Energy storage inverter and resonance frequency self-checking method thereof

Abstract

The application discloses a kind of energy storage inverters and its resonance frequency self-checking method, resonance frequency self-checking method includes: control energy storage inverter output preset resonance detection power, with current switching frequency operation;The input voltage and output voltage of power conversion module are obtained, and the output voltage deviation is calculated;Judge whether the absolute value of output voltage deviation is less than the preset error tolerance, if yes, the resonance frequency is assigned as the current switching frequency, and the current self-checking is ended;If no, according to the change trend of the absolute value of output voltage deviation, the frequency disturbance direction applied to the switching device is determined;Based on the frequency disturbance direction and the preset frequency disturbance step, a new switching frequency is generated;The switching frequency is updated to the new switching frequency, and the switching device is controlled using the updated switching frequency at preset disturbance period intervals, and the output voltage deviation is judged again.The application ensures that energy storage inverter can maintain high efficiency and high reliability operation throughout its life cycle.

Description

Technical Field

[0001] This invention relates to the field of energy storage equipment technology, and in particular to an energy storage inverter and its resonant frequency self-testing method. Background Technology

[0002] In energy storage systems, the energy storage inverter is the core device for bidirectional conversion between DC and AC power. An energy storage inverter typically consists of a DC / DC module and an inverter module. The DC / DC power conversion module often employs a resonant topology, such as a dual active bridge (DAB) topology, utilizing its soft-switching characteristics to improve efficiency. In this topology, frequency modulation control is commonly used, and the resonant frequency is a key parameter.

[0003] However, in practical applications, the resonant frequency is not a constant value. First, due to manufacturing tolerances in resonant components (such as inductors and capacitors) produced in mass production, the actual resonant frequency will differ between different devices. Second, as the equipment operates over time, the parameters of the resonant components will drift due to aging, causing the resonant frequency to change. Changes in the resonant frequency alter the converter's gain characteristic curve, causing the originally planned frequency adjustment range (especially the lower limit) to deviate from the actual optimal operating point. In severe cases, it can cause the system operating point to deviate from the soft-switching region (e.g., enter the capacitive region), disrupting the zero-voltage switching (ZVS) condition of the power switching devices, resulting in a sharp increase in switching losses, a decrease in efficiency, and even damage to the devices.

[0004] The above background information is provided only to aid in understanding the concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed on the filing date of this patent application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes an energy storage inverter and its resonant frequency self-testing method, which can ensure that the energy storage inverter can maintain high efficiency and high reliability throughout its entire life cycle.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention discloses a self-testing method for the resonant frequency of an energy storage inverter, the energy storage inverter including a power conversion module with switching devices, comprising the following steps: S1: Controls the energy storage inverter to output a preset resonant detection power and operate at the current switching frequency; S2: Obtain the input voltage and output voltage of the power conversion module, and calculate the output voltage deviation based on the input voltage and the output voltage; S3: Determine whether the absolute value of the output voltage deviation is less than the preset error tolerance. If not, proceed to step S4; if yes, proceed to step S7. S4: Determine the direction of the frequency disturbance applied to the switching device based on the changing trend of the absolute value of the output voltage deviation; S5: Generate a new switching frequency based on the frequency disturbance direction and the preset frequency disturbance step size; S6: Update the current switching frequency to the new switching frequency, and then control the switching device with the updated switching frequency at a preset disturbance period interval, and return to step S2; S7: Assign the resonant frequency to the current switching frequency and end this round of self-test.

[0007] Preferably, before S1, the method further includes: periodically determining whether the triggering condition for resonant frequency detection is met, wherein the triggering condition includes that the resonant frequency self-test completion flag bit is not set after the current power-on; S7 also includes setting the resonant frequency self-test completion flag.

[0008] Preferably, before S1, the method further includes: periodically determining whether the triggering condition for resonant frequency detection is met, wherein the triggering condition includes the time since the last self-test completion exceeding a preset self-test cycle; S7 also includes: resetting the time since the last self-test to zero.

[0009] Preferably, before S1, the method further includes: determining the operating state of the energy storage inverter and controlling the energy storage inverter to enter or maintain a power state capable of resonant frequency detection; wherein, if the operating state of the energy storage inverter is grid-connected, then step S1 is executed; if the energy storage inverter is off-grid, then it is determined whether the load power meets the resonant frequency detection requirements, and if so, step S1 is executed.

[0010] Preferably, the formula for calculating the output voltage deviation in S2 is: Verr = Vout - Vin * K, where Verr is the output voltage deviation, Vin is the input voltage of the power conversion module, Vout is the output voltage of the power conversion module, and K is the transformer turns ratio.

[0011] Preferably, S4 specifically includes: determining whether the absolute value of the output voltage deviation calculated in the current self-test is less than the absolute value of the output voltage deviation calculated in the previous self-test; if yes, then keeping the current frequency disturbance direction unchanged; if no, then reversing the current frequency disturbance direction.

[0012] Preferably, S5 specifically includes: the specific calculation method for generating a new switching frequency is: New_Freq = Old_Freq + Dir * Self_Freq, where New_Freq is the new switching frequency, Old_Freq is the current switching frequency, and Dir is the direction of frequency perturbation.

[0013] Preferably, the preset error tolerance is set based on the combined maximum deviation of the output voltage level of the power conversion module and the device parameters; the preset frequency disturbance step size is set based on the disturbance frequency range, disturbance period, and maximum expected identification time.

[0014] In a second aspect, the present invention discloses an energy storage inverter, including a power conversion module, an inverter module and a control module. The power conversion module is a dual active bridge topology containing switching devices. The control module is connected to the power conversion module and the inverter module and is configured to perform the resonant frequency self-test method described in the first aspect.

[0015] Thirdly, the present invention discloses a computer-readable storage medium storing a computer program, wherein the computer program is configured to be run by a processor to perform the resonant frequency self-test method described in the first aspect.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: The resonant frequency self-testing method provided by this invention calculates the output voltage deviation of the power conversion module in real time and adaptively adjusts the disturbance direction of the switching frequency based on the changing trend of the absolute value of the deviation. This allows it to automatically and accurately track the actual resonant frequency of the system in the current state (i.e., the point where the gain is 1). This method effectively overcomes the resonant frequency drift problem caused by production differences and device aging, ensuring that the power conversion module of the energy storage inverter always operates near the optimal frequency point, maintaining zero-voltage switching conditions, reducing switching losses, and thus ensuring the efficiency and reliability of the energy storage inverter in long-term operation. This ensures that the energy storage inverter can maintain high efficiency and high reliability throughout its entire life cycle.

[0017] In a further embodiment, the present invention also has the following beneficial effects: (1) By setting the trigger conditions for power-on self-test and periodic self-test, the timeliness and effectiveness of resonant frequency detection are ensured.

[0018] (2) By controlling the inverter to work within a suitable resonant detection power range under different operating modes, detection errors caused by excessive or insufficient power are avoided, and the accuracy of the resonant frequency detection results is further improved.

[0019] (3) By judging the trend of the change of the absolute value of the output voltage deviation, the direction of frequency disturbance is determined, thus realizing a fast and adaptive optimization process.

[0020] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0021] Figure 1 This is a flowchart of the resonant frequency self-testing method for an energy storage inverter disclosed in Embodiment 1 of the present invention; Figure 2 This is a topology circuit diagram of a DC / DC module according to a specific embodiment of the present invention; Figure 3 This is a flowchart of the resonant frequency self-test method for an energy storage inverter according to a specific embodiment of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope and application of the present invention.

[0023] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for both fixing and circuit / signal connectivity.

[0024] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0025] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0026] The core of this invention lies in providing an online, automatic resonant frequency self-checking mechanism. Its basic principle utilizes the characteristic that the gain of a dual active bridge topology is 1 at the resonant frequency. By fine-tuning the switching frequency and observing the deviation of the output voltage relative to the input voltage multiplied by the turns ratio, it adaptively optimizes (finding the frequency point that makes the gain closest to 1), ultimately converging the switching frequency to the actual resonant frequency. Furthermore, by setting reasonable detection trigger conditions and resonant detection power range, online, automatic, and accurate resonant frequency self-checking is achieved to compensate for the effects of component differences and aging, avoiding efficiency degradation and potential risks caused by the operating frequency deviating from the optimal resonant point, satisfying the zero-voltage switching (ZVS) condition, and ensuring that the inverter always operates in optimal condition, thereby further ensuring the stable and efficient operation of the energy storage inverter throughout its entire lifespan.

[0027] like Figure 1 As shown, Embodiment 1 of the present invention discloses a self-testing method for the resonant frequency of an energy storage inverter. The energy storage inverter includes a power conversion module with switching devices, and includes the following steps: S1: Controls the energy storage inverter to output a preset resonant detection power and operate at the current switching frequency.

[0028] The preset resonant detection power should not be too high or too low. If the resonant detection power is too high, the output voltage of the power conversion module (DC / DC module) will be too low, resulting in a lower detected resonant frequency. If the resonant detection power is too low, the charging ripple of the output capacitor cannot be effectively filtered out, resulting in a higher measured output voltage, which in turn results in a higher detected resonant frequency. As a preferred embodiment, the preset resonant detection power range is [80W, 150W].

[0029] In practical control, the resonant detection power is independently adjusted by the current / voltage closed loop, while the switching frequency is an independent disturbance variable used to search for the resonant point. The power closed loop maintains a constant output power, while the frequency disturbance algorithm fine-tunes the switching frequency, thus decoupling the two control methods.

[0030] S2: Obtain the input voltage and output voltage of the power conversion module, calculate the output voltage deviation based on the input voltage and output voltage, and then proceed to step S3.

[0031] The formula for calculating the output voltage deviation is: Verr = Vout - Vin * K, where Verr is the output voltage deviation, Vin is the input voltage of the power conversion module, Vout is the output voltage of the power conversion module, and K is the transformer turns ratio.

[0032] S3: Determine whether the absolute value of the output voltage deviation is less than the preset error tolerance. If not, proceed to step S4; if yes, proceed to step S7.

[0033] The preset error tolerance is set based on the combined maximum deviation of the power conversion module's output voltage level and device parameters. By determining whether the absolute value of the output voltage deviation is less than the error tolerance as a convergence condition, the algorithm can quickly stabilize, avoid oscillations near the resonance point, and improve detection efficiency.

[0034] S4: Based on the changing trend of the absolute value of the output voltage deviation, determine the direction of the frequency disturbance applied to the switching device, and then proceed to step S5.

[0035] Specifically, this step includes: determining whether the absolute value of the output voltage deviation calculated in the current self-test, |Verr|, is less than the absolute value of the output voltage deviation calculated in the previous self-test, |Verr_Last|; if yes, the current frequency perturbation direction remains unchanged; if not, the current frequency perturbation direction is reversed. In continuous self-test algorithm calls, the output voltage deviation value at the time of the previous perturbation needs to be stored for comparison. Through adaptive reversal of the frequency perturbation direction, the algorithm possesses self-optimization capabilities, intelligently adjusting the frequency in the direction of reducing output voltage deviation, thus exhibiting strong robustness.

[0036] S5: Based on the frequency disturbance direction and the preset frequency disturbance step size, generate a new switching frequency, and then proceed to step S6.

[0037] Specifically, this step includes the following: The calculation method for generating a new switching frequency (New_Freq) is as follows: New_Freq = Old_Freq + Dir * Self_Freq, where New_Freq is the new switching frequency, Old_Freq is the switching frequency updated during the previous self-test, Dir is the frequency perturbation direction, and Self_Freq is the preset frequency perturbation step size.

[0038] The preset frequency perturbation step size is set based on the perturbation frequency range, the perturbation period, and the maximum expected identification time. The perturbation period Ts refers to the periodic execution of the resonant frequency self-test algorithm at fixed time intervals; within each perturbation period Ts, the algorithm executes a complete step once. The maximum expected identification time refers to the maximum allowable time from the start of the resonant frequency search (i.e., the first frequency perturbation) to the completion of resonant frequency identification (i.e., finding a frequency point where |Verr| is less than the error tolerance). As a preferred implementation, the frequency perturbation step size = (frequency perturbation range * perturbation period) / maximum expected time. Assuming the frequency perturbation range is 3kHz (i.e., the upper and lower limits of the search frequency, for example, from f_res - 1.5kHz to f_res + 1.5kHz), the perturbation period is 50μs (i.e., the resonant frequency self-test algorithm is executed once every 50 microseconds), and the maximum expected time is 2ms, then the frequency perturbation step size is 0.075kHz.

[0039] S6: Update the current switching frequency to the new switching frequency, and use the updated switching frequency to control the switching device, then return to step S2.

[0040] S7: Assign the resonant frequency to the current switching frequency and end this round of self-test.

[0041] In a further embodiment, before S1, B1 is included: periodically determining whether the triggering condition for resonant frequency detection is met. On one hand, the triggering condition may include the resonant frequency self-test completion flag not being set after the current power-on (Flag = 0); if it is determined that the resonant frequency self-test completion flag is set (Flag = 1), then the current self-test ends directly; if it is determined that the resonant frequency self-test completion flag is not set, then step S1 is executed or step B2 is executed before step S1 is executed; correspondingly, S7 also includes: setting the resonant frequency self-test completion flag. On the other hand, the triggering condition may also include the time since the last self-test completion exceeding a preset self-test period CheckPeriod; if it is determined that the time since the last self-test completion has not exceeded the preset self-test period, then the current self-test ends directly; if it is determined that the time since the last self-test completion has exceeded the preset self-test period, then the self-test completion flag is de-set again and step S1 is executed or step B2 is executed before step S1 is executed; correspondingly, S7 also includes: clearing the time since the last self-test completion to zero.

[0042] The CheckPeriod self-test period refers to the time interval during normal operation after a resonant frequency test is completed, during which the system waits for the next test to start. This period is used to avoid performing tests too frequently, thereby reducing interference with the main power control and accommodating long-term drift such as device aging. As a preferred implementation, CheckPeriod = 180 days.

[0043] In a further embodiment, step B2 is included before step S1: determining the operating state of the energy storage inverter and controlling the energy storage inverter to enter or maintain a power state capable of resonant frequency detection; wherein, if the energy storage inverter is in grid-connected operation, step S1 is executed; if the energy storage inverter is in off-grid operation, it is determined whether the load power meets the resonant frequency detection requirements; if yes, step S1 is executed; if no, the self-test ends directly. Step B2 can be executed after step B1.

[0044] The resonant frequency self-test method provided in Embodiment 1 of this invention calculates the output voltage deviation of the power conversion module in real time and adaptively adjusts the disturbance direction of the switching frequency based on the changing trend of the absolute value of the deviation, thereby automatically and accurately tracking the current actual resonant frequency point (i.e., the point where the gain is 1). This method ensures that the power conversion module of the energy storage inverter can be controlled based on the accurate actual resonant frequency throughout its entire life cycle. In this embodiment of the invention, firstly, by setting trigger conditions (such as the first power-on detection or self-test cycle), the automation and periodicity of the detection are realized, solving the problem of resonant frequency drift caused by initial differences in devices and long-term aging; secondly, by controlling the power state during detection (grid-connected discharge power or off-grid load power within a suitable range), the output voltage measurement error caused by excessive or insufficient power is eliminated, thereby ensuring the accuracy of the resonant frequency self-test results; finally, the accurate resonant frequency ensures the rationality of the operating frequency range setting, maintains the zero-voltage switching (ZVS) condition of the power switching devices, thereby effectively reducing switching losses, improving system efficiency, and enhancing the long-term reliability of the system.

[0045] Embodiment 2 of the present invention discloses an energy storage inverter, including a power conversion module, an inverter module, and a control module. The power conversion module is a dual active bridge topology containing switching devices. The control module is connected to the power conversion module and the inverter module and is configured to execute the resonant frequency self-test method described in Embodiment 1 above. Integrating the resonant frequency self-test function into the control module of the energy storage inverter realizes the intelligence of the device, enabling maintenance testing to be completed without the intervention of external equipment.

[0046] The energy storage inverter of Embodiment 2 of the present invention includes a power conversion module with switching devices, such as... Figure 2As shown, this power conversion module is specifically a resonant DAB (Dual Active Bridge) topology DC / DC module. Battery BAT serves as the DC input power supply, and capacitor C8 is the input filter capacitor used to stabilize the input voltage and suppress ripple and noise. Switches Q1 and Q2 are primary-side power switches, which work in conjunction with the primary winding of transformer T to convert the input DC voltage into a high-frequency AC voltage on the transformer primary side. Capacitors C4 and C5 are connected in parallel with switches Q1 and Q2, respectively, to suppress voltage spikes during switch turn-on / turn-off, protecting the switches and optimizing electromagnetic compatibility. Transformer T achieves energy transfer from the primary side (input side) to the secondary side (output side) through electromagnetic induction. Switches Q3 and Q4 are secondary-side power switches, which work in conjunction with the secondary winding of transformer T to convert the high-frequency AC voltage on the transformer secondary side into DC voltage. Capacitors C6 and C7 are connected in parallel with switches Q3 and Q4, respectively, to suppress voltage spikes or optimize rectification efficiency. Capacitor C3 is the output filter capacitor, used to smooth the output DC voltage, reduce ripple, and provide a stable DC output. Capacitors C1 and C2 are secondary-side filter capacitors (or resonant capacitors), which work in conjunction with switching transistors Q3 and Q4 to optimize the stability of the output voltage or achieve resonant rectification.

[0047] In one modulation scheme, switches Q2 and Q4 have the same duty cycle, and switches Q1 and Q3 have the same duty cycle, with a 180° phase deviation between switches Q1 and Q3. In frequency modulation control, the resonant frequency is a critical parameter. However, due to variations in resonant devices between different devices during mass production, and the aging of these devices over time, the resonant frequency can change. This change alters the gain characteristic curve of the DC / DC module, potentially causing the intended frequency adjustment range (especially the lower limit) to deviate from the optimal operating point. In severe cases, this can cause the system operating point to deviate from the soft-switching region (e.g., entering the capacitive region), disrupting the zero-voltage switching (ZVS) condition of the power switching devices, resulting in a sharp increase in switching losses, decreased efficiency, and even device damage.

[0048] To address the aforementioned problems in DC / DC modules, a specific embodiment of the present invention introduces a resonant frequency self-test method, comprising the following steps: A1: Determine whether the resonant frequency self-test completion flag is set (Flag = 1, indicating that the resonant frequency self-test has been completed). If yes, proceed to step A2; otherwise, proceed to step A4. A2: The time counter TimeCnt increments, proceed to step A3; A3: Determine if TimeCnt is greater than the self-test cycle. If yes, reset the self-test completion flag (Flag=0) and proceed to step A4; otherwise, proceed to step A18. The self-test period is denoted as CheckPeriod. Based on device aging data, a CheckPeriod that is too short is meaningless, while a checkperiod that is too long may lead to the aforementioned risks. In this embodiment, the value of CheckPeriod ranges from 90 days to 365 days, and more preferably from 150 days to 210 days. For example, CheckPeriod is 180 days.

[0049] A4: If the current switching frequency Old_Freq is not initialized, then Old_Freq = default resonant frequency; determine whether the energy storage inverter is in grid-connected operation. If yes, proceed to step A7; otherwise, proceed to step A5. A5: Determine whether the energy storage inverter is in off-grid operation. If yes, proceed to step A6; otherwise, proceed to step A18. A6: Determine whether the off-grid load power meets the resonant frequency detection requirements. If yes, proceed to step A8; otherwise, proceed to step A18. In the off-grid operation mode of the energy storage inverter, the off-grid load power is the resonant detection power. In this step, it is determined whether the resonant detection power (off-grid load power) is within the resonant detection power range to confirm whether to execute the subsequent steps. The lower limit of the resonant detection power range is set to avoid the output voltage from being too high due to overcharging of the capacitor, and the upper limit is set to avoid the output voltage from being too low due to additional voltage drop. In one embodiment, the resonant detection power range is set to [80W, 150W], that is, the load power range that meets the resonant frequency detection requirements is [80W, 150W].

[0050] A7: Control the energy storage inverter to discharge with the resonant detection power as the power target and operate at the current switching frequency. Next, proceed to step A8. In this step, the grid-connected discharge power of the energy storage inverter in grid-connected operation is the resonant detection power. The grid-connected discharge power within the resonant detection power range is controlled to discharge as the power target. The lower limit of the resonant detection power range is set to avoid the output voltage from being too high due to overcharging of the capacitor, and the upper limit is set to avoid the output voltage from being too low due to additional voltage drop, which is usually 1% to 3% of the rated power. In one embodiment, for an energy storage inverter with a rated power of 5kW, the resonant detection power range is set to [80W, 150W].

[0051] A8: Read the voltage of capacitors C8 and C3, then proceed to step A9; Among them, the voltages of capacitors C8 and C3 are the input voltage and output voltage of the DC / DC module. Specifically, in this step, the voltage at capacitor C8 is read as the input voltage Vin, and the voltage at capacitor C3 is read as the output voltage Vout.

[0052] A9: Calculate the output voltage deviation, denoted as Verr=Vout-Vin*K, where K is the transformer turns ratio. Proceed to step A10 next. K can be set by combining the battery voltage operating range and the DAB output voltage requirements (the output is usually directly connected to the subsequent inverter circuit). It needs to meet the minimum battery operating voltage *K to meet the inverter circuit's requirements for DC input voltage.

[0053] A10: Determine whether abs(Verr) is less than the preset error tolerance Volt1. If yes, proceed to step A16; otherwise, proceed to step A11. Here, abs() is an absolute value function. The preset error tolerance Volt1 is related to the DAB output voltage level and device deviations (especially subtle differences in transformer turns ratio). Therefore, the preset error tolerance Volt1 can be calculated as a range value based on the rated output voltage of the DC / DC module and the preset percentage of the overall device deviation. In this embodiment, it is designed based on a maximum overall device deviation of 1.25%. In a specific implementation, Volt1 (the preset error tolerance) is calculated based on an output voltage of 400V: 400 * 1.25% = 5V.

[0054] The switching frequency directly affects the output voltage, also known as the gain. The gain at the resonant frequency is 1. Therefore, in this embodiment of the invention, the resonant frequency can be found by fine-tuning the switching frequency and observing the change in the output voltage deviation Verr. In this step, when abs(Verr) is less than the preset error tolerance Volt1, it indicates that the resonant frequency has been found, thus achieving the goal of this self-test method.

[0055] A11: Determine if abs(Verr) is less than abs(Verr_Last), where Verr_Last is the Verr calculated during the previous perturbation. If yes, proceed to step A13; otherwise, proceed to step A12.

[0056] A12: The frequency disturbance direction Dir is reversed, i.e., Dir = -Dir, where Dir is the frequency disturbance direction, with an initial value of 1. Next, proceed to step A13;

[0057] A13: Generate a new switching frequency New_Freq = Old_Freq + Dir*Self_Freq, where Old_Freq is the current switching frequency (i.e., the switching frequency output during the last perturbation), and Self_Freq is the frequency perturbation step size. Next, execute step A14;

[0058] The frequency perturbation step size is related to the perturbation frequency range (3kHz in one embodiment; when the frequency deviation exceeds 3kHz, a device malfunction can be considered), the perturbation period (the self-test method is called once every 50μs in this embodiment), and the maximum expected identification time (2ms in one embodiment). Therefore, the frequency perturbation step size can be determined by comprehensively considering the expected frequency perturbation frequency, the perturbation period, and the expected maximum identification time. The frequency perturbation step size (Self_Freq) needs to be set according to the system characteristics, typically ranging from tens of hertz to hundreds of hertz. For example, in a system with a perturbation period of 50μs and an expectation of completing the search within milliseconds, a setting of 100Hz to 500Hz can be attempted, and the optimal value can be determined experimentally. In a specific embodiment, the frequency perturbation step size can be calculated as follows: 3kHz * 50μs / 2ms = 0.075kHz.

[0059] A14: Reassign Old_Freq, Old_Freq = New_Freq. Next, proceed to step A15;

[0060] A15: Using the preset disturbance period as an interval, use Old_Freq as the switching frequency of switching transistors Q1~Q4 to perform DC / DC module control, and return to step A8; In this step, Old_Freq is used as the switching frequency, and a dual active bridge (DAB) phase-shift control strategy (such as single phase-shift control) is used to drive the switching transistors Q1~Q4.

[0061] A16: Assign the resonant frequency to Old_Freq and set the resonant frequency self-test completion flag (Flag = 1). Proceed to step A17. A17: Clear the counter TimeCnt. Next step: Execute step A18;

[0062] A18: This round of calls has ended.

[0063] In actual operation, the energy storage inverter can call the resonant frequency self-test method of the present invention after power-on with a preset disturbance period (e.g., 50μs), so as to quickly find the resonant frequency that matches the current state of the device and avoid the situation of a sharp increase in switching losses, a decrease in efficiency, or even damage to the device.

[0064] The trigger detection conditions for the resonant frequency self-testing method in this invention mention the off-grid load range and the power actively output by the grid-connected system, ensuring the effectiveness of resonant frequency detection. Excessive power on the inverter side will cause an additional voltage drop at the output capacitor of the DC / DC module, leading to a lower detected resonant frequency; conversely, insufficient power cannot effectively filter out the phenomenon of excessive overcharging at the output capacitor of the DC / DC module, resulting in a higher detected resonant frequency. In actual operation, the self-testing cycle (180 days) can be designed based on the equipment's operating conditions. Using the self-testing method of this invention, the most suitable resonant frequency for the current machine status can be accurately found. The periodic re-identification of the resonant frequency avoids the common industry problem of unstable soft-switching characteristics due to long-term use or component differences, ensuring high-efficiency operation throughout the machine's lifecycle and promoting product sales. Therefore, this online automatic detection algorithm, while solving the problem of long-term operating resonant frequencies not matching actual values, also ensures the accuracy of the automatically detected resonant frequency output.

[0065] Embodiment 3 of the present invention discloses a computer-readable storage medium storing a computer program, wherein the computer program is configured to be run by a processor to perform the steps of the resonant frequency self-test method for the energy storage inverter in Embodiment 1 above.

[0066] Optionally, the aforementioned computer-readable storage media may include, but are not limited to, various media capable of storing computer programs, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0067] The background section of this invention may include background information about the problems or circumstances surrounding the invention, rather than a description of prior art by others. Therefore, the content included in the background section is not an admission of prior art by the applicant.

[0068] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate different embodiments or examples and features of different embodiments or examples described in this specification without contradiction. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope defined by the appended claims.

Claims

1. A method for self-testing the resonant frequency of an energy storage inverter, wherein the energy storage inverter includes a power conversion module with switching devices, characterized in that, Includes the following steps: S1: Controls the energy storage inverter to output a preset resonant detection power and operate at the current switching frequency; S2: Obtain the input voltage and output voltage of the power conversion module, and calculate the output voltage deviation based on the input voltage and the output voltage; S3: Determine whether the absolute value of the output voltage deviation is less than the preset error tolerance. If not, proceed to step S4; if yes, proceed to step S7. S4: Determine the direction of the frequency disturbance applied to the switching device based on the changing trend of the absolute value of the output voltage deviation; S5: Generate a new switching frequency based on the frequency disturbance direction and the preset frequency disturbance step size; S6: Update the current switching frequency to the new switching frequency, and then control the switching device with the updated switching frequency at a preset disturbance period interval, and return to step S2; S7: Assign the resonant frequency to the current switching frequency and end this round of self-test.

2. The resonant frequency self-testing method according to claim 1, characterized in that, Before S1, it also includes: periodically determining whether the triggering condition for resonant frequency detection is met, wherein the triggering condition includes that the resonant frequency self-test completion flag bit is not set after this power-on; S7 also includes setting the resonant frequency self-test completion flag.

3. The resonant frequency self-testing method according to claim 1, characterized in that, Before S1, it also includes: periodically determining whether the triggering condition for resonant frequency detection is met, wherein the triggering condition includes the time since the last self-test is completed exceeding a preset self-test cycle; S7 also includes: resetting the time since the last self-test to zero.

4. The resonant frequency self-testing method according to claim 1, characterized in that, Before S1, the method further includes: determining the operating state of the energy storage inverter and controlling the energy storage inverter to enter or maintain a power state capable of resonant frequency detection; wherein, if the operating state of the energy storage inverter is grid-connected, then step S1 is executed; if the energy storage inverter is off-grid, then it is determined whether the load power meets the resonant frequency detection requirements, and if so, step S1 is executed.

5. The resonant frequency self-testing method according to claim 1, characterized in that, The formula for calculating the output voltage deviation in S2 is: Verr = Vout - Vin * K, where Verr is the output voltage deviation, Vin is the input voltage of the power conversion module, Vout is the output voltage of the power conversion module, and K is the transformer turns ratio.

6. The resonant frequency self-testing method according to claim 1, characterized in that, S4 specifically includes: determining whether the absolute value of the output voltage deviation calculated in the current self-test is less than the absolute value of the output voltage deviation calculated in the previous self-test; if yes, then keeping the current frequency disturbance direction unchanged; if no, then reversing the current frequency disturbance direction.

7. The resonant frequency self-testing method according to claim 1, characterized in that, S5 specifically includes: The specific calculation method for generating a new switching frequency is: New_Freq = Old_Freq + Dir * Self_Freq, where New_Freq is the new switching frequency, Old_Freq is the current switching frequency, and Dir is the direction of frequency perturbation.

8. The resonant frequency self-testing method according to claim 1, characterized in that, The preset error tolerance is set based on the combined maximum deviation of the output voltage level of the power conversion module and the device parameters; the preset frequency disturbance step size is set based on the disturbance frequency range, disturbance period, and maximum expected identification time.

9. An energy storage inverter, characterized in that, The device includes a power conversion module, an inverter module, and a control module. The power conversion module is a dual active bridge topology containing switching devices. The control module is connected to the power conversion module and the inverter module and is configured to perform the resonant frequency self-test method according to any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, wherein the computer program is configured to be run by a processor to perform the resonant frequency self-test method according to any one of claims 1 to 8.

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