WO2019202016A1 - Hybrid converter and control method thereof - Google Patents

Hybrid converter and control method thereof Download PDF

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Publication number
WO2019202016A1
WO2019202016A1 PCT/EP2019/059964 EP2019059964W WO2019202016A1 WO 2019202016 A1 WO2019202016 A1 WO 2019202016A1 EP 2019059964 W EP2019059964 W EP 2019059964W WO 2019202016 A1 WO2019202016 A1 WO 2019202016A1
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WO
WIPO (PCT)
Prior art keywords
voltage
bus
current source
power
direct current
Prior art date
Application number
PCT/EP2019/059964
Other languages
French (fr)
Inventor
Andres Agudo Araque
Original Assignee
Siemens Gamesa Renewable Energy Innovation & Technology S.L.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Gamesa Renewable Energy Innovation & Technology S.L. filed Critical Siemens Gamesa Renewable Energy Innovation & Technology S.L.
Publication of WO2019202016A1 publication Critical patent/WO2019202016A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S10/00—PV power plants; Combinations of PV energy systems with other systems for the generation of electric power
    • H02S10/10—PV power plants; Combinations of PV energy systems with other systems for the generation of electric power including a supplementary source of electric power, e.g. hybrid diesel-PV energy systems
    • H02S10/12—Hybrid wind-PV energy systems
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

Definitions

  • the object of the present invention is a hybrid converter and the control method thereof, particularly a hybrid converter for wind systems combined with photovoltaic systems or battery banks .
  • wind generators use a wind converter or power converter in back-to-back topology.
  • This back-to-back topology converter is characterized by coupling two three phase bridges by means of a DC bus, wherein the first three phase bridge (AC/DC) is connected to the wind generator and the second three phase bridge (DC/AC) is connected to the electricity grid.
  • Alternating voltage of the electricity grid is limited and defined in the in the grid codes, thereby being usual that wind generators include a set-up transformer which allows increasing voltage from 690Vrms to the average voltage of the wind plant.
  • power converter for photovoltaic systems commonly referred to as photovoltaic inverters
  • photovoltaic inverters have single conversion step that would be equivalent to the second three phase bridge (DC/AC) connected to the wind back-to-back converter network. Therefore, photovoltaic panels are directly connected to the DC bus, wherein the first three phase bridge (AC/DC) of a wind converter is not necessary.
  • connection of photovoltaic panels to the DC bus has been considered in hybrid generation systems so as to reduce the number of power elements, as well as the installation costs.
  • the DC bus voltage ranges of the back-to-back topology power converter and the DC bus of the operating photovoltaic systems do not make this direct coupling possible, since currently the direct voltage ranges of each converter are different, particularly for the back-to-back power converter between 1000 and 1200VDC and for the operating photovoltaic system between 900 and 1500VDC.
  • Chen describes a multi-input hybrid converter consisting of a multi-input DC-DC converter of the buck/buck- boost type fused with a full-bridge (DC-AC) inverter, where an input is intended for the wind system and another input for the photovoltaic system, and the output of the full-bridge inverter (DC/AC) is connected to the electricity grid.
  • DC-AC full-bridge inverter
  • the hybrid converter used comprises a Cuk- SEPIC converter, that is, two fused converters (DC/DC) which can supply electricity to the load separately, that is, only from the photovoltaic system or from the wind system, or together (both systems) according to the availability of both energy sources.
  • DC/DC fused converters
  • This hybrid system is connected to grid through a three phase inverter (DC/AC) and is controlled to make the injected current to be sinusoidal.
  • a first aspect of the present invention describes a hybrid converter for connecting a rotating machine, preferably a wind system, combined with a direct current source, to an electricity grid, wherein the direct current source is preferably selected from a photovoltaic system with a maximum power point tracking (MPPT) device for the photovoltaic field or a battery bank with power and charge state control device.
  • MPPT maximum power point tracking
  • the hybrid converter comprises:
  • a power converter AC/AC, which in turn comprises a first AC/DC three phase bridge and a second DC/AC three phase bridge coupled to each other by means of a DC bus, where the first AC/DC three phase bridge is connected to the rotating machine, and the second DC/AC three phase bridge is connected to the electricity grid,
  • connection and disconnection unit configured for directly linking and unlinking the source of direct current with the DC bus
  • a measuring unit for measuring voltage and current of the DC bus to which the direct current source is connected control unit linked to the measuring unit and the connection and disconnection unit which in turn comprises:
  • control logic device • a control logic device, linked to the memory, where the instructions configure the control logic device for:
  • the predetermined voltage range of the DC bus com prises a first limit being the same as the minimum operating voltage of the rotating machine, and the second limit is the same as the maximum voltage of the direct current source.
  • the in structions configure the control logic device for:
  • the instructions configure the control logic device for:
  • connection and disconnection unit comprises a switch linked to the control unit configured for connecting the direct current source with the DC bus when the DC bus voltage is within the predetermined voltage range; and for disconnecting the direct current source from the DC bus when the DC bus voltage is out of the predetermined voltage range.
  • the instructions configure the control logic device for:
  • the instructions configure the control logic device also for:
  • a second aspect of the present invention describes a control method for the hybrid converter of the first aspect of the invention, wherein the control method comprises the following steps : • establishing a predetermined voltage range of the DC bus, and
  • control signals are sent to the second DC/AC three phase bridge, varying the DC bus voltage so as to drawn the desired power from the direct current source.
  • control signals are sent to the second DC/AC three phase bridge such that the power of the rotating machine is achieved at the maximum direct voltage.
  • the production of alternating power of the rotating machine is monitored, the production of the direct power is monitored, and the power drawn from the rotating machine and the power drawn from the direct current source are determined.
  • a hybrid converter is obtained that allows directly connecting, without any additional power step, a rotating machine with a direct current source, preferably wind systems with photovoltaic systems or battery banks, and adjusts levels of the DC bus voltage of the direct current source to the direct voltage levels of the rotating machine.
  • a direct current source preferably wind systems with photovoltaic systems or battery banks
  • Figure 1. It shows a hybrid converter according to the state of the art where the direct current source is a photovoltaic system.
  • Figure 2. It shows a graph of the voltage with a limited photovoltaic system arranged in the hybrid converter of Figure
  • Figure 3. It shows a graph of the voltage with a not limited photovoltaic system arranged in the hybrid converter of Figure
  • Figure 4.- It shows a hybrid converter according to the invention wherein the direct current source is a photovoltaic system.
  • Figure 5. It shows a graph of the voltage of the limited photovoltaic system arranged in the hybrid converter of Figure
  • Figure 6. It shows a graph of the voltage with a not limited photovoltaic system arranged in the hybrid converter of Figure
  • Figure 7.- It shows a hybrid converter according to the state of the art where the direct current source is a battery bank.
  • Figure 8.- It shows a graph of the voltage of the battery bank with high charge state arranged in the hybrid converter of Figure 7.
  • Figure 9. It shows a graph of the voltage of the battery bank with a low charge state arranged in the hybrid converter of Figure 7.
  • Figure 10.- It shows a hybrid converter according to the invention where the direct current source is a battery bank.
  • Figure 11.- It shows a graph of the voltage of the battery bank with high charge state arranged in the hybrid converter of Figure 10.
  • Figure 12. It shows a graph of the voltage of the battery bank with a low charge state arranged in the hybrid converter of Figure 10.
  • a first preferred embodiment of the invention is a hybrid converter (1) for connecting a rotating machine, which in this exemplary embodiment is a photovoltaic system (3) with a maximum power point tracking (MPPT) device for the photovoltaic field, to an electricity grid (4) .
  • MPPT maximum power point tracking
  • the hybrid converter (1) comprises an AC/AC power converter which in turn comprises a first and a second three phase bridge (5, 6) coupled to each other by means of a
  • the AC/AC power converter can have a two-level or multi-level topology.
  • the converter design must be capable of managing the open circuit maximum voltage of solar panels of the photovoltaic system (3) or the maximum operating voltage of a capacitor bank.
  • the photovoltaic system (3) allows configurations with open circuit voltages of 1500Vdc and when it is operating, the photovoltaic field voltage varies between 900 and 1500Vdc. Additionally, by means of the maximum power point tracking (MPPT) device for the photovoltaic field it is possible to situate the field voltage at the maximum point of the curve in Figures 2 to 5.
  • MPPT maximum power point tracking
  • hybrid converter (1) comprises:
  • connection and disconnection unit (7) configured for directly linking and unlinking, that is, electrically connecting without any previous treatment, the photovoltaic system (3) with the DC bus of the AC/AC power converter, a measuring unit (8) for measuring voltage and current of the DC bus connected to the direct current source,
  • control unit (9) linked to the connection/disconnection unit (7) and the measuring unit (8) .
  • the control unit (9) comprises: • a memory with the instructions and a predetermined voltage range in the electricity grid, in the rotating machine and in the direct current source, and
  • control logic device preferably a microprocessor, linked to the memory, wherein the instructions configure the microprocessor for:
  • the predetermined voltage range of the DC bus com prises a first limit being the same as the minimum operating voltage of the photovoltaic system (3) , in this case the same as 900Vdc, and the second limit is the same as the open cir cuit voltage of the photovoltaic system (3) , in this case in particular the same as 1500Vdc.
  • the instruc tions configure the microprocessor for:
  • the instructions configure the microprocessor for: • monitoring the production of direct power by means of maximum power point tracking (MPPT) device for the photovoltaic field,
  • MPPT maximum power point tracking
  • connection and disconnection unit comprises a switch, either electromechanical or solid state, linked to the control unit (9) configured for connecting the photovoltaic system (3) or the battery bank (10) with the DC bus when the DC bus voltage is within the predetermined voltage range; and for disconnecting the direct current source of the DC bus when the DC bus voltage is out of the predetermined voltage range.
  • the instructions configure the microprocessor for:
  • the invention describes a control method for the hybrid converter (1) described in the first preferred embodiment, where the control method is characterized in that it comprises the following steps:

Abstract

The present invention describes a hybrid converter and a control method thereof, particularly a hybrid converter for wind systems combined with photovoltaic systems or battery banks. Particularly, the hybrid converter comprises a power converter (AC/AC) which in turn comprises a first and a second three phase bridge (coupled to each other by means of a DC bus, wherein the first three phase bridge (AC/DC) is connected to the wind system and the second three phase bridge (DC/AC) is connected to the electricity grid and the photovoltaic system or the battery bank is directly connected, without converter (CC/CC) to the DC bus.

Description

Figure imgf000002_0001
HYBRID CONVERTER AND CONTROL METHOD THEREOF
OBJECT OF THE INVENTION
The object of the present invention is a hybrid converter and the control method thereof, particularly a hybrid converter for wind systems combined with photovoltaic systems or battery banks .
BACKGROUND OF THE INVENTION
Currently, it is known that the wind systems combined with photovoltaic systems are complementary, since habitually sunny days are days with low speed winds and cloudy days are usually related to strong winds. Thus, combination of these systems turns out to be highly reliable in order to produce electricity in a continuous way.
In spite of this, both wind systems and photovoltaic systems require power converters so as to adapt the electric energy generated to the quality requirements demanded by the electricity grid.
Usually, wind generators use a wind converter or power converter in back-to-back topology. This back-to-back topology converter is characterized by coupling two three phase bridges by means of a DC bus, wherein the first three phase bridge (AC/DC) is connected to the wind generator and the second three phase bridge (DC/AC) is connected to the electricity grid. Alternating voltage of the electricity grid is limited and defined in the in the grid codes, thereby being usual that wind generators include a set-up transformer which allows increasing voltage from 690Vrms to the average voltage of the wind plant. On the other hand power converter for photovoltaic systems, commonly referred to as photovoltaic inverters, have single conversion step that would be equivalent to the second three phase bridge (DC/AC) connected to the wind back-to-back converter network. Therefore, photovoltaic panels are directly connected to the DC bus, wherein the first three phase bridge (AC/DC) of a wind converter is not necessary.
Thus, currently, connection of photovoltaic panels to the DC bus has been considered in hybrid generation systems so as to reduce the number of power elements, as well as the installation costs.
However, the DC bus voltage ranges of the back-to-back topology power converter and the DC bus of the operating photovoltaic systems (that is, when these are connected to the photovoltaic inverter) , do not make this direct coupling possible, since currently the direct voltage ranges of each converter are different, particularly for the back-to-back power converter between 1000 and 1200VDC and for the operating photovoltaic system between 900 and 1500VDC.
A similar example of the hybrid converter connected to the electricity grid is described by Chen et al, in "Multi-Input Inverter for Grid-Connected Hybrid PV/Wind Power System". More particularly, Chen describes a multi-input hybrid converter consisting of a multi-input DC-DC converter of the buck/buck- boost type fused with a full-bridge (DC-AC) inverter, where an input is intended for the wind system and another input for the photovoltaic system, and the output of the full-bridge inverter (DC/AC) is connected to the electricity grid. The advantage of this system is that it does not require a DC/DC converter independently for each system to be coupled to the DC bus, since it uses a multi-input converter which can work with several inputs that do not require different generation technologies. In spite of this, in order to use said hybrid converter a first power converter (AC/DC) being linked to the wind system is required. Another similar example of the hybrid converter connected to the electricity grid is described by Saha et al . in "Fused converter topology for wind-solar hybrid systems". Saha discloses a hybrid energy system combining photovoltaic energy and wind energy for generating energy connected to the grid. The hybrid system is configured using separated pulse converters for the photovoltaic system and the wind system.
More particularly, the hybrid converter used comprises a Cuk- SEPIC converter, that is, two fused converters (DC/DC) which can supply electricity to the load separately, that is, only from the photovoltaic system or from the wind system, or together (both systems) according to the availability of both energy sources. This hybrid system is connected to grid through a three phase inverter (DC/AC) and is controlled to make the injected current to be sinusoidal.
Thus, currently, in order to solve this problem it is necessary to include a DC/DC converter that adjust the direct voltage levels of the photovoltaic system or of the battery banks to the direct voltage levels of the wind converter, by adding power elements to the system which complicate the control and reduce the hybrid system performance.
DESCRIPTION OF THE INVENTION
A first aspect of the present invention describes a hybrid converter for connecting a rotating machine, preferably a wind system, combined with a direct current source, to an electricity grid, wherein the direct current source is preferably selected from a photovoltaic system with a maximum power point tracking (MPPT) device for the photovoltaic field or a battery bank with power and charge state control device.
More particularly, the hybrid converter comprises:
a power converter, AC/AC, which in turn comprises a first AC/DC three phase bridge and a second DC/AC three phase bridge coupled to each other by means of a DC bus, where the first AC/DC three phase bridge is connected to the rotating machine, and the second DC/AC three phase bridge is connected to the electricity grid,
a connection and disconnection unit configured for directly linking and unlinking the source of direct current with the DC bus,
a measuring unit for measuring voltage and current of the DC bus to which the direct current source is connected, control unit linked to the measuring unit and the connection and disconnection unit which in turn comprises:
• a memory with instructions and a predetermined voltage range in the electricity grid, in the rotating machine and in the direct current source, and
• a control logic device, linked to the memory, where the instructions configure the control logic device for:
o establishing the predetermined voltage range in the DC bus, and
o regulating the DC bus voltage such that voltage in the DC bus is within the predetermined voltage range .
Preferably, the predetermined voltage range of the DC bus com prises a first limit being the same as the minimum operating voltage of the rotating machine, and the second limit is the same as the maximum voltage of the direct current source.
Preferably, in order to regulate the DC bus voltage, the in structions configure the control logic device for:
• monitoring, by means of the measuring unit, the voltage and DC bus current,
• determining a first voltage drawn from the direct current source,
• determining a second voltage drawn from the rotating machine and which is the same as the input voltage of the DC bus,
• defining the maximum DC voltage between the first voltage and the second voltage; and • defining the maximum DC voltage between the first voltage and the second voltage, and
• regulating, by means of the second DC/AC three phase bridge, the direct voltage to the maximum voltage previously defined and that must be within the predetermined voltage range.
Preferably, for determining the first voltage, the instructions configure the control logic device for:
• sending control signals to the second DC/AC three phase bridge, varying voltage of the DC bus so as to draw the desired power from the direct current source
Preferably, the connection and disconnection unit comprises a switch linked to the control unit configured for connecting the direct current source with the DC bus when the DC bus voltage is within the predetermined voltage range; and for disconnecting the direct current source from the DC bus when the DC bus voltage is out of the predetermined voltage range.
Preferably, for determining the second voltage the instructions configure the control logic device for:
• sending control signals to the second DC/AC three phase bridge, such that the rotating machine power is achieved at the maximum DC voltage defined above.
Preferably, for determining the second voltage the instructions configure the control logic device also for:
• monitoring the production of alternating power of the rotating machine, monitoring the production of direct power and determining the power drawn from the rotating machine and the power drawn from the direct current source
A second aspect of the present invention describes a control method for the hybrid converter of the first aspect of the invention, wherein the control method comprises the following steps : • establishing a predetermined voltage range of the DC bus, and
• regulating the DC bus voltage such that the voltage in the bus is within the predetermined voltage range.
Additionally, it comprises the following steps:
• monitoring, by means of the measuring unit, the voltage and the DC bus current,
• determining a first voltage drawn from the direct current source,
• determining a second voltage drawn from the rotating machine and which is the same as the input voltage of the DC bus .
• defining the regulating voltage for the DC bus as the maximum between the first voltage and the second voltage,
• sending control signals to the second DC/AC three phase bridge, for the DC bus voltage to be the maximum between the first voltage and the second voltage, and for it to be within the predetermined voltage range.
Preferably, in order to determine the first voltage, control signals are sent to the second DC/AC three phase bridge, varying the DC bus voltage so as to drawn the desired power from the direct current source.
Preferably, for determining the second voltage, control signals are sent to the second DC/AC three phase bridge such that the power of the rotating machine is achieved at the maximum direct voltage.
Preferably, for determining the second voltage, the production of alternating power of the rotating machine is monitored, the production of the direct power is monitored, and the power drawn from the rotating machine and the power drawn from the direct current source are determined.
Thus, a hybrid converter is obtained that allows directly connecting, without any additional power step, a rotating machine with a direct current source, preferably wind systems with photovoltaic systems or battery banks, and adjusts levels of the DC bus voltage of the direct current source to the direct voltage levels of the rotating machine.
Additionally, it allows using only one of the generating technologies when the other is not available, for example for maintenance reasons or because of the weather conditions.
DESCRIPTION OF THE DRAWINGS
To implement the present description being made and in order to provide a better understanding of the characteristics of the invention, according to a preferred practical embodiment thereof, a set of drawings is attached as part of this description, with an illustrative but not limitative purpose, which represents the following:
Figure 1.- It shows a hybrid converter according to the state of the art where the direct current source is a photovoltaic system.
Figure 2.- It shows a graph of the voltage with a limited photovoltaic system arranged in the hybrid converter of Figure
1.
Figure 3.- It shows a graph of the voltage with a not limited photovoltaic system arranged in the hybrid converter of Figure
1.
Figure 4.- It shows a hybrid converter according to the invention wherein the direct current source is a photovoltaic system.
Figure 5.- It shows a graph of the voltage of the limited photovoltaic system arranged in the hybrid converter of Figure
4. Figure 6.- It shows a graph of the voltage with a not limited photovoltaic system arranged in the hybrid converter of Figure
4.
Figure 7.- It shows a hybrid converter according to the state of the art where the direct current source is a battery bank.
Figure 8.- It shows a graph of the voltage of the battery bank with high charge state arranged in the hybrid converter of Figure 7.
Figure 9.- It shows a graph of the voltage of the battery bank with a low charge state arranged in the hybrid converter of Figure 7.
Figure 10.- It shows a hybrid converter according to the invention where the direct current source is a battery bank.
Figure 11.- It shows a graph of the voltage of the battery bank with high charge state arranged in the hybrid converter of Figure 10.
Figure 12.- It shows a graph of the voltage of the battery bank with a low charge state arranged in the hybrid converter of Figure 10.
PREFERRED EMBODIMENT OF THE INVENTION
A first preferred embodiment of the invention, such as it is shown in figure 1, is a hybrid converter (1) for connecting a rotating machine, which in this exemplary embodiment is a photovoltaic system (3) with a maximum power point tracking (MPPT) device for the photovoltaic field, to an electricity grid (4) .
Usually, alternating voltage of the electricity grid (4) is limited and defined in different grid codes and therefore, the wind system (2) and the photovoltaic system (3) must comply with those.
Particularly, the hybrid converter (1) comprises an AC/AC power converter which in turn comprises a first and a second three phase bridge (5, 6) coupled to each other by means of a
DC bus, wherein the first AC/DC three phase bridge (5) is connected to the wind system (2) and the second DC/AC three phase bridge (6) is connected to the electricity grid (4) .
Alternatively, the AC/AC power converter can have a two-level or multi-level topology.
Additionally, the converter design must be capable of managing the open circuit maximum voltage of solar panels of the photovoltaic system (3) or the maximum operating voltage of a capacitor bank.
On the other hand, preferably, the photovoltaic system (3) allows configurations with open circuit voltages of 1500Vdc and when it is operating, the photovoltaic field voltage varies between 900 and 1500Vdc. Additionally, by means of the maximum power point tracking (MPPT) device for the photovoltaic field it is possible to situate the field voltage at the maximum point of the curve in Figures 2 to 5.
Additionally the hybrid converter (1) comprises:
a connection and disconnection unit (7) configured for directly linking and unlinking, that is, electrically connecting without any previous treatment, the photovoltaic system (3) with the DC bus of the AC/AC power converter, a measuring unit (8) for measuring voltage and current of the DC bus connected to the direct current source,
control unit (9) linked to the connection/disconnection unit (7) and the measuring unit (8) .
The control unit (9) comprises: • a memory with the instructions and a predetermined voltage range in the electricity grid, in the rotating machine and in the direct current source, and
• a control logic device, preferably a microprocessor, linked to the memory, wherein the instructions configure the microprocessor for:
o establishing the predetermined voltage range in the DC bus, and
o regulating the DC bus voltage such that the voltage in the DC bus is within a predetermined voltage range .
Preferably, the predetermined voltage range of the DC bus com prises a first limit being the same as the minimum operating voltage of the photovoltaic system (3) , in this case the same as 900Vdc, and the second limit is the same as the open cir cuit voltage of the photovoltaic system (3) , in this case in particular the same as 1500Vdc.
Preferably, for regulating the DC bus voltage, the instruc tions configure the microprocessor for:
• monitoring, by means of the measuring unit (8), the voltage and the DC bus current,
• determining a first voltage drawn from the photovoltaic system (3) or the battery bank (10),
• determining a second voltage drawn from the wind system (2) and being the same as the input voltage of the DC bus, based on the voltage of the electricity grid (4) and the wind system (2) ,
• defining the maximum direct voltage between the first voltage and the second voltage, and
• regulating by means of the second DC/AC three phase bridge, the direct voltage to the maximum voltage previously defined and that must be found within the predetermined voltage range.
Preferably, for determining the first voltage, the instructions configure the microprocessor for: • monitoring the production of direct power by means of maximum power point tracking (MPPT) device for the photovoltaic field,
• monitoring the total power supplied by the hybrid system, and
• sending control signals to the second DC/AC three phase bridge (6) varying the voltage of the DC bus for drawing the desired power of the direct current source.
Additionally, the connection and disconnection unit comprises a switch, either electromechanical or solid state, linked to the control unit (9) configured for connecting the photovoltaic system (3) or the battery bank (10) with the DC bus when the DC bus voltage is within the predetermined voltage range; and for disconnecting the direct current source of the DC bus when the DC bus voltage is out of the predetermined voltage range.
Preferably, for determining the second voltage the instructions configure the microprocessor for:
• monitoring the production of alternating power of the wind system (2)
• monitoring the voltage of the electricity grid and the wind system (2), and
• sending control signals to the second DC/AC three phase bridge such that the direct voltage is the same as the maximum direct voltage defined above.
The invention describes a control method for the hybrid converter (1) described in the first preferred embodiment, where the control method is characterized in that it comprises the following steps:
• establishing a predetermined voltage range of the DC bus,
• regulating the DC bus voltage such that the bus voltage is within the predetermined voltage range,
• regulating the voltage of the DC bus such that the bus voltage is within the predetermined voltage range. • monitoring, by means of the measuring unit, the voltage and current of the DC bus,
• determining a first voltage drawn from the direct current source,
• determining a second voltage drawn from the rotating machine and being the same as the input voltage of the DC bus ,
• defining the regulating voltage for the DC bus as the maximum between the first voltage and the second voltage,
• sending control signals to the second three phase bridge (DC/AC) for the DC voltage to be the maximum between the first voltage and the second voltage and to be within the predetermined voltage range.

Claims

C L A I M S
1. Hybrid converter (1) for connecting a rotating machine (2) combined with a direct current source (3, 10) , to an electric ity grid (4), wherein the hybrid converter (1) comprises:
an AC/AC power converter, which in turn comprises a first AC/DC three phase bridge (5) and a second DC/AC three phase bridge (6) coupled to each other by means of a DC bus, wherein the first AC/DC three phase bridge (5) is connected to the rotating machine (7) , and the second DC/AC three phase bridge (6), is connected to the electricity grid (4), a connection and disconnection unit (7) configured for directly linking and unlinking the direct current source (3, 10) with the DC bus,
a measuring unit (8) for measuring the voltage and current of the DC bus to which the direct current source (3, 10) is connected,
control unit (9) linked to the measuring unit (8) and the connection and disconnection unit (7) which in turn comprises :
• a memory with instructions and a predetermined voltage range in the electricity grid (4) , in the rotating machine (2) and in the direct current source (3, 10), and
• a control logic device, linked to the memory, wherein the instructions configure the control logic device for:
o establishing the predetermined voltage range in the DC bus, and
o regulating the voltage in the DC bus such that the voltage in the DC bus is within the predetermined voltage range.
2. Hybrid converter (1) according to claim 1 characterized in that the predetermined voltage range of the DC bus comprises a first limit being the same as the minimum operating voltage of the rotating machine (2) and the second limit being the same as the maximum voltage of the direct current source (3, 10) .
3. Hybrid converter (1) according to any of the previous claims characterized in that in order to regulate the DC bus voltage, the instructions configure the control logic device for :
• monitoring, by means of the measuring unit (7), the voltage and the current of the DC bus,
• determining a first tension drawn from the direct current source (3, 10) ,
• determining a second voltage drawn from the rotating machine (2) and being the same as the input voltage of the DC bus,
• defining the maximum direct voltage between the first voltage and the second voltage, and
• regulating, by means of the second DC/AC three phase bridge (6), the maximum direct voltage between the first voltage and the second voltage as long as it is within the predetermined voltage range.
4. Hybrid converter (1) according to claim 3 characterized in that in order to determine the first voltage, the instructions configure the control logic device for:
• sending control signals to the second DC/AC three phase bridge (6), varying the DC bus voltage so as to drawn the desired power from the direct current source (3, 10) .
5. Hybrid converter (1) according to any of claims 3 or 4 characterized in that in order to determine the second voltage, the instructions configure the control logic device for :
• sending control signals to the second DC/AC three phase bridge (6) such that the power of the rotating machine (2) is achieved at the maximum direct voltage.
6. Hybrid converter (1) according to claim 5 characterized in that in order to determine the second voltage the instructions configure the control logic device for:
• monitoring the production of alternating power of the rotating machine (2) , monitoring the production of the direct power and determining the power drawn from the rotating machine (2) and the power drawn from the direct current source.
7. Hybrid converter (1) according to any of the previous claims characterized in that the connection and disconnection unit (7) comprises a switch linked with the control unit (9) configured for connecting the direct current source (3, 10) with the DC bus when the DC bus voltage is within the predetermined voltage range; and for disconnecting the direct current source (3, 10) of the DC bus when the DC bus voltage is out of the predetermined voltage range.
8. Hybrid converter (1) according to any of the previous claims characterized in that the rotating machine (2) is a wind system.
9. Hybrid converter (1) according to any of the previous claims characterized in that the direct current source is se lected from the photovoltaic system with a maximum power point tracking (MPPT) device for the photovoltaic field and a bat tery bank (10) with a power and charge state control device.
10. Control method for the hybrid converter according to any of the previous claims, characterized in that the control method comprises the following steps:
• establishing a predetermined voltage range of the DC bus, and
• regulating the DC bus voltage such that the voltage in the bus is within the predetermined voltage range.
11. Control method for the hybrid converter according to claim 10, characterized in that it also comprises the following steps :
• monitoring, by means of the measuring unit, the voltage and the DC bus current,
• determining a first voltage drawn from the direct current source (3, 10) , • determining a second voltage drawn from the rotating machine (2) and which is the same as the input voltage of the DC bus.
• defining the regulating voltage for the DC bus as the maximum between the first voltage and the second voltage,
• sending control signals to the second DC/AC three phase bridge (6), for the DC bus voltage to be the maximum between the first voltage and the second voltage, and for it to be within the predetermined voltage range.
12. Control method for the hybrid converter according to claim 11 characterized in that in order to determine the first voltage, control signals are sent to the second DC/AC three phase bridge (6), varying the DC bus voltage so as to draw the desired power from the direct current source (3, 10) .
13. Control method for the hybrid converter according to any of claims 11 or 12 characterized in that in order to determine the second voltage, control signals are sent to the second DC/AC three phase bridge (6) such that the rotating machine (2) power is achieved at the maximum direct voltage.
14. Control method for the hybrid converter according to claim 13 characterized in that, in order to determine the second voltage, the production of alternating power of the rotating machine (2) is also monitored, the production of direct power of the rotating machine (2) is monitored and the power drawn from the rotating machine (2) and the power drawn from the direct current source (3, 10) is determined.
PCT/EP2019/059964 2018-04-17 2019-04-17 Hybrid converter and control method thereof WO2019202016A1 (en)

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