Control method and device for switching grid connection to grid disconnection of energy storage system

Abstract

The invention discloses a control method and device for switching grid connection to grid disconnection of an energy storage system. The control method comprises the following steps: acquiring a phase voltage and a bus voltage on a line when the energy storage system is controlled to be switched to an off-grid state; determining the maximum open-loop duty ratio according to the phase voltage and the bus voltage; within preset time, the energy storage system is controlled to be in an open-loop driving state, and the duty ratio of a driving signal sent to the energy storage inverter is controlled to be monotonically decreased from the maximum open-loop duty ratio, so that the voltage output by the energy storage inverter is controlled to be gradually decreased to be close to zero, therefore, the voltage output by the energy storage inverter and the voltage on the filter capacitor connected with the output side of the energy storage inverter are not opposite in phase, the oscillation of the output voltage is avoided, the impact current of the output port is suppressed, and the stable operation of the energy storage inverter of the energy storage system is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage, and in particular to a control method and device for grid connection and disconnection of an energy storage system. Background Art

[0002] With the development of the green economy, people's demand for photovoltaic energy storage systems is increasing. Household energy storage products support the current source grid connection working mode and the off-grid voltage source mode to independently supply power to loads. When the distributed power generation is sufficient and the state of charge of the energy storage system is good, electric energy is transmitted to the grid through the energy storage inverter, and it works in the grid connection mode at this time. When there is a grid fault or line maintenance, in order to ensure that the load at the output end can operate uninterruptedly, it is necessary to disconnect the grid connection relay at this time, and the energy storage system switches to the off-grid mode of operation, and the photovoltaic and energy storage inverter maintain the system bus, output voltage and frequency.

[0003] When the energy storage system switches to the off-grid mode of operation during a grid fault or line maintenance, there is a filter capacitor on the output side of the photovoltaic energy storage. The voltage on the filter capacitor cannot change suddenly. If conventional control is still used at this time, if the target output voltage calculated by the software loop of the energy storage inverter is opposite to the voltage phase on the filter capacitor, the superposition of the two will cause problems such as impact current and output voltage oscillation. Therefore, it is of great significance to study the grid connection and disconnection of the energy storage inverter for the safe and stable operation of the energy storage system. Summary of the Invention

[0004] The present invention provides a control method and device for grid connection and disconnection of an energy storage system to solve the problems of voltage oscillation and impact current caused by grid connection and disconnection of the energy storage system.

[0005] According to one aspect of the present invention, a control method for grid connection and disconnection of an energy storage system is provided, and the energy storage system includes an energy storage inverter;

[0006] The control method for grid connection and disconnection of the energy storage system includes:

[0007] At the moment of controlling the energy storage system to switch to the off-grid state, obtain the phase voltage and bus voltage on the line;

[0008] Determine the maximum open-loop duty ratio according to the phase voltage and the bus voltage;

[0009] Within a preset time, control the energy storage system to be in an open-loop drive state, and control the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio.

[0010] Optionally, controlling the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio includes:

[0011] Determine the number of times of sending a driving signal to the energy storage inverter within the preset time according to the preset time and the control frequency of the energy storage inverter;

[0012] Control the duty cycle of the driving signal sent to the energy storage inverter for the kth time to be less than the duty cycle of the driving signal sent to the energy storage inverter for the (k - 1)th time; k is an integer greater than or equal to 2 and less than or equal to M, M is the number of times of sending a driving signal to the energy storage inverter within the preset time, M is an integer greater than or equal to 2, and the duty cycle of the driving signal sent to the energy storage inverter for the first time is less than the maximum open-loop duty cycle.

[0013] Optionally, the driving signal D sent to the energy storage inverter for the nth time n Satisfies:

[0014] D n = D0 - (D0 / M) * n; where D0 is the maximum open-loop duty cycle, and n is an integer greater than or equal to 1 and less than or equal to M.

[0015] Optionally, the phase voltage includes the A-phase voltage, the B-phase voltage, and the C-phase voltage;

[0016] Determining the maximum open-loop duty cycle according to the phase voltage and the bus voltage includes:

[0017] Determine the maximum open-loop duty cycle of the A phase according to the A-phase voltage and the bus voltage, determine the maximum open-loop duty cycle of the B phase according to the B-phase voltage and the bus voltage, and determine the maximum open-loop duty cycle of the C phase according to the C-phase voltage and the bus voltage;

[0018] The control that the duty cycle of the driving signal sent to the energy storage inverter monotonically decreases from the maximum open-loop duty cycle includes:

[0019] Control the duty cycle of the driving signal corresponding to the A phase sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty cycle of the A phase, control the duty cycle of the driving signal corresponding to the B phase sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty cycle of the B phase, and control the duty cycle of the driving signal corresponding to the C phase sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty cycle of the C phase.

[0020] Optionally, determining the maximum open-loop duty cycle of the A phase according to the A-phase voltage and the bus voltage includes:

[0021] Determine the ratio of the A-phase voltage to the bus voltage as the maximum open-loop duty cycle of the A phase;

[0022] Determining the maximum open-loop duty cycle of the B phase according to the B-phase voltage and the bus voltage includes:

[0023] Determine the ratio of the B-phase voltage to the bus voltage as the maximum open-loop duty ratio of the B phase;

[0024] Determining the maximum open-loop duty ratio of the C phase according to the C-phase voltage and the bus voltage includes:

[0025] Determine the ratio of the C-phase voltage to the bus voltage as the maximum open-loop duty ratio of the C phase.

[0026] Optionally, the energy storage system further includes a power grid, a first switch, a second switch, and a load; the energy storage inverter is connected to the load through the first switch, the power grid is connected to the load through the second switch, and the energy storage inverter is connected to the power grid through the first switch and the second switch;

[0027] Before obtaining the phase voltage and the bus voltage on the line at the moment of controlling the energy storage system to switch to the off-grid state, it further includes:

[0028] When it is determined that the energy storage system needs to switch to the off-grid state, control the second switch to disconnect so that the energy storage system switches to the off-grid state.

[0029] Optionally, before obtaining the phase voltage and the bus voltage on the line at the moment of controlling the energy storage system to switch to the off-grid state, it further includes:

[0030] Obtain at least two parameter information of the power grid in real time; the at least two parameter information includes the voltage of the power grid and the frequency of the power grid;

[0031] When at least one parameter information of the power grid exceeds the normal value range corresponding to the parameter information, determine that the energy storage system needs to switch to the off-grid state.

[0032] Optionally, after controlling the energy storage system to be in the open-loop drive state within a preset time and controlling the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio, it further includes:

[0033] Control the energy storage system to be in a closed-loop state.

[0034] According to another aspect of the present invention, there is provided a control device for grid connection and off-grid switching of an energy storage system, and the energy storage system includes an energy storage inverter;

[0035] The control device for grid connection and off-grid switching of the energy storage system includes:

[0036] An acquisition module, configured to acquire the phase voltage and the bus voltage on the line at the moment of controlling the energy storage system to switch to the off-grid state;

[0037] A duty ratio determination module, configured to determine a maximum open-loop duty ratio according to the phase voltage and the bus voltage;

[0038] An open-loop driving module, configured to control the energy storage system to be in an open-loop driving state within a preset time, and control the duty ratio of a driving signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio.

[0039] Optionally, the open-loop driving module includes:

[0040] A driving times determination unit, configured to determine the number of times of sending a driving signal to the energy storage inverter within the preset time according to the preset time and the control frequency of the energy storage inverter;

[0041] An open-loop driving unit, configured to control the duty ratio of the driving signal sent to the energy storage inverter for the kth time to be less than the duty ratio of the driving signal sent to the energy storage inverter for the (k - 1)th time; k is an integer greater than or equal to 2 and less than or equal to M, M is the number of times of sending a driving signal to the energy storage inverter within the preset time, M is an integer greater than or equal to 2, and the duty ratio of the driving signal sent to the energy storage inverter for the first time is less than the maximum open-loop duty ratio.

[0042] The technical solution of the embodiment of the present invention, when the energy storage system is switched from grid-connected to off-grid, controls the duty ratio of the driving signal sent to the energy storage inverter of the energy storage system to monotonically decrease from the maximum open-loop duty ratio calculated according to the phase voltage obtained at the off-grid moment, so as to control the voltage output by the energy storage inverter to gradually decrease and approach zero, thereby preventing the voltage output by the energy storage inverter and the voltage on the filter capacitor connected to the output side of the energy storage inverter from being out of phase, avoiding the oscillation of the output voltage and suppressing the impact current at the output port, and ensuring the stable operation of the energy storage inverter of the energy storage system.

[0043] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understandable through the following description. Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0045] Figure 1 It is a flowchart of a control method for grid-connected and off-grid switching of an energy storage system provided by an embodiment of the present invention;

[0046] Figure 2 Flow chart of another control method for grid connection and disconnection of the energy storage system provided by the embodiment of the present invention;

[0047] Figure 3 Structural schematic diagram of an energy storage system provided by the embodiment of the present invention;

[0048] Figure 4 Flow chart of a control method for grid connection and disconnection of an energy system provided by the embodiment of the present invention;

[0049] Figure 5 Flow chart of another control method for grid connection and disconnection provided by the embodiment of the present invention;

[0050] Figure 6 Flow chart of another control method for grid connection and disconnection provided by the embodiment of the present invention;

[0051] Figure 7 Loop waveform diagram of an energy storage system during the process of switching from grid-connected state to off-grid state provided by the embodiment of the present invention;

[0052] Figure 8 Structural schematic diagram of a control device for grid connection and disconnection of an energy storage system provided by the embodiment of the present invention. Detailed implementation manners

[0053] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0054] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order different from those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0055] Figure 1The flowchart of a control method for grid-connected and off-grid switching of an energy storage system provided by an embodiment of the present invention. This embodiment is applicable to the situation of safely and stably operating the energy storage system when switching from grid-connected to off-grid. This method can be executed by a control device for grid-connected and off-grid switching of the energy storage system, and the control device for grid-connected and off-grid switching of the energy storage system can be implemented in the form of hardware and software. As Figure 1 shown, the method includes:

[0056] S110: At the moment of controlling the energy storage system to switch to the off-grid state, obtain the phase voltage and bus voltage on the line.

[0057] The energy storage system includes an energy storage inverter, a power grid, and a filter capacitor, or the energy storage system includes an energy storage inverter, a power grid, a filter capacitor, and a load. In this embodiment, taking the case of including a load as an example, the energy storage inverter is used to convert the electric energy generated by the photovoltaic panel into alternating current and then output it to the power grid and / or the load, and the power grid is used to supply power to the load. When the power generation of the photovoltaic panel is sufficient, the energy storage inverter converts the electric energy output by the photovoltaic panel into alternating current and then outputs it to the power grid, or converts the electric energy output by the photovoltaic panel into alternating current and then provides it to the battery to charge the battery. In some working conditions, such as when a power grid fault occurs or line maintenance is required on the power grid side, the connection between the power grid and the energy storage inverter needs to be cut off, that is, switched to the off-grid state. The off-grid state of the energy storage system is the state where the connection between the power grid and the energy storage inverter is cut off. In the off-grid state, the voltage output by the energy storage inverter supplies power to the load to ensure uninterrupted power supply to the load.

[0058] At the moment of controlling the energy storage system to switch to the off-grid state, obtain the magnitudes of the phase voltage and bus voltage respectively through a voltage sensor.

[0059] S120: Determine the maximum open-loop duty ratio according to the phase voltage and the bus voltage.

[0060] Determine the ratio of the phase voltage to the bus voltage as the maximum open-loop duty ratio.

[0061] S130: Within a preset time, control the energy storage system to be in an open-loop drive state, and control the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio.

[0062] The energy storage inverter includes a transistor, and the magnitude of the voltage output by the energy storage inverter is controlled by controlling the magnitude of the duty ratio of the drive signal sent to the transistor. The duty ratio of the drive signal is positively correlated with the magnitude of the voltage output by the energy storage inverter.

[0063] The open-loop drive state is a drive mode in which when sending a drive signal to the energy storage inverter, the voltage output by the energy storage inverter is not fed back. In the open-loop drive state, a drive signal is directly sent to the energy storage inverter, and the energy storage inverter correspondingly outputs a voltage. The closed-loop drive state is a state in which the duty cycle of the drive signal sent to the energy storage inverter is adjusted according to the fed-back voltage output by the energy storage inverter to further adjust the magnitude of the voltage output by the energy storage inverter. The preset time can be obtained based on experience or set manually by the user. The preset time cannot be too large to avoid intermittent power supply to the load, and the preset time cannot be too small to avoid the voltage on the filter capacitor still being very large. Exemplarily, the preset time can be 3 ms - 5 ms.

[0064] Within the preset time, the duty cycle of the drive signal sent to the energy storage inverter is monotonically changed from the maximum open-loop duty cycle, so that starting from the moment when the energy storage system is in the off-grid state, the voltage output by the energy storage inverter becomes smaller and smaller and then approaches zero, avoiding the situation where the voltage is opposite in phase to the voltage on the filter capacitor when the voltage output by the energy storage inverter is not zero, resulting in problems such as voltage oscillation and excessive current. After the preset time, the charge on the filter capacitor flows and discharges continuously, so that the voltage on the filter capacitor approaches zero after the preset time, facilitating the subsequent normal sending of drive signals to the energy storage inverter and enabling the energy storage system to operate normally in the off-grid state.

[0065] In the technical solution of the embodiment of the present invention, when the energy storage system is switched from grid-connected to off-grid, the duty cycle of the drive signal sent to the energy storage inverter of the energy storage system is monotonically decreased from the maximum open-loop duty cycle calculated according to the phase voltage obtained at the moment of grid disconnection, so as to control the amplitude of the voltage output by the energy storage inverter to gradually decrease and approach zero, thereby preventing the voltage output by the energy storage inverter from being opposite in phase to the voltage on the filter capacitor connected to the output side of the energy storage inverter, avoiding the oscillation of the output voltage and suppressing the impact current at the output port, and ensuring the stable operation of the energy storage inverter of the energy storage system.

[0066] Figure 2 This is a flowchart of another control method for grid connection and disconnection of the energy storage system provided by the embodiment of the present invention. Refer to Figure 2 Optionally, the method includes:

[0067] S111: At the moment of controlling the energy storage system to switch to the off-grid state, obtain the phase voltage and bus voltage on the line.

[0068] S121: Determine the maximum open-loop duty cycle according to the phase voltage and bus voltage.

[0069] S131: Determine the number of times of sending drive signals to the energy storage inverter within the preset time according to the preset time and the control frequency of the energy storage inverter.

[0070] The control frequency of the energy storage inverter can be understood as the frequency at which the control system executes the control loop, that is, the number of times the control loop is executed per second. Or, it can be understood as the number of times the drive signal is updated. The product of the preset time T and the control frequency f of the energy storage inverter is used as the number of times M of sending the drive signal to the energy storage inverter within the preset time, that is, M = T * f.

[0071] S141: Control the duty cycle of the drive signal sent to the energy storage inverter for the k-th time to be less than the duty cycle of the drive signal sent to the energy storage inverter for the (k - 1)-th time; k is an integer greater than or equal to 2 and less than or equal to M, M is the number of times of sending the drive signal to the energy storage inverter within the preset time, M is an integer greater than or equal to 2, and the duty cycle of the drive signal sent to the energy storage inverter for the first time is less than the maximum open-loop duty cycle.

[0072] Within the preset time, it is necessary to send the drive signal to the energy storage inverter M times. Therefore, during the process of sending the drive signal to the energy storage inverter M times, control the duty cycle of the drive signal sent to the energy storage inverter to monotonically change from the maximum open-loop duty cycle, so that since the moment when the energy storage system is in the off-grid state, the voltage after the voltage output by the energy storage inverter is superimposed on the voltage of the filter capacitor becomes smaller and smaller, thereby avoiding problems such as voltage oscillation and excessive current.

[0073] Optionally, the drive signal D sent to the energy storage inverter for the n-th time n Satisfies:

[0074] D n = D0 - (D0 / M) * n; where D0 is the maximum open-loop duty cycle, and n is an integer greater than or equal to 1 and less than or equal to M.

[0075] For the first time: D1 = D0 - (D0 / M) * 1;

[0076] For the second time: D2 = D0 - (D0 / M) * 2;

[0077] For the third time: D3 = D0 - (D0 / M) * 3;

[0078] …;

[0079] For the (M - 1)-th time: D M-1 = D0 - [D0 / (M - 1)] * 1;

[0080] For the M-th time: D M = D0 - D0 / M * M.

[0081] The difference in the duty cycle between every two adjacent times of sending the drive signal is the same, making the drive signal output to the energy storage inverter change uniformly, and further making the magnitude of the voltage output by the energy storage inverter change uniformly, avoiding system instability caused by voltage mutation of the voltage output by the energy storage inverter.

[0082] Figure 3 The figure is a schematic structural diagram of an energy storage system provided by an embodiment of the present invention. The energy storage system further includes a power grid 10, a first switch 11, a second switch 12, and a load 13; the energy storage inverter 14 is connected to the load 13 through the first switch 11, the power grid 10 is connected to the load 13 through the second switch 12, and the energy storage inverter 14 is connected to the power grid 10 through the first switch 11 and the second switch 12. Figure 4 The figure is a flowchart of a control method for grid connection and grid disconnection of an energy storage system provided by an embodiment of the present invention. Refer to Figure 3 and Figure 4 , optionally, the inverter is a three-phase inverter, and the phase voltages include phase A voltage, phase B voltage, and phase C voltage. The method includes:

[0083] S112: At the moment of controlling the energy storage system to switch to the off-grid state, obtain the phase A voltage, phase B voltage, phase C voltage, and bus voltage on the line respectively.

[0084] As Figure 3 shown, the energy storage system further includes a first filter inductor L1, a second filter inductor L2, and a third filter inductor L3, a first filter capacitor C1, a second filter capacitor C2, and a third filter capacitor C3. The first switch 11 includes a first sub-switch K11, a second sub-switch K12, a third sub-switch K13, and a fourth sub-switch K14. The second switch 12 includes a fifth sub-switch K15, a sixth sub-switch K16, and a seventh sub-switch K17. In this embodiment, the load is exemplarily shown as a resistor. For the specific connection relationship between the various components of the energy storage system, refer to Figure 3 , which will not be elaborated here. Among them, the first filter inductor L1, the first sub-switch K11, and the fifth sub-switch K15 are connected to the phase A line, the second filter inductor L2, the second sub-switch K12, and the sixth sub-switch K16 are connected to the phase B line, the third filter inductor L3, the third sub-switch K13, and the seventh sub-switch K17 are connected to the phase C line, and the fourth sub-switch K14 is connected to the neutral line N. The energy storage inverter 14 is also connected to the power supply module 15, and the power supply module includes a photovoltaic panel.

[0085] At the moment of controlling the energy storage system to switch to the off-grid state, obtain the voltage between the phase A line and the neutral line N, that is, the phase A voltage, obtain the voltage between the phase B line and the neutral line N, that is, the phase B voltage, obtain the voltage between the phase C line and the neutral line N, that is, the phase C voltage. The bus voltage is the voltage between the bus and the neutral line. The above-mentioned phase voltages and bus voltage are obtained through voltage sensors.

[0086] S122: Determine the maximum open-loop duty ratio of phase A according to the phase A voltage and the bus voltage, determine the maximum open-loop duty ratio of phase B according to the phase B voltage and the bus voltage, and determine the maximum open-loop duty ratio of phase C according to the phase C voltage and the bus voltage.

[0087] Determine the ratio of the phase-A voltage to the bus voltage as the maximum open-loop duty ratio of phase A;

[0088] Determine the ratio of the phase-B voltage to the bus voltage as the maximum open-loop duty ratio of phase B;

[0089] Determine the ratio of the phase-C voltage to the bus voltage as the maximum open-loop duty ratio of phase C.

[0090] S132: Control the duty ratio of the drive signal corresponding to phase A sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio of phase A, control the duty ratio of the drive signal corresponding to phase B sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio of phase B, and control the duty ratio of the drive signal corresponding to phase C sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio of phase C.

[0091] For a three-phase energy storage inverter, each phase corresponds to an inverter bridge, and the inverter bridge is composed of multiple transistors. By sending a drive signal to the inverter bridge of a certain phase, the magnitude of the voltage output by this phase is controlled.

[0092] Control the duty ratio of the drive signal corresponding to phase A sent to the energy storage inverter to monotonically change from the maximum open-loop duty ratio of phase A, control the duty ratio of the drive signal corresponding to phase B sent to the energy storage inverter to monotonically change from the maximum open-loop duty ratio of phase B, and control the duty ratio of the drive signal corresponding to phase C sent to the energy storage inverter to monotonically change from the maximum open-loop duty ratio of phase C, so that the voltage corresponding to any phase gradually decreases until it approaches zero, and further, the situation where the voltage corresponding to any phase is out of phase with the voltage of the filter capacitor corresponding to this phase will not occur.

[0093] For any phase, controlling the duty ratio of the drive signal corresponding to this phase sent to the energy storage inverter to monotonically change from the maximum open-loop duty ratio corresponding to this phase can further refer to S141 and will not be elaborated here.

[0094] Figure 5 This is a flowchart of another grid-connected to off-grid control method provided by the embodiment of the present invention. Refer to Figure 3 and Figure 5 , this method includes:

[0095] S113: Real-time obtain at least two parameter information of the power grid; the at least two parameter information includes the voltage of the power grid and the frequency of the power grid.

[0096] S123: When at least one parameter information of the power grid exceeds the normal value range corresponding to the parameter information, determine that the energy storage system needs to switch to the off-grid state.

[0097] When the voltage of the power grid exceeds the normal voltage range, specifically when it is greater than a preset multiple of the rated voltage. For example, if the rated voltage is 220V and the preset multiple is 1.1 times, then when the voltage of the power grid is greater than 220 * 1.1, it is determined that a fault occurs in the power grid, or when the power grid frequency exceeds the normal value range, it is determined that a fault occurs in the power grid. When at least one of the voltage and frequency of the power grid is abnormal, the energy storage system is controlled to switch to the off-grid state.

[0098] S133: When it is determined that the energy storage system needs to switch to the off-grid state, control the second switch to disconnect, so that the energy storage system switches to the off-grid state.

[0099] After the second switch 12 is disconnected, the connection between the power grid 10 and the energy storage inverter 14 is disconnected, and the connection between the power grid 10 and the load 13 is disconnected. The energy storage system supplies power to the load 13 through the energy storage inverter 14, and the energy storage system switches to the off-grid state.

[0100] S143: At the moment of controlling the energy storage system to switch to the off-grid state, obtain the phase voltage and bus voltage on the line.

[0101] S153: Determine the maximum open-loop duty ratio according to the phase voltage and bus voltage.

[0102] S163: Within a preset time, control the energy storage system to be in the open-loop drive state, and control the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio.

[0103] S173: Control the energy storage system to be in the closed-loop state.

[0104] After a preset time, the voltages of the three filter capacitors gradually approach zero through discharging. At this time, control the energy storage system to be in the closed-loop state, and adjust the magnitude of the drive signal sent to each phase of the energy storage inverter according to the deviation between the voltage output by the energy storage inverter and the desired voltage, so that the voltage output by the energy storage inverter approaches the desired voltage, realizing the closed-loop control of the energy storage system.

[0105] In this embodiment, by detecting the parameter information of the power grid, when a fault occurs in the power grid, the energy storage system is timely controlled to switch to the off-grid state to avoid the interruption of load power supply caused by the power grid fault. At the same time, after a preset time of controlling the energy storage system to switch to the off-grid state, when the voltage on the filter capacitor gradually decreases to a very small value, control the energy storage system to operate in the closed-loop state to ensure that the voltage output by the inverter approaches the desired voltage and ensure the accuracy of power supply.

[0106] Figure 6 It is a flowchart of another control method for grid-connected to off-grid switching provided by an embodiment of the present invention. Figure 7 It is a loop waveform diagram of an energy storage system during the process of switching from grid-connected state to off-grid state provided by an embodiment of the present invention. Refer to Figure 6 andFigure 7 , the method includes:

[0107] S114: Obtain at least two parameter information of the power grid in real time; the at least two parameter information includes the voltage of the power grid and the frequency of the power grid.

[0108] S124: Determine whether the energy storage system switches to the off-grid state according to the at least two parameter information of the power grid. If so, execute S134; if not, execute S184.

[0109] Specifically, if at least one of the voltage of the power grid and the frequency of the power grid exceeds the corresponding normal value range, it is determined that the energy storage system needs to switch to the off-grid state, and S134 is executed. If both the voltage of the power grid and the frequency of the power grid are within the corresponding normal value ranges, S184 is executed.

[0110] S134: Control the second switch to disconnect, so that the energy storage system switches to the off-grid state.

[0111] S144: Control the energy storage system to operate to the off-grid loop and output a voltage sampling mark.

[0112] S154: At the moment of controlling the energy storage system to switch to the off-grid state, obtain the phase voltage and the bus voltage on the line.

[0113] S164: Determine the maximum open-loop duty ratio according to the phase voltage and the bus voltage. Within a preset time, control the energy storage system to be in the open-loop drive state, and control the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio.

[0114] S174: Control the energy storage system to be in the closed-loop state.

[0115] S184: Control the energy storage system to be in the grid-connected state.

[0116] Figure 7 The blue curve represents the phase voltage Va of phase A, the green curve represents the phase voltage Vb of phase B, the orange curve represents the phase voltage Vc of phase C. For the waveforms of the three-phase voltages in step S114, refer to the first stage 101; for the waveforms of the three-phase voltages in step S124, refer to the second stage 102; for the waveforms of the three-phase voltages in step S134, refer to the third stage 103; for the waveforms of the three-phase voltages in step S144, refer to the fourth stage 104; the waveforms of the three-phase voltages in step S154 and the waveforms of the three-phase voltages in step S164 are the same. For the waveforms of the three-phase voltages in step S154, refer to the fifth stage 105; for the waveforms of the three-phase voltages in step S164 and the steps, refer to the sixth stage 106; for the waveforms of the three-phase voltages in step S174, refer to the seventh stage 107.

[0117] The embodiment of the present invention also provides a control device for grid-connected and off-grid switching of an energy storage system,Figure 8 The structural schematic diagram of a control device for grid connection and disconnection of an energy storage system provided by an embodiment of the present invention is referred to Figure 8 , and the energy storage system includes an energy storage inverter;

[0118] The control device for grid connection and disconnection of the energy storage system includes:

[0119] An acquisition module 20, configured to acquire the phase voltage and bus voltage on the line at the moment of controlling the energy storage system to switch to the off-grid state;

[0120] A duty ratio determination module 21, configured to determine the maximum open-loop duty ratio according to the phase voltage and bus voltage;

[0121] An open-loop drive module 23, configured to control the energy storage system to be in an open-loop drive state within a preset time, and control the duty ratio of the drive signal sent to the energy storage inverter to decrease monotonically.

[0122] The beneficial effects of the control device for grid connection and disconnection of the energy storage system are the same as those of the control method for grid connection and disconnection of the energy storage system, and will not be elaborated here.

[0123] Optionally, the open-loop drive module includes:

[0124] A drive times determination unit, configured to determine the number of drive signals sent to the energy storage inverter within the preset time according to the preset time and the control frequency of the energy storage inverter;

[0125] An open-loop drive unit, configured to control the duty ratio of the kth drive signal sent to the energy storage inverter to be less than the duty ratio of the (k - 1)th drive signal sent to the energy storage inverter; k is an integer greater than or equal to 2 and less than or equal to M, M is the number of drive signals sent to the energy storage inverter within the preset time, M is an integer greater than or equal to 2, and the duty ratio of the first drive signal sent to the energy storage inverter is less than the maximum open-loop duty ratio.

[0126] The control device for grid connection and disconnection of the energy storage system provided by the embodiment of the present invention can execute the control method for grid connection and disconnection of the energy storage system provided by any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method.

[0127] It should be understood that various forms of the processes shown above can be used, steps can be reordered, added or deleted. For example, the steps described in the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved, and no limitation is made herein.

[0128] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A control method for grid connection and disconnection of an energy storage system, characterized in that The energy storage system includes an energy storage inverter; The control method for grid connection and disconnection of the energy storage system includes: At the moment of controlling the energy storage system to switch to the off-grid state, obtain the phase voltage and bus voltage on the line; Determine the maximum open-loop duty ratio according to the phase voltage and the bus voltage; Within a preset time, control the energy storage system to be in an open-loop drive state, and control the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio.

2. The control method for grid connection and disconnection of the energy storage system according to claim 1, characterized in that, Controlling the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio includes: Determine the number of drive signals sent to the energy storage inverter within the preset time according to the preset time and the control frequency of the energy storage inverter; Control the duty ratio of the kth drive signal sent to the energy storage inverter to be less than the duty ratio of the (k - 1)th drive signal sent to the energy storage inverter; k is an integer greater than or equal to 2 and less than or equal to M, M is the number of drive signals sent to the energy storage inverter within the preset time, M is an integer greater than or equal to 2, and the duty ratio of the first drive signal sent to the energy storage inverter is less than the maximum open-loop duty ratio.

3. The control method for grid connection and disconnection of the energy storage system according to claim 2, wherein, The drive signal D sent to the energy storage inverter for the nth time n Satisfies: D n = D0 - (D0 / M) * n; where D0 is the maximum open-loop duty cycle and n is an integer greater than or equal to 1 and less than or equal to M.

4. The control method for grid connection and disconnection of the energy storage system according to any one of claims 1-3, characterized in that , The phase voltage includes the A-phase voltage, B-phase voltage, and C-phase voltage; Determining the maximum open-loop duty ratio according to the phase voltage and the bus voltage includes: Determine the maximum open-loop duty ratio of the A phase according to the A-phase voltage and the bus voltage, determine the maximum open-loop duty ratio of the B phase according to the B-phase voltage and the bus voltage, and determine the maximum open-loop duty ratio of the C phase according to the C-phase voltage and the bus voltage; Controlling the duty ratio of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio includes: Control the duty ratio of the drive signal corresponding to the A phase sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio of the A phase, control the duty ratio of the drive signal corresponding to the B phase sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio of the B phase, and control the duty ratio of the drive signal corresponding to the C phase sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty ratio of the C phase.

5. The control method for grid connection and disconnection of the energy storage system according to claim 4, characterized in that, Determining the maximum open-loop duty ratio of the A phase according to the A-phase voltage and the bus voltage includes: Determine the ratio of the A-phase voltage to the bus voltage as the maximum open-loop duty ratio of the A phase; Determining the maximum open-loop duty ratio of the B phase according to the B-phase voltage and the bus voltage includes: Determine the ratio of the B-phase voltage to the bus voltage as the maximum open-loop duty ratio of the B phase; Determining the maximum open-loop duty ratio of the C phase according to the C-phase voltage and the bus voltage includes: Determine the ratio of the C-phase voltage to the bus voltage as the maximum open-loop duty ratio of the C phase.

6. The control method for grid connection and disconnection of the energy storage system according to claim 1, characterized in that, The energy storage system further includes a power grid, a first switch, a second switch, and a load; the energy storage inverter is connected to the load through the first switch, the power grid is connected to the load through the second switch, and the energy storage inverter is connected to the power grid through the first switch and the second switch; Before obtaining the phase voltage and bus voltage on the line at the moment of controlling the energy storage system to switch to the off-grid state, the following steps are also included: When it is determined that the energy storage system needs to switch to the off-grid state, control the second switch to disconnect, so that the energy storage system switches to the off-grid state.

7. The control method for grid connection and disconnection of the energy storage system according to claim 6, wherein Before obtaining the phase voltage and bus voltage on the line at the moment of controlling the energy storage system to switch to the off-grid state, the following steps are also included: Obtain at least two parameter information of the power grid in real time; the at least two parameter information includes the voltage of the power grid and the frequency of the power grid; When at least one parameter information of the power grid exceeds the normal value range corresponding to the parameter information, determine that the energy storage system needs to switch to the off-grid state.

8. The control method for grid connection and disconnection of the energy storage system according to claim 1, characterized in that, After controlling the energy storage system to be in the open-loop drive state within a preset time and controlling the duty cycle of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty cycle, the following steps are also included: Control the energy storage system to be in the closed-loop state.

9. A control device for grid connection and disconnection of an energy storage system, characterized in that, The energy storage system includes an energy storage inverter; The control device for the grid-connected and off-grid switching of the energy storage system includes: An acquisition module, configured to obtain the phase voltage and bus voltage on the line at the moment of controlling the energy storage system to switch to the off-grid state; A duty cycle determination module, configured to determine the maximum open-loop duty cycle according to the phase voltage and the bus voltage; An open-loop drive module, configured to control the energy storage system to be in the open-loop drive state within a preset time, and control the duty cycle of the drive signal sent to the energy storage inverter to monotonically decrease from the maximum open-loop duty cycle.

10. The control device for grid connection and disconnection of the energy storage system according to claim 9, characterized in that, The open-loop drive module includes: A drive times determination unit, configured to determine the number of times of sending drive signals to the energy storage inverter within the preset time according to the preset time and the control frequency of the energy storage inverter; An open-loop drive unit, configured to control the duty cycle of the drive signal sent to the energy storage inverter for the kth time to be less than the duty cycle of the drive signal sent to the energy storage inverter for the (k - 1)th time; k is an integer greater than or equal to 2 and less than or equal to M, M is the number of times of sending drive signals to the energy storage inverter within the preset time, M is an integer greater than or equal to 2, and the duty cycle of the drive signal sent to the energy storage inverter for the first time is less than the maximum open-loop duty cycle.

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