DE102013102433A1 - Inverter i.e. solar inverter, for feeding electrical power from photovoltaic generator into AC network, has interface circuitry activated to apply direct voltage to series arrangement, and converter operated in frequency within preset range - Google Patents

Abstract

The inverter (1) has a direct current (DC)/DC converter (10) comprising a DC/alternating current (AC)-partial converter (13), and a transformer (14) excited by AC. An interface circuitry (6) is optionally activated to apply additive direct voltage (U-a) reduced at 50% relative to input direct voltage (U-IN) to a partial series arrangement. The DC/AC partial converter is designed as a resonance converter, which is operated with the activated DC/DC converter in a frequency within a range of plus or minus 20% of resonance frequency.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to an inverter for a variable DC input voltage having the features of the preamble of independent claim 1.

In particular, the invention relates to so-called solar inverters, with which electrical energy is fed from a photovoltaic generator in an AC grid. In such a solar inverter, the magnitude of the DC input voltage provided by the photovoltaic generator varies not only with the change of the daytime solar radiation but also due to shadows or clouds and other weather events. If a solar inverter is to be able to feed electrical energy into an AC grid not only when the DC input voltage directly reaches a limit value to be observed for the feeding of electrical energy into the AC grid, the DC input voltage should be able to be increased as required. Such a limit value is set, for example, by a peak value of the AC voltage of the AC network.

STATE OF THE ART

A known inverter for a variable input DC voltage has a three-point circuit as an inverter subcircuit, which is connected in addition to the positive and negative pole of the DC intermediate circuit with a midpoint of two interconnected to form a DC link capacitance DC link capacitors. In order to increase the DC link voltage, if necessary, in relation to a DC input voltage applied to input terminals, a step-up converter is provided between the input terminals and the DC link. The components of this boost converter must be designed to carry all the electrical energy. In this case, the diode and the coil of the boost converter permanently in current flow between the input terminals and the intermediate circuit and cause so even then losses when the boost converter is not in operation. These losses can only be avoided if an additional bypass path is provided. In any case, considerable losses occur when the boost voltage increases the input voltage. In addition, a noise development is usually associated with the operation of the boost converter, since it can not be readily operated with good efficiency at switching frequencies above the audible range.

From the EP 2 023 475 A1 is an inverter for a grounded DC voltage source, in particular a photovoltaic generator, known in which an input-side DC / DC converter is designed as a resonant circuit inverter and at least two bipolar output voltages supplied, which are each applied via one of several series-connected DC link capacitors of a DC intermediate circuit , In this way, the individual bipolar output voltages are superimposed additively to an increased DC link voltage. The individual bipolar output voltages are all provided by the same DC / DC converter whose one output is branched. The individual branches, via which the individual bipolar output voltages are provided, are galvanically isolated in a capacitive manner.

From the EP 1 033 804 A2 is a resonant DC / DC converter is known, which is operated at a fixed switching frequency below the resonant frequency of its resonant circuit, in addition to a voltage applied between two lines DC to provide a contrast reduced second DC voltage. The DC / DC converter comprises a DC / AC partial converter generating a high-frequency AC voltage, a transformer shunting the high-frequency AC voltage, and an AC / DC partial converter rectifying the down-voltage high-frequency AC voltage. The latter is realized in that a secondary-side center tap of the transformer forms one output pole, while the two ends of the secondary winding of the transformer lead via two rectifier diodes to the other output pole. Between these two output poles, a smoothing capacitor is connected.

In an inverter having the features of the preamble of independent claim 1, from the DE 10 2011 011 973 B4 is known, a portion of the input voltage is passed through a galvanically isolated DC / DC converter. The DC / DC converter generates a galvanically isolated and variable additional DC voltage from the DC input voltage. The additional DC voltage is connected in series with the DC input voltage, and the sum of DC input voltage and additional DC voltage results in an output DC link voltage. This DC link voltage is the voltage source for a mains supply with a DC / AC converter. The DC / DC converter is controlled so that the DC link voltage remains below 1000 V DC at no load of a DC voltage generator providing the DC voltage, and a voltage drop across the photovoltaic generator when the DC link is loaded is partially compensated by the DC / AC converter by the additional DC voltage. In this case, the additional DC voltage is adjusted so that the DC link voltage of the system is so large that a direct mains supply through the DC / AC converter is possible. This eliminates the otherwise necessary matching transformer between the DC / AC converter and an AC voltage network, in which the DC / AC converter feeds. The additional DC voltage is in the known inverter via a capacitor connected in series with a capacitor to which the DC input voltage is applied directly. These two capacitors, a third capacitor is connected in parallel in the DC voltage intermediate circuit. In this case, the capacitor, via which the additional DC voltage is applied, a diode connected in parallel, which should allow a simple and reliable behavior of the DC intermediate circuit at the first load by the connected DC / AC converter. Initially, the additional DC voltage is still small and the flowing initial current at the DC intermediate circuit reduces the voltage to the associated capacitor. The diode ensures that the additional DC voltage can not become smaller than the forward voltage of the diode.

OBJECT OF THE INVENTION

The invention has for its object to provide an inverter for a variable DC input voltage, in which an intermediate circuit voltage can be increased if necessary compared to the DC input voltage, without this considerable noise developments or permanent losses are connected.

SOLUTION

The object of the invention is achieved by an inverter having the features of independent claim 1. Preferred embodiments of the new inverter are defined in the dependent claims.

DESCRIPTION OF THE INVENTION

An inverter according to the invention for a variable DC input voltage has an inverter subcircuit which converts an intermediate circuit voltage applied via a DC voltage intermediate circuit into an output AC voltage, and a matching subcircuit which, if necessary, increases the intermediate circuit voltage with respect to the input direct voltage present between two input terminals. The DC intermediate circuit comprises capacitors connected in series. The matching subcircuit connects the input terminals directly to the two sides of at least one of the capacitors ( 8th ) first sub-series circuit, so that the input DC voltage is applied over it. Furthermore, the adapting subcircuit has a DC / DC converter with galvanic isolation, which is connected on the input side to the input terminals and on the output side to the two sides of at least one other of the capacitors comprising second sub-series circuit and selectively activated to one compared to the input DC voltage by at least 50% reduced, but the DC link voltage additively increased additional DC voltage applied to the second sub-series circuit. The DC / DC converter comprises a DC / AC partial converter generating an AC voltage, a transformer clamping down the AC voltage, and an AC / DC partial converter rectifying the AC voltage down-clamped. In this case, the DC / AC converter is a resonant converter, which is operated at a frequency in the range of ± 20% to its resonant frequency with activated DC / DC converter. In addition, the adaptive subcircuit has a bypass path which runs parallel to the second sub-series circuit and in which at least one switching element preventing a short circuit of the additional direct voltage is arranged.

In the inverter according to the invention, therefore, the input DC voltage is always directly applied to the first sub-series circuit of the DC intermediate circuit. If this DC input voltage is sufficient for the operation of the inverter subcircuit of the inverter, the second sub-series circuit of the DC intermediate circuit connected in series with the first sub-series circuit is bridged by the bypass path, so that the DC input voltage makes up the entire intermediate circuit voltage.

However, if the DC input voltage becomes too low, an additional DC voltage is applied to the second sub-series circuit with the DC / DC converter of the matching subcircuit. Although this additional DC voltage is generated from the DC input voltage, but is at least 50% smaller than this, so that over the DC / DC converter and less than one third of the total electrical power is performed. This is equivalent to the fact that a maximum of one third of the total electrical power is affected by losses of the DC / DC converter. In addition, the components of the DC / DC converter must also be designed only for this small proportion of the electrical power. If the DC / DC converter applies the additional DC voltage to the second sub-series circuit, a short circuit of the additional DC voltage is prevented by at least one switching element, which is a diode, but also with a an external switching signal switchable switching element can act. Due to the additional DC voltage, the DC link voltage can be increased compared to the DC input voltage, that, for example, despite low input DC voltage, a feed of electrical energy to the inverter is possible in an AC network. For example, the electrical energy which can be fed in by a photovoltaic generator over one day can be significantly increased.

In the inverter according to the invention, the matching subcircuit is activated as required for a period of several periods of the AC output voltage. This means that with the matching subcircuit, for example, no additional voltage level is provided for current shaping during each period of the alternating current output by the output-side DC / AC converter, but in principle the intermediate circuit voltage of the DC intermediate circuit is increased. However, this does not exclude that several voltage levels can be tapped off from the DC voltage intermediate circuit, so that the output-side DC / AC converter can definitely have a multipoint circuit.

In the inverter according to the invention, the matching subcircuit is designed as simple as possible to increase the input DC voltage, if necessary, from a level at which the output side DC / AC converter no grid feed would be possible to a level at which this network feed is still possible. This requires no controllability of the DC / DC converter of the matching subcircuit of the inverter according to the invention, because the example provided by a photovoltaic generator input DC voltage varies anyway and a photovoltaic inverter is designed according to regularly so that it is not dependent on a constant DC link voltage. One only activatable, d. H. only switchable on and off but not controllable, DC / DC converter is simpler, cheaper and more easily optimized for maximum efficiency and low noise than a controllable DC / DC converter, with which the DC link voltage can be kept constant.

The fact that the DC / AC partial converter of the DC / DC converter of the inverter according to the invention generates a high-frequency alternating voltage, the spanning transformer can be kept small. In addition, it is easily possible to select the high-frequency AC voltage above the audible range, so that the operation of the DC / DC converter no perceptible noise results.

In order to avoid audible noise, switches of the DC / AC partial converter are clocked at a frequency of at least 16 kHz, preferably at least 30 kHz, and even more preferably at least 45 kHz.

For the efficiency of the inverter according to the invention, even if its DC / DC converter is operated to increase the DC link voltage compared to the DC input voltage, it is favorable that its DC / AC partial converter is a resonant converter. The resonant converter operates at a frequency in the range of ± 20% around its resonant frequency when the DC / DC converter is activated. This frequency preferably remains fixed.

Furthermore, it is preferred if the DC / AC partial converter of the inverter according to the invention is operated with constant operating parameters after the additional DC voltage has been established across the second partial row circuit of the DC intermediate circuit. At the beginning of the operation of the DC / AC partial converter, a current which initially flows on the secondary side of the transformer without reverse voltage must be limited. This can be done by limiting the pulse width when driving the switches of the DC / AC converter. Once the additional DC voltage is built up across the second sub-series circuit on the secondary side of the transformer, the DC / AC converter can be operated constant with a duty cycle of typically almost 50% at the already mentioned frequency near its resonance frequency. This not only simplifies the operation of the DC / DC converter of the inverter according to the invention, but also maximizes its efficiency.

The requirements for the switches of the DC / AC converter can be met in a favorable manner with silicon carbide semiconductor switches. Silicon carbide semiconductor switches have a high dielectric strength, which is easily sufficient for the input DC voltage of the inverter according to the invention. Although silicon carbide semiconductor switches are only suitable for limited currents and thus for limited powers. In the case of the inverter according to the invention, however, only a part of the total electrical energy flows via the DC / AC converter. Silicon carbide semiconductor switches are also characterized by low switching losses, so that even the small portion of the electrical energy flowing through the DC / AC partial converter is not associated with high losses.

Concretely, the DC / AC partial converter may have a series resonant circuit between two half bridges connecting the input terminals. A resonance inductance of this resonant circuit includes the transformer. In principle, however, an additional inductance can also be provided. A resonant capacitance of the series resonant circuit may be provided by capacitors forming a passive half-bridge at one end of the series resonant circuit between the input terminals. In this case, the other half-bridge is formed of active controllable switches. In any case, the two half bridges have a total of at least two actively controllable switch. Preferably, they are semiconductor switches. More preferably, each of the two half-bridges at the ends of the series resonant circuit has a pair of such switches. Then, the resonant capacitance of the series resonant circuit is formed by a capacitor connected in series with the primary winding of the transformer between the two half-bridges. The passive components of the resonant converter. ie, for example, the leakage inductance of the transformer and the capacitance of the series capacitor or the half-bridge capacitor, determine its resonant frequency in a known manner.

When the AC / DC converter converts a secondary-side center tap of the transformer to one side of the second sub-series circuit and the two ends of the secondary of the transformer via two rectifier diodes to the other side of the second sub-series circuit, the two halves of the secondary winding of the transformer can have two parallel branches form the bypass path to the second sub-series circuit, in each case one of the rectifier diodes prevents the short circuit of the additional DC voltage. In this circuit, the secondary-side current flows half-wave from or to the center tap by the two partial windings of the secondary winding. At low forward voltage of the two rectifier diodes, the losses for the current flowing through the two branches of the bypass path current remain low, especially since the secondary winding of a compact transformer, which is tuned to high frequencies, does not have a large ohmic resistance. At least the losses permanently occurring here are lower than when the current through the diode and the coil of an inactive boost converter would flow, because the diode blocking voltage need not be designed for the total voltage but only for the voltage applied across the second partial series circuit. Diodes with low reverse voltage also have low forward losses.

It has already been mentioned that the DC / DC converter of the inverter according to the invention is preferably not regulated but, after the additional DC voltage has been established, is operated with constant operating parameters. By a DC converter, such as a boost converter, but in particular a buck converter is preceded by this DC / DC converter, the additional DC voltage can still be varied, if desired. The adapter can be kept simple, so in particular transformerless, and it carries only the part of the electrical energy, which also flows through the DC / DC converter. Ie. it can remain small dimensioned, and even a moderate efficiency of the adapter does not significantly affect the overall efficiency of the inverter according to the invention.

In the case of the inverter according to the invention, a higher voltage drops across the first partial row circuit of the DC intermediate circuit than over the second partial series circuit. In order nevertheless to provide equal charges at the two poles of the DC intermediate circuit even when the DC / DC converter is activated, the capacitances of the first and the second partial row circuit may be in inverse proportion to the DC input voltage and the additional DC voltage.

If the inverter subcircuit of the inverter according to the invention is a three- or multi-point circuit, the series-connected capacitors in the DC voltage intermediate circuit, a series circuit of a plurality of DC link capacitors with equal capacitance can be connected in parallel. Then, the inverter subcircuit may be connected to at least one intermediate point between the intermediate circuit capacitors.

In an inverter according to the invention, the adapting subcircuit can also have a plurality of subcircuits each having a DC / DC converter with galvanic isolation, the input side connected to the input terminals and the output side to the two sides of the second or another at least one other of the capacitors part series circuit and selectively activated is to create a relation to the DC input voltage by at least 50% reduced, but the DC link voltage additively increasing additional DC voltage to the sub-series circuit. In this case, the plurality of sub-circuits can jointly build an additional DC voltage across the second sub-series circuit. Alternatively, the plurality of sub-circuits may construct a plurality of auxiliary DC voltages across different sub-row circuits.

Furthermore, it is possible for the subcircuits to have common components. Thus, a single DC / DC converter can be provided with a series resonant circuit on the primary side of a transformer having a plurality of separate secondary windings, each with an AC / DC converter part subcircuit another with apply an additional DC voltage. In this case, for example, the second and a third sub-series circuit can be arranged symmetrically on the two sides of the first sub-series circuit, to which the input DC voltage is applied. So then takes place the increase of the intermediate circuit voltage of the input DC voltage in a symmetrical form. This is of particular interest when direct or virtual grounding of a midpoint of a DC voltage source such as a photovoltaic generator is desired. On the other hand, if one of the two input terminals is grounded, it is preferable that the second sub-row circuit through which the auxiliary DC voltage is built up be connected to the other input terminal. It is irrelevant whether this is the positive or negative pole of the DC input voltage.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings. The advantages of features and of combinations of several features mentioned in the introduction to the description are merely exemplary and can be effective as an alternative or cumulatively without the advantages necessarily having to be achieved by all embodiments according to the invention. Without altering the subject matter of the appended claims, as regards the disclosure of the original application documents and the patent, the following applies: Further features can be found in the drawings, in particular the illustrated relative arrangements and operative connections of several components. The combination of features of different embodiments of the invention or of features of different claims is also possible deviating from the chosen relationships of the claims and is hereby stimulated. This also applies to those features which are shown in separate drawings or are mentioned in their description. These features can also be combined with features of different claims. Likewise, in the claims listed features for further embodiments of the invention can be omitted. In addition, the features listed in the claims can be supplemented by other features as well as define the only components that make up the inverter.

The features mentioned in the patent claims and the description are to be understood in terms of their number that exactly this number or a greater number than the said number is present, without requiring an explicit use of the adverb "at least". For example, when talking about an element, it should be understood that there is exactly one element, two elements or more elements. These features may be supplemented by other features or be the only characteristics that make up the product in question.

The reference numerals contained in the claims do not limit the scope of the objects protected by the claims. They are for the sole purpose of making the claims easier to understand.

BRIEF DESCRIPTION OF THE FIGURES

The invention is explained in more detail below with reference to embodiments with reference to the accompanying drawings and described.

1 is a schematic diagram of an inverter according to the invention in a first embodiment.

2 is a schematic diagram of the inverter according to the invention in a second, more concrete embodiment.

3 is a schematic diagram of the inverter according to the invention in a further somewhat more concrete embodiment than in 1 ,

4 is a schematic diagram of the inverter according to the invention in yet another somewhat more concrete embodiment than in 1 ,

5 is a schematic diagram of the inverter according to the invention in a respect to a DC / AC converter further concretized embodiment.

6 is a schematic diagram of the inverter according to the invention in an embodiment also concretized with respect to an inverter subcircuit, wherein the inverter subcircuit is a three-point circuit.

7 is a schematic diagram of the inverter according to the invention, in which the DC / AC partial converter is preceded by an additional step-down converter; and

8th is a schematic diagram of the inverter according to the invention, in which the inverter subcircuit is designed as a four-point converter.

DESCRIPTION OF THE FIGURES

The in 1 illustrated inverter 1 is for one between two input terminals 2 and 3 applied variable input DC voltage U _in and outputs an AC output voltage. When using this AC output voltage an alternating current into an AC mains 4 is to be fed, the DC input voltage U _in per se must be greater than the peak voltage of the AC network 4 , Even at lower input DC voltage U _into an alternating current and thus electrical energy in the AC network 4 to be fed, is at the inverter 1 the DC input voltage U _in to a higher intermediate circuit voltage U _Z via a DC voltage intermediate circuit 5 increases, then from the electrical energy into the AC grid 4 is fed. This voltage increase takes place with a matching subcircuit 6 , which is an inverter subcircuit 7 upstream. The inverter subcircuit here is a two-point circuit and outputs a single-phase alternating current.

The adaptation subcircuit 6 sets the DC input voltage U _in directly to a capacitor 8th in the DC voltage intermediate circuit 5 with another capacitor 9 is connected in series. At this other capacitor 9 sets a DC / DC converter 10 with galvanic isolation to an additional DC voltage U _A , which increases the DC input voltage U _in additively to the desired intermediate circuit voltage U _Z. However, if the DC input voltage U _in is large enough to be without increasing electrical energy in the AC grid 4 feed is the DC / DC converter 10 disabled. Then the capacitor discharges 9 until the additional DC voltage U _{A is} reduced. Subsequently, the stream can pass through a bypass path 11 flow, in which a diode as a switching element 12 is arranged to prevent a short circuit of the additional DC voltage U _A. In other words, the switching element locks 12 the bypass path 11 as long as the additional DC voltage U _A across the other capacitor 9 is present, and opens it as soon as the additional DC voltage U _{A is} reduced. The increase of the DC input voltage U _in to the higher intermediate circuit voltage U _Z by the DC / DC converter 10 has the advantage of having the DC / DC converter 10 only a small part of the total electrical energy flows, and only when it is needed. As long as it is not needed, the current flows on the DC side of the inverter subcircuit 7 only in addition by the switching element 12 , In this case, the switching element 12 Instead of a diode and an actively controlled switch, such as a mechanical switch with very low line losses, so that the efficiency compared to an inverter without input side DC / DC converter is only minimally reduced.

2 shows a possible construction of the DC / DC converter 10 from a DC / AC converter 13 , a transformer 14 and an AC / DC converter 15 , The transformer 14 transforms a high frequency AC voltage generated by the DC / AC converter that is received from the AC / DC converter 15 rectified and to the other capacitor 9 is created. Specifically, this is a center tap 16 the secondary winding 17 of the transformer 14 with one side of the capacitor 9 connected while the two ends of the secondary winding 17 via one rectifier diode each 18 with the other side of the capacitor 9 are connected. The two partial windings of the secondary winding 17 of the transformer 14 at the same time make the bypass path 11 ready, the capacitor 9 is connected in parallel and in which the rectifier diodes 18 as switching elements, a short circuit across the capacitor 9 prevent adjacent additional DC voltage U _A. The DC / AC converter 13 is designed so that it after an initial build up of the additional DC voltage U _A , in which the flow of large currents to the capacitor 9 must be avoided, operated with constant operating parameters, which are tuned to an optimal efficiency. To be able to make a change in the additional DC voltage U _A for the compensation of different large DC input voltages U _in , is the DC / AC partial converter 13 an adapter plate 19 , For example, a buck converter, upstream. The inverter subcircuit 7 Here is a three-point circuit that outputs a three-phase AC. In order to provide a centrally located third connection point for this three-point circuit, the capacitors 8th and 9 , which typically have different capacitances, a pair of series-connected, equal-sized DC link capacitors 20 connected in parallel, its center 21 in addition to the inverter subcircuit 7 connected is.

The inverter 1 according to 3 has a matching subcircuit 6 on, the two subcircuits 22 includes. Each subcircuit includes a DC / DC converter 10 with a DC / AC converter 13 , a transformer 14 and an AC / DC converter 15 , Here are the two DC / DC converters 10 between the outputs of the adapter 19 and the capacitor 9 connected in parallel, and both AC / DC converters 15 are the same as the one AC / DC converter 15 in 2 educated. If the two DC / AC converters 13 Clocked offset by 90 ° to each other, the charging current to the capacitor 9 evened out and thus the intermediate _circuit voltage U _Z stabilized. The inverter subcircuit 7 Here is a two-point circuit that outputs a single-phase AC.

The inverter 1 according to 4 has a transformer 14 with a primary winding 23 but two secondary windings 17 on. With the help of everyone secondary winding 17 and a connected AC / DC converter 15 is over each a different capacitor 9 an additional DC voltage U _A applied. These other capacitors 9 are here with a sub-series circuit of two capacitors 8th , in which the input DC voltage U _in is applied, connected in series, and all the capacitors connected in series 8th and 9 together form the DC voltage intermediate circuit. In this way, the series connection of the capacitors 8th and 9 symmetrical to its center 21 constructed, and also the DC link voltage UZ is symmetrically distributed. So have the capacitors 8th and 9 no equally large DC link capacitors for providing such a center 21 be switched in parallel. In addition, a shift of the electric potential of the center 21 with activating the DC / DC converter 10 avoided. The inverter subcircuit 7 Here is an example of a three-point circuit that outputs a three-phase alternating current.

The inverter 1 according to 5 shows a possible embodiment of the DC / AC partial converter 13 as a resonant converter with a series resonant circuit 24 between two half-bridges 25 and 26 containing the two input terminations 2 and 3 connect. It is a half bridge 25 from two switches 27 built while the other half bridge 26 from two capacitors 28 is constructed. The series resonant circuit 24 connects the centers of the two half-bridges, wherein the resonance inductance of the primary winding 23 of the transformer 14 and the resonance capacity of the capacitors 28 is formed. The switches 27 become close to the resonant frequency of the series resonant circuit 24 with high frequency above the listening range, ie clocked at least 16 kHz to the excitation of audible vibrations when activating the DC / DC converter 10 to avoid. Also in the inverter subcircuit 7 , which again outputs a three-phase alternating current, all switches are clocked as possible with a frequency above the limit of the listening area in order to avoid noise.

6 shows a further concretized embodiment of the inverter 1 , Provided here is the DC input voltage U _in from a photovoltaic generator 29 , The DC / AC converter 13 has two half-bridges 25 and 26 from semiconductor switches 30 with inherent diodes 31 on. The series resonant circuit 24 has its own capacitor accordingly 32 to provide its resonant capacity. The inverter subcircuit 7 is a three-point circuit of semiconductor switches 33 with inherent diodes 34 and additional diodes 35 and an output side LC filter 36 , This inverter subcircuit 7 is known as such.

At the in 7 illustrated embodiment of the inverter is additionally the adapter plate 19 in the form of a buck converter of a semiconductor switch 37 , a throttle 38 and a diode 39 as well as with a DC link capacitor 40 at the input of the DC / DC converter 10 intended. Otherwise, the structure corresponds 6 ,

In 8th is a concretization of the inverter 1 according to 4 to see. Here is the semiconductor switch 37 with an inherent diode 41 shown. In addition, an additional input-side DC link capacitor 42 intended. The DC / DC converter 10 corresponds to the primary winding 23 of the transformer 14 the 6 and 7 , The two secondary windings 17 and the connected AC / DC converters 15 correspond 4 , The inverter subcircuit 7 is a four-point converter with a total of nine semiconductor switches 43 with inherent diodes 44 , This circuit is known as such.

It is preferred if the transmission ratio of the transformer 14 based on the over each sub-winding of the secondary winding 17 between the center tap 16 and one of the rectifier diodes 18 applied voltage in the range of 1: 2 to 1:10, preferably in the range of 1: 4 to 1: 8. It is also an advantage of the inverter according to the invention that, even with a comparatively small increase _in the DC input voltage U _{in, there} is a not insignificant overlap area around the additional DC voltage U _A , in which both the partial inverter circuit is operated 7 with activated DC / DC converter 10 as well as without is possible. This overlap area allows frequent activation and deactivation of the DC / DC converter 10 to avoid, by increasing input DC voltage U _in only to the upper end of the overlap region, ie to comparatively large input DC voltages U _in , the DC / DC converter 10 is deactivated. Even if the input DC voltage U _in subsequently drops again, it may at least initially remain at this deactivation. Conversely, with a decreasing input DC voltage U _in the DC / DC converter, it is activated only at the lower end of the transitional range, ie at a comparatively small DC input voltage U _in . This avoids that it must be switched off again at short notice. The absolute size of the overlap area depends on the limits of the intermediate circuit _voltage U _Z , in which the inverter subcircuit 7 can feed electrical energy into, for example, an AC grid with certain peak voltage, and of it, like the transformer 14 is designed with regard to its transmission ratio. In this case, the lower limit of the intermediate circuit _voltage U _Z , down to the inverter subcircuit down 7 is able to work, be moved down by so-called overmodulation. Conversely, the upper limit of the overlap range of the input DC voltage U _in using the Anpassstellers 19 are shifted upward by the DC input voltage of the DC / DC converter and correspondingly the additional DC voltage U _{A is} reduced.

LIST OF REFERENCE NUMBERS

1

 inverter

2

 input port

3

 input port

4

 AC power

5

 Dc link

6

 Anpassteilschaltung

7

 Inverter circuit section

8th

 capacitor

9

 capacitor

10

 DC / DC converter

11

 bypass path

12

 diode

13

 DC / AC converter elements

14

 transformer

15

 AC / DC converter elements

16

 Mittelpunktanzapf

17

 secondary winding

18

 Rectifier diode

19

 matching controller

20

 Link capacitor

21

 Focus

22

 subcircuit

23

 primary

24

 Series resonant circuit

25

 half bridge

26

 half bridge

27

 switch

28

 capacitor

29

 photovoltaic generator

30

 Semiconductor switches

31

 diode

32

 capacitor

33

 Semiconductor switches

34

 diode

35

 diode

36

 LC filter

37

 Semiconductor switches

38

 throttle

39

 diode

40

 Link capacitor

41

 diode

42

 Link capacitor

43

 Semiconductor switches

44

 diode

U _in

 DC input voltage

U _Z

 Intermediate circuit voltage

U _A

 Additional DC

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• EP 2023475 A1 [0004]
• EP 1033804 A2 [0005]
• DE 102011011973 B4 [0006]

Claims (18)

Inverter ( 1 ) for a variable input DC voltage (U _in ) comprising: - an inverter subcircuit ( 7 ), one via a DC voltage link ( 5 ) applied intermediate circuit voltage (U _Z ) converts to an output AC voltage, and - a matching subcircuit ( 6 ) for increasing the intermediate _circuit voltage (U _Z ) in relation to that between two input terminals ( 2 . 3 ) applied DC input voltage (U _in ), - wherein the DC voltage intermediate circuit ( 5 ) connected in series capacitors ( 8th . 9 ), wherein the adaptation subcircuit ( 6 ) the input terminals ( 2 . 3 ) directly with the two sides of at least one of the capacitors ( 8th ), so that the input DC voltage (U _in ) is applied across the first sub-series circuit, - wherein the matching sub-circuit ( 6 ) a DC / DC converter ( 10 ) with galvanic isolation, the input side to the input terminals ( 2 . 3 ) and on the output side to the two sides of at least one other of the capacitors ( 9 ) comprehensive second sub-series circuit is connected to an intermediate circuit voltage (U _Z ) additively increasing additional DC voltage (U _A ) to be applied to the second sub-series circuit, - wherein the matching subcircuit ( 6 ) a bypass path extending parallel to the second sub-series circuit ( 11 ), in which at least one short circuit of the additional direct voltage (U _A ) preventing switching element ( 12 ), and - wherein the DC / DC converter ( 10 ) an AC voltage generating DC / AC partial converter ( 13 ), an AC voltage-reducing transformer ( 14 ) and an AC / DC partial converter rectifying the reduced AC voltage ( 15 ), characterized in that - the matching subcircuit ( 6 ) is selectively activated in order to apply an additional direct voltage (U _A ) which is reduced by at least 50% with respect to the DC input voltage (U _in ) to the second sub-series circuit, and - that the DC / AC partial converter ( 13 ) is a resonant converter which, with activated DC / DC converter ( 10 ) is operated at a frequency in the range of ± 20% about its resonant frequency. Inverter ( 1 ) according to claim 1, characterized in that the DC / AC partial converter ( 13 ) is operated at a fixed frequency. Inverter ( 1 ) according to claim 1 or 2, characterized in that the adjustment subcircuit ( 6 ) is activated as needed for a period of several periods of the AC output voltage. Inverter ( 1 ) according to one of the preceding claims, characterized in that the DC / AC partial converter ( 13 ) is operated after establishing the additional DC voltage (U _A ) with constant operating parameters. Inverter ( 1 ) according to one of the preceding claims, characterized in that the high-frequency AC voltage has a frequency above the audible range. Inverter ( 1 ) according to one of the preceding claims, characterized in that switches ( 27 . 30 ) of the DC / AC partial converter ( 13 ) are clocked at a frequency of at least 16 kHz, preferably at least 30 kHz and even more preferably at least 45 kHz. Inverter ( 1 ) according to one of the preceding claims, characterized in that the switches ( 27 . 30 ) of the DC / AC partial converter ( 13 ) Are silicon carbide semiconductor switches. Inverter ( 1 ) according to one of the preceding claims, characterized in that the DC / AC partial converter ( 13 ) a series resonant circuit ( 24 ) between two half bridges connecting the input terminals ( 25 . 26 ) having. Inverter ( 1 ) according to one of the preceding claims, characterized in that the AC / DC partial converter ( 15 ) a secondary-side center tap ( 16 ) of the transformer ( 14 ) with one side of the second sub-series circuit and the two ends of the secondary winding ( 17 ) of the transformer ( 14 ) via two rectifier diodes ( 18 ) connects to the other side of the second sub-series circuit, the two halves of the secondary winding ( 17 ) of the transformer ( 14 ) two parallel branches of the bypass path ( 11 ), in each of which one of the rectifier diodes ( 18 ) prevents the short circuit of the additional DC voltage (U _A ). Inverter ( 1 ) according to one of the preceding claims, characterized in that the DC / DC converter ( 10 ) has an input side buck converter. Inverter ( 1 ) according to one of the preceding claims, characterized in that the capacitances of the first and the second partial row circuit are of different sizes. Inverter ( 1 ) according to claim 11, characterized in that the capacitances of the first and the second partial row circuit are in inverse proportion to the DC input voltage (U _in ) and the additional DC voltage (U _A ). Inverter ( 1 ) according to one of the preceding claims, characterized in that the capacitors connected in series ( 8th . 9 ) in the DC voltage intermediate circuit ( 5 ) a series connection of several DC link capacitors ( 20 ) is connected in parallel with the same large capacity, wherein the inverter subcircuit ( 7 ) to at least one intermediate point ( 21 ) between the DC link capacitors ( 20 ) connected. Inverter ( 1 ) according to one of the preceding claims, characterized in that the adjustment subcircuit ( 6 ) several subcircuits ( 22 ) each with a DC / DC converter ( 10 ) with galvanic isolation, the input side to the input terminals ( 2 and 3 ) and on the output side to the two sides of the second or another at least one other of the capacitors ( 9 ) is connected and selectively activated to one compared to the DC input voltage (U _in ) reduced by at least 50%, but the intermediate circuit voltage (U _Z ) additively increasing additional DC voltage (U _A ) to create the sub-series circuit. Inverter ( 1 ) according to claim 14, characterized in that the DC / DC converters ( 10 ) of the several subcircuits ( 22 ) are all connected to the two sides of the second sub-series circuit on the output side. Inverter ( 1 ) according to claim 14, characterized in that two DC / DC converters ( 10 ) of the several subcircuits ( 22 ) on the output side to the two sides of the second and a third at least one other of the capacitors ( 9 ) are connected, wherein the second and the third sub-series circuit are arranged symmetrically on the two sides of the first sub-series circuit. Inverter ( 1 ) according to one of claims 14 to 16, characterized in that the DC / DC converters ( 10 ) of the several subcircuits ( 22 ) have common components. Inverter ( 1 ) according to claim 17, characterized in that the DC / DC converters ( 10 ) of the several subcircuits ( 22 ) a common high-frequency AC voltage generating DC / AC partial converter ( 13 ), a common primary ( 23 ) as well as separate secondary windings ( 17 ) of a high frequency AC voltage shunting transformer ( 14 ) and separate AC / DC partial transducers rectifying the reduced high-frequency AC voltages ( 15 ) exhibit.

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