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EP-4742524-A1 - BALANCED VOLTAGE GENERATION SYSTEM AND POWER CONVERSION SYSTEM INCLUDING SAID BALANCED VOLTAGE GENERATION SYSTEM

EP4742524A1EP 4742524 A1EP4742524 A1EP 4742524A1EP-4742524-A1

Abstract

The invention provides a voltage generation system (100), comprising: an input bus (10) providing a direct current input voltage (E inv ); an inverter (20) configured to deliver a square voltage (v inv ) at its output (T r+ , T r- ); N resonant power blocks (25 1 , ..., 25 n , ..., 25 N ), where N>1, each connected to its respective input in parallel with the output of the inverter (20), wherein each resonant power block (25 1 , ..., 25 n , ..., 25 N ) comprises a series resonant capacitor (C r1 , C r2 , ...), a single-phase transformer (40 1 , ..., 40 n , ..., 40 N ), a rectifier (50 1 , ..., 50 n , ..., 50 N ), an output capacitor (C 1s,1 ..., C s,n , ..., C s,N ) and a direct current bus (60 1 , ..., 60 n , ..., 60 N ) connected to the output (T 1+ , T 1- ; ..., T n+ , T n- ;..., T N+ , T N- ) of a respective rectifier (50 1 , ..., 50 n , ..., 50 N ), with each resonant power block (25 1 , ..., 25 n , ..., 25 N ) being configured to operate in discontinuous conduction mode with a constant voltage gain independent of the operating power; wherein the inverter (20) is configured to switch to a frequency less than or equal to the resonance frequency of the resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) and to operate in discontinuous conduction mode (DCM), with each resonant power block (25 1 , ..., 25 n , ..., 25 N ) being configured to deliver a rectified voltage (E rect,1 , E rect,2 , E rect,3 ) to each respective direct current bus (60 1 , ..., 60 n , ..., 60 N ), with each rectified voltage (E rect,1 , ..., E rect,n , ..., E rect,N ) being constant and proportional to the direct current voltage (E inv ) of the input bus (10); the voltage generation system (100) offering a rectified voltage level (E rect,1 , ..., E rect,n , ..., E rect,N ) for each resonant power block (25 1 , ..., 25 n , ..., 25 N ).

Inventors

  • LAREQUI GARAYOA, Iñaki
  • ZABALETA MAEZTU, MIKEL
  • ELIZONDO MARTÍNEZ, David
  • BARRIOS RÍPODAS, Ernesto L.
  • SANCHÍS GÚRPIDE, Pablo
  • URSÚA RUBIO, Alfredo

Assignees

  • Ingeteam Power Technology, S.A.

Dates

Publication Date
20260513
Application Date
20230704

Claims (14)

  1. A voltage generation system (100), comprising: an input bus (10) providing a direct current input voltage (E inv ); an inverter (20) configured to deliver a square voltage (v inv ) at its output (T r+ , T r- ); N resonant power blocks (25 1 , ..., 25 n , ..., 25 N ), where N>1, each connected at its respective input in parallel at the output of the inverter (20), wherein each resonant power block (25 1 , ..., 25 n , ..., 25 N ) comprises a series resonant capacitor (C r1 , C r2 , ...), a single-phase transformer (40 1 , ..., 40 n , ..., 40 N ), a rectifier (50 1 , ..., 50 n , ..., 50 N ), an output capacitor (C 1s,1 ..., C s,n , ..., C s,N ) and a direct current bus (60 1 , ..., 60 n , ..., 60 N ) connected to the output (T 1+ , T 1- ; ..., T n+ , T n- ;..., T N+ , T N- ) of a respective rectifier (50 1 , ..., 50 n , ..., 50 N ), each resonant power block (25 1 , ..., 25 n , ..., 25 N ) being configured to operate in discontinuous conduction mode with a constant voltage gain independent of the operating power; wherein the inverter (20) is configured to switch at a frequency less than or equal to the resonance frequency of the resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) and to operate in discontinuous conduction mode (DCM); each resonant power block (25 1 , ..., 25 n , ..., 25 N ) being configured to deliver a rectified voltage (E rect,1 , E rect,2 , E rect,N ) to each respective direct current bus (60 1 , ..., 60 n , ..., 60 N ), each rectified voltage (E rect,1 , ..., E rect,n , ..., E rect,N ) being constant and proportional to the direct current voltage (E inv ) of the input bus (10), the voltage generation system (100) offering a rectified voltage level (E rect,1 , ..., E rect,n , ..., E rect,N ) for each resonant power block (25 1 , ..., 25 n , ..., 25 N ).
  2. The voltage generation system (100) of claim 1, wherein at least one of the resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) is different from the others and has a different rated power from the rest.
  3. The voltage generation system (100) of claim 1, wherein the resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) are all equal to each other.
  4. The voltage generation system (100) of any of claims 1 or 2, wherein the single-phase transformer (40 1 , ..., 40 n , ..., 40 N ) of at least one of the resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) has a different transformation ratio than the transformation ratio of the single-phase transformer of the rest of the resonant power blocks.
  5. The voltage generation system (100) of any of claims 1-4, wherein the inverter (20) is configured as an H-bridge formed by two branches, a first branch formed by two diodes (D 1 , D 2 ) in anti-parallel with their respective switches (S 1 , S 2 ), and a second branch formed by two diodes (D 3 , D 4 ) in anti-parallel with their two respective switches (S 3 , S 4 ).
  6. The voltage generation system (100) of any of claims 1-5, wherein the inverter (20) is operated with a branch duty cycle of approximately 50%.
  7. The voltage generation system (100) of any of claims 1-6, wherein the input bus (10) is connected to a power source or to a power storage system, either directly or indirectly, for example through contactors or through a power electronics converter.
  8. The voltage generation system (100) of any of claims 1-7, wherein the output of each resonant power block of the plurality of resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) is connected in series to the output of another resonant power block of the plurality of resonant power blocks (25 1 , ..., 25 n , ..., 25 N ).
  9. The voltage generation system (100) of any of claims 1-7, wherein the output of at least one resonant power block of the plurality of resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) is independent of the outputs of the rest of the resonant power blocks.
  10. A power conversion system (1000) comprising: a voltage generation system (100) according to any of claims 1-9 and a regulating converter (200) having a plurality of inputs and providing an output voltage (E out ) at its output, the direct current bus (60 1 , ..., 60 n , ..., 60 N ) of each resonant power block (25 1 , ..., 25 n , ..., 25 N ) of the voltage generation system (100) being connected to an input of the regulating converter (200).
  11. The power conversion system (1000) of claim 10, wherein the voltage generation system (100) is a voltage generation system (100) according to claim 8, wherein the regulating converter (200) has N inputs, and wherein the output voltage (E out ) of the regulating converter (200) provides a voltage level that can be selected from among at least N+1 different voltage levels from N different voltage levels provided by the voltage generation system (100), each of the N voltage levels being a respective input of the N inputs of the regulating converter (200).
  12. The power conversion system (1000) of claim 10, wherein the voltage generation system (100) is a voltage generation system (100) according to any of claims 1-7, wherein pairs of resonant power blocks (25 1 , ..., 25 n , ..., 25 N ) have their respective outputs connected in series, and wherein each pair of output buses (60 1 , 60 2 ; 60 3 , 60 4 ) of each respective pair of resonant power blocks is connected to a regulating converter (200 1-2 , 200 3-4 ) that provides an output voltage (T o+,a - T o-,a ; T o+,b - T o-,b ) at its output, said regulating converters (200 1-2 , 200 3-4 ) being connected in series with each other at the output.
  13. Use of the power conversion system (1000) of any one of claims 10-12, for recharging an electric vehicle, wherein the regulating converter (200) is a direct current-direct current (DC/DC) converter, in which some recharging poles of the electric vehicle are connected to the output poles (T o+ T o- ) of the regulating converter (200).
  14. Use of the power conversion system (1000) of any one of claims 10-12, for a photovoltaic power generation system, wherein the regulating converter (200) is a direct current-direct current (DC/DC) converter or a direct current-alternating current (DC/AC) converter.

Description

FIELD OF THE INVENTION The present invention belongs to the field of power electronics and, more specifically, to multilevel converters that provide several voltage levels. PRIOR STATE OF THE ART Multilevel converters are widely used in all types of industrial applications, such as in power generation systems that use renewable sources (for example, photovoltaic and wind sources), in solid-state transformers (SST) for high voltage direct current (HVDC) grids, in static synchronous compensators (STATCOM), in electric vehicle chargers, in railway and marine traction, and in medium and high-power drive systems (L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo and M. A. M. Prats, "The age of multilevel converters arrives", in IEEE Industrial Electronics Magazine, vol. 2, no. 2, pp. 28-39, June 2008, doi: 10.1109/MIE.2008.923519; S. Kouro et al., "Recent Advances and Industrial Applications of Multilevel Converters", in IEEE Transactions on Industrial Electronics, vol. 57, no. 8, pp. 2553-2580, Aug. 2010, doi: 10.1109/TIE.2010.2049719). Topologies of this type are especially used in DC/AC applications and also often in DC/DC applications. Multilevel converters must have different levels of direct current input voltage. To do this, multilevel converters start from a current bus divided into N voltage levels that can be equal or have different values (asymmetrical). From this bus, multiple voltage levels are obtained per branch at the output, typically N+1 levels, achieving better quality in the output waveform and allowing a lower filtering requirement in the converter (if compared to two-level converters). Furthermore, they allow the cut-off voltage of the semiconductors to be reduced for one same application voltage, reducing both the switching losses and the conduction losses, thus obtaining greater efficiency. They also allow better thermal management of the converter, which is a very relevant factor in high power converters. The N voltage levels at the input of the converter can be obtained in several ways. One of them is through several direct current sources. Another way is through capacitive dividers (capacitors connected in series) that should ideally behave as voltage sources. However, capacitors are charged/discharged based on the current or power that they deliver/absorb, where the voltage at their terminals can vary. The greatest drawback of these multilevel topologies is that it must be ensured that the voltage is suitably distributed among the different bus capacitors at all times, meaning that the correct balancing of the capacitor voltages must be ensured so that each capacity acts as a constant voltage source (direct current level). This task is often carried out by the control system of the converter. The balancing of capacitor voltages has been and continues to be a subject of great interest both in the industrial field and in academic research. A complete review of the different methods for balancing these voltages can be found in S. Alepuz et al., "A Survey on Capacitor Voltage Control in Neutral-Point-Clamped Multilevel Converters", Electronics, vol. 11, no. 4, p. 527, Feb. 2022, doi: 10.3390/electronics11040527. The methods for balancing capacitor voltages can be grouped according to their operating principle: 1. Hardware balancing: it consists of including additional components to balance the voltages. In turn, the different solutions can be classified into: a) Active hardware: voltage balancing circuits connected to the voltage point to be balanced are included and the capacitor voltages are actively balanced by means of control loops. These circuits can be dedicated DC/DC converters for each of the capacitors (as described, for example, in K. A. Corzine, J. Yuen and J. R. Baker, "Analysis of a four-level DC/DC buck converter", in IEEE Transactions on Industrial Electronics, vol. 49, no. 4, pp. 746-751, Aug. 2002, doi: 10.1109/TIE.2002.801075) or additional multilevel branches connected to the point which voltage is to be balanced, forming "four-legged or branched" inverters (as described, for example, in Ning-Yi Dai, Man-Chung Wong and Ying-Duo Han, "Application of a three-level NPC inverter as a three-phase four-wire power quality compensator by generalized 3DSVM", in IEEE Transactions on Power Electronics, vol. 21, no. 2, pp. 440-449, March 2006, doi: 10.1109/TPEL.2005.869755).b) Passive hardware with natural balancing: it consists of introducing a series RLC circuit in the output of the multilevel converter called a "balancing circuit" (see, for example, H. du Toit Mouton, "Natural balancing of three-level neutral-point-clamped PWM inverters", in IEEE Transactions on Industrial Electronics, vol. 49, no. 5, pp. 1017-1025, Oct. 2002, doi: 10.1109/TIE.2002.803205). This circuit responds to the frequencies at which voltage components appear at the output when there is a voltage imbalance. In this way, it dissipates power at those frequencies, making it possible to balance