Control method of energy storage inverter and related assembly

Abstract

The invention discloses a control method of an energy storage inverter and a related component, the power grid voltage fluctuation quantity is determined in each power grid period, and when the energy storage inverter is in grid-connected operation, if the power grid voltage fluctuation quantity is determined to be greater than a preset fluctuation quantity threshold value, the energy storage inverter is started. If yes, accumulating a first duration for keeping the power grid voltage fluctuation quantity greater than a preset fluctuation quantity threshold value, and controlling the energy storage inverter to be switched to an off-grid operation state under the condition that the first duration is greater than a first preset time threshold value. The energy storage inverter is not controlled to be switched from the grid-connected operation state to the off-grid operation state when the power grid voltage fluctuation quantity is detected to be greater than the preset fluctuation quantity threshold value, but the condition that the power grid is abnormal is accurately determined after the condition that the power grid voltage fluctuation quantity is greater than the preset fluctuation quantity threshold value lasts for the preset time threshold value; and then the energy storage inverter is controlled to be switched to the off-grid operation state, so that false triggering of operation state switching of the energy storage inverter is avoided, and the frequency of operation state switching of the energy storage inverter is reduced.

Description

Technical Field

[0001] This invention relates to the field of energy storage inverter control, and particularly to a control method and related components for an energy storage inverter. Background Technology

[0002] The energy storage system includes photovoltaic modules, batteries, and energy storage inverters. The photovoltaic modules can convert solar energy into electrical energy and transmit it to the energy storage inverter. Alternatively, the batteries can output electrical energy to the energy storage inverter when they are fully charged. When the grid is normal, the energy storage inverter operates in parallel with the grid, converting the electrical energy output by the photovoltaic modules or batteries and then connecting it to the grid to supply power to the load. When the grid is abnormal, the energy storage inverter operates off-grid and supplies power to the load.

[0003] In existing technologies, to achieve uninterrupted power supply to the load, the energy storage inverter is immediately switched from grid-connected operation to off-grid operation when a grid anomaly is detected. This switches the power supply from the grid to the energy storage inverter. However, when the grid quality is poor or the grid itself is unstable, the grid voltage may contain a large number of harmonics and spike fluctuations, which may be misjudged as grid anomalies. This can cause the energy storage inverter to frequently switch between grid-connected and off-grid operation, and frequent switching of operating states can damage the energy storage inverter.

[0004] Therefore, how to control energy storage inverters to avoid frequent switching of operating states is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a control method and related components for an energy storage inverter. Instead of immediately controlling the energy storage inverter to switch from grid-connected operation to off-grid operation when the detected grid voltage fluctuation exceeds a preset fluctuation threshold, the method accurately determines that an anomaly has occurred in the grid after determining that the grid voltage fluctuation has exceeded the preset fluctuation threshold for a preset time threshold, and then controls the energy storage inverter to switch to off-grid operation. This avoids false triggering of the energy storage inverter's operation state switching and reduces the frequency of the energy storage inverter's operation state switching.

[0006] To solve the above-mentioned technical problems, the present invention provides a control method for an energy storage inverter, comprising:

[0007] The amount of grid voltage fluctuation is determined based on the real-time voltage value and the target voltage value of the grid within each grid cycle;

[0008] If the energy storage inverter is in grid-connected operation, then determine the first duration during which the grid voltage fluctuation exceeds the preset fluctuation threshold.

[0009] If the first duration is determined to be greater than the first preset time threshold, the energy storage inverter is controlled to switch to off-grid operation mode so that the energy storage inverter can supply power to the load.

[0010] Preferably, determining the grid voltage fluctuation based on the real-time grid voltage value and the target voltage value within each grid cycle includes:

[0011] Obtain the real-time voltage value of the power grid during the current power grid cycle;

[0012] The real-time voltage value is subjected to FFT calculation to obtain the spectrum of the real-time voltage value;

[0013] Determine the effective value of the fundamental grid voltage within the current grid cycle from the spectrum diagram;

[0014] The real-time voltage value is phase-locked by a phase-locked loop to determine the phase angle of the real-time voltage value in the current power grid cycle;

[0015] The target voltage value is determined based on the phase angle and the effective value of the fundamental grid voltage.

[0016] The absolute value of the first difference between the real-time voltage value and the target voltage value is determined as the grid voltage fluctuation.

[0017] Preferably, if the energy storage inverter is in grid-connected operation, after determining that the grid voltage fluctuation is greater than a preset fluctuation threshold for a first duration, the method further includes:

[0018] If the first duration is not greater than a first preset time threshold, the energy storage inverter is controlled to maintain the grid-connected operation state so that the grid supplies power to the load.

[0019] Preferably, the preset fluctuation threshold is a first value;

[0020] After determining that the first duration is greater than a first preset time threshold, the method further includes controlling the energy storage inverter to switch to off-grid operation.

[0021] The effective value of the first fundamental grid voltage is determined based on the spectrum of the real-time voltage value of the grid during the current grid cycle.

[0022] The effective value of the second fundamental grid voltage in the previous grid cycle is determined based on the spectrum of the real-time voltage value of the grid in the previous grid cycle of the current grid cycle.

[0023] Determine the absolute value of the second difference between the effective value of the first fundamental grid voltage and the effective value of the second fundamental grid voltage;

[0024] If the absolute value of the second difference is not greater than the preset difference threshold, then the value of the preset fluctuation threshold is set to the second value.

[0025] If the absolute value of the second difference is greater than the preset difference threshold, then the value of the preset fluctuation threshold is set to the first value;

[0026] The first value is less than the second value.

[0027] Preferably, before setting the value of the preset fluctuation threshold to the second value, the method further includes:

[0028] Determine the comparison between the absolute value of the second difference and the preset difference threshold for the most recent N times the energy storage inverter was switched to off-grid operation within a historical time frame based on the current time; N is a positive integer;

[0029] Determine whether there exists a situation where, during N instances of controlling the energy storage inverter to switch to off-grid operation, the absolute value of the second difference is not greater than the preset difference threshold.

[0030] If so, proceed to the step of setting the value of the preset fluctuation threshold to the second value;

[0031] If not, the value of the preset fluctuation threshold will be maintained as the preset fluctuation threshold of the previous power grid cycle.

[0032] Preferably, before setting the value of the preset fluctuation threshold to the first value, the method further includes:

[0033] Determine the comparison between the absolute value of the second difference and the preset difference threshold during the most recent N times the energy storage inverter was switched to off-grid operation, based on the current time in the historical time frame; N is a positive integer;

[0034] Determine whether there is a situation where the absolute value of the second difference is greater than the preset difference threshold when the energy storage inverter is switched to off-grid operation state N times;

[0035] If so, proceed to the step of setting the value of the preset fluctuation threshold to the first value;

[0036] If not, the value of the preset fluctuation threshold will be maintained as the preset fluctuation threshold of the previous power grid cycle.

[0037] Preferably, after controlling the energy storage inverter to switch to off-grid operation when it is determined that the first duration is greater than a first preset time threshold, the method further includes:

[0038] When the detected grid voltage fluctuation is not greater than the preset fluctuation threshold, a second duration for which the grid voltage fluctuation is not greater than the preset fluctuation threshold is determined;

[0039] If the second duration is greater than the second preset time threshold, then the power grid is determined to be in a stable and normal state.

[0040] If the third duration of the grid being in a stable and normal state is greater than a third preset time threshold, then the energy storage inverter is controlled to switch to grid-connected operation.

[0041] Preferably, after controlling the energy storage inverter to switch to grid-connected operation, the method further includes:

[0042] If the energy storage inverter is switched to off-grid operation within the fourth preset time threshold, the third preset time threshold is increased.

[0043] Preferably, after controlling the energy storage inverter to switch to grid-connected operation, the method further includes:

[0044] If it is determined that the energy storage inverter is still in grid-connected operation after the fifth preset time threshold, then the third preset time threshold is reduced; the fifth preset time threshold is greater than the fourth preset time threshold.

[0045] To solve the above-mentioned technical problems, the present invention provides a control device for an energy storage inverter, comprising:

[0046] Memory, used to store computer programs;

[0047] A processor is used to implement the steps of the control method for the energy storage inverter as described above when executing a computer program.

[0048] This application provides a control method and related components for an energy storage inverter. The method determines the grid voltage fluctuation within each grid cycle. When the energy storage inverter is operating in grid-connected mode, if the grid voltage fluctuation is determined to be greater than a preset fluctuation threshold, a first duration is accumulated to maintain the grid voltage fluctuation above the preset fluctuation threshold. If the first duration exceeds a first preset time threshold, the energy storage inverter is controlled to switch to off-grid operation. Based on this, this application does not immediately control the energy storage inverter to switch from grid-connected to off-grid operation when the grid voltage fluctuation is detected to be greater than the preset fluctuation threshold. Instead, it accurately determines that a grid anomaly has occurred after the grid voltage fluctuation has been greater than the preset fluctuation threshold for a preset time threshold before controlling the energy storage inverter to switch to off-grid operation. This avoids false triggering of the energy storage inverter's operating state switching and reduces the frequency of operating state switching. Attached Figure Description

[0049] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 A flowchart illustrating a control method for an energy storage inverter provided in this application;

[0051] Figure 2 A schematic diagram of the control system of an energy storage inverter provided in this application;

[0052] Figure 3 A schematic diagram of the control device for an energy storage inverter provided in this application;

[0053] Figure 4 This is a schematic diagram of the structure of a computer-readable storage medium provided in this application. Detailed Implementation

[0054] The core of this invention is to provide a control method and related components for an energy storage inverter. Instead of immediately controlling the energy storage inverter to switch from grid-connected operation to off-grid operation when the detected grid voltage fluctuation exceeds a preset fluctuation threshold, the method accurately determines that an anomaly has occurred in the grid after determining that the grid voltage fluctuation has exceeded the preset fluctuation threshold for a preset time threshold, and then controls the energy storage inverter to switch to off-grid operation. This avoids false triggering of the energy storage inverter's operation state switching and reduces the frequency of the energy storage inverter's operation state switching.

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Please refer to Figure 1 , Figure 1 A flowchart illustrating a control method for an energy storage inverter provided in this application, the method comprising:

[0057] S11: Determine the grid voltage fluctuation based on the real-time voltage value and target voltage value of the grid within each grid cycle;

[0058] In an energy storage system, photovoltaic (PV) modules convert solar energy into electrical energy. An energy storage inverter then converts this electrical energy from the PV modules into AC power. Batteries, when fully charged, can also supply power to the energy storage inverter, which converts this power back into AC power. Furthermore, when batteries are low on power, they can be charged using energy from the PV modules, maximizing energy utilization. Under normal grid conditions, the energy storage inverter operates in grid-connected mode, transmitting AC power to the grid to supply power to the loads. Under abnormal grid conditions, the inverter can switch from grid-connected to off-grid mode, transmitting AC power to the loads directly and preventing grid outages caused by transmitting AC power back to the grid. Once the grid returns to normal, the inverter can switch back to grid-connected mode, with the grid supplying power to the loads again. This ensures uninterrupted power supply to the loads.

[0059] Abnormal grid conditions can manifest as abnormal fluctuations in grid voltage or frequency. When the grid experiences abnormal spikes due to interference, the energy storage inverter will switch from grid-connected to off-grid operation upon detecting these spikes. However, the grid will quickly return to normal after the spikes, and the inverter will then switch back to grid-connected operation within a short period. If the grid quality is poor, frequent short-term fluctuations will occur, causing the inverter to switch frequently between grid-connected and off-grid operation, potentially leading to abnormal damage.

[0060] To avoid frequent switching between grid-connected and off-grid operation states of energy storage inverters, this application provides a control method for energy storage inverters, particularly a control method for switching between grid-connected and off-grid operation states. Specifically, the grid voltage fluctuation is first determined based on the real-time and target voltage values ​​of the grid within each grid cycle to determine in real time whether grid voltage fluctuations occur.

[0061] S12: If the energy storage inverter is in grid-connected operation, determine the first duration during which the grid voltage fluctuation exceeds the preset fluctuation threshold.

[0062] During the process of determining the grid voltage fluctuation in each grid cycle, if the detected grid voltage fluctuation is greater than the preset fluctuation threshold, although it can be determined that the grid voltage has fluctuated significantly, in order to avoid the current detected fluctuation being caused by interference, the energy storage inverter is not immediately switched from grid-connected operation to off-grid operation. Instead, the timing begins when the grid voltage fluctuation is determined to be greater than the preset fluctuation threshold for the first duration. During the timing process, the grid voltage fluctuation remains greater than the preset fluctuation threshold. The duration during which the grid voltage fluctuation remains greater than the preset fluctuation threshold is the first duration.

[0063] S13: If the first duration is determined to be greater than the first preset time threshold, control the energy storage inverter to switch to off-grid operation state so that the energy storage inverter can supply power to the load.

[0064] During the accumulation of the first duration, if the first duration is greater than the first preset time threshold, it can be determined that the grid voltage has remained in a state where the grid voltage fluctuation is greater than the preset fluctuation threshold for a longer period of time, rather than simply a case of instantaneous voltage fluctuation. This allows for accurate determination that the grid is indeed in an abnormal state, and then the energy storage inverter can be switched to off-grid operation mode to supply power to the load, thus avoiding load failure when the grid supplies power to the load in an abnormal state.

[0065] In summary, this application does not immediately control the energy storage inverter to switch from grid-connected operation to off-grid operation when the grid voltage fluctuation is detected to be greater than the preset fluctuation threshold. Instead, it accurately determines that an anomaly has occurred in the grid after the grid voltage fluctuation has been greater than the preset fluctuation threshold for a preset time threshold, and then controls the energy storage inverter to switch to off-grid operation. This avoids false triggering of the energy storage inverter's operation state switching and reduces the frequency of the energy storage inverter's operation state switching.

[0066] Based on the above embodiments:

[0067] As a preferred embodiment, determining the grid voltage fluctuation based on the real-time grid voltage value and the target voltage value within each grid cycle includes:

[0068] Obtain the real-time voltage value of the power grid within the current power grid cycle;

[0069] The real-time voltage value is calculated using FFT (Fast Fourier Transform) to obtain the spectrum of the real-time voltage value;

[0070] Determine the effective value of the fundamental grid voltage within the current grid cycle from the spectrum diagram;

[0071] The real-time voltage value is locked in phase by a phase-locked loop to determine the phase angle of the real-time voltage value in the current power grid cycle.

[0072] The target voltage value is determined based on the phase angle and the effective value of the fundamental grid voltage.

[0073] The absolute value of the first difference between the real-time voltage value and the target voltage value is determined as the grid voltage fluctuation.

[0074] In this embodiment, when determining the grid voltage fluctuation, it is necessary to calculate the grid voltage fluctuation in each grid cycle. Based on this, this embodiment uses the current grid cycle as an example to explain the calculation of grid voltage fluctuation.

[0075] Specifically, in a power system, the desired grid voltage is a standard, fixed-frequency sine wave, known as the fundamental wave. This fundamental wave is a key parameter for evaluating the core power supply quality of the grid, ensuring the safe and efficient operation of power equipment, and performing precise power management and system protection. Within the current grid cycle, the real-time grid voltage value is first acquired, and then FFT calculations are performed to obtain the spectrum of the real-time voltage value. The spectrum includes the fundamental wave and multiple harmonics of the grid voltage. Therefore, the effective value of the fundamental grid voltage within the current grid cycle, excluding other harmonic components, can be determined from the spectrum, such as the effective value of a 50Hz power frequency sine wave.

[0076] Simultaneously, the real-time voltage is phase-locked using a phase-locked loop to determine the phase angle of the power grid in the current grid cycle, thereby determining the target voltage value. For example, the phase angle determined within the current grid cycle is... If the effective value of the fundamental grid voltage is V, then the target voltage value is... The real-time voltage value is Then the voltage fluctuation of the power grid is In other words, when the power grid is in normal operating condition, and further, when the grid voltage is in a stable state, the grid voltage should be the target voltage value within the current grid cycle. However, due to interference from, but not limited to, converters and rectifiers, the grid voltage will inevitably experience some interference, which will lead to distortion of the current waveform. The distortion of the current waveform will in turn cause the waveform of the grid voltage to also be distorted. That is, many high-frequency sine waves with frequencies that are integer multiples of the fundamental frequency are superimposed on the fundamental frequency, i.e., harmonics. Therefore, the real-time voltage value is the voltage superimposed on the fundamental frequency. By subtracting the target voltage value from the real-time voltage value, the amount of grid voltage fluctuation can be determined, i.e., the amount of grid voltage fluctuation.

[0077] As a preferred embodiment, if the energy storage inverter is in grid-connected operation, after determining the first duration during which the grid voltage fluctuation exceeds a preset fluctuation threshold, the method further includes:

[0078] If the first duration is not greater than the first preset time threshold, the energy storage inverter is controlled to maintain grid-connected operation so that the grid supplies power to the load.

[0079] If the grid voltage fluctuation is detected to be greater than the preset fluctuation threshold when the energy storage inverter is in grid-connected operation, but the first duration of the grid voltage fluctuation being greater than the preset fluctuation threshold is not greater than the first preset time threshold, it can be determined that the reason for the grid voltage fluctuation being greater than the preset fluctuation threshold may be that the grid has been subjected to a brief disturbance. The grid can be restored to normal as soon as possible without affecting the load. At this time, the working state of the energy storage inverter is not switched, but the energy storage inverter is kept in grid-connected operation and the first duration is reset to zero.

[0080] For example, if the first time threshold is 2ms, when the grid voltage fluctuation exceeds the preset fluctuation threshold for a first duration greater than 2ms, the energy storage inverter will switch from grid-connected operation to off-grid operation. However, if the grid voltage fluctuation exceeds the preset fluctuation threshold for a first duration of only 1ms, and then the grid voltage fluctuation decreases to no greater than the preset fluctuation threshold, the energy storage inverter will remain in grid-connected operation, and the first duration will be reset to zero.

[0081] It should be noted that the accumulation of the first duration and the calculation of the grid voltage fluctuation within each grid cycle do not conflict. For example, if the first preset time threshold is 2ms and the duration of each grid cycle is 50us, then the grid voltage fluctuation can still be calculated within each grid cycle, and the grid voltage fluctuation can be compared with the preset fluctuation threshold to determine the magnitude relationship between the grid voltage fluctuation and the preset fluctuation in real time, and then determine whether to continue accumulating the first duration.

[0082] In a preferred embodiment, the preset fluctuation threshold is a first value;

[0083] After determining that the first duration is greater than the first preset time threshold, the process of switching the energy storage inverter to off-grid operation also includes:

[0084] The effective value of the first fundamental grid voltage is determined based on the spectrum of the real-time voltage value of the grid during the current grid cycle.

[0085] The effective value of the second fundamental grid voltage in the previous grid cycle is determined based on the spectrum of the real-time voltage value of the grid in the previous grid cycle.

[0086] Determine the absolute value of the second difference between the effective value of the first fundamental grid voltage and the effective value of the second fundamental grid voltage;

[0087] If the absolute value of the second difference is not greater than the preset difference threshold, then the value of the preset fluctuation threshold is set to the second value.

[0088] If the absolute value of the second difference is greater than the preset difference threshold, then the value of the preset fluctuation threshold is set to the first value.

[0089] The first value is less than the second value.

[0090] In this embodiment, a preset fluctuation threshold is first set to a first value. Within the current grid cycle corresponding to a first duration greater than the first preset time threshold, not only is the energy storage inverter controlled to switch from grid-connected operation to off-grid operation, but also the effective value of the first fundamental grid voltage within the current grid cycle is determined based on the spectrum of the real-time voltage value of the grid within the current grid cycle. Furthermore, the effective value of the second fundamental grid voltage in the previous grid cycle is determined. If the absolute value of the second difference between the effective value of the first fundamental grid voltage and the effective value of the second fundamental grid voltage is not greater than a preset difference threshold, then two adjacent fundamental grid voltages can be determined. During the grid cycle, the effective value of the fundamental grid voltage did not change significantly. However, the voltage fluctuation between the real-time voltage value and the target voltage value was greater than the preset fluctuation threshold. Therefore, it can be determined that the grid quality is poor and the grid voltage is prone to small fluctuations. In order to avoid small voltage fluctuations being misjudged as the grid being in an abnormal state, the preset fluctuation threshold can be set to a larger second value. That is, the operation state of the energy storage converter will only be switched when the voltage fluctuation in the next grid cycle is large enough and the first duration is greater than the first preset time threshold, thus avoiding frequent switching of the operation state of the energy storage inverter.

[0091] If the absolute value of the second difference is greater than the preset difference threshold, it can be determined that when the voltage fluctuation of the power grid is greater than the preset fluctuation threshold, the effective value of the fundamental voltage of the power grid in two adjacent power grid cycles has also changed significantly. This indicates that the power grid is relatively stable, and the preset fluctuation threshold can be kept at a small first value, thereby ensuring the accuracy of the judgment on whether the power grid is fluctuating.

[0092] It should be noted that the first value can be a value not less than 0, and the specific value is determined based on the actual quality of the power grid. This application does not impose any restrictions on this. For example, if the first value is X1 and the second value is X2, and 0 < X1 < X2, first set the preset fluctuation threshold to X1. If the absolute value of the second difference is not greater than the preset difference threshold, set the preset fluctuation threshold to X2. If the absolute value of the second difference is greater than the preset difference threshold, keep the preset fluctuation threshold to X1.

[0093] The preset difference threshold can be determined based on the grid voltage, such as 5% of the local grid voltage reference value, or more specifically, 5% of 220V. This application does not limit this.

[0094] As a preferred embodiment, before setting the value of the preset fluctuation threshold to the second value, the method further includes:

[0095] Determine the comparison between the absolute value of the second difference and the preset difference threshold for the most recent N times the energy storage inverter was switched to off-grid operation, based on the current time in the historical time frame; N is a positive integer;

[0096] Determine if there is a situation where the absolute value of the second difference is not greater than the preset difference threshold when the energy storage inverter is switched to off-grid operation state N times;

[0097] If so, proceed to the step of setting the preset fluctuation threshold value to the second value;

[0098] If not, the value of the preset fluctuation threshold will remain the same as the preset fluctuation threshold of the previous power grid cycle.

[0099] In this embodiment, after determining that the absolute value of the second difference is not greater than the preset difference threshold, and before setting the value of the preset fluctuation threshold to the second value, it is further determined whether, within the historical time frame based on the current moment, there is a situation where the absolute value of the second difference is not greater than the preset difference threshold for N consecutive times when the energy storage inverter is switched to off-grid operation. That is, whether the absolute value of the second difference between the first fundamental grid voltage effective value and the second fundamental grid voltage effective value determined when the grid voltage fluctuation is detected to be greater than the preset fluctuation threshold and the first duration is greater than the first preset time threshold is also not greater than the preset difference threshold. If this situation exists for N consecutive times when the energy storage inverter is switched to off-grid operation, the grid quality can be further accurately determined to be poor. Only then is the value of the preset fluctuation threshold set to the second value. Otherwise, the value of the preset fluctuation threshold is kept unchanged from the preset fluctuation threshold of the previous grid cycle.

[0100] As a preferred embodiment, before setting the value of the preset fluctuation threshold to the first value, the method further includes:

[0101] Determine the comparison between the absolute value of the second difference and the preset difference threshold for the most recent N times the energy storage inverter was switched to off-grid operation, based on the current time in the historical time frame; N is a positive integer;

[0102] Determine if there is a situation where the absolute value of the second difference is greater than the preset difference threshold when the energy storage inverter is switched to off-grid operation state N times;

[0103] If so, proceed to the step of setting the value of the preset fluctuation threshold to the first value;

[0104] If not, the value of the preset fluctuation threshold will remain the same as the preset fluctuation threshold of the previous power grid cycle.

[0105] In this embodiment, after determining that the absolute value of the second difference is greater than the preset difference threshold, and before setting the value of the preset fluctuation threshold to the first value, it is further determined that the absolute value of the second difference and the preset difference threshold are compared in the most recent N times the energy storage inverter was switched to off-grid operation state within the historical time based on the current time. That is, when the grid voltage fluctuation is detected to be greater than the preset fluctuation threshold during the N consecutive times the energy storage inverter was switched to off-grid operation state, if this situation exists in all N consecutive times the energy storage inverter was switched to off-grid operation state, it can be further determined that the grid quality has been somewhat alleviated. Only then is the value of the preset fluctuation threshold set to the first value. Otherwise, the value of the preset fluctuation threshold is kept unchanged at the preset fluctuation threshold of the previous grid cycle.

[0106] It should be noted that N represents the number of times the energy storage inverter has recently switched to off-grid operation. Each switch corresponds to a comparison between the absolute value of the second difference and a preset difference threshold. N switches correspond to the comparison between the absolute value of the second difference and the preset difference threshold over N historical switches. For example, when N is 1, it means referring to the most recent switch of the energy storage inverter to off-grid operation, i.e., the comparison between the absolute value of the second difference and the preset difference threshold when the energy storage inverter was switched to off-grid operation last time. N can be, but is not limited to, 1. N can also be 2 or 3. In this case, it is necessary to further check the comparison between the absolute value of the second difference and the preset difference threshold when the energy storage inverter was switched to off-grid operation 2 or 3 times earlier.

[0107] For example, if N is 1, when the energy storage inverter switches to the off-grid operation state for the eighth time, the most recent time in the historical time frame based on the current moment was the seventh time the energy storage inverter was switched to the off-grid operation state. If the absolute value of the second difference when the energy storage inverter switches to off-grid operation for the eighth time is not greater than the preset difference threshold, and the absolute value of the second difference when the energy storage inverter switches to off-grid operation for the seventh time is also not greater than the preset difference threshold, it can be determined that the eighth and seventh times are two consecutive cases where the absolute value of the second difference when the energy storage inverter switches to off-grid operation is not greater than the preset difference threshold, and thus the value of the preset fluctuation threshold is set to the second value; if the absolute value of the second difference when the energy storage inverter switches to off-grid operation for the seventh time is greater than the preset difference threshold, but the absolute value of the second difference when the energy storage inverter switches to off-grid operation for the eighth time is not greater than the preset difference threshold, that is, the eighth and seventh times are not two consecutive cases where the absolute value of the second difference when the energy storage inverter switches to off-grid operation is not greater than the preset difference threshold, thus the preset fluctuation threshold remains unchanged. For example, if the current preset fluctuation threshold is the first value, then the preset fluctuation threshold is kept at the first value.

[0108] If the absolute values ​​of the second difference when the energy storage inverter switches to off-grid operation for the seventh and eighth times are both greater than the preset difference threshold, it can be determined that the eighth and seventh times are two consecutive instances where the absolute values ​​of the second difference when the energy storage inverter switches to off-grid operation are both greater than the preset difference threshold, and thus the value of the preset fluctuation threshold is set to the first value. If the absolute value of the second difference when the energy storage inverter switches to off-grid operation for the seventh time is greater than the preset difference threshold, but the absolute value of the second difference when the energy storage inverter switches to off-grid operation for the eighth time is not greater than the preset difference threshold, that is, the eighth and seventh times are not two consecutive instances where the absolute value of the second difference when the energy storage inverter switches to off-grid operation is greater than the preset difference threshold, then the preset fluctuation threshold is kept unchanged. For example, if the current preset fluctuation threshold is the second value, then the preset fluctuation threshold is kept at the second value.

[0109] As a preferred embodiment, after controlling the energy storage inverter to switch to off-grid operation when the first duration is determined to be greater than the first preset time threshold, the method further includes:

[0110] When the detected grid voltage fluctuation is not greater than a preset fluctuation threshold, a second duration is determined for the grid voltage fluctuation not to be greater than the preset fluctuation threshold.

[0111] If the second duration is greater than the second preset time threshold, then the power grid is determined to be in a stable and normal state.

[0112] If the third duration of the grid being in a stable and normal state is greater than the third preset time threshold, the energy storage inverter will be switched to grid-connected operation.

[0113] After the energy storage inverter is switched to off-grid operation, the grid voltage fluctuation is calculated and compared with the preset fluctuation threshold. If the grid voltage fluctuation decreases to no more than the preset fluctuation threshold, it can be determined that the grid voltage has returned to stability. However, the energy storage inverter is not directly switched to grid-connected operation at this time. Instead, the grid is accurately determined to be in a stable and normal state only when the second duration of the grid voltage fluctuation not exceeding the preset fluctuation threshold is greater than the second preset time threshold. It should be noted that the grid is not switched to grid-connected operation at this time. The grid is switched to grid-connected operation only after the third duration of stable grid operation is greater than the third preset time threshold to ensure accurate control of the energy storage inverter.

[0114] For example, timing begins when the detected grid voltage fluctuation is not greater than a preset fluctuation threshold. This timing period is the second duration. When the second duration exceeds the second preset time threshold, timing begins for the third duration. During the timing of the third duration, the determination of whether the grid voltage fluctuation is not greater than the preset fluctuation threshold continues. If the grid voltage fluctuation remains not greater than the preset fluctuation threshold and the third duration reaches the third preset time threshold, the energy storage inverter is switched to grid-connected operation, and the second and third durations are reset to zero. Alternatively, the second duration can be reset to zero when it is determined that the second duration is greater than the second preset time threshold, so that the accumulation of the second and third durations can continue.

[0115] As a preferred embodiment, after controlling the energy storage inverter to switch to grid-connected operation, the method further includes:

[0116] If the energy storage inverter is switched to off-grid operation within the fourth preset time threshold, the third preset time threshold is increased.

[0117] After switching the energy storage inverter back to grid-connected operation, if the grid voltage fluctuation is detected to be greater than the preset fluctuation threshold within the fourth preset time threshold, and the first duration is greater than the first preset time threshold, and the energy storage inverter is switched back to off-grid operation, then the third preset time threshold is increased. That is, the third duration is ensured to be long enough before switching the energy storage inverter back to grid-connected operation, further avoiding frequent switching of the energy storage inverter's operating state.

[0118] For example, based on the grid voltage quality or grid voltage parameter, the stability is set to M, where 1 ≤ M ≤ 6. The third preset time threshold is initially set to 5 × M. If, after switching the energy storage inverter back to grid-connected operation, it is switched back to off-grid operation within 10 minutes (e.g., within the fourth preset time threshold), then M = M + 1 to increase the third preset time threshold. For instance, if M is initially set to 3, and the third preset time threshold is 5 × M = 15, and after switching the energy storage inverter back to grid-connected operation, it is switched back to off-grid operation within the fourth preset time threshold, then M = M + 1. In this case, M becomes 4, and the third preset time threshold is increased to 5 × 4 = 20.

[0119] As a preferred embodiment, after controlling the energy storage inverter to switch to grid-connected operation, the method further includes:

[0120] If it is determined that the energy storage inverter is still in grid-connected operation after the fifth preset time threshold, then the third preset time threshold is reduced; the fifth preset time threshold is greater than the fourth preset time threshold.

[0121] After the energy storage inverter is switched back to grid-connected operation, if the grid voltage fluctuation is not greater than the preset fluctuation threshold within the fifth preset time threshold, or if the grid voltage fluctuation is not greater than the preset fluctuation threshold but the first duration is not greater than the first preset time threshold, the energy storage inverter can maintain grid-connected operation and determine that the grid is sufficiently stable, thereby reducing the third preset time threshold. This shortens the judgment time for whether the grid is in a stable and normal state and improves the switching efficiency of the energy storage inverter when the grid is in a stable and normal state to switch back to grid-connected operation.

[0122] For example, based on the grid voltage quality or grid voltage parameter, the stability is set to M, where 1 ≤ M ≤ 6. Initially, the third preset time threshold is set to 5 × M. If, after switching the energy storage inverter back to grid-connected operation, the inverter remains in grid-connected operation after the fifth preset time threshold (e.g., 30 minutes), then M = M - 1, reducing the third preset time threshold. Alternatively, if M is initially set to 3, and the third preset time threshold is 5 × M = 15, and after switching back to grid-connected operation, the inverter remains in grid-connected operation after the fifth preset time threshold, then M = M - 1. In this case, M becomes 2, and the third preset time threshold is reduced to 5 × 2 = 10. It should be noted that timing begins when the energy storage inverter is switched back from off-grid to grid-connected operation. If the inverter remains in grid-connected operation after the fifth preset time threshold is reached, the third preset time threshold is reduced.

[0123] It should be noted that the above control method applies to any of the following: single-phase, two-phase, and three-phase inverters. Furthermore, the logic for determining grid stability during grid-connected / off-grid switching needs to be considered in conjunction with local grid-connected safety regulations and inverter over / under voltage protection conditions. If any condition is not met, the grid is abnormal, and the energy storage inverter must be switched off-grid. Only when all conditions are met can the grid return to normal, allowing the energy storage inverter to operate back on-grid.

[0124] Please refer to Figure 2 , Figure 2 A schematic diagram of the control system for an energy storage inverter provided in this application is provided. The system includes:

[0125] The first determining unit 21 is used to determine the grid voltage fluctuation based on the real-time voltage value and the target voltage value of the grid in each grid cycle;

[0126] The second determining unit 22 is used to determine the first duration during which the grid voltage fluctuation is greater than a preset fluctuation threshold if the energy storage inverter is in grid-connected operation.

[0127] The control unit 23 is used to control the energy storage inverter to switch to off-grid operation state when it is determined that the first duration is greater than the first preset time threshold, so that the energy storage inverter can supply power to the load.

[0128] For a description of the control system of the energy storage inverter provided by the present invention, please refer to the above method embodiments; the present invention will not be described again here.

[0129] Please refer to Figure 3 , Figure 3 This application provides a schematic diagram of the structure of a control device for an energy storage inverter. The system includes:

[0130] Memory 31 is used to store computer programs;

[0131] The processor 32 is used to implement the steps of the control method for the energy storage inverter as described above when executing a computer program.

[0132] For a description of the control device for the energy storage inverter provided by the present invention, please refer to the above method embodiments; the present invention will not be described again here.

[0133] Please refer to Figure 4 , Figure 4 This is a schematic diagram of the structure of a computer-readable storage medium provided in this application. The computer-readable storage medium 41 in this invention stores a computer program 42. When the computer program 42 is executed by the processor 32, it implements the steps of the control method of the energy storage inverter as described above.

[0134] For a description of the computer-readable storage medium provided by the present invention, please refer to the above method embodiments; the present invention will not be described again here.

[0135] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0136] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method of an energy storage inverter, characterized by, The method comprises the following steps: determining the grid voltage fluctuation amount based on the real-time voltage value and the target voltage value of the grid in each grid cycle; if the energy storage inverter is in a grid-connected operation state, determining a first duration during which the grid voltage fluctuation amount is greater than a preset fluctuation threshold value; in the case where the first duration is greater than a first preset time threshold value, controlling the energy storage inverter to switch to an off-grid operation state to make the energy storage inverter supply power to the load.

2. The control method of the energy storage inverter according to claim 1, wherein The method for determining the grid voltage fluctuation amount based on the real-time voltage value and the target voltage value of the grid in each grid cycle comprises the following steps: obtaining the real-time voltage value of the grid in the current grid cycle; performing FFT calculation on the real-time voltage value to obtain a frequency spectrum diagram of the real-time voltage value; determining the fundamental grid voltage effective value in the current grid cycle from the frequency spectrum diagram; performing phase locking on the real-time voltage value through a phase-locked loop to determine the phase angle of the real-time voltage value in the current grid cycle; determining the target voltage value based on the phase angle and the fundamental grid voltage effective value; determining the absolute value of the first difference between the real-time voltage value and the target voltage value as the grid voltage fluctuation amount.

3. The control method of the energy storage inverter according to claim 1, wherein If the energy storage inverter is in a grid-connected operation state, after determining the first duration during which the grid voltage fluctuation amount is greater than a preset fluctuation threshold value, the method further comprises the following steps: in the case where the first duration is not greater than a first preset time threshold value, controlling the energy storage inverter to remain in the grid-connected operation state to make the grid supply power to the load.

4. The control method of the energy storage inverter according to claim 1, wherein The preset fluctuation threshold value is a first numerical value. After determining that the first duration is greater than a first preset time threshold value, the method further comprises the following steps: determining a first fundamental grid voltage effective value based on the frequency spectrum diagram of the real-time voltage value of the grid in the current grid cycle; determining a second fundamental grid voltage effective value in the previous grid cycle of the current grid cycle based on the frequency spectrum diagram of the real-time voltage value of the grid in the previous grid cycle of the current grid cycle; determining the absolute value of the second difference between the first fundamental grid voltage effective value and the second fundamental grid voltage effective value; if the absolute value of the second difference is not greater than a preset difference threshold value, setting the numerical value of the preset fluctuation threshold value as a second numerical value; if the absolute value of the second difference is greater than the preset difference threshold value, setting the numerical value of the preset fluctuation threshold value as the first numerical value; the first numerical value is smaller than the second numerical value.

5. The control method of the energy storage inverter according to claim 4, wherein Before setting the numerical value of the preset fluctuation threshold value as a second numerical value, the method further comprises the following steps: determining the comparison between the absolute value of the second difference and the preset difference threshold value when the energy storage inverter is controlled to switch to an off-grid operation state for the last N times in the historical time with the current time as the reference; N is a positive integer; determining whether there is a case where the absolute value of the second difference is not greater than the preset difference threshold value when the energy storage inverter is controlled to switch to an off-grid operation state for N times; if yes, entering the step of setting the numerical value of the preset fluctuation threshold value as a second numerical value; If not, the value of the preset fluctuation threshold is maintained as the preset fluctuation threshold of the previous power grid cycle.

6. The control method of the energy storage inverter according to claim 4, wherein Before setting the value of the preset fluctuation threshold as the first value, the method further comprises: determining a comparison condition between the absolute value of the second difference and the preset difference threshold when the energy storage inverter is controlled to switch to the off-grid operation state for the last N times within a historical time based on the current time; N is a positive integer; determining whether there is a condition that the absolute value of the second difference is greater than the preset difference threshold when the energy storage inverter is controlled to switch to the off-grid operation state for N times; if yes, entering the step of setting the value of the preset fluctuation threshold as the first value; if not, maintaining the value of the preset fluctuation threshold as the preset fluctuation threshold of the previous power grid cycle.

7. The control method of the energy storage inverter according to any one of claims 1 to 6, characterized by, After controlling the energy storage inverter to switch to the off-grid operation state under the condition that the first duration is greater than the first preset time threshold, the method further comprises: when detecting that the grid voltage fluctuation is not greater than the preset fluctuation threshold, determining a second duration that the grid voltage fluctuation is not greater than the preset fluctuation threshold; if the second duration is greater than a second preset time threshold, determining that the grid is in a stable normal state; if a third duration that the grid is in the stable normal state is greater than a third preset time threshold, controlling the energy storage inverter to switch to the grid-connected operation state.

8. The control method of the energy storage inverter according to claim 7, wherein After controlling the energy storage inverter to switch to the grid-connected operation state, the method further comprises: if the energy storage inverter is switched to the off-grid operation state within a fourth preset time threshold, increasing the third preset time threshold.

9. The control method of the energy storage inverter according to claim 8, wherein, After controlling the energy storage inverter to switch to the grid-connected operation state, the method further comprises: if it is determined that the energy storage inverter is still in the grid-connected operation state after a fifth preset time threshold, decreasing the third preset time threshold; the fifth preset time threshold is greater than the fourth preset time threshold.

10. A control device of an energy storage inverter, characterized by comprising: comprise: a memory for storing a computer program; a processor for implementing the steps of the control method of the energy storage inverter according to any one of claims 1-9 when executing the computer program.

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