DE202012004347U1 - inverter - Google Patents

Abstract

Inverter (1) for generating an alternating voltage from a direct voltage, comprising - a direct voltage intermediate circuit (6) for providing the direct voltage with - a first intermediate circuit capacitance (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 (UDC1) and - a second intermediate circuit capacitance (10), connected between the center point (16) and a negative direct voltage node (14), for providing a negative partial direct voltage (UDC2), the first partial direct voltage (UDC1) and the second partial direct voltage (UDC2) 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 generating a sinusoidal alternating voltage, - a positive branch (18) between the positive connection node (12) and the Alternating voltage ngsknoden (22) with at least one first semiconductor switch (24) for generating part of the pulsed alternating voltage, in particular for generating a positive half-wave of the alternating voltage, - a negative branch (20) between the alternating voltage node (22) and negative connection node (14) with at least a second semiconductor switch (28) for generating a further part of the pulsed alternating voltage, in particular for generating a negative half-wave of the alternating voltage, - a balancing circuit (32) with at least two auxiliary semiconductor switches (34) arranged between the midpoint (16) and the alternating voltage node (22), 36) for balancing the DC voltage of the DC voltage intermediate circuit (6), - a network node (44) for feeding electrical current into a supply network (48), - a network choke (42) connected between the AC voltage node (22) and the network node (44), - one between the network node (44) and a reference node (52), the in particular has ground potential, connected filter capacitance (50) and - at least one mains disconnector (46, 46 ') for separating the inverter (1), in particular the mains connection node (44), from the supply network (48), the inverter (1) being prepared for this to modulate an alternating voltage on the filter capacitance (50) with the mains isolating switch (46, 46 ') open, and to control the first semiconductor switch (24), the second semiconductor switch (28) and the balancing circuit (2) in such a way that equalizing currents for balancing the DC voltage intermediate circuit (6) flow so that the first and second partial DC voltages (UDC1, UDC2) are as equal as possible.

Description

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 provided on a divided DC voltage intermediate circuit, namely an intermediate circuit constructed from two series-connected DC link capacitors. 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, can be set to parts of the inverter too high, possibly hazardous components voltage. 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 counter this problem, the international application fails WO 2008/049441 A1 an inverter with output side resistor. 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 o. G. To address problems. In particular, an improved solution is to be created, which can achieve balancing of the DC intermediate circuit with as few losses as possible. 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 is also referred to as an auxiliary circuit can be. 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 arranged in particular between the network connection node and the supply network.

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 alternating voltage node. The negative half-wave thus loads the first and second DC link capacitance equally. In this example, there is a disconnection from the mains, and the sinusoidal current described as generating the positive and negative half wave flows only through the line choke and the filter capacitance, and accordingly this current is a reactive current which, apart from parasitic effects, does not produce any power or consumes energy 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 to modulate the AC voltage at the filter capacitor as an approximately sinusoidal AC mains voltage when the power disconnect switch is open so that there is 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, when the power disconnect switch is open, that is, in the separate state from the 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 be 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 advantageous if the inverter operates with the power disconnector 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 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.

1 shows a circuit arrangement of an inverter according to the invention.

1 schematically shows an inverter 1 , the input side to a solar generator 2 is connected and is supplied from there with a DC voltage. About a boost converter 4 becomes a DC voltage from the solar generator 2 brought to an intermediate circuit voltage, which is connected to a DC voltage intermediate circuit 6 provided. The DC voltage intermediate circuit 6 is formed from a first DC link capacity 8th and a second DC link capacity 10 , The first DC link capacity 8th is between a positive DC node 12 and a center 16 of the DC intermediate circuit 6 connected. The second link capacity is between the center node 16 and connected to a negative DC node. The middle node 16 is connected to ground. At the first DC link capacity 8th is a first Teilgleichspannung the DC voltage intermediate _circuit U _DC1 , to, namely from the positive DC node 12 to the middle node 16 ,

Between the middle node 16 and the negative DC node 14 the second _{DC link capacitance is} connected, which carries a second DC partial _{voltage of the DC link} , namely U _DC2 .

The DC link voltage of the DC intermediate circuit 6 is thus between the positive DC node 12 and the negative DC node 14 is provided and is the sum of the first and second partial _{DC voltage} U _DC1 and U _DC2 . Relative to the middle node 16 thus becomes a positive partial DC voltage at the positive DC node 12 and a negative partial DC voltage at the negative DC node 14 provided.

Based on the through the DC link 6 provided energy or DC voltage can now with the help of a positive branch 18 and negative branch 20 a pulsed AC voltage at the AC node 22 be generated. This is indicated by the positive branch 18 a first semiconductor switch 24 with anti-parallel connected first diode 26 on. Accordingly, the negative branch 20 a second semiconductor switch 28 with anti-parallel connected second diode 30 on.

Furthermore, a balancing circuit 32 between the center 16 and the AC node 22 intended. The balancing circuit 32 , which may also be referred to as an auxiliary circuit, may be 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 respectively. 36 each with anti-parallel connected third and fourth diode 38 respectively. 40 , on.

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

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

In feed mode, when electrical power in the supply network 48 is the mains disconnect switch 46 and 46 ' closed and a pulsed voltage at the AC node 22 leads in particular through the mains choke 42 to a usually approximately sinusoidal inductor current i _L. At the network node 44 is also a filter capacity 50 provided that against mass 52 connected. At the filter capacity 50 Thus, a filter voltage u _{C is applied} . The filter capacity 50 is preferably a common filter capacity and is used to filter disturbances during feeding, as they may occur, inter alia, by the pulsed operation. It flows according to a filter current i _C from the network node 44 in the filter capacity 50 , In feed-in mode, a mains current i _N is correspondingly in the supply network 48 fed, which has substantially the amplitude of the inductor current i _L.

Are the power disconnect switches 46 and 46 ' opened, is the inverter 1 basically from the supply network 48 separated. If now the inverter for the first time or again to the supply network 48 should be connected to the network 48 To feed, it is first proposed the DC voltage intermediate circuit 6 to be balanced, so that the first and second partial _{DC voltage} U _DC1 and U _{DC2 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 partial _{DC voltage} U _{DC1 is} greater than the second _DC partial _voltage U _{DC2 of} the inverters 1 initially operated in 3-point operation such that a voltage pulse pattern at the AC node 22 is generated, that is a current through the mains choke 42 and in the filter capacity 50 established. Due to the open power disconnect switch 46 and 46 ' In this case, the inductor current i _L corresponds to the filter current i _C. 3-point operation generates energy from the first DC link capacitor 8th or the first DC link capacity 8th used.

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 thus flows out of the filter capacity 50 back again. Due to the changed operation, namely from 3-point operation to 2-point operation, this returning current flows into the DC voltage intermediate circuit 6 In its entirety. So it is for both DC link capacities 8th and 10 effective.

In this way, by changing between 3-point and 2-point operation, an alternating current in the filter capacity 50 be generated, thereby causing a transfer of energy from the DC link capacity 8th or 10 in the other DC link capacity 10 or 8th leads. 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 capacitances 8th and 10 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 a balancing in disconnected from the grid case solely by the use of the inverter 1 with mains choke 42 and filter capacity 50 be performed. 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.

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

• WO 2008/049441 A1 [0004]

Claims (6)

Inverter ( 1 ) for generating an AC voltage from a DC voltage, comprising - a DC voltage intermediate circuit ( 6 ) for providing the DC voltage with - a first DC link capacitance ( 8th ) connected between a positive DC node ( 12 ) and a midpoint ( 16 ) of the DC intermediate circuit ( 6 ), for providing a positive partial DC voltage (U _DC1 ) and - a second _{DC link capacitance} ( 10 ), connected between the midpoint ( 16 ) and a negative DC node ( 14 ), for providing a negative partial DC voltage (U _DC2 ), wherein the first DC partial voltage (U _DC1 ) and the second DC partial voltage (U _DC2 ) together the DC voltage of the DC intermediate _circuit ( 6 ), - an AC node ( 22 ) for providing a pulsed AC voltage for generating a sinusoidal AC 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-wave of the AC voltage, - a negative branch ( 20 ) between the AC node ( 22 ) and negative connection nodes ( 14 ) with at least one second semiconductor switch ( 28 ) for generating a further part of the pulsed alternating voltage, in particular for generating a negative half-wave of the alternating 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 ), - one between the AC node ( 22 ) and the network node ( 44 ) connected line reactor ( 42 ), - one between the network node ( 44 ) and a reference node ( 52 ), which in particular has earth potential, connected filter capacity ( 50 ) and - 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 ), where the inverter ( 1 ) is prepared, with the mains disconnect switch ( 46 . 46 ' ) an AC voltage at the filter capacity ( 50 ) and the first semiconductor switch ( 24 ), the second semiconductor switch ( 28 ) and the balancing circuit ( 2 ) so that compensating currents for balancing the DC intermediate circuit ( 6 ), so that the first and second partial _{DC voltage} (U _DC1 , U _DC2 ) are as equal as possible. Inverter ( 1 ) according to claim 1, characterized in that between the network node ( 44 ) and the reference node ( 52 ) no ohmic resistance is provided. Inverter ( 1 ) according to claim 1 or 2, characterized in that the inverter ( 1 ) is prepared, with the mains disconnect switch ( 46 . 46 ' ) the AC voltage at the filter capacitance as ( 50 ) to modulate approximately sinusoidal AC voltage so that a reactive current results. Inverter ( 1 ) according to claim 3, characterized in that the inverter ( 1 ) is prepared so that the reactive current leads to a partial transfer of the two DC link capacities ( 8th . 10 ) leads if they have different sized partial DC voltages. Inverter ( 1 ) according to one of the preceding claims, characterized in that the inverter ( 1 ) is prepared, with the disconnector ( 46 . 46 ' ) - depending on a ratio of the first partial voltage (U _DC1 ) to the second partial voltage (U _DC2 ) and / or - depending on a sign of the or a reactive current of the filter capacitor ( 50 ) - to work in a 3-point operation in which the balancing circuit ( 32 ), or - to operate in a 2-point operation in which the balancing circuit ( 32 ) is not controlled and an electrical separation between the center ( 16 ) and the AC node ( 22 ). Inverter ( 1 ) according to claim 5, characterized in that the inverter ( 1 ) is prepared with the mains disconnect switch open ( 46 . 46 ' ), - to work in 3-point operation, if - the first DC partial voltage (U _DC1 ) is greater than the second _DC partial _voltage (U _DC2 ) and the Reactive current from the AC node ( 22 ) to the network node ( 44 ) is positive or - the first DC partial voltage (U _DC1 ) is smaller than the second _DC partial voltage (U _DC2 ) and the reactive current from the AC _node ( 22 ) to the network node ( 44 ) is negative and / or - to work in 2-point operation, if - the first DC partial voltage (U _DC1 ) is greater than the second _DC partial voltage (U _DC2 ) and the reactive current from the AC _node ( 22 ) to the network node negative ( 44 ) or - the first DC partial voltage (U _DC1 ) is smaller than the second _DC partial voltage (U _DC2 ) and the reactive current from the AC _node ( 22 ) to the network node ( 44 ) is positive.

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