Converter with additional voltage addition or subtraction at the output

• US 6,621,719 B2
• Filed: 04/17/2002
• Issued: 09/16/2003
• Est. Priority Date: 04/25/2001
• Status: Active Grant

• Current Assignee: ABB Schweiz AG (ABB Limited)
• Original Assignee: ABB Schweiz AG (ABB Limited)
• Inventors: Steimer, Peter, Veenstra, Martin
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/123,321
• Publication Number:
  US 20030026111A1
• Time in Patent Office: 517 Days
• Field of Search: 363/71, 363/43, 363/63, 363/65, 363/129, 363/132, 363/136, 307/82, 307/45, 327/129
• US Class Current: 363/43
• CPC Class Codes: H02M 1/0095 Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
• CPC Class Codes: H02M 7/4835 comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters

Abstract

A circuit for transmitting real power from a DC voltage side to AC voltage-side connections has a first power converter (4) with load connections (5) connected in series with second power converters (7) having a lower intermediate-circuit capacitor voltage. This allows finer voltage graduation of a sum voltage at the AC voltage-side connections (10). Voltages of intermediate-circuit capacitances of power converters (4, 7) and a common-mode voltage of the AC voltage-side connections can be jointly regulated. The intermediate-circuit capacitor voltages can be kept essentially constant. The second power converters (7) can interchange real power with a load (11) and the first power converter (4). Changes in the intermediate-circuit capacitor voltages can be calculated in advance using a model of the converter. The common-mode voltage can be selected to minimize a weighted sum of the squares of the errors between the intermediate-circuit capacitor voltages and the respective nominal values.

Claims

1. A power-electronic circuit arrangement for transmitting real power from a DC voltage-side to at least two AC voltage-side connections or vice versa, comprising

a first power converter which is connected to a DC voltage source with a first intermediate-circuit capacitor voltage and has at least two load connections,

and at least one second power converter, which is connected to one of the load connections and is connected to an AC voltage-side connection, and which has a second intermediate-circuit capacitor voltage and in which case, by means of the second power converter, one or more of:

the positive second intermediate-circuit capacitor voltage, the negative second intermediate-circuit capacitor voltage or zero volts can be added to a voltage value which can be connected by the first power converter to its load connection,

wherein the at least one second power converter does not have its own power supply means.

2. The circuit arrangement as claimed in claim 1, wherein the circuit arrangement has a regulating device for joint regulation of at least one intermediate-circuit capacitor voltage of the at least one second power converter, and a common-mode voltage at the AC voltage-side connections of the circuit arrangement, as well as means for driving semiconductor switches in the first power converter and in the at least one second power converter on the basis of output variables from this regulating device.

3. The circuit arrangement as claimed in claim 2, wherein the regulating device is designed for regulating an intermediate-circuit capacitor voltage of the first power converter.

4. The circuit arrangement as claimed in claim 2, wherein the regulating device is designed for minimizing a weighted sum of the squares of the errors between the regulated intermediate-circuit capacitor voltages, the common-mode voltage and any rate of change of the common-mode voltage and a respective nominal value.

5. The circuit arrangement as claimed in claim 2, wherein the regulating device has a converter model for predicting the regulated intermediate-circuit capacitor voltages as a function of the common-mode voltage and of further system variables.

6. The circuit arrangement as claimed in claim 1, wherein two second power converters are in each case connected in series between a load connection and an AC voltage-side connection, with each of these second power converters being connected via a first bridge connection of a first converter bridge and via a second bridge connection of a second converter bridge, and having a second DC voltage intermediate circuit with a second intermediate-circuit capacitor voltage, which is connected in parallel with the first and second converter bridges.

7. A method for transmitting real power by means of power-electronic circuit arrangement from a DC voltage side to at least two AC voltage-side connections of the circuit arrangement, or vice versa, with

a) an associated voltage value being connected to each of at least two load connections of the first power converter by means of said first power converter, which is connected to a DC voltage source with a first intermediate-circuit capacitor voltage,

b) one or more of:

the positive second intermediate-circuit capacitor voltage, the negative second intermediate-circuit capacitor voltage or zero volts being added to the voltage value of the load connection by means of at least one second power converter, which is connected to one of the load connections and is connected to an AC-voltage side connection and has a second intermediate-circuit capacitor voltage, wherein

c) at least one intermediate-circuit capacitor voltage of the at least one second power converter and one common-mode voltage of the AC voltage-side connections of the circuit arrangement are regulated by means of joint regulation, and

d) semiconductor switches for the first power converter and for the at least one second power converter are driven on the basis of output variables from this regulating device.

8. The method as claimed in claim 7, wherein the joint regulation regulates an intermediate-circuit capacitor voltage of the first power converter.

9. The method as claimed in claim 7, wherein a cost function, which is a weighted sum of the squares of the errors between the regulated voltages and a respective nominal value, is minimized, so that the regulated intermediate-circuit capacitor voltages are regulated, averaged over time, essentially at constant values, and in that variation of the common-mode voltage is permissible.

10. The method as claimed in claim 7, wherein a cost function, which is a weighted sum of the squares of the errors between the regulated voltages and a respective nominal value, is minimized, so that the regulated intermediate-circuit capacitor voltages are regulated, averaged over time, essentially at constant values, and in that any variation of the common-mode voltage is minimized.

11. The method as claimed in claim 9, wherein the following steps are carried out:

a) prediction of a change in the regulated intermediate-circuit capacitor voltages as a function of the common-mode voltage and of further system variables by means of a converter model for sampling regulation at a first sampling time,

b) the establishment of a common-mode voltage, which minimizes the cost function at at least a next sampling time, by means of optimization,

c) the addition of this common-mode voltage to load voltage nominal values, which are predetermined for driving the load, of the AC voltage-side connections, thus resulting in modified load voltage nominal values at the respective AC voltage-side connections,

d) driving or modulation of the first power converter and of the at least one second power converter on the basis of these modified load voltage nominal values.