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EP-4742486-A1 - SYSTEM AND METHOD FOR PREVENTING RENEWABLE SOURCES POWER TRANSFER FAULTS IN A GRID-CONNECTED CONVERTER

EP4742486A1EP 4742486 A1EP4742486 A1EP 4742486A1EP-4742486-A1

Abstract

The present invention is related to an electric power system for controlling and improving power availability to a load (5), said system comprising a renewable energy generating unit (1) for producing DC power, and connected to an external non-controlled inverter (2) ; an AC load (5) ; an electric energy storage unit (4) ; a converter (3) having a bidirectional output AC port (34), a DC port (33) and, optionally, an input AC port (32) that may be grid-interactive ; and optionally an AC grid (8) ; wherein said input AC port (32) is normally connected to the AC grid (8) as the case may be, said bidirectional output AC port (34) is normally connected to the inverter (2) and to the load (5) and said DC port (33) is normally connected to the electric energy storage unit (4) ; characterized in that the converter (3) is equipped with an internal device (6) which is capable to store or dissipate an energy amount otherwise entering into the converter (3) that goes up to or above the nominal power of the converter (3) multiplied by a predetermined time, preferably 200ms, and more preferably 300 ms.

Inventors

  • MILSTEIN, François
  • Joannes, Thierry
  • FUCITO, Amory
  • VAN DOORNE, Bente
  • FREBEL, FABRICE
  • BIDAINE, BENOIT

Assignees

  • CE+T Power Luxembourg SA

Dates

Publication Date
20260513
Application Date
20241108

Claims (15)

  1. An electric power system for controlling and improving power availability to a load (5), said system comprising : - an renewable energy generating unit (1) for producing DC power, and connected to an external non-controlled inverter (2) ; - an AC load (5) ; - an electric energy storage unit (4) ; - a converter (3) having a bidirectional output AC port (34), a DC port (33) and, optionally, an input AC port (32) that may be grid-interactive ; - optionally an AC grid (8) ; wherein said input AC port (32) is normally connected to the AC grid (8) as the case may be, said bidirectional output AC port (34) is normally connected to the inverter (2) and to the load (5) and said DC port (33) is normally connected to the electric energy storage unit (4) ; characterized in that the converter (3) is equipped with an internal device (6) which is capable to store or dissipate an energy amount otherwise entering into the converter (3) that goes up to or above the nominal power of the converter (3) multiplied by a predetermined time, preferably 200ms, and more preferably 300 ms.
  2. The electric power system according to claim 1, wherein said internal device (6) comprises a resistor, a capacitor or a supercapacitor.
  3. The electric power system according to claim 1, wherein said internal device (6) is a power supply safety module connected in parallel to said converter (3) between said input AC port (32) and said output AC port (34), said power supply safety module (6) being configured to protect the converter (3) by providing an additional current limited to a multiple α, α integer>1, of the nominal input current flowing in the converter, α.In out , at the output AC port (34), in case of detecting an excess of incoming power condition at or downstream of the output AC port (34) so as to absorb, i.e. dissipate or store, the corresponding excess energy during said predetermined time.
  4. The electric power system according to claim 3, wherein the power supply safety module (6) comprises a bidirectional switch (7), control means (71) for closing said bidirectional switch (7) and a current limiter (9), preferably an impedance, connected in series to said bidirectional switch (7) to limit the current that can flow through the power supply safety module (6) to a maximum current of α.In out , wherein α has a value between 5 and 20, preferably between 7 and 13, and most preferably about 10.
  5. The electric power system according to claim 4, wherein the current limiter (9) is a resistor R boost .
  6. The electric power system according to claim 5, wherein the converter (3) is driven to generate a voltage on its input AC port (32) to help dissipating the excess energy through the power supply safety module (6), according to : P boost = V ACout − V ACin 2 R boost
  7. The electric power system according to claim 4, wherein the bidirectional switch (7) is a triac.
  8. The electric power system according to claim 1, wherein the renewable energy generating unit (1) comprises a photovoltaic, or PV, generation system, a wind generation system, a hydroelectricity generation system, a biomass generator, or fuel cells.
  9. The electric power system according to claim 1, wherein the electric energy storage unit (4) comprises a battery.
  10. The electric power system according to claim 1, wherein the AC grid (8) is a utility grid, such as a national grid, regional grid, microgrid, or smartgrid.
  11. The electric power system according to claim 1, wherein the DC port (33) and the input AC port (32) are bidirectional.
  12. A method for protecting the converter (3) in the electric power system for controlling and improving power availability to a load (5) according to anyone of claims 3 to 11, in case an excess of incoming power is detected at the output AC port (34) of the converter (3), comprising the steps of : - detecting an excess of incoming power at or downstream of the output AC port (34) ; - opening a relay at the input AC port (32) ; - closing said bidirectional switch (7) ; - providing an additional current corresponding to a multiple α, α integer>1, of the nominal input current, α.In out , in the power backup circuit (6) connected in parallel to the converter (3) between the input AC port (32) and the output AC port (34), wherein α has a value between 5 and 20, so as to dissipate the excess energy corresponding to the excess of incoming power during a predetermined time ; - forcing shutdown of the external non-controlled inverter (2) owing to AC voltage increase at the output AC port (34) ; - when the system has returned to predetermined conditions, opening said bidirectional switch (7) ; - closing the relay at the input AC port (32).
  13. The method according to claim 12, wherein an excess of incoming power condition to be detected is that the power flowing into the converter (3) is greater than the sum of the power flowing into the AC grid (8) and the power flowing into the electric energy storage unit (4).
  14. The method according to claim 12, wherein an excess of incoming power condition to be detected is that, in case the system has no grid (8) or has a converter AC input (32) fed by a genset or by any power generator that cannot receive power, the electric energy storage unit (4) is suddenly disconnected.
  15. The method according to claim 12, wherein an excess of incoming power condition to be detected is that, in case the system has no grid (8) or has a converter AC input (32) fed by a genset or any power generator that cannot receive power, and the electric energy storage unit (4) is power limited or already loaded, the load (5) is suddenly shed.

Description

Field of the Invention The present invention relates to systems equipped with electrical source (e.g. grid, genset) - connected converters and to methods capable, in such systems, to manage parameters governing power transfer between an energy generation system and the electrical source, in particular in fault conditions or load impact. The range of applications producing DC current to be converted to AC current in a grid encompasses for example photovoltaic (PV) generation systems, wind generation systems, micro-hydroelectricity generation systems, biomass generators, fuel cells, renewable energy storage systems such as batteries and other renewable energy systems, and high-voltage DC (HVDC) transmission. Background and Prior Art Today, there is a worldwide endeavour to substitute traditional energy sources based on fossil fuels with renewable energy. This wide-ranging transformation stems from the consensus that fossil fuels have been identified as major contributors mainly to environmental contamination, climate change, and greenhouse effect. With the significant development of renewable energy sources, there has been a corresponding increase in the demand for power converters, as the conversion of direct current energy into alternating current energy becomes imperative. Typically, grid-connected converters are required to achieve this conversion. Grid-connected converters are frequently utilized in energy transfer management of systems such as those in which renewable energy sources or storage installations are interconnected with an electrical grid. Usually the electrical grids mentioned in this application are utility AC grids, also known as electrical utility grids, which are generally the systems responsible for generating, transmitting, and distributing electricity to consumers. These grids can vary in structure, size, and complexity depending on the geographic region, population density, and available resources. Some examples of AC utility grids are national grids, regional grids, microgrids, smartgrids, etc. Further, based on two observations, firstly the generalized need for electrification in replacement of fossil fuels and secondly that storage systems are becoming popular for businesses and homes to store energy from solar panels for a future use, an interest is seen for two parties to collaborate. On the one side, the AC electrical grid has a demand for energy while on the other side, the prosumers have an excess of energy that shall be stored and managed. In this respect regulators have taken proactive measures, such as implementing so-called grid-interactive certifications, to facilitate this collaboration. There are several standards for grid-interactive energy storage systems (e.g. EN50549, VDE4105 and AS4777.2). These certifications ensure the safety, interoperability, and compatibility of the systems with the electrical grid. They aim at harmonizing the technical requirements for the connection of decentralized energy resources capable of operating in parallel with the grid. Concretely, the "grid-interactive" functionality of an energy storage system allows it to work seamlessly with the electrical grid. This functionality provides several benefits : increased energy efficiency (reduce energy waste and increase overall energy efficiency) ; improved grid stability (stabilize the electrical grid, even out the fluctuations in the grid caused by the unpredictable nature of renewable energy sources and reduce the need for traditional power plants) and revenue generation for prosumers with grid-interactive energy storage systems (power utilities offering incentives to participate in balancing services, so providing an additional source of revenue). The applicant already brought to market a power converter module, branded as Sierra™ and equipped with the so-called ECI™ technology (for Enhanced Conversion Innovation), which will be simply named below as "the (grid-interactive) converter". This converter is able to play a key role in the needed solution. It is a triple port bidirectional AC/DC/AC converter, with two independent AC ports. ECI™ is a UPS modular technology with: no single point of failure; high MTBF; true redundancy; best in-class protection to disturbances; and no maintenance (or maintenance-free technology). As shown in FIG. 1, each ECI module 3 has an AC bi-directional input 32 and a DC bi-directional input 33, while providing a pure sine wave output 34 that is also bi-directional. The ECI™ is patented under US 8,044,535 B2. The block diagram depicted in FIG. 2 gives an explicit description of the full topology of the converter embodiment and its operation. The power flows either from AC or DC source under the control of a DSP controller. Thanks to the converter's internal energy buffering, transferring connection of the load between two input sources is achieved instantly. The converter is capable to detect short circuit conditions at the AC output level and activate a dedicat