Method and apparatus for operating a converter circuit having plural input and output phase connections and plural two-pole switching cells

1. A method for operating a converter circuit, wherein the converter circuit includes n input phase connections and p output phase connections, where n≧2 and p≧2, and (n·p) two-pole switching cells for switching at least one positive and at least one negative voltage between the poles, wherein each output phase connection is connected in series to each input phase connection by means of a switching cell, respectively, and each switching cell having drivable bidirectional power semiconductor switches with a controlled unidirectional current guidance direction, and a capacitive energy storage means, wherein the method comprises:

driving the power semiconductor switches of the switching cells by means of a drive signal;

connecting at least one inductance into each series connection, with a switching cell together with an inductance in each case forming a phase module;

for each phase module, forming the drive signal from a reference signal in respect of a voltage across the phase module and from a voltage signal across the inductance; and

forming the voltage signal across the inductance from an intermediate setpoint value of the current through the phase module.

2. The method as claimed in claim 1 , wherein:

each switching cell includes four drivable bidirectional power semiconductor switches with a controlled unidirectional current guidance direction;

the power semiconductor switches are connected in the manner of a bridge circuit, and a capacitive energy storage means which is connected parallel to the bridge circuit of the power semiconductor switches;

the phase module includes at least one further two-pole switching cell, which is connected into the series connection, for switching at least one positive and at least one negative voltage between the poles; and

the intermediate setpoint value of the current through the phase module is formed from a sum of the voltages across the capacitive energy storage means of the switching cells of the phase module and from a sum voltage setpoint value.

3. The method as claimed in claim 2 , wherein the intermediate setpoint value of the current through the phase module is formed from a predefinable controller function.

4. The method as claimed in claim 3 , wherein the intermediate setpoint value of the current through the phase module is formed from a predefinable decoupling matrix which serves to decouple circulating currents through the phase modules for the currents in the output phase connections.

5. An apparatus for operating a converter circuit, wherein the converter circuit includes n input phase connections and p output phase connections, where n≧2 and p≧2, and (n·p) two-pole switching cells for switching at least one positive and at least one negative voltage between the poles, wherein each output phase connection is connected in series to each input phase connection in each case by means of a switching cell, respectively, and each switching cell has drivable bidirectional power semiconductor switches with a controlled unidirectional current guidance direction, and a capacitive energy storage means, wherein the apparatus comprises:

a drive circuit configured to generate a drive signal, the drive circuit being connected to the power semiconductor switches of the switching cell;

at least one inductance connected into each series connection, with a switching cell together with an inductance in each case forming a phase module, and, in respect of each phase module, a sum of a reference signal in respect of a voltage across the phase module and of a voltage signal across the inductance being supplied to the drive circuit for forming the drive signal; and

for each phase module, a first calculation unit for forming the voltage signal across the inductance from an intermediate setpoint value of the current through the phase module.

6. The apparatus as claimed in claim 5 , wherein:

each switching cell includes four drivable bidirectional power semiconductor switches with a controlled unidirectional current guidance direction;

the power semiconductor switches are connected in the manner of a bridge circuit, and a capacitive energy storage means which is connected parallel to the bridge circuit of the power semiconductor switches;

the phase module includes at least one further two-pole switching cell, which is connected into the series connection, for switching at least one positive and at least one negative voltage between the poles; and

for each phase module, the apparatus includes a second calculation unit for forming the intermediate setpoint value of the current through the phase module from a sum of the voltages across the capacitive energy storage means of the switching cells of the phase module and from a sum voltage setpoint value.

7. The apparatus as claimed in claim 6 , wherein the second calculation unit is configured to form the intermediate setpoint value of the current through the phase module from a predefinable controller function.

8. An apparatus for operating a converter circuit, wherein the converter circuit includes n input phase connections and p output phase connections, where n≧2 and p≧2, and (n·p) two-pole switching cells for switching at least one positive and at least one negative voltage between the poles, each output phase circuit being connected in series to each input phase connection in each case by means of a switching cell, respectively, and each switching cell having drivable bidirectional power semiconductor switches with a controlled unidirectional current guidance direction, and a capacitive energy storage means, wherein the apparatus comprises:

a drive circuit configured to generate a drive signal, the drive circuit being connected to the power semiconductor switches of the switching cell;

at least one voltage connected into each series connection, with a switching cell together with an inductance in each case forming a phase module, and, in respect of each phase module, the sum of a reference signal in respect of the voltage across the phase module and of a voltage signal across the inductance being supplied to the drive circuit for forming the drive signal; and

for all the phase modules, a common first calculation unit for forming the voltage signal across the inductance of the respectively associated phase module from an intermediate setpoint value of the current through the phase module.

9. The apparatus as claimed in claim 8 , wherein:

each switching cells includes four drivable bidirectional power semiconductor switches with a controlled unidirectional current guidance direction;

the power semiconductor switches are connected in the manner of a bridge circuit, and a capacitive energy storage means which is connected parallel to the bridge circuit of the power semiconductor switches;

the phase module additionally has at least one further two-pole switching cell, which is connected into the series connection, for switching at least one positive and at least one negative voltage between the poles, and, for all the phase modules, a common second calculation unit for forming the intermediate setpoint value (Δi U1 ) of the current (i U1 ) through all the phase modules from a sum (Usum 1 ) of the voltages across the capacitive energy storage means of the switching cells of the phase modules and from a sum voltage setpoint value (V ref,UC ) is provided.

10. The apparatus as claimed in claim 9 , wherein the common second calculation unit is configured to form the intermediate setpoint value of the current through the phase modules from a predefinable controller function.

11. The apparatus as claimed in claim 10 , wherein the common second calculation unit is configured to form the intermediate setpoint value of the current through phase modules from a predefinable decoupling matrix which decouples circulating currents through the phase modules from the currents in the output phase connections.