Flywheel energy storage system and device

Abstract

The flywheel energy storage system comprises a grid-connected circuit, a direct current-direct current (DC-DC) circuit, an inverter circuit and a flywheel energy storage device, the DC-DC circuit is respectively connected with the grid-connected circuit and the inverter circuit; the inverter circuit is connected with the flywheel energy storage device; the grid-connected circuit is connected with a power grid and is used for converting high-voltage alternating current in the power grid into high-voltage direct current; the DC-DC circuit is used for converting the high-voltage direct current into low-voltage direct current; the inverter circuit is used for converting the low-voltage direct current into low-voltage alternating current; and the flywheel energy storage device is used for converting the low-voltage alternating current into mechanical energy.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and particularly to a flywheel energy storage system and device. Background Art

[0002] Flywheel energy storage technology has the advantages of fast charge and discharge speed, high energy conversion efficiency, long service life, safety and environmental protection, etc., and has excellent application prospects in the fields of power frequency modulation, energy storage devices, etc. Existing flywheel energy storage systems operate with special voltage levels, such as 750V, 1500V, etc., which do not match the grid voltage level; therefore, existing flywheel energy storage systems need to use power frequency transformers to connect to the grid, resulting in a complex and large overall structure and large circuit losses, and thus low energy conversion efficiency. For this problem, there is currently no effective solution. Summary of the Invention

[0003] In view of this, embodiments of the present application are expected to provide a flywheel energy storage system and device.

[0004] The technical embodiments of the embodiments of the present application are implemented as follows:

[0005] Embodiments of the present application provide a flywheel energy storage system, the system includes: a grid connection circuit, a direct current-direct current (DC-DC) circuit, an inverter circuit, and a flywheel energy storage device; the DC-DC circuit is respectively connected to the grid connection circuit and the inverter circuit; the inverter circuit is connected to the flywheel energy storage device;

[0006] The grid connection circuit is connected to the grid and is used to convert the high-voltage alternating current in the grid into high-voltage direct current;

[0007] The DC-DC circuit is used to convert the high-voltage direct current into low-voltage direct current;

[0008] The inverter circuit is used to convert the low-voltage direct current into low-voltage alternating current;

[0009] The flywheel energy storage device is used to convert the low-voltage alternating current into mechanical energy.

[0010] In the above solution, the DC-DC circuit includes M first sub-modules, M is a positive integer greater than or equal to 1; the first side of the first sub-module is connected in parallel with the grid connection circuit; the second side of the first sub-module is connected in series with the inverter circuit; M is determined by the ratio of the voltage on the first side to the voltage on the second side.

[0011] In the above solution, the grid-connected circuit includes a modular multilevel topology circuit; the multilevel topology circuit includes a three-phase circuit; each branch of the three-phase circuit includes upper and lower bridge arms, and each bridge arm includes N second sub-modules, where N is a positive integer greater than or equal to 1; N is determined by the voltage value of the grid-connected circuit and the withstand voltage level of the second sub-module;

[0012] The second sub-module is used for controllable rectification of the power grid.

[0013] In the above solution, the inverter circuit includes multiple groups of inverter sub-modules; the multiple groups of inverter sub-modules are connected in parallel; the number of inverter sub-modules is determined by the number of flywheel energy storage devices to be controlled.

[0014] In the above solution, the multiple groups of inverter sub-modules are connected to the same DC bus; each group of inverter sub-modules is used to control one flywheel energy storage device to charge or discharge.

[0015] In the above solution, the second sub-module adopts a half-bridge structure or a full-bridge structure; the half-bridge structure includes 2 controllable switch tubes and 1 energy storage capacitor; the full-bridge structure includes 4 controllable switch tubes and 1 energy storage capacitor.

[0016] In the above solution, the first sub-module adopts a DC-DC module with high-frequency transformer isolation or a buck-boost Buck-Boost circuit; the DC-DC module includes an H-type full-bridge circuit, a capacitor, and an isolation transformer; the Buck-Boost circuit includes a controllable switch tube, a capacitor, and an inductor.

[0017] In the above solution, the turns ratio of the isolation transformer is 1:1 or determined according to preset design requirements.

[0018] In the above solution, the inverter sub-module adopts a three-phase two-level inverter topology, a three-phase three-level NPC inverter topology, or a three-phase three-level ANPC inverter topology; the three-phase two-level inverter topology, the three-phase three-level NPC inverter topology, and the three-phase three-level ANPC inverter topology all include controllable switch tubes and support capacitors.

[0019] The embodiment of the present application further provides a control device for flywheel energy storage, and the control device for flywheel energy storage includes any one of the above systems.

[0020] A flywheel energy storage system and device provided by an embodiment of the present application. The system includes: a grid-connected circuit, a DC-DC circuit, an inverter circuit, and a flywheel energy storage device; the DC-DC circuit is respectively connected to the grid-connected circuit and the inverter circuit; the inverter circuit is connected to the flywheel energy storage device; the grid-connected circuit is connected to the power grid and is used to convert high-voltage alternating current in the power grid into high-voltage direct current; the DC-DC circuit is used to convert the high-voltage direct current into low-voltage direct current; the inverter circuit is used to convert the low-voltage direct current into low-voltage alternating current; the flywheel energy storage device is used to convert the low-voltage alternating current into mechanical energy; that is, the high-voltage alternating current in the power grid is converted into high-voltage direct current through the grid-connected circuit, the high-voltage direct current is converted into low-voltage direct current by the DC-DC circuit, the low-voltage direct current is converted into low-voltage alternating current by the inverter circuit, and the flywheel energy storage device converts the low-voltage alternating current into mechanical energy, realizing direct grid connection, avoiding the need for a flywheel energy storage system to use a power frequency transformer to access the power grid, resulting in a complex and large overall structure and large circuit losses, and solving the problem of low energy conversion efficiency. Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of a flywheel energy storage system provided by an embodiment of the present application;

[0022] Figure 2 It is a topological schematic diagram of a flywheel energy storage system provided by an embodiment of the present application;

[0023] Figure 3 It is a schematic diagram of the second sub-module adopting a half-bridge structure in an embodiment of the present application;

[0024] Figure 4 It is a schematic diagram of the second sub-module adopting a full-bridge structure in an embodiment of the present application;

[0025] Figure 5 It is a schematic diagram of the first sub-module adopting a DC-DC module with high-frequency transformer isolation in an embodiment of the present application;

[0026] Figure 6 It is a schematic diagram of the first sub-module adopting a Buck-Boost circuit in an embodiment of the present application;

[0027] Figure 7 It is a schematic diagram of the inverter sub-module adopting a three-phase two-level inverter topology circuit in an embodiment of the present application;

[0028] Figure 8 It is a schematic diagram of the inverter sub-module adopting a three-phase three-level NPC inverter topology in an embodiment of the present application;

[0029] Figure 9 It is a schematic diagram of the inverter sub-module adopting a three-phase three-level ANPC inverter topology in an embodiment of the present application. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will further describe in detail the specific technical solutions of the invention with reference to the accompanying drawings in the embodiments of the present application. The following embodiments are used to illustrate the present application but are not intended to limit the scope of the present application.

[0031] This embodiment provides a flywheel energy storage system. Figure 1 is a schematic structural diagram of a flywheel energy storage system provided by an embodiment of the present application; Figure 2 is a topological schematic diagram of a flywheel energy storage system provided by an embodiment of the present application; The following will be described by way of example with reference to Figure 1 and Figure 2 The system 100 includes: a grid connection circuit 101, a DC-DC circuit 102, an inverter circuit 103, and a flywheel energy storage device 104; the DC-DC circuit 102 is respectively connected to the grid connection circuit 101 and the inverter circuit 103; the inverter circuit 103 is connected to the flywheel energy storage device 104;

[0032] The grid connection circuit 101 is connected to the power grid and is used to convert the high-voltage alternating current in the power grid into high-voltage direct current;

[0033] The DC-DC circuit 102 is used to convert the high-voltage direct current into low-voltage direct current;

[0034] The inverter circuit 103 is used to convert the low-voltage direct current into low-voltage alternating current;

[0035] The flywheel energy storage device 104 is used to convert the low-voltage alternating current into mechanical energy.

[0036] It should be noted that the flywheel energy storage system can be determined according to actual situations and is not limited herein. As an example, the flywheel energy storage system can be a flywheel energy storage system that is connected to the grid using power electronic devices.

[0037] The power grid can be determined according to actual situations and is not limited herein. As an example, the voltage of the power grid can be 10 KV, and the frequency of the power grid can be 50 Hz.

[0038] The grid connection circuit 101 can be determined according to actual situations and is not limited herein. As an example, the grid connection circuit 101 includes a modular multilevel topology circuit, which can achieve controllable rectification and realize the bidirectional conversion between the three-phase alternating current of 10 KV and 50 Hz of the power grid and high-voltage direct current.

[0039] The DC-DC circuit 102 can be determined according to actual circumstances and is not limited herein. As an example, the DC-DC circuit 102 may include multiple groups of identical DC-DC conversion modules; in practical applications, the DC-DC circuit 102 may also be referred to as an intermediate DC-DC circuit, and the intermediate DC-DC circuit uses multiple groups of identical DC-DC conversion modules.

[0040] The inverter circuit 103 can be determined according to actual circumstances and is not limited herein. As an example, the inverter circuit 103 may include multiple groups of inverter sub-modules.

[0041] Convert the high-voltage alternating current in the power grid into high-voltage direct current; wherein, both the high-voltage alternating current and the high-voltage direct current can be determined according to actual circumstances and are not limited herein. As an example, the high-voltage alternating current may be three-phase alternating current of 10 kV and 50 Hz. In practical applications, the grid-connected circuit uses a modular multilevel topology to achieve controllable rectification and realize the bidirectional conversion between the 10 kV 50 Hz three-phase alternating current in the power grid and the high-voltage direct current.

[0042] Convert the high-voltage direct current into low-voltage direct current; wherein, both the high-voltage direct current and the low-voltage direct current can be determined according to actual circumstances and are not limited herein. In practical applications, the DC-DC circuit 102 is called an intermediate DC-DC circuit, and the intermediate DC-DC circuit uses multiple groups of identical DC-DC conversion modules, uses a series structure on the high-voltage DC side, and a parallel structure on the low-voltage DC side, thereby achieving a wide range of DC step-down.

[0043] Convert the low-voltage direct current into low-voltage alternating current; wherein, both the low-voltage direct current and the low-voltage alternating current can be determined according to actual circumstances and are not limited herein. In practical applications, the inverter circuit is used to achieve the bidirectional conversion between the low-voltage direct current and the low-voltage alternating current, converting the low-voltage direct current into low-voltage alternating current to drive the flywheel to accelerate during charging, and converting the low-voltage alternating current into low-voltage direct current during discharging.

[0044] Convert the low-voltage alternating current into mechanical energy. Wherein, both the low-voltage alternating current and the mechanical energy can be determined according to actual circumstances and are not limited herein. In practical applications, the flywheel energy storage device stores and releases energy using the mechanical energy of the flywheel rotation.

[0045] In the embodiment of the present application, the grid-connected circuit converts the high-voltage alternating current in the power grid into high-voltage direct current, the DC-DC circuit converts the high-voltage direct current into low-voltage direct current; the inverter circuit converts the low-voltage direct current into low-voltage alternating current; the flywheel energy storage device converts the low-voltage alternating current into mechanical energy to achieve direct grid connection, avoiding the need for a power frequency transformer in the flywheel energy storage system to access the power grid, resulting in a complex and large overall structure and large circuit losses, and solving the problem of low energy conversion efficiency.

[0046] In an alternative embodiment of the present application, the DC-DC circuit 102 includes M first sub-modules 1021, where M is a positive integer greater than or equal to 1; the first side of the first sub-module 1021 is connected in parallel with the grid-connected circuit 101; the second side of the first sub-module 1021 is connected in series with the inverter circuit 103; M is determined by the ratio of the voltage on the first side to the voltage on the second side.

[0047] In this embodiment, the first sub-module 1021 can be determined according to actual conditions and is not limited here. As an example, the first sub-module 1021 can be a circuit sub-module. In practical applications, the DC-DC circuit 102 can be referred to as an intermediate DCDC circuit, and the first sub-module 1021 can be referred to as an intermediate circuit sub-module.

[0048] The first side can be determined according to actual conditions and is not limited here. As an example, the first side can be the high-voltage DC side.

[0049] The second side can be determined according to actual conditions and is not limited here. As an example, the second side can be the low-voltage DC side.

[0050] The specific process by which M is determined by the ratio of the voltage on the first side to the voltage on the second side can be determined according to actual conditions and is not limited here. As an example, the number of M is determined by the ratio of the DC voltages on both sides, M is an integer, and M should be as small as possible to reduce device usage and control difficulty.

[0051] In practical applications, the DC-DC circuit 102 is an intermediate DC-DC circuit, and the first sub-module 1021 is an intermediate circuit sub-module. The intermediate DC-DC circuit uses multiple groups of identical DC-DC conversion modules, with a series structure on the high-voltage DC side and a parallel structure on the low-voltage DC side, thereby achieving a wide range of DC voltage step-down. The intermediate DC-DC circuit uses M identical intermediate circuit sub-modules, with a parallel structure on the grid-connected circuit side and a series structure on the inverter circuit side, reducing the DC voltage value on the inverter circuit side to 1 / M of the DC voltage value on the grid-connected circuit side. The value of M is determined by the ratio of the DC voltages on both sides. M is an integer and should be as small as possible to reduce the number of devices used and the control difficulty. Multiple groups of intermediate circuit sub-modules can use techniques such as carrier phase shift during control to improve the quality of the DC voltage on the inverter circuit side.

[0052] In an alternative embodiment of the present application, the grid-connected circuit 101 includes a modular multi-level topology circuit; the multi-level topology circuit includes a three-phase circuit; each branch of the three-phase circuit includes upper and lower bridge arms, and each bridge arm includes N second sub-modules 1011, where N is a positive integer greater than or equal to 1; N is determined by the voltage value of the grid-connected circuit and the withstand voltage level of the second sub-module 1011;

[0053] The second sub-module 1011 is used for controllable rectification of the power grid.

[0054] In this embodiment, the second sub-module 1011 can be determined according to the actual situation and is not limited herein. As an example, the second sub-module 1011 can also be referred to as a sub-module.

[0055] The specific process of determining N by the voltage value of the grid-connected circuit and the withstand voltage level of the second sub-module 1011 can be determined according to the actual situation and is not limited herein. As an example, the number of N is determined by the grid-connected voltage value and the withstand voltage level of the sub-module electronic devices. N should be as small as possible while ensuring the normal operating voltage of the sub-module to reduce the number of sub-modules used and the control difficulty.

[0056] In practical applications, the grid-connected circuit uses a modular multi-level topology to achieve controllable rectification. Each branch of the three-phase circuit is divided into upper and lower bridge arms, and each bridge arm uses N sub-modules. The number of N is determined by the grid-connected voltage value and the withstand voltage level of the sub-module electronic devices. N should be as small as possible while ensuring the normal operating voltage of the sub-module to reduce the number of sub-modules used and the control difficulty.

[0057] In an alternative embodiment of the present application, the inverter circuit 103 includes multiple groups of inverter sub-modules 1031; the multiple groups of inverter sub-modules are connected in parallel; the number of inverter sub-modules 1031 is determined by the number of flywheel energy storage devices 104 to be controlled.

[0058] In this embodiment, the inverter sub-module 1031 can be determined according to actual situations and will not be limited herein. As an example, the inverter sub-module 1031 can be referred to as an inverter circuit sub-module.

[0059] The specific process for determining the number of the inverter sub-modules 1031 according to the number of the flywheel energy storage devices 104 can be determined according to actual situations and will not be limited herein.

[0060] In practical applications, the inverter circuit uses a parallel connection method of multiple inverter circuit sub-modules and is connected to the same DC bus. Each inverter circuit sub-module can control a flywheel energy storage device to charge and discharge, and the number of inverter circuit sub-modules is determined by the flywheel energy storage devices controlled by the system.

[0061] In an alternative embodiment of the present application, the multiple groups of inverter sub-modules 1031 are connected to the same DC bus; each group of the inverter sub-modules 1031 is configured to control one of the flywheel energy storage devices 104 to charge or discharge.

[0062] In practical applications, the inverter sub-module 1031 can be referred to as an inverter circuit sub-module, which is used to realize the bidirectional conversion between low-voltage direct current and low-voltage alternating current. During charging, it converts low-voltage direct current into low-voltage alternating current to drive the flywheel to accelerate, and during discharging, it converts low-voltage alternating current into low-voltage direct current. The inverter circuit uses a parallel connection method of multiple inverter circuit sub-modules and is connected to the same DC bus. Each inverter circuit sub-module can control a flywheel energy storage device to charge and discharge, and the number of inverter circuit sub-modules is determined by the flywheel energy storage devices controlled by the system.

[0063] In an alternative embodiment of the present application, the second sub-module 1011 adopts a half-bridge structure or a full-bridge structure; the half-bridge structure includes 2 controllable switch tubes and 1 energy storage capacitor; the full-bridge structure includes 4 controllable switch tubes and 1 energy storage capacitor.

[0064] In this embodiment, the half-bridge structure includes 2 controllable switch tubes and 1 energy storage capacitor. Among them, the controllable switch tubes can be determined according to actual situations and will not be limited herein. As an example, the controllable switch tubes can include IGBT, MOSFET, etc. In practical applications, the 2 controllable switch tubes can be respectively denoted as Q1 and Q2; the 1 energy storage capacitor can be denoted as C1; for easy understanding, it can be combined with Figure 3 for understanding. Figure 3 is a schematic diagram of the second sub-module adopting a half-bridge structure in the embodiment of the present application.

[0065] The full-bridge structure includes 4 controllable switching tubes and 1 energy storage capacitor. Among them, the controllable switching tubes can be determined according to actual situations and are not limited herein. In practical applications, the 4 controllable switching tubes can be respectively denoted as Q1, Q2, Q3, and Q4; the 1 energy storage capacitor can be denoted as C1; for the convenience of understanding, it can be combined with Figure 4 for understanding. Figure 4 This is a schematic diagram of the second sub-module in the embodiment of the present application adopting a full-bridge structure.

[0066] In practical applications, the grid-connected circuit sub-module can use a half-bridge structure, which consists of 2 controllable switching tubes (including IGBT, MOSFET, etc.) and 1 energy storage capacitor. The grid-connected circuit sub-module can use a full-bridge structure, which consists of 4 controllable switching tubes and 1 energy storage capacitor. Compared with the half-bridge structure, the number of devices used increases, and the control performance is improved.

[0067] In an alternative embodiment of the present application, the first sub-module 1021 adopts a DC-DC module with high-frequency transformer isolation or a buck-boost Buck-Boost circuit; the DC-DC module includes an H-type full-bridge circuit, a capacitor, and an isolation transformer; the Buck-Boost circuit includes a controllable switching tube, a capacitor, and an inductor.

[0068] In this embodiment, the DC-DC module with high-frequency transformer isolation can be determined according to actual situations and is not limited herein. For the convenience of understanding, an example is given here, and it can be combined with Figure 5 for understanding. Figure 5 This is a schematic diagram of the first sub-module in the embodiment of the present application adopting a DC-DC module with high-frequency transformer isolation.

[0069] The Buck-Boost circuit can be determined according to actual situations and is not limited herein. For the convenience of understanding, an example is given here, and it can be combined with Figure 6 for understanding. Figure 6 This is a schematic diagram of the first sub-module in the embodiment of the present application adopting a Buck-Boost circuit.

[0070] In practical applications, the first sub-module 1021 is an intermediate circuit sub-module. The intermediate circuit sub-module can use a DCDC module with high-frequency transformer isolation. The module consists of an H-type full-bridge circuit composed of controllable switching tubes, an intermediate support capacitor, and an intermediate isolation transformer. The H-type full-bridge circuit is used to convert direct current into high-frequency alternating current, and the high-frequency transformer is used to achieve electrical isolation between the input side and the output side. The intermediate circuit sub-module can also use a Buck-Boost circuit, which consists of controllable switching tubes, a support capacitor, and an inductor. Compared with the DCDC module with high-frequency transformer isolation, the Buck-Boost circuit uses fewer devices and has a smaller volume and weight, but it cannot achieve electrical isolation between the input and output sides, and is suitable for application scenarios with strict requirements for volume and weight but no electrical isolation requirements.

[0071] In an alternative embodiment of the present application, the turns ratio of the isolation transformer is 1:1 or determined according to preset design requirements.

[0072] In this embodiment, the isolation transformer can also be referred to as an intermediate isolation transformer.

[0073] The preset design requirements can be determined according to the actual situation and are not limited herein.

[0074] In practical applications, the intermediate isolation transformer can use a turns ratio of 1:1 or adjust the turns ratio according to the system design requirements.

[0075] In an alternative embodiment of the present application, the inverter sub-module 1031 adopts a three-phase two-level inverter topology, a three-phase three-level NPC inverter topology, or a three-phase three-level ANPC inverter topology; the three-phase two-level inverter topology, the three-phase three-level NPC inverter topology, and the three-phase three-level ANPC inverter topology all include controllable switching tubes and support capacitors.

[0076] In this embodiment, the three-phase two-level inverter topology can be determined according to the actual situation and is not limited herein. For the convenience of understanding, an example is given here. It can be understood in combination with Figure 7 for understanding. Figure 7 is a schematic diagram of the three-phase two-level inverter topology circuit adopted by the inverter sub-module in the embodiment of the present application.

[0077] The three-phase three-level NPC inverter topology can be determined according to the actual situation and is not limited herein. For the convenience of understanding, an example is given here. It can be understood in combination with Figure 8 for understanding. Figure 8 is a schematic diagram of the three-phase three-level NPC inverter topology adopted by the inverter sub-module in the embodiment of the present application.

[0078] The three-phase three-level ANPC inverter topology can be determined according to the actual situation and will not be limited here. For the convenience of understanding, an example is given here. It can be understood in combination with Figure 9 for understanding. Figure 9 FIG. is a schematic diagram of the inverter sub-module of the embodiment of the present application adopting a three-phase three-level ANPC inverter topology.

[0079] In practical applications, the inverter circuit sub-module can use a three-phase two-level inverter topology, which consists of controllable switch tubes and supporting capacitors and can realize the bidirectional conversion between direct current and three-phase alternating current. The inverter circuit sub-module can use a three-phase three-level NPC inverter topology, which consists of controllable switch tubes and supporting capacitors. Compared with the three-phase two-level topology, more switching devices are used, and at the same time, the power quality of the output voltage is improved. The inverter circuit sub-module can use a three-phase three-level ANPC inverter topology, which consists of controllable switch tubes and supporting capacitors. Compared with the NPC topology, the difference in the switching frequency of each switch tube inside the topology can be reduced, making the device heating more uniform and improving the service life of the device.

[0080] The flywheel energy storage system of the present application can be directly connected to the grid, avoiding the problems that the flywheel energy storage system needs to use a power frequency transformer to access the grid, resulting in a complex and large overall structure, large circuit losses, and low energy conversion efficiency.

[0081] For better understanding, here the flywheel energy storage system is exemplified as a flywheel energy storage system using power electronic devices to connect to the grid to illustrate and solve the problems of large system volume and weight and high loss in the existing flywheel energy storage system using a power frequency transformer grid connection scheme.

[0082] First, the flywheel energy storage system of the present application mainly includes a grid connection circuit, an intermediate DCDC circuit, an inverter circuit, and a flywheel energy storage device, and is used to realize the bidirectional energy flow between the flywheel energy storage system and the grid.

[0083] Second, the grid connection circuit uses a modular multilevel topology to achieve controllable rectification and realizes the bidirectional conversion between the three-phase alternating current of 10KV 50Hz of the grid and high-voltage direct current.

[0084] Third, the intermediate DCDC circuit uses multiple groups of identical DCDC conversion modules, with a series structure on the high-voltage DC side and a parallel structure on the low-voltage DC side, so as to realize a large range of DC step-down. The DCDC conversion module can use a non-isolated Buck-Boost circuit or a bidirectional DCDC structure with a high-frequency isolation transformer.

[0085] Fourth, the inverter circuit is used to achieve bidirectional conversion between low-voltage direct current and low-voltage alternating current. During charging, it converts low-voltage direct current into low-voltage alternating current to drive the flywheel to accelerate, and during discharging, it converts low-voltage alternating current into low-voltage direct current. The inverter circuit can use a three-phase two-level full-bridge topology or a three-phase three-level full-bridge topology.

[0086] Fifth, the flywheel energy storage device stores and releases energy using the mechanical energy of the flywheel rotation.

[0087] For easy understanding, an example is given here.

[0088] 1. The flywheel energy storage system of this application can be understood in combination with Figure 1 It mainly includes four parts: a grid-connected circuit, an intermediate DCDC circuit, an inverter circuit, and a flywheel energy storage device. Among them, the grid-connected circuit is used to achieve bidirectional conversion between the three-phase alternating current of 10KV 50Hz of the power grid and high-voltage direct current. The intermediate DCDC circuit is used to achieve the conversion of high and low voltage direct current. The inverter circuit is used to achieve the conversion between low-voltage direct current and low-voltage three-phase alternating current. The flywheel energy storage device is used to achieve the conversion between electrical energy and the mechanical energy of the flywheel, so as to achieve bidirectional conversion between the electrical energy of the power grid and the mechanical energy of the flywheel energy storage system.

[0089] 2. Understood in combination with Figure 2 The implementation scheme of the flywheel energy storage system topology in this application is as follows: The grid-connected circuit uses a modular multilevel topology to achieve controllable rectification. Each branch of the three-phase circuit is divided into upper and lower bridge arms, and each bridge arm uses N sub-modules. The number of N is determined by the grid-connected voltage value and the withstand voltage level of the electronic devices of the sub-module. N should be as small as possible under the condition of ensuring the normal working voltage of the sub-module to reduce the number of sub-modules used and the control difficulty. The intermediate DCDC circuit uses M identical intermediate circuit sub-modules, with a parallel structure on the grid-connected circuit side and a series structure on the inverter circuit side, so that the DC voltage value on the inverter circuit side is reduced to 1 / M of the DC voltage value on the grid-connected circuit side. The number of M is determined by the ratio of the DC voltages on both sides. M takes an integer and M should be as small as possible to reduce device usage and control difficulty. Multiple groups of intermediate circuit sub-modules can use technologies such as carrier phase shift equalization during control to improve the DC voltage quality on the inverter circuit side. The inverter circuit uses a parallel connection method of multiple groups of inverter circuit sub-modules, connected to the same DC bus. Each inverter circuit sub-module can control a flywheel energy storage device for charging and discharging. The number of inverter circuit sub-modules is determined by the flywheel energy storage device controlled by the system.

[0090] 3. The grid-connected circuit sub-module can use Figure 3 The half-bridge structure shown, which consists of 2 controllable switch tubes (including IGBT, MOSFET, etc.) and 1 energy storage capacitor.

[0091] 4. The grid-connected circuit sub-module can useFigure 4 The full-bridge structure shown, which consists of 4 controllable switch tubes and 1 energy storage capacitor. Compared with the half-bridge structure, the number of components used increases, and the control performance is improved.

[0092] 5. The intermediate circuit sub-module can use Figure 5 The DCDC module with high-frequency transformer isolation shown. The module consists of an H-type full-bridge circuit composed of controllable switch tubes, an intermediate support capacitor, and an intermediate isolation transformer. The H-type full-bridge circuit is used to convert direct current into high-frequency alternating current, and the high-frequency transformer is used to achieve electrical isolation between the input side and the output side. The intermediate isolation transformer can use a turns ratio of 1:1 or can adjust the turns ratio according to the system design requirements.

[0093] 6. The intermediate circuit sub-module can use Figure 6 The Buck-Boost circuit shown, which consists of a controllable switch tube, a support capacitor, and an inductor. Compared with the DCDC module with high-frequency transformer isolation, the Buck-Boost circuit uses fewer components, has a smaller volume and weight, but cannot achieve electrical isolation between the input and output sides, and is suitable for application scenarios with strict requirements for volume and weight and no electrical isolation requirements.

[0094] 7. The inverter circuit sub-module can use Figure 7 The three-phase two-level inverter topology shown, which consists of controllable switch tubes and a support capacitor and can achieve bidirectional conversion between direct current and three-phase alternating current.

[0095] 8. The inverter circuit sub-module can use Figure 8 The three-phase three-level NPC inverter topology shown, which consists of controllable switch tubes and a support capacitor. Compared with the three-phase two-level topology, more switch devices are used, and at the same time, the power quality of the output voltage is improved.

[0096] 9. The inverter circuit sub-module can use Figure 9 The three-phase three-level ANPC inverter topology shown, which consists of controllable switch tubes and a support capacitor. Compared with the NPC topology, it can reduce the difference in the switching frequency of each switch tube inside the topology, make the device heating more uniform, and at the same time improve the service life of the device.

[0097] The flywheel energy storage system of this application can achieve direct grid connection, avoiding the problem that the flywheel energy storage system needs to use a power frequency transformer to access the grid, resulting in a complex and large overall structure, large circuit losses, and low energy conversion efficiency.

[0098] In practical applications, the flywheel energy storage system includes four parts: a grid-connected circuit, an intermediate DCDC circuit, an inverter circuit and a flywheel energy storage device. The grid-connected circuit is connected to the high-voltage power grid to realize the conversion between high-voltage AC and high-voltage DC. The intermediate DCDC circuit realizes the conversion between high-voltage DC and low-voltage DC. The inverter circuit realizes the conversion between low-voltage DC and low-voltage AC, and connects the flywheel energy storage device, thereby realizing the two-way flow of electric energy between the power grid and the flywheel energy storage device.

[0099] As an example, the flywheel energy storage system may use a main circuit topology structure composed of a half-bridge grid-connected circuit submodule, a DCDC module isolated by a high-frequency transformer, and a three-phase two-level inverter circuit.

[0100] As an example, the flywheel energy storage system may use a main circuit topology structure composed of a half-bridge grid-connected circuit submodule, a DCDC module isolated by a high-frequency transformer, and a three-phase three-level NPC inverter circuit.

[0101] As an example, the flywheel energy storage system may use a main circuit topology structure composed of a half-bridge grid-connected circuit submodule, a DCDC module isolated by a high-frequency transformer, and a three-phase three-level ANPC inverter circuit.

[0102] As an example, the flywheel energy storage system may use a main circuit topology structure composed of a half-bridge grid-connected circuit submodule, a Buck-Boost circuit module, and a three-phase two-level inverter circuit.

[0103] As an example, the flywheel energy storage system can use a main circuit topology structure composed of a half-bridge grid-connected circuit submodule, a Buck-Boost circuit module, and a three-phase three-level NPC inverter circuit; use a main circuit topology structure composed of a half-bridge grid-connected circuit submodule, a Buck-Boost circuit module, and a three-phase three-level ANPC inverter circuit.

[0104] As an example, the flywheel energy storage system may use a main circuit topology structure composed of a full-bridge grid-connected circuit submodule, a DCDC module isolated by a high-frequency transformer, and a three-phase two-level inverter circuit.

[0105] As an example, the flywheel energy storage system may use a main circuit topology structure composed of a full-bridge grid-connected circuit submodule, a DCDC module isolated by a high-frequency transformer, and a three-phase three-level NPC inverter circuit.

[0106] As an example, the flywheel energy storage system may use a main circuit topology structure composed of a full-bridge grid-connected circuit submodule, a DCDC module isolated by a high-frequency transformer, and a three-phase three-level ANPC inverter circuit.

[0107] As an example, the flywheel energy storage system may use a main circuit topology structure jointly composed of a full-bridge grid-connected circuit sub-module, a Buck-Boost circuit module, and a three-phase two-level inverter circuit.

[0108] As an example, the flywheel energy storage system may use a main circuit topology structure jointly composed of a full-bridge grid-connected circuit sub-module, a Buck-Boost circuit module, and a three-phase three-level NPC inverter circuit.

[0109] As an example, the flywheel energy storage system may use a main circuit topology structure jointly composed of a full-bridge grid-connected circuit sub-module, a Buck-Boost circuit module, and a three-phase three-level ANPC inverter circuit.

[0110] The embodiment of the present application also provides a control device for flywheel energy storage. The control device for flywheel energy storage includes any one of the above-mentioned systems.

[0111] In this embodiment, reference may be made to the descriptions in any one of the above-mentioned systems, which will not be elaborated herein.

[0112] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

[0113] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A flywheel energy storage system, characterized in that, The system includes: a grid-connected circuit, a DC-DC circuit, an inverter circuit, and a flywheel energy storage device; the DC-DC circuit is respectively connected to the grid-connected circuit and the inverter circuit; the inverter circuit is connected to the flywheel energy storage device; The grid-connected circuit is connected to the power grid and is used to convert the high-voltage alternating current in the power grid into high-voltage direct current; The DC-DC circuit is used to convert the high-voltage direct current into low-voltage direct current; The inverter circuit is used to convert the low-voltage direct current into low-voltage alternating current; The flywheel energy storage device is used to convert the low-voltage alternating current into mechanical energy.

2. The system according to claim 1, characterized in that, The DC-DC circuit includes M first sub-modules, where M is a positive integer greater than or equal to 1; the first side of the first sub-module is connected in parallel with the grid-connected circuit; the second side of the first sub-module is connected in series with the inverter circuit; M is determined by the ratio of the voltage on the first side to the voltage on the second side.

3. The system according to claim 2, wherein The grid-connected circuit includes a modular multilevel topology circuit; the multilevel topology circuit includes a three-phase circuit; each branch of the three-phase circuit includes upper and lower bridge arms, and each bridge arm includes N second sub-modules, where N is a positive integer greater than or equal to 1; N is determined by the voltage value of the grid-connected circuit and the withstand voltage level of the second sub-module; The second sub-module is used to perform controlled rectification on the power grid.

4. The system according to claim 3, wherein The inverter circuit includes multiple groups of inverter sub-modules; the multiple groups of inverter sub-modules are connected in parallel; the number of inverter sub-modules is determined by the number of flywheel energy storage devices to be controlled.

5. The system according to claim 4, wherein The multiple groups of inverter sub-modules are connected to the same DC bus; each group of inverter sub-modules is used to control one flywheel energy storage device to charge or discharge.

6. The system according to claim 3, wherein The second sub-module adopts a half-bridge structure or a full-bridge structure; the half-bridge structure includes 2 controllable switch tubes and 1 energy storage capacitor; the full-bridge structure includes 4 controllable switch tubes and 1 energy storage capacitor.

7. According to the system described in claim 2, the first sub-module adopts a DC-DC module with high-frequency transformer isolation or a buck-boost Buck-Boost circuit; the DC-DC module includes an H-type full-bridge circuit, a capacitor, and an isolation transformer; the Buck-Boost circuit includes a controllable switch tube, a capacitor, and an inductor.

8. The system according to claim 7, wherein, The turns ratio of the isolation transformer is 1:1 or is determined according to preset design requirements.

9. According to the system described in claim 5, the inverter sub-module adopts a three-phase two-level inverter topology, a three-phase three-level NPC inverter topology, or a three-phase three-level ANPC inverter topology; the three-phase two-level inverter topology, the three-phase three-level NPC inverter topology, and the three-phase three-level ANPC inverter topology all include controllable switch tubes and support capacitors.

10. A control device for flywheel energy storage, characterized in that, The control device includes the system according to any one of claims 1-9.

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