Title of Invention

CURRRENT INVERTER

Abstract

The invention describes a current inverter (2) for a photovoltaic solar unit, comprising at least one DC-DC converter (3) which can be activated on the basis of pulse-width modulation, an inter-connecting circuit (4) and a DC-AC converter (5), to which a power source (6) or a power generator, in particular a solar module (7), and/or a battery can be connected and the latter can be connected to an alternating voltage network (8) and/or one or more power con- sumers (9). A transformer (12) of the DC-DC converter (3) has several primary windings (17, 18, 21) for different input voltage ranges on the primary side (16) and the primary windings (17, 18, 21) can be selectively switched in series by means of at least one switching system (11) depending on the level of the delivered input voltage, whereby different transformation ratios of the transformer (12) can be set and the keying ratio of the pulse width modulation of the DC-DC converter (3) can always be operated in the vicinity of optimum efficiency. Fur- ther a method of regulating the current inverter (2) in this manner is described.

Full Text

The invention relates to a current inverter for a photovoltaic solar unit and method of regulat- ing the current inverter. A power supply for electrical power consumers is known from patent specification US 4 415 964, which automatically switches depending on the level and nature of the prevailing input voltage in order to produce a same output voltage. The power supply incorporates a trans- former, with two primary windings for the different possible input alternating voltages of 115 V or 230V on the primary side and the primary windings are selectively switched in se- ries via a switching system depending on the level of the delivered input alternating voltage. If a direct voltage is switched into the power supply system, a DC-AC converter is activated, which converts the direct voltage to an appropriate alternating voltage for the transformer. In a power supply system of this type, only specific voltages such as a 115V or 230V alter- nating voltage or 12V or 24V direct voltage can be applied, so mat an automatic switch is made accordingly to the connected input voltage. This being the case, when direct voltage is applied, it is converted into alternating voltage of 115V or 230V by the DC-AC converter, which can then be delivered to the transformer. A three-phase solar current inverter for networked and isolated operation is also known from patent specification DE 199 37 410 A1, which adapts the voltage level to the public power supply network by boosting and rectifying the direct voltage drawn from solar cells. The cur- rent inverter is a DC-AC converter, to which the solar modules are connected, a transformer and a DC-AC converter. The problem which occurs with the solar current inverter disclosed in DE 199 37 410 Al is that different direct voltages are generated depending on irradiation from the sun. In order to be able to generate a constant output voltage, however, the different input voltages each have to be rectified by the DC-DC converter by pulse width modulation, which means that the solar current inverter does not always operate at optimum efficiency. Current inverters are already known, whereby a power source, in particular a solar module, is connected to a DC-DC converter. The DC-DC converter inter-connects with an intermediate circuit, made up of one or more capacitors. A DC-AC converter is connected to the interme- diate circuit and the output of the DC-AC converter is connected to an alternating voltage supply for delivering power or to at least one power consumer. The DC-DC converter is set up to deliver a direct voltage and the DC-AC converter is set up to deliver an alternating voltage. Also known are DC-DC converters, comprising a bridge circuit, a transformer and a current. The bridge circuit in this instance is activated by an automatic control or a control system on the basis of pulse-width modulation so that a virtually constant output voltage is delivered at the output of the DC-DC converter. The transformer used with the current inverter or the DC-DC converter is set up for a specific transformation ratio, which is selected for the lowest input voltage of the power source. However, if the input voltage at the current inverter or the DC-DC converter changes, espe- cially if it increases, the transformer does not operate efficiently due to the specifically fixed transformation ratio. To this end, the keying ratio of the pulse width modulation for the bridge circuit connected upstream becomes ever lower, which leads to inefficient use of the transformer and hence a poor degree of efficiency. On the other hand, the peak output voltage at the current inverter is disproportionately high, which, places a high demand on the load capacity of the components, driving up the costs components with a higher rating than neces- sary, in particular the rectifier diodes connected downstream. The underlying objective of the invention is to propose a current inverter as well as a method of regulating a current inverter, whereby the DC-DC converter and the transformer are adapted to the delivered voltage, in particular to the input voltage. This objective is achieved due to the fact that the transformer of the DC-DC converter has several primary windings for different input voltage ranges on the primary side and the pri- mary windings can be selectively switched in series by means of at least one switching sys- tem depending on the level of the delivered input voltage, whereby different transformation ratios of the transformer can be set and the keying ratio of the pulse width modulation of the DC-DC converter can always be operated in the vicinity of optimum efficiency. Further the objective of the invention is achieved due to the fact, that the DC-DC converter is regulated so that at least one switching system for a primary side of the transformer is activated by a control system depending on the level of the input voltage and a switch made between sev- eral primary windings of the transformer and hence different transformation ratios set, so mat the keying ratio of the pulse-width modulation of the DC-DC converter is always operated in the vicinity of optimum efficiency. The advantage of this approach is that the current inverter is able to cover a broad input volt- age range without incurring any major disadvantages because the transformation ratio of the transformer can be adapted to the prevailing input voltage. This also ensures that the bridge circuit connected upstream of the transformer is always operated at its maximum efficiency. Another major advantage primarily resides in the fact that the components connected down- stream can be designed for a significantly lower rating because the same voltage is always delivered by the DC-DC converter, in particular by the output of the transformer, due to the adapted transformation ratio, irrespective of the prevailing input voltage, and the components therefore no longer have to be rated for the maximum level of voltage which is to be antici- pated by applying a predefined fixed transformation ratio. Other advantageous features may be found in the description. The invention will be described in more detail below, with reference to an embodiment illus- trated in the accompanying drawings. Fig. 1 is a simplified schematic diagram in the form of a block diagram, illustrating a current inverter for a solar unit with the key components, in particular the DC-DC converter; Fig. 2 is a simplified, schematic diagram, also in the form of a block diagram, showing another embodiment of the current inverter for a solar unit with the key compo- nents, in particular the DC-DC converter. Firstly, it should be pointed out that the same parts described ia the different embodiments are denoted by the same reference numbers and the same component names and the disclo- sures made throughout the description can be transposed in terms of meaning to same parts bearing the same reference numbers or same component names. Furthermore, the positions chosen for the purposes of the description, such as top, bottom, side, etc, relate to the draw- ing specifically being described and can be transposed in terms of meaning to a new position when another position is being described. Individual features or combinations of features from the different embodiments illustrated and described may be construed as independent inventive solutions or solutions proposed by the invention in their own right. Figs. 1 and 2 illustrate a standard structure, in particular in the form of a block diagram, of a current inverter system 1 with a current inverter 2 (enclosed by a dotted-dashed line). Since the individual components or groups of components and functions of the current inverter sys- tem 1 are already known, these will not be discussed in further detail. The current inverter 2 has a DC-DC-converter 3 (enclosed by a broken line), an inter- connecting circuit 4 and a DC-AC converter 5, for example. Connected to the DC-DC con- verter 3 is a power source 6 or a power generator, which may be comprise one or more solar modules 7 connected in parallel and/or in series and known as a solar generator for example, or a battery (not illustrated). At its outputs, the DC-AC converter 5 is connected to an alter- nating voltage network 8 and/or one or more power consumers 9 for example, such as a re- frigerator, a radio set, etc.. The DC-DC converter 3 preferably incorporates at least one bridge circuit 10, in particular a full bridge or half-bridge, a switching system 11, a transformer 12 and a rectifier 13. The inter-connecting circuit 4 consists of one or more capacitors. To enable a desired alternating voltage to be generated for the alternating voltage network 8 or the power consumers 9, the DC-AC converter 5 is an appropriate inverter, which converts direct voltage into an alternat- ing voltage. Other components or groups of components, such as filters, smoothing capaci- tors, etc., have been left out of the embodiment illustrated as an example here. The current inverter 2 additionally has an automatic controller or control system 14, which maybe provided in the form of a microprocessor, a micro-controller or a computer for exam- ple. The individual groups of components, in particular the switch elements incorporated in them, may be controlled accordingly by means of the control system 14. The individual regu- lating and control procedures needed for this purpose are stored in the control system 14 in the requisite software programmes and/or data and characteristic curves. The control system 14 is provided with one or more measuring systems 15 for detecting the current and the volt- age at the various different points of the current inverter system 1. A special DC-DC converter 3 is used with the solution proposed by the invention, in which the transformer 12 on the primary side 16 has several primary windings 17, 18 for different input voltage ranges and the primary windings 17, 18 can be switched in series by means of at least one switching system 11 depending on the level of the delivered input voltage. This being the case, the transformer 12 has at least two primary windings 17, 18 or one primary winding 17 with at least one central tap (not illustrated), whilst only a single secondary wind- ing 20 or alternatively several secondary windings 20 may be provided on a secondary side 19 of the transformer 12. Naturally it would be possible to provide any number of primary windings 17, 18, on condi- tion that every individual primary winding 17, 18 used can be switched via the switching system 11 connected upstream to another primary winding 17, 18, 21. To this end, the em- bodiment illustrated in Fig. 2 as an example has three primary windings 17, 18, 21, for exam- ple, and the switching system 11 connected upstream has been modified so that every indi- vidual primary winding can be activated in turn and hence switched in series. The primary windings 17, 18 and optionally 21 of the transformer are therefore inter- connected so mat each terminal - for example the winding end - of die primary winding 17 is connected to a terminal - for example the beginning of the winding - of the second primary winding 18 and optionally the other terminal - for example the winding end- of the second primary winding 18 is connected to a tenninal - for example the beginning of the winding - of another primary winding 21, etc.. To enable the individual primary windings 17 , 18, 21 to be selectively activated by the control system 14, the switching system 11 is connected to the primary windings 17 , 18, 21 so that when the switching system 11 comprising the individual switch elements 22 is switched or activated, the primary windings 17 , 18, 21 are switched in series, thereby changing the transformation ratio of the transformer. Instead of the primary windings 17 , 18, 21 being connected from the outset by means of hardware as described above, the primary windings 17 , 18, 21 may not be electrically inter- connected until the switching system 11 panics into play. In the embodiment illustrated as an example in Fig. 1, the switch element 22 is disposed be- tween the terminals of the second primary winding 18. Consequently, at a normal input volt- age of 200 V DC, for example, it is possible to activate only one primary winding 17 in order to generate an output voltage of 280 V DC, for example, as is the case with switch element 22 shown by broken lines, i.e. current flows via the primary winding 17 only because the other terminal of the second primary winding 18 does not have an electrical connection to the bridge circuit 10 connected upstream. If, for example, the input voltage rises above a defined value, for example to 400 V DC, this will be detected by the control system 14 via the measuring systems 15 and the transforma- tion ratio of the transformer 12 can then be adapted to the new input voltage. To this end, the control system 14 activates the switching system 11, in particular the switch element 22, so that it is switched from the position indicated by broken lines to the position indicated by solid lines. This then causes the other terminal of the second primary winding 18 to be acti- vated and current now flows across the two primary windings 17 and 18 connected in series, i.e. the switch element 22 of the switching system 11 switches between the left-hand terminal of the primary winding 18 and the central tap or connected terminals of the primary windings 17, causing a change in the transformation ratio. If the transformation ratio were not adapted in this way, which is what happens at the mo- ment in the prior art systems, and the other components remained in their existing state of activation, the fixed, pre-set transformation ratio would lead to a doubling of the input volt- age producing an output voltage of 2 x 380 V DC for example, in other words 760 V DC. To prevent this from happening in the prior art systems, the activation state of the components is changed by the control system 14 to the degree that an output voltage of only 380 V DC is obtained, i.e. the pulse width or the pulse breadth for the bridge circuit 10 connected up- stream is reduced and no other meaningful regulation can be applied to make any further ad- aptations. In the solution proposed by the invention, on the other hand, the transformation ratio can be adapted, in other words a reduction in the pulse width can be prevented using simple means by switching several primary windings 17, 18, 21, thereby achieving significantly better con- trol and regulation of the current inverter and DC-DC converter 3 because the entire spectrum for the pulse width or pulse breadth is still available. Specifically, when a situation of the type described above occurs, the transformation ratio is changed by switching to the other primary winding 18 so that the output voltage of 380 V DC, for example, remains constant for a doubling of the input voltage, in other words from 200 V DC to 400 V DC, i.e. in this case, the transformation ratio from the primary side 16 to the secondary side 19 is reduced by switching to other windings, in particular the primary winding 18, in addition to the primary winding 17 on the primary side 16, so that the same output voltage is always obtained. This means that another input voltage range can be catered for without incurring any major disad- vantages. In particular, the keying ratio of the pulse width modulation is always operated in the vicinity of the optimum. The principle of connecting primary windings 17, 18, 21 in series may naturally be extended by providing several windings, as illustrated in the other embodiment show in Fig. 2, and several switch elements 22 in the switching system 11. In this respect, it may be seen from the embodiment illustrated as an example in Fig. 2 that by adapting the switching system 11 accordingly, in other words by adding extra switch ele- ments 22 and using several primary windings 17, 18, 21, every individual additional primary winding 18, 21 can in turn be connected to primary winding 17. Consequently, any number of primary windings 17, 18, 21 may be used. The advantage of a solution of this type with more man two primary windings 17, 18, 21 is that it enables even better adaptation to the input voltage, i.e. a finer staging is obtained for the input voltage range, which significantly improves the degree of efficiency of the DC-DC converter 3 and current inverter 1. In the embodiment illustrated as an example in Fig. 2, an appropriate circuit is in turn con- nected upstream of the input terminals of the transformer 12, in particular upstream of the switching system 11, and is activated accordingly in order to keep the output voltage of the DC-DC converter 3 more or less constant, i.e. a bridge circuit 10, preferably a full bridge or half-bridge, is connected upstream of the transformer 12 of the DC-DC converter 3, which is activated by an automatic controller or the control system 14 on the basis of pulse-width modulation. A full-wave rectifier is provided as standard at the output of the transformer 12, in other words on the secondary side 19. For the sake of good order, it should finally be pointed out that in order to provide a clearer understanding of the structure of the current inverter system 1 and the DC-DC converter 3, they and their constituent parts are illustrated to a certain extent out of proportion and/or on a larger scale and/or on a reduced scale. The independent inventive solutions to the underlying objective may be found in the descrip- tion. Above all, the individual aspects of the subject matter illustrated in the embodiments depicted in Figs. 1,2 may be construed as independent solutions proposed by the invention. The ob- jectives and the related solutions proposed by the invention may be found in the detailed de- scriptions of these drawings. List of reference numbers 1 Rectifier inverter system 2 Rectifier inverter 3 DC-DC converter 4 Inter-connecting circuit 5 DC-AC converter 6 Power source 7 Solar module 8 Alternating voltage network 9 Power consumer 10 Bridge circuit 11 Switching system 12 Transformer 13 Rectifier 14 Control system 15 Measuring system 16 Primary side 17 Primary winding 18 Primary winding 19 Secondary side 20 Secondary winding 21 Primary winding 22 Switch element We Claim: 1. Current inverter for a photovoltaic solar unit, comprising at least one DC-DC con- verter which can be activated on the basis of pulse-width modulation, an inter-connecting circuit and a DC-AC converter, to which a power source or a power generator, in particular a solar module, and/or a battery can be connected and the latter can be connected to an alternat- ing voltage network and/or one or more power consumers, and the DC-DC converter has a bridge circuit, a transformer and a rectifier, characterised in that the transformer (12) of the DC-DC converter (3) has several primary windings (17, 18, 21) for different input voltage ranges on the primary side (16) and the primary windings (17, 18, 21) can be selectively switched in series by means of at least one switching system (11) depending on the level of the delivered input voltage, whereby different transformation ratios of the transformer (12) can be set and the keying ratio of the pulse width modulation of the DC-DC converter (3) can always be operated in the vicinity of optimum efficiency. 2. Current inverter as claimed in claim 1, wherein the transformer (12) has at least two primary windings (17, 18, 21) or a primary winding (17, 18, 21) with at least one central tap. 3. Current inverter as claimed in claim 1 or 2, wherein a terminal - winding end - of the primary winding (17, 18, 21) is connected respectively to a terminal - start of winding - of the second primary winding (17, 18, 21) and optionally the other terminal - winding end - of the second primary winding (17, 18, 21) is connected to a terminal - start of winding - of another primary winding (17, 18, 21), etc.. 4. Current inverter as claimed in one or more of the preceding claims, wherein the switching system (11) is connected to the primary windings (17, 18, 21) so mat when the switching system (11) is switched or activated, the primary windings (17, 18, 21) are switched in series, thereby applying a change in the transformation ratio of the transformer. 5. Current inverter as claimed in one or more of the preceding claims, wherein a bridge circuit (10), preferably a full bridge or half-bridge, is connected upstream of the trans- former (12) of the DC-DC converter (3), which is activated on the basis of pulse width modu- lation. 6. Method of regulating the current inverter as claimed in claim 1 in which electrical power is generated and/or supplied via a power source, in particular via at least one solar module or via a battery, which is transferred via at least one DC-DC converter 3 operated on the basis of pulse-width modulation to an inter-connecting circuit 4 and fed from it via a DC- AC converter 5 to an alternating voltage network 8 and/or delivered to a power consumer, wherein the DC-DC converter is regulated so that at least one switching system 11 for a pri- mary side 16 of the transformer is activated by a control system 14 depending on the level of the input voltage and a switch 22 made between several primary windings of the transformer and hence different transformation ratios set, so that the keying ratio of the pulse-width modulation of the DC-DC converter is always operated in the vicinity of optimum efficiency. The invention describes a current inverter (2) for a photovoltaic solar unit, comprising at least one DC-DC converter (3) which can be activated on the basis of pulse-width modulation, an inter-connecting circuit (4) and a DC-AC converter (5), to which a power source (6) or a power generator, in particular a solar module (7), and/or a battery can be connected and the latter can be connected to an alternating voltage network (8) and/or one or more power con- sumers (9). A transformer (12) of the DC-DC converter (3) has several primary windings (17, 18, 21) for different input voltage ranges on the primary side (16) and the primary windings (17, 18, 21) can be selectively switched in series by means of at least one switching system (11) depending on the level of the delivered input voltage, whereby different transformation ratios of the transformer (12) can be set and the keying ratio of the pulse width modulation of the DC-DC converter (3) can always be operated in the vicinity of optimum efficiency. Fur- ther a method of regulating the current inverter (2) in this manner is described.

Documents:

1486-kolnp-2003-abstract.pdf

1486-kolnp-2003-claims.pdf

1486-KOLNP-2003-CORRESPONDENCE.1.1.pdf

1486-kolnp-2003-correspondence.pdf

1486-kolnp-2003-description (complete).pdf

1486-kolnp-2003-drawings.pdf

1486-KOLNP-2003-EXAMINATION REPORT.1.1.pdf

1486-kolnp-2003-examination report.pdf

1486-kolnp-2003-form 1.pdf

1486-kolnp-2003-form 18.pdf

1486-KOLNP-2003-FORM 2.1.1.pdf

1486-kolnp-2003-form 2.pdf

1486-kolnp-2003-form 26.pdf

1486-KOLNP-2003-FORM 27.pdf

1486-kolnp-2003-form 3.pdf

1486-kolnp-2003-form 5.pdf

1486-KOLNP-2003-FORM-27.pdf

1486-kolnp-2003-granted-abstract.pdf

1486-kolnp-2003-granted-claims.pdf

1486-kolnp-2003-granted-correspondence.pdf

1486-kolnp-2003-granted-description (complete).pdf

1486-kolnp-2003-granted-drawings.pdf

1486-kolnp-2003-granted-examination report.pdf

1486-kolnp-2003-granted-form 1.pdf

1486-kolnp-2003-granted-form 18.pdf

1486-kolnp-2003-granted-form 2.pdf

1486-kolnp-2003-granted-form 26.pdf

1486-kolnp-2003-granted-form 3.pdf

1486-kolnp-2003-granted-form 5.pdf

1486-kolnp-2003-granted-reply to examination report.pdf

1486-kolnp-2003-granted-specification.pdf

1486-kolnp-2003-reply to examination report.pdf

1486-kolnp-2003-specification.pdf