CN112600216B - Bus voltage and power control method - Google Patents
Bus voltage and power control method Download PDFInfo
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- CN112600216B CN112600216B CN202011375417.8A CN202011375417A CN112600216B CN 112600216 B CN112600216 B CN 112600216B CN 202011375417 A CN202011375417 A CN 202011375417A CN 112600216 B CN112600216 B CN 112600216B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/14—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- Charge And Discharge Circuits For Batteries Or The Like (AREA)
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Abstract
The invention relates to the technical field of electrical engineering, and discloses a bus voltage and power control method, which comprises the steps of judging the running state of an energy storage system; when the energy storage system is in a grid-connected operation state, the DC/AC converter is utilized to control the total power injected into a direct current bus, and the DC/DC converter is utilized to control the bus voltage at the high-voltage side of the direct current bus; and when the energy storage system is in an off-grid running state, the DC/DC converter is utilized to control the stability of the bus voltage. When the bus voltage and power control method provided by the invention is applied to an energy storage system, the bus voltage is regulated by using the DC/DC converter during grid-connected operation and off-grid operation, and the DC/DC converter is always in a constant voltage control mode. Therefore, when the energy storage system is switched between the grid-connected operation state and the off-grid operation state, the control mode of the DC/DC converter does not need to be switched additionally, and therefore the control steps are simplified.
Description
Technical Field
The invention relates to the technical field of electrical engineering, in particular to a method for controlling bus voltage and power.
Background
The energy storage device can store and release electric energy according to the running requirement of the system so as to maintain the balance of supply and demand of the energy in the whole system and improve the electric energy quality and the power supply reliability of the power supply of the power system. For the control of the bus voltage and power, the conventional control method is to control the bus voltage by a bidirectional DC/AC converter, control the current of the high-voltage side by the bidirectional DC/DC converter, and adjust the charging and discharging power by setting the current magnitude and direction of the high-voltage side of the bidirectional DC/DC converter, but the bidirectional DC/DC converter needs to be switched to control the bus voltage when the bidirectional DC/DC converter is off the grid, and the mode switching is complex.
Disclosure of Invention
Therefore, it is necessary to provide a method for controlling bus voltage and power, which aims at the problem that when the energy storage device is controlled by using the control method in the prior art, the mode switching of the energy storage device during off-grid operation is complex.
A control method of bus voltage and power is applied to an energy storage system, the energy storage system comprises a DC/AC converter and a DC/DC converter, and the method comprises the steps of judging the running state of the energy storage system; when the energy storage system is in a grid-connected operation state, the DC/AC converter is utilized to control the total power injected into a direct current bus, and the DC/DC converter is utilized to control the bus voltage at the high-voltage side of the direct current bus; and when the energy storage system is in an off-grid running state, the DC/DC converter is utilized to control the stability of the bus voltage.
The control method of the bus voltage and the power judges the running state of the energy storage system. The operation state of the energy storage system comprises a grid-connected operation state and an off-grid operation state. When the energy storage system is in a grid-connected state, the DC/AC converter is used for injecting total power into the direct current bus, and the DC/DC converter is used for controlling the bus voltage of the direct current bus. When the energy storage system is in an off-grid running state, the DC/DC converter is used for controlling the stability of the bus voltage on the direct current bus. When the bus voltage and power control method provided by the invention is applied to an energy storage system, the DC/DC converter regulates the bus voltage of the direct-current bus in grid-connected operation and off-grid operation, and the DC/DC converter is always in a constant voltage control mode. Therefore, the control mode of the DC/DC converter does not need to be adjusted when the operating state of the energy storage system changes. Compared with the existing control method, the control method for the bus voltage and the power provided by the invention avoids the need of switching the control mode of the DC/DC energy storage converter between the constant current control mode and the constant voltage control mode during grid-connected and off-grid switching, and simplifies the steps required during grid-connected and off-grid switching.
In one embodiment, the DC bus is connected to an AC power grid through the DC/AC converter, and the determining the operating state of the energy storage system includes that the energy storage system is in a grid-connected operating state when the AC power grid is operating normally; and when the alternating current power grid fails, the energy storage system is in an off-grid running state.
In one embodiment, the energy storage system is brought into an off-grid operation state by disconnecting the direct current bus from the alternating current grid.
In one embodiment, when the energy storage system is in a grid-connected operation state, the controlling of the total power injected into the direct current bus by using the DC/AC converter and the controlling of the bus voltage on the high-voltage side of the direct current bus by using the DC/DC converter comprise controlling the total power injected into the direct current bus by using the DC/AC converter according to a regulating current instruction; and switching a charge-discharge mode according to the bus voltage, and controlling the bus voltage of the high-voltage side of the direct-current bus through the DC/DC converter.
In one embodiment, the switching of the charge-discharge mode according to the bus voltage by controlling the bus voltage on the high-voltage side of the direct-current bus through the DC/DC converter includes controlling the DC/DC converter to switch to the discharge mode to raise the bus voltage when the bus voltage is less than a discharge threshold; and when the bus voltage is larger than a charging threshold value, controlling the DC/DC converter to be switched to a charging mode so as to reduce the bus voltage.
In one embodiment, the energy storage system further includes a plurality of battery modules, and the plurality of battery modules are respectively connected to the DC bus through the plurality of DC/DC converters, where when the bus voltage is smaller than a discharge threshold, the DC/DC converter is switched to a discharge mode to raise the bus voltage, including determining battery states of the plurality of battery modules; controlling each DC/DC converter to distribute discharge power according to the battery states of different battery modules; discharging to the direct current bus through the battery module to lift the bus voltage.
In one embodiment, when the bus voltage is greater than a charging threshold, the DC/DC converter switches to a charging mode to reduce the bus voltage, including determining battery states of a plurality of battery modules; controlling each DC/DC converter to distribute charging power according to the battery states of different battery modules; and charging the battery module through the direct current bus so as to reduce the bus voltage.
In one embodiment, the DC/DC converters are connected in parallel through droop control, and each DC/DC converter adjusts output power according to a change of the bus voltage through a preset U/I control characteristic curve.
In one embodiment, the droop slope of the U/I control characteristic curve is adjusted to adjust the control rate of the DC/DC converter to the bus voltage.
In one embodiment, the method further includes maintaining the bus voltage of the dc bus by discharging the battery modules when the energy storage system is in an off-grid operating state.
Drawings
FIG. 1 is a flow chart of a method of controlling bus voltage and power in one embodiment of the present invention;
FIG. 2 is a circuit topology of an energy storage system according to an embodiment of the invention;
fig. 3 is a flowchart of a method for determining an operating state of an energy storage system according to an embodiment of the present invention;
fig. 4 is a flowchart of a control method when the energy storage system is in a grid-connected operation state according to an embodiment of the present invention;
FIG. 5 is a flow chart of a method for controlling a bus voltage by a DC/DC converter according to an embodiment of the present invention;
FIG. 6 is a flowchart of a method for controlling the boost bus voltage of the DC/DC converter according to an embodiment of the present invention;
FIG. 7 is a flowchart of a method for controlling the reduction of the bus voltage by the DC/DC converter according to an embodiment of the present invention;
FIG. 8 is a U/I control characteristic of the DC/DC converter according to an embodiment of the present invention.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. As used herein, the terms "vertical," "horizontal," "left," "right," "upper," "lower," "front," "rear," "circumferential," and the like are based on the orientation or positional relationship shown in the drawings for ease of description and simplicity of description, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In a conventional control method for an energy storage system, in order to realize control of bus voltage and power, a bidirectional DC/AC converter is used for controlling the bus voltage, and a bidirectional DC/DC converter is used for controlling high-voltage side current. When the energy storage system is in grid-connected operation, the bidirectional DC/DC converter is in a constant current control mode, and the charging and discharging power of the direct current bus is adjusted by giving the magnitude and the direction of the current of the high-voltage side of the bidirectional DC/DC converter. When the energy storage system has a fault and needs to run off the grid, the control mode of the bidirectional DC/DC converter needs to be switched from a constant current control mode to a constant voltage control mode, and the bus voltage of the direct current bus is controlled through the bidirectional DC/DC converter. However, the mode switching process of the bidirectional DC/DC converter is complicated, and thus, the control method for the energy storage system is complicated. According to the bus voltage and power control method provided by the invention, when grid connection and grid disconnection are switched, the control mode of the bidirectional DC/DC converter does not need to be switched, so that the control step is simplified.
Fig. 1 is a flowchart of a method for controlling bus voltage and power according to an embodiment of the present invention. The invention provides a bus voltage and power control method which is applied to an energy storage system, wherein the energy storage system comprises a DC/AC converter and a DC/DC converter. In one embodiment, the bus voltage and power control method includes the following steps S100 to S300.
S100: and judging the running state of the energy storage system.
S200: when the energy storage system is in a grid-connected operation state, the DC/AC converter is utilized to control the total power injected into the direct-current bus, and the DC/DC converter is utilized to control the bus voltage at the high-voltage side of the direct-current bus.
S300: and when the energy storage system is in an off-grid running state, the DC/DC converter is utilized to control the stability of the bus voltage.
In this embodiment, the DC/DC converter is a bidirectional DC/DC converter, and the DC/AC converter is a bidirectional DC/AC converter.
Fig. 2 is a circuit topology diagram of an energy storage system in an embodiment of the present invention, where the energy storage system is composed of a battery module, a bidirectional DC/DC converter, and a bidirectional DC/AC converter for implementing grid connection. The battery module is connected with the direct current bus through the bidirectional DC/DC converter, and the direct current bus is connected with the alternating current power grid through the bidirectional DC/AC converter.
And judging the running state of the energy storage system, wherein the running state comprises a grid-connected running state and an off-grid running state. When the energy storage system is in a grid-connected operation state, the bidirectional DC/AC converter controls the total power injected into the direct current bus by controlling the total current output by the bidirectional DC/AC converter. Meanwhile, the bidirectional DC/DC converter is in a constant voltage control mode, and regulates the bus voltage at the high-voltage side of the direct current bus to control the bus voltage within a certain range.
When the energy storage system is in an off-grid running state, the energy storage system regulates the bus voltage on the direct current bus only through the bidirectional DC/DC converter. The bidirectional DC/DC converter is in a constant voltage control mode, and the voltage of the bus is controlled within a certain range, so that the direct current bus can still stably run after being off the grid.
Because the bidirectional DC/DC converter is in the constant voltage control mode in the grid-connected operation state and the off-grid operation state, when the energy storage system is switched in the grid-connected and off-grid state, the operation of switching the control mode of the bidirectional DC/DC converter is not required to be additionally added, so that the steps of the control method of the bus voltage and the power are simplified, and the control process is simpler and more convenient.
Fig. 3 is a flowchart of a method for determining an operating state of an energy storage system according to an embodiment of the present invention, where in an embodiment, the determining the operating state of the energy storage system includes the following steps S110 to S120.
S110: and when the alternating current power grid normally works, the energy storage system is in a grid-connected operation state.
S120: and when the alternating current power grid fails, the energy storage system is in an off-grid running state.
In general, when an ac grid is operating normally, the energy storage system is in a grid-connected operation state, and the ac grid supplies electric energy to the dc bus. The bidirectional DC/AC converter is respectively connected with the alternating current power grid and the direct current bus and is used for rectifying alternating current electric energy in the alternating current power grid and then merging the rectified alternating current electric energy into the direct current bus so that the direct current bus can charge a load; or the direct current bus is used for converting the direct current electric energy in the direct current bus into alternating current electric energy and then merging the alternating current electric energy into the alternating current power grid.
When the alternating current power grid breaks down or is damaged, in order to avoid influencing the direct current bus, the energy storage system needs to enter an off-grid running state, the alternating current power grid does not provide electric energy for the direct current bus, and the electric energy stored in the battery module is used for providing electric energy for the direct current bus. The bidirectional DC/DC converter is used for boosting the electric energy in the battery module and then merging the electric energy into the direct current bus, or reducing the voltage of the electric energy in the direct current bus and then charging the electric energy into the battery module.
In one embodiment, the energy storage system is brought into an off-grid operation state by disconnecting the direct current bus from the alternating current grid. When the ac power grid fails or is damaged, in order to avoid the influence of the fault on the dc bus and the influence of the dc bus on the normal power supply of the load, the connection path between the dc bus and the ac power grid needs to be disconnected. The electric energy is not provided to the direct current bus by the alternating current power grid, but the electric energy stored in the battery module is used for providing the electric energy to the direct current bus, so that the direct current bus can still run normally by depending on the electric energy stored in the battery module after being off-grid.
Fig. 4 is a flowchart of a control method when the energy storage system is in a grid-connected operating state in one embodiment of the present invention, where in one embodiment, when the energy storage system is in a grid-connected operating state, the DC/AC converter is used to control the total power injected into the DC bus, and the DC/DC converter is used to control the bus voltage on the high-voltage side of the DC bus, including the following steps S210 to S220.
S210: and controlling the total power injected into the direct current bus through the DC/AC converter according to the regulating current instruction.
S220: and switching a charge-discharge mode according to the bus voltage, and controlling the bus voltage of the high-voltage side of the direct-current bus through the DC/DC converter.
When the energy storage system is in a grid-connected operation state, the alternating current power grid provides electric energy for the direct current bus. The bidirectional DC/AC converter controls the total power injected into the direct current bus in a mode of adjusting a current instruction. The current instruction is used for adjusting the size and the direction of current injected to the direct current bus of the bidirectional DC/AC converter, namely adjusting the size and the direction of power injected to the direct current bus of the bidirectional DC/AC converter. When the bidirectional DC/AC converter injects power into the direct-current bus, the bus voltage of the direct-current bus rises; when the bidirectional DC/AC converter draws power to the DC bus, the bus voltage of the DC bus drops.
The bidirectional DC/DC converter is in a constant voltage control mode and is used for controlling the bus voltage within a certain voltage range. Therefore, the bidirectional DC/DC converter needs to switch the charging and discharging modes according to the bus voltage, so that the adjustment of the direct current bus is realized, and the bus voltage is ensured to be stabilized within a certain voltage range.
Fig. 5 is a flowchart of a method for controlling a bus voltage by a DC/DC converter in an embodiment of the present invention, where in an embodiment, the switching of a charge-discharge mode according to the bus voltage and the control of the bus voltage on a high-voltage side of the DC bus by the DC/DC converter include the following steps S221 to S222.
S221: and when the bus voltage is smaller than a discharge threshold value, controlling the DC/DC converter to be switched to a discharge mode so as to raise the bus voltage.
S222: and when the bus voltage is larger than a charging threshold value, controlling the DC/DC converter to be switched to a charging mode so as to reduce the bus voltage.
In order to avoid the oscillation phenomenon caused by the back-and-forth switching of the charging and power generation modes of the bidirectional DC/DC converter due to the frequent floating of the bus voltage, different charging thresholds and discharging thresholds need to be designed for the bidirectional DC/DC converter, and the discharging threshold U is set 1 And a charging threshold U 2 。
When the power which is extracted from the bidirectional DC/AC converter to the direct current bus is excessive, the bus voltage of the direct current bus is reduced excessively, and the bus voltage is smaller than the discharge threshold U 1 In time, when the bus voltage is too low, the direct current bus needs to be charged. And switching the bidirectional DC/DC converter to a discharging mode to control the battery module to discharge the bus voltage so as to lift the bus voltage and lift the voltage to a preset range.
When the power injected into the direct current bus by the bidirectional DC/AC converter is excessive, the bus voltage of the direct current bus is increased excessively, and the bus voltage is larger than the charging threshold U 2 At this time, the dc bus needs to be discharged when the bus voltage is too high. And the bidirectional DC/DC converter is switched to a charging mode, and the battery module is charged by utilizing the bus voltage so as to reduce the bus voltage and reduce the voltage of the battery module to be within a preset range.
Fig. 6 is a flowchart of a method for controlling the boost bus voltage of the DC/DC converter according to an embodiment of the present invention. In one embodiment, when the bus voltage is smaller than the discharging threshold, the DC/DC converter switches to the discharging mode to raise the bus voltage, including the following steps S10 to S30.
S10: and judging the battery states of the plurality of battery modules.
S20: and controlling the DC/DC converters to distribute the discharge power according to the battery states of the different battery modules.
S30: discharging to the direct current bus through the battery module to lift the bus voltage.
Referring to fig. 2, when a plurality of battery modules are provided in the energy storage system, the battery modules are respectively connected to the DC bus through a plurality of DC/DC converters. When the bus voltage is reduced to be less than the discharge threshold value U 1 In this case, the bidirectional DC/DC converter needs to control each battery module to charge the DC bus. Since the energy storage system includes a plurality of battery modules, and the electric energy stored in the battery modules is different, the discharge power needs to be distributed according to the battery states of the different battery modules. For example, when a certain battery module stores more electric energy, the battery module is allocated with more discharge power; when the electric energy stored in a certain battery module is less, less discharge power is distributed to the battery module; when electric energy is not stored in a certain battery module, no discharge power is distributed to the battery module. Through judging the battery state of each battery module, the bidirectional DC/DC converter distributes the discharge power according to the battery states of different battery modules, and the battery modules can be prevented from being damaged due to over-discharge.
Fig. 7 is a flowchart illustrating a method for controlling a DC/DC converter to decrease a bus voltage according to an embodiment of the present invention, where in an embodiment, when the bus voltage is greater than a charging threshold, the DC/DC converter switches to a charging mode to decrease the bus voltage, and the method includes steps S40 to S60 as follows.
S40: and judging the battery states of the plurality of battery modules.
S50: and controlling the DC/DC converters to distribute charging power according to the battery states of the different battery modules.
S60: and charging the battery module through the direct current bus so as to reduce the bus voltage.
When the bus voltage rises to be greater than the charging threshold value U 2 In this case, the bidirectional DC/DC converter needs to control the DC bus to charge each battery module. Since the energy storage system includes a plurality of battery modules, and the electric energy to be stored in the battery modules is different, the charging power needs to be distributed according to the battery states of the different battery modules. For example, when the amount of electric energy stored in a certain battery module is large, the battery capacity available for storing electric energy is small, and a small amount of charging power is allocated to the battery module; when the electric energy stored in a certain battery module is less, the battery capacity for storing the electric energy is more, and more charging power is distributed to the battery module; when a certain battery module is fully charged, the battery module group is not allocated with charging power. Through judging the battery state of each battery module, the bidirectional DC/DC converter distributes charging power according to the battery states of different battery modules, and the battery modules can be prevented from being damaged due to overcharging.
In one embodiment, the DC/DC converters are connected in parallel through droop control, and the same specific U/I control characteristic curve is preset in each DC/DC converter. The bidirectional DC/DC converter regulates the output power according to the change of the bus voltage on the direct current bus. FIG. 8 is a U/I control characteristic curve of the DC/DC converter in one embodiment of the present invention, where in FIG. 8, U L And U H And regulating a lower limit and a regulating upper limit for the bus voltage. When the bus voltage is less than the discharge threshold U 1 And when the bus voltage is increased, the bidirectional DC/DC converter raises the bus voltage according to the set regulation mode of the U/I control characteristic curve. And voltage and current droop control is adopted, and power distribution is carried out on discharge power according to different battery states of different battery modules, so that parallel stable operation of the multiple converters is realized. Likewise, when the bus voltage is greater than the discharge threshold U 2 And when the bus voltage is reduced, the bidirectional DC/DC converter reduces the bus voltage according to the regulation mode of the set U/I control characteristic curve. The voltage and current droop control is adopted to carry out discharging and charging according to different battery states of different battery modulesAnd power distribution is carried out, and parallel stable operation of the multiple converters is realized.
In one embodiment, the droop slope of the U/I control characteristic curve is adjusted to adjust the control rate of the DC/DC converter to the bus voltage. Referring to fig. 8, k is the droop slope of the U/I control characteristic curve of the bi-directional DC/DC converter. In practical application, the droop slope k is changed according to the requirement on the regulation speed of the bus voltage. For example, if the bus voltage needs to be slowly adjusted, the absolute value of the droop slope k is set to be small; if the bus voltage needs to be adjusted slowly, the absolute value of the droop slope k is set to be large.
In one embodiment, the method further includes maintaining the bus voltage of the dc bus by discharging the battery modules when the energy storage system is in an off-grid operating state. When the bidirectional DC/DC converter is in an off-grid operation state, the bidirectional DC/DC converter is still in a constant voltage control mode and is used for maintaining the bus voltage on the direct current bus within a certain voltage range. When the energy storage system is in an off-grid operation state, the direct-current bus is disconnected from the connection path of the alternating-current power grid, and the alternating-current power grid cannot continuously provide electric energy for the direct-current bus, so that in order to maintain the stable operation of the direct-current bus, the battery module is required to discharge to support the bus voltage, so that the battery module can continuously supply power to the load. Because the bidirectional DC/DC converter is in the constant voltage control mode in the grid-connected operation state and the off-grid operation state, when the energy storage system is switched in the grid-connected and off-grid state, the operation of switching the control mode of the bidirectional DC/DC converter is not required to be additionally added, so that the steps of the control method of the bus voltage and the power are simplified, and the control process is simpler and more convenient.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent should be subject to the appended claims.
Claims (8)
1. A bus voltage and power control method is applied to an energy storage system, the energy storage system comprises a DC/AC converter and a DC/DC converter, and the method is characterized by comprising the following steps:
judging the running state of the energy storage system;
when the energy storage system is in a grid-connected operation state, the DC/AC converter is used for controlling the total power injected into a direct current bus, the DC/DC converter is used for controlling the bus voltage at the high-voltage side of the direct current bus, the DC/DC converters are connected in parallel through droop control, and the DC/DC converters regulate the output power according to the change of the bus voltage through a preset U/I control characteristic curve; adjusting the control rate of the DC/DC converter to the bus voltage by adjusting the droop slope of the U/I control characteristic curve;
and when the energy storage system is in an off-grid running state, the DC/DC converter is utilized to control the stability of the bus voltage.
2. The method for controlling bus voltage and power according to claim 1, wherein the DC bus is connected to an AC power grid through the DC/AC converter, and the determining the operating state of the energy storage system comprises:
when the alternating current power grid normally works, the energy storage system is in a grid-connected operation state;
and when the alternating current power grid fails, the energy storage system is in an off-grid running state.
3. The method of claim 2, wherein the energy storage system is placed in an off-grid operating state by disconnecting the dc bus from the ac power grid.
4. The method for controlling the bus voltage and power according to claim 1 or 2, wherein the controlling the total power injected into the DC bus by the DC/AC converter and the bus voltage on the high-voltage side of the DC bus by the DC/DC converter when the energy storage system is in a grid-connected operation state comprises:
controlling the total power injected into the direct current bus through the DC/AC converter according to a regulating current instruction;
and switching a charge-discharge mode according to the bus voltage, and controlling the bus voltage of the high-voltage side of the direct-current bus through the DC/DC converter.
5. The method for controlling the bus voltage and the power according to claim 4, wherein the switching of the charge-discharge mode according to the bus voltage to control the bus voltage on the high-voltage side of the direct-current bus by the DC/DC converter comprises:
when the bus voltage is smaller than a discharge threshold value, controlling the DC/DC converter to be switched to a discharge mode so as to raise the bus voltage;
and when the bus voltage is larger than a charging threshold value, controlling the DC/DC converter to be switched to a charging mode so as to reduce the bus voltage.
6. The method for controlling bus voltage and power according to claim 4, wherein the energy storage system further comprises a plurality of battery modules, and the plurality of battery modules are respectively connected with the direct current bus through a plurality of DC/DC converters, and when the bus voltage is less than a discharge threshold value, the DC/DC converter is switched to a discharge mode to raise the bus voltage, and the method comprises the following steps:
judging the battery states of the plurality of battery modules;
controlling each DC/DC converter to distribute discharge power according to the battery states of different battery modules;
discharging to the direct current bus through the battery module to lift the bus voltage.
7. The method of claim 6, wherein the switching the DC/DC converter to a charging mode to reduce the bus voltage when the bus voltage is greater than a charging threshold comprises:
judging the battery states of the plurality of battery modules;
controlling each DC/DC converter to distribute charging power according to the battery states of different battery modules;
and charging the battery module through the direct current bus so as to reduce the bus voltage.
8. The method of bus voltage and power control of claim 6, further comprising:
when the energy storage system is in an off-grid running state, the bus voltage of the direct current bus is maintained through discharging of the battery modules.
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| CN113746170B (en) * | 2021-09-03 | 2024-02-09 | 阳光电源（上海）有限公司 | Energy storage system and off-grid overload protection method thereof |
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