WO2016012465A1

WO2016012465A1 - Switching assembly for an npc multi-point inverter having relief network

Info

Publication number: WO2016012465A1
Application number: PCT/EP2015/066680
Authority: WO
Inventors: Andrzej Mondzik; Adam PENCZEK; Marek Rylko; Robert Stala; Milosz SZAREK; Slawomir Szot
Original assignee: Sma Solar Technology Ag
Priority date: 2014-07-24
Filing date: 2015-07-21
Publication date: 2016-01-28

Abstract

The invention relates to a switching assembly (1) for a multi-point inverter, having an input connection (11) for a positive pole and an input connection (21) for a negative pole of an input DC voltage (U _in), a centre tap (3) for a voltage centre point of the input DC voltage (U _in), an output connection (4) for emitting an output alternating current (iload), two outer circuit breakers (13, 23), each of which is connected to one of the two input connections (11, 21), two inner circuit breakers (14, 24), which are each connected directly or via a diode (5) to the centre tap (3) on one side, and connected directly or via a diode (5) to the output connection (4) on the other side, and a relief network (6). The relief network (6) comprises at least one capacitor (15, 25), wherein a charging path (19, 29) runs between the output connection (4) and the centre tap (3) for each of the capacitors (15, 25) of the relief network (6), in which charging path the respective capacitor (15, 25) is connected in series with an inductor (16, 26). A discharging path (20, 30) for one of the capacitors (15, 25) runs between the output connection (4) and each of the input connections (11, 21), wherein the discharging path (20, 30) branches off, in a junction (35), from the respective charging path (19, 29), down stream of the respective capacitor (15, 25) and upstream of the inductor (16, 26) from the perspective of the output connection (4), and wherein a uni-directional switching element (18, 28) is arranged in the discharging path (20, 30), between the junction (35) and the input connection (21, 11), which uni-directional switching element is oriented in a reverse direction, in relation to the pole of the input DC voltage (U _in) at those input connections (11, 21) to which the discharging path (20, 30) is connected. In each of the charging paths (19, 29), a switching device (17, 27) is connected in series with the capacitor (15, 25) and the inductor (16, 26), which switching device can be actively actuated for every forward direction of each of the uni-directional switching elements (18, 19) in all discharging paths (20, 30) connected to the respective charging path (19, 29, 49), in order to temporarily permit a uni-directional current in an opposite direction to the forward direction, from the perspective of the output connection (4).

Description

CIRCUIT ARRANGEMENT FOR A NPC MULTIPORT INVERTER WITH

RELIEF NETWORK

TECHNICAL FIELD OF THE INVENTION

The invention relates to a circuit arrangement for a multipoint inverter with a discharge network. More particularly, the invention relates to a circuit arrangement having the features of the preamble of independent claim 1. A multipoint inverter is understood to mean in particular a three-phase inverter in which an output connection via which an output alternating current is output is alternately also connected to a neutral electrical potential in addition to a positive electrical potential and a negative electrical potential in order to form the alternating output current. The multipoint inverter with the relief network can also be a five-point inverter or even a seven-point inverter.

STATE OF THE ART

A three-point inverter called NPC (Neutral Point Clamped) is available from Akira Nabae et al., A New Neutral-Point-Clamped PWM Inverter, IEEE Transactions on Industry Applications, Vol. 1A-17, no. 5, September / October 1981, pages 518 to 523. Here, four power switches are connected in series between input terminals for a DC input voltage. The center of this series connection leads to an output terminal, via which an output alternating current is output. The intermediate points of the series connection on both sides of the center are each connected via reverse-biased diodes to a center tap of a DC input voltage applied to the input terminals. In order to form an output alternating current output at the output terminal, during each half cycle of an output alternating voltage applied to the output terminal of one of the input terminals connected to the outer switch of the series circuit complementary to the located on the other side of the output terminal inner circuit breaker is clocked. The lying on the same side of the output terminal inner switch is permanently closed and the outer switch located on the other side of the output terminal permanently open. Various variants of the NPC three-level inverter have been developed. These include the so-called BSNPC (Bidirectional Switch Neutral Point Clamped) Inverter, see A. Nabae et al .: A New Neutral-Point Clamped PWM Inverter, IEEE Transactions on Industry Applications, Vol. 1A-17, no. 5, Septem ber / October 1981, Fig. 10. In the BSNPC inverter, the outer power switches connected at one end to the input terminals are connected at their other end directly to the output terminal, while the inner power switches are connected between the Center tap of the DC input voltage and the output terminal are connected in series or in parallel, that with one inner power switch, the current flow in one and with the other inner power switch, the current flow in the other direction between the center tap and the output terminal can be switched off. Thus, a switching device which can be switched separately in both directions is realized between the center tap and the output terminal. The schematic of a BSNPC inverter is basically the same as that described above for an N PC inverter.

A known as ARCP (Auxiliary Resonant Commutation Pole) inverter variant of the BSNPC inverter is known from US 2004/0246756 A1. Here, a throttle between the center tap of the DC input voltage and the output terminal is connected in series with the two inner circuit breakers. In addition, a current flowing through the throttle is detected. Only when a zero current is measured during this detection, the respectively clocked inner circuit breaker is opened. The occurrence of the zero current is ensured by a resonant circuit in which the inductor is arranged as a resonance inductance, and which extends over the center tap to link capacitors of an input side DC link of the ARCP inverter. For the outer circuit breaker of the known ARCP inverter, a parallel-connected capacitor is provided for switching relief.

From DE 10 2010 008 426 B4 a circuit arrangement for a three-level inverter with a relief network is known, having the features of the preamble of independent claim 1. The relief network is formed of at least one coil, two capacitors and a series circuit of four poled in the same direction diodes, of which the two outer diodes are each connected directly to the input terminals for the positive and negative pole of a DC input voltage. The midpoint between the two inner diodes is connected on the one hand via the coil with a center tap of the DC input voltage and on the other hand with a central bridge branch of the three-phase inverter. The two capacitors are each one on the other hand connected to an intermediate point between one of the inner and one of the outer diodes and on the other hand to the output terminal. Together with the coil, the capacitors each form a resonant circuit. This resonant circuit is used to charge the respective capacitor to the DC input voltage when the outer circuit breaker opposite it is opened. When closing this external circuit breaker discharges the previously charged capacitor and thus takes over the current flowing through the circuit breaker current and thus provides a switching discharge for this circuit breaker. For complete discharge of the capacitor another, across the output terminal across the throttle formed resonant circuit is used. In this known multi-point inverter, also referred to as S3L (Soft Switching Three Level) inverter, the pulses of complementary clocking one of the outer circuit breakers with one of the inner circuit breakers, unlike other NPC inverters requiring dead time between these pulses, may also be mutually exclusive overlap. However, any current from the center tap to the output port forcibly flows through the throttle. Accordingly, this choke must be dimensioned for the maximum current of this current.

Such a relief network in conjunction with a half-bridge circuit for inverters is also known from DE 42 19 644 A1.

OBJECT OF THE INVENTION It is an object of the invention to provide a circuit arrangement for a multipoint inverter with a de-energizing network, which has additional functionalities by means of which, for B. is particularly suitable for cost-effective training of a multi-phase multipoint inverter.

SOLUTION The object of the invention is achieved by a circuit arrangement having the features of independent patent claim 1. Preferred embodiments of the circuit arrangement according to the invention are defined in the dependent claims. DESCRIPTION OF THE INVENTION

The multipoint inverter circuit arrangement according to the invention has a positive pole input terminal and a negative input DC terminal input terminal, a DC center voltage center voltage tap center, an output terminal for output AC output, two outer power switches each having one connected to the two input terminals, two inner power switches, which are each connected on the one hand directly or via a diode to the center tap and on the other hand directly or via a diode to the output terminal, and a discharge network for the outer power switch on. The relief network comprises at least one capacitor, wherein for each of the capacitors, a charging path between the output terminal and the center tap, in which the respective capacitor is connected in series with a throttle. Between the output terminal and each of the input terminals also extends a discharge path for one of the capacitors, said discharge path branches from the output terminal seen behind the respective capacitor and before the throttle in a branch of the respective charging path and wherein between the branch and the input terminal a unidirectional Switching element is arranged in this discharge path and thus not in the Aufladepfad, which is aligned with respect to the pole of the input DC voltage at that of the input terminals to which the discharge path is connected in the reverse direction. Furthermore, in each of the charging paths, a switching device is connected in series with the capacitor and the choke, which is actively activatable for each forward direction of each of the unidirectional switching elements in all discharge paths connected to the respective charging path to temporarily allow a unidirectional current in one direction, which is the opposite of the respective forward direction seen from the output terminal. With the help of this active controllability, a unidirectional current in the respective direction z. B. also be prevented to prevent unwanted charging of the capacitor, or also to limit a desired charging of the capacitor.

That the inner circuit breakers are connected directly or via a diode to the center tap or the output terminal means that they are permanently electrically conductive with the center tap or the output terminal for each direct current or at least for a direct current of a predetermined by the forward direction of the respective diode direction are connected. This does not exclude that in the respective compound additionally an inductive tives or resistive component is arranged. With the diode even more diodes of the same forward direction can be connected in parallel or in series.

Between the input terminals for the input DC voltage of the circuit arrangement according to the invention, a divided DC voltage intermediate circuit is usually arranged, whose center forms the center tap for the voltage center of the DC input voltage. The divided DC voltage intermediate circuit can be composed of two or more capacitors.

In the circuit arrangement according to the invention can be arranged in each of the charging paths, a separate throttle from the output terminal on the one hand behind the branch of the discharge path and thus not in the discharge path and on the other hand before the connection of the inner circuit breaker with the center tap. None of these separate chokes in each of the charging paths will then be in communication between the inner power switches and the center tap, and none of the separate chokes must therefore carry the current flowing between the center tap and the output port via the inner power switches. Accordingly, it must be designed only for the current flowing through the charging path.

When charging the respective capacitor, the throttle assigned to it separately has basically the same function as the one throttle of the circuit arrangement according to DE 10 2010 008 426 B4. At discharge of the respective capacitor in the switching discharge, the separate throttle is not involved. The discharge of the respective capacitor is neither via a resonant circuit in which the separate throttle is arranged, nor is a current from the capacitor to the center tap attenuated by the separate throttle. This must be taken into account in the pulsed control of the middle circuit breakers.

Compared to the expense for the large throttle of the known from DE 10 2010 008 426 B4 circuit arrangement, the cost of each separate throttle this embodiment of the circuit arrangement according to the invention is small. This advantage in the production of a multipoint inverter with relief network in the circuit arrangement according to the invention is also not lost by the fact that in the circuit arrangement according to the invention, the switching device provided in each charging path is actively controllable. With the aid of this active controllability, a unidirectional current flowing in a fundamentally suitable direction for charging the capacitor can also be prevented in order to prevent unwanted charging of the capacitor. Specifically, the actively controllable switching device present in each charging path can comprise for each forward direction of each of the unidirectional switching elements in all discharge paths connected to the respective charging path a further non-actively activatable unidirectional switching element, ie a diode, and an actively activatable switching element. The non-actively controllable unidirectional switching element must not be at the same time in the associated discharge path. This also applies to a one-piece switching device, for example in the form of an actively controllable unidirectional switching element or more generally for the part of the actively controllable switching device, which dictates the unidirectionality of the unidirectional streams selectively permitted by it. If only one discharge path branches off from the charging path, any other part of the actively activatable switching device can also be located where the charging path and the discharge path coincide. Thus, the actively controllable switching element can also be arranged between the output terminal and the branch of the discharge path of the Aufladepfad. In that case, however, it must be a bidirectional switching element that is closed at the time of the switching discharge to be provided with the respective capacitor, as long as it also shuts off a current flow in the discharge direction of the capacitor in the opened state.

In the actively controllable switching element means "bidirectional" that it allows a flow of current in both directions, but this can not necessarily switch off in both directions. Specifically, the actively controllable bidirectional switching element may be a transistor having an anti-parallel diode, whose forward direction is then oriented opposite to the forward direction of the diode, which forms the unidirectional switching element that can not be actively activated. The antiparallel diode may, for example, be a body diode of the transistor.

The non-actively controllable unidirectional switching element and the actively controllable switching element of the switching device of the circuit arrangement according to the invention can be connected in series with the interposition of the capacitor and / or the throttle in the Aufladepfad. They can also be arranged on the same side of the condenser and / or the throttle.

The unidirectional switching element provided in each discharge path between the input terminal and the branch of the respective charging path is preferably a passive unidirectional switching element, ie, a diode. In the case of the circuit arrangement according to the invention, each discharge path can be connected directly to the respective input connection. Each charging path and thus also each discharge path is preferably connected directly to the output terminal in the circuit arrangement according to the invention in order to realize its charging and also its discharging for switching discharge independently of the switching position of the inner circuit breaker.

At its other end, each charging path may be directly or through the connection of the inner power switches with the center tap to the center tap. In this case, a common throttle for all charging paths in the connection of the inner circuit breaker may be arranged with the center tap. If there is a separate choke in each of the charging paths, an additional auxiliary choke may be provided in the connection of the inner circuit breaker to the center tap to attenuate currents which may flow from the respective capacitor serving for switching discharge but not fully discharged, when the inner circuit breaker clocked in complement to the switch-relieved outer circuit breaker is closed. The auxiliary choke can be arranged not only in the region of the connection of the inner circuit breaker with the center tap, run on the all charging paths, but also outside this area. In addition, the auxiliary choke may also be arranged in the connection of the inner circuit breakers to the output terminal, then from the inner circuit breakers before the connection of the charging paths and discharge paths to the output terminal, or - in series with inner circuit breakers - between the inner circuit breakers. Even with such an additional auxiliary throttle is the cost of all the chokes of the circuit arrangement according to the invention with separate chokes in two Aufladepfaden small compared to the cost of the large throttle of DE 10 2010 008 426 B4 known circuit arrangement. It should be noted that an inductance of each separate throttle in each charging path is typically at least as large as an inductance of this auxiliary throttle. The inductance of each separate inductor in each charging path can also be at least twice, five times or ten times as large as an inductance of this auxiliary inductor. The smaller the relative inductance of the auxiliary inductor, the less it affects the total inductance in each charging path and thus the resonant circuit formed by the respective capacitor and the associated separate inductor, even if the auxiliary inductor is also in the charging path is arranged. Specifically, the auxiliary throttle can be designed as an air throttle.

In one embodiment of the inventive circuit arrangement for a multipoint inverter, the relief network has two capacitors, each one of the associated external circuit breaker and for each of which a charging path and a discharge path are available. In this case, the on-direction of the one switching element in the discharge path and the direction of the unidirectional current through the switching device in the charging path for each capacitor are opposite to each other from the output exclusion. The unidirectional switching elements are reverse-biased with respect to the input voltage pole at that of the input terminals to which the discharge path is connected. The unidirectional switching elements of the circuit arrangement according to the invention thus largely correspond to the outer diodes of the known from DE 10 2010 08 426 B4 circuit arrangement, while the local inner diodes are replaced in the circuit arrangement according to the invention by actively controllable switching devices to parts also elsewhere in the respective Charging path can be arranged.

The essential features of this embodiment of the inventive circuit arrangement for a multipoint inverter can also be summarized as follows. it includes

a positive terminal input terminal and a negative terminal input terminal of an input DC voltage, having a center tap for a DC voltage center of voltage;

an output terminal for outputting an AC output current,

two external circuit breakers, one connected to one of the two input terminals,

two inner circuit breakers, which are each connected on the one hand directly or via a diode to the center tap and on the other hand directly or via a diode to the output terminal, and

- a discharge circuit for the external circuit breakers, comprising two capacitors,

wherein for each of the capacitors

a charging path between the output terminal and the center tap, in which the respective capacitor is connected in series with a unidirectional switching element and a throttle, and

a discharge path between the output terminal and one of the input terminals,

wherein the discharge path branches off behind the respective condenser and upstream of the throttle in a diverting from the charging path for the respective condenser, viewed from the output terminal, and wherein between the branch and the input terminal, another unidirectional switching element is arranged in the discharge path, which is in the reverse direction with respect to the pole of the input DC voltage at that of the input terminals to which the discharge path is connected,

wherein the unidirectional switching element in each of the charging paths has a forward direction opposite to the forward direction of the further unidirectional switching element in the discharge path connected to the respective charging path from the output terminal, and

- That the unidirectional switching element in each of the charging paths is actively controlled to temporarily allow a unidirectional current in its forward direction

Although this does not fall under the claims, it is also possible in this embodiment of the circuit arrangement according to the invention, instead of the actively controllable switching devices to use separate throttles in the two Aufladepfaden and the auxiliary throttle described above to decouple the two charging paths.

In another embodiment of the circuit arrangement for a multipoint inverter according to the invention, the relieving network has a capacitor for which a bidirectional charging path is present from which discharge paths branch off to both input terminals. The switching device in the bidirectional charging path is actively controllable to temporarily allow a unidirectional current in one or the other direction.

an input terminal for a positive pole and an input terminal for a negative pole of an input DC voltage,

a center tap for a voltage center of the DC input voltage, an output terminal for outputting an AC output current,

two external circuit breakers, one connected to one of the two input terminals, two inner circuit breakers, each of which on the one hand directly or via a diode with the middle labgriff and on the other hand are connected directly or via a diode to the output terminal, and

a discharge circuit for the external circuit breakers, comprising a capacitor,

wherein for the capacitor, a bidirectional charging path between the output terminal and the center labgriff runs, in which the capacitor is connected in series in the bidirectional charging path with a switching device and a throttle,

wherein the switching means has two passage directions and is actively drivable in each of the two passage directions to temporarily allow a unidirectional flow in the respective passage direction, and wherein a discharge path for the condenser runs between the output port and each of the input ports;

wherein the discharge path branches off behind the condenser and upstream of the throttle in a branch from the bidirectional charging path, viewed from the output terminal, and

wherein between the branch and the input terminal, a unidirectional switching element is arranged in the discharge path, which is aligned in the reverse direction with respect to the pole of the input DC voltage at that of the input terminals to which the discharge path is connected

In this embodiment of the circuit arrangement according to the invention, the switching device can have two actively activatable switching elements which are each arranged in one of two unidirectionally current-carrying antiparallel partial paths of the charging path. The directions of the unidirectional current flow through the sub-paths can each be predetermined by a non-actively controllable unidirectional switching element. The two partial paths of the bidirectional charging path can intersect. When the sub-paths are electrically conductively connected to one another in the region of their intersection, the non-actively controllable unidirectional switching element in one and the actively activatable switching element in the other sub-path as well as after the crossing, the actively controllable switching element in the to arrange one and the unidirectional switching element which can not be actively activated in the other partial path. This then corresponds to a series connection of two actively activatable switching elements with antiparallel diodes, such as, for example, MOSFETs with body diodes, the diodes of the diodes facing away from one another as seen from the output terminal. The circuit arrangement according to the invention can be applied to a multiplicity of three-point and multipoint inverters. These include N PC Inverters, BSNPC Inverters, ARCP and S3L Inverters.

For timing the circuit breaker and also each actively controllable switching device of the circuit arrangement according to the invention a control is provided. In particular, when describing what actions this controller can perform, this implies that the controller is properly set up to perform those same actions. This control may drive the switching means in the charging path from which the discharge path leads to the one input terminal within a period of time over which it shuts the outer power switch in pulses connected to the other input terminal. In this case, the controller controls the switching means in the period so as to allow a unidirectional current in the opposite direction to the forward direction of the unidirectional switching element in the discharge path leading to the one input terminal. For this closed in Pulsen outer power switch, the capacitor, which is provided for the charging path, as a switching relief. If another capacitor of the relief network is provided as a switching relief for the other external power switch, this should, as long as the other external power switch is not clocked, not be charged, in particular to cause any unwanted discharge currents. Therefore, the controller holds open the actively controllable switching device in the Aufladepfad as long as the other external power switch is not clocked. Similarly, if only one capacitor is placed in a bidirectional charging path, then while the one outer switch is being clocked, that capacitor will always be charged in one direction only, i.e. H. the switching means arranged in the bidirectional charging path also allow only one unidirectional current for charging the capacitor in one direction.

Preferably, the control of the circuit arrangement according to the invention controls the actively controllable switching device only within a sub-period of the period over which it clocks the respective outer circuit breaker, ie in pulses closes. This partial period is characterized in that an amount of an instantaneous value of the output alternating current output via the output connection complies with a lower limit value and that the instantaneous value of the output alternating current and an instantaneous value of the output alternating voltage have the same sign. The limit value is to be dimensioned such that the condenser serving for switching discharge is discharged at least substantially completely at each discharge process, and within a short time. This time must as Dead time between the pulses remain in which the outer circuit breaker and the complementary clocked inner circuit breaker are closed.

The control of the circuit arrangement according to the invention can control the actively controllable switching device not only once per half cycle of the output AC output current, but also in pulses having the same frequency as the pulses in which it closes the respective circuit breaker. These pulses are preferably completely within the pulses in which the controller closes the outer circuit breaker. Ideally, the pulses for which the actively actuable switching device is driven are synchronized with the pulses in which the control closes the outer circuit breaker. The width of these pulses, for which the actively controllable switching device is activated, can also be used to influence the degree of charging of the switch which relieves the load on the external circuit breaker. The width of the pulses, for which the actively controllable switching device is driven, but can also be constant.

A circuit arrangement for a multiphase multipoint inverter according to the invention has for each phase an output terminal, two external power switches, one of which is connected to one of the two input terminals, two internal circuit breakers and a discharge network for the outer circuit breakers with at least one capacitor and a charging path for each of the capacitors. In this case, the charging paths for all capacitors which are provided for switching discharge for those of the circuit breakers, which are connected to the same of the two input terminals, each lead via a common throttle, or even lead all charging paths via a single common throttle, directly to the center tap connected is. Then, the multiphase multipoint inverter has only one or two reactors shared by all relief networks of the different phases. In this case, there is at least then no mutual interference when charging the individual capacitors, if only one of the actively controllable switching devices in the Aufladepfaden is driven. The common throttle, over which the charging paths lead, but can also be provided as an auxiliary throttle, d. H. in addition to separate chokes in all the individual charging paths or to two common chokes of all the charging paths for each of the capacitors provided for switching discharge for those of the circuit breakers connected to the same of the two input terminals.

Another circuit arrangement for a multiphase multipoint inverter according to the invention has for each phase an output terminal, two external circuit breakers, each of which is connected to one of the two input terminals, and two inner power switches and a discharge circuit for the outer power switch with a capacitor and a bidirectional charging path for the capacitor. The outer and the inner circuit breakers are connected in the manner of a BSNPC inverter, wherein the inner circuit breakers comprise a series circuit of two actively activatable switching elements, each of which a non-actively controllable unidirectional switching element is connected in anti-parallel. In a corresponding manner, the switching device in each Aufladepfad comprises a series circuit of two active controllable switching elements, each of which a non-actively controllable unidirectional switching element is connected in anti-parallel. In this case, each bidirectional charging path of the discharge network runs for one phase via one of the two actively activatable switching elements of the inner circuit breaker another phase to the center tap, this actively controllable switching element is also one of the actively controllable switching elements of the switching device. In other words, each bidirectional charging path has only one additional actively activatable switching element with antiparallel-switched non-actively activatable unidirectional switching element, and it uses an actively controllable switching element with antiparallel switched non-actively controllable unidirectional switching element of the inner circuit breaker another phase. This is possible at least in those timing methods in which the inner power switches of the other phases are inactive in each case when the actively activatable switching elements are to be actuated in the bidirectional charging path of the relief network for the one phase.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings. The advantages of features and of combinations of several features mentioned in the description are merely exemplary and can take effect alternatively or cumulatively, without the advantages having to be achieved by embodiments according to the invention. Without altering the subject matter of the appended claims, as regards the disclosure content of the original application documents and of the patent, the following applies: Further features can be found in the drawings, in particular the relative arrangement and operative connections of several components. The combination of features of different embodiments of the invention or of features of different claims is also possible deviating from the chosen relationships of the claims and is hereby stimulated. This also applies to those features which are shown in separate drawings or are mentioned in their description. These features can also vary with features Claims are combined. Likewise, in the claims listed features for further embodiments of the invention can be omitted.

The features mentioned in the patent claims and the description are to be understood in terms of their number that exactly this number or a greater number than the said number is present, without requiring an explicit use of the adverb "at least". For example, when talking about an element, it should be understood that there is exactly one element, two elements or more elements. These features may be supplemented by other features or be the only characteristics that make up the product in question.

The reference signs contained in the patent claims do not limit the scope of the objects protected by the claims. They are for the sole purpose of making the claims easier to understand.

BRIEF DESCRIPTION OF THE FIGURES

In the following the invention will be further explained and described with reference to preferred embodiments shown in the figures.

1 shows a circuit arrangement according to the invention in a first embodiment based on a BSNPC inverter.

FIG. 2 illustrates the driving of actively activatable unidirectional switching elements of the circuit arrangement according to FIG. 1 in an embodiment with a phase angle of zero between the output AC output voltage and the output AC voltage.

FIG. 3 illustrates the activation of the actively activatable unidirectional switching elements of the circuit arrangement according to FIG. 1 in an embodiment with an alternating output voltage lagging the AC output voltage. 4 shows the circuit arrangement according to the invention in a second embodiment based on an N PC inverter. 5 shows the circuit arrangement according to the invention in a further embodiment based on a BSNPC inverter.

Fig. 6 shows the circuit arrangement according to the invention in still another

Embodiment based on a BSNPC inverter.

Fig. 7 shows the circuit arrangement according to the invention in yet another embodiment based on a three-phase BSNPC inverter.

8 shows the circuit arrangement according to the invention in yet a further embodiment, likewise based on a three-phase BSNPC inverter.

9 shows the circuit arrangement according to the invention in yet a further embodiment, based on a 3-phase BSNPC inverter.

Fig. 10 shows the circuit arrangement according to the invention in a further embodiment, based on a single-phase BSNPC inverter, wherein a discharge network has only one capacitor.

FIG. 11 shows the circuit arrangement according to the invention in an embodiment modified from FIG. 10, likewise based on a single-phase BSNPC inverter.

FIG. 12 shows the circuit arrangement according to the invention in a further embodiment, based on a single-phase N PC inverter, wherein a relieving network also has only one capacitor here.

13 shows the circuit arrangement according to the invention in a further embodiment, based on a three-phase BSNPC inverter, wherein each one of the three phases provided relief network has only one capacitor.

FIG. 14 shows the circuit arrangement according to the invention in a modification with respect to FIG. 13 with only one throttle for all three discharge networks. shows the circuit arrangement according to the invention in a further embodiment, based on a three-phase BSNPC inverter, wherein each provided for each one of the three phases discharge network has only one capacitor. Fig. 16 shows the circuit arrangement according to the invention in a modification with respect to the embodiment of FIG. 15 with only a single throttle for all three phases.

17 shows the circuit arrangement according to the invention in yet another embodiment, based on a three-phase BSNPC inverter with only one capacitor per discharge network for one of the three phases and a reduced total number of switching elements to be actively controlled; and

Fig. 18 shows the circuit arrangement according to the invention in yet another embodiment, based on a three-phase BSNPC inverter with only one capacitor per discharge network for each one of the three phases with analogous to Fig. 17 reduced total number of actively to be controlled switching elements and only a single throttle for all three phases.

DESCRIPTION OF THE FIGURES

The circuit arrangement 1 shown in FIG. 1 is based on a BSNPC inverter. It has two input terminals 1 1 and 21 for a positive and a negative pole of a DC input voltage u _in . The DC input voltage u _in is applied via a DC voltage intermediate circuit 2 with two DC link capacitors 12 and 22 and a center tap 3. Between the input terminals 1 1 and 21, two outer power switches 13 and 23 are connected in series. Between the circuit breakers 13 and 23 is an output terminal 4, via which an output _alternating current i _{load is} output. The output terminal 4 is connected to the center tap 3 via series-connected internal power switches 14 and 24. The power switches 13, 14, 23 and 24 are each formed here as IGBTs with antiparallel diodes 5. The anti-parallel diodes 5 of the outer power switches 13 and 23 are the input DC voltage u aligned _{in the} reverse direction with respect to. The anti-parallel diodes 5 of the inner power switches 14 and 24 have mutually opposing reverse directions. The power switches 13, 14, 23 and 24 are driven in the circuit 1 as well as in a conventional BSNPC inverter. To relieve the external circuit breakers 13 and 23, a relief network 6 is provided, the two capacitors 15 and 25, two throttles 16 and 26, two switching devices 17, 27 and two unidirectional switching elements 18, 28 has. In this case, in each case one of the capacitors 15 and 25 is connected in series with one of the reactors 16 and 26 and one of the switching devices 17 and 27 in a charging path 19 or 29. This Aufladepfad 19 and 29 is connected to a capacitor end with the output terminal 4 and a throttle end with a connection 38 between the middle labgriff 3 and the series circuit of the inner circuit breaker 14 and 24 connected. From each of the charging paths 19 and 29 branches off between the respective capacitor 15 and 25 and the respective throttle 16 and 26, a discharge path 20 and 30 in a branch 35 from. From the output terminal 4 to the branches 35, the discharge paths 20 and 30 are identical to the charging paths 19 and 29. Beyond the branches 35, the discharge paths 20 and 30 are connected to the input terminals 21 and 11, respectively, via the unidirectional switching elements 18 and 28. The unidirectional switching elements 18 and 28 are here not actively controllable switching elements, specifically to diodes 7. The switching devices 17 and 27 are actively controlled and formed here of series circuits of body diodes 8 having MOSFETs 9 with diodes 10 having a direction of a current pretend that can flow when driving the switching devices 17, 27. Seen from the output terminal 4 via the charging paths 19 and 29 and the discharge paths 20 and 30, the forward directions of the diodes 7 and 10 are opposite to each other. Between the input terminals 1 1 and 21, all diodes 7 and 10 are connected in series, with their center here on the connection 38 falls and their intermediate points on each side of the center on the branches 35 and wherein all diodes 7 and 10 with respect to the input DC voltage u _in are aligned in the reverse direction.

In the relief network 6, the capacitor 15 is provided for switching discharge of the outer circuit breaker 13 and the capacitor 25 for switching discharge of the outer circuit breaker 23. In the following, the charging and discharging of the capacitor 15 will be described as an example. The charging and discharging of the capacitor 25 takes place accordingly. With a closed power switch 13 and at the same time closed MOSFET 9 of the switching device 17, a current / flows ^_'13 through the power switch 13 not only at the output terminal 4 of issued output AC ^/' | _0ad to a connected, but not shown here load, but temporarily partly through the Aufladepfad 19 to the capacitor 15 and from there via the switching device 17 and through the throttle 16 to the center tap 3. That here temporarily a current must flow results yourself from the fact that the half DC input voltage u 2 falling across the DC link capacitor 12 must completely drop over the loop extending through the power switch 13 and via the charging path 19 to the center tap 3. In fact, the capacitor 15 is not only charged to half the DC input voltage u 2 because the inductor 16 continues to maintain the current initially flowing through it until charging of the capacitor to the full DC input voltage u _{in is} achieved. A subsequent discharge of the capacitor 15 is prevented by the diode 10 located in the charging path 19.

In other words, the capacitor 15 with the inductor 16 forms a series resonant circuit in which the current flowing through the charging path 19 until charging the capacitor 15 to u 2 during a first quarter of a resonant period also energizes the inductor 16, which then energizes it during a second Quarter of the resonance period of the series resonant circuit with further charging of the capacitor 15 to u _in again gives. However, the resonant oscillation is subsequently terminated by the diode 10 in the series resonant circuit, so that the capacitor 15 can not discharge under renewed energization of the inductor 16. The discharge of the capacitor 15 takes place rather then, when the power switch 13 is opened, so that the current / ^_'13 can no longer flow. By the capacitor 15 through its discharge the output AC / ^'| _0ad takes over, with the diode 7 in its discharge path 20 is conductive, it prevents a sudden increase in the voltage across the circuit breaker 13 voltage y _i3 . This voltage y _i3 is the sum of the DC input voltage u _in and the voltage Ui ₅ dropping across the capacitor 15. Since the capacitor 15 has been charged to u _in , the voltage y _i3 across the power switch 13 is therefore initially zero and does not rise until the voltage ui _{5 of} the capacitor 15 drops below u _in . In this way, a switching discharge is realized by de-energized switching of the circuit breaker 13.

So that the capacitor 15 subsequently does not disturb the function of the BSNPC inverter, it must discharge as completely as possible during the switching discharge. An undesirable charging in the wrong direction is opposed by the antiparallel diode 5 of the circuit breaker 23. A complete discharge of the capacitor 15 in the discharge circuit of the power switch 13 is achieved when the time of opening the power switch 13 at least one output AC / ^'| _0ad flows, which is taken over by the capacitor 15 and discharges it. In Fig. 2, for a phase angle zero, between an output AC voltage u _out at the output terminal 4 of Fig. 1 and the AC output current / ^' | _0ad part periods 31 and 32 are _plotted , in which the amount of an instantaneous value of AC output current / | _0a d exceeds a limit i _min . These are part-time periods 31 and 32 of the two half-waves of the AC output voltage u _out , via which in each case one of the power switches 13, 23 is clocked, namely the power switch 13 at the positive half-wave and the power switch 23 at the negative half-wave. Over the sub-period 31 of the positive half-wave, the actively controllable switching device 17 is driven as shown in FIG. 1, to allow a unidirectional current in the forward direction of the diode 10. About the sub-period 32 of the negative half-wave, the actively controllable switching device 27 is driven accordingly. By not driving the respective other actively activatable switching device 27 or 17, ie by keeping open the respective MOSFET 9, so that even in the forward direction of the respective diode 10 no current can flow, it is ensured during the part-time periods 31 and 32 that the previously charged capacitor 15 or 25 when opening the respective circuit breaker to be relieved 13 and 23 is not partially discharged via the other capacitor 25 and 15 respectively. Such an undesirably charged capacitor 25 or 15 would be as short circuited during the subsequent driving of the complementary to the outer circuit breaker 13 or 23 clocked inner circuit breaker 24 bzw.14 as in the case of discharge not yet completely discharged capacitor 15 and 25. A non-actuated switching device 17 or 27 in the respective charging path 19 or 29 prevents the undesired charging of the capacitor 15 or 25 arranged in the charging path. FIG. 3 illustrates that at one of the alternating output voltage u _{out, the} trailing alternating current / ^' | _0a d the partial periods 31 and 32, in which the switching means 17 and 27 are driven, within the half-waves of the output AC voltage u _out only begin when the magnitude of the instantaneous value of the AC output current | _0a d at the same sign of the instantaneous values of the output _alternating voltage u _out and the output alternating current | _0a d has exceeded the limit i _min . The part-time periods 31 and 32 end but at the latest with the sign change of the output AC voltage u _out , is changed in the clocking between the external power semiconductor switches 13 and 23. Furthermore, FIG. 3 shows that it is also possible not to permanently actuate the switching devices 17 and 27 for the entire subregions 31 and 32, but only for pulses which are synchronized with the pulses for which the respective external power switches 13 and 23 when the bar is closed. By the relative position of the pulses, with which the switching means 17 and 27 are driven to close the respective MOSFET 9, within the pulses for which the respective outer power switch 13 and 23 is closed, the course of the respective switching means 17 and 27 are influenced to the respective capacitor 15 and 25 flowing unidirectional charging current. Preferably, the Pulse, with which the switching means 17 and 27 are driven, at least as long as half the resonance period of the series resonant circuit of the capacitor 15 and 25 and the throttle 16 and 26 by shorter pulses than half the resonance period of the series resonant circuit, the charging of the respective Capacitors 15 and 25 are also limited to less than Uin to its discharge even at low output AC / ^' | _To ensure _0ad . However, then there is no complete switching discharge, ie no completely dead switching of the respective circuit breaker 13 and 23rd

2 and 3, it should also be noted that the actual output AC voltage Uout that is actually output is not shown, which is a pulse-width-modulated square-wave signal. Rather, it is the desired output AC voltage u _out , ie a specification for the pulse width modulation in the control of the outer power switches 13 and 23, which is in phase with the fundamental wave of the voltage at the output terminal 4.

Fig. 4 shows a circuit arrangement according to the invention, which starts from an NPC inverter, in which the outer power switches 13 and 23 and the inner power switches 14 and 24 are connected in series, wherein the center of the series circuit forms the output terminal 4. In this case, result of intermediate points 33 between the outer power switches 13 and 23 and the internal power switches 14 and 24, diodes 34, which are U aligned with respect to the input DC voltage _in reverse direction to the center tap 3. these diodes 34 are also the inner breaker 14 and 24 on the one hand connected to the center tap 3, while on the other hand are connected directly to the output terminal 4. The relief network 6 is here basically designed in the same way as in FIG. 1, even if the actively activatable switching devices 17 and 27 are shown here only schematically. It is irrelevant that the sequence of actively activatable switching devices 17 and 27 on the one hand and the throttles 16 and 26 on the other hand in the Aufladepfaden 19 and 29 with respect to FIG. 1 is reversed. This results in no fundamental change in the function of the discharge network 6 for the switching discharge of the outer power switches 13 and 23. The power switches 13, 14, 23 and 24 are driven in the circuit arrangement 1 shown in FIG. 4 as well as in a conventional NPC inverter. The embodiment of the circuit arrangement according to the invention according to FIG. 5 is again based on a BSNPC inverter. The following variations are illustrated with respect to FIG. 1, which can also be implemented independently of each other. Instead of the internal switching elements 14 and 24 of series-connected transistors with anti-parallel Forming diodes 5, wherein the antiparallel diode 5 of the one transistor each provides for a unidirectional current flow through the other transistor, here are two reverse-blocking transistors 36, ie directly unidirectionally formed switching elements, connected in parallel. Furthermore, the actively controllable switching devices 17 and 27, which pass through a unidirectional current when driving, each designed as thyristors, which also manage without additional diodes 10 as in Fig. 1. In addition, an auxiliary throttle 39 is provided in the connection 38 between the inner circuit breakers 14 and 24 and the center tap 3. With this auxiliary inductor 39 currents can be limited, which flow due to the short-circuiting of the possibly not completely discharged capacitors 15 and 25 to the center tap 3.

Basically, z. 1, the auxiliary choke 39 may also be provided between the inner circuit breakers 14 and 24 or between the inner circuit breakers 14 and 24 and the output terminal 4, but then from the inner circuit breakers 14 and 24 seen before the common connection of the charging paths 19, 29 and discharge paths 20, 30 to the output terminal 4. In addition, the auxiliary inductor 39 is so small that they even if they are in the series resonant circuit with the respective capacitor 15 or 25 and the respective Throttle 16 or 26 is located, whose resonance inductance does not significantly affect. The embodiment of the circuit arrangement 1 according to the invention shown in Fig. 6 differs from that according to FIG. 1 in that the actively controllable switching devices 17 and 27, which transmit a unidirectional current when driving, not only in diodes 10 and others, not unidirectionally trained and Here, only schematically illustrated bidirectional active switching elements 40 are divided, but that these parts 10 and 40 are also located on different sides of the capacitors 15 and 25. This also does not fundamentally change the function of the relief network 6.

FIG. 7 illustrates a circuit arrangement 1 according to the invention for a three-phase BSNPC inverter, the structure of each phase corresponding to FIG. As the only difference to FIG. 1, the actively activatable switching devices 17 and 27 are only shown schematically here. They can also be realized differently than shown in FIG. 1, as is also the case for all other embodiments of the circuit arrangement according to the invention. The circuit arrangement according to FIG. 7 has three output connections 4, at which it outputs one phase each of the three-phase output alternating current. 8 illustrates a circuit arrangement 1 according to the invention for a further three-phase BSNPC inverter, the structure corresponding to FIG. 7, except that all charging paths 19 lead via a common throttle 16 and lead all charging paths 29 via a common throttle 26. That is, the chokes 16 and 26 are shared by the relief networks 6 for all three phases. If only one of the actively activatable switching devices 17, 27 in the charging path 19, 29 is closed at all times, there is nevertheless no mutual interference in the resonant charging of the individual capacitors 15 and 25.

FIG. 9 illustrates a circuit arrangement 1 according to the invention for a further three-phase BSNPC inverter, the structure corresponding to FIG. 7, except that all the charging paths 19, 29 lead via a common choke 16. The throttle 16 is arranged here in the connections 38 between the middle labgriff 3 and the respective inner circuit breakers 14 and 24 for the individual phases. This location of the throttle 16 basically corresponds to that of a throttle in the case of the circuit arrangement known from DE 10 2010 008 426 B4. Notwithstanding DE 10 2010 008 426 B4, however, an actively controllable switching device 17 or 27 is arranged in the inventive circuit arrangement 1 in each of the charging paths 19 and 29 in order to selectively activate the charging paths unidirectionally, and in the embodiment shown here only the one Throttle 16 for all three phases available. It also comes with the use of only one throttle 16 to no mutual interference during resonant charging of the individual capacitors 15 and 25, if arranged by the in the Aufladepfaden 19, 29 actively controllable switching devices 17 or 27 at any time only one to to pass a unidirectional current.

10 shows an embodiment of the circuit arrangement 1 according to the invention based on a single-phase BSNPC inverter, in which the relief network 6 has only a single capacitor 45, which is charged via a bidirectional charging path 49 with different polarity and of which in the junction 35 the two Discharge paths 20 and 30 to the two input terminals 1 1 and 21 branch off. In this case, in the bidirectional charging path 49, a throttle 46, which is located between the branch 35 and the center tap 3, and an actively controllable switching device 41 is provided, which is connected in series with the throttle 46. The switching device 41 is actively controllable to selectively pass either a current with opposite direction with respect to the forward direction of the diode 7 in the discharge path 20 or a current with opposite direction with respect to the forward direction of the diode 7 in the discharge path 30, through which Capacitor 45 is charged with one or the other polarity. It includes the Partial paths of the bidirectional charging path 49 for the two unidirectional currents of opposite direction each extend through an actively controllable switching element 50 of the one and the body diode 8 of the other MOSFETs 9, the direction of the electricity. A resulting from the series connection of the MOSFETs cross-connection between the actively controllable switching elements 50 and the body diodes 8 is the function of the switching device 41 to allow unidirectional current in only one direction, not contrary.

Compared with FIG. 1, in the circuit arrangement 1 according to FIG. 10, the sequence of the throttle 46 is interchanged with the switching device 41 between the branch 35 and the center tap 3, which is not decisive for the function of the circuit arrangement 1. It is also not decisive for the function that in FIG. 10 the two charging paths 19 and 29 separated in FIG. 1 are combined to form the bidirectional charging path 49, in which only one capacitor 45, a throttle 46 and a combined switching device 41 are arranged are. The two capacitors 15 and 25 of FIG. 1 are never used simultaneously for switching discharge. This finding is used in accordance with FIG. 10 to save one of the capacitors and also one of the chokes and to charge the remaining capacitor 45 selectively with unidirectional currents of different direction through the switching device 41 and thus with different polarity, depending on which with the bidirectional charging path 49 the two outer circuit breaker 13 and 23 is relieved when switching. The charging of the capacitor 45 with different polarity is realized by different activation of the switching device 41, namely by closing the one or the other switching element 50. Due to the diodes 7 as unidirectional switching elements 18 and 28 in the discharge paths 20 and 30, these are always active only in the currently appropriate discharge direction without active activation, so that their connection at the junction 35 in the embodiment of the circuit arrangement 1 according to FIG. 10 without any problems is.

FIG. 11 shows a modification of the circuit arrangement 1 according to FIG. 10, in which the switching device 41 is formed by two antiparallel-connected thyristors 37. When each one of the two thyristors is driven, the switching device 41 allows a unidirectional current in the forward direction of the controlled thyristor through the charging path 49. The basic function of the circuit arrangement 1 according to FIG. 11 is the same as that of the embodiment of the circuit arrangement 1 according to FIG. 10. The embodiment of the circuit arrangement 1 according to FIG. 12 is based on a single-phase N PC inverter. Otherwise, it is constructed analogously to FIG. 10. In comparison with FIG. 4, the throttles 16 and 26 are combined to form the throttle 46, the switching devices 17 and 27 are connected to the switching device 41, and the capacitors 15 and 25 are combined to form the capacitor 45 which is used alternately for switching the external power switches 13 and 13 23 serves.

The throttle 46 lying in FIGS. 10 to 12 in each case only in the bidirectional charging path 49 and not in the connection 38 of the center tap 3 with the internal power switches 14 and 24 can be combined with an auxiliary throttle 39 arranged in this connection 38, as shown in FIG or a throttle 46 may be displaced into this connection 38 as in an S3L inverter (see Fig. 16, bottom).

Fig. 13 shows a circuit arrangement according to the invention based on a three-phase BSNPC inverter. Here, a relief network 6 according to FIG. 10 is provided for each of the three phases in addition to the external circuit breakers 13 and 23 and the internal circuit breakers 14 and 24. The circuit arrangement 1 according to FIG. 14 is likewise based on a three-phase BSNPC inverter, wherein each phase, including the relief network 6, is fundamentally constructed as in FIG. 1 1. Deviating from FIG. 11, however, the sequence of the choke 46 and the active is controllable switching device 41 in the form of anti-parallel thyristors 37 between the respective junction 35 and the middle labgriff 3 reversed. In addition, only a single common throttle 46 is provided for all three relief networks 6, but not in the connections 38 of the center tap 3 with the inner circuit breakers 14 and 24, but only in the branching therefrom bidirectional Aufladepfaden 49th

The circuit arrangement 1 according to FIG. 15 is likewise based on a three-phase BSNPC inverter. The discharge networks 6 for the individual phases are basically the same as in FIG. 10, except that the order of the respective throttle 46 and the actively activatable switching device 41 is reversed and the throttle 46 in the respective connection 38 of the center tap 3 with the inner circuit breakers 14, 24 lies.

In the circuit arrangement 1 according to FIG. 16, the chokes 46 of the three discharge networks 6 for all three phases are compared with FIG. 15 by a single common choke 46 between the center tap 3 and the branching of the connections 38 to the internal circuit breakers 14, 24 of the individual phases replaced. The use of only one common throttle 46 in the circuit arrangements 1 according to FIGS. 14 and 16 is possible because this throttle 46 is needed at any time only for the resonant charging of one of the capacitors 45.

The circuit arrangement 1 according to FIG. 17 is to be regarded as a variant of the circuit arrangement 1 according to FIG. 13. In this case, one of the two series-connected MOSFETs 9 of the actively activatable switching device 41 is formed in each bidirectional charging path 49 of the discharge network 6 for one phase by one of the two MOSFETs 9, which together form the inner power switches 14 and 24 of a different phase. Specifically, here is the MOSFET 9, which forms the actively controllable switching element 50 of one of the inner circuit breaker 24 of a different phase, as a second MOSFET 9 in the bidirectional charging path 49 of the discharge network 6 for the one phase. This is possible because, when the actively controllable switching device 41 is driven in the bidirectional charging path 49 of the discharge network 6 for the one phase, the inner circuit breakers 14 and 24 of the other phase are not actuated, at least as far as the control of the inner power switch 14 and 24 according to a standard clocking method for BSNPC inverter takes place. Furthermore, it is a prerequisite for the double use of a respective MOSFET 9 both for the actively controllable switching device 41 in one of the bidirectional charging paths 49 of the discharge network 6 for one phase and for the inner power switches 14 and 24 for another phase, that the actively controllable switching device 41st and the inner power switches 14 and 24 are each formed by two series-connected MOSFETs 9 in the opposite forward direction of their body diodes 5 and 8, respectively.

In the case of the circuit arrangement 1 according to FIG. 18, all the throttles 46 from the bidirectional charging path 49 of the relief networks 6 for the individual phases are replaced by a single common throttle 46 analogously to FIG. 16. In this way, the number of components of a three-phase inverter according to the present invention is minimized. REFERENCE LIST Circuitry

Dc link

center tap

output port

Antiparallel diode

Relief Network

diode

body diode

MOSFET

diode

input port

Link capacitor

breakers

capacitor

throttle

switching device

switching element

charging path

discharging

input port

Link capacitor

breakers

capacitor

throttle

switching device

switching element

charging path

discharging

subregion

intermediate point diode

Branch transistor thyristor connection auxiliary inductor switching element switching device capacitor choke charging path switching element

Claims

1 . Circuit arrangement (1) for a multipoint inverter,

- having an input terminal (1 1) for a positive pole and an input terminal (21) for a negative pole of a DC input voltage (y _in ),

- With a center tap (3) for a voltage center of the DC input voltage (t in).

- with an output _terminal (4) for outputting an _AC output current (/ | _0ad ), - with two external power _switches (13, 23), one of which is connected to one of the two input terminals (1 1, 21),

- With two inner circuit breakers (14, 24) which are each connected on the one hand directly or via a diode (5, 34) to the center tap (3) and on the other hand directly or via a diode (5) to the output terminal (4), and

- having a discharge network (6) for the outer circuit breakers (13, 23), which comprises at least one capacitor (15, 25, 45),

- Wherein for each of the capacitors (15, 25, 45) a charging path (19, 29, 49) between the output terminal (4) and the center tap (3), in which the respective capacitor (15, 25, 45) with a Throttle (16, 26, 46) is connected in series, and

- Between the output terminal (4) and each of the input terminals (1 1, 21) a discharge path (20, 30) for one of the capacitors (15, 25, 45),

- Wherein the discharge path (20, 30) seen from the output terminal (4) behind the respective capacitor (15, 25, 45) and before the throttle (16, 26, 46) in a branch (35) of the respective charging path ( 19, 29, 49) branches off and

- Wherein between the branch (35) and the input terminal (21, 1 1) a unidirectional switching element (18, 28) in the discharge path (20, 30) is arranged, with respect to the pole of the input DC voltage (u _m ) to that of Input terminals (1 1, 21) to which the discharge path (20, 30) is connected, is aligned in the reverse direction, and

wherein in each of the charging paths (19, 29, 49) a switching device (17, 27, 41) is connected in series with the capacitor (15, 25, 45) and the throttle (16, 26, 46), characterized

that the switching means (17, 27, 41) for each forward direction of each of the unidirectional switching elements (18, 28) in all connected to the respective charging path (19, 29, 49) Discharge path (20, 30) is actively controlled to temporarily allow a unidirectional current in a direction opposite to the respective passage direction from the output terminal (4) seen from.

2. Circuit arrangement (1) according to claim 1, characterized in that in each of the charging paths (19, 29, 49) a separate throttle (16, 26, 46) from the output terminal (4) from behind the branch (35) of the Discharge paths (20, 30) and before a connection of the respective Aufladepfads (19, 29) to a connection (38) of the inner power switch (14, 24) with the center tap (3) is arranged.

3. Circuit arrangement (1) according to claim 1 or 2, characterized in that the switching device (17, 27, 41) for each forward direction of each of the unidirectional switching elements (18, 19) in all of the respective charging path (19, 29, 49) connected discharge paths (20, 30) comprises a further non-actively controllable unidirectional switching element and an actively controllable switching element (40, 50).

4. Circuit arrangement (1) according to claim 3, characterized in that the non-actively controllable unidirectional switching element and the actively controllable switching element (40, 50) in the respective charging path (19, 29) are connected in series.

5. Circuit arrangement (1) according to claim 4, characterized in that the non-actively controllable unidirectional switching element and the actively controllable switching element (40, 50) with interposition of the capacitor (15, 25, 45) and / or the throttle (16, 26 ) are connected in series in the respective charging path (19, 29).

6. Circuit arrangement (1) according to one of the preceding claims, characterized in that the unidirectional switching element (18, 28) in each discharge path (20, 30) is a non-actively controllable switching element.

7. Circuit arrangement (1) according to one of the preceding claims, characterized in that each discharge path (20, 30) directly to the respective input terminal (21, 1 1) is connected and / or that each charging path (19, 29, 49) directly connected to the output terminal (4).

8. Circuit arrangement (1) according to one of the preceding claims, characterized in that an auxiliary throttle (39) in a connection (38) of the inner circuit breaker (14, 24) with the center tap (3) or

in a connection of the inner circuit breakers (14, 24) to the output terminal (4), seen from the inner circuit breakers (14, 24) before the connection of the charging paths (19, 29, 49) and discharge paths (20, 30) to the Output connection (4) or

with series-connected internal circuit breakers (14, 24), between the internal circuit breakers (14, 24) is arranged.

9. Circuit arrangement (1) according to claim 2 and claim 8, characterized in that an inductance of each separate throttle (16, 26, 46) in each Aufladepfad is at least as large as an inductance of the auxiliary throttle (39).

10. Circuit arrangement (1) according to one of the preceding claims, characterized in that the relief network (6) comprises two capacitors (15, 25), for each of which a charging path (19, 29) and a discharge path (20, 30) are present ,

1 1. Circuit arrangement (1) according to one of Claims 1 to 9, characterized in that the relief network (6) has a capacitor (45), from the charging path (49) of which discharge paths (20, 30) branch off to both input terminals (1 1, 21) in that the switching device (17, 27) is actively activatable to temporarily allow a unidirectional current in one or the other direction.

12. Circuit arrangement (1) according to claim 1 1, characterized in that the switching device (17, 27) comprises two actively controllable switching elements (50) which are each arranged in one of two unidirectional current-carrying anti-parallel partial paths of the charging path (49).

13. Circuit arrangement (1) according to one of the preceding claims, characterized in that the power switches (13, 14, 23, 24) according to Art

an N PC inverter,

a BSNPC inverter,

- an ARCP inverter or

- an S3L changer

are interconnected.

14. Circuit arrangement (1) according to one of the preceding claims, characterized in that a control is provided which is adapted to the switching device (17, 27, 41) in the Aufladepfad (19, 29, 49), of which the discharge path (20, 30) leads to the one input terminal (21, 11) to drive within a period of time over which it shunts the outer power switch (13, 23) in pulses connected to the other input terminal (11, 21 ), wherein the controller drives the switching means (17, 27, 41) in the period to supply a unidirectional current in an opposite direction to the forward direction of the unidirectional switching element (18, 28) in the discharge path (20, 30) the one input terminal (21, 1 1) leads to allow.

15. Circuit arrangement (1) according to claim 14, characterized in that the control system actuates the switching device (17, 27, 41) only within a sub-period (31, 32) of the time period, wherein in the sub-period (31, 32) Amount of an instantaneous value of the output alternating current (/ | _Oad ) a lower limit (/ _min ) complies and wherein the instantaneous value of the output alternating current (/ | _0ad ) and an instantaneous value of the output AC voltage (u _out ) have the same sign.

16. Circuit arrangement (1) according to claim 14 or 15, characterized in that the controller controls the switching device (17, 27, 41) in pulses, which synchronizes with the pulses in which it closes the outer circuit breaker (13, 23) are.

17. Circuit arrangement (1) according to one of the preceding claims, characterized in that a control is provided which is adapted to each one of the inner circuit breaker (14, 24) based on an AC output voltage at the output terminal half-wave close and the other of the internal power switch (14, 24) at least temporarily complementary to the respective pulsed outer power switch (13, 23) in pulses to close, with dead times between the pulses of the inner and outer circuit breaker (13, 23) remain in which the when the external circuit breaker (13, 23) discharges charging capacitor (15, 25, 45) of the discharge network (6).

18. Circuit arrangement (1) according to one of the preceding claims for a multi-phase multipoint inverter, for each phase

an output terminal (4),

- two outer circuit breakers (13, 23), one of which is connected to one of the two input terminals (1 1, 21), - two inner circuit breakers (14, 24), and

- A discharge network (6) for the outer circuit breakers (13, 23) with at least one capacitor (15, 25, 45) and a Aufladepfad (19, 29, 49) for each of the capacitors (15, 25, 45)

having,

characterized in that at least the charging paths (19, 29, 49) for all capacitors (15, 25, 45) provided for switching discharge for those of the power switches (13, 23) are connected to the same of the two input terminals (1 1, 21), via a common throttle (16, 26, 46) lead, which is directly connected to the center tap (3).

19. Circuit arrangement (1) according to claim 1 1 or 12 for a multi-phase multipoint inverter, for each phase

an output terminal (4),

- two outer circuit breakers (13, 23), one of which is connected to one of the two input terminals (1 1, 21), and two inner circuit breakers (14, 24), the circuit breakers (13, 14, 23, 24) are interconnected in the manner of a BSN PC inverter, wherein the inner circuit breakers (14, 24) comprise a series circuit of two actively controllable switching elements, each of which a non-actively controllable unidirectional switching element is connected in anti-parallel, and

a discharge network (6) for the outer power switches (13, 23) with a capacitor (45) and a bidirectional charging path (49) for the capacitor (45),

characterized,

- That the switching device (41) in each Aufladepfad (49) comprises a series circuit of two actively controllable switching elements, each of which a non-actively controllable unidirectional switching element is connected in anti-parallel, and

- That each Aufladepfad (49) of the discharge network (6) for one phase via one of the two actively controllable switching elements of the inner power switch (14, 24) of another phase to the center tap (3), said actively activatable switching element at the same time one of the active controllable switching elements of the switching device (41).

20. Circuit arrangement (1) for a multipoint inverter,

- With a center tap (3) for a voltage center of the DC input voltage (t in).

- with a discharge network (6) for the outer circuit breakers (13, 23) comprising two capacitors (15, 25),

- wherein for each of the capacitors (15, 25)

- A charging path (19, 29) between the output terminal (4) and the center tap (3) extends, in which the respective capacitor (15, 25) with a unidirectional switching element (17, 27) and a throttle (16, 26) in Row is connected, and

- A discharge path (20, 30) between the output terminal (4) and one of the input terminals (1 1, 21) runs,

- Wherein the discharge path (20, 30) seen from the output terminal (4) behind the respective condenser (15, 25) and before the throttle (16, 26) in a branch (35) of the Aufladepfad (19, 29) for the respective capacitor (15, 25) branches off and

- Wherein between the branch (35) and the input terminal (21, 1 1) another unidirectional switching element (18, 28) in the discharge path (20, 30) is arranged, with respect to the pole of the input DC voltage (u _m ) at the one of the input terminals (1 1, 21) to which the discharge path is connected, is aligned in the reverse direction, and - wherein the unidirectional switching element (17, 27) in each of the charging paths (19, 29) has a forward direction the forward direction of the further unidirectional switching element (18, 19) is opposite in the discharge path (20, 30) connected to the respective charging path (19, 29) from the output terminal (4),

characterized, - That the unidirectional switching element (17, 27) in each of the charging paths (19, 29) is actively controlled to temporarily allow a unidirectional current in its forward direction.

21. Circuit arrangement (1) for a multipoint inverter,

- With a center tap (3) for a voltage center of the DC input voltage (t in).

- with a discharge network (6) for the outer circuit breakers (13, 23), which comprises a capacitor (45),

- wherein for the capacitor (45) a bidirectional charging path (49) between the output terminal (4) and the center tap (3), in which the capacitor (45) in the bidirectional charging path (49) with a switching device (41) and a Throttle (46) is connected in series,

- wherein the switching means (41) has two passage directions and is actively controllable in each of the two passage directions to temporarily allow a unidirectional current in the respective forward direction, and - wherein between the output terminal (4) and each of the input terminals (1 1, 21) a discharge path (20, 30) for the capacitor (45) runs,

- Wherein the discharge path (20, 30) as seen from the output terminal (4) behind the condenser (45) and before the throttle (46) in a branch (35) branches off from the bidirectional charging path (49) and - between the branch (35) and the input terminal (21, 1 1) a unidirectional switching element (18, 28) in the discharge path (20, 30) is arranged, with respect to the pole of the input DC voltage (u _m ) at that of the input terminals (1 1, 21), with which the discharge path (20, 30) is connected, is aligned in the reverse direction.