EP1878106A2

EP1878106A2 - Plurality of solar cell modules, each of which is coupled to a voltage transformer via a switch element

Info

Publication number: EP1878106A2
Application number: EP06724221A
Authority: EP
Inventors: Rainer Merz
Original assignee: Universitaet Stuttgart
Current assignee: Universitaet Stuttgart
Priority date: 2005-05-02
Filing date: 2006-04-11
Publication date: 2008-01-16
Also published as: US7911082B2; DE102005021152B4; DE102005021152A1; WO2006117061A3; WO2006117061A2; US20080105292A1

Abstract

The invention relates to a solar cell device comprising a plurality of solar cell modules (Zl, Z2, Z3, ..., Zn) whose voltage outputs (UE1, UE2, UE3, ..., UEn) are respectively coupled to a voltage transformer (12) by means of a switch element (Tl, 12, T3, ..., Tn), wherein said voltage transformer is preferably constructed in the form of an inverted converter or a step-up converter. The partial disconnections of the individual solar cell modules make it possible to avoid losses by the independent operation thereof. The voltage transformer (12) makes it possible to adapt an output voltage in a large extend. A microprocessor control (16) makes it possible to attain an optimal energy output of the integral system.

Description

Solarzellenvorrichtunq

The invention relates to a solar cell device with at least one solar cell module, which is designed to supply a consumer.

If solar cells are to be used to supply electrical consumers, it is usually necessary for this purpose to interconnect a large number of solar cells with one another. The connection of individual solar cells or solar cell modules usually takes place in parallel or series connection. By Shadowing of individual cells or modules can lead to severe losses in short-circuit current, no-load voltage and output power in these types of wiring. In order to avoid such losses, wiring variants with bypass or coupling diodes are usually used.

To obtain output voltages with higher values than those of a single cell or a single module, there are basically two options available.

According to a first variant, an output voltage which corresponds to an integer multiple of the voltage of a single cell or of a single module is achieved by series connection of identical, identical individual cells or modules, in which case a monolithic integrated series connection, which is customary in thin-film modules, is carried out.

Alternatively, a voltage conversion can be performed via energy transformation. In this case, an inductance stores the electrical energy that is supplied to it via a switching transistor and then outputs it again. Depending on the time of the energy release, this is a flux or flyback converter.

If no higher output voltage is desired than that of the individual cells or of the modules, then one uses the parallel connection of the cells or of the modules.

A series connection of individual solar cells or modules has the disadvantage that the weakest cell has the maximum Electricity determined. The weakest cell is the one that provides the lowest power under the given lighting conditions.

In monolithic integrated serial connection of solar cells, unwanted resistances occur parallel to the single cell during interconnection. In addition, due to illumination differences results in a maximum output current of the interconnected cells or modules, which is smaller or at most equal to the current output of the weakest cell. Just when solar cells or modules are integrated for mobile use, for example, in garments, so not all individual cells or modules can be lit the same. Since the input power of the individual cells or modules is very low due to the usually poor lighting, such losses due to shadowing are extremely problematic. On the other hand, if the cells or modules are connected in parallel, output currents occur between the individual cells or modules. The currents cause an adaptation of the individual voltages, since in a parallel connection, the individual cells or modules must all have the same potential.

The object of the invention is therefore to provide an improved solar cell device in which an adjustment of the output voltage can be made in the lowest possible loss manner.

This object is achieved by a solar cell device having a plurality of solar cell modules whose voltage outputs are each coupled via a switching element with a switchable voltage converter. In this way, circuit losses that could arise via series circuits and series circuits are basically avoided. Rather, each solar cell module can be controlled via its own switching element in a suitable manner to deliver its power to the Nutzspannungsausgang.

The switchable voltage converter may in this case be designed, for example, as a flyback converter or as a flux converter.

In this case, an embodiment as inverting flyback converter is conceivable (also known under inverse boost converter or in English flyback Converter or buck-boost Converter). This has the advantage that also output voltages can be achieved which are higher than the input voltage. In addition, it is possible to form the switching elements of the solar cell modules as part of the voltage converter, so that eliminates additional switching elements of the voltage converter.

In an alternative embodiment, however, the inverting flyback converter has its own switching element at its input.

This has the advantage that the timing of the flyback converter can be decoupled from the timing of the solar cell modules.

According to a further variant of the invention, the flyback converter is designed as a step-up converter (also known as an up-converter or in English under boost converter or step-up converter). The individual solar cell modules are preferably controlled sequentially via the switching elements.

At the output of the voltage converter, a capacitor may be connected parallel to the Nutzspannungsausgang, as far as this is preferred for the particular application.

The Nutzspannungsausgang can be connected directly to a consumer. Alternatively or additionally, it is possible to connect to the NutzSpannungsausgang an accumulator.

In a preferred embodiment of the invention, the voltage converter has a switching element (for example in the form of a FET) for tapping a rectified voltage.

This switching element may be arranged parallel to a rectifier diode of the voltage converter of the voltage converter. The switching element is driven such that a switching occurs when the diode is conductive.

Possibly. the rectifier diode can also be omitted altogether.

In this way, losses of the otherwise usual rectifier diode can be reduced, in particular for low-voltage and low-power applications. Here, the voltage drop across the track resistance of the switching element should be less than the voltage drop across the diode. For this purpose, the switching element (the transistor) should be operated in the saturation region. According to a further embodiment of the invention, at least one of the solar cell modules is formed as a single solar cell.

According to a further embodiment of the invention, at least one solar cell module has a plurality of interconnected solar cells.

Thus, it is possible to control each individual solar cell via a switching transistor or several solar cells together by means of only one switching transistor. The design used depends on the particular application, the total cost being naturally influenced by the number of switching transistors used.

In a preferred development of the invention, the switching transistors have control inputs which are controlled by a central controller, preferably by a microcontroller.

In this way, the switching times of the individual switching transistors can be optimized, on the one hand to obtain the desired output voltage and on the other hand to ensure the highest possible efficiency.

In this case, the switching transistors are preferably driven sequentially as a function of the performance data of the solar cell modules. For this purpose, the microprocessor can store data, which are characteristic of the performance of the individual modules, in an internal memory. Thus, optimal adjustments of the overall system to the lighting conditions and production-related variations of the characteristic data of individual solar cells or modules possible. Completely shadowed or defective cells or modules can also be switched off completely if required.

According to a further embodiment of the invention, the central controller is designed to control the ratio of the turn-on times to the ratio of the turn-off times of the switching transistors.

In this way, by changing the duty cycle, the output voltage can be adjusted within a certain frame to a desired setpoint.

The choice of switching times should take into account the capacities of the individual solar cell modules. In this case, it may be advantageous to additionally use a capacitor in parallel with its voltage output in one or more of the solar cell modules.

The switching transistors are preferably designed as field-effect transistors, in particular as MOS-FET's.

This ensures a particularly low-loss circuit.

According to a further embodiment of the invention, at least one solar cell is integrated with at least one switching transistor.

Thus, by integrated versions of solar cells and switching transistors further efficiency improvements can be achieved become. It may also be useful to form a whole series of solar cells with associated switching transistors as a single integrated circuit. If necessary, parts of the flyback converter or the entire flyback converter can also be included for this purpose.

Furthermore, it is also conceivable to carry out a combination with the microprocessor control on a chip.

According to a variant of the invention, the number of solar cells or modules can be limited to only one.

In this case, which is preferably conceivable for particularly simple and inexpensive designs for the supply of small consumers, a higher efficiency over conventional arrangements is achieved by the switching element.

It is understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the invention.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. Show it:

FIG. 1 shows a circuit diagram of a solar cell device according to the invention; Figure 2 is a schematic representation of the drive signals for a sequential control of the switching transistors used;

FIG. 3 shows a version of a solar cell device according to the invention, which is generalized with respect to the embodiment according to FIG. 1;

FIG. 4 shows a modification of the embodiment according to FIG. 3

1 shows a solar cell device according to the invention is shown schematically and generally designated by the numeral 10.

The solar cell device 10 has a plurality of solar cell modules Z1, Z2, Z3,..., Zn. In the illustrated example, each solar cell module Z1,... Zn is a solar cell, which in each case outputs a voltage U _E1 , U _E2 , U _E3 ,..., UE _n . The output of each solar cell module Z1, Z2, Z3,..., Zn is in each case coupled to a flyback converter 12 via a switching element, which is preferably designed as a FET or MOS-FET.

In the flyback converter 12 is an inverting flyback converter whose input voltage is applied to an inductance Ll in the form of a coil. The voltage across the coil Ll is tapped via a rectifier diode Dl and applied to a capacitor Cl and a Nutzspannungsausgang 14, where the useful voltage U _A drops and is used by a connected consumer. Parallel to the capacitor Cl, a Accumulator be provided, which can be charged via the flyback converter 12.

Parallel to the rectifier diode Dl a switching element TDl is connected, through which the rectifier diode Dl can be supported.

To control the overall system is a central control in the form of a microprocessor 16, which is connected to the control inputs of the switching elements Tl, T2, T3, ..., Tn and the switching element TDl.

The switching elements Tl, T2, T3, ..., Tn are sequentially controlled by the microprocessor 16, whereby both the timing of the flyback converter 12 and a suitable selection of the solar cell modules Zl, Z2, Z3, ..., Zn depending on the respective Performance data is done. In the blocking phases, the photocurrent charges the self-capacitance of the respective solar cell modules Z1, Z2, Z3,..., Zn. Depending on the nature of the respective solar cell modules Z1, Z2, Z3,..., Zn, an additional capacitance in the form of a capacitor can be provided parallel to the respective solar cell module.

Due to the additional switching element TDl in parallel to the rectifier diode Dl whose losses are reduced, which is particularly advantageous for low voltage and low power applications. In this case, the voltage drop across the track resistance of the switching element TDl should be less than the voltage drop across the diode. The switching elements TDl, Tl, T2, T3, ..., Tn should be operated in the saturation region for this purpose. A possible timing of the solar cell modules Z1, Z2, Z3,..., Zn via a suitable control software is shown by way of example in FIG.

In the simplest case, all solar cell modules Z1, Z2, Z3,. •. , Zn are sequentially connected in succession, the turn-on time T ₃ and the turn-off time T _L of each solar cell module being the same.

The switching element TDl parallel to the rectifier diode Dl must always conduct when the diode Dl must also turn through to maintain the current flow in the inductance Ll. This is always the case when all switching elements Tl, T2, T3, ..., Tn lock. Possibly. can the diode Dl also completely eliminated.

The microprocessor 16 now advantageously records performance data about the individual solar cell modules Z 1,..., Zn and stores them in an internal memory. About the blocking or switching times of the switching elements Tl, ..., Tn the states of the individual solar cell modules Zl, ..., Zn can be detected and so a respective cell more often or longer be selected than the others. The overall system can thus be optimally adapted to the lighting conditions and to a production-related scattering of the characteristic data of individual solar cell modules. In this case, completely shaded or defective solar cell modules can be detected and correspondingly less taken into account or, if necessary, switched off completely. The switching frequency f = 1 / (Tl + ... + Tn) of the circuit is determined by the number of solar cell modules Z1,. •., Zn dependent, as well as their own capacity. The optimum switching times can be determined for each application.

The choice of switching times should take into account the cell capacity. At high switching frequencies, possibly high-frequency effects, such as characteristic impedance of cells, must be taken into account.

Since the circuit works according to the converter principle, the output voltage U _{A can be set} within a certain range to any values above and below the individual input voltages U _E1 ,..., U _En . For this purpose, only the duty cycle, that is, the ratio between T _L and the total duration T of a respective switching cycle must be adjusted. An increase in the duty cycle leads to an increase in the output voltage.

Since the individual solar cell modules do not influence each other, losses due to differences in illumination or different characteristics are excluded. Power losses through coupling and bypass diodes as in the prior art are avoided.

Since the rectifier diode Dl and the parallel switching element TDl are in the reverse direction, when the control is switched off and the output side, an already charged battery is connected, the discharge of the battery is low.

It is understood that, as explained above, either each solar cell module Z1, Z2, Z3,..., Zn can be represented by a single solar cell or that a plurality of solar cells are combined to form a solar cell module may be, which is connected via a switching element to the flyback converter.

Likewise, it is understood that, depending on the desired degree of integration, the switching elements can be embodied integrated with the relevant solar cell modules, it also being possible for a plurality of solar cells with switching elements to be accommodated on a single chip or, if appropriate, also for the integration of the voltage converter or the microcontroller. > can be dragged.

Fig. 3 shows a modification of the embodiment of the invention, which is generalized with respect to the embodiment of FIG. 1 and is generally designated 10a. In this case, the inverting flyback converter 12a has its own switching element Tk. This allows a decoupling of the switching frequencies of the inverting flyback converter and the solar cell modules. In addition, a conceivable capacitance is indicated parallel to the input of the flyback converter 12a. Otherwise, the circuit corresponds to the previously described embodiment according to FIG. 1

Fig. 4 shows a further modification of the invention, in which the flyback converter 12b is formed as a boost converter. This results in no inverted output voltage as in the above-mentioned embodiments. The output voltage U _A can assume no smaller values than the input voltage.

Claims

claims

1. Solar cell device having a plurality of solar cell modules (Z1, Z2, Z3,..., Zn) whose voltage outputs (U _B1 , U _E2 , U _E3 ,..., U _En ) are each connected via a switching element (T1, T2, T3, ..., Tn) are coupled to a switchable voltage converter (12, 12a, 12b).

2. Solar cell device according to claim 1, wherein the voltage converter (12, 12a, 12b) is designed as a flyback converter or as a flux converter.

3. Solar cell device according to claim 1, wherein the voltage converter is designed as an inverting flyback converter (12, 12a).

4. Solar cell device according to one of the preceding claims, wherein the switching elements (Tl, T2, T3, ..., Tn) of the solar cell modules (Zl, Z2, Z3, ..., Zn) are formed as part of the voltage converter (12) ,

5. Solar cell device according to claim 1, wherein the voltage converter is designed as a step-up converter (12b).

6. Solar cell device according to one of the preceding claims, wherein parallel to a NutzSpannungsausgang (14), a capacitor (Cl) or an accumulator is connected.

7. Solar cell device according to one of claims 2 to 6, wherein the voltage converter (12, 12 a, 12 b) a switching element (TDl) for tapping a rectified voltage.

8. Solar cell device according to claim 7, wherein the switching element (TDl) is arranged parallel to a diode (Dl) and is controlled via a controller (16) such that a switching occurs when the diode (Dl) is conductive.

9. Solar cell device according to one of the preceding claims, wherein at least one solar cell module (Zl, Z2, Z3, ..., Zn) is formed as a single solar cell.

10. Solar cell device according to one of the preceding claims, wherein at least one solar cell module (Zl, Z2, Z3, ..., Zn) has a plurality of interconnected solar cells.

11. Solar cell device according to one of the preceding claims, wherein the switching elements (Tl, T2, T3, ..., Tn) control inputs, which are controlled by a central controller (16), preferably by a microcontroller.

12. Solar cell device according to claim 11, wherein the central controller (16) for the sequential control of the switching elements (Tl, T2, T3, ..., Tn) of the solar cell modules (Zl, Z2, Z3, ..., Zn) is formed ,

13. solar cell Vorriσhtung according to claim 11 or 12, wherein the central controller (16) for controlling the Schaltele- (Tl, T2, T3, • -., Tn) depending on performance of the solar cell modules (Zl, Z2, Z3, ..., Zn) is formed.

14. Solar cell device according to one of claims 11 to 13, wherein the central controller (16) is adapted to the ratio of the turn-on (T ₃ ) to the ratio of the turn-off (T _L ) of the switching elements (Tl, T2, T3, .. ., Tn).

15. Solar cell device according to one of the preceding claims, wherein at least one of the solar cell modules (Zl, Z2, Z3, ..., Zn) a capacitor in parallel with the voltage output (U _E1 , U _E2 , ü _E3 , ..., U _En ) having.

16. Solar cell device according to one of the preceding claims, wherein at least one switching element (Tl, T2, T3, ..., Tn, TDl) as a switching transistor, preferably as a field effect transistor is formed.

17. Solar cell device according to one of the preceding claims, wherein at least one solar cell with at least one switching element (Tl, T2, T3, ..., Tn) is integrally formed.

18. Solar cell device having at least one solar cell module (Z1, Z2, Z3,..., Zn) whose voltage output (U _E1 , U _E2A U _E3 ,..., U _En ) is connected via a switching element (T1, T2, T3,. .., Tn) with an inductance (Ll) of a switchable voltage converter (12, 12a, 12b) is coupled, at which the voltage via a switchable rectifier (TDl) abge- and coupled to a Nutzspannungsausgang (14) is coupled.

19. A solar cell device according to claim 18, wherein the switchable rectifier (TDl) is arranged parallel to a diode (Dl) and is controlled via a controller (16) such that a switching occurs when the diode (Dl) is conductive.