EP1380097A2

EP1380097A2 - Current inverter

Info

Publication number: EP1380097A2
Application number: EP02764021A
Authority: EP
Inventors: Christoph Panhuber; Gerhard Rimpler
Original assignee: Fronius International GmbH
Current assignee: Fronius International GmbH
Priority date: 2001-04-20
Filing date: 2002-04-11
Publication date: 2004-01-14
Also published as: WO2002087062A3; AU2002338437A1; CN1528042B; BR0208979A; CN1528042A; WO2002087062A2

Abstract

The invention relates to a current inverter (2), in particular for a photovoltaic solar unit, comprising at least one DC-DC converter (3), an intermediate circuit (4) and a DC-AC converter (5), to which an energy source (6), or an energy generator, in particular a solar unit (7) and/or a battery, may be connected and the above may be connected to an AC network (8) and/or one or several users (9). A transformer (12) in the DC-DC converter (3) comprises, on the primary side (16) thereof, several primary windings (17, 18) for various input voltage ranges. The primary windings (17, 18) may be selectively connected in series, by means of at least one switching device (11), according to the size of the supply input voltage, resulting in the possibility of setting various conversion ratios for the transformer (12).

Description

inverter

The invention relates to an inverter, a DC-DC converter and a method for regulating an inverter and / or a DC-DC converter, as described in the preambles of claims 1, 2 and 8.

Inverters are already known in which an energy source, in particular a solar module, is connected to a DC-DC converter. The DC-DC converter is connected to an intermediate circuit which is formed from one or more capacitors. A DC-AC converter is connected to the intermediate circuit, the output of the DC-AC converter being connected to an AC voltage network for energy supply or at least to a consumer. The DC-DC converter is designed to supply a DC voltage and the DC-AC converter to supply an AC voltage.

Furthermore, DC-DC converters are known which are constructed from a bridge circuit, a transformer and a rectifier. The bridge circuit is controlled by a controller or a control device with pulse width modulation, so that an approximately constant output voltage is supplied at the output of the DC-DC converter.

In the case of the inverter or the DC-DC converter, the transformer is designed for a certain transmission ratio, this being chosen for the smallest input voltage from the energy source. However, if the input voltage on the inverter or on the DC-DC converter changes, in particular it increases, the transformer is operated unfavorably by the fixed transmission ratio. For this purpose, the pulse duty factor of the pulse width modulation for the upstream bridge circuit is getting smaller, which leads to poor utilization of the transformer and thus to poor efficiency. On the other hand, the peak output voltage at the inverter becomes disproportionately high, which places increased demands on the load-bearing capacity of the components and thus drives up the prices for the oversized components, in particular the downstream rectifier diodes.

The invention has for its object to provide an inverter and / or a DC-DC converter and a method for controlling an inverter and / or a DC-DC converter, in which the DC-DC converter or the transformer the voltage applied, in particular to the input voltage, is adapted. This object of the invention is achieved in such a way that a transformer of the DC-DC converter has a plurality of primary windings for different input voltage ranges on the primary side and the primary windings can be connected in series according to the level of the input voltage supplied via at least one switching device, with which different transmission ratios can be set are.

It is advantageous here that the inverter or the DC-DC converter can cover a wide input voltage range without major disadvantages, since the transformation ratio of the transformer can be adapted to the input voltage present. This also ensures that the bridge circuit upstream of the transformer is always operated optimally. Another major advantage is that the downstream components can be dimensioned much smaller, since the DC-DC converter, in particular the output of the transformer, always delivers the same voltage regardless of the input voltage due to the adapted transmission ratio thus the components no longer reach the maximum expected

Voltage level must be dimensioned by a fixed transmission ratio of the transformer.

Further advantageous measures are described in claims 3 to 8. The resulting advantages can be found in the description.

The invention is described in more detail by an embodiment.

Show it:

1 shows a block diagram of an inverter for a solar system with the essential components, in particular the DC-DC converter, in a simplified, schematic representation;

Fig. 2 shows another embodiment of a block diagram of the inverter for a solar system with the essential components, in particular the DC-DC converter, in a simplified, schematic representation.

In the introduction it should be noted that in the differently described embodiments the same parts are provided with the same reference numerals or the same component names. the, the disclosures contained in the entire description can be applied analogously to the same parts with the same reference numerals or the same component names. The position information selected in the description, such as, for example, top, bottom, side, etc., are based on the figure described and illustrated immediately, and are to be transferred accordingly to the new position in the event of a change in position. Furthermore, individual features or combinations of features from the different exemplary embodiments shown and described can also represent independent, inventive or inventive solutions.

1 and 2 show a conventional structure, in particular a block diagram, of an inverter system 1 with an inverter 2 (with dash-dotted lines). Since the individual components or assemblies and functions of the inverter system 1 are already known, they will not be discussed in more detail.

The inverter 2 has, for example, a DC-DC converter 3 (with dashed lines), an intermediate circuit 4 and a DC-AC converter 5. An energy source 6 or an energy generator is connected to the DC-DC converter 3 and can be formed, for example, from one or more solar modules 7 connected in parallel and / or in series with one another, which are referred to as solar generators, or a battery (not shown) , The outputs of the DC-AC converter 5 are connected, for example, to an AC voltage network 8 and / or one or more consumers 9, such as a refrigerator, a radio, etc.

The DC-DC converter 3 is preferably formed at least from a bridge circuit 10, in particular from a full or half bridge, a switching device 11, a transformer 12 and a rectifier 13. The intermediate circuit 4 is constructed from one or more capacitors. So that a desired alternating voltage can be generated for the alternating voltage network 8 or the loads 9, the DC-AC converter 5 is formed by a corresponding inverter, which converts the direct voltage into an alternating voltage. Further components or assemblies, such as filters, smoothing capacitors, etc., are not shown in the exemplary embodiment shown.

Furthermore, the inverter 2 has a regulator or a control device 14, which can be formed, for example, by a microprocessor, a microcontroller or a computer. Corresponding control of the individual - 4 -

NEN modules, in particular the switching elements arranged therein, are made. For this purpose, the individual regulating or control processes are stored in the control device 14 by means of corresponding software programs and / or data or characteristic curves. Furthermore, one or more measuring systems 15 for detecting the current and voltage are or are arranged at the most varied points of the inverter system 1 with the control device 14.

In the solution according to the invention, a special DC-DC converter 3 is used, in which the transformer 12 on the primary side 16 has a plurality of primary windings 17, 18 for different input voltage ranges and the primary windings 17, 18 according to the level of the input voltage supplied via at least one Switching device 11 can be switched in series, with which different transmission ratios can be set. Here, the transformer 12 has at least two primary windings 17, 18 or a primary winding 17 with at least one center tap (not shown), with only a single secondary winding 20 or more on a secondary side 19 of the transformer 12

Secondary windings 20 can be arranged.

Of course, it is possible for any number of primary windings 17, 18 to be present, it only being necessary to ensure that each individual primary winding 17, 18 used can be activated to form a further primary winding 17, 18, 21 via the upstream switching device 11 , For this purpose, an exemplary embodiment with three primary windings 17, 18, 21 is shown in FIG. 2, the upstream switching device 11 having been changed such that each individual primary winding 17, 18, 21 can be activated again and can thus be connected in series.

The primary windings 17, 18 and possibly 21 of the transformer are interconnected such that one connection - for example the winding end - of the primary winding 17 with one connection - for example the winding start - of the second primary winding 18 and optionally the further connection - for example the winding end - The second primary winding 18 is connected to a connection - for example the beginning of the winding - a further primary winding 21 etc. So that the individual primary windings 17, 18, 21 can optionally be activated by the control device 14, the switching device 11 is connected to the primary windings 17, 18, 21 in such a way that when switching or activating the switching device 11, which is triggered by individual switching elements 22 is constructed, a series connection of the primary windings 17, 18, 21 and thus one Change in the gear ratio of the transformer 12 takes place.

It is also possible that the individual primary windings 17, 18, 21 are not already connected by hardware, as described above, but rather that the primary windings 17, 18, 21 are only interconnected electrotechnically via the switching device 11.

In the exemplary embodiment shown in FIG. 1, the switching element 22 is arranged between the connections of the second primary winding 18. It is thus possible that with a normal input voltage, for example of 200 V DC, only one primary winding 17 is activated to generate an output voltage, for example of 380 V DC, as is the case with the switching element 22 with dashed lines, ie that the current flows only through the primary winding 17, since the further connection of the second primary winding 18 has no electrical connection with the upstream bridge circuit 10.

If, for example, the input voltage rises above a defined value, for example to 400 V DC, this is recognized by the control device 14 via the measuring systems 15, and the transformation ratio of the transformer 12 can now be adapted to the new input voltage. For this purpose, the control device 14 activates the switching device 11, in particular the switching element 22, so that it is switched from the dashed position to the position drawn with full lines. As a result, the further connection of the second primary winding 18 is now activated and a current flow now forms over the two primary windings 17 and 18 connected in series, ie that by means of the switching element 22 of the switching device 11, a switchover between the left connection of the primary winding 18 and the center tap or the connected connections of the primary windings 17 and 18 and thus a change in the transmission ratio takes place.

If the transmission ratio were not to be adjusted in this way, as is currently the case in the prior art, then with constant control of the remaining components by doubling the input voltage, an output voltage of, for example, 2 x 380 V DC would be achieved by doubling the input voltage. that is 760 V DC. To prevent this from happening in the prior art, the control of the components is changed by the control device 14 to such an extent that in turn only an output voltage of 380 V DC is calibrated, ie the pulse width or the pulse width for the upstream bridge circuit 10 is reduced so that for any further Adjustments can no longer be carried out in a meaningful way.

In the solution according to the invention, on the other hand, by adapting the transmission ratio, that is to say by connecting a plurality of primary windings 17, 18, 21 in series, the reduction in the pulse width can be avoided in a simple form and thus a much better regulation or control of the inverter 1 or the DC-DC converter 3 can be achieved because the entire spectrum for the pulse width or pulse width is still available. If such a case occurs, as described above, the connection ratio is changed by switching on the further primary winding 18 in such a way that, for example, when the input voltage is doubled, ie from 200 V DC to 400 V

DC, the output voltage of, for example, 380 V DC remains the same, that is to say that in this case the transmission ratio from the primary side 16 to the secondary side 19 is reduced by adding further turns, in particular the primary winding 18, to the primary winding 17 on the primary side 16 and thus always the same output voltage is calibrated. This ensures that a further input voltage range can be covered without major disadvantages. In particular, the pulse duty factor of the pulse width modulation can always be operated in the vicinity of the optimum.

The principle of the series connection of primary windings 17, 18, 21 can of course be carried out by several windings, as the further exemplary embodiment in FIG. 2 shows, and several

Switching elements 22 in the switching device 11 are removed.

If one looks at the exemplary embodiment in FIG. 2, it can be seen that by appropriately adapting the switching device 11, that is to say by adding further switching elements 22, each additional primary winding 18, 21 is in turn connected to the primary winding 17 in the case of a plurality of primary windings 17, 18, 21 can. It is therefore possible that any number of primary windings 17, 18, 21 can be used. The advantage of such a solution with more than two primary windings 17, 18, 21 is that an even better adaptation to the input voltage can be made, i.e. that a finer gradation is achieved for the input voltage range and thus the

Efficiency of the DC-DC converter 3 and the inverter 1 is significantly improved.

In the exemplary embodiment shown in FIG. 2, the input terminals of the transformer 12, in particular in front of the switching device 11, are again a suitable circuit connected upstream, which is controlled accordingly, in order to keep the output voltage of the DC-DC converter 3 approximately constant, ie that the transformer 12 of the DC-DC converter 3 is preferably connected upstream of a bridge circuit 10, in particular a full bridge or half bridge, which is pulse width modulated by a controller or the control device 14. A full-wave rectifier is usually arranged at the output of the transformer 12, that is to say on the secondary side 19.

For the sake of order, it should finally be pointed out that, for a better understanding of the structure of the inverter system 1 or of the DC-DC converter 3, these or their constituent parts have been partially shown to scale and / or enlarged and / or reduced.

The object on which the independent inventive solutions are based can be found in the description.

Above all, the individual versions shown in FIGS. 1, 2 can form the subject of independent solutions according to the invention. The relevant tasks and solutions according to the invention can be found in the detailed descriptions of these figures.

REFERENCE NUMBERS

Inverter system Inverter DC-DC converter DC link DC-AC converter Energy source Solar module AC voltage network Consumer Bridge circuit Switching device Transformer Rectifier Control device Measuring system Primary side Primary winding Primary winding Secondary side Secondary winding Primary winding Switching element

Claims

Patent claims

1. Inverter, in particular for a photovoltaic solar system, which consists at least of a DC-DC converter, an intermediate circuit and a DC-AC converter to which an energy source or an energy generator, in particular a solar module, and / or

Battery can be connected and this can be connected to an AC voltage network and / or one or more consumers, characterized in that a transformer (12) of the DC-DC converter (3) on the primary side (16) has a plurality of primary windings (17, 18, 21 ) for different input voltage ranges and the primary windings (17, 18, 21) can be switched in series via at least one switching device (11) according to the level of the input voltage supplied, whereby different transformation ratios of the transformer (12) can be set.

2. DC-DC converter, characterized in that a transformer (12) on the primary side (16) has a plurality of primary windings (17, 18, 21) for different input voltage ranges and the primary windings (17, 18, 21) corresponding to The level of the input voltage supplied can be optionally connected in series via at least one switching device (11), with which different transformation ratios of the transformer (12) can be set.

3. Inverter or DC-DC converter according to claim 1 or 2, characterized in that the DC-DC converter (3) preferably has a bridge circuit (10), a transformer (12) and a rectifier (13).

4. Inverter or DC-DC converter according to one or more of the preceding claims, characterized in that the transformer (12) at least two primary windings (17, 18, 21) or a primary winding (17, 18, 21) with at least one center tap having.

5. Inverter or DC-DC converter according to claim 1 or 2, characterized in that in each case one connection - winding end - the primary winding (17, 18, 21) with one connection - winding start - the second primary winding (17, 18, 21) and optionally the further connection - winding end - of the second primary winding (17, 18, 21) with a connection - winding start - a further primary winding (17, 18, 21) etc. can be connected.

6. Inverter or DC-DC converter according to one or more of the preceding claims, characterized in that the switching device (11) is connected to the primary windings (17, 18, 21) such that when switching or activating the switching device (11 ) a series connection of the primary windings (17, 18, 21) and thus a change in the transformation ratio of the transformer takes place.

7. Inverter or DC-DC converter according to one or more of the preceding claims, characterized in that the transformer (12) of the DC-DC converter (3) is preferably connected upstream of a bridge circuit (10), in particular a full bridge or half bridge which is controlled by pulse width modulation.

8. Method for regulating an inverter or a DC-DC converter, in which electrical energy is generated and / or supplied by an energy source, in particular by at least one solar module or by a battery, which is generated by at least one DC-DC wall 1er transferred to an intermediate circuit and from there via a DC-AC converter

AC voltage is fed in and / or fed to a consumer, characterized in that the DC-DC converter is controlled in such a way that, depending on the level of the input voltage, at least one switching device for a primary side of the transformer is controlled by a control device and thereby a switchover between several pri - Märwickungen the transformer is carried out and thus different gear ratios are set.