DE202022101174U1 - System for integrating a microgrid with the grid through a flexible asynchronous AC link - Google Patents

Abstract

A system (100) for integrating a microgrid with the utility grid through a flexible AC asynchronous link, comprising at least one free-wheeling doubly-fed induction machine (DFIM) (108) along with a voltage regulator (106) such that power transfer from the utility grid ( 102) to the microgrid, the microgrid being a renewable energy (RE) based power system;
a wind energy conversion system (WECS) (132) along with an AC-DC converter (136);
a battery energy storage system (BESS) (138);
a DC bus (124) with local DC load (140);
an AC bus (114) with adjustable frequency and local AC loads (122);
a wind energy conversion system 1 (WECS1) (120) with AC output;
an AC-DC interface converter (116) between the AC bus and the DC bus (124); and
an interface DC-to-AC converter (118) between the DC bus (124) and the AC bus that varies frequency to allow power flow from primary to secondary or from stator (110) to controlling the rotor (112) so that the secondary winding or the winding of the rotor (112) is connected to a voltage regulator that supplies power to the utility grid (102); wherein the microgrid is a solar photovoltaic (SPV) system (126) together with a maximum power point tracker (MPPT) (130);
wherein the utility grid (102) is a conventional power grid and the voltage regulator is a three-phase AC regulator or a three-phase autotransformer with power flowing from the high frequency side to the low frequency side of the DFIM (108); and
whereby the magnitude and direction of power transfer is controlled by controlling the frequency and voltage.

Description

FIELD OF THE INVENTION

The present disclosure relates to a system for integrating a microgrid with the utility grid, and more particularly to a system for integrating a microgrid with the utility grid through the flexible asynchronous AC link.

BACKGROUND

Climate change is one of the greatest challenges facing the world today. Greenhouse gas (GHG) emissions are monitored and controlled worldwide using various technologies. The renewable energy sources (RES, e.g. sun, wind, etc.) are used to limit emissions from conventional energy sources. In addition, renewable energies are used to cover local needs and to feed surpluses or reduce deficits into/from the supply network. The modern power supply system is now evolving towards hybrid generation systems based on renewable energies. Locally connected loads and generation centers form a microgrid (MG). Connected to the utility grid, these microgrids offer many advantages, e.g. B. Reliability and stability of power systems.

Microgrid (MG) consists of microgenerators, renewable energy sources, small energy storage systems (ESS), regulators, inverters and DC-DC converters, as well as critical and non-critical loads. Researchers' main focus is now on the reliability and power quality of the power generated by DG. The concept of microgrid energy management system (MEMS) was developed, which has complete control over the microgrid. The MEMS makes the microgrid a complete system that can operate either autonomously or in grid-connected mode. The IEEE, USA has established a standard (IEEE 2030.7-2017 doi: 10.1109/IEEESTD.2018.8340204) for power quality maintenance that increases the reliability of the microgrid.

Another important area are the technologies for integrating microgrid (MG) into the supply network. The integration of MG into the utility grid can solve several typical problems of traditional AC grids, such as: B. Energy security and cost savings. One of the challenges of the grid-tied microgrid is to inject energy into the utility grid while maintaining system stability after a failure caused by a fault.

The integration of MG into the supply network is mainly done via a direct AC connection (Xia et al., IEEE Transactions on Power Electronics (2017), vol. 32, pp. 4949-4959, doi: 10.1109/TPEL.2016.2603066) and bidirectional AC/DC converters (Xia et al., IEEE Transactions on Power Electronics (2018), vol. 33, pp. 3520-3533, doi: 10.1109/TPEL.2017.2705133 and Liu et al., IEEE Transactions on Industrial Electronics (2019) , vol. 66, pp. 3477-3485, doi: 10.1109/TIE.2018.2856210). However, both technologies lack the ability to provide natural cushioning. In addition, the converters are complicated to control and generate harmonics that are filtered out with special filters, which increases costs.

The aim of this invention is therefore to provide a system for the integration of a microgrid with the utility grid through a flexible asynchronous AC link system (FASAL) for controlling the power flow from microgrids to the utility grid and vice versa. It offers energy security, reliability and cost savings.

Efforts have been made in issued patents and published patent applications to address and solve the various problems of microgrids. The US patent no. U.S. 8,751,036 B2 on June 10, 2014 discloses systems and methods for power generation and management of microgrids with selective shutdown. In addition, methods for the selective activation and/or shutdown of decentralized power generators from the microgrid or network and for controlling the power supply for distribution and/or storage are proposed.

The US patent no. U.S. 8,649,914 B2 discloses a power router element installable in a microgrid module and capable of sensing the power demand of another microgrid module and controlling the flow of power to and from the other microgrid module.

US patent no. US 9,225,173 B2 discloses power generation systems and methods that selectively turn on and utilize backup generators to generate power for distribution via a microgrid and/or for storage pending later distribution.

U.S. Pub. No. U.S. 2019/0140477 A1 , proposes a dedicated control system for a microgrid that coordinates the components for efficient energy use and also uses the availability of different energy sources to optimize power to manage factors integrated into the control of the microgrid.

U.S. Pub. No. U.S. 2020/0401176 A1 , provides systems and methods for the management of energy delivered over an electrical power network by a utility and other market participants to multiple network elements and devices for supply and load shedding.

U.S. Pub. No. U.S. 2020/0334609 A1 , discloses a rapid and adaptive planning method for microgrids and distributed energy resources (DER) that takes into account cost calculations, emissions calculations, technology investments and operation in a computer- or cloud-based environment. The disclosed adaptive method repeatedly solves a solution for either a one-year or a multi-year horizon, making investment decisions at the beginning of the horizon (e.g., before the first year).

Indian Patent No. 296524 discloses a flexible asynchronous AC interconnect system (FASAL) for interconnecting power grids or electric power grids. However, it does not address the integration of a microgrid with a renewable energy-based hybrid generation system and supply grid.

Therefore, none of the prior art systems, methods, or devices provide solutions for integrating a microgrid with a renewable energy-based hybrid generation system and a utility grid that include inertial for natural damping, fault-tolerant, and elastic systems that control the flow of energy between them . Therefore, there is a need for a system for integrating a microgrid into the utility grid and for controlling bi-directional current flow between them depending on the operating conditions of the microgrid to overcome the deficiencies of the prior art.

OBJECT OF THE INVENTION

The main objective of the invention is to provide a system for the integration of microgrids with the utility grid through a flexible asynchronous AC link for bi-directional power flow control from microgrids to the utility grid.

Another object of the invention is to provide a system for integrating microgrids with the utility grid through a flexible asynchronous AC link to control the flow of power from the utility grid to the microgrids.

Another object of the invention is to provide a system for integrating microgrids with the utility grid through a flexible asynchronous AC link that is fault tolerant and resilient.

SUMMARY OF THE INVENTION

The present invention discloses a system for integrating a microgrid with the utility grid through a flexible AC asynchronous link (FASAL) to connect the microgrid to the utility grid, comprising at least one free-wheeling doubly-fed induction machine (DFIM) along with a voltage regulator such that the Energy transfer takes place from the utility grid to the microgrid, where the microgrid is a renewable energy (RE) based energy system that includes a solar photovoltaic system (SPV) together with a maximum power point tracker (MPPT), a wind energy conversion system (WECS) together with an AC DC converter can be, a battery energy storage system (BESS), a DC bus with local DC load, an AC bus with adjustable frequency and local AC load, a wind energy conversion system 1 (WECS 1) with AC output, an AC-DC converter as an interface between en the AC bus and the DC bus and a DC-to-AC converter to interface between the DC bus and the AC bus, which varies the frequency to control the flow of power using freely rotating RT from the primary winding to the secondary winding or from the stator to the rotor so that the secondary winding or the rotor winding is connected to a voltage regulator that supplies power to the utility grid; wherein the utility grid is a conventional power grid and the voltage regulator can be a three-phase AC regulator or a three-phase autotransformer with power flowing from the high-frequency side to the low-frequency side of the DFIM; and wherein the magnitude and direction of power transfer is controlled by controlling the frequency and voltage.

In one aspect of the present disclosure, the utility is a conventional power grid connected to the Flexible AC Asynchronous Link (FASAL) consisting of the Free-Running Doubly-Fed Induction Machine (DFIM) and a voltage regulator.

In one aspect of the present disclosure, the flexible AC asynchronous link (FASAL) consists of the free-wheeling doubly-fed induction machine (DFIM) with three-phase windings on both the stator and rotor and a three-phase voltage regulator, which may be a three-phase AC regulator or a three-phase autotransformer, and the supply network is connected to the rotor windings through the voltage regulator, and the micro network is connected directly to the stator windings, with energy transfer between the air gap taking place through magnetic coupling.

In one aspect of the present disclosure, the adjustable frequency AC bus acts as an interface bus between the microgrid and the FASAL, receiving power from the utility grid or providing power from the microgrid to the utility grid depending on generation capacity or operational status of the microgrid.

In one aspect of the present disclosure, the interface DC-to-AC converter between the DC bus and the AC bus varies frequency to control the flow of power from the microgrid to the utility grid or from the utility grid to the microgrid depending on the operating state of the microgrid.

In one aspect of the present disclosure, the AC-DC converter interface between the AC bus and the DC bus that supplies the power from the utility grid to the microgrid depending on the operating condition of the microgrid.

In one aspect of the present disclosure, the Wind Energy Conversion System-1 (WECS1) that produces AC power is injected into the AC adjustable frequency bus for use by the AC load or for delivery to the utility grid.

In one aspect of the present disclosure, the AC load is connected to the adjustable frequency AC bus, which receives power from either the microgrid or the utility grid depending on the operating state of the microgrid.

In one aspect of the present disclosure, the DC bus receives power from the SPV system, the WECS2, and the Battery Energy Storage System (BESS), with the power being supplied to the DC load or the DC-AC converter and the FASAL system supplied to the utility grid when the electricity generated by the microgrid is in excess.

In one aspect of the present disclosure, the SPV system generates power along with MPPT and injects it onto the DC bus where it is consumed by the DC load or injected into the utility grid.

In another aspect of the present disclosure, the Wind Energy Conversion System (WECS2) along with the AC-DC converter generates power and provides it to the DC bus (124) where it is used by the DC load or provided to the utility grid.

In another aspect of the present disclosure, the battery energy storage system (BESS) supplies energy to the DC bus or charges with the energy of the DC bus.

In another aspect of the present disclosure, the DC load is connected to the DC bus, which receives power from the microgrid or the utility grid depending on the operational state of the microgrid.

character list

• zeigt ein Blockdiagramm eines Systems zur Integration eines Kleinstnetzes in das Versorgungsnetz durch eine flexible asynchrone Wechselstromverbindung gemäß einer Ausführungsform der vorliegenden Erfindung.
• zeigt ein detailliertes Anschlussdiagramm des Systems zur Integration des Mikronetzes mit dem Versorgungsnetz durch eine flexible asynchrone Wechselstromverbindung, wie in dargestellt, gemäß einer Ausführungsform der vorliegenden Erfindung.

The accompanying drawings are provided for further understanding of the present disclosure and are a part of this specification. The drawings illustrate example embodiments of the present disclosure and together with the description serve to explain the principles of the present disclosure.

• 12 is a block diagram of a system for integrating a micro-grid into the utility grid through a flexible AC asynchronous link according to an embodiment of the present invention.
• shows a detailed connection diagram of the system for integrating the microgrid with the utility grid through a flexible AC asynchronous link, as in illustrated, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to the accompanying drawings, which illustrate preferred embodiments of this invention by way of non-limiting example.

In one embodiment of the present disclosure Figure 12 is a block diagram of the system (100) for integrating a microgrid with the utility grid through a flexible AC asynchronous link in accordance with an embodiment of the present invention. the system tem (100) includes a power grid (102), a flexible asynchronous AC interconnection system (FASAL) (104), a voltage regulator (106), a doubly fed induction machine (DFIM) consisting of three-phase windings on both the stator (110) and at the rotor (112), an AC bus (114) with adjustable frequency, an AC-DC converter (116), a DC-AC converter (118), a wind energy conversion system 1 (WECS1) (120). , AC load (122), DC bus (124), a solar photovoltaic system (SPV) (126) consisting of SPV (128), MPPT (130), a wind energy conversion system (WEC) (132). wind energy conversion system 2 (WECS2) (134) and AC-DC converter (136), battery energy storage system (BESS) (138) and DC load (140) so that power flows from the utility grid to the microgrid and vice versa.

In one embodiment of the present disclosure Figure 12 illustrates a system connection diagram for integrating the microgrid with the utility grid (102) through a flexible asynchronous AC link according to the present invention. The utility grid (102) is a conventional power system connected via a flexible asynchronous AC link system (FASAL) (104) , comprising at least one free-wheeling doubly-fed induction machine (DFIM) (108) and a voltage regulator (106) connected to the micro-grid such that energy transfer occurs from the utility grid (102) to the micro-grid, the micro-grid being a renewable energy (RE ) based energy system, which can be a solar photovoltaic system (126), a wind energy system (132), a battery energy storage system (BESS) or a hybrid system (138), a DC bus (124) with a local DC load (140), an adjustable frequency AC bus (114) with local AC loads (122) and WECS (120) with alternation Oil power output, an AC bus (142) of the utility grid, an interface DC-to-AC converter (118) between the DC bus (124) and the AC bus (114) that varies the frequency to power flow using Freely rotating RT from the primary winding to the secondary winding or from the stator (110) to the rotor (112) so that the secondary winding or the winding of the rotor (112) is connected to a voltage regulator (106) which supplies power to the utility grid (102 ) supplies, and the voltage regulator (106) can be an AC regulator or a tapping transformer or a servo motor based voltage stabilizer. Power flows from the high frequency side to the low frequency side of the DFIM (108), with the magnitude and direction of power transfer being determined by controlling the frequency and the tension is controlled.

In one embodiment of the present disclosure, a free-wheeling, doubly-fed induction machine (108) used to integrate the microgrid with the utility grid (102). The magnitude and direction of power flow are controlled independently by regulating voltage and frequency.

In an embodiment of the present disclosure, the electricity is generated by a microgrid consisting of different energy sources, e.g. B. from decentralized generators based on renewable energy sources (RE), such. B. a solar photovoltaic system (126), a wind energy system (WES) (132), a battery energy storage system (BESS) (138) or a hybrid system. When there is excess power in the microgrid, the FASAL system (104) can be used to transfer power from the microgrid to the utility grid (102). In this case, the DC-AC converter (118) in the microgrid generates power at a slightly higher frequency (f1 > f2), and the current flow is effectively controlled by the voltage regulator (106). In this way, the current flows from the microgrid to the utility grid (102).

In an embodiment of the present disclosure, when there is a power shortage (for local loads in the microgrid) in the microgrid, f1 is controlled by the DC-AC converter (118) to become slightly lower than f2 (i.e., f1<f2). Therefore, the current flows from the grid (102) to the microgrid via the AC/DC converter (116).

In one embodiment of the present disclosure, the speed of the DFIM (108) self-adjusts during the error condition to compensate for it. Even in the event of a severe triple line fault (LLL) or a triple line fault to earth (LLLG), a limited effect is slowly transmitted to another side of the power grid as the DFIM (108) slowly increases its speed. In this condition, the DFIM (108) behaves like a shorted rotor circuit of a double-fed induction motor (DFIM). There is therefore no electrical power flow to the error side, since this is short-circuited. Only a small amount of power is required to accelerate the free-running, unloaded and mechanically free (uncoupled) rotor of the DFIM (108). It therefore only slowly requires a small amount of additional power for acceleration from the healthy power grid. Therefore, it provides sufficient buffer time for power grid recovery and resilience. Since the micro-grid and the supply grid (102) are connected via the FASAL system (104), a fault affects one Side of the DFIM (108) only slowly on the other side, since both systems are not electrically but magnetically coupled. Therefore, the stability of the healthy side of the power grid (utility grid or microgrid) will not be seriously affected.

Reference List

100

System for integrating a microgrid with the utility grid through a flexible asynchronous AC link

102

power grid

104

Flexible Asynchronous AC Link (FASAL)

106

voltage regulator

108

Dual Fed Induction Machine (DFIM)

110

stator

112

rotor

114

Frequency AC Bus

116

Interface AC-DC converter

118

Interface DC-AC converter

120

Wind Energy Conversion System 1 (WECS1)

122

AC load

124

DC bus

126

Solar Photovoltaic System (SPV)

128

Solar Photovoltaic (SPV)

130

Maximum Power Point Tracker (MPPT)

132

Wind Energy Conversion System (WEC)

134

Wind Energy Conversion System 2 (WECS2)

136

AC-DC converter

138

Battery Energy Storage System (BESS)

140

DC load

142

AC bus of the utility grid

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 8751036 B2 [0007]
• US8649914B2 [0008]
• US 9225173 B2 [0009]
• US20190140477A1[0010]
• US 20200401176 A1 [0011]
• US 20200334609 A1 [0012]
• IN 296524 [0013]

Claims (10)

A system (100) for integrating a microgrid with the utility grid through a flexible AC asynchronous link, comprising at least one free-wheeling doubly-fed induction machine (DFIM) (108) along with a voltage regulator (106) such that power transfer from the utility grid ( 102) to the microgrid, the microgrid being a renewable energy (RE) based power system; a wind energy conversion system (WECS) (132) along with an AC-DC converter (136); a battery energy storage system (BESS) (138); a DC bus (124) with local DC load (140); an AC bus (114) with adjustable frequency and local AC loads (122); a wind energy conversion system 1 (WECS1) (120) with AC output; an AC-DC interface converter (116) between the AC bus and the DC bus (124); and an interface DC-to-AC converter (118) between the DC bus (124) and the AC bus that varies frequency to allow power flow from primary to secondary or from stator (110) to controlling the rotor (112) so that the secondary winding or the winding of the rotor (112) is connected to a voltage regulator that supplies power to the utility grid (102); wherein the microgrid is a solar photovoltaic (SPV) system (126) together with a maximum power point tracker (MPPT) (130); wherein the utility grid (102) is a conventional power grid and the voltage regulator is a three-phase AC regulator or a three-phase autotransformer with power flowing from the high frequency side to the low frequency side of the DFIM (108); and whereby the magnitude and direction of power transfer is controlled by controlling the frequency and voltage. The system (100) for integrating a microgrid with the utility grid through a flexible asynchronous AC link according to FIG claim 1 , wherein the utility grid (102) is a conventional power grid connected to the flexible AC asynchronous link (FASAL) (104) consisting of the free-running doubly-fed induction machine (DFIM) (108) and a voltage regulator (106). The system (100) for integrating a microgrid with the utility grid through a flexible asynchronous AC link according to FIG claim 1 , where the flexible AC asynchronous link (FASAL) (104) consists of the free-wheeling double-fed induction machine (DFIM) (108) with three-phase windings on both the stator (110) and rotor (112), and a three-phase voltage regulator in which it is a three-phase AC regulator or a three-phase autotransformer, and the supply network (102) is connected to the windings of the rotor (112) via the voltage regulator and the microgrid is connected directly to the windings of the stator (110), the power transmission between the Air gaps via the magnetic coupling takes place. The system (100) for integrating a microgrid with the utility grid through a flexible AC asynchronous link according to FIG claim 1 wherein the adjustable frequency AC bus (114) acts as an interface bus between the microgrid and the FASAL (104), receiving power from the utility grid (102) or supplying power to the utility grid (102) depending on the generation capacity or operational status of the microgrid . The system (100) for integrating a microgrid with the utility grid through a flexible asynchronous AC link according to FIG claim 1 wherein the interface DC-to-AC converter (118) varies frequency between the DC bus (124) and the AC bus to facilitate power flow from the microgrid to the utility grid (102) or from the utility grid (102) to the microgrid depending on the operational state of the microgrid to control. The system (100) for integrating a microgrid with the utility grid through a flexible AC asynchronous link claim 1 wherein the interface AC-to-DC converter (116) between the AC bus and the DC bus (124) that supplies power from the utility grid (102) to the microgrid is dependent on the operating state of the microgrid. The system (100) for integrating a microgrid with the utility grid through a flexible asynchronous AC link according to FIG claim 1 wherein the Wind Energy Conversion System-1 (WECS1) (120) generating AC power is injected into the AC adjustable frequency bus (208) for use by the AC load (122) or for injection into the utility grid (102). The system (100) for integrating a microgrid with the utility grid through a flexible asynchronous AC link according to FIG claim 1 , wherein the AC load (122) is connected to the AC bus (114) with adjustable Fre quenz is connected, depending on the operating state of the microgrid power either from the microgrid or from the grid (102) receives. The system (100) for integrating a microgrid with the utility grid through a flexible AC asynchronous link according to FIG claim 1 , wherein the DC bus (124) receives power from an SPV system (126), WECS2 (134), and a Battery Energy Storage System (BESS) (138), and the power is supplied via a DC-to-AC converter (118) and a FASAL system (104) is supplied to the DC load (140) or to the utility grid (102) when the power generated by the microgrid is in excess. The system (100) for integrating a microgrid with the utility grid through a flexible asynchronous AC link according to FIG claim 1 wherein the SPV system (126) together with MPPT (130) generates and supplies power to the DC bus (124) where it is used by the DC load (140) or supplied to the utility grid (102).

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