Energy storage system and control method

Abstract

Disclosed in the present application are a hybrid energy storage system and a control method. The system comprises a first-type energy storage device and at least one second-type energy storage device, wherein the first-type energy storage device comprises a first energy storage medium and a first energy storage converter; the second-type energy storage device comprises a second energy storage medium and a second energy storage converter; the charging and discharging speed of the first energy storage medium is greater than the charging and discharging speed of the second energy storage medium; the first energy storage medium is connected to a direct-current side of the first energy storage converter, and the direct-current side of the first energy storage converter is connected to a direct-current bus; the second energy storage medium is connected to a direct-current side of the second energy storage converter, and the direct-current side of the second energy storage converter is connected to the direct-current bus; and an alternating-current side of the first energy storage converter and an alternating-current side of the second energy storage converter are both connected to a point of common coupling. In the case of a power grid anomaly, a plurality of energy storage converters operate in parallel to supplement a power grid with the electric energy of a first energy storage medium; and the rated currents of the energy storage converters are set to be relatively low, thereby reducing the stress on the energy storage converters, and thus reducing the costs.

Description

Energy storage system and control method

[0001] This application claims priority to Chinese patent application number 202410239137.6, filed with the State Intellectual Property Office of China on March 1, 2024, entitled “A Hybrid Energy Storage System and Control Method,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of energy storage technology, and in particular to a hybrid energy storage system and a control method. Background Art

[0003] The capacity of grid-connected energy storage power stations is increasing, ranging from hundreds of MWh to GWh. The main purpose of using new energy sources such as photovoltaics and wind power is to achieve stability on the power supply side, which is usually dominated by capacity requirements. However, from the perspective of grid stability requirements, the demands are slightly different, such as meeting the short-term high-power output requirements of the grid instantaneous frequency regulation and the grid-connected energy storage requirements to meet grid stability.

[0004] Currently, most energy storage systems use low-rate devices, such as lithium batteries. However, when power grid anomalies occur, these devices cannot quickly assist the grid in recovering to normal. Summary of the Invention

[0005] In view of this, the present application provides a hybrid energy storage system and a control method, which can assist the power grid to return to normal quickly when an abnormality occurs in the power grid.

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] The present application provides a hybrid energy storage system, comprising: a first-type energy storage device and at least one second-type energy storage device; the first-type energy storage device comprises a first energy storage medium and a first energy storage converter; the second-type energy storage device comprises a second energy storage medium and a second energy storage converter; the charging and discharging speed of the first energy storage medium is greater than the charging and discharging speed of the second energy storage medium; the first energy storage medium is connected to the DC side of the first energy storage converter, and the DC side of the first energy storage converter is connected to a DC bus; the second energy storage medium is connected to the DC side of the second energy storage converter, and the DC side of the second energy storage converter is connected to the DC bus; the AC side of the first energy storage converter and the AC side of the second energy storage converter are both connected to a bus bar.

[0008] In one possible implementation, the hybrid energy storage system provided in the present application further includes: a controller; the controller is configured to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, and the operating modes include a voltage source mode and a current source mode.

[0009] In one possible implementation, the hybrid energy storage system provided in the present application also includes: a controller; the controller is configured to control the first energy storage medium to be connected to the first energy storage converter, and control the second energy storage medium to be disconnected from the second energy storage converter when the voltage or frequency at the bus point exceeds a first preset interval, the DC side of the first energy storage converter and the DC side of the second energy storage converter are connected in parallel through the DC bus, and the first energy storage converter is controlled to operate in a voltage source mode and the second energy storage converter is controlled to operate in a current source mode.

[0010] In one possible implementation, the hybrid energy storage system provided in the present application also includes: a controller; the second-type energy storage device also includes a second-type energy storage first device and a second-type energy storage second device; the controller is configured to control the first energy storage medium to be connected to the first energy storage converter, control the second energy storage medium in the second-type energy storage first device to be disconnected from the corresponding second energy storage converter, and control the second energy storage medium in the second-type energy storage second device to be connected to the corresponding second energy storage converter when the voltage or frequency at the junction exceeds a second preset interval; the DC side of the first energy storage converter and the DC sides of all the second energy storage converters are connected in parallel through the DC bus, and the first energy storage converter and all the second energy storage converters are controlled to operate in voltage source mode.

[0011] In one possible implementation, the controller further includes a configuration configured to, when the voltage or frequency at the bus point is within the first preset range, control the first energy storage medium to be disconnected from the first energy storage converter, control the second energy storage medium to be connected to the second energy storage converter, the DC side of the first energy storage converter and the DC side of the second energy storage converter to be connected in parallel through the DC bus, control the first energy storage converter to operate in voltage source mode, and control the second energy storage converter to operate in current source mode.

[0012] In one possible implementation, the second type of energy storage device includes a second type of energy storage first device and a second type of energy storage second device; the controller also includes a device configured to control the first energy storage medium to be disconnected from the first energy storage converter when the voltage or frequency at the bus point is within the first preset range, control the second energy storage medium in the second type of energy storage first device to be connected to the corresponding second energy storage converter, control the second energy storage medium in the second type of energy storage second device to be connected to the corresponding second energy storage converter, the DC side of the first energy storage converter and the DC sides of all the second energy storage converters are connected in parallel through the DC bus, and control the first energy storage converter and all the second energy storage converters to operate in current source mode.

[0013] In one possible implementation, the first type of energy storage device further includes: a first switch group and a second switch group; the first energy storage medium is connected to the DC bus through the first switch group; and the first energy storage converter is connected to the DC bus through the second switch group.

[0014] In one possible implementation, the second type of energy storage device further includes: a third switch group and a fourth switch group; the second energy storage medium is connected to the DC bus through the third switch group; and the second energy storage converter is connected to the DC bus through the fourth switch group.

[0015] A possible implementation further includes: a fifth switch group; the DC bus connected to the first type energy storage device and the DC bus connected to the second type energy storage device are connected via the fifth switch group.

[0016] In a possible implementation, the second type of energy storage device further includes: an equalizer; the equalizer is connected between the negative electrode of the second energy storage medium and the DC bus.

[0017] In one possible implementation, the first type of energy storage device is located in a first cabinet, the second type of energy storage device is located in a second cabinet, the DC side of the first cabinet is connected to the DC side of the second cabinet, and the AC side of the first cabinet is connected to the AC side of the second cabinet.

[0018] The embodiment of the present application also provides a control method for a hybrid energy storage system, which includes: a first type of energy storage device and at least one second type of energy storage device; the first type of energy storage device includes a first energy storage medium and a first energy storage converter; the second type of energy storage device includes a second energy storage medium and a second energy storage converter; the charging and discharging speed of the first energy storage medium is greater than the charging and discharging speed of the second energy storage medium; the first energy storage medium is connected to the DC side of the first energy storage converter, and the DC side of the first energy storage converter is connected to a DC bus; the second energy storage medium is connected to the DC side of the second energy storage converter, and the DC side of the second energy storage converter is connected to the DC bus; the AC side of the first energy storage converter and the AC side of the second energy storage converter are both connected to a bus bar;

[0019] The method includes: detecting the voltage or frequency of the bus point; switching the working mode of the first energy storage converter and the working mode of the second energy storage converter according to the voltage or frequency of the bus point, the working modes including voltage source mode and current source mode; the first energy storage converter operates in voltage source mode by default, and the second energy storage converter operates in current source mode by default.

[0020] A possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: when the voltage or frequency of the bus point exceeds a first preset interval, controlling the first energy storage medium to start working and controlling the second energy storage medium not to start working, controlling the DC side of the first energy storage converter and the DC side of the second energy storage converter to be connected in parallel through the DC bus, controlling the first energy storage converter to operate in voltage source mode, and controlling the second energy storage converter to operate in current source mode.

[0021] A possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: when the voltage or frequency of the bus point exceeds a second preset interval, controlling the first energy storage medium to be put into operation, controlling part of the second energy storage medium to be put into operation, and controlling the remaining second energy storage medium not to be put into operation; and controlling the first energy storage converter and all the second energy storage converters to operate in voltage source mode.

[0022] A possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: when the voltage or frequency of the bus point exceeds a second preset interval, controlling the first energy storage medium to be put into operation and controlling all the second energy storage media to be put into operation; controlling the first energy storage converter and all the second energy storage converters to operate in voltage source mode.

[0023] A possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: obtaining a power angle according to the voltage of the bus point, and switching the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the power angle.

[0024] A possible implementation method, wherein the operating mode of the first energy storage converter and the operating mode of the second energy storage converter are switched according to the voltage or frequency of the confluence point, specifically includes: the master controller of the hybrid energy storage system obtains a first control instruction and a second control instruction according to the voltage or frequency of the confluence point and the power dispatch instruction issued by the energy management system EMS, sends the first control instruction to the first control unit corresponding to the first energy storage converter, and sends the second control instruction to the second control unit corresponding to the second energy storage converter, the first control unit switches the operating mode of the first energy storage converter according to the first control instruction, and the second control unit switches the operating mode of the second energy storage converter according to the second control instruction.

[0025] The hybrid energy storage system provided in the embodiment of the present application includes two different types of energy storage media, wherein the discharge rate of the first energy storage medium is greater than the discharge rate of the second energy storage medium. Therefore, when an abnormality occurs in the power grid, such as when the voltage is too high or too low, the first energy storage medium can discharge quickly to support the grid voltage and quickly assist the grid voltage to return to normal. When the power grid is normal, the second energy storage medium can discharge a large capacity, and the first energy storage medium can stop working at this time. Since the DC sides of multiple energy storage converters are connected in parallel, when the power grid is abnormal, multiple energy storage converters can work in parallel to jointly supplement the electric energy of the first energy storage medium to the power grid. Therefore, the rated current of each energy storage converter can be set lower, and does not need to be set according to the rated current of the first energy storage medium, thereby reducing the stress of each energy storage converter and reducing costs.

[0026] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a schematic diagram of a hybrid energy storage system provided in an embodiment of the present application;

[0028] FIG2 is a schematic diagram of another hybrid energy storage system provided in an embodiment of the present application;

[0029] FIG3 is a schematic diagram of another hybrid energy storage system provided in an embodiment of the present application;

[0030] FIG4 is a schematic diagram of another hybrid energy storage system provided in an embodiment of the present application;

[0031] FIG5 is a schematic diagram of another hybrid energy storage system provided in an embodiment of the present application;

[0032] FIG6 is a flow chart of a control method for a hybrid energy storage system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the embodiments of the present application are further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0034] See Figure 1, which is a schematic diagram of a hybrid energy storage system provided in an embodiment of the present application.

[0035] The hybrid energy storage system provided in the embodiment of the present application includes: two different types of energy storage devices, namely, a first type of energy storage device 100 and at least one second type of energy storage device 200; the first type of energy storage device 100 includes a first energy storage medium 101 and a first energy storage converter (PCS, Power Conversion System) 102.

[0036] The second type of energy storage device 200 includes a second energy storage medium 201 and a second energy storage converter 202 .

[0037] The charge and discharge rate of the first energy storage medium 101 is greater than the charge and discharge rate of the second energy storage medium 201 .

[0038] The first energy storage medium 101 is connected to the DC side of the first energy storage converter 102 , and the DC side of the first energy storage converter 102 is connected to the DC bus BUS.

[0039] The second energy storage medium 201 is connected to the DC side of the second energy storage converter 202 , and the DC side of the second energy storage converter 202 is connected to the DC bus BUS.

[0040] The AC side of the first energy storage converter 102 and the AC side of the second energy storage converter 202 are both connected to the bus point PCC.

[0041] The embodiment of the present application does not specifically limit the device to which the bus point PCC is connected. For example, the bus point PCC may be connected to a first end of a transformer, and a second end of the transformer may be connected to a power grid.

[0042] The embodiments of the present application do not specifically limit the specific implementation of the first energy storage medium 101. For example, it may include at least one of a supercapacitor and a flywheel. The first energy storage medium 101 is a high-rate energy storage medium with relatively large inertia. The power grid may experience abnormalities at any time, which is unplanned. The first energy storage medium 101 can always be in a hot standby state. When the power grid is abnormal, for example, when the grid voltage is low, the first energy storage medium 101 can release a large amount of energy in a short period of time to support the grid voltage and enable the grid to return to normal more quickly. The first energy storage converter 102 operates in voltage source mode by default.

[0043] Similarly, the embodiments of the present application do not specifically limit the specific implementation of the second energy storage medium 201. For example, it may include an electrochemical cell such as a lithium-ion battery. The second energy storage medium 201 is a low-rate energy storage medium. Generally, the first energy storage medium 201 has a low-rate of several C, for example, 2C or less, while the first energy storage medium 101 is a high-rate energy storage medium, such as a supercapacitor with a capacity of tens of C. The second energy storage medium 201 operates in a planned manner, and the second energy storage converter 202 operates in current source mode by default. Only when the power grid is abnormal can the second energy storage converter 202 change its operating mode to voltage source mode. The second energy storage converter 202 and the first energy storage converter 102 work together to support the power grid through the abnormal period.

[0044] It should be understood that when the hybrid energy storage system includes multiple second energy storage devices, when the power grid is abnormal, the second energy storage converters in all second energy storage devices can operate in voltage source mode, or the second energy storage converters in some second energy storage devices can operate in voltage source mode, and the second energy storage converters in some second energy storage devices can operate in current source mode. Specifically, the proportion of the second energy storage converters operating in current source mode and voltage source mode can be selected according to the abnormal situation of the power grid. The power grid abnormality can be determined by detecting the voltage or frequency of the power grid. Specifically, the voltage or frequency of the power grid can be detected by each energy storage converter. Since the AC sides of each energy storage converter are connected in parallel, the voltage on the AC side of each energy storage converter can reflect the voltage of the power grid.

[0045] Since the DC sides of the various energy storage converters are connected together in the hybrid energy storage system provided by the embodiment of the present application, the various parallel energy storage converters can work together. For example, when the power grid is normal, the first energy storage medium 101 can be disconnected from the first energy storage converter 102, and the energy of the second energy storage medium 201 can be simultaneously converted through the first energy storage converter 102 and the second energy storage converter 202 to be connected to the grid. Similarly, when the power grid is abnormal, the second energy storage medium 201 can be disconnected from the second energy storage converter 202, and the energy of the first energy storage medium 101 can be simultaneously converted through the first energy storage converter 102 and the second energy storage converter 202. It should be understood that the first energy storage medium 101 can absorb energy from the power grid and release energy to the power grid.

[0046] Due to the hybrid energy storage system provided by the embodiment of the present application, multiple energy storage converters are connected in parallel on the DC side, so that the multiple energy storage converters can work together, which can maximize the ability of the first energy storage medium to quickly charge and discharge. As a result, the first energy storage converter can be designed with a reduced rating and must be designed according to the rated current of the supercapacitor to reduce the stress of the first energy storage converter, thereby reducing the cost of the first energy storage converter.

[0047] The following is a detailed description using an example in which the first energy storage medium is a supercapacitor and the second energy storage medium is a lithium-ion battery.

[0048] See FIG2 , which is a schematic diagram of another hybrid energy storage system provided in an embodiment of the present application.

[0049] In the embodiments of this application, a hybrid energy storage system including one first-class energy storage device and multiple second-class energy storage devices is used as an example. The embodiments of this application do not specifically limit the number of second-class energy storage devices. FIG2 illustrates only two second-class energy storage devices as an example, and a greater number of second-class energy storage devices may also be included.

[0050] In the hybrid energy storage system provided in the embodiment of the present application, the first type of energy storage device also includes: a first switch group (K12 and K13) and a second switch group K15; it should be understood that the DC bus includes a DC positive bus and a DC negative bus, and the energy storage converter also includes a positive pole and a negative pole. Therefore, the switch groups in the embodiment of the present application include two switches, which are respectively connected to the positive pole and the negative pole.

[0051] The first energy storage medium (supercapacitor) is connected to the DC bus through the first switch group (K12 and K13); the first energy storage converter PCS1 is connected to the DC bus through the second switch group K15.

[0052] In addition, a fuse FUSE12 is connected in series between the supercapacitor and the first switch group.

[0053] In the hybrid energy storage system provided in the embodiment of the present application, the second type of energy storage device further includes: a third switch group (K22 and K23) and a fourth switch group K25.

[0054] The second energy storage medium (lithium-ion battery 1) is connected to the DC bus through the third switch group (K22 and K23); the second energy storage converter PCS2 is connected to the DC bus through the fourth switch group K25.

[0055] Similar to the fuse in the first type of energy storage device, the second type of energy storage device also includes a fuse, and a fuse FUSE22 is further connected in series between the lithium-ion battery 1 and the third switch group ( K22 and K23 ).

[0056] The nth energy storage medium (lithium-ion battery n) is connected to the DC bus through the third switch group (Kn2 and Kn3); the third energy storage converter PCS3 is connected to the DC bus through the fourth switch group Kn5.

[0057] A fuse FUSEn2 is further connected in series between the lithium-ion battery n and the third switch group ( Kn2 and Kn3 ).

[0058] In order to isolate the energy storage converters, the DC bus also includes a switch group, that is, it also includes: a fifth switch group; the DC bus connected to the first type energy storage device and the DC bus connected to the second type energy storage device are connected through the fifth switch group.

[0059] As shown in FIG2 , each energy storage device may include a fifth switch group. The first-type energy storage device 100 includes a fifth switch group K01, which is connected between the first-type energy storage device and the second-type energy storage first device. The second-type energy storage first device includes a fifth switch group K02. If the lithium-ion battery n is the last second energy storage medium, the corresponding energy storage device may not include the fifth switch group. If other second-type energy storage devices are included, the energy storage device where the lithium-ion battery n is located also includes the fifth switch group K0n.

[0060] In addition, in the hybrid energy storage system provided in the embodiment of the present application, a sixth switch group and a fuse are connected in series between each energy storage converter and the bus junction. For example, PCS1 is connected to the bus junction through K11 and FUSE11 connected in series, PCS2 is connected to the bus junction through K21 and FUSE21 connected in series, and PCS3 is connected to the bus junction through Kn1 and FUSEn1 connected in series.

[0061] Since the two adjacent devices are directly connected to the switch group, the hybrid energy storage system provided in the embodiment of the present application also includes a controller (not shown in the figure). The controller can control the connection relationship between the two devices by controlling the state of the switch group. For example, controlling K12 and K13 to disconnect can disconnect the supercapacitor from PCS1, and can also disconnect the supercapacitor from the DC bus. The controller controls K01 to disconnect, which can disconnect the connection between the first type of energy storage device and the second type of energy storage device. The controller can also control K11 to disconnect, disconnecting PCS1 from the junction point. Similarly, it can also control the switch states of K21 and Kn1.

[0062] The hybrid energy storage system provided in the embodiment of the present application may further include a box-type transformer cabinet, in which a transformer is provided, and the junction point is connected to the power grid through the box-type transformer cabinet. A circuit breaker QF and a fuse FUSE01 are also connected in series between the box-type transformer cabinet and the junction point.

[0063] The hybrid energy storage system provided in the embodiment of the present application includes a controller for switching the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point. The operating modes include a voltage source mode and a current source mode.

[0064] In one specific implementation, a controller is configured to connect the first energy storage medium to the first energy storage converter and disconnect the second energy storage medium from the second energy storage converter when the voltage or frequency at the bus junction exceeds a first preset range. The DC side of the first energy storage converter and the DC side of the second energy storage converter are connected in parallel via a DC bus, and the first energy storage converter is controlled to operate in voltage source mode and the second energy storage converter in current source mode. It should be understood that both the first and second energy storage converters can also be controlled to operate in voltage source mode.

[0065] The hybrid energy storage system provided in the embodiment of the present application can use two energy storage converters in parallel to convert the energy of the supercapacitor to support the grid voltage when the grid is abnormal. Since the supercapacitor can quickly release or absorb energy, the two energy storage converters can be used in parallel to work.

[0066] A specific implementation method is described by taking a hybrid energy storage system including two second-type energy storage devices as an example. The second-type energy storage device includes a second-type energy storage first device and a second-type energy storage second device;

[0067] When the power grid is abnormal and a single Class II energy storage device cannot meet the power demand of the grid, and the duration of the power demand exceeds the allowable range of the supercapacitor, the energy storage converters in multiple Class II energy storage devices can be put into operation. It should be understood that when the energy storage converters in multiple Class II energy storage devices are put into operation, the operating mode can be selected based on the actual needs of the power grid. They can all operate in voltage source mode, or some can operate in voltage source mode and some in current source mode. The greater the power demand of the power grid, the greater the proportion of energy storage converters in the Class II energy storage devices operating in voltage source mode.

[0068] The controller is used to control the first energy storage medium to be connected to the first energy storage converter, control the second energy storage medium in the second type energy storage first device to be disconnected from the corresponding second energy storage converter, and control the second energy storage medium in the second type energy storage second device to be connected to the corresponding second energy storage converter when the voltage or frequency at the bus point exceeds a second preset interval; the DC side of the first energy storage converter and the DC sides of all the second energy storage converters are connected in parallel through a DC bus, and the first energy storage converter and all the second energy storage converters are controlled to operate in a voltage source mode.

[0069] In the second preset interval, the voltage or frequency at the bus point deviates more from the normal value than in the first preset interval, i.e., the grid anomaly is more serious. For example, the minimum absolute value of the second preset interval is greater than the maximum absolute value of the first preset interval. For example, if the grid voltage is expressed in per-unit values, the first preset interval is greater than -0.1 and less than +0.1, while the second preset interval is greater than -0.2 and less than or equal to -0.1, and greater than or equal to 0.1 and less than 0.2.

[0070] In the hybrid energy storage system provided in the embodiment of the present application, when the voltage or frequency at the confluence point exceeds the second preset interval, it indicates that the grid abnormality is more serious than when the voltage exceeds the first preset interval. At this time, all energy storage converters are required to operate in voltage source mode to provide maximum voltage support for the grid, so that the grid can quickly pass through the abnormal interval.

[0071] The above descriptions are all about the working modes when the power grid is abnormal. The following describes the working modes of the hybrid energy storage system when the power grid is normal.

[0072] The controller is further configured to disconnect the first energy storage medium from the first energy storage converter, for example, by disconnecting the supercapacitor from the first energy storage converter when the voltage or frequency at the bus junction is within a first preset range. In this case, the supercapacitor does not need to be put into operation. The controller is further configured to connect the second energy storage medium to the second energy storage converter, connecting the DC side of the first energy storage converter and the DC side of the second energy storage converter in parallel via a DC bus. The controller controls the first energy storage converter to operate in voltage source mode and the second energy storage converter to operate in current source mode. At this point, the lithium-ion battery is put into operation, and the system operates with capacity output as its goal.

[0073] At this time, the power grid is normal, and the hybrid energy storage system mainly aims at capacity output, that is, the supercapacitor can be put into operation, and only the lithium-ion battery is put into operation. The energy storage converters corresponding to the lithium-ion battery all work in current source mode.

[0074] In addition, when the hybrid energy storage system includes multiple second-type energy storage devices, when the power grid is normal, all second-type energy storage devices can be put into operation.

[0075] The controller is further configured to, when the voltage or frequency at the bus point is within a first preset range, control the first energy storage medium to be disconnected from the first energy storage converter, control the second energy storage medium in the second type energy storage first device to be connected to the corresponding second energy storage converter, control the second energy storage medium in the second type energy storage second device to be connected to the corresponding second energy storage converter, connect the DC side of the first energy storage converter and the DC sides of all the second energy storage converters in parallel through a DC bus, and control the first energy storage converter and all the second energy storage converters to operate in current source mode.

[0076] To ensure more flexible control when the supercapacitor is operational, the hybrid energy storage system provided in the embodiments of the present application also includes a DC-DC circuit. To achieve balancing between the lithium-ion batteries in each second-category energy storage device, the hybrid energy storage system provided in the embodiments of the present application also includes a balancer. It should be understood that the lithium-ion batteries of each second-category energy storage device constitute a battery cluster, comprising multiple cells, and each second-category energy storage device includes a balancer. This is described in detail below with reference to the accompanying drawings.

[0077] See FIG3 , which is a schematic diagram of another hybrid energy storage system provided in an embodiment of the present application.

[0078] The first type of energy storage device 100 in FIG3 includes a DCDC circuit 103 , a first end of the DCDC circuit 103 is connected to a supercapacitor, and a second end of the DCDC circuit 103 is connected to a DC bus via a series-connected FUSE 12 and a switch group ( K12 and K13 ).

[0079] The controller can control the charging and discharging speed of the supercapacitor by controlling the DCDC circuit 103 , for example, controlling the charging and discharging current of the supercapacitor.

[0080] In the hybrid energy storage system provided by the embodiment of the present application, each second-class energy storage device further includes: an equalizer; FIG3 is introduced by taking two second-class energy storage devices as an example, as shown in the figure, equalizer 1 and equalizer 2, and equalizer 1 and equalizer 2 are respectively connected between the negative pole of the second energy storage medium and the DC bus. In addition, the first end of the equalizer 1 is connected to the lithium-ion battery 1 through the switch K24, and the second end of the equalizer 1 is connected to the DC bus. When K23 is closed, the equalizer 1 can be bypassed. When the equalizer 1 plays a balancing role, K24 is closed. Similarly, the first end of the equalizer 2 is connected to the lithium-ion battery n through the switch Kn4, and the second end of the equalizer n is connected to the DC bus. When Kn3 is closed, the equalizer n can be bypassed. When the equalizer n plays a balancing role, Kn4 is closed.

[0081] The embodiment of the present application does not specifically limit the specific topology of the equalizer. In one possible implementation, the equalizer may include a switch and a DCDC circuit, and balance is achieved between the lithium-ion battery clusters by controlling the DCDC circuit.

[0082] The hybrid energy storage system provided in the embodiments of the present application realizes reconstruction of the DC bus by cross-connecting a high-rate energy storage medium and a low-rate energy storage medium on the DC side. Specifically, the DC bus can be reconstructed according to the state of the switch. The energy storage converter or battery can be independently switched in and out through the corresponding switch group, so that the rate and capacity of the hybrid energy storage system can be flexibly adjusted according to the state of the power grid to meet the needs of different projects.

[0083] The hybrid energy storage system provided in the embodiment of the present application, through the reconstruction of the DC bus, realizes that the energy storage converter corresponding to the high-rate energy storage medium can reuse the energy storage converter corresponding to the low-rate energy storage unit, or the energy storage converter corresponding to the low-rate energy storage medium can reuse the energy storage converter corresponding to the high-rate energy storage medium, thereby improving the utilization rate of the energy storage converter and reducing system costs. In addition, the operating mode of the energy storage converter in each energy storage device can also switch the operating mode according to the state of the power grid, that is, the voltage source mode or the current source mode, thereby realizing different combinations of high-rate energy storage medium and low-rate energy storage medium to meet the power grid stability requirements of different time scales.

[0084] The embodiments of this application do not specifically limit the hybrid energy storage system. For example, as shown in Figure 3, each energy storage device can be a separate cabinet. After multiple cabinets are seamlessly spliced ​​and connected in parallel, they are connected to the box-type transformer cabinet. To ensure temperature uniformity of the batteries across the cabinets, liquid cooling can be selected as the thermal management method for the lithium-ion batteries. The first type of energy storage device is located in the first cabinet, and the second type of energy storage device is located in the second cabinet. The DC side of the first cabinet is connected to the DC side of the second cabinet, and the AC side of the first cabinet is connected to the AC side of the second cabinet.

[0085] One possible implementation method is to integrate the circuit breaker QF and the fuse FUSE01 into an independent cabinet, or to integrate the circuit breaker QF and the fuse FUSE01 into the box-type transformer cabinet as an independent cabinet.

[0086] The embodiments of the present application do not specifically limit the number of controllers included in the hybrid energy storage system. For example, each energy storage device may include a control unit, that is, each energy storage converter corresponds to a control unit. In addition, the hybrid energy storage system may also include a master controller.

[0087] A specific control architecture of the hybrid energy storage system is described below with reference to the accompanying drawings.

[0088] See FIG4 , which is a schematic diagram of another hybrid energy storage system provided in an embodiment of the present application.

[0089] The hybrid energy storage system provided in this embodiment also includes a master controller 401 and multiple control units. Each energy storage device includes an energy storage converter, and each energy storage converter corresponds to a control unit. Figure 4 uses two energy storage converters, PCS1 and PCS2, as an example. The control units corresponding to the three energy storage converters are 403 and 404, respectively.

[0090] The master controller 401 of the hybrid energy storage system obtains the first control instruction and the second control instruction according to the voltage or frequency of the junction point and the power dispatch instruction issued by the energy management system EMS402. The junction point generally includes three phases, and the voltage of the junction point is v abc , the current is i abc . The frequency of the bus point can be obtained by the voltage or current of the bus point. The main controller 401 sends a first control instruction to the first control unit 403 corresponding to the first energy storage converter PCS1, and the main controller 401 sends a second control instruction to the second control unit 404 corresponding to the second energy storage converter PCS2. The first control unit 403 switches the working mode of the first energy storage converter PCS1 according to the first control instruction, and the second control unit 404 switches the working mode of the second energy storage converter PCS2 according to the second control instruction.

[0091] The power dispatch instruction issued by the EMS 402 may include at least one of active power dispatch and reactive power dispatch.

[0092] Figure 4 illustrates a hybrid energy storage system including two energy storage devices, corresponding to two energy storage converters. It should be understood that the hybrid energy storage system can also include a larger number of energy storage devices. Figure 5 takes three energy storage devices, corresponding to three energy storage converters, as an example. The difference between Figure 5 and Figure 4 is that it also includes a third energy storage converter PCS3 and a third control unit 405. The main controller 401 also sends a third control instruction to the third control unit 405. The third control unit 405 controls the working mode of the third energy storage converter PCS3 according to the third control instruction. The rest of the control principles can be found in the description of Figure 4 and will not be repeated here.

[0093] Based on the hybrid energy storage system provided in the above embodiment, an embodiment of the present application further provides a control method for the hybrid energy storage system, which is described in detail below with reference to the accompanying drawings.

[0094] See FIG6 , which is a flow chart of a control method for a hybrid energy storage system provided in an embodiment of the present application.

[0095] The control method of the hybrid energy storage system provided in the embodiment of the present application, the hybrid energy storage system includes: a first type of energy storage device and at least one second type of energy storage device; the first type of energy storage device includes a first energy storage medium and a first energy storage converter; the second type of energy storage device includes a second energy storage medium and a second energy storage converter; the charging and discharging speed of the first energy storage medium is greater than the charging and discharging speed of the second energy storage medium; the first energy storage medium is connected to the DC side of the first energy storage converter, and the DC side of the first energy storage converter is connected to the DC bus; the second energy storage medium is connected to the DC side of the second energy storage converter, and the DC side of the second energy storage converter is connected to the DC bus; the AC side of the first energy storage converter and the AC side of the second energy storage converter are both connected to a bus bar;

[0096] The method includes:

[0097] S401: Detecting the voltage or frequency of the busbar;

[0098] S402: Switch the working mode of the first energy storage converter and the working mode of the second energy storage converter according to the voltage or frequency of the bus point. The working modes include voltage source mode and current source mode. The first energy storage converter works in voltage source mode by default, and the second energy storage converter works in current source mode by default.

[0099] The embodiment of the present application does not specifically limit the parameters for determining grid abnormality, and can be determined by voltage or frequency. Specifically, each energy storage converter can detect the voltage at the confluence point to reflect the state of the grid.

[0100] The first energy storage medium is a high-rate energy storage medium with relatively high inertia. Grid anomalies can occur at any time, unplanned, and the first energy storage medium can remain in a hot standby state. During grid anomalies, such as low grid voltage, the first energy storage medium can release a large amount of energy in a short period of time to support the grid voltage and quickly restore the grid to normal. The first energy storage converter operates in voltage source mode by default.

[0101] The second energy storage medium is a low-rate energy storage medium. It operates in a planned manner, and the second energy storage converter defaults to current source mode. Only when the grid experiences an anomaly does the second energy storage converter change its operating mode to voltage source mode. Together with the first energy storage converter, the second energy storage converter supports the grid through the abnormal period.

[0102] In the control method for a hybrid energy storage system provided in an embodiment of the present application, multiple energy storage converters are connected in parallel on the DC side, allowing them to work together. This maximizes the rapid charging and discharging capabilities of the first energy storage medium, allowing the first energy storage converter to be designed with a reduced rating, specifically designed according to the rated current of the supercapacitor. This reduces the stress on the first energy storage converter, thereby reducing its cost. Furthermore, when an abnormality occurs in the power grid, the operating mode of each energy storage converter can be changed, thereby enabling the grid to quickly pass through the abnormal period.

[0103] When the power grid is abnormal and a single Class II energy storage device cannot meet the power demand of the grid, and the duration of the power demand exceeds the allowable range of the supercapacitor, the energy storage converters in multiple Class II energy storage devices can be put into operation. It should be understood that when the energy storage converters in multiple Class II energy storage devices are put into operation, the operating mode can be selected based on the actual needs of the power grid. They can all operate in voltage source mode, or some can operate in voltage source mode and some in current source mode. The greater the power demand of the power grid, the greater the proportion of energy storage converters in the Class II energy storage devices operating in voltage source mode.

[0104] One possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: when the voltage or frequency of the bus point exceeds the first preset interval, controlling the first energy storage medium to start working and controlling the second energy storage medium not to start working, controlling the DC side of the first energy storage converter and the DC side of the second energy storage converter to be connected in parallel through the DC bus, controlling the first energy storage converter to operate in voltage source mode, and controlling the second energy storage converter to operate in current source mode.

[0105] One possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: when the voltage or frequency of the bus point exceeds the second preset interval, controlling the first energy storage medium to start working, controlling part of the second energy storage medium to start working, and controlling the remaining second energy storage medium not to start working; controlling the first energy storage converter and all the second energy storage converters to operate in voltage source mode.

[0106] For example, a hybrid energy storage system includes a first-class energy storage device and a second-class energy storage device. When the power grid is abnormal, the two energy storage converters can be connected in parallel to convert the energy of the supercapacitor to support the grid voltage. Since the supercapacitor can quickly release or absorb energy, the two energy storage converters can be used in parallel to work.

[0107] One possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: when the voltage or frequency of the bus point exceeds the second preset interval, controlling the first energy storage medium to start working and controlling all second energy storage media to start working; controlling the first energy storage converter and all second energy storage converters to operate in voltage source mode.

[0108] The control method of the hybrid energy storage system provided in the embodiment of the present application is that when the voltage or frequency at the confluence point exceeds the second preset interval, it indicates that the grid abnormality is more serious than when the voltage exceeds the first preset interval. At this time, all energy storage converters are required to operate in voltage source mode to provide maximum voltage support for the grid, so that the grid can quickly pass through the abnormal interval.

[0109] One possible implementation method is to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, specifically including: obtaining the power angle according to the voltage of the bus point, and switching the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the power angle.

[0110] Switching the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point specifically includes:

[0111] The master controller of the hybrid energy storage system obtains the first control instruction and the second control instruction according to the voltage or frequency of the junction point and the power dispatch instruction issued by the energy management system EMS, sends the first control instruction to the first control unit corresponding to the first energy storage converter, and sends the second control instruction to the second control unit corresponding to the second energy storage converter. The first control unit switches the working mode of the first energy storage converter according to the first control instruction, and the second control unit switches the working mode of the second energy storage converter according to the second control instruction.

[0112] The control method of the hybrid energy storage system provided in the embodiment of the present application, through the reconstruction of the DC bus, realizes that the energy storage converter corresponding to the high-rate energy storage medium can reuse the energy storage converter corresponding to the low-rate energy storage unit, or the energy storage converter corresponding to the low-rate energy storage medium can reuse the energy storage converter corresponding to the high-rate energy storage medium, thereby improving the utilization rate of the energy storage converter and reducing system costs. In addition, the operating mode of the energy storage converter in each energy storage device can also switch the operating mode according to the state of the power grid, that is, the voltage source mode or the current source mode, so as to realize different combinations of high-rate energy storage medium and low-rate energy storage medium to meet the power grid stability requirements of different time scales.

[0113] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems or devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0114] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hybrid energy storage system, wherein: include: a first type of energy storage device and at least one second type of energy storage device; The first type of energy storage device includes a first energy storage medium and a first energy storage converter; The second type of energy storage device includes a second energy storage medium and a second energy storage converter; the charging and discharging speed of the first energy storage medium is greater than the charging and discharging speed of the second energy storage medium; the first energy storage medium is connected to the DC side of the first energy storage converter, and the DC side of the first energy storage converter is connected to the DC bus; the second energy storage medium is connected to the DC side of the second energy storage converter, and the DC side of the second energy storage converter is connected to the DC bus; the AC side of the first energy storage converter and the AC side of the second energy storage converter are both connected to a bus bar.

2. The system according to claim 1, wherein: Also includes: Controller; The controller is configured to switch the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point, wherein the operating modes include a voltage source mode and a current source mode.

3. The system according to claim 2, wherein: The controller also includes a device configured to control the first energy storage medium to be connected to the first energy storage converter, and the second energy storage medium to be disconnected from the second energy storage converter when the voltage or frequency at the bus point exceeds a first preset interval. The DC side of the first energy storage converter and the DC side of the second energy storage converter are connected in parallel through the DC bus, and the first energy storage converter is controlled to operate in a voltage source mode and the second energy storage converter is controlled to operate in a current source mode.

4. The system according to claim 2, wherein: The second type of energy storage device further includes a second type of energy storage first device and a second type of energy storage second device; the controller is configured to control the first energy storage medium to be connected to the first energy storage converter, control the second energy storage medium in the second type of energy storage first device to be disconnected from the corresponding second energy storage converter, and control the second energy storage medium in the second type of energy storage second device to be connected to the corresponding second energy storage converter when the voltage or frequency at the confluence point exceeds a second preset interval; The DC side of the first energy storage converter and the DC sides of all the second energy storage converters are connected in parallel through the DC bus, and the first energy storage converter and all the second energy storage converters are controlled to operate in a voltage source mode.

5. The system according to claim 3, wherein: The controller also includes a device configured to control the first energy storage medium to be disconnected from the first energy storage converter and the second energy storage medium to be connected to the second energy storage converter when the voltage or frequency at the bus point is within the first preset range, the DC side of the first energy storage converter and the DC side of the second energy storage converter are connected in parallel through the DC bus, the first energy storage converter is controlled to operate in a voltage source mode, and the second energy storage converter is controlled to operate in a current source mode.

6. The system according to claim 3, wherein: The second type of energy storage device includes a second type of energy storage first device and a second type of energy storage second device; the controller also includes a device configured to control the first energy storage medium to be disconnected from the first energy storage converter when the voltage or frequency at the bus point is within the first preset interval, control the second energy storage medium in the second type of energy storage first device to be connected to the corresponding second energy storage converter, control the second energy storage medium in the second type of energy storage second device to be connected to the corresponding second energy storage converter, the DC side of the first energy storage converter and the DC sides of all the second energy storage converters are connected in parallel through the DC bus, and control the first energy storage converter and all the second energy storage converters to operate in current source mode.

7. The system according to any one of claims 1 to 6, wherein: The first type of energy storage device further includes: a first switch group and a second switch group; the first energy storage medium is connected to the DC bus through the first switch group; and the first energy storage converter is connected to the DC bus through the second switch group.

8. The system according to any one of claims 1 to 6, wherein: The second type of energy storage device further includes: a third switch group and a fourth switch group; the second energy storage medium is connected to the DC bus through the third switch group; and the second energy storage converter is connected to the DC bus through the fourth switch group.

9. The system according to claim 7 or 8, wherein: Also includes: fifth switch group; The DC bus connected to the first type energy storage device and the DC bus connected to the second type energy storage device are connected via the fifth switch group.

10. The system according to any one of claims 1 to 9, wherein: The second type of energy storage device further includes: an equalizer; the equalizer is connected between the negative electrode of the second energy storage medium and the DC bus.

11. The system according to any one of claims 1 to 6, characterized in that: The first type of energy storage device is located in a first cabinet, the second type of energy storage device is located in a second cabinet, the DC side of the first cabinet is connected to the DC side of the second cabinet, and the AC side of the first cabinet is connected to the AC side of the second cabinet.

12. A control method for a hybrid energy storage system, wherein: The hybrid energy storage system includes: a first type of energy storage device and at least one second type of energy storage device; the first type of energy storage device includes a first energy storage medium and a first energy storage converter; the second type of energy storage device includes a second energy storage medium and a second energy storage converter; the charging and discharging speed of the first energy storage medium is greater than the charging and discharging speed of the second energy storage medium; the first energy storage medium is connected to the DC side of the first energy storage converter, and the DC side of the first energy storage converter is connected to the DC bus; the second energy storage medium is connected to the DC side of the second energy storage converter, and the DC side of the second energy storage converter is connected to the DC bus; the AC side of the first energy storage converter and the AC side of the second energy storage converter are both connected to a bus bar; The method includes: detecting the voltage or frequency of the bus point; According to the voltage or frequency of the bus point, the operating mode of the first energy storage converter and the operating mode of the second energy storage converter are switched, and the operating modes include voltage source mode and current source mode; the first energy storage converter operates in voltage source mode by default, and the second energy storage converter operates in current source mode by default.

13. The method according to claim 12, wherein: The switching of the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point includes: When the voltage or frequency at the bus point exceeds a first preset interval, the first energy storage medium is controlled to be put into operation, the second energy storage medium is controlled not to be put into operation, the DC side of the first energy storage converter and the DC side of the second energy storage converter are controlled to be connected in parallel through the DC bus, the first energy storage converter is controlled to operate in a voltage source mode, and the second energy storage converter is controlled to operate in a current source mode.

14. The method according to claim 12, wherein: The switching of the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point includes: When the voltage or frequency of the busbar exceeds a second preset interval, the first energy storage medium is controlled to be put into operation, part of the second energy storage medium is controlled to be put into operation, and the remaining second energy storage medium is controlled not to be put into operation; the first energy storage converter and all the second energy storage converters are controlled to operate in voltage source mode.

15. The method according to claim 12, wherein: The switching of the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point specifically includes: When the voltage or frequency at the junction exceeds a second preset interval, the first energy storage medium is controlled to be put into operation, and all the second energy storage media are controlled to be put into operation; and the first energy storage converter and all the second energy storage converters are controlled to operate in a voltage source mode.

16. The method according to any one of claims 12 to 15, wherein: The switching of the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point specifically includes: A power angle is obtained according to the voltage of the bus point, and an operating mode of the first energy storage converter and an operating mode of the second energy storage converter are switched according to the power angle.

17. The method according to any one of claims 12 to 15, wherein: The switching of the operating mode of the first energy storage converter and the operating mode of the second energy storage converter according to the voltage or frequency of the bus point specifically includes: The master controller of the hybrid energy storage system obtains a first control instruction and a second control instruction according to the voltage or frequency of the confluence point and the power dispatch instruction issued by the energy management system EMS, sends the first control instruction to a first control unit corresponding to the first energy storage converter, and sends the second control instruction to a second control unit corresponding to the second energy storage converter. The first control unit switches the working mode of the first energy storage converter according to the first control instruction, and the second control unit switches the working mode of the second energy storage converter according to the second control instruction.

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