DE102013007077A1 - Circuit arrangement for conversion between DC and AC voltage - Google Patents

Abstract

The present invention relates to a circuit arrangement for converting between a DC voltage and an AC voltage, in which a pole of the DC voltage connection is connected to a pole of the AC voltage connection. The circuit arrangement is designed in such a way that energy is transferred from the DC voltage side to the AC voltage side or vice versa via a step-down or step-up converter, as long as the sign of the DC voltage corresponds to the sign of the AC voltage and in the other case the energy is stored temporarily in a capacitor between the two Pages is transferred. The proposed circuit arrangement manages with a small number of power semiconductors, has low losses and can be used as an inverter for thin-film solar cells or rear-contacted solar cells.

Description

Technical application

The present invention relates to a circuit arrangement for converting between a DC voltage and an AC voltage, wherein one pole of the DC voltage terminal is connected to one pole of the AC voltage terminal.

Such a circuit arrangement can be used, for example, to feed photovoltaically generated energy into the power grid or thus to operate an electrical stand-alone grid. Thus, when operating thin-film solar cells, it is necessary for the negative pole of the solar generator to be at earth potential in order to prevent irreversible damage to the solar cells due to TCO (Transparent Conductive Oxide) corrosion. When operating back-contacted solar cells, however, it is necessary that the positive pole of the solar generator is at ground potential, because otherwise the cell efficiency deteriorates due to a reversible polarization effect. These requirements are met with a circuit arrangement for converting the DC voltage from the solar generator into AC voltage, wherein one pole of the DC voltage terminal is connected to one pole of the AC voltage terminal. This connection also meets requirements for personal protection, since no capacitive leakage currents flow through the solar generator.

State of the art

Many known circuits for converting DC into AC voltage either do not allow one pole of the solar generator to be grounded or use transformers to separate the input potential from the output potential. However, inverters with transformers have the disadvantage of a higher weight, a larger overall volume and a lower efficiency compared to transformerless circuits.

From the DE 10 2008 048 841 B3 a circuit arrangement for the conversion between a DC voltage and an AC voltage is known, which meets the above requirements for the operation of a solar generator and can isolate the solar generator potential from the output potential via disconnectors. For the energy transfer between the DC voltage connection and the AC voltage connection, a capacitor for buffering the energy is used for both half cycles of the AC voltage. However, this circuit requires a large number of power components and generated by their construction additional losses.

The object of the present invention is to provide a circuit arrangement for the conversion between a DC voltage and an AC voltage, which is suitable for the operation of thin-film solar cells or back-contacted solar cells, a small volume and weight and low losses and has a small number Can realize power components. The circuit should also be able to provide reactive power at the AC voltage port.

Presentation of the invention

The object is achieved with the circuit arrangement according to claim 1. Advantageous embodiments of the circuit arrangement are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

The proposed circuit arrangement for the conversion between a DC voltage and an AC voltage has, in a known manner, a DC voltage side with a DC voltage connection and an AC voltage side with an AC voltage connection. A first pole of the DC voltage terminal is connected in the circuit arrangement with a first pole of the AC voltage terminal, so that when operating the circuit arrangement on a thin-film solar cell or a back-contacted solar cell of the negative or positive pole of the solar generator can be set to ground potential. Between the DC voltage and the AC voltage connection, a step-down converter from the DC voltage to the AC voltage connection or a step-up converter from the AC voltage to the DC voltage terminal is formed by a plurality of switches, can be transmitted by the energy from the DC voltage to the AC voltage terminal or vice versa, as long as the sign of the DC voltage at the DC voltage terminal the sign corresponds to the AC voltage at the AC voltage terminal. At least a first capacitor is connected in the proposed circuit arrangement between the DC voltage and the AC voltage terminal, that the energy is transferable by caching in this capacitor from the DC voltage to the AC terminal or vice versa, as long as the sign of the DC voltage at the DC voltage terminal does not follow the sign of the AC voltage AC voltage connection corresponds. Preferably, the circuit arrangement also has at least one second capacitor, which is connected in parallel to the DC voltage connection.

In the proposed circuit arrangement is thus in contrast to the above-mentioned DE 10 2008 048 841 B3 not the full power of both half-waves cached across the first capacitor, but only the energy during a half-wave. The energy transfer in the second half-wave then takes place via the buck or boost converter without intermediate storage in the first capacitor. This refinement reduces the losses compared with the circuit arrangement of the cited document, resulting in a higher efficiency of the voltage conversion. Furthermore, the proposed circuit arrangement can be realized with a smaller number of power components and thus leads to a cost-effective design. The proposed circuit does not require a transformer which would add weight and additional losses. When used as a solar inverter, one pole of the solar generator can be connected to the neutral conductor, which is virtually at ground potential. This allows the operation of thin-film solar cells or back-contacted solar cells with the proposed circuit arrangement. Furthermore, the fixed potential also has a favorable effect on the electromagnetic compatibility and prevents capacitive leakage currents from flowing via the solar generator. The circuit is capable of providing both active and reactive capacitive and inductive reactive power, as loudly VDE-AR-N 4105 for solar inverters that feed into the grid, from a capacity of 3.68 kVA is required. In addition to the feeding of energy into the power grid, the proposed circuit arrangement can also supply AC consumers in an isolated grid. Depending on the configuration, the circuit arrangement can be operated as an inverter, as a rectifier or as a DC and an inverter.

The proposed circuit arrangement has, in addition to the first capacitor, at least four switches, a first coil for limiting the capacitor current of the first capacitor, and a second coil for smoothing the alternating current at the AC voltage terminal. A basic structure of the proposed circuit arrangement is in the description of the embodiments in the 1a and 1b shown, on the one hand, the minimum components used are visible and the other optional components are indicated by dashed connections. The circuit arrangement thus comprises a plurality of switches, which are formed by turn-off power semiconductors, diodes, coils and capacitors. The turn-off power semiconductors used can be, for example, IGBTs, MOSFETs, JFETs or bipolar transistors with a parallel-connected diode. The diode can be integrated in the component. Of course, other advantageous for the particular application components can be integrated into the circuit structure. Examples of such components are EMC filters (EMC: electromagnetic compatibility), separating elements or separation relays, DC-DC regulators (DC: Direct Current), a capacitor pre-charge circuit or a measuring device. Accordingly, in addition to a direct electrical connection without an intermediate electrical component, the connection of a component to another component or one of the DC or AC voltage terminals also means a connection via one or more of the above-mentioned components or via a purely resistive electrical component.

In all proposed embodiments of the present circuit arrangement is preferably a first terminal of the first capacitor via the first coil and a first switch or a first diode - or alternatively a series connection of a first switch or a first diode and a second diode - with the second pole of DC voltage source connected. Parallel to the first capacitor, a series circuit of a second and a third switch, each with parallel-connected diode is formed. A center tap between the second and third switches is connected to the first pole of the DC voltage source. The second terminal of the first capacitor is connected via a series circuit of a fifth and fourth switch, each with a diode connected in parallel, directly or via the first switch or the first diode to the second pole of the DC voltage source and via a center tap between the fourth and the fifth switch connected via a second coil to the second pole of the AC voltage source. By such an arrangement is achieved with appropriate control of the switch that the energy from the DC voltage connection to the AC voltage terminal or vice versa by means of a buck converter or boost converter, consisting of the fourth and fifth switch, transmitted as long as the sign of the voltage at the AC voltage terminal the sign of the voltage corresponds to the DC voltage connection. In the period in which the voltage at the AC terminal has the opposite sign of the voltage at the DC terminal, the energy transfer from the DC terminal to the AC terminal or vice versa, by the fact that the energy in the first capacitor is cached. The individual switches are known in the proposed circuit arrangement Mode driven via pulse width modulated switching signals to achieve the conversion between the DC and AC voltage.

The proposed circuit arrangement operates in the conversion of DC into AC voltage or vice versa as a so-called three-step converter. The voltage at that pole of the second coil, which is connected to the center tap of the fourth and fifth switches, can assume three voltage levels with respect to the first pole of the AC voltage source, positive voltage, zero and negative voltage. Compared to a two-position inverter this causes lower losses and the second coil can be smaller. When reloading the first capacitor, the first switch can be de-energized, so that switching losses are reduced.

It is particularly advantageous to realize a circuit arrangement according to a first embodiment which requires only five switches or actively switchable power semiconductors. The blocking voltages of all semiconductors do not significantly exceed the voltage of a solar generator connected to the DC voltage connection, so that the use of conventional semiconductors is made possible. This embodiment leads to a relatively inexpensive construction and low switching losses. In this embodiment, the first terminal of the first capacitor via the first coil, a first diode and a first switch with a parallel diode is connected to the second pole of the DC voltage terminal. A second diode connects the first pole of the DC voltage source to a center tap between the first switch and the first diode. The series connection of the fifth and fourth switches is connected via this center tap and the first switch to the second pole of the DC voltage source.

The proposed circuit arrangement is suitable in the embodiment as an inverter particularly for the operation of thin-film solar cells or back-contacted solar cells. However, the application of the circuit arrangement is not limited only to the field of photovoltaics. The circuit can be used wherever it is necessary to convert DC voltage into AC voltage or AC voltage into DC voltage. Apart from solar generators, batteries or fuel cells can also be connected to the DC side, for example. In a DC side composite of a solar generator and an electrical energy storage energy can be fed into both the AC side connected power grid, as well as the energy storage are charged from the network. The circuit arrangement is also suitable not only for operation on single-phase AC sources or AC loads, but also for operation on multi-phase sources or loads. For this purpose, only several of the proposed circuit arrangements for the individual phases must be connected to each other. To extend the permissible voltage range on the DC side, the circuit arrangement may also have an additional DC-DC controller.

Brief description of the drawings

The proposed circuit arrangement will be explained in more detail using exemplary embodiments in conjunction with the drawings. Hereby show:

1 two possible design variants of the circuit arrangement with partially optional components;

2 a first circuit variant of the circuit arrangement for operation as an inverter;

3 a second circuit variant of the circuit arrangement for operation as an inverter;

4 a third circuit variant of the circuit arrangement for operation as an inverter;

5 a fourth circuit variant of the circuit arrangement for operation as a DC and inverter;

6 a fifth circuit variant of the circuit arrangement for operation as a rectifier;

7 a sixth circuit variant of the circuit arrangement for operation as a rectifier;

8th a seventh circuit variant of the circuit arrangement for operation as a DC and inverter;

9 a representation of the different circuit states in the operation of the first or second circuit variant;

10 an example of the circuit patterns of the first circuit variant for the switches S1 to S5 in a schematic representation;

11 a representation of the charging of the first capacitor C2 in the state 4 of 9 ;

12 a representation of the different circuit states in the operation of the third or fourth circuit variant;

13 an example of the circuit patterns of the third circuit variant for the switches S1 to S5 in a schematic representation;

14 a representation of the different circuit states in the operation of the fifth circuit variant;

15 an example of the circuit patterns of the fifth circuit variant for the switches S2 to S6 in a schematic representation;

16 an example of the different circuit states in the operation of the seventh circuit variant;

17 an example of switching patterns of the seventh circuit variant in rectifier operation for the switches S1 to S6 in a schematic representation;

18 an example of the use of three of the described circuit arrangements for operation on three-phase AC sources and loads; and

19 an example of an embodiment of the proposed circuit arrangement with an additional DC-DC controller.

Ways to carry out the invention

The proposed circuit arrangement can be constructed in different variants as a rectifier, as an inverter or as a DC and inverter. 1 shows in the sub-figures a) and b) the basic structure of the circuit arrangement, wherein optional components are indicated by the connections shown in dashed lines. The different circuit variants differ in which of the dashed connections are each realized. In the proposed circuit arrangement, either the negative pole or the positive pole of the DC side can be connected to a pole of the AC side. 1a shows the connection of the negative pole of the DC side with the AC side, 1b the connection of the positive pole of the DC side with the AC side. In the following embodiments, only the variants are shown in each case, in which the negative pole is connected to the AC voltage side. In order to connect the positive pole to the AC side, then only the polarity of all semiconductors and capacitors has to be reversed. Any required EMC filters are not shown in the figures for the sake of clarity.

G1 represents a DC voltage source or a DC load, which is connected to the DC voltage terminals of the circuit arrangement. W1 represents an AC voltage source or an AC load, which is connected to the two AC voltage terminals of the circuit arrangement. S1 to S6 are switches in the form of turn-off power semiconductors, each with parallel-connected diode. The switches S1 and S6 can be replaced by the diodes D1 and D6 depending on the application. The switch S6 can also be omitted altogether. A capacitor C1, referred to in the foregoing description as a second capacitor, is connected in parallel with the DC voltage source G1. This capacitor could also be integrated in the DC voltage source. The second coil L2 serves to smooth the alternating current i _A. The diode D7 can be used depending on the application in one of the two directions drawn or replaced by a direct connection. The capacitor C3 is required for operating an isolated network, but can be omitted in an operation of the circuit arrangement on the power grid.

Characteristic of the proposed circuit topology is that energy from G1 to W1 or vice versa by means of a buck / boost converter, consisting of S4 and S5, is transmitted, as long as the sign of the voltage u _A at the AC voltage terminal corresponds to the sign of the voltage U _D at the DC voltage terminal , In the period in which the voltage u _{A has} the opposite sign of the voltage U _D , the energy transfer from G1 to W1 or vice versa, in that energy in the capacitor C2 is latched, referred to in the foregoing description as the first capacitor. The first coil L1 serves to limit the capacitor current i _C2 .

In the following representations of the 2 to 8th seven different circuit variants of the proposed circuit arrangement are exemplified. The 9 to 17 show the different operating states of these circuit variants when operating as a DC or inverter and the switching pattern for the control of the respective switch.

The simplest circuit variants for inverter operation are those in the 2 to 5 illustrated circuit variants 1 to 4. The source G1 provides electrical energy z. B. in the form of a solar generator. W1 is an AC load, an AC mains or a phase of the three-phase network. To supply reactive power at the output can be cached energy from W1 in the capacitors C1 and C2, respectively, and be returned to W1 at another time. In circuit variant 1, the first coil L1 is connected via the diode D7 and the switch S1 to the second pole of the DC voltage source. A diode D6 is connected between the first pole of the DC voltage source and the center tap between switch S1 and diode D7. The switch S4 is also connected to this center tap. Circuit variant 3 shows a very similar construction in which only the diode D7 was dispensed with. Circuit variant 2 differs from circuit variant 1 in that the switch S4 is not connected via the switch 51, but directly to the second pole of the DC voltage source. Thus, even lower losses can be achieved. This also applies to circuit variant 4, in which again the diode D7 is omitted.

In circuit variants 1 and 3, the power semiconductors S1 to S5 and D6 and D7 need not be able to block significantly higher voltages than the voltage U _D. In the case of the circuit variants 2 and 4, the maximum occurring voltage at the switch S4 is greater and corresponds approximately to twice the value of the voltage U _D. The circuit variants 3 and 4 are particularly suitable for operation on solar cells with a voltage <approximately 500 V at a mains voltage of 230 V.

The components L1 (first coil) and C2 (first capacitor) form a resonant circuit. In the circuit variants 1 and 2, after the closing of the switch S1, the charging current of the capacitor C2 returns to zero by itself, since the diode D7 prevents the capacitor C2 from being discharged again via the coil L1. In circuit variants 3 and 4, this diode D7 is not present. The charging current of the capacitor C2 must be actively switched on and off via S1 there.

For operation as a rectifier, the circuit variants 4 to 7 are the 5 to 8th , In this case, energy is transmitted from the AC voltage source W1 to the DC load G1. The AC voltage source is taken from a sinusoidal current. In addition, reactive power can be taken from the AC source. The circuit variants 4 and 7 allow both an inverter operation and a rectifier operation, so that energy can be transmitted both from G1 to W1 and from W1 to G1. Circuit variant 5 differs from circuit variant 1 by replacing the switch S1 with a diode D1. The diode D7 is polarized in the opposite direction, the diode D6 is replaced by the switch S6. In circuit variant 7, in contrast to circuit variant 4, the diode D6 is replaced by the switch S6. Circuit variant 6 has neither the switch S6 nor the diode D6. The coil L1 is in this case connected via the diode D1 to the second pole of the DC voltage terminal, the switch S4 is connected directly to the DC voltage terminal.

9 shows the different operating states when operating the inverter circuit variant 1 in detail. In the four states, the current flow is indicated by the bold lines. Circuit variant 2 works on the same principle, but the blocking voltages at switch S4 are higher.

To set a positive voltage u _A , the circuit is alternately set to states 1 and 2. It is assumed that the voltage u _{C2 is} initially at least as great as the voltage U _D. In state 1, the switches S1, S3 and S4 are closed, the switches S2 and S5 open. The current i _A flows through S1, S4 and L2. In the case of positive current i _A , energy flows from G1 or C1 to W1; in the case of negative current i _A , energy flows from W1 into capacitor C1. In state 2, the switches S1, S3 and S5 are closed, the switches S2 and S4 open. The current i _A flows through S3, S5 and L2.

To set a negative voltage u _A , the circuit is alternately set to states 3 and 4. In state 3, the switches S2 and S5 are closed, the switches S1, S3 and S4 open. The current i _A flows through C2, S2, S5 and L2. With negative current i _A , energy flows from C2 to W1, with positive current i _A , energy flows from W1 to C2. In state 4, the switches S1, S3 and S5 are closed, the switches S2 and S4 open. The current i _A flows through S3, S5 and L2. If the capacitor voltage u _{C2 is} smaller than the voltage U _D , the capacitor C2 is recharged via G1, S1, D7, L1 and S3.

The periods in which the circuit is in states 1 to 4 are determined by a pulse width modulation, with which the individual switches S1 to S5 are driven. 10 shows exemplary switching pattern of the circuit variant 1 for the switches S1 to S5. The phase of the current i _A may be shifted to the phase of the voltage u _A when reactive power is to be supplied to the AC side. This is in the upper part of the 10 indicated by the double arrow. The diode D6 is operatively powered, but in this example serves as a protection diode to limit the voltage across the switch S1 during the switching operations and in the event of a fault.

11 shows in the first circuit variant, the charging of the capacitor C2 in the state 4. The corresponding current waveform in the circuit diagram is in the lower part of the figure shown. The charging current i _{C2 first} increases after switching on the switches S1 and S3, reaches its highest point when u _{C2 is} approximately U _D , and then becomes zero again. The switch S1 can then be switched off without power.

12 shows the different operating states when operating the inverter circuit variant 3. Variation 4 works on the same principle, the reverse voltages at S4, however, are higher and the switch S1 can also be switched off in state 1. Depending on the design of the components, the circuit according to variant 4 can also be used as a rectifier in certain operating points in order to transfer energy from W1 to G1. The current flow in the different operating states is again indicated by the bold lines.

To set a positive voltage u _A , the circuit is alternately in the state 1 and one of the freewheeling states 3 and 4 offset. In state 1, the switches S1, S3 and S4 are closed, the switches S2 and S5 are open. The current i _A flows through S1, S4 and L2. With positive current i _A , energy flows from G1 or C1 to W1, with negative current i _A , energy flows from W1 into the capacitor C1. If the capacitor voltage u _{C2 is} smaller than the voltage U _D , the capacitor _charging current i _C2 builds up via the coil L1.

To set a negative voltage u _A , the circuit is alternately in the state 2 and one of the freewheeling states 3 and 4 offset. In state 2, the switches S2 and S5 are closed, the switches S1, S3 and S4 open. The current i _A flows through C2, S2, S5 and L2. With negative current i _A , energy flows from C2 to W1, with positive current i _A , energy flows from W1 to C2. If, when changing to state 2, current still flows through coil L1, this current flow is maintained via D6 and S2.

In the freewheeling states 3 and 4, the switches S3 and S5 are closed, the switches S2 and S4 open. The current i _A flows through S3, S5 and L2. In the free-running state 3, the switch S1 is closed and the capacitor charging _current i _C2 , which flows through the components G1, S1, L1, C2 and S3, increases, provided that the voltage u _{C2 is} smaller than the voltage U _D. In the freewheeling state 4, the switch S1 is opened and the capacitor charging _current i _C2 , which flows through the components D6, L1, C2 and S3, is reduced. Once it reaches zero, diode D6 will turn off.

The periods in which the circuit is in the states 1 to 4 are again determined by a pulse width modulation, as exemplified in the 13 is shown. This figure shows the circuit patterns of the circuit variant 3 for the switches S1 to S5 and the corresponding course of the AC voltage u _A and the alternating current i _A. The phase of the current i _A can here also be shifted to the phase of the voltage u _A , if reactive power is to be supplied to the AC voltage side. This is indicated by the double arrow in the diagram of the current i _A.

14 shows the various operating states of the rectifier circuit variant 5. The current waveform is again illustrated by the bold lines.

At a positive voltage u _A , the circuit is alternately set to states 1 and 2. It is assumed that the voltage u _{C2 is} initially smaller than the voltage U _D. In state 1, the switches S3 and S4 are closed, the switches S2, S5 and S6 open. With positive current i _A , energy flows from capacitor C2 via L1, D7, S4, L2 and S3 to W1, with negative current i _A , energy flows from W1 via L2, S4 and D1 to G1. In state 2, the switches S3 and S5 are closed, the switches S2, S4 and S6 open. The current i _A flows through S3, S5 and L2.

At a negative voltage u _A , the circuit is alternately set to states 3 and 4. In state 3, the switches S2, S5 and S6 are closed, the switches S3 and S4 open. The current i _A flows through C2, S2, S5 and L2. With negative current i _A , energy flows from C2 to W1, with positive current i _A , energy flows from W1 to C2. In state 4, the switches S3 and S5 are closed, the switches S2, S4 and S6 open. The current i _A flows through S3, S5 and L2. If the capacitor voltage u _{C2 is} greater than the voltage U _D , the capacitor C2 is discharged via G1, D1, D7, L1 and S3.

The switch S6 is used to limit the voltage across the switch S4 in state 3, so that S4 does not have to lock much higher voltages than U _D.

Circuit variant 6 works on the same principle. However, the voltages to be blocked at S4 are approximately twice as high as in Variant 5. The components S6 and D7 can be dispensed with, since in variant 5 they only serve to limit the voltage across S4. The provision of reactive power on the AC side is done during the positive voltage half cycle not via C2, but because of the direct connection between S4 and C1 via C1.

The periods in which the circuit is in the states 1 to 4 are again determined by a pulse width modulation, as determined by the switching pattern of the 15 for the switches S2 to S6 of the circuit variant 5 by way of example are shown. The phase of the current i _A may be shifted to the phase of the voltage uA, if reactive power to be taken at the AC side. This is also indicated here via the double arrow in the diagram of the current i _A.

16 shows an example of the different operating states when operating the circuit variant 7. The circuit variant 7 is both suitable to transfer energy from inverter G1 to W1 in inverter operation, as well as to transmit energy from W1 to G1 in rectifier operation. For operation as an inverter, the switches S1 to S5 are to be controlled exactly as in variant 4, the switch S6 remains open. 16 shows an example of the operation as a rectifier, again the current flow is indicated by the bold lines.

At a positive voltage u _A , the circuit is alternately set in the state 1 and one of the freewheeling states 3 and 4. In state 1, the switches S3 and S4 are closed, the switches S1, S2, S5 and S6 are open. The current i _A flows through S4 and L2. With positive current i _A , energy flows from C1 to W1, with negative current i _A , energy flows from W1 to G1 or C1.

At a negative voltage u _A , the circuit is alternately set to state 2 and one of the freewheeling states 3 and 4. In state 2, the switches S2 and S5 are closed, the switches S1, S3, S4 and S6 open. The current i _A flows through C2, S2, S5 and L2. With negative current i _A , energy flows from C2 to W1, with positive current i _A , energy flows from W1 to C2.

In the freewheeling states 3 and 4, the switches S3 and S5 are closed, the switches S1, S2 and S4 open. The current i _A flows through S3, S5 and L2. In the free-running state 3, the switch S6 is closed and the capacitor current i _C2 , which flows through the components C2, L1, S6 and S3, is negative. In the free-running state 4, the switch S6 is opened and the capacitor current i _C2 , which flows through the components C2, L1, S1, G1 and S3, is reduced. Energy flows from C2 to G1.

The periods in which the circuit is in states 1 to 4 are determined by a pulse width modulation. 17 shows an example of the switching pattern of the circuit variant 7 in rectifier operation for the switches S1 to S6. The phase of the current i _A can in turn be shifted to the phase of the voltage u _A , if reactive power is to be taken at the AC voltage side. This is in the flow chart of 17 indicated by the double arrow.

The proposed circuit arrangement is suitable not only for operation on single-phase AC power sources or AC loads, but also for operation on multi-phase AC power sources or AC loads. For this purpose, only several of the circuits described are to be connected to each other. This is exemplary in 18 shown for three phases P1 to P3, where three of the circuits are used here.

19 finally shows another example of the proposed circuit arrangement as shown in FIG 1a is illustrated. In this case, an additional DC-DC controller is used to expand the permissible voltage range on the DC voltage side. Depending on the voltage range, switch S4 can then be connected directly to G1 or to the DC-DC controller. In order to avoid losses, the DC-DC controller can also be completely bypassed with the switch S8, which is optionally shown in the figure, when it is not needed. The bridging can z. B. be made via a relay.

In the following, exemplary dimensions of the components for the example of an inverter of the circuit variant 1 are indicated during operation on a solar generator. It is assumed that an effective value of the mains voltage of 230 V (+15% / - 20%), a grid frequency of 50 Hz, a voltage at the solar cell of at least 500 V at a power of the solar inverter of 3 kVA and a switching frequency of 16 kHz , In the circuit variant 1, the capacitor C2 buffers the energy that is released to the network as long as u _{A has} the opposite sign of U _D. The charging process of C2, as he in conjunction with the 9 and 11 must be completed within the time in which the switches S1 and S3 are turned on. The minimum on-time of S1 and S3 can be calculated approximately using the PWM scheme:

U ^ _Amax is the highest amplitude of the output voltage, U _C2min the smallest voltage across the capacitor C2 and f _switching the switching frequency. It is assumed that U _{C2min corresponds} approximately to the lowest voltage on the solar cell U _Dmin .

With U ^ _Amax = √ 2 · U _{Aeff, max} = √ 2 · 230V · 1.15 = 374.1V and U _C2min ≈ U _Dmin = _500V This results in the minimum switch-on time of S1 / S3 T _S1min = T _S3min ≈ 15.8 μs

The in 11 illustrated current waveform of i _C2 is a half-wave of the resonant circuit of L1 and C2. The duration of the half- _oscillation may not exceed T _S1min . This must satisfy the following condition:

The resonant frequency of L1 and C2 determines the product of the values of the two components. The ratio of L1 / C2 then represents one more degree of freedom for optimization with regard to losses and size. For circuit variant 1, the following component values can then be used for the capacitors and coils of circuit variant 1:
L1 = 470 nH
C2 = 47 μF
C1 = 1000 μF
L2 = 5 mH.

Basically, the mains frequency of the proposed inverter is freely selectable. It thus works both on the 50 Hz network and, for example, on a 60 Hz network. The switching frequency depends on the technology of the power semiconductors used. When built with silicon IGBTs or silicon MOSFETs, this moves in the lower double-digit kHz range. If silicon carbide semiconductors are used, the switching frequency can be increased up to the three-digit kHz range. The switches S1 to S6 and the diodes D1 to D7 may consist in the proposed circuit arrangement of individual power semiconductors or from a series circuit of several power semiconductors, optionally in conjunction with a suitable circuit for limiting the voltage to the individual semiconductors. Further components can be integrated into the circuit arrangement as needed.

LIST OF REFERENCE NUMBERS

G1

DC voltage source / load

W1

AC voltage source / load

S1 to S6

Switchable power semiconductors

D1 to D7

diodes

C1

second capacitor

C2

first capacitor

C3

third capacitor

L1

first coil

L2

second coil

S8

Power semiconductor / relay contact

DC

DC-DC regulator

P1-P3

phases

N

neutral

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

• DE 102008048841 B3 [0004, 0008]

Cited non-patent literature

• VDE-AR-N 4105 [0008]

Claims (12)

Circuit arrangement for the conversion between a DC voltage and an AC voltage with A DC voltage terminal and an AC voltage terminal, wherein a first pole of the DC voltage terminal is connected to a first pole of the AC voltage terminal, A buck converter from the DC to the AC voltage terminal or a boost converter from the AC to DC terminal through which energy can be transferred from the DC to AC terminal or from the AC to DC terminal as long as the sign of a DC voltage at the DC terminal corresponds to the sign of an AC voltage at the AC terminal, and - At least one capacitor via which energy can be transferred from the DC voltage to the AC voltage terminal or from the AC voltage to the DC voltage terminal by means of intermediate storage, as long as the sign of the DC voltage at the DC voltage terminal does not correspond to the sign of the AC voltage at the AC voltage terminal. Circuit arrangement according to claim 1, characterized in that the circuit arrangement comprises at least four switches, a first coil for limiting a capacitor current of the capacitor and a second coil for smoothing an alternating current at the AC voltage terminal. Circuit arrangement according to claim 2, characterized in that a first terminal of the capacitor via the first coil and a first switch or a first diode to the second pole of the DC voltage terminal is connected, that parallel to the capacitor, a series circuit of a second and a third switch, the each having parallel diodes is formed, wherein a center tap between the second and the third switch to the first pole of the DC voltage terminal is connected, and that a second terminal of the capacitor via a series circuit of a fourth and a fifth switch, each having parallel diodes , is connected directly or via the first switch or the first diode to the second pole of the DC voltage terminal, wherein a center tap between the fourth and the fifth switch via the second coil is connected to the second pole of the AC voltage terminal. Circuit arrangement according to claim 2, characterized in that a first terminal of the capacitor via the first coil and a series circuit of a first switch or a first diode and a second diode to the second pole of the DC voltage terminal is connected, that parallel to the capacitor, a series circuit of a a second tap and a third switch, each having parallel diodes, is formed, wherein a center tap between the second and the third switch to the first pole of the DC voltage terminal is connected, and that a second terminal of the capacitor via a series circuit of a fourth and a fifth Switch, each having parallel diodes, is connected directly or via the first switch or the first diode to the second pole of the DC voltage terminal, wherein a center tap between the fourth and the fifth switch via the second coil with the second pole of the Wechselspannu ngsanschlusses is connected. Circuit arrangement according to claim 3, characterized in that the first terminal of the capacitor via the first coil and a sixth switch, which has a parallel diode, or a second diode is connected to the first pole of the DC voltage terminal. Circuit arrangement according to claim 4, characterized in that the first terminal of the capacitor via the first coil, the second diode and a sixth switch, which has a parallel diode, or a third diode is connected to the first pole of the DC voltage terminal. Circuit arrangement according to claim 2, characterized in that a first terminal of the capacitor via the first coil and a series circuit of a first switch and a first diode with the second pole of the DC voltage terminal is connected, that the first terminal of the capacitor via the first coil, the first diode and a second diode is connected to the first pole of the DC voltage terminal, that in parallel to the capacitor, a series connection of a second and a third switch, respectively parallel diodes is formed, wherein a center tap between the second and the third switch is connected to the first pole of the DC voltage terminal, that a second terminal of the capacitor via a series circuit of a fourth and a fifth switch, each having parallel diodes, and the first switch is connected to the second pole of the DC voltage terminal, and that the second terminal of the capacitor is connected via the series circuit of the fourth and the fifth switch and the second diode to the first pole of the DC voltage terminal, wherein a center tap between the the fourth and the fifth switch is connected via the second coil to the second pole of the AC voltage terminal. Circuit arrangement according to claim 2, characterized in that a first terminal of the capacitor via the first coil and a series circuit of a first switch and a first diode to the second pole of the DC voltage terminal is connected, that the first terminal of the capacitor via the first coil, the first diode and a second diode is connected to the first pole of the DC voltage terminal, that parallel to the capacitor, a series circuit of a second and a third switch, each having parallel diodes, is formed, wherein a center tap between the second and the third switch with the connected to the first pole of the DC voltage terminal, that a second terminal of the capacitor via a series circuit of a fourth and a fifth switch, each having parallel diodes connected to the second pole of the DC voltage terminal, wherein a center tap between the fourth and de m fifth switch is connected via the second coil to the second pole of the AC voltage terminal. Circuit arrangement according to claim 2, characterized in that a first terminal of the capacitor via the first coil and a first switch to the second pole of the DC voltage terminal is connected, that the first terminal of the capacitor via the first coil and a first diode to the first pole of the DC terminal is connected, that parallel to the capacitor, a series circuit of a second and a third switch, each having parallel diodes is formed, wherein a center tap between the second and the third switch is connected to the first pole of the DC voltage terminal that a second terminal of the capacitor via a series circuit of a fourth and a fifth switch, each having parallel diodes connected to the second pole of the DC voltage terminal, wherein a center tap between the fourth and the fifth switch via the second coil to the second pole of AC voltage connection is connected. Circuit arrangement according to claim 2, characterized in that a first terminal of the capacitor via the first coil and a first switch to the second pole of the DC voltage terminal is connected, that the first terminal of the capacitor via the first coil and a first diode to the first pole of the DC terminal is connected, that parallel to the capacitor, a series circuit of a second and a third switch, each having parallel diodes is formed, wherein a center tap between the second and the third switch is connected to the first pole of the DC voltage terminal that a second terminal of the capacitor via a series circuit of a fourth and a fifth switch, each having parallel diodes, and the first switch is connected to the second pole of the DC voltage terminal, and that the second terminal of the capacitor via the series circuit of the fourth and the fifth switch and the first diode is connected to the first pole of the DC voltage terminal, wherein a center tap between the fourth and the fifth switch is connected via the second coil to the second pole of the AC voltage terminal. Circuit arrangement according to one of claims 1 to 10, characterized in that a second capacitor is connected in parallel with the DC voltage connection. Circuit arrangement according to one of claims 1 to 11, characterized in that a further capacitor is connected in parallel to the AC voltage terminal.

Images