Method and system for estimating capacitor parameters of mmc based on extended input window

Abstract

The application belongs to the technical field of power electronic equipment state monitoring, and particularly discloses an MMC capacitor parameter estimation method and system based on an extended input window, which comprises the following steps: defining the time period when all sub-modules in a bridge arm are simultaneously put into operation as an input window, and detecting the input number of the sub-modules in each bridge arm of the MMC in real time; when the input number of the sub-modules is equal to the number of the continuous control periods of the total number of the sub-modules in the bridge arm and exceeds a preset delay factor threshold, determining the start and end times of the input window according to the start time and the end time when the input number of the sub-modules is equal to the total number of the sub-modules in the bridge arm; monitoring the bridge arm current direction in real time, and calculating the capacitor voltage increment of each sub-module according to whether effective current commutation occurs in the input window; and estimating the capacitor parameters of each sub-module based on the capacitor voltage increment. The application moves the start point of the input window to the first full input time, so that the voltage change information in the initial stage of the window can be fully utilized.

Description

Technical Field

[0001] This invention relates to the field of power electronic equipment condition monitoring technology, and in particular to a method and system for estimating MMC capacitor parameters based on an extended input window. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Modular multilevel converters (MMCs) have become the mainstream topology in high-voltage direct current transmission, static synchronous compensators, and medium- and high-voltage motor drive systems due to their advantages such as modular structure, high output waveform quality, and ease of expansion.

[0004] An MMC (Multi-Module Control) consists of multiple sub-modules connected in series, each containing power switching devices and energy storage capacitors. During long-term operation, capacitors are affected by current ripple, voltage stress, and temperature changes, causing their capacitance to gradually decrease, thus impacting system performance and potentially leading to malfunctions. Therefore, online monitoring of the capacitor parameters of MMC sub-modules is crucial for assessing their health.

[0005] To achieve online monitoring of capacitor health status, it is necessary to obtain voltage characteristic information reflecting changes in capacitor parameters without affecting the normal operation of the MMC (Multi-Module Control). Existing capacitor parameter estimation methods based on an "operation window" are based on the following idea: when all sub-modules within an MMC arm are simultaneously operational, the capacitor voltage sorting control algorithm temporarily fails. At this time, all sub-module capacitors are charged and discharged through the same arm current, forming an operating range called the "operation window." Within this range, the voltage changes of each sub-module capacitor are mainly determined by its capacitor parameters; therefore, the capacitor parameters can be estimated using the voltage increment within the operation window.

[0006] In existing technologies, when identifying the input window, a delay factor is set. When the number of sub-modules input in the bridge arm is equal to the total number of sub-modules N, the delay factor starts counting. When the delay factor exceeds a preset threshold, it is considered to have entered a valid input window. When a bridge arm current reversal occurs or a sub-module exits the fully input state within the input window, the input window is determined to have ended.

[0007] However, existing methods only consider a module entering the input window after the delay factor exceeds a threshold, resulting in the discarding of a large amount of effective voltage change information at the beginning of the window, thus reducing data utilization. When a bridge arm current commutation occurs within the input window, traditional methods directly terminate the current window, discarding potentially usable voltage change information and further compressing the effective data length. Furthermore, the delay factor only reflects the current potential for a stable window but cannot predict whether the submodule will remain fully operational in the future. Therefore, when the input window immediately ends after the delay factor exceeds the threshold, an extremely short input window is still generated, at which point the capacitor voltage increment approaches noise levels, leading to low reliability of the calculated capacitor values. Summary of the Invention

[0008] To address the aforementioned issues, this invention proposes a method and system for estimating MMC capacitor parameters based on an extended input window. By tracing back to the starting point of the input window, it fully utilizes the voltage change information at the beginning of the window. Simultaneously, through a current commutation segmentation processing mechanism, it avoids premature window termination caused by current commutation.

[0009] In some implementations, the following technical solutions are adopted: A method for estimating MMC capacitance parameters based on an extended input window includes: The time period during which all sub-modules in the bridge arm are put into operation simultaneously is defined as the input window. The number of input sub-modules in each bridge arm of the MMC is detected in real time. When the number of input sub-modules equals the number of continuous control cycles of the total number of bridge arm sub-modules and exceeds the preset delay factor threshold, the start and end times of the input window are determined according to the start and end times of the number of input sub-modules equaling the total number of bridge arm sub-modules. Simultaneously monitor the current direction of the bridge arm in real time, and calculate the capacitor voltage increment of each submodule based on whether an effective current commutation occurs within the input window. Based on the capacitor voltage increment, the capacitance parameters of each submodule are estimated.

[0010] As a further solution, the start and end times of the deployment window are determined based on the start and end times of the number of sub-modules deployed equaling the total number of bridge arm sub-modules. Specifically: Record the time when the number of sub-modules deployed is first detected to equal the total number of bridge arm sub-modules. And the capacitor voltage values ​​of each submodule at the corresponding time; When the number of submodules engaged equals the total number of bridge arm submodules and the number of continuous control cycles exceeds a preset delay factor threshold, the system is determined to have entered a valid engagement window, and the time is recorded. As the starting point for the investment window; When the number of sub-modules put into operation is no longer equal to the total number of bridge arm sub-modules, the operation window is determined to end. The time at this time is recorded as the end time of the operation window, and the capacitor voltage value of each sub-module at this time is also recorded.

[0011] As a further solution, the method for determining whether effective current commutation occurs within the input window is as follows: When the number of sub-modules engaged is first detected to be equal to the total number of bridge arm sub-modules, the bridge arm current is monitored synchronously. If a change in the direction of the bridge arm current is detected and the engagement window is valid at this time, the current commutation is determined to be valid. The engagement window being valid means that the number of continuous control cycles in which the number of sub-modules engaged is equal to the total number of bridge arm sub-modules exceeds a preset delay factor threshold.

[0012] As a further solution, the capacitor voltage increment of each submodule is calculated based on whether a valid current commutation occurs within the input window, specifically as follows: If no current commutation occurs within the input window, the voltage increment is calculated based on the capacitor voltages of each submodule at the start and end times of the input window. If current commutation occurs within the input window, the voltage increment is calculated based on the capacitor voltages of each submodule at the start, commutation, and end times of the input window.

[0013] As a further option, if no current commutation occurs within the input window, the voltage increment is calculated as follows: The voltage increment of the i-th submodule is the absolute value of the difference between the capacitor voltage value of the i-th submodule at the end of the input window and the capacitor voltage value of the i-th submodule at the beginning of the input window.

[0014] As a further solution, if current commutation occurs within the input window, the voltage increment is calculated as follows: Calculate the absolute value of the difference between the capacitor voltage value of the i-th submodule at the end of the input window and the capacitor voltage value of the corresponding submodule at the commutation time, and the absolute value of the difference between the capacitor voltage value of the i-th submodule at the commutation time and the capacitor voltage value of the corresponding submodule at the start of the input window; the sum of the two absolute values ​​is taken as the voltage increment of the i-th submodule.

[0015] As a further option, the delay factor threshold is determined based on the requirements of monitoring accuracy and monitoring frequency. The larger the delay factor threshold, the higher the monitoring accuracy, but the lower the detection frequency. The maximum value of the delay factor threshold is determined based on the highest number of control cycles that can be achieved when all submodules are fully engaged in actual operation.

[0016] In other embodiments, the following technical solutions are adopted: A system for estimating MMC capacitance parameters based on an extended input window, comprising: The input window determination module is configured to define the time period during which all sub-modules in the bridge arm are put into operation simultaneously as the input window. It monitors the number of input sub-modules in each bridge arm of the MMC in real time. When the number of input sub-modules equals the number of continuous control cycles of the total number of bridge arm sub-modules and exceeds the preset delay factor threshold, it determines the start and end times of the input window based on the start and end times of the number of input sub-modules equaling the total number of bridge arm sub-modules. The capacitor voltage increment calculation module is configured to simultaneously monitor the current direction of the bridge arm in real time, and calculate the capacitor voltage increment of each sub-module according to whether an effective current commutation occurs within the input window. The capacitor parameter estimation module is configured to estimate the capacitor parameters of each submodule based on the capacitor voltage increment.

[0017] In other embodiments, the following technical solutions are adopted: A terminal device includes a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions adapted to be loaded and executed by the processor to perform the above-described MMC capacitance parameter estimation method based on an extended input window.

[0018] In other embodiments, the following technical solutions are adopted: A computer-readable storage medium storing a plurality of instructions adapted for loading and execution by a processor of a terminal device of the above-described method for estimating MMC capacitance parameters based on an extended input window.

[0019] Compared with the prior art, the beneficial effects of the present invention are: The present invention records the capacitor voltage of each submodule when the submodule is first detected to be fully engaged, and after the duration threshold is met, the starting point of the engagement window is moved forward to the moment of first full engagement, so as to make full use of the voltage change information in the early stage of the window.

[0020] This invention calculates the voltage increment during the current commutation process in segments, allowing the input window to continue to be used after the current commutation occurs. This fully utilizes the voltage change information that was discarded in the original method and effectively improves the data utilization rate within the window.

[0021] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] Figure 1 MMC topology diagram; Figure 2 Here is a flowchart of the MMC capacitor voltage equalization algorithm; Figure 3This is a schematic diagram of the input window in an embodiment of the present invention; Figure 4 A schematic diagram illustrating the changes in capacitor voltage of the monitoring submodule and the reference submodule within the input window; Figure 5 A schematic diagram of the input window utilized by existing methods; Figure 6 This is a schematic diagram of the MMC capacitor parameter estimation method based on an extended input window in an embodiment of the present invention. Detailed Implementation

[0023] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] Example 1 In one or more embodiments, an MMC capacitor parameter estimation method based on an extended input window is disclosed. By tracing back to the starting point of the input window, the voltage change information at the beginning of the window is fully utilized; by using a current commutation segmentation processing mechanism, the window is prevented from ending prematurely due to current commutation; at the same time, based on tracing back to the starting point of the input window, the window length is guaranteed and the data noise resistance is improved by increasing the delay factor threshold to filter out short input windows.

[0026] The following sections introduce the topology and operating principle of MMC, the capacitor voltage equalization control of MMC, the failure phenomenon of capacitor voltage equalization control during the input window, the principle of submodule capacitor estimation based on the input window, the existing method for obtaining MMC capacitor parameter estimation data based on the input window, and the method for obtaining MMC capacitor parameter estimation data based on the extended input window proposed in this embodiment.

[0027] The topology of MMC is as follows Figure 1 As shown. Each phase consists of two bridge arms, upper and lower. Each bridge arm consists of... N One half-bridge or full-bridge submodule and one bridge arm inductor The components are connected in series. This paper focuses on MMCs composed of half-bridge submodules. Each half-bridge submodule consists of two insulated-gate bipolar transistors S1 and S2 with complementary switching signals, and two anti-parallel diodes D1 and D2. and a capacitor composition.

[0028] This indicates three phases, and j indicates the upper or lower arm of the bridge. i This indicates the sequence number of the bridge arm submodule. express Phase j-arm current, express The switching state of the i-th submodule of the phase j-arm bridge arm. express The capacitor voltage of the i-th submodule of phase j bridge arm.

[0029] Based on the switching status of the submodule and the direction of the bridge arm current, the submodule can be divided into 3 working states, and each working state has 2 working modes, as shown in Table 1.

[0030] When S1 is on and S2 is off, the submodule is in the active state, and its output voltage is the capacitor voltage, with the capacitor in a charging or discharging state. When S1 is off and S2 is on, the submodule is in bypass state, and the SM output voltage is 0, while the capacitor voltage remains unchanged. When both S1 and S2 are off, the submodule is in a locked state, which is typically only activated during a fault.

[0031] Table 1 Submodule Working Status

[0032] Submodule output voltage It can be expressed by the following formula: (1) Submodule capacitor It can be expressed by the following formula: (2) The specific process of capacitor voltage equalization control for MMC is as follows: Each bridge arm of an MMC has numerous submodules. Balancing the capacitor voltages among these submodules is a crucial control objective for ensuring the safe and stable operation of the MMC. This is typically achieved using a sorting-based capacitor voltage balancing algorithm, as shown in the flowchart below. Figure 2 As shown.

[0033] Obtain the number of submodules that should be deployed in the bridge arm during each control cycle. Then, based on the bridge arm current The direction of the control prioritizes the capacitor voltages of the bridge arm submodules according to positive or negative order. When the bridge arm current is positive, submodules with lower capacitor voltages are activated first to charge and increase their voltage; when the bridge arm current is negative, submodules with higher capacitor voltages are activated first to discharge and decrease their voltage. After selecting the specific submodule to activate, a specific drive pulse sequence is generated and sent to the corresponding submodule. This control method achieves better voltage balance among the submodule capacitors in the same bridge arm.

[0034] The time period during which all sub-modules within the bridge arm are simultaneously put into operation is defined as the operation window, such as... Figure 3 As shown. During this period, all submodules in the bridge arm are in the active state to meet the needs of MMC operation control, and there are no redundant submodules available for selection for activation or bypass. Therefore, the capacitor voltage equalization control that relies on the rotational activation of submodules fails during the activation window, and the change in the capacitor voltage of each submodule is determined only by the bridge arm current and its own capacitance parameters.

[0035] Let the input window interval be According to equation (2), the capacitor voltage of the submodule during the input window can be expressed as: (3) in, This refers to the capacitor voltage when the submodule enters the input window. .

[0036] Therefore, the submodule capacitor voltage increment during the input window can be obtained. for: (4) Select a submodule that is in good health and has stable performance as a reference submodule, and its capacitance value can be regarded as the nominal capacitance value, that is, a known quantity.

[0037] Assume the capacitor voltages of the monitoring submodule and the reference submodule are respectively and The capacitances are respectively and . Figure 4 The changes in the capacitor voltages of the monitoring submodule and the reference submodule within the input window are shown.

[0038] Since both experience the exact same bridge arm current during the input window, the ratio of their capacitor voltage increments satisfies: (5) Therefore, by simply obtaining the voltage changes of the capacitors of the reference submodule and the monitoring submodule during the input window, the capacitance of the monitoring submodule can be calculated. for: (6) This allows for online quantitative identification of the capacitance parameters of abnormal submodules without introducing additional sensors or affecting the normal operation of the system.

[0039] The specific process of the existing method for obtaining MMC capacitance parameter estimation data based on the input window is as follows: (1) Input window identification and delay determination: Taking finite set model predictive control as an example, each control cycle can obtain the switching state of each submodule within a single arm of the MMC and the corresponding number of submodules in operation. Real-time monitoring of the number of sub-modules deployed within the bridge arm. To filter out extremely short deployment windows, when the number of deployed sub-modules within the bridge arm is detected to be equal to... N At that time, it is not immediately considered to have entered an effective input window; instead, a counting delay factor is introduced. d The duration of the fully operational state of submodules is statistically analyzed. When the number of submodules in operation is continuously equal to... N The number of control cycles exceeds the preset threshold. When the time is right, it is determined that the system has entered a valid input window, and the capacitor voltage value of each submodule at that moment is recorded as the starting voltage of the input window.

[0040] (2) Determination of the end of the input window: Within the input window, the change in the direction of the bridge arm current is detected in real time. If current commutation is detected within the input window, the current input window is considered to have ended, and subsequent voltage data acquisition is terminated. If no current commutation occurs within the input window, the current input window is determined to have ended until the number of submodules input changes.

[0041] (3) Calculation and parameter estimation of the voltage difference between sub-module capacitors: Select a fixed submodule as the reference submodule. Assume that this submodule is in a healthy state and its capacitance value is known. The capacitor voltage increment of the monitoring submodule and the reference submodule within the input window is calculated according to equation (4), and the capacitor parameters of the monitoring submodule are further estimated using equation (6).

[0042] The above method utilizes an input window diagram as shown in the figure. Figure 5 As shown. According to Figure 5 As can be seen, existing methods introduce a delay factor threshold to confirm the full engagement state and terminate the current engagement window in advance when a bridge arm current commutation is detected in order to improve the reliability of engagement window determination. While these methods ensure the stability of window determination to a certain extent, they also compress the actual engagement window length that can be used for capacitor parameter estimation, resulting in some effective voltage change information not being fully utilized.

[0043] Based on this, the MMC capacitance parameter estimation method based on the extended input window is proposed in this embodiment, combined with Figure 6 Specifically, it includes the following processes: Step 1: Define the time period during which all sub-modules in the bridge arm are simultaneously put into operation as the input window. Real-time detection of the number of input sub-modules in each bridge arm of the MMC. When the number of input sub-modules equals the number of continuous control cycles of the total number of bridge arm sub-modules and exceeds the preset delay factor threshold, determine the start and end times of the input window based on the start and end times of the number of input sub-modules equaling the total number of bridge arm sub-modules.

[0044] As mentioned above, a single MMC bridge arm contains: N Each submodule, under finite set model predictive control, yields the number of submodules in operation and their corresponding switching signals in each control cycle. The number of submodules in operation within the bridge arm is detected in real time; when the first operation number is detected... Equal to the total number of bridge arm submodules N Time, record this time as Record the capacitor voltage value of each submodule at that moment.

[0045] Similarly, a counting delay factor is introduced. d and its threshold ,when The number of continuous control cycles exceeds the threshold. When the system determines that a valid input window has been entered, the input window flag is set. W =1. Backtrack the starting point of the input window to Moment, that is ,Will The capacitor voltage of each submodule at any time This serves as the starting voltage for each submodule.

[0046] When the number of submodules is detected When the value is no longer equal to N, the input window is considered to have ended. This is denoted as N = 1. Record the capacitor voltage values ​​of each submodule. .

[0047] In this embodiment, the delay factor threshold can be manually selected based on the requirements of monitoring accuracy and frequency, combined with actual operating conditions. The maximum value of the delay factor threshold is determined by the maximum number of control cycles (assuming N cycles) that can be achieved with all submodules fully engaged under actual operation. If high monitoring accuracy is required, the threshold can be set to N control cycles; in this case, the engagement window is the largest, resulting in higher monitoring accuracy. However, such a long engagement window may not occur as frequently, so the monitoring frequency may decrease; conversely, when frequent monitoring is desired, a smaller threshold can be set according to requirements.

[0048] By appropriately increasing the delay factor threshold, the length of the input window can be guaranteed without sacrificing the utilization rate of effective voltage information within the window.

[0049] Step 2: Simultaneously monitor the current direction of the bridge arm in real time, and determine whether an effective current commutation occurs within the input window.

[0050] When first detected Simultaneously, the bridge arm current is monitored. Assuming... After a certain period of time, the direction of the bridge arm current remains positive. When detected... When the value is less than 0, it is determined that a current commutation has occurred, and this time is recorded as _____. And record the capacitor voltage of each submodule at that moment. .

[0051] When the current commutates, if at this time W =1 (Entered the valid input window), directly determine that the capacitor voltage at the recorded commutation moment is valid, and set the current commutation flag. K =1; if at this time W If the value is 0 (not yet within the valid window), the recorded capacitor voltage is temporarily stored and continuously monitored. W ,when W The current commutation flag is set only when the voltage changes from 0 to 1, indicating that the recorded commutation moment capacitor voltage is valid. K =1; If no current commutation is detected within the entire input window, the recorded capacitor voltage at the commutation moment is deemed invalid, and the current commutation flag is set. K =0.

[0052] Step 3: Calculate the capacitor voltage increment for each submodule.

[0053] Calculate the capacitor voltage increment of each submodule based on whether a valid current commutation occurs within the input window. If no current commutation occurs within the input window, calculate the voltage increment based on the capacitor voltage of each submodule at the start and end times of the input window; if current commutation occurs within the input window, calculate the voltage increment based on the capacitor voltage of each submodule at the start, commutation, and end times of the input window.

[0054] Specifically, when there is no effective current commutation during the input window ( K =0), the voltage increment of the i-th submodule is the absolute value of the difference between the capacitor voltage value of the i-th submodule at the end of the input window and the capacitor voltage value of the i-th submodule at the beginning of the input window. The specific calculation formula is as follows: (7) When there is effective current commutation during the input window ( K=1), calculate the absolute value of the difference between the capacitor voltage value of the i-th submodule at the end of the input window and the capacitor voltage value of the corresponding submodule at the commutation time, and the absolute value of the difference between the capacitor voltage value of the i-th submodule at the commutation time and the capacitor voltage value of the corresponding submodule at the start of the input window; the sum of the two absolute values ​​is taken as the voltage increment of the i-th submodule. The specific formula for calculating the voltage increment is as follows: (8) Step 4: Based on the calculated capacitor voltage increment, estimate the capacitor parameters of each submodule.

[0055] After selecting a reference submodule and obtaining the capacitor voltage increments of the reference submodule and the monitoring submodule within the input window, the capacitor parameters of the monitoring submodule are estimated using equation (6).

[0056] The method proposed in this embodiment introduces a backtracking mechanism for the start of the input window, avoiding the loss of effective voltage change information due to delayed judgment and improving the usability of voltage data within a single input window. Furthermore, based on the backtracking of the input window start, by increasing the delay factor threshold, only input windows that meet the duration requirements are analyzed, effectively filtering out invalid windows with excessively short durations and low signal-to-noise ratios. This ensures the length of the input window without sacrificing the utilization rate of effective voltage information within the window, improving the anti-interference capability of capacitor voltage increment characteristics against noise and operating condition fluctuations. Simultaneously, the end condition of the input window is defined as the moment when the submodule exits from the fully engaged state, no longer affected by current commutation events, thus preventing premature window truncation and effectively extending the duration of the input window.

[0057] Compared to existing methods that discard subsequent voltage information immediately after detecting current commutation, the method proposed in this embodiment processes the voltage changes before and after commutation in segments within the same input window, thus preserving the effective voltage characteristics during the current commutation process. This processing significantly expands the effective data range that can be used for capacitor state monitoring without adding additional measurement conditions.

[0058] Example 2 In one or more embodiments, an MMC capacitance parameter estimation system based on an extended input window is disclosed, specifically including: The input window determination module is configured to define the time period during which all sub-modules in the bridge arm are put into operation simultaneously as the input window. It monitors the number of input sub-modules in each bridge arm of the MMC in real time. When the number of input sub-modules equals the number of continuous control cycles of the total number of bridge arm sub-modules and exceeds the preset delay factor threshold, it determines the start and end times of the input window based on the start and end times of the number of input sub-modules equaling the total number of bridge arm sub-modules. The capacitor voltage increment calculation module is configured to simultaneously monitor the current direction of the bridge arm in real time, and calculate the capacitor voltage increment of each sub-module according to whether an effective current commutation occurs within the input window. The capacitor parameter estimation module is configured to estimate the capacitor parameters of each submodule based on the capacitor voltage increment.

[0059] It should be noted that the specific implementation methods of the above modules are exactly the same as those in Example 1, and will not be described in detail again.

[0060] Example 3 In one or more embodiments, a terminal device is disclosed, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions adapted to be loaded by the processor and executed by the processor to perform the MMC capacitance parameter estimation method based on the extended input window described in Embodiment 1.

[0061] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0062] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0063] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0064] Example 4 In one or more embodiments, a computer-readable storage medium is disclosed, wherein a plurality of instructions are stored, the instructions being adapted to be loaded by a processor of a terminal device and executed by the MMC capacitance parameter estimation method based on the extended input window described in Embodiment 1.

[0065] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for estimating MMC capacitance parameters based on an extended input window, characterized in that, include: The time period during which all sub-modules in the bridge arm are put into operation simultaneously is defined as the input window. The number of input sub-modules in each bridge arm of the MMC is detected in real time. When the number of input sub-modules equals the number of continuous control cycles of the total number of bridge arm sub-modules and exceeds the preset delay factor threshold, the start and end times of the input window are determined according to the start and end times of the number of input sub-modules equaling the total number of bridge arm sub-modules. Simultaneously monitor the current direction of the bridge arm in real time, and calculate the capacitor voltage increment of each submodule based on whether an effective current commutation occurs within the input window. Based on the capacitor voltage increment, the capacitance parameters of each submodule are estimated.

2. The method for estimating MMC capacitance parameters based on an extended input window as described in claim 1, characterized in that, Based on the start and end times of the number of sub-modules deployed equaling the total number of bridge arm sub-modules, the start and end times of the deployment window are determined as follows: Record the time when the number of sub-modules deployed is first detected to equal the total number of bridge arm sub-modules. And the capacitor voltage values ​​of each submodule at the corresponding time; When the number of submodules engaged equals the total number of bridge arm submodules and the number of continuous control cycles exceeds a preset delay factor threshold, the system is determined to have entered a valid engagement window, and the time is recorded. As the starting point for the investment window; When the number of sub-modules put into operation is no longer equal to the total number of bridge arm sub-modules, the operation window is determined to end. The time at this time is recorded as the end time of the operation window, and the capacitor voltage value of each sub-module at this time is also recorded.

3. The method for estimating MMC capacitance parameters based on an extended input window as described in claim 1, characterized in that, The method for determining whether a valid current commutation has occurred within the input window is as follows: When the number of sub-modules engaged is first detected to be equal to the total number of bridge arm sub-modules, the bridge arm current is monitored synchronously. If a change in the direction of the bridge arm current is detected and the engagement window is valid at this time, the current commutation is determined to be valid. The engagement window being valid means that the number of continuous control cycles in which the number of sub-modules engaged is equal to the total number of bridge arm sub-modules exceeds a preset delay factor threshold.

4. The method for estimating MMC capacitance parameters based on an extended input window as described in claim 1, characterized in that, Based on whether a valid current commutation occurs within the input window, the capacitor voltage increment of each submodule is calculated separately, as follows: If no current commutation occurs within the input window, the voltage increment is calculated based on the capacitor voltages of each submodule at the start and end times of the input window. If current commutation occurs within the input window, the voltage increment is calculated based on the capacitor voltages of each submodule at the start, commutation, and end times of the input window.

5. The method for estimating MMC capacitance parameters based on an extended input window as described in claim 4, characterized in that, If no current commutation occurs within the input window, the voltage increment is calculated as follows: The voltage increment of the i-th submodule is the absolute value of the difference between the capacitor voltage value of the i-th submodule at the end of the input window and the capacitor voltage value of the i-th submodule at the beginning of the input window.

6. The method for estimating MMC capacitance parameters based on an extended input window as described in claim 4, characterized in that, If current commutation occurs within the input window, the voltage increment is calculated as follows: Calculate the absolute value of the difference between the capacitor voltage value of the i-th submodule at the end of the input window and the capacitor voltage value of the corresponding submodule at the commutation time, and the absolute value of the difference between the capacitor voltage value of the i-th submodule at the commutation time and the capacitor voltage value of the corresponding submodule at the start of the input window; the sum of the two absolute values ​​is taken as the voltage increment of the i-th submodule.

7. The method for estimating MMC capacitance parameters based on an extended input window as described in claim 1, characterized in that, The delay factor threshold is determined based on the requirements of monitoring accuracy and monitoring frequency. The larger the delay factor threshold, the higher the monitoring accuracy, but the lower the detection frequency. The maximum value of the delay factor threshold is determined based on the highest number of control cycles that can be achieved when all submodules are fully engaged in actual operation.

8. A system for estimating MMC capacitance parameters based on an extended input window, characterized in that, include: The input window determination module is configured to define the time period during which all sub-modules in the bridge arm are put into operation simultaneously as the input window. It monitors the number of input sub-modules in each bridge arm of the MMC in real time. When the number of input sub-modules equals the number of continuous control cycles of the total number of bridge arm sub-modules and exceeds the preset delay factor threshold, it determines the start and end times of the input window based on the start and end times of the number of input sub-modules equaling the total number of bridge arm sub-modules. The capacitor voltage increment calculation module is configured to simultaneously monitor the current direction of the bridge arm in real time, and calculate the capacitor voltage increment of each sub-module according to whether an effective current commutation occurs within the input window. The capacitor parameter estimation module is configured to estimate the capacitor parameters of each submodule based on the capacitor voltage increment.

9. A terminal device comprising a processor and a memory, the processor for implementing instructions; the memory for storing multiple instructions, characterized in that, The instructions are adapted to be loaded by a processor and executed by the MMC capacitance parameter estimation method based on any one of claims 1-7.

10. A computer-readable storage medium storing a plurality of instructions, characterized in that, The instructions are adapted to be loaded by the processor of the terminal device and executed by the MMC capacitance parameter estimation method based on any one of claims 1-7.

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