Energy storage converter grid-connected and off-grid switching device and control method thereof
By determining the target grid voltage and phase when the energy storage converter is connected to the grid, adjusting the output voltage, and generating the pull-in command in advance, the problems of insufficient energy and shortened relay life during grid connection of the energy storage converter are solved, and a more stable grid connection process is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN ANKEXUCHUANG TECHNOLOGY CO LTD
- Filing Date
- 2025-12-29
- Publication Date
- 2026-04-24
Smart Images
Figure CN121923213A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of energy storage technology, specifically to an energy storage converter and off-grid switching device and its control method. Background Technology
[0002] For power conversion systems (PCS) operating off-grid, if the grid resumes power supply, the grid connection relay needs to be activated to achieve grid connection. However, occasionally, insufficient DC input energy of the power conversion system may trigger overload protection. In addition, overcurrent may reduce the service life of the grid connection relay. Summary of the Invention
[0003] This application provides a control method for switching an energy storage converter to and from the grid, which can solve the problems of false triggering of overload protection due to insufficient DC side energy when the energy storage converter is restored to grid connection, and the shortened service life of relays due to overcurrent impact.
[0004] This application provides a control method for switching an energy storage converter to off-grid operation, comprising: determining a target voltage amplitude of the grid voltage and tracking a target phase of the grid voltage when the grid restores power supply; adjusting the phase of the output voltage of the energy storage converter according to the target phase; generating a closing command for controlling the grid-connected relay to close at a first moment within a preset voltage cycle; adjusting the voltage amplitude of the output voltage of the energy storage converter at a second moment after the first moment so that the difference between the voltage amplitude of the output voltage and the target voltage amplitude satisfies a preset condition; and controlling the operating mode of the energy storage converter to switch from voltage source mode to current source mode at a target moment after the second moment, wherein the second moment is earlier than the zero-crossing point of the grid voltage within the preset voltage cycle.
[0005] This application provides an energy storage converter on-grid / off-grid switching device, comprising: a determination module, configured to determine the target voltage amplitude of the grid voltage and track the target phase of the grid voltage when the grid restores power supply; a control module, coupled to the determination module, configured to adjust the phase of the output voltage of the energy storage converter according to the target phase, and to generate a closing command for controlling the grid-connected relay to close at a first moment within a preset voltage cycle; the control module is configured to adjust the voltage amplitude of the output voltage of the energy storage converter at a second moment after the first moment, so that the difference between the voltage amplitude of the output voltage and the target voltage amplitude meets a preset condition; the control module is configured to control the operating mode of the energy storage converter to switch from voltage source mode to current source mode at a target moment after the second moment, wherein the second moment is earlier than the grid voltage zero-crossing point within the preset voltage cycle.
[0006] This application provides an energy storage converter, including a control device, wherein the energy storage converter is connected to the power grid via a grid-connected relay, and the control device is used to implement the method described above.
[0007] This application provides an energy storage device, including the energy storage converter described above and a battery module, wherein the battery module is electrically connected to the energy storage converter.
[0008] This application provides a power supply system including a control device, a power grid, and an energy storage converter. At least one of the power grid and the energy storage converter is connected to a load, and the other energy storage converter is connected to the power grid through a grid-connected relay. The control device is connected to the energy storage converter and the grid-connected relay, and the control device is used to implement the method described above.
[0009] This application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described above.
[0010] The beneficial effects of this application are as follows: This application utilizes the sinusoidal characteristics of inverter voltage, that is, the inverter voltage only requires a high bus voltage of the energy storage converter when the instantaneous value is large. By determining the target voltage amplitude and tracking the target phase to adjust the output voltage, and generating the pull-in command in advance at the first moment, the grid-connected relay can be expected to complete the pull-in near the zero-crossing point of the grid voltage. This strategy ensures that the output voltage of the energy storage converter is in a range with a low instantaneous value and meets the preset conditions with the grid voltage during grid connection switching, thereby reducing the bus voltage requirement of the energy storage converter, effectively avoiding the occurrence of overload protection triggered by insufficient DC side input energy, and also reducing the impact on the grid-connected relay, thus improving product performance. Attached Figure Description
[0011] Figure 1 This is a schematic diagram of the power supply system in some embodiments of this application; Figure 2 This is a control flowchart of the energy storage converter being connected to the power grid in some embodiments of this application; Figure 3 This is a schematic diagram illustrating the grid-to-grid and off-grid switching of the energy storage converter in some embodiments of this application; Figure 4 This is a control flowchart of the energy storage converter and its off-grid switching in some embodiments of this application; Figure 5 This is a control flowchart of the energy storage converter and its off-grid switching in some embodiments of this application; Figure 6 This is a schematic diagram of the grid-connected switching device for the energy storage converter in some embodiments of this application; Figure 7 These are schematic diagrams of the electronic devices in some embodiments of this application; Figure 8 This is a schematic diagram of the structure of an embodiment of the computer-readable storage medium of this application. Detailed Implementation
[0012] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.
[0013] The reference to "embodiment" in this application means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.
[0014] Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed in this application.
[0015] Furthermore, in some embodiments, a technical feature is described, which may be used in conjunction with another technical feature, or even with multiple technical features, in this embodiment. However, the structure and function of this technical feature, if clearly and reasonably described, should not be affected or limited by other technical features in this embodiment, but can be further applied to other embodiments that include this technical feature, so that the technical feature described in other embodiments can also be combined with at least part of the structure and / or at least part of the function of the technical feature described in this embodiment. The new embodiments formed thereby should also fall within the scope of protection of this application.
[0016] Please see Figure 1 , Figure 1This is a schematic diagram of the power supply system framework in some embodiments of this application. The power supply system 100 may include a control device 13, a power grid 20, and an energy storage converter 12. One of the energy storage converter 12 and the power grid 20 is connected to the load network 30, and the other is connected to the load network 30 via a grid-connected relay 14. The control device 13 can be used to control the grid-connected relay 14 to activate, enabling grid-connected operation of the energy storage converter 12 and the power grid 20, for example, connecting the energy storage converter 12 to the power grid 20, or vice versa. Alternatively, the energy storage converter 12 can also be connected to the power grid 20 via the grid-connected relay 14, and the power grid can then connect to the load network 30.
[0017] Energy storage converters can convert alternating current (AC) to direct current (DC) and can be further applied to energy storage. In some embodiments, energy storage converters may include inverters (i.e., inverter circuits).
[0018] In some embodiments, the energy storage converter 12 can operate in parallel with the power grid 20 to supply power to the load network. The energy storage converter 12 can also operate off-grid to supply power to the load network. After grid connection, the voltage of the energy storage converter 12 is clamped by the power grid 20, and the energy storage converter 12 should control the current to output power. Therefore, the energy storage converter 12 can operate in current source mode when grid connected and in voltage source mode when off-grid. Furthermore, in the power supply system 100, the control device 13 can control the switching of the operating mode of the energy storage converter 12, for example, switching the operating mode from current source mode to voltage source mode, and vice versa.
[0019] The control device 13 can be an electronic device with a processor, such as a microcontroller, or a mobile terminal such as a computer or mobile phone, or even a server. It is understood that the control device 13 is not limited to the embodiments listed herein, but can also be other devices known to those skilled in the art capable of data processing and generating control commands, which will not be elaborated upon further.
[0020] In some embodiments, the energy storage converter 12 has built-in devices with control functions, and thus can be referred to as a control device because it can play a control role as the control device 13. That is, the control device can be the energy storage converter 12 or a part of the energy storage converter 12.
[0021] In some embodiments, the power supply system 100 may further include an energy storage module 11. The energy storage module 11 may be electrically connected to an energy storage converter 12, which is connected to the power grid 20 via a grid-connected relay 14, so as to deliver the electrical energy in the energy storage module 11 to the power grid 20 and further to the load network 30.
[0022] The energy storage module 11 can be a chemical energy storage device such as a lead-acid battery, a redox flow battery, a sodium-sulfur battery, and / or a lithium-ion battery. It can also be a photovoltaic energy storage device that stores electrical energy generated by photovoltaic power generation, or other energy storage devices well-known to those skilled in the art, which will not be elaborated upon. In some embodiments, the energy storage module 11 can be a photovoltaic energy storage device that can be installed on a balcony. Of course, other types of energy storage devices can also be installed on balconies, or even indoors or on the roof. In some embodiments, the photovoltaic energy storage device uses photovoltaic power generation. Photovoltaic power generation mainly takes two forms depending on the inverter. One is using a centralized inverter, characterized by large capacity (very large relative capacity), a narrow voltage range (generally 450V to 820V), significant weather influence, and a high failure rate of the DC combiner box. This mainly involves a large number of photovoltaic modules being simply grouped, then the DC current is collected and enters the DC combiner box, and then the inverter. The process follows: photovoltaic modules → DC cable → DC combiner box → DC cable → centralized inverter → AC cable → step-up transformer. Another method utilizes string inverters, characterized by small capacity, modularity, a wide voltage range (typically 250V–800V), less susceptibility to weather conditions, and longer power generation time. It primarily consists of photovoltaic modules connected in series to form one circuit, with multiple circuits connected to an inverter. The inverter contains MPPT (Maximum Power Point Tracking), with each photovoltaic array corresponding to one inverter. The large number of inverters, especially when connected in parallel, leads to harmonic superposition, making control more difficult. The process follows this flow: Photovoltaic modules → DC cable → string inverter → AC cable → AC combiner box → AC cable → step-up transformer.
[0023] In some embodiments, the energy storage converter 12, the control device 13 and the energy storage module 11 may constitute an energy storage device 10. Of course, the energy storage device 10 may also include others, which will not be elaborated here.
[0024] In some embodiments, when the energy storage module 11 is a chemical energy storage device such as a lead-acid battery, a redox flow battery, a sodium-sulfur battery, and / or a lithium-ion battery, it may also be referred to as a battery module.
[0025] The following describes a control method for switching between on-grid and off-grid operation of an energy storage converter. This method can be used to achieve grid-connected operation of the energy storage converter 12 and the power grid 20, for example, connecting the energy storage converter 12 to the power grid 20, or vice versa. This method can be applied to the control device 11, the energy storage device 10, and the power supply system 100.
[0026] Please see Figure 2 , Figure 2 This is a control flowchart illustrating the grid connection of an energy storage converter with the power grid in some embodiments of this application. The method may include: Step S101: When the power grid is restored, determine the target voltage amplitude of the grid voltage and the target phase of the grid voltage.
[0027] When the power grid stops supplying power, the energy storage converter operates off-grid. When the power grid resumes supplying power, the energy storage converter needs to switch between on-grid and off-grid operation to achieve grid-connected operation between the energy storage converter and the power grid.
[0028] By locking the target voltage amplitude and target phase, the energy storage converter can invert to produce the same voltage amplitude and phase as the power grid. In some embodiments, a phase-locked loop (PLL) can be used to perform phase-locking processing on the power grid to obtain the target phase. Setting the target phase allows the energy storage converter to invert to produce the same phase as the power grid, facilitating grid connection between the energy storage converter and the power grid.
[0029] In some embodiments, voltage information of the power grid, or voltage-related information, can be measured by means of a voltmeter, oscilloscope, AC millivoltmeter, voltage transformer, Hall voltage sensor, etc., and then further processed to obtain the target voltage amplitude.
[0030] Please see Figure 3 , Figure 3 This diagram illustrates the grid-to-grid and grid-off switching of the energy storage converter in some embodiments of this application. The dashed line represents the grid voltage, and the solid line represents the inverter voltage of the energy storage converter. During step S101, the target voltage amplitude Vgrid and target phase of the grid can be locked. The energy storage converter can adjust its output voltage amplitude and phase to match the grid near the voltage zero-crossing point, and invert the voltage amplitude Vinv to the target voltage amplitude Vgrid, ultimately completing grid connection.
[0031] Step S102: Adjust the phase of the output voltage of the energy storage converter according to the target phase.
[0032] Step S103: At the first moment within the preset voltage cycle, generate a energizing command to control the grid-connected relay to energize.
[0033] Within a preset voltage cycle, the first moment is spaced apart from the grid voltage zero-crossing point by a first preset time interval, and is located before the grid voltage zero-crossing point.
[0034] When the power grid is restored, the control equipment first calculates the delay of the grid-connected relay (e.g., it needs to close within 15ms). To ensure that the grid-connected relay closes precisely at the zero-crossing point, the control equipment pre-calculates the specific cycle in which the closing command should be issued. The voltage cycle can be the cycle of an AC voltage.
[0035] The activation command can control the grid-connected relay, enabling the energy storage converter to complete grid connection with the power grid within a first preset time period via the grid-connected relay.
[0036] In some embodiments, the grid-connected relay is used in a network that connects the grid to the energy storage converter for power supply, and of course, it can also be used in a network that connects the energy storage converter to the grid for power supply.
[0037] Because grid-connected relays require time to engage, issuing an engagement command at the grid voltage zero-crossing point may not guarantee engagement at that exact moment. Engaging outside the zero-crossing point could lead to overcurrent and reduce the relay's lifespan. Therefore, during off-grid switching to grid connection, the engagement command can be issued in advance, based on the relay's engagement time, to ensure engagement at the grid voltage zero-crossing point.
[0038] like Figure 3 As shown, a energizing command for controlling the grid-connected relay to energize can be generated at the first time t1, with the aim of completing the energizing of the grid-connected relay at the voltage zero-crossing point after the first time t1, so as to smoothly complete the grid connection.
[0039] In some embodiments, the first preset duration can be the time for the grid-connected relay to engage. However, based on errors and the operating conditions of the grid-connected relay, the first preset duration can be greater or less than the engagement time. In some embodiments, the operating conditions of the grid-connected relay can affect its engagement time, making it difficult to guarantee that the relay will engage within the first preset duration. Therefore, the first preset duration can be the engagement time tested under the worst operating conditions. Furthermore, when the grid-connected relay engages within the first preset duration, the instantaneous inverter voltage of the energy storage converter will coincide with the grid voltage within a lower voltage range. This reduces the bus voltage requirements of the energy storage converter and effectively prevents insufficient DC-side input energy from triggering overload protection.
[0040] In some embodiments, in order to better ensure that the grid-connected relay completes its engagement at the zero-crossing point of the grid voltage, the first preset duration can also be the engagement time of the grid-connected relay when the energy storage converter was previously connected to the grid.
[0041] Step S104: At the second moment after the first moment, adjust the voltage amplitude of the output voltage of the energy storage converter so that the difference between the output voltage amplitude and the target voltage amplitude meets the preset condition.
[0042] The second time interval between the grid voltage zero-crossing point and the grid voltage zero-crossing point is a second preset time, and it is located before the grid voltage zero-crossing point. The first preset time is longer than the second preset time.
[0043] The energy storage converter can invert the output voltage to the target voltage amplitude and target phase within a second preset time period. For example, it can... Figure 3The second moment t2 allows the energy storage converter to adjust the output voltage in advance, so that the energy storage converter can invert the output voltage with the same voltage amplitude and phase as the grid voltage. This makes it easier to complete the grid connection of the energy storage converter near the zero-crossing point of the grid voltage, or even at the zero-crossing point of the grid voltage.
[0044] Furthermore, during the period from the second moment (or after the second moment) until the grid voltage zero-crossing point, as the instantaneous value of the inverter voltage gradually decreases and approaches zero, the demand of the energy storage converter on the DC bus voltage also continuously decreases. Therefore, even if there is a momentary energy shortage on the battery side or a drop in the bus voltage at this time, the energy storage converter can still maintain a sufficient bus voltage to invert an amplitude that matches the grid voltage. This characteristic allows the output voltage of the energy storage converter to remain highly consistent with the grid voltage during the grid connection window near the voltage zero-crossing point, thereby ensuring that the grid-connected relay completes physical engagement in the voltage overlap region (i.e., the low voltage difference region), effectively avoiding hard engagement.
[0045] In some embodiments, the preset conditions are set to match the voltage amplitude of the energy storage converter's output voltage with a target voltage amplitude. For example, the voltage amplitude of the energy storage converter's output voltage is the same as the target voltage amplitude; the ratio of the output voltage amplitude to the target voltage amplitude is within a predetermined range; the difference between the output voltage amplitude and the target voltage amplitude is within a predetermined range; the difference between the output voltage amplitude and the target voltage amplitude is 0; or the ratio of the difference between the output voltage amplitude and the target voltage amplitude to the target voltage amplitude is within a predetermined range. Of course, the preset conditions can also be other conditions for evaluating the relationship between the output voltage amplitude and the target voltage amplitude of the energy storage converter.
[0046] Step S105: At the target time after the second time, control the energy storage converter to switch its operating mode from voltage source mode to current source mode.
[0047] As described above, after grid connection, the voltage is clamped by the grid. The energy storage converter should control the current to output power. Therefore, after confirming grid connection, the operating mode of the energy storage converter needs to be adjusted to current source mode, and power regulation can be achieved by controlling the current. The target time can be the grid voltage zero-crossing point or near the grid voltage zero-crossing point. Thus, the energy storage converter and the grid can be connected at or near the grid voltage zero-crossing point, and the operating mode of the energy storage converter can be switched from voltage source mode to current source mode.
[0048] This application anticipates the inverter to engage at the overvoltage zero-crossing point in the first instant, and then ensures that the inverter voltage matches the grid voltage near the overvoltage zero-crossing point in the second instant. Specifically, it utilizes the sinusoidal characteristics of the inverter voltage. When grid connection is required, the high bus voltage requirement for the energy storage converter only arises when the instantaneous grid voltage is large. By determining the target voltage amplitude and tracking the target phase, the off-grid inverter output voltage of the energy storage converter achieves the same amplitude and phase as the grid voltage. Furthermore, by generating an engagement command in advance and controlling the grid-connected relay, the grid-connected relay can engage near the zero point. This ensures that the inverter voltage of the energy storage converter fully overlaps with the grid voltage within a low instantaneous voltage range, reducing the bus voltage requirement for the energy storage converter. This effectively prevents insufficient DC-side input energy from triggering overload protection and also reduces the impact on the grid-connected relay, improving product performance.
[0049] In some embodiments, please refer to Figure 4 , Figure 4 This is a control flowchart for the energy storage converter and its off-grid switching in some embodiments of this application. Before step S105, the method may further include: Step S201: During the time period from the second time point to the target time point, obtain the first current value on the grid side or the energy storage converter side.
[0050] like Figure 3 As shown, since the grid connection of the energy storage converter and the grid occurs after the second time t2, the current measured at or after the second time can be used to characterize whether the energy storage converter and the grid have completed the grid connection relay activation and are in the grid-connected state.
[0051] To ensure that the energy storage converter and the grid are connected at the grid voltage zero-crossing point as close as possible, the interval between the second time point and the grid voltage zero-crossing point can be pre-designed in some scenarios. In some embodiments, the second time point can be determined based on the load-carrying capacity of the energy storage converter. In some embodiments, the second time point can also be determined based on the bus capacitor capacity of the energy storage converter.
[0052] In some embodiments, based on the sinusoidal characteristics of the inverter voltage, the high bus voltage requirement for the energy storage converter is only imposed when the instantaneous value of the grid voltage to be connected to is large. This ensures that the inverter voltage of the energy storage converter remains within a lower range of the current voltage cycle during the period from the second time t2 to the target time t3, thereby reducing the bus voltage requirement for the energy storage converter and effectively preventing insufficient DC-side input energy from triggering overload protection. Furthermore, the energy storage converter and the grid can be connected before or at the target time t3, which can be after, before, or after the grid voltage zero-crossing point. The time interval from the second time t2 to the target time t3 can be half a voltage cycle, i.e., the product of the reciprocal of the target phase and π. In a further embodiment, the time interval from the second time to the voltage zero-crossing point is half a preset duration.
[0053] Step S202: When the first current value meets the preset condition, determine that the grid-connected relay is activated.
[0054] When the energy storage converter is connected to the grid, the current at the grid connection point will fluctuate. Therefore, the grid connection can be confirmed based on the current at the grid connection point. That is, the grid connection relay can be judged based on the current.
[0055] Since the switching of the operating mode of the energy storage converter from voltage source mode to current source mode occurs after grid connection, the timing of the current source switching command can also be determined based on the current.
[0056] In some embodiments, the preset condition may be whether the first current value matches the current value before grid connection. If they match, the grid-connected relay is considered not to be engaged; if they do not match, the grid-connected relay is considered to be engaged. In some embodiments, the current value before grid connection is the target current value. The target current value can be obtained between the first and second moments, or before the first moment, or at the first moment, or at the second moment. The target current value can be obtained within the current voltage cycle or from historical data. The preset condition only needs to reflect the changes in the energy storage converter before and after grid connection. In this embodiment, current is used, but voltage or other electrical parameters can also be used.
[0057] In some embodiments, when the first current value is the current on the grid side at the grid connection point, the target current value is also the current on the grid side at the grid connection point. In some embodiments, when the first current value is the current on the energy storage converter side at the grid connection point, the target current value is also the current on the energy storage converter side at the grid connection point.
[0058] In some embodiments, the preset condition may be whether the first current value matches the historical current value when the energy storage converter was connected to the grid. That is, if they do not match, it is determined that the grid-connected relay has not been activated; if they match, it is considered that the grid-connected relay has been activated. In some embodiments, the historical current value when the energy storage converter was connected to the grid is the target current.
[0059] In some embodiments, whether a first current value matches a target current value depends on whether the absolute value of the difference between the first current value and the target current value is greater than a preset threshold. In some scenarios, if the absolute value of the difference between the first current value and the target current value is greater than the preset threshold, then they match; if the absolute value of the difference between the first current value and the target current value is less than or equal to the preset threshold, then they do not match.
[0060] Of course, whether the first current value matches the target current value can also be set based on other conditions, which will not be elaborated here.
[0061] In some embodiments, step S201 determines the grid connection status based on current changes. When the absolute value of the difference between the first current value and the target current is greater than a preset threshold, it indicates that the grid connection relay has been activated (i.e., grid connection is completed). Then, at this time, the working mode of the energy storage converter can be switched from voltage source mode to current source mode.
[0062] In some embodiments, step S105 may include determining the activation time of the grid-connected relay as the target time when the grid-connected relay is detected to be activated, and controlling the operating mode of the energy storage converter to switch from voltage source mode to current source mode.
[0063] In some embodiments, step S105 may include determining a time interval of a preset time after the second time as the target time, and controlling the operating mode of the energy storage converter to switch from voltage source mode to current source mode.
[0064] That is, if the first current value obtained before the target time does not meet the preset conditions, it cannot be determined by the fluctuation of the first current value that the current grid-connected relay has been activated. Therefore, the operating mode of the energy storage converter will be forcibly switched from voltage source mode to current source mode at the target time.
[0065] Because determining whether the grid-connected relay has closed based on the first current value may contain errors in actual operation. For example, if the circuit or device used to detect the current malfunctions within the current voltage cycle, or if a communication delay occurs within the current voltage cycle, preventing the timely application of the obtained first current value to the grid-connected relay closure determination process, a forced switching of operating modes is required after a preset interval following the second time point. If the grid-connected relay has not yet engaged, further delaying the mode switch will not only affect the accuracy of subsequent engagement time calculations but may also reduce the safety of the energy storage converter's grid connection due to prolonged abnormal grid connection waiting. Therefore, the system needs to forcibly generate a current source switching command to switch from voltage source mode to current source mode.
[0066] Optionally, in the initial period after mode switching, the output current command of the energy storage converter can be set to zero or a minimum value.
[0067] Based on the pull-in command issued at the first moment, the grid connection operation is expected to be completed at the voltage zero-crossing point. If grid connection is not confirmed by comparing the first current value with the target current within the interval after the second moment, it indicates that the pull-in time of the grid connection relay is abnormally prolonged due to deteriorating operating conditions (such as aging). In this case, if the mode switch is further delayed, it will not only affect the accuracy of subsequent predictions of the grid connection relay's pull-in time, but also reduce grid connection safety. Therefore, the system will forcibly generate a current source switching command within the interval after the second moment, controlling the energy storage converter to switch from voltage source mode to current source mode, and this third moment will be determined as the target moment.
[0068] In some embodiments, in step S105, since the current at the grid connection point will fluctuate when the energy storage converter is connected to the grid, the grid connection can be confirmed based on the current at the grid connection point. Therefore, the timing for controlling the energy storage converter to switch its operating mode from voltage source mode to current source mode can be determined based on the current.
[0069] Please see Figure 5 , Figure 5 This is a control flowchart for the energy storage converter and its off-grid switching in some embodiments of this application. The method also includes: In some cases, information such as voltage and current can be obtained through detection to determine the time when the energy storage converter switches from operating mode to current source mode, which can then be used as the target time.
[0070] Step S302: Determine the time for generating the pull-in command in the next preset voltage cycle based on the time interval between the target time and the first time.
[0071] That is, the time interval between the target time and the first time is used as the first preset duration.
[0072] The switching of the energy storage converter from voltage source mode to current source mode indicates that the energy storage converter has completed grid connection with the grid. Therefore, the time interval from the target time to the first time is the activation time of the grid connection relay. The time interval from the target time to the first time can be used as the first time when the energy storage converter switches from off-grid to grid connection again. When the above method is executed, the activation command corresponding to the activation of the grid connection relay is generated within the preset voltage cycle to improve the control accuracy of the grid connection relay, so that the energy storage converter and the grid can complete grid connection at a time closer to the grid voltage zero crossing point.
[0073] The following describes an energy storage converter grid-connected / off-grid switching device. This device can be used to enable grid-connected operation of the energy storage converter 12 and the power grid 20, for example, connecting the energy storage converter 12 to the power grid 20, or vice versa. The energy storage converter grid-connected / off-grid switching device can be applied to the control device 11 described above, the energy storage device 10 described above, or the power supply system 100 described above. In some embodiments, the energy storage converter grid-connected / off-grid switching device can be the control device 11 described above.
[0074] Please see Figure 6 , Figure 6 This is a schematic diagram of the grid-connected / off-grid switching device for an energy storage converter in some embodiments of this application. The grid-connected / off-grid switching device 200 for the energy storage converter may include a determination module 201 and a control module 202 coupled together.
[0075] In some embodiments, the determining module 201 is used to determine the target voltage amplitude of the grid voltage and the target phase of the grid voltage when the grid power supply is restored.
[0076] In some embodiments, the control module 202 is used to adjust the phase of the output voltage of the energy storage converter according to the target phase, and to generate a closing command to control the grid-connected relay to close at the first moment within a preset voltage cycle.
[0077] In some embodiments, the control module 202 is used to adjust the voltage amplitude of the output voltage of the energy storage converter at a second time after the first time, so that the difference between the voltage amplitude of the output voltage and the target voltage amplitude meets a preset condition.
[0078] In some embodiments, the control module 202 is used to control the operating mode of the energy storage converter to switch from voltage source mode to current source mode at a target time after the second time.
[0079] In some embodiments, the control module 202 is used to determine the activation time of the grid-connected relay as the target time when the grid-connected relay is detected to activate, and control the operating mode of the energy storage converter to switch from voltage source mode to current source mode.
[0080] In some embodiments, the control module 202 is used to control the operating mode of the energy storage converter to switch from voltage source mode to current source mode when a target time is determined to be a time after a preset time interval from the second time.
[0081] In some embodiments, the energy storage converter grid-connected switching device 200 may further include a coupled acquisition module 203 and a control module 202.
[0082] In some embodiments, the acquisition module 203 and the control module 202 are used to acquire a first current value on the grid side or the energy storage converter side within a time period from the second time to the target time.
[0083] In some embodiments, the control module 202 is used to determine that the grid-connected relay is engaged when the first current value meets a preset condition.
[0084] In some embodiments, the acquisition module 203 is used to acquire the target current value.
[0085] In some embodiments, the control module 202 is used to determine that the grid-connected relay is engaged when the absolute value of the difference between the first current value and the target current value is greater than a preset threshold.
[0086] In some embodiments, the acquisition module 203 is used to acquire the current on the grid side as the target current at a first moment.
[0087] In some embodiments, the acquisition module 203 is used to acquire the first current value on the grid side within a preset time period after the second time.
[0088] In some embodiments, the acquisition module 203 is used to acquire the current on the energy storage converter side as the target current at a first moment.
[0089] In some embodiments, the acquisition module 203 is used to acquire the first current value on the energy storage converter side within a preset time period after the second time.
[0090] In some embodiments, the acquisition module 203 is used to record the target time when the operating mode of the energy storage converter is switched from voltage source mode to current source mode; and to determine the time when the pull-in command is generated in the next preset voltage cycle based on the time interval between the target time and the first time.
[0091] This application utilizes the sinusoidal characteristics of inverter voltage, meaning that the inverter voltage only requires a high bus voltage from the energy storage converter when the instantaneous value is large. By determining the target voltage amplitude and tracking the target phase to adjust the output voltage, and generating a pull-in command in advance at the first moment, the grid-connected relay can be expected to complete the pull-in near the zero-crossing point of the grid voltage. This strategy ensures that the output voltage of the energy storage converter is within a low instantaneous value range and meets the preset conditions with the grid voltage during grid connection switching, thereby reducing the bus voltage requirement of the energy storage converter, effectively avoiding the occurrence of overload protection triggered by insufficient DC side input energy, and also reducing the impact on the grid-connected relay, thus improving product performance.
[0092] In addition, this application also provides an electronic device. Please refer to [link / reference]. Figure 7 , Figure 7 This is a schematic diagram of the structure of an electronic device in some embodiments of this application. The electronic device 300 includes a memory 301 and a processor 302. A computer program is stored in the memory 301 and can run on the processor 302. When the processor 302 executes the computer program, it implements the steps of any of the methods described above.
[0093] The processor 302 can also be referred to as a CPU (Central Processing Unit). The processor 302 may be an integrated circuit chip with signal processing capabilities. The processor 302 can also be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. The general-purpose processor can be a microprocessor, or the processor 302 can be any conventional processor.
[0094] Memory 301 may include random access memory (RAM), read-only memory (ROM), flash memory, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disk, removable disk, CD-ROM, etc. Memory 301 may store program data, which may include, for example, a single instruction or many instructions, and may be distributed across several different code segments, distributed among different programs, and distributed across multiple memories. Memory 301 may be coupled to processor 302 so that processor 302 can read and write information to / from memory 301. Of course, memory 301 may be integrated into processor 302; this application does not limit this, and those skilled in the art can choose according to actual needs.
[0095] Please see Figure 8 , Figure 8This is a schematic diagram of a computer-readable storage medium according to an embodiment of this application. The computer-readable storage medium 400 stores a computer program, which, when executed by a processor, implements the steps of any of the measurement methods described above. The technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage device and includes several instructions (program data) to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods of various embodiments of this invention. The aforementioned storage device includes various media such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks, as well as electronic devices such as computers, mobile phones, laptops, tablets, and cameras that have the aforementioned storage media.
[0096] In the several embodiments provided in this application, it should be understood that the disclosed methods and devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed.
[0097] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.
[0098] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.
[0099] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. A control method for switching between grid-connected and off-grid operation of an energy storage converter, characterized in that, include: When the power grid restores power, the target voltage amplitude of the grid voltage and the target phase of the grid voltage are determined; The phase of the output voltage of the energy storage converter is adjusted according to the target phase; At the first moment within the preset voltage cycle, a energizing command is generated to control the energizing of the grid-connected relay; At a second time after the first time, the voltage amplitude of the output voltage of the energy storage converter is adjusted so that the difference between the voltage amplitude of the output voltage and the target voltage amplitude meets a preset condition. At a target time after the second time point, the operating mode of the energy storage converter is switched from voltage source mode to current source mode. The second time point is earlier than the zero-crossing point of the grid voltage within the preset voltage cycle.
2. The method according to claim 1, characterized in that, At the target time after the second time point, controlling the operating mode of the energy storage converter to switch from voltage source mode to current source mode includes: When the grid-connected relay is detected to be energized, the energization time of the grid-connected relay is determined as the target time, and the operating mode of the energy storage converter is switched from voltage source mode to current source mode.
3. The method according to claim 1, characterized in that, At the target time after the second time point, controlling the operating mode of the energy storage converter to switch from voltage source mode to current source mode includes: The target time is determined by setting a time interval of a preset duration after the second time, and the operating mode of the energy storage converter is switched from voltage source mode to current source mode.
4. The method according to claim 2, characterized in that, Before switching the operating mode of the energy storage converter from voltage source mode to current source mode, the method further includes: During the time interval from the second moment to the target moment, the first current value on the grid side or the energy storage converter side is obtained; When the first current value meets the preset conditions, the grid-connected relay is determined to be energized.
5. The method according to claim 4, characterized in that, Before determining that the grid-connected relay is engaged when the first current value meets a preset condition, the method further includes: Obtain the target current value; The step of determining that the grid-connected relay is engaged when the first current meets a preset condition includes: When the absolute value of the difference between the first current value and the target current value is greater than a preset threshold, the grid-connected relay is determined to be engaged.
6. The method according to claim 5, characterized in that, The acquisition of the target current value includes: At the first moment, the current on the grid side is acquired as the target current; Correspondingly, obtaining the first current value on the grid side or the energy storage converter side includes: Obtain the first current value on the grid side; or, At the first moment, the current on the energy storage converter is obtained as the target current; Correspondingly, obtaining the first current value on the grid side or the energy storage converter side includes: Obtain the first current value on the energy storage converter side.
7. The method according to claim 3, characterized in that, The second moment is determined based on the load-carrying capacity of the energy storage converter; And / or, the second time step is determined based on the bus capacitor capacity of the energy storage converter; And / or, the time interval from the second moment to the moment when the grid voltage crosses zero is half of the preset duration; And / or, the preset duration is greater than or equal to 0, and less than or equal to half of the voltage cycle.
8. The method according to claim 2, characterized in that, After generating the activation command for controlling the grid-connected relay to activate, the method further includes: Based on the time interval between the target time and the first time, the time at which the pull-in command is generated in the next preset voltage cycle is determined.
9. A grid-connected / off-grid switching device for an energy storage converter, characterized in that, include: The determination module is used to determine the target voltage amplitude of the grid voltage and track the target phase of the grid voltage when the grid power supply is restored. The control module, coupled to the determining module, is used to adjust the phase of the output voltage of the energy storage converter according to the target phase, and to generate a closing command to control the grid-connected relay to close at the first moment within a preset voltage cycle. The control module is used to adjust the voltage amplitude of the output voltage of the energy storage converter at a second time after the first time, so that the difference between the voltage amplitude of the output voltage and the target voltage amplitude meets a preset condition. The control module is used to control the operating mode of the energy storage converter to switch from voltage source mode to current source mode at a target time after the second time, wherein the second time is earlier than the zero-crossing point of the grid voltage within the preset voltage cycle.
10. An energy storage converter, characterized in that, The device includes a control unit, wherein the energy storage converter is connected to the power grid via a grid-connected relay, and the control unit is used to implement the method as described in any one of claims 1-8.
11. An energy storage device, characterized in that, It includes the energy storage converter as described in claim 10 and the battery module, wherein the battery module is electrically connected to the energy storage converter.
12. A power supply system, characterized in that, The device includes a control unit, a power grid, and an energy storage converter, wherein at least one of the power grid and the energy storage converter is connected to a load, and the other energy storage converter is connected to the power grid via a grid-connected relay. The control unit is connected to the energy storage converter and the grid-connected relay, and the control unit is used to implement the method as described in any one of claims 1-8.
13. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-8.