DE102017115000A1 - Photovoltaic unit, photovoltaic system, method for operating a photovoltaic unit and method for operating a photovoltaic system - Google Patents

Abstract

The invention relates to a photovoltaic unit (1) with a photovoltaic module (2), an adjustable boost converter (3) and a control unit (9). The control unit (9) controls the boost converter (3) so that it is operated resonantly. Furthermore, the invention relates to a photovoltaic system with a plurality of photovoltaic units (1), wherein each photovoltaic unit (1) comprises a photovoltaic module (2) and a variable boost converter (3). The photovoltaic units (1) are connected in parallel with the respective output sides of the boost converter (3). Corresponding operating methods are also shown.

Description

The invention relates to a photovoltaic unit with a photovoltaic module, as well as a photovoltaic system with a plurality of photovoltaic units. Furthermore, the invention relates to a method for operating a photovoltaic unit or a photovoltaic system of the type mentioned.

The radiation energy of the sun should be converted as efficiently as possible by photovoltaic cells into electrical energy. This electrical energy is to be stored and / or converted into usable electrical energy. Due to a decline in the price of photovoltaic modules, applications with non-ideal alignment are now becoming commercially interesting. This photovoltaic modules can be combined in a system with different orientation and varying degrees of shading.

It is now standard practice for private as well as public buildings (for example single-family homes, multi-family dwellings, public buildings and industrial plants) to be equipped with photovoltaic systems. First, the radiant energy of the sun is converted into electrical energy by means of photovoltaic cells. There are currently two different concepts for photovoltaic systems. According to one concept, larger photovoltaic plants (for example plants with a peak power of more than 1 kWp) are currently divided into so-called photovoltaic strings. It is a variety (for example, between 6 and 14 ) connected in series by photovoltaic modules. The individual photovoltaic modules also consist of series-connected individual photovoltaic cells. Typically, many photovoltaic cells are connected in series within a photovoltaic module in order to allow the most efficient use of electrical energy. This creates photovoltaic strings with partly over 100 series photovoltaic cells.

A disadvantage of such photovoltaic strings is that the performance of a photovoltaic string due to the series connection of the weakest photovoltaic cell (that is, of the photovoltaic cell with the lowest energy yield) is determined. If one or more photovoltaic cells are now shaded or exposed to very low radiant energy or are e.g. faulty, the operating point of all series-connected photovoltaic cells is negatively affected. If photovoltaic systems with different orientation (for example, south, east, west) are constructed, conventionally, the photovoltaic modules of the same orientation must always be combined in a photovoltaic string. In other words, all series-connected photovoltaic cells or photovoltaic modules of a photovoltaic string should be irradiated as uniformly as possible in order to counteract as far as possible a negative influence on the operating point.

Furthermore, in such systems with multiple photovoltaic strings of different orientation each photovoltaic string is usually operated with its own inverter. As a result, the inverters of the plants are usually operated only in a partial load operation and have a poor conversion efficiency.

In addition to this concept of larger photovoltaic systems, there is yet another concept for the use of radiant energy, which has been used so far in very small systems, which usually consist of only one photovoltaic module. An inverter must be used for exactly this single photovoltaic module. The cost-benefit ratio of such systems is thus relatively poor. In some cases, so-called maximum power point trackers (MPP trackers) are used, which adjust the electrical load of a photovoltaic cell or a photovoltaic module such that the photovoltaic cell or the photovoltaic module, the maximum electrical power can be removed. Such power electronic circuits are usually expensive and still have low partial load efficiencies. Single modular inverters also usually have only a moderate efficiency, are expensive and usually do not meet the technical connection requirements.

Furthermore, all currently available photovoltaic systems can provide their energy only at the time of the incidence of radiation and are thus source-dependent. Adaptation to consumption can currently only be achieved by the use of additional energy storage devices. These additional storage systems significantly increase the conversion losses of a photovoltaic system.

It is an object of the present invention to provide photovoltaic units or photovoltaic systems and their method of operation of the type mentioned, which allow alignment of a photovoltaic module according to the structural requirements, without limitation due to an electrical topology of the corresponding system, and also improved compared with conventional solutions efficiency achieve.

This object is achieved according to a first aspect by a photovoltaic device according to claim 1.

The photovoltaic unit has a photovoltaic module and a variable boost converter. The variable boost converter is configured to regulate a DC voltage of the photovoltaic module at an input side of the boost converter to a higher DC output voltage at an output side of the boost converter for controlled removal of electrical power provided by the photovoltaic module.

Furthermore, the photovoltaic unit has a control unit for controlling the boost converter. The control unit has an input side for supplying signal values of at least one electrical variable of the photovoltaic unit and an output side for providing at least one control signal for actuating at least one switching means of the controllable up-converter. The control unit is set up to regulate by means of the at least one control signal in addition to a variable switching ratio also a switching frequency and / or a switching dead time of the at least one switching means such that the boost converter is operated resonantly.

By using such a resonant switching boost converter, the efficiency of the photovoltaic device can be kept very high over almost the entire work area. By controlling the boost converter in a resonant mode, ie operating the boost converter with a specific (possibly operating point-dependent) switching frequency or switching dead time (as will be explained in more detail below), it is achieved that the energy taken from the photovoltaic module assumes a maximum value. By an appropriate regulation of the up-converter, the latter thus adjusts the current of the photovoltaic module in such a way that, given a given radiation intensity, the energy yield of the photovoltaic unit becomes maximum. In this way, the photovoltaic unit can be operated in an individual, possibly temporally variable, operating point, whereby the radiation energy can be optimally converted into electrical energy with the highest efficiency. An optimal operating point is constantly readjusted by means of the control despite changing operating conditions (daytime-dependent radiation intensity or changing degree of shading), so that the boost converter is always operated resonantly and ensures the best possible energy yield of the photovoltaic module. In this way, the efficiency of a photovoltaic system, in which such a photovoltaic unit is used, can be significantly increased compared to conventional solutions.

Elaborate MPP tracker can be omitted in such a photovoltaic unit either entirely or be extended by the explained control concept, so that the efficiency of the photovoltaic unit or an entire photovoltaic system or their cost-benefit ratio is improved.

The at least one electrical variable of the photovoltaic unit, which can be fed to the control unit at its input side, can be, for example, an electrical voltage or an electrical current at the photovoltaic module and / or an output voltage at the output side of the photovoltaic unit. The control unit may, by means of the at least one control signal, predefine a variable switching ratio of the at least one switching means in the up-converter, for example by a pulse-width-modulated (PWM) signal. In addition, as explained, the switching frequency of the at least one switching means can be made variable so that it can be regulated. Alternatively or additionally, a switching dead time of the switching means can be regulated. The switching dead time in this case describes a period of a delay of the switching of the switching means between the switching states. By a controlled Schalttotzeit switching of the switching means can be tuned to timings in which the switching means, a voltage near zero (ideally zero) is reached. That is, the switching dead time provides a controlled delay of switching, with switching delayed until the switching means reaches a voltage near zero (ideally zero). In this way, switching losses in the switching means can be minimized. A controlling intervention of the control unit at least in one of the parameters switching frequency and switching dead time of the at least one switching means of the boost converter in addition to the variable switching ratio allows a regulation of the boost converter in a resonant mode with the advantages explained above.

The resonant up-converter is operated, for example, with very high switching frequencies between 100 and 500 kHz. This makes it possible to make the passive components of the power electronics very compact. Thus, the manufacturing costs of the resonant up-converter are significantly cheaper than currently available power electronics, such as inverters, which are used for typical photovoltaic units or photovoltaic systems.

The above object is achieved according to a second aspect by a photovoltaic system according to claim 2.

The photovoltaic system has a variety N of photovoltaic units, each one Photovoltaic unit comprises a photovoltaic module and a variable boost converter. Each controllable boost converter is configured to regulate DC voltage of the respective photovoltaic module at an input side of the respective boost converter to a higher output DC voltage at an output side of the respective boost converter for controlled extraction of electrical power provided by the respective photovoltaic module. The photovoltaic units are connected in parallel with the respective output sides of the boost converter.

In such a photovoltaic system thus receives each photovoltaic module own power electronics (boost converter or boost converter), which is able to adjust the operating point of each photovoltaic module independently of other photovoltaic modules ideal and thus ensure the highest energy yield for each individual photovoltaic module, that is Adjust current of a respective photovoltaic module such that at a given radiation intensity of the energy yield is maximum. However, this power electronics is not, as usual, designed as an inverter, but as a boost converter or boost converter. An up-converter has a much better efficiency than an inverter. In this way, the overall efficiency of the photovoltaic system compared to conventional solutions can be significantly increased. Each individual photovoltaic module of the photovoltaic system can thus be operated and regulated in its individual, time-varying operating point, whereby the radiation energy of the sun can be optimally converted into electrical energy with the highest efficiency.

The respective boost converters of the respective photovoltaic units convert the DC voltage of a respective photovoltaic module to a higher voltage level at a respective output side of the respective boost converter. This makes it possible in a simple manner to interconnect the photovoltaic units with their respective output sides of the boost converter in parallel. It is thus no longer necessary in the photovoltaic system of the type described, photovoltaic modules, as previously customary, connect in series in order to achieve a correspondingly high output voltage for further processing (for example by one or more inverters). Thus, the disadvantages of a performance penalty of conventional systems due to a series connection of photovoltaic modules, as they have been explained in the beginning, are also eliminated.

On the contrary, in a photovoltaic system of the type described here, each photovoltaic module individually contributes to power delivery without the photovoltaic system being reduced to the performance of the weakest photovoltaic module or a weakest photovoltaic string having the lowest energy yield. Rather, the overall efficiency of the photovoltaic system is increased because the summed energy yield of all photovoltaic modules despite possibly different radiation intensities or shading due to the parallel connection of the respective photovoltaic modules in the photovoltaic system is taken into account. As explained, in addition, the operating point of each photovoltaic module can be individually adjusted and readjusted by the respective up-converter of the photovoltaic units, which further increases the overall efficiency of the photovoltaic system.

The respective boost converters can be integrated directly into the respective photovoltaic module and form a common unit with it. The photovoltaic units thus formed can then be connected in parallel directly to the respective output sides via two (or more) conductors.

In various embodiments, the photovoltaic system comprises at least one inverter, wherein the at least one inverter is connected to an input side parallel to the photovoltaic units for converting a DC voltage at the input side of the at least one inverter into an AC voltage at an output side of the inverter. The at least one inverter is advantageous for a summed current consumption of a plurality M , With M greater than 1, designed by photovoltaic units. In such an implementation of the photovoltaic system, not every photovoltaic unit needs its own inverter. Conventionally partially used single-module inverters with moderate to poor efficiency thus omitted in the photovoltaic system described here. Rather, one or more inverters are used, which are connected in parallel with the photovoltaic units and in each case for a summed current consumption from a plurality M , With M greater than 1, are designed by photovoltaic units.

By such a modularization of the photovoltaic system, wherein in each case an inverter is designed for a summed current consumption from a plurality of parallel to the inverter photovoltaic units, it is possible to increase the utilization of a single inverter and thus to achieve a very high overall conversion efficiency. In this way, the inverter or statistically more often work in a favorable for their efficiency range, even if the respective energy yields of the photovoltaic units for Example fluctuate due to a different radiation energy or a different degree of shading of the respective photovoltaic modules. This minimizes conversion losses and significantly increases the yield of the photovoltaic system.

In various embodiments of the photovoltaic system, one or more of the photovoltaic units are designed according to the above-mentioned type. This means that a respective control unit is arranged in the respective photovoltaic units, which, according to the manner explained above, controls the at least one switching means of the respective boost converter in such a way that the boost converter is operated resonantly. Ideally, all the photovoltaic units of the photovoltaic system are designed in this way. Thus, the efficiency of the individual photovoltaic units and ultimately the entire photovoltaic system over almost the entire work area can be kept very high. Experiments resulted in an efficiency of more than 99% in the typical working range of the photovoltaic units and a partial load efficiency of over 98%. In contrast, commercially available power electronics usually only achieve efficiencies of up to 95% at the best operating point. Such efficiency of conventional solutions falls under part load very quickly below 90%.

The above object is achieved according to a third aspect by a method for operating a photovoltaic device according to claim 7.

The method is implemented for operating a photovoltaic unit of the type described above, wherein the control unit is supplied with signal values of at least one electrical variable of the photovoltaic unit and the control unit provides at least one control signal for driving the at least one switching means of the variable boost converter. The control unit regulates by means of at least one control signal in addition to a variable switching ratio and a switching frequency and / or a switching dead time of the at least one switching means, so that the boost converter is operated resonantly.

The implementation of such a method has the advantages, as have been explained above in connection with the correspondingly equipped photovoltaic unit or the correspondingly equipped photovoltaic system. By such a method of operation of a photovoltaic unit, the efficiency over conventional solutions can be significantly increased in this way.

The above object is achieved according to a fourth aspect by a method for operating a photovoltaic system according to claim 8.

The method is implemented for operating a photovoltaic system of the type discussed above, wherein the respective boost converters of the respective photovoltaic units independently set the respective photovoltaic modules individually to a specific operating point of power extraction.

Such a method also has the advantages as described above in connection with a corresponding photovoltaic system. By such a method of operation of a photovoltaic system, the overall conversion efficiency compared to conventional solutions can be significantly increased.

In various implementations of the method of operating a photovoltaic system, the value of the DC output voltage is variably set on an output side of a respective boost converter. However, the value of the DC output voltage is set above the value of the highest DC voltage generated by the photovoltaic modules. In this way, the operation of the photovoltaic system with respect to the generated output DC voltage of the respective boost converter can be made variable. Nevertheless, it is possible to set the maximum energy yield of the strongest photovoltaic module (the photovoltaic module with the highest DC voltage generated).

The respective boost converters of the photovoltaic system can be set or parameterized in various implementations of the method such that the output voltage of the respective boost converter can not rise above a corresponding maximum. In this way, the DC output voltage is limited at the output sides of the boost converter and the risk of damage to downstream components, other components in the parallel connection of the photovoltaic system or an operating staff prevented. In principle, however, the output DC voltage of a respective boost converter is advantageous, within the limits explained, variable. In this way, the parallel connection of all photovoltaic units can be adapted, for example, to the characteristics of parallel-connected inverters or energy stores. It is also conceivable to supplement the photovoltaic system with other photovoltaic units in a simple manner in a modular manner. In this case, the output direct voltage of the respective boost converter could be variably adapted to a modularly extended photovoltaic system or an alternating direction of the through the photovoltaic units to flexibly handle the electrical power supplied for feeding into an AC grid.

In various implementations of a method of operating a photovoltaic system, one or more, or advantageously all, of the photovoltaic units are operated in accordance with a method of operating a photovoltaic device of the type discussed above, that is, a resonant up-converter of the photovoltaic device. Due to a resonant operation of one or more or all of the up-converters of the photovoltaic units in the photovoltaic system, the overall conversion efficiency of the photovoltaic system during operation, as explained above, can be further increased.

All aspects and embodiments of the implementations of said methods are reflected in structural features and aspects of the above-explained photovoltaic units or photovoltaic systems and vice versa. This means that all implementations of the methods of the type described above can be applied to corresponding photovoltaic units or photovoltaic systems of the type explained above. Conversely, according to the operating method explained above, the photovoltaic units or photovoltaic systems can be designed structurally in accordance with the above-explained photovoltaic units and photovoltaic systems.

Further advantageous aspects are disclosed in the associated subclaims.

The invention will be explained in more detail below with the aid of several drawings.

• 1 eine schematisierte Darstellung einer Photovoltaikeinheit,
• 2 eine schematisierte Darstellung einer Regelung einer Photovoltaikeinheit gemäß 1 und
• 3 eine schematisierte Darstellung eines Teils eines Photovoltaiksystems mit einer Vielzahl von Photovoltaikeinheiten gemäß 1.

Show it:

• 1 a schematic representation of a photovoltaic unit,
• 2 a schematic representation of a control of a photovoltaic device according to 1 and
• 3 a schematic representation of a portion of a photovoltaic system with a plurality of photovoltaic units according to 1 ,

1 shows a schematic representation of a photovoltaic device 1 with a photovoltaic module 2 and a boost converter 3 , The photovoltaic module 2 can have a plurality of serially interconnected photovoltaic cells, the radiation energy of the sun convert into electrical energy and thus an electrical power at the photovoltaic module 2 provide. This is the case with the photovoltaic module 2 a characteristic DC voltage U_in starting with a characteristic direct current I_in from the photovoltaic module 2 is removable. These electrical sizes of the photovoltaic module 2 are at input terminals of the boost converter 3 at.

The up-converter 3 includes a coil or inductance 4 , a diode 5 , a storage capacity 6 , as well as a controlled switching means 7 , The switching means 7 can according to the embodiment in 1 a semiconductor switch (for example MOSFET). The switching means 7 may have an internal (parasitic) capacitance, which is common to the inductance 4 an LC-resonant behavior of the up-converter 3 is determined. Alternatively or additionally, one may be the switching means 7 parallel connected capacity 7 ' (in 1 dashed lines), by means of which a special capacitive behavior of the boost converter 3 influenced and the LC-resonant behavior is given. The up-converter 3 is set up, the DC voltage U_in the photovoltaic module 2 controlled at the input side in a higher DC output voltage U_out at an output side of the up-converter 3 to change. By controlled switching of the switching means 7 with a specific switching ratio between a switch-on phase and a switch-off phase, according to 1 can be controlled via a pulse width-controlled signal (PWM), as well as with a controlled switching dead time t_tot and a controlled switching frequency f_s, electrical energy from the photovoltaic module 2 in the inductance 4 be cached and according to the diode 5 in the capacity 6 which are the increased DC output voltage U_out at the output side of the boost converter 3 holds.

By controlling the switching means 7 The up-converter is set via the three parameters: switching ratio PWM, switching dead-time t_tot and switching frequency f_s 3 is controlled so that it is operated at a characteristic switching frequency, so that it operates resonantly. In this way, the from the photovoltaic module 2 taken current I_in be adjusted such that the energy transferred a maximum value in the respective operating point or operating point of the photovoltaic module 2 reached. Thus, the energy yield of the photovoltaic module 2 by said regulation of the up-converter 3 maximum or best possible. Especially with time varying operating point, among other things of the radiation intensity, of the temperature at the photovoltaic module 2 and the type of photovoltaic module 2 or in the photovoltaic module 2 used photovoltaic cells depends, can in this way the efficiency in each phase of operation of the photovoltaic module 2 be optimally adjusted, in particular with varying daytime and orientation-dependent varying radiation intensity.

By using the resonant switching boost converter 3 according to 1 Thus, the efficiency over almost the entire working range of the photovoltaic unit 1 be kept very high. Experiments resulted in an efficiency above 99% in the typical working range and a partial load efficiency of over 98%.

The parameters PWM, t_tot and f_s for controlling the switching means 7 be via a corresponding control unit (in 1 not shown, compare this 2 ) provided. For this purpose, the control unit can generate one or more control signals, wherein the parameters PWM, t_tot and f_s are adjusted in a control-dependent manner.

Alternatively to the in 1 illustrated embodiment, the switching means 7 Have a plurality of switching elements, which are controlled via corresponding control signals with the parameters PWM, t_tot and f_s for the controlled operation of the up-converter 3 according to the explained type.

The switching dead time t_tot describes a period of delay of the switching of the switching means 7 between the switching states. The switching dead time t_tot is controlled such that switching of the switching means 7 is delayed controlled until the switching means, a voltage near zero (ideally zero) is reached. In this way switching losses can be minimized.

Through a photovoltaic unit 1 according to 1 can be a very high efficiency over almost the entire working range of the photovoltaic module 2 be achieved.

2 shows a schematic representation of a control for a photovoltaic device 1 according to 1 , In 2 are an MPP tracker unit 8th as well as a control unit 9 shown. The MPP tracker unit 8th receives on an input side the electrical quantities U_in and I_in of the photovoltaic module 2 (See explanatory notes to 1 ). The MPP tracker unit 8th calculates a corresponding operating behavior of the photovoltaic module from these electrical variables 2 so that the photovoltaic module 2 ideally be operated in a plant with maximum energy yield. The MPP tracker unit 8th can be constructed, for example, in the form of a microcontroller, which provides a corresponding functionality.

Settings or information (eg control information) of the MPP tracker unit 8th can be in the form of a control signal 10 to the control unit 9 be handed over. For example, the control signal 10 specify a setpoint of the current I_in. The control unit 9 In addition, at its input side, the electrical quantities U_in, I_in and U_out of the photovoltaic unit are obtained 1 (See also the comments to 1 ). The control unit calculates from these electrical variables 9 Finally, the variable parameters PWM, t_tot and f_s for resonance control of the boost converter 3 according to 1 , This way is according to 2 implements a control concept, the advantages of a conventional MPP tracking with a resonance control of an up-converter explained here 3 according to 1 combined. In this way, for each operating state of the photovoltaic module 2 An optimal operating point with maximum energy yield can be determined, so that the efficiency of the photovoltaic unit 1 according to 1 optimized as best as possible.

Alternatively to the embodiment according to 2 can be an MPP tracker unit 8th also omitted. In this case, there is only one control unit 9 provided on its input side, the electrical quantities U_in, I_in and U_out the photovoltaic unit 1 according to 1 receives and the corresponding control signals PWM, t_tot and f_s for resonance control of the up-converter 3 according to 1 certainly.

3 shows a schematic representation of a portion of a photovoltaic system comprising a plurality of photovoltaic units 1 according to 1 having. Every photovoltaic unit 1 includes a photovoltaic module 2 and a resonantly controlled boost converter 3 as they too 1 have been explained. The photovoltaic units 1 are with the corresponding output sides of the respective boost converter 3 over two conductors S1 and S2 connected in parallel. Further, the photovoltaic system in the embodiment according to 3 two inverters 11 to convert one through the photovoltaic units 1 provided DC voltage or a DC power provided in a corresponding AC voltage or an AC current for feeding into an AC voltage network. These are the inverters 11 with their respective entry sides at the ladders S1 and S2 parallel to the photovoltaic units 1 connected. Corresponding output sides of the inverter 11 are interconnected with corresponding phases or conductors of an AC voltage network. Is concrete in 3 the left inverter 11 with the phase L3 , the neutral conductor N and the protective conductor PE interconnected while the right inverter 11 in 3 with the phase L2 , the neutral conductor N and the protective conductor PE is interconnected. Thus, the inverters form 11 in 3 so-called single-phase inverters. Alternatively to the embodiment in FIG 3 Three-phase inverters can also be used. These can be used, for example, in very large photovoltaic systems.

According to 3 can each be an inverter 11 for a majority M of photovoltaic units 1 used and dimensioned. For example, an inverter 11 for every four to eight photovoltaic units 1 be used. It is advantageous, the inverter 11 each in the middle of the corresponding photovoltaic units 1 to the ladder S1 and S2 connect to the cross section or the current carrying capacity of the two conductors S1 and S2 to minimize. Are many photovoltaic units 1 , as in 3 The case, present in the photovoltaic system, will be multiple inverters 11 distributed in the photovoltaic system, the inverters 11 as explained, can be connected to different phases of the AC mains. It makes sense that this should be split up to match the normal load distribution in the local AC grid. For example, any single-phase inverter 11 according to 3 be designed for a maximum power of 3.6 kVA and can thus be integrated into any domestic installation.

In larger photovoltaic systems, where more than three inverters 11 can work, individual inverters 11 be switched off in partial load operation. This increases the utilization of the remaining inverters 11 and thus their efficiency.

Finally, in the photovoltaic system according to 3 another energy storage device 12 provided with an input side over the two conductors S1 and S2 is connected in parallel to the other components. The energy storage device 12 indicates in the embodiment according to 3 an inverter module 13 to the direction of change in the energy storage device 12 stored electrical energy for feeding into the AC voltage network. The energy storage device 12 is about her inverter module 13 with the phase L1 , the neutral conductor N and the protective conductor PE connected on the output side. The inverter module 13 can perform tasks analogous to the other inverters 11 take. In this way, inverters can 11 be saved.

In alternative embodiments, the energy storage device may 12 also have only a battery management without special power electronics. In this embodiment, the energy storage device 12 as a battery for storing electrical energy from the respective photovoltaic units 1 serve. In further alternative embodiments, the energy storage device 12 instead of an inverter module 13 a converter module having one or more phases L1 to L3 the AC voltage network is connected or connected in parallel to the DC voltage network. By such a converter module, the energy storage device 12 be operated bidirectionally, ie once from the DC network S1 . S2 and once from the AC mains L1 to L3 . N . PE be supplied. By a supply from the AC voltage network, for example, electrical energy for the operation of components, such as the inverter 11 , to be provided.

The placement of the energy storage device 12 advantageously takes place according to the same criteria as the placement of the inverter 11 , The energy storage device 12 is advantageously designed so that the minimum charge voltage just above the lowest DC output voltage on the output side of the corresponding boost converter 3 lies. In this way, the energy storage device charged 12 the photovoltaic units 1 not immediately at the lowest possible energy yield. Furthermore, the photovoltaic system is advantageously dimensioned such that the maximum output DC voltage that the respective boost converter 3 allow under the end-of-charge voltage of the energy storage device 12 lies. In this way it prevents the energy storage device 12 by an excessive output DC voltage of the boost converter 3 is destroyed or takes damage. Furthermore, the maximum charging current of the energy storage device should 12 be at least such that the sum of all the output-side currents of the boost converter 3 less the maximum currents of the inverters 11 not fallen below. Also in this way is to be prevented that the energy storage device 12 Takes damage.

In addition, the capacity of the energy storage device should 12 are so high that the integral of the output side currents of the boost converter 3 less the maximum currents of the inverters 11 is reached over a corresponding period of the highest energy yield, that is, the excess converted energy of the photovoltaic units 1 not through the inverter 11 can be delivered to the AC voltage network, in the energy storage device 12 can be cached.

Alternative to embodiment in 3 are of course several energy storage devices 12 the type explained conceivable.

Due to the fact that the individual boosters 3 a DC voltage U_in the individual photovoltaic modules 2 (see 1 ) into a higher output-side DC output voltage, the photovoltaic units 1 , as in 3 shown, be connected in parallel. A parallel connection of the individual photovoltaic units 1 has the advantage over conventional architectures that a series connection of the individual photovoltaic modules 2 eliminated. In this way, also performance losses, as they occur in conventional solutions, when the performance of the photovoltaic system on the lowest energy yield of one or more photovoltaic modules 2 be limited. Such a performance penalty is in the system according to 3 avoided. Because of the parallel connection of the photovoltaic units 1 wear in time-varying operating conditions or operating points of the individual photovoltaic units 1 due to a different radiation intensity or orientation of the photovoltaic units 1 nevertheless all photovoltaic units 1 to a total energy yield of the system, because all of the individual photovoltaic units 1 Add the removed currents to a total current. Due to the resonant up-converter 3 the respective photovoltaic units 1 is also the respective efficiency of the individual photovoltaic units 1 further increased, so that the total conversion efficiency of the photovoltaic system according to 3 is increased compared to conventional solutions.

In addition, the photovoltaic system is according to 3 robust against failure of individual photovoltaic units 1 , For example, if a photovoltaic unit fails 1 out, so can the other photovoltaic units 1 continue to operate. It may only have system parameters such as the output DC voltages of the remaining photovoltaic units 1 or parameter of the inverter 11 or the energy storage devices 12 be readjusted.

The embodiment according to 3 shows in addition to the previously discussed components nor a management component 14 , This can, for example, a higher-level control for controlling the various components of the photovoltaic system according to 3 include. In this way, an intelligent operation management can be achieved, so that the photovoltaic system according to 3 is flexibly adaptable to different and above all temporally varying conditions. Even a modular expandability of the photovoltaic system by means of various of the components explained can be made flexible in this way. For example, via the parent operating component 14 an adjustment of the output DC voltages of the respective boost converter 3 the photovoltaic units 1 or the parameter of the inverter 11 or the energy storage devices 12 be adapted according to the equipment and utilization of the photovoltaic system. Here are many variants conceivable.

The photovoltaic system according to 3 For example, a photovoltaic system with mixed alignment of the photovoltaic units 1 be. For example, various photovoltaic units 1 be aligned to the south, east or west. All photovoltaic units 1 are wired in parallel. In the morning, the feed of the east-facing photovoltaic units predominates 1 At noon, the east, west and predominantly south-facing photovoltaic units carry 1 and in the evening the west-facing photovoltaic units 1 to the energy yield of the photovoltaic system. All photovoltaic units 1 be through the integrated boost converter 3 optimally controlled. Combining all orientations can be calculated (for example, within a smart operation component 14 ), which maximum performance is expected. The system can be designed for the combined maximum power. This gives you a significantly higher utilization of the inverter over the day 11 and thus a significantly higher energy yield compared to conventional systems, since the conversion losses are significantly lower at higher utilization. Is the maximum power of photovoltaic units 1 greater than the simultaneous minimum consumption, energy storage devices can 12 of the type explained are simply integrated into the system. However, because of the high investment costs and the relatively high charging and discharging loss, these should be used only in extreme operating conditions if possible.

As explained, in the photovoltaic system according to 3 all photovoltaic units 1 neither directly connected in series, nor connected in parallel by means of a modular inverter on the AC side. The connection of the individual photovoltaic units 1 rather takes place on the DC side via a parallel connection. The operating point of each individual photovoltaic module 2 becomes individual with the respective up-converter 3 set. This up-converter 3 is operated resonantly and thereby achieves a very high peak efficiency of at least 99% and an over a wide working range only slightly decreasing efficiency, usually over 98% in the working range between 20% and 100% of the module capacity. The inverters 11 are then placed centrally in the photovoltaic system so that the cross sections of the conductors can be minimized. By modularization, that is, assignment of individual inverters 11 to a majority M of photovoltaic units 1 , it is possible the utilization of each inverter 11 increase and thus achieve a very high overall conversion efficiency. The retrofitting with energy storage devices 12 is possible without problems. The system can therefore be easily adapted to changing requirements.

In this way, in a photovoltaic system according to 3 every single photovoltaic unit 1 be placed according to structural constraints. A special orientation that depends on the electrical topology is no longer necessary. Only voltages in the range of the protective DC voltage occur in the photovoltaic system, so that the photovoltaic system is safe for people.

Furthermore, according to the photovoltaic system 3 with combined alignment of the individual photovoltaic units 1 the ratio of peak power to the mean value of the power significantly lower than in conventional solutions. Because the inverters 11 always have to be designed for peak performance, are the specific investment costs for the inverter 11 significantly lower than conventional solutions. At the same time, the inverters are working 11 statistically more often in a favorable for their efficiency range. In this way, conversion losses are minimized and the yield of the plant increased significantly.

The photovoltaic system according to 3 Can easily with energy storage devices 12 or other battery storage can be combined. Separate power electronics for corresponding battery storage is not necessary (no corresponding investments, no corresponding conversion losses).

Further, the cost of the necessary up-converters 3 very low, as this according to 1 represent one of the simplest power electronic basic circuits and for each photovoltaic unit 1 can be manufactured in very high quantities.

In addition, the photovoltaic system is according to 3 intrinsically safe, since the individual photovoltaic units 1 only in the common DC link (ladder S1 and S2 ) when the DC voltage of the photovoltaic modules 2 is increased, since the output side DC voltage of the boost converter 3 always above the DC voltage of the photovoltaic modules 2 is held. The decoupling of the individual photovoltaic units 1 takes place through the respective diodes 5 the up-converter 3 (please refer 1 ). The photovoltaic system can be extended at any time.

The illustrated embodiments are merely exemplary.

LIST OF REFERENCE NUMBERS

1

photovoltaic unit

2

photovoltaic module

3

boost converter

4

Coil / inductance

5

diode

6

capacity

7

controlled switching means

8th

MPP tracker Unit

9

control unit

10

Control signal of the MPP tracker unit

11

inverter

12

Energy storage device

13

Inverter Module

14

Betriebsführungs component

U_in

DC voltage of a photovoltaic module

I_in

DC of a photovoltaic module

u_out

DC output voltage of a photovoltaic unit

PWM

Pulse width signal

f_s

switching frequency

t_tot

switching dead

S1

DC line

S2

DC line

L1

phase

L2

phase

L3

phase

N

neutral

PE

protective conductor

Claims (10)

Photovoltaic unit (1), comprising: - a photovoltaic module (2), - an adjustable boost converter (3) for the controlled conversion of a direct voltage of the photovoltaic module (2) at an input side of the boost converter (3) into a higher DC output voltage at an output side of the boost converter (3 ) for a controlled removal of an electrical power provided by the photovoltaic module (2), and a control unit (9) for controlling the boost converter (3), wherein the control unit (9) has an input side for supplying signal values of at least one electrical quantity (U_in, I_in, U_out) of the photovoltaic unit (1) and an output side for providing at least one control signal to Controlling at least one switching means (7) of the variable boost converter (3), wherein the control unit (9) is arranged by means of the at least one control signal in addition to a variable switching ratio (PWM) and a switching frequency (f_s) and / or a switching dead time (t_tot ) of the at least one switching means (7) such that the boost converter (3) is operated resonantly. A photovoltaic system comprising a plurality N of photovoltaic units (1), each photovoltaic unit (1) comprising a photovoltaic module (2) and a variable boost converter (3) for the controlled conversion of a DC voltage of the respective photovoltaic module (2) at an input side of the respective boost converter (3 ) to a higher DC output voltage at an output side of the respective boost converter (3) for controlled removal of an electrical power provided by the respective photovoltaic module (2), the photovoltaic units (1) being connected in parallel with the respective output sides of the boosters (3). Photovoltaic system after Claim 2 , at least one inverter (11), wherein the at least one inverter (11) is connected to an input side parallel to the photovoltaic units (1) for converting a DC voltage at the input side of the at least one inverter (11) into an AC voltage at an output side of the Inverter (11), and wherein the at least one inverter (11) for a summed current consumption of a plurality M, with M greater than 1, of photovoltaic units (1) is designed. Photovoltaic system after Claim 2 or 3 , wherein one or more of the photovoltaic units (1) according to Claim 1 are executed. Photovoltaic system according to one of the Claims 2 to 4 , with at least one energy storage device (12) for storing electrical energy provided by the photovoltaic units (1), wherein the at least one energy storage device (12) is connected to an input side parallel to the photovoltaic units (1). Photovoltaic system after Claim 5 wherein the energy storage device (12) comprises a converter module for storing electrical energy from an AC voltage in the energy storage device (12) or for converting a DC voltage stored in the energy storage device (12) into an AC voltage on an output side of Energy storage device (12). Method for operating a photovoltaic unit (1) according to Claim 1 in that signal values of at least one electrical variable (U_in, I_in, U_out) of the photovoltaic unit (1) are supplied to the control unit (9) and the control unit (9) has at least one control signal for driving the at least one switching means (7) of the controllable boost converter (3). wherein the control unit (9) also controls a switching frequency (f_s) and / or a switching dead time (t_tot) of the at least one switching means (7) by means of the at least one control signal, in addition to a variable switching ratio (PWM), so that the boost converter (3 ) is operated resonantly. Method for operating a photovoltaic system according to one of Claims 2 to 6 in which the respective boost converters (3) of the respective photovoltaic units (1) independently of one another set the respective photovoltaic modules (2) individually to a respective specific operating point of a power extraction. Method according to Claim 8 wherein the value of the DC output voltage is variably set on an output side of each boost converter (3), but set above the value of the highest DC voltage generated by the photovoltaic modules (2). Method according to Claim 8 or 9 , wherein one or more of the photovoltaic units (1) according to a method according to Claim 7 operate.

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