DE102019135718A1 - Inverter and method for operating an inverter - Google Patents

Abstract

The invention relates to an inverter (2) for converting direct voltage into 2N-phase alternating voltage, where N is a natural number, comprising 2N half-bridges (3), the half-bridges (3) being connected in parallel to one another and to a direct voltage source (1) can be switched in parallel, with each half bridge (3) comprising two main switches (4) connected in series, the point between the main switches (4) being referred to as the half-bridge center (5), the half-bridge center (5) with one of the 2N phases (6 ) is connectable, and each half bridge (3) has at least one capacitance (17), N clamping circuits (7), each clamping circuit (7) having a resonance inductance (8) and an auxiliary switch arrangement (9) connected in series with the resonance inductance (8) ) and wherein the clamping circuit (7) is connected between two half-bridge centers (5) which are assigned to two opposite phases (6), and a control unit (10) for controlling the main switch (4) and the auxiliary switch arrangements (9). The invention also relates to a method for operating an inverter (2).

Description

The invention relates to an inverter for converting direct voltage into 2N-phase alternating voltage, where N is a natural number, as well as a method for operating an inverter.

State of the art

Inverters for converting direct voltage into alternating voltage and methods for operating these inverters are generally known. In particular in the context of mobile devices, such as for example in electromobility, it is important to build such inverters compactly.

In inverters known from the prior art, high losses often occur when electrical switches are switched. These losses can be reduced by complex circuits.

Task and solution

The object of the present invention is therefore to propose an inverter and a method for operating an inverter which avoid the disadvantages of the prior art and in particular have only low losses.

This object is achieved by an inverter according to claim 1 and a method for operating an inverter according to claim 13. The independent claims describe advantageous developments.

A proposed inverter is designed to convert direct voltage into 2N-phase alternating voltage, where N is a natural number. Losses during switching are greatly reduced by a clamping circuit which is arranged between two half bridges in each case, these two half bridges being assigned to phases running in opposite directions. This is achieved, in particular, in that an electric current flowing into a first phase and from a second phase which is opposite to the first phase commutates to a resonance inductance in the clamping circuit when the inverter is switched. It is thus possible to switch the main switch of the inverter without loss when the voltage is low or zero.

An inverter is proposed for converting direct voltage into 2N-phase alternating voltage, where N is a natural number. It is important that two of the phases of the alternating current are in opposite directions, that is, offset by 180 ° from one another. The amounts of the electrical current that flows through two opposing phases must also be the same or at least approximately the same. Furthermore, it is possible, but not necessary, for the 2N phases to have a phase offset of 180 ° / N with respect to one another.

The inverter has 2N half bridges. These half bridges are connected in parallel to one another and can be connected in parallel to a DC voltage source. The DC voltage source can be, for example, a battery or an accumulator.

Each half bridge comprises two main switches connected in series. The point between the main switches is called the half-bridge center point and can be connected to one of the 2N phases. Furthermore, each half bridge has at least one capacitance. The capacitance can be an intrinsic capacitance of a main switch and / or a snubber capacitor.

The inverter also comprises N clamping circuits, each clamping circuit comprising a resonance inductance and an auxiliary switch arrangement. The clamping circuit is connected between two half-bridge centers, which are assigned to two opposite phases.

The resonance inductance can be a discrete component but also a parasitic inductance of the circuit. Preferably, clamping diodes are additionally connected to the connections of the resonance inductance in order to reduce high-frequency oscillations.

Finally, the inverter comprises a control unit for controlling the main switch and the auxiliary switch arrangements. This is done, for example, in such a way that, in order to switch the main switches with as little loss as possible, the auxiliary switch arrangements are switched in such a way that the electrical current temporarily flows from one phase via the clamping circuit into the phase opposite to the first phase. This works best when the amounts of the electrical current flowing through the two opposing phases are the same or at least approximately the same. This enables the main switches to be largely de-energized, which means that the losses when switching the main switch are very low. It is also conceivable that the main switches are not switched completely voltage-free or only with a reduced current, the losses when switching the main switch still being greatly reduced.

Advantageously, each main switch for electrical current flow is one polarity into one Forward direction permeable and switchable for electrical current flow of the same polarity in a switching direction opposite to the forward direction. In the forward direction, the main switch is therefore always permeable to the flow of electrical current, while in the switching direction it is only permeable to the flow of electrical current when the main switch is switched accordingly. The flow directions of the main switches connected in series are the same, that is, if electrical current flows through both main switches one after the other, it flows either through both in the forward direction or through both in the switching direction. If the half bridge is connected to the DC voltage source, the main switches are arranged in such a way that electrical current that would flow from the positive electrode of the DC voltage source would flow through both main switches of the half bridge in the switching direction to the negative electrode of the DC voltage source.

It is advantageous if each main switch comprises a switching element and a diode connected in parallel to the switching element. The diode can be a discrete component but also an intrinsic diode of the switching element, for example a body diode of a MOSFET. The diode allows the flow of electrical current in the forward direction, while that allows in the switching direction and prevents electrical current flow in the switching direction when the main switch is open. The switching element and the diode can be different electronic components or can be combined in one electronic component.

It is advantageous if each main switch comprises a transistor, in particular a power transistor, and / or a thyristor. A transistor is an electrically switchable switching element and is switched by the control unit. Depending on the design, the transistor can also include the diode. A thyristor is also a semiconductor component, can be switched on and switches itself off if the current falls below a minimum.

Each auxiliary switch arrangement advantageously comprises two auxiliary switches connected in series. Each auxiliary switch is permeable for electrical current flow in one forward direction and can be switched for electrical current flow in a switching direction opposite to the forward direction. The conduction directions of the auxiliary switches connected in series are opposite to one another, that is, when electrical current flows through both auxiliary switches, it flows through one auxiliary switch in the conduction direction and through the other auxiliary switch in the switching direction. By means of said auxiliary switch arrangement, the electrical current flow can be allowed or completely prevented in one direction or in the direction opposite to one direction. The electrical current flow through the clamping circuit can thus be controlled, in particular by means of the control unit.

It is advantageous if the resonance inductance is connected in series with the auxiliary switch arrangement. The resonance inductance can be arranged between the two auxiliary switches. A first connection of the resonance inductance is therefore connected to a connection of the first auxiliary switch and a second connection of the resonance inductance is connected to a connection of the second auxiliary switch. A preferred position of the reference potentials of the auxiliary switches is thus achieved.

It is advantageous if each auxiliary switch comprises an auxiliary switching element and an auxiliary diode connected in parallel to the auxiliary switching element. The auxiliary diode can be a discrete component but also an intrinsic diode of the auxiliary switching element, for example a body diode of a MOSFET. The auxiliary diode allows the electrical current to flow in the forward direction, while the electrical current flow can be switched in the switching direction by means of the auxiliary switching element. The auxiliary switching element is preferably switched by means of the control unit. The auxiliary switching element particularly preferably comprises a transistor and / or a thyristor.

As an alternative to the two auxiliary switches connected in series, the auxiliary switch arrangement can also comprise a bidirectional thyristor triode. The bidirectional thyristor triode can be switched, preferably by means of the control unit, for electrical current flow in one direction or in the direction opposite to one direction.

The at least one capacitance is advantageously connected in parallel to one of the main switches.

It is advantageous if the at least one capacitance comprises at least one intrinsic capacitance of the main switch. The intrinsic capacitance can be, for example, an output capacitance and / or a parasitic capacitance.

As an alternative or in addition, the at least one capacitance can also comprise at least one snubber capacitor, which is connected in parallel to one of the main switches. The snubber capacitor can reduce high-frequency electromagnetic interference, lower the resonance frequency and reduce the steepness of the voltage at the main switch.

A method for operating an inverter is also proposed. The inverter is designed in accordance with the preceding description and is operated with pulse width modulation. In the following, only one half oscillation is described, with the other half oscillation taking place analogously.

The starting point of the method is a state a) in which an electric current flows into a first phase through a first main switch of a first half bridge, which is connected to a negative electrode of a direct voltage source. Furthermore, the electrical current flows from a second phase, which is opposite to the first phase, through a first main switch of a second half-bridge, which is connected to a positive electrode of the DC voltage source. It is important here that the amount of the electric current flowing into the first phase is the same or at least approximately the same as the amount of the electric current flowing out of the second phase.

To initiate a switching process, b) an auxiliary switch arrangement of a clamping circuit arranged between half-bridge centers of the first half-bridge and the second half-bridge is switched in such a way that electrical current can flow from the second phase through the clamping circuit into the first phase. This means that a switch is opened that enables this electrical current to flow. The clamping circuit comprises a resonance inductance, so that the electrical current flow through the clamping circuit also causes electrical current to flow through the resonance inductance, whereby energy is stored.

After the electrical current has been commutated to the clamping circuit and capacitances in the first half-bridge and the second half-bridge have been reloaded, c) a second main switch of the first half-bridge and a second main switch of the second half-bridge are switched on. The second main switch of the first half bridge is connected to the positive electrode of the DC voltage source, while the second main switch of the second half bridge is connected to the negative electrode of the DC voltage source. The second main switch of the first half-bridge and the second main switch of the second half-bridge are switched on largely without voltage and therefore with particularly low losses.

When the electrical current flow is commutated in such a way that electrical current no longer flows through the clamping circuit, the clamping circuit blocks further electrical current flow, since it is not switched to be conductive for electrical current flow in the reverse direction. Now also d) the auxiliary switch arrangement is switched in such a way that it blocks electrical current flow through the auxiliary switch arrangement and thus through the clamping circuit in both directions. This switching takes place without current and thus with little loss and can take place by means of a control unit, but also by switching off a bidirectional thyristor triode or a thyristor.

After a time specified by the pulse width modulation, e) the second main switch of the first half bridge and the second main switch of the second half bridge are switched off. This is followed by a commutation of the electrical current flow back to the initial state a).

After a further time predetermined by the pulse width modulation, f) the method from step b) is repeated. This repetition takes place until a first half-oscillation is completed. For a second half oscillation, the method is analogous to that described above, with the current direction reversing in the phases and the second main switches of the half bridges and vice versa being switched in each case instead of the first main switch of the half bridges.

In the case of the first half oscillation in step a), the electrical current advantageously flows in the forward direction through the first main switch of the first half bridge and in the forward direction through the first main switch of the second half bridge.

It is advantageous if, after step b), the electrical current flow commutates in such a way that the entire electrical current flows from the second phase through the clamping circuit into the first phase. This is referred to as step b1). The duration of this commutation is determined, among other things, by the resonance inductance.

It is also advantageous if, before step c), the resonance inductance of the clamping circuit goes into resonance with the capacitances of the first half-bridge and the second half-bridge, so that the capacitances of the first half-bridge and the second half-bridge are reloaded. This enables the main switch to be switched largely voltage-free in step c). The capacitances of the first half-bridge and the second half-bridge can be intrinsic capacitances of the main switches, for example output capacitances and / or parasitic capacitances, or snubber capacitors connected in parallel to the main switches.

Advantageously, the electrical current flow commutates after step c) in such a way that the electrical current in the switching direction through the second main switch of the first half bridge into the first phase and flows from the second phase in the switching direction through the second main switch of the second half-bridge. The energy stored in the resonance inductance of the clamping circuit is thus released again and the electrical current flow through the clamping circuit disappears, so that the switching of the auxiliary switch arrangement in step d) can take place without current, and thus with particularly low losses.

It is advantageous if, after step e), the capacitances of the first half-bridge and the second half-bridge are recharged and the electrical current flow commutates in such a way that the electrical current through the first main switch of the first half-bridge into the first phase and from the second phase through the first main switch of the second half bridge flows. This step is referred to as e1). This reloading of the capacities and commutation of the electrical current flow naturally takes place through the current flows in the circuit.

It is advantageous if the first main switch of the first half bridge and the first main switch of the second half bridge are switched on after step e1) and switched off after step b1). This reduces the conduction losses in the main switches.

Advantageously, in step e), the auxiliary switch arrangement is additionally switched in such a way that electrical current can flow from the half-bridge center point of the first half-bridge via the clamping circuit to the half-bridge center point of the second half-bridge; Go resonance and after step e1) the auxiliary switch arrangement is switched in such a way that it blocks electrical current flow through the auxiliary switch arrangement. This accelerates the reloading of the capacities of the half bridges, especially in the case of small electrical currents from and into the phases.

Figure list

• 1 shows a circuit diagram of an inverter,
• 2 shows a circuit diagram of an inverter with a connected electric motor,
• 3 shows a circuit diagram of a further embodiment of an inverter and
• 4a - 4d show the chronological sequence of switch positions, electrical voltages and electrical currents.

Identical reference symbols are used in the figures for elements of the invention that are the same or have the same effect. Furthermore, for the sake of clarity, only reference symbols are shown in the individual figures that are necessary for the description of the respective figure.

1 shows a circuit diagram of a parallel to a DC voltage source 1 switched inverter 2 for converting DC voltage into 2N-phase AC voltage, where N is a natural number. The inverter 2 includes 2N half bridges 3 . For the sake of clarity, in 1 only two half bridges 3 shown, possible further half bridges 3 are indicated by ellipses. The half bridges 3 are also connected in parallel to each other.

Every half bridge 3 includes two main switches connected in series 4th , being the point between the main switches 4th as the half-bridge center 5 referred to as. Every half-bridge center 5 defines one of the 2N phases 6th . Furthermore, each half bridge has 3 at least one capacity, which is not shown here. The capacity can be an intrinsic capacity of the main switch 4th like an output capacitance or parasitic capacitance or around a parallel to a main switch 4th act switched snubber capacitor.

The inverter also includes 2N clamping circuits 7th . Each clamping circuit has 7th a resonance inductance 8th and one with the resonance inductance 8th Auxiliary switch arrangement connected in series 9 on. The clamp circuit 7th is between two half-bridge centers 5 switched, these half-bridge centers 5 Half bridges 3 assigned to opposite phases 6th be connected. Under opposing phases 6th are phases 6th understood that are offset by 180 ° to each other.

A control unit is indicated only schematically 10 of the inverter 2 , by means of which the main switch 4th and the auxiliary switch arrangement 9 be switched.

2 shows the inverter 2 with a connected electric motor 11 . A 6-phase electric motor 11 is shown as an example, but other electric motors are also used 11 conceivable as long as the number of their phases 6th is straight. The two in the 2 half-bridge centers shown 5 caused by the clamp circuit 7th are connected to each other, are in two opposite phases 6th of the electric motor 11 connected.

3 shows a further embodiment of an inverter 2 . Every main switch 4th here comprises a switching element 12th and one parallel to the switching element 12th switched diode 13th . With the switching element 12th it can be for example be a transistor and the diode 13th can be a separate component or part of the switching element 12th be. The diode 13th gives a direction of passage D. before, being the one of the forward direction D. opposite direction than switching direction S. referred to as. The main switch 4th are arranged in such a way that their passage directions D. to match. Starting from a positive electrode 1.1 the DC voltage source 1 one arrives in the switching direction S. through the two main switches 4th the half bridge 3 to a negative electrode 1.2 the source of direct voltage.

The auxiliary switch arrangement 9 includes two auxiliary switches 14th that with the resonance inductance 8th are connected in series, the resonance inductance 8th between the auxiliary switches 14th is arranged so that a connection of the resonance inductance 8th with an auxiliary switch 14th and the other terminal of the resonance inductance 8th with the other auxiliary switch 14th connected is.

Every auxiliary switch 14th includes an auxiliary switching element 15th and one parallel to the auxiliary switching element 15th switched auxiliary diode 16 . The auxiliary diode 16 gives the direction of passage again D. in front. The auxiliary switches 14th are arranged in such a way that their passage directions D. are opposite to each other.

Alternative to the two auxiliary switches 14th can the auxiliary switching arrangement 9 also include a bidirectional thyristor triode, not shown here.

In addition, there is one main switch in each case 4th a half bridge 3 Snubber capacitors 17th switched. It is also conceivable that further snubber capacitors 17th parallel to the other main switch 4th the half bridge 3 are switched.

4a to 4d show the sequence of a pulse width modulation cycle. It shows 4a the chronological sequence of the switch positions of a first, with the negative electrode 1.2 the DC voltage source 1 connected, main switch 4.1 of a first half bridge 3.1 and a first, with the positive electrode 1.1 the DC voltage source 1 connected, main switch 4.1 of a second half bridge 3.2 as a solid line. Also shows 4a the chronological sequence of the switch positions of a second main switch 4.2 of the first half bridge 3.1 and a second main switch 4.2 of the second half bridge 3.2 as a dashed line. 4b shows the timing of the switch positions of an auxiliary switch 14 of the clamping circuit 7th as a solid line and a further auxiliary switch 14 of the clamping circuit 7th as a dashed line. 4c shows the amount of the time course of the electrical currents through the first main switch 4.1 of the first half bridge 3.1 and the first main switch 4.1 of the second half bridge 3.2 as a solid line through the second main switch 4.2 of the first half bridge 3.1 and the second main switch 4.2 of the second half bridge 3.2 as a dashed line and through the clamping circuit 7th as a dotted line. The scale for the current intensity is chosen arbitrarily, but the same for all three lines. Finally shows 4d the time course of the first main switch 4.1 of the first half bridge 3.1 applied voltage as a solid line, that of the second main switch 4.2 of the second half-bridge 3.2 applied voltage as a dashed line and again the electrical current through the clamping circuit 7th as a dotted line. The scales for the voltages and currents are chosen arbitrarily, but the scales for the voltages are the same for both lines.

First (state a)) an electric current flows through the first main switch 4.1 of the first half bridge 3.1 in a first phase 6.1 and from a second phase 6.2 that the first phase 6.1 is opposite, by the first main switch 4.1 of the second half bridge 3.2 . The electric current flows in the forward direction D. by the first main switch 4.1 of the first half bridge 3.1 and in the forward direction D. by the first main switch 4.1 of the second half bridge 3.2 .

Now (step b)) the auxiliary switch arrangement 9 the clamping circuit 7th switched in such a way that electric current from the second phase 6.2 through the clamping circuit 7th in the first phase 6.1 can flow, whereupon the electric current flow also in this way from the half bridges 3 on the clamping circuit 7th commutates (step b1)) that the electric current from the second phase 6.2 through the clamping circuit 7th in the first phase 6.1 flows. That leaves those from the second phase 6.2 and in the first phase 6.1 flowing electrical currents at least largely constant.

When the electric current is completely from the half bridges 3 on the clamping circuit 7th is commutated, the resonance inductance goes 8th with the capacities, for example the snubber capacitors 17th , the first half bridge 3.1 and the second half bridge 3.2 in resonance, so that the capacities of the first half-bridge 3.1 and the second half bridge 3.2 are reloaded (step b3)).

Now (step c)) a second main switch 4.2 of the first half bridge 3.1 and a second main switch 4.2 of the second half bridge 3.2 switched on. This switch-on process takes place largely without voltage and therefore with very little loss.

This is followed by a further commutation of the electrical current flow (step c1)), so that the electrical current is in the switching direction S. by the second main switch 4.2 of the first half bridge 3.1 in the first phase 6.1 and from the second phase 6.2 in switching direction S. by the second main switch 4.2 of the second half bridge 3.2 flows. The clamp circuit 7th then blocks further electrical current flow, since it is not switched to be conductive for electrical current flow in the opposite direction. Thereupon (step d)) the auxiliary switch arrangement is also 9 switched in such a way that it allows electrical current to flow through the auxiliary switch arrangement 9 locks. This switching process takes place without current and therefore also with very little loss.

After a time specified by the pulse width modulation, the second main switch 4.2 of the first half bridge 3.1 and the second main switch 4.2 of the second half bridge 3.2 switched off (step e)), whereupon (step e1)) the capacitances of the first half-bridge 3.1 and the second half bridge 3.2 are reloaded and the electrical current flow commutated in such a way that the electrical current through the first main switch 4.1 of the first half bridge 3.1 in the first phase 6.1 and from the second phase 6.2 by the first main switch 4.1 of the second half bridge 3.2 flows. In order to accelerate this process, the auxiliary switch arrangement can also be used for the duration of the charge reversal of the capacitances and the commutation of the electrical current flow 9 be switched in such a way that electric current from the half-bridge center point 5 the first half bridge 3.1 via the clamping circuit 7th to the half-bridge center 5 the second half bridge 3.2 can flow. The capacities of the first half bridge go here 3.1 and the second half bridge 3.2 with the resonance inductance 8th the clamping circuit 7th in resonance, which speeds up the reloading of capacities.

For the time in which the first main switch 4.1 of the first half bridge 3.1 and the first main switch 4.1 of the second half bridge 3.2 in the forward direction D. Conduct electrical current, the first main switch 4.1 of the first half bridge can also 3.1 and the first main switch 4.1 of the second half bridge 3.2 be switched on. Switching on takes place as step e2), switching off as step b2).

The present invention is not limited to the illustrated and described exemplary embodiments. Modifications within the scope of the patent claims are just as possible as any combination of the features described, even if they are shown and described in different parts of the description or the claims or in different exemplary embodiments.

List of reference symbols

1

DC voltage source

1.1

positive electrode

1.2

negative electrode

2

Inverter

3

Half bridge

3.1

first half bridge

3.2

second half bridge

4th

Main switch

5

Half-bridge center

6th

phase

6.1

first phase

6.2

second phase

7th

Clamping circuit

8th

Resonance inductance

9

Auxiliary switch arrangement

10

Control unit

11

Electric motor

12th

Switching element

13th

diode

14th

Auxiliary switch

15th

Auxiliary switching element

16

Auxiliary diode

17th

Snubber capacitor

D.

Forward direction

S.

Switching direction

Claims (20)

Inverter for converting direct voltage into 2N phase alternating voltage, where N is a natural number, comprising 2N half bridges (3), the half bridges (3) being connected in parallel to one another and being connectable in parallel to a direct voltage source (1), each half bridge (3) comprises two main switches (4) connected in series, the point between the main switches (4) being referred to as the half-bridge center (5), the half-bridge center (5) being connectable to one of the 2N phases (6), and each Half-bridge (3) has at least one capacitance (17), N clamping circuits (7), wherein each clamping circuit (7) comprises a resonance inductance (8) and an auxiliary switch arrangement (9) and wherein the clamping circuit (7) is between two Half bridge centers (5) is connected, which are assigned to two opposite phases (6), and a control unit (10) for controlling the main switch (4) and the auxiliary switch arrangements (9). Inverter according to Claim 1 , wherein each main switch (4) is permeable for electrical current flow in a forward direction (D) and can be switched for electrical current flow in a switching direction (S) opposite to the forward direction (D), the forward directions (D) of the main switches (4 ) to match. Inverter according to one of the preceding claims, wherein each main switch (4) comprises a switching element (12) and a diode (13) connected in parallel to the switching element (12). Inverter according to one of the preceding claims, wherein each main switch (4) comprises a transistor, in particular a power transistor, and / or a thyristor. Inverter according to one of the preceding claims, wherein each auxiliary switch arrangement (9) comprises two auxiliary switches (14) connected in series, each auxiliary switch (14) being permeable for electrical current flow in a forward direction (D) and for electrical current flow in one of the forward direction (D ) opposite switching direction (S) can be switched and the forward directions (D) of the auxiliary switches (14) connected in series are opposite. Inverter according to one of the preceding claims, wherein the resonance inductance (8) is connected in series with the auxiliary switch arrangement (9) and in particular is arranged between the two auxiliary switches (14). Inverter according to one of the preceding claims, wherein the resonance inductance (8) is a parasitic inductance. Inverter according to one of the Claims 5 to 7th wherein each auxiliary switch (14) comprises an auxiliary switching element (15) and an auxiliary diode (16) connected in parallel to the auxiliary switching element (15). Inverter according to one of the preceding claims, wherein the auxiliary switch arrangement (9) comprises a bidirectional thyristor triode. Inverter according to one of the preceding claims, wherein the at least one capacitance (17) is connected in parallel to one of the main switches (4). Inverter according to one of the preceding claims, wherein the at least one capacitance (17) comprises at least one intrinsic capacitance of the main switch (4). Inverter according to one of the preceding claims, wherein the at least one capacitance (17) comprises at least one snubber capacitor (17) which is connected in parallel to one of the main switches (4). Method for operating an inverter (2) according to one of the preceding claims, wherein a) an electric current through a first main switch (4.1.1), connected to a negative electrode (1.2) of a DC voltage source (1), of a first half-bridge (3.1) into a first phase (6.1) and from a second phase (6.2) , which is opposite to the first phase (6.1), flows through a first main switch (4.2.1) of a second half bridge (3.2) connected to a positive electrode (1.1) of the direct voltage source (1), b) an auxiliary switch arrangement (9) of a clamping circuit (7) arranged between half-bridge centers (5) of the first half-bridge (3.1) and the second half-bridge (3.2) is switched in such a way that electrical current from the second phase (6.2) passes through the clamping circuit (7 ) can flow into the first phase (6.1), c) a second main switch (4.1.2) of the first half bridge (3.1) and a second main switch (4.2.2) of the second half bridge (3.2) are switched on, d) the auxiliary switch arrangement (9) is switched in such a way that it blocks electrical current flow through the auxiliary switch arrangement (9), e) after a time predetermined by pulse width modulation, the second main switch (4.1.2) of the first half bridge (3.1) and the second main switch (4.2.2) of the second half bridge (3.2) are switched off, and f) after a further time predetermined by the pulse width modulation, the method from step b) is repeated. Procedure according to Claim 13 , wherein in step a) the electrical current in the forward direction (D) through the first main switch (4.1.1) of the first half bridge (3.1) and in the forward direction (D) through the first main switch (4.2.1) of the second half bridge (3.2) flows. Procedure according to Claim 13 or 14th , wherein after step b) b1) the electrical current flow commutates in such a way that the electrical current flows from the second phase (6.2) through the clamping circuit (7) into the first phase (6.1). Method according to one of the Claims 13 to 15th , wherein before step c) a resonance inductance (8) of the clamping circuit (7) with capacitances of the first Half bridge (3.1) and the second half bridge (3.2) goes into resonance, so that the capacities of the first half bridge (3.1) and the second half bridge (3.2) are reloaded. Method according to one of the Claims 13 to 16 , wherein after step c) the electrical current flow commutates in such a way that the electrical current in the switching direction (S) through the second main switch (4.1.2) of the first half bridge (3.1) into the first phase (6.1) and out of the second phase (6.2 ) flows in switching direction (S) through the second main switch (4.2.2) of the second half bridge (3.2). Method according to one of the Claims 13 to 17th , wherein after step e) e1) the capacities of the first half bridge (3.1) and the second half bridge (3.2) are reloaded and the electrical current flow commutates in such a way that the electrical current through the first main switch (4.1.1) of the first half bridge (3.1 ) flows into the first phase (6.1) and from the second phase (6.2) through the first main switch (4.2.1) of the second half-bridge (3.2). Procedure according to Claim 18 , the first main switch (4.1.1) of the first half bridge (3.1) and the first main switch (4.2.1) of the second half bridge (3.2) being switched off after step b1) and switched on after step e1). Procedure according to Claim 18 or 19th , wherein in step e) the auxiliary switch arrangement (9) is additionally switched in such a way that electrical current can flow from the half-bridge center point (5) of the first half-bridge (3.1) via the clamping circuit (7) to the half-bridge center point (5) of the second half-bridge (3.2), in step e1) the capacitances of the first half bridge (3.1) and the second half bridge (3.2) go into resonance with the resonance inductance (8) of the clamping circuit (7) and after step e1) the auxiliary switch arrangement (9) is switched in such a way that it is electrical Current flow through the auxiliary switch arrangement (9) blocks.

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