1, 2 or 3, characterized in that the voltage threshold of an active cell, in which the module in the "reduced output mode" switches is at a voltage, at least at the open circuit voltage, which is a representative cell at - Generated 30 ° at 1000 W / m ² irradiance. Integrated circuit with a PV module can be supplemented to enable the functions of claim 1, 2, 3 or 4.

Images