WO2015018439A1

WO2015018439A1 - Inverter

Info

Publication number: WO2015018439A1
Application number: PCT/EP2013/066481
Authority: WO
Inventors: Karl Koch; Peter Knaup; Thomas Lenz
Original assignee: Robert Bosch Gmbh
Priority date: 2013-08-06
Filing date: 2013-08-06
Publication date: 2015-02-12

Abstract

The invention relates to an inverter (1) for producing an alternating voltage from a direct voltage, comprising: a direct-voltage intermediate circuit (6) for providing the direct voltage, having a first intermediate-circuit capacitor (8), connected between a positive direct-voltage node (12) and a center point (16) of the direct-voltage intermediate circuit (6), for providing a positive partial direct voltage (U_DC1) and a second intermediate-circuit capacitor (10), connected between the center point (16) and a negative direct-voltage node (14), for providing a negative partial direct voltage (U_DC2), wherein the first partial direct voltage (U_DC1) and the second partial direct voltage (U_DC2) together result in the direct voltage of the direct-voltage intermediate circuit (6); an alternating-voltage node (22) for providing a clocked alternating voltage for producing a sinusoidal alternating voltage; a positive branch (18) between the positive connection node (12) and the alternating-voltage node (22) having at least one first semiconductor switch (24) for producing a part of the clocked alternating voltage, in particular for producing a positive half-wave of the alternating voltage; a negative branch (20) between the alternating-voltage node (22) and the negative connection node (14) having at least one second semiconductor switch (28) for producing an additional part of the clocked alternating voltage, in particular for producing a negative half-wave of the alternating voltage; a balancing circuit (32) arranged between the center point (16) and the alternating-voltage node (22) and having at least two auxiliary semiconductor switches (34, 36) for balancing the direct voltage of the direct-voltage intermediate circuit (6); a network node (44) for feeding electric current into a supply network (48); a network choke (42) connected between the alternating-voltage node (22) and the network node (44); a filter capacitor (50) connected between the network node (44) and a reference node (52), which reference node in particular has ground potential; and at least one network disconnect switch (46, 46') for disconnecting the inverter (1), in particular the network connection node (44), from the supply network (48); wherein the inverter (1) is prepared for modulating an alternating voltage at the filter capacitor (50) while the network disconnect switch (46, 46') is open and for controlling the first semiconductor switch (24), the second semiconductor switch (28), and the balancing circuit (2) in such a way that balancing currents for balancing the direct-voltage intermediate circuit (6) flow, such that the first and second partial direct voltages (U_DC1, U_DC2) become as equal in magnitude as possible.

Description

description

title

inverter

The present invention relates to an inverter for generating an AC voltage from a DC voltage, and the present invention relates to a method for operating such an inverter.

Inverters are well known, they generate an AC voltage from a DC voltage. The DC voltage is often shared at one

DC intermediate circuit provided, namely a built-up of two series-connected DC link capacitive intermediate circuit. In this case, a symmetry is desirable such that each of these two DC link capacitances has the same voltage, namely in each case half the DC link voltage. In operation, it may happen that the two capacitors or capacitors are charged differently or discharged differently, so that sets an asymmetry. In this case, one of the two DC link capacitors has a larger charge and thus a higher voltage than the other DC link capacitance. Such asymmetries are undesirable for various reasons. In particular, parts of the

Inverter set too high voltage that could potentially damage components. Furthermore, such asymmetry may also affect the AC voltage generated. Accordingly, it is also undesirable to connect the inverter to the AC electrical network in which it is to feed, if such asymmetry exists.

To counteract this problem, the international application WO 2008/049441 AI proposes an inverter with output-side resistance. This resistor can be connected to the output of the inverter when the inverter output is disconnected from the mains to be fed. In this case, charge compensation can be carried out via this resistor, in particular in such a way that the intermediate circuit capacitance having too much voltage is partially discharged via this resistor to ground. Here, the midpoint between the two DC link capacitances is connected to ground and the said resistor is also connected to ground, so that the said partial discharge can be made via this resistor.

The disadvantage here is that energy is dissipated by the relevant intermediate circuit capacitor, which can also be felt in a heating of the said resistance. Thus, this method is associated with undesirable losses.

The present invention is therefore based on the object, one of the o.g. To address problems. In particular, an improved solution is to be created that balances as little as possible with a balance of the

DC DC link can reach. At least an alternative solution should be proposed.

According to the invention, an inverter according to claim 1 is thus proposed. This inverter is prepared for generating an AC voltage from a DC voltage. It comprises a DC voltage intermediate circuit for providing the DC voltage. The DC voltage intermediate circuit comprises a first DC link capacitance and a second DC link capacitance. The first DC link capacitance is connected between a positive DC node and a center node of the DC link and provides a positive DC partial voltage. The second link capacitance is connected between the center point and a negative DC node and provides a negative DC partial voltage. The first and second partial DC voltage are connected in series and result in accordance with the DC voltage of the DC intermediate circuit. Furthermore, an alternating voltage node is provided on which a pulsed alternating voltage is provided, which is used for generating an approximately sinusoidal alternating voltage, namely in particular with the further use of a corresponding output choke.

Furthermore, a positive branch is provided between the positive terminal node and the AC voltage node, which has at least one first semiconductor switch for generating a part of the pulsed AC voltage. In particular, such a positive branch is used for generating a positive half-wave of the alternating voltage to be generated.

Furthermore, a negative branch is provided between the AC voltage node and the negative terminal node, which has at least one second semiconductor switch for generating a further part of the pulsed AC voltage. In particular, such a negative branch is used for generating a negative half-wave of the alternating voltage to be generated.

Between the midpoint between the two DC link capacitances and the AC voltage node, a balancing circuit is provided which can also be referred to as an auxiliary circuit. This balancing circuit comprises at least two auxiliary semiconductor switches, which are in particular provided to enable a current from the center point to the AC voltage node or from the AC voltage node to the center or to prevent such a current. Furthermore, a network node is provided for feeding electrical current into a supply network. This network node is essentially connected to the supply network when it is to be fed into the supply network. A mains choke is connected between the AC voltage node and the network node. In particular, such a line choke serves to integrate an approximately sinusoidal signal from the pulsed signal which the positive branch and the negative branch generate. Furthermore, a filter capacitor is connected between the network node and a reference node. This reference node may, for example, have ground potential and be correspondingly connected to ground.

Furthermore, a power disconnect switch for disconnecting the inverter from the supply network is provided. This power disconnect switch is in particular between

Grid connection node and the supply network arranged.

In accordance with the invention, the inverter is prepared to modulate an AC voltage at the filter capacitor when the mains disconnect switch is open, and to control the first semiconductor switch, the second semiconductor switch and the balancing circuit so that equalizing currents flow for balancing the DC intermediate circuit so that the first and second partial DC voltages are as equal as possible become. In that regard, the inverter has a programmed for this control, in which the corresponding commands for generating the desired switching actions of the affected switches are generated.

Accordingly, an AC voltage is modulated at the filter capacitance, namely in particular when the inverter is disconnected from the supply network due to the open mains disconnect switch. The modulation takes place in such a way that the currents finally flow as equalizing currents and achieve symmetrization of the voltages at the two DC link capacitances.

Illustratively and simply, this can be explained by an example. If, for example, there is a higher voltage at the first DC link capacitance compared to the second DC link capacitance, the positive branch can first be pulsed in such a way that a positive half-wave of a sinusoidal current sets via the line choke, which leads to a current into the filter capacitance. If this is done in conjunction with the Balierungsschaltung, in particular so that a connection between the center and the AC node is made, the energy for said current half-wave is used only from the first DC link capacity. This operation is called 3-point operation. The subsequent negative half-wave is now generated in 2-point operation, namely without the use of the balancing circuit or in the Symmetrierungsschaltung open switches and thus at a separate center and AC nodes. The negative half-wave thus loads the first and second DC link capacitance equally. In this example, there is one

Separation from the grid before and the sinusoidal current, which has been described the generation of the positive and negative half-wave flows only through the line choke and the filter capacitance and accordingly this current is a reactive current - apart from parasitic effects - no power or energy consumed and basically only leads to a balance between the two DC link capacitances, namely in the example mentioned to a balance of energy from the first DC link capacity towards the second DC link capacity.

In particular, it is proposed that there is no ohmic resistance between the network node and the reference node, that is to say in particular between network node and ground. Thus, it is avoided to derive a balance between the two DC link capacities current through a resistor to ground and thus consume power or energy. In fact, according to the invention, it has been recognized that a compensation with a reactive current and thus ideally without losses can be made if only the filter capacity is used. Preferably, the inverter is thus prepared when open

Mains breaker to modulate the AC voltage at the filter capacity as approximately sinusoidal AC mains voltage so that results in a reactive current.

It is thus favorable that the inverter is prepared to be operated so that the reactive current leads to a partial reloading of the two DC link capacitances, if they have different partial voltages.

According to one embodiment, it is proposed that the inverter is prepared to work with open mains disconnect switch, ie in disconnected from the mains power supply, specifically depending on the current operating point in a 3-point operation or a 2-point operation. In particular, it is proposed that these two operating modes are selected depending on a ratio of the first partial voltage to the second partial voltage and / or depending on a sign of the reactive current of the filter capacitor. Dependent on it is thus worked in a 3-point operation, in which the balancing circuit is driven, or it is working a 2-point operation, in which the balancing circuit is not driven and forms an electrical isolation between the center and the AC node.

It is favorable if the inverter operates with the power supply switch open in 3-point operation, when the first partial DC voltage is greater than the second DC partial voltage and the reactive current from the AC voltage node to the network node is positive. In this case, namely, the first link capacitance is loaded to generate this positive current. Or it works in 3-point operation, when the first partial DC voltage is smaller than the second DC partial voltage and the reactive current from the AC node to the network node is negative. In this case, energy is taken from the second DC link capacity.

Preferably, 2-point operation is used when the first partial DC voltage is greater than the second DC partial voltage and the reactive current from the AC voltage node to the network node is negative. In this case, both DC link capacitances are substantially equally loaded and this 2-point operation alternates in particular with the above-mentioned 3-point operation, namely, when the first DC partial voltage is greater than the second DC partial voltage and the reactive current from the AC node to the network node is positive ,

It is also favorable to operate in 2-point operation when the first partial DC voltage is less than the second DC partial voltage and the reactive current from the AC voltage node to the network node is positive. This second 2-point operation alternates in particular with the last-mentioned 3-point operation in which the first partial DC voltage is less than the second DC partial voltage and the reactive current from the AC voltage node to the network node is negative. In addition, a method for operating an inverter is proposed, as results from at least one of the above-described embodiments of the inverter. Accordingly, an alternating voltage is modulated at the filter capacitance, in particular when the mains disconnect switch is open, and the first semiconductor switch, the second semiconductor switch and the balancing circuit are driven such that equalizing currents flow for balancing the DC intermediate circuit, namely such that the first and second partial DC voltages become as equal as possible.

It is thus advantageous if the AC voltage at the filter capacitor is modulated as an approximately sinusoidal AC voltage in such a way that a reactive current results.

It is therefore advantageous, in principle, to carry out a method for the operation of which the inverter is already prepared, in particular by means of an appropriate preprogramming on a microprocessor or control computer or the like contained in the inverter.

It is particularly advantageous to operate the inverter so that a balancing, so the compensation of different voltages at the first and second DC link capacity is performed when the inverter is disconnected from the mains, especially if the or the power disconnect switch is open or is. After successful balancing then the at least one power disconnect switch can be closed, the inverter can be connected to the supply network and then start feeding into the grid. The interconnection with the network or the connection of the filter capacity preferably remains unchanged. The filter capacity can thus be used in a dual function, namely as filter capacity when the inverter to the supply network - also abbreviated as network - is connected and fed into this, and as an auxiliary element for generating a reactive current for balancing the two DC link capacitances.

The invention will be explained in more detail with reference to an embodiment with reference to the accompanying figure. FIG. 1 shows a circuit arrangement of an inverter according to the invention.

Figure 1 shows schematically an inverter 1, which is connected on the input side to a solar generator 2 and is supplied from there with a DC voltage. About a boost converter 4, a DC voltage from the solar generator 2 is brought to an intermediate circuit voltage, which is provided to a DC voltage intermediate circuit 6. The DC intermediate circuit 6 is formed from a first DC link capacitor 8 and a second DC link capacitor 10. The first DC link capacitor 8 is connected between a positive DC node 12 and a center 16 of the DC intermediate circuit 6. The second link capacitance is connected between the center node 16 and a negative DC node. The center node 16 is connected to ground. At the first intermediate circuit capacitor 8 is a first Teilgleichspannung the DC intermediate circuit U _DC i, namely from the positive DC node 12 to the center node 16. Between the center node 16 and the negative DC node 14, the second DC link capacitance is connected, which carries a second DC part of the DC link, namely U _DC 2-

The DC link voltage of the DC intermediate circuit 6 is thus provided between the positive DC node 12 and the negative DC node 14 and is the sum of the first and second

Partial _DC voltage U _DC i and U _DC 2- Relative to the center node 16, a positive DC part voltage is thus provided at the positive DC node 12 and a negative DC partial voltage at the negative DC node 14. Based on the energy or DC voltage provided by the DC voltage intermediate circuit 6, a clocked AC voltage can now be generated at the AC voltage node 22 with the aid of a positive branch 18 and negative branch 20. For this purpose, the positive branch 18 has a first semiconductor switch 24 with anti-parallel connected first diode 26. Accordingly, the negative Branch 20 a second semiconductor switch 28 with antiparallel connected second diode 30 on.

Furthermore, a balancing circuit 32 is provided between the center 16 and the AC node 22. The balancing circuit 32, which may also be referred to as an auxiliary circuit, can pass a current from the center node 16 to the AC node 22 or vice versa. This balancing circuit 32 or auxiliary circuit 32 has two auxiliary semiconductor switches, namely a third and fourth semiconductor switch 34 and 36, each with third or fourth diode 38 and 40 connected in anti-parallel connection.

When a pulsed voltage is generated at the AC node 22 by means of the positive branch 18, the negative branch 20 and the balancing circuit 32, there is a so-called 3-point operation. When the third and fourth semiconductor switches are opened, the midpoint 16 is disconnected from the AC node 22, and operation of the inverter in this state, only by driving the first and second semiconductor switches 24 and 28, respectively, forms a 2-point operation.

On the output side of the AC voltage node 22, a network choke 42 is connected and has a network node 44 on the network side or is connected to such a network node 44. The network node 44 is connected via a network disconnect switch 46 to a supply network 48, which is illustrated here only as a simple block. In addition, a power disconnect switch 46 'is provided between the ground point 52 and the utility network 48, which is switched together with the power disconnect switch 46 between the network node 44 and the power grid 48. As a precaution, it should be noted that the present description describes the inverter and feeding for a 1-phase case. Accordingly, the inverter 1 shown in FIG. 1 is connected to a phase of the supply network 48. Basically, however, a 3-phase version of the inverter and according to a connection to a 3-phase supply network 48 is basically provided.

In feed mode, when electrical power is fed into the utility grid 48, the mains disconnect switches 46 and 46 'are closed and a pulsed voltage at the AC voltage node 22 leads in particular through the line choke 42 to a usually approximately sinusoidal inductor current i _L. At the network node 44, a filter capacity 50 is also provided, which is connected to ground 52. At the filter capacitor 50 thus falls to a filter voltage u _c . The filter capacity 50 is preferably a conventional filter capacity and is used to filter disturbances during feeding, as they may occur, inter alia, by the pulsed operation. Accordingly, a filter current i _{c flows} from the network node 44 into the filter capacitor 50. In the feed mode, a mains current i _N is correspondingly fed into the supply network 48, which essentially has the amplitude of the inductor current i _L.

If the power disconnectors 46 and 46 'open, the inverter 1 is basically separated from the power supply 48. If, for the first time, the inverter is to be connected to the supply network 48 in order to feed into the network 48, it is proposed first to balance the DC intermediate circuit 6 so that the first and second partial _DC voltages U _DC i and U _DC 2 have the same amplitude , For this purpose, a corresponding change between 3-point operation and 2-point operation is proposed. Thus, for example, in the event that the first _DC partial voltage U _DC i is greater than the second _DC partial voltage U _DC 2 of the inverter 1 are first operated in 3-point operation so that a voltage pulse pattern is generated at the AC node 22 that a Current through the line choke 42 and in the filter capacity 50 sets. Due to the open power disconnect switches 46 and 46 'corresponds in this case, the inductor current i _L the filter current i _c . Energy from the first DC link capacitor 8 or the first DC link capacitor 8 is used by the 3-point operation.

Overall, however, an alternating current is generated. When current is reversed, ie a negative half-wave is then switched to 2-point operation. Plastically speaking, the current from the filter capacitor 50 thus flows back again. Due to the changed operation, namely from 3-point operation to 2-point operation, this returning current but flows into the DC voltage intermediate circuit 6 in its entirety. It is therefore effective for both DC link capacities 8 and 10.

In this way, by changing between 3-point and 2-point operation, an alternating current in the filter capacitance 50 can be generated, resulting in a transhipment of energy from the DC link capacity 8 or 10 leads to the other DC link capacity 10 or 8. Apart from smaller parasitic losses, a reactive current is generated because no ohmic consumer is involved. Thus, the reactive current for balancing the two DC link capacities 8 and 10 can be used.

The operation has been illustrated partially explained with reference to a positive or negative half cycle, which term usually refers to a sinusoidal waveform. However, in order to perform the balancing, a sinusoidal characteristic is not absolutely necessary as long as an alternating current is generated, which as a result is a reactive current.

It can thus be carried out by the use of the inverter 1 with line choke 42 and filter capacity 50, a balancing in separate from the network case alone. However, this balancing is also generally proposed for the embodiment shown in the case in which the inverter is disconnected from the supply network in order subsequently to establish a connection to the network in which the DC intermediate circuit of the inverter is balanced. Additional components are avoided. In particular, the use of a Symmetrierungswiderstandes is avoided in parallel with the filter capacitance and, accordingly, a corresponding switch for switching or disconnecting such Symmetrierungswiderstandes is avoided.

Claims

claims

An inverter (1) for generating an AC voltage from a DC voltage, comprising

- A DC intermediate circuit (6) for providing the DC voltage with - a first DC link capacitance (8), connected between a positive

DC node (12) and a center (16) of the DC intermediate circuit (6), for providing a positive _DC partial voltage (U _DC i) and

- a second intermediate circuit capacitor (10) connected between the midpoint (16) and a negative DC voltage node (14), for providing a negative partial DC voltage (U _DC 2), wherein the first partial DC voltage (U _DC i) and the second partial DC voltage (U _DC 2) together give the DC voltage of the DC intermediate circuit (6),

an alternating voltage node (22) for providing a pulsed alternating voltage for generating a sinusoidal alternating voltage,

- A positive branch (18) between the positive terminal node (12) and the AC node (22) with at least one first semiconductor switch (24) for generating a portion of the pulsed AC voltage, in particular for generating a positive half cycle of the AC voltage,

- A negative branch (20) between the AC voltage node (22) and negative terminal node (14) with at least one second semiconductor switch (28) for generating a further portion of the pulsed AC voltage, in particular for generating a negative half cycle of the AC voltage,

- One between the center (16) and the AC node (22) arranged balancing circuit (32) with at least two

Auxiliary semiconductor switches (34, 36) for balancing the DC voltage of the DC intermediate circuit (6),

a network node (44) for feeding electrical power into a supply network (48), a mains choke (42) connected between the AC voltage node (22) and the network node (44),

a filter capacitance (50) connected between the network node (44) and a reference node (52), which in particular has ground potential

- At least one power disconnect switch (46, 46 ') for disconnecting the inverter (1), in particular the network connection node (44), from the supply network (48),

wherein the inverter (1) is prepared to modulate an AC voltage on the filter capacitance (50) when the power disconnect switch (46, 46 ') is open, and the first semiconductor switch (24), the second semiconductor switch (28) and the balancing circuit (2) to control so that compensating currents for balancing the DC voltage intermediate circuit (6) flow, so that the first and second partial DC voltage (U _DC i, U _DC2 ) are as equal as possible.

2. inverter (1) according to claim 1,

characterized in that no ohmic resistance is provided between the network node (44) and the reference node (52).

3. inverter (1) according to claim 1 or 2,

characterized in that the inverter (1) is prepared to modulate the AC voltage at the filter capacitor as (50) approximately sinusoidal AC voltage when the power disconnect switch (46, 46 ') is open so that a reactive current results.

4. inverter (1) according to claim 3,

characterized in that the inverter (1) is prepared so that the reactive current leads to a partial reloading of the two DC link capacitances (8, 10), if they have different sized partial DC voltages.

5. Inverter (1) according to one of the preceding claims,

characterized in that the inverter (1) is prepared to operate with the circuit breaker (46, 46 ') open

- Depending on a ratio of the first partial voltage (U _DC i) to the second partial voltage (U _DC2 ) and / or

- depending on a sign of the or a reactive current of the filter capacity (50) - To work in a 3-point operation in which the balancing circuit (32) is driven, or

- To operate in a two-point operation, in which the balancing circuit (32) is not driven and forms an electrical isolation between the center (16) and the AC node (22).

6. inverter (1) according to claim 5,

characterized in that the inverter (1) is prepared with the mains disconnect switch (46, 46 ') open,

- to work in 3-point operation, if

- The first partial _DC voltage (U _DC i) is greater than the second _DC partial voltage

(UDC2) and the reactive current from the AC node (22) to the network node (44) is positive or

- The first _DC partial voltage (U _DC i) is smaller than the second _DC partial voltage (UDC2) and the reactive current from the AC node (22) to the network node (44) is negative and / or

- work in 2-point operation when

- The first _DC partial voltage (U _DC i) is greater than the second _DC partial voltage (UDC2) and the reactive current from the AC node (22) to the network node is negative (44) or

- The first partial _DC voltage (U _DC i) is smaller than the second _DC partial voltage

(UDC2) and the reactive current from the AC node (22) to the network node (44) is positive.

7. A method for operating an inverter (1) according to any one of the preceding claims, wherein when the mains disconnect switch (46, 46 ') an AC voltage to the filter capacitor (50) is modulated, and the first

Semiconductor switch (24), the second semiconductor switch (28) and the balancing circuit (32) are driven so that compensating currents for balancing the DC voltage intermediate circuit (6) flow, so that the first and second _DC partial voltage (U _DC i, U _DC 2) as equal as possible grow up.

8. The method according to claim 7, characterized in that the AC voltage at the filter capacitance (50) is modulated as approximately sinusoidal AC voltage so as to give a reactive current.

9. The method according to any one of claims 7 or 8,

characterized in that the reactive current leads to a partial reloading of the two _DC link capacitances (8, 10) if they have different sized partial _DC voltages (U _DC i, U _DC 2).

10. The method according to any one of claims 7 to 9,

characterized in that when the power disconnector (46, 46 ') is open

- Depending on a ratio of the first partial voltage (U _DC i) to the second partial voltage (U _DC 2) and / or

- depending on a sign of the or a reactive current of the filter capacity (50)

- To work in a 3-point operation in which the balancing circuit (32) is driven, or

to operate in a 2-point operation, in which the balancing circuit (32) is not driven and forms an electrical separation between the center and the AC node.

11. The method according to claim 10,

characterized in that the inverter (1) with open power disconnect switch (46, 46 '),

- Works in 3-point mode, if

- The first _DC partial voltage (U _DC i) is greater than the second _DC partial voltage (UDC2) and the reactive current from the AC node (22) to the network node (44) is positive or

- works in 2-point operation when

- The first partial _DC voltage (U _DC i) is greater than the second _DC partial voltage (UDC2) and the reactive current from the AC node (22) to the network node (44) is negative or - The first _DC partial voltage (U _DC i) is smaller than the second _DC partial voltage (UDC2) and the reactive current from the AC node (22) to the network node (44) is positive.

12. Method for operating an inverter (1),

characterized in that a balancing according to a method according to any one of claims 7 to 11 is carried out before the inverter (1) is connected to the supply network (48), and the power disconnect switch (46, 46 ') for connecting the inverter (1) is closed with the supply network (48) when a balancing has been substantially completed and the first and second partial _DC voltage (U _DC i, U _DC 2) are about the same size.