Zero-sequence component calculation method for controlling potential balance of converter and related device

Abstract

The invention discloses a zero-sequence component calculation method for controlling potential balance of a converter and a related device, and the method comprises the steps: judging whether a zero-sequence calculation component obtained through calculation based on a preset zero-sequence calculation formula is within a zero-sequence limit value range, if yes, entering a symbol judgment process, and if not, entering a symbol judgment process; the zero-sequence limit range comprises a zero-sequence component minimum value and a zero-sequence component maximum value; and dividing the voltage symbols of the three-phase reference voltage into four types, and judging and analyzing the zero-sequence calculation component by combining the three-phase reference maximum value, the three-phase reference intermediate value, the three-phase reference minimum value and the initial zero-sequence set value to obtain an updated target zero-sequence component. The voltage symbols are divided into four conditions for limit value judgment and analysis, the target zero-sequence component can be accurately obtained, and more times of tentative judgment or calculation processes are not needed. The technical problems that an existing zero-sequence component determination method depends on positive-sequence reference voltage or tentative calculation, results are lack of accuracy, and efficiency is low can be solved.

Description

Technical Field

[0001] This application relates to the technical field of electrical equipment, and particularly to a zero-sequence component calculation method and related devices for controlling the potential balance of a converter. Background Art

[0002] Compared with traditional two-level converters, three-level converters have more levels of phase voltage and line voltage output, which makes their output voltage waveforms closer to sine waves. At the same switching frequency, the harmonic content of the output waveform can be significantly reduced. At the same time, devices with lower withstand voltage and lower switching frequencies can be used to achieve the expected voltage output. Therefore, three-level converters have been widely used in medium and high voltage high-power conversion applications.

[0003] However, three-level converters also face a significant problem, namely the balance problem of the midpoint voltage. This problem may be caused by various factors, including mismatches in DC bus capacitors, load imbalances, and differences in circuit structures and modulation strategies. The imbalance of the midpoint voltage will cause distortion of the output voltage, resulting in inconsistent voltages borne by the switching devices. At the same time, the fluctuations in the DC side capacitor voltage may shorten the life of the capacitor, and in the worst case, may damage the switching devices and filter capacitors. To solve the problem of midpoint voltage imbalance, hardware-based or software-based methods can be adopted. Hardware methods require additional circuits, but will increase system complexity and cost. Software methods mainly integrate the midpoint voltage balance algorithm into the control strategy without any modification to the hardware.

[0004] Existing technologies often use a sinusoidal pulse width modulation method based on zero-sequence component injection to balance the midpoint voltage of a three-level converter, that is, to achieve voltage balance by injecting a specific zero-sequence voltage component into the modulation wave; however, currently, this technology either relies too much on the positive-sequence reference voltage, resulting in inaccurate zero-sequence component results, or requires many trial-and-error iterative calculations to obtain the results, with low efficiency and a certain degree of uncertainty. Summary of the Invention

[0005] This application provides a zero-sequence component calculation method and related devices for controlling the potential balance of a converter, which are used to solve the technical problems that the existing zero-sequence component determination methods rely on positive-sequence reference voltages or trial-and-error calculations, resulting in inaccurate results and low efficiency.

[0006] In view of this, a first aspect of this application provides a zero-sequence component calculation method for controlling the potential balance of a converter, including:

[0007] Determine whether the zero-sequence calculation component calculated based on a preset zero-sequence calculation formula is within the zero-sequence limit range. If so, enter the sign judgment process, and the zero-sequence limit range includes a zero-sequence component minimum value and a zero-sequence component maximum value;

[0008] The symbol judgment process is as follows:

[0009] If the voltage symbol of the three-phase reference voltage is of the first type, it is judged whether the zero-sequence calculation component is less than or equal to the negative value of the three-phase reference maximum value. If so, the zero-sequence calculation component is used as the target zero-sequence component;

[0010] If the voltage symbol of the three-phase reference voltage is of the second type, it is judged whether the zero-sequence calculation component is between the negative value of the three-phase reference maximum value and the negative value of the three-phase reference intermediate value, and less than the initial zero-sequence setting value. If so, the zero-sequence calculation component is used as the target zero-sequence component;

[0011] If the voltage symbol of the three-phase reference voltage is of the third type, it is judged whether the zero-sequence calculation component is between the negative value of the three-phase reference intermediate value and the negative value of the three-phase reference minimum value, and less than the initial zero-sequence setting value. If so, the zero-sequence calculation component is used as the target zero-sequence component;

[0012] If the voltage symbol of the three-phase reference voltage is of the fourth type, it is judged whether the zero-sequence calculation component is greater than or equal to the negative value of the three-phase reference minimum value. If so, the zero-sequence calculation component is used as the target zero-sequence component.

[0013] Preferably, before the above-mentioned judgment is based on whether the zero-sequence calculation component calculated according to the preset zero-sequence calculation formula is within the zero-sequence limit range. If so, entering the symbol judgment process further includes:

[0014] Determine the three-phase reference voltage based on the positive and negative half-bus voltages of the converter by means of voltage limiting;

[0015] Sort the voltage values of the three-phase reference voltage in descending order to obtain the three-phase reference maximum value, the three-phase reference intermediate value, and the three-phase reference minimum value;

[0016] Calculate the maximum value of the zero-sequence component and the minimum value of the zero-sequence component according to the three-phase reference maximum value and the three-phase reference minimum value.

[0017] Preferably, after the above-mentioned judgment is based on whether the zero-sequence calculation component calculated according to the preset zero-sequence calculation formula is within the zero-sequence limit range. If so, entering the symbol judgment process further includes:

[0018] If the zero-sequence calculation component is greater than the maximum value of the zero-sequence component, calculate the difference between the positive and negative half-bus voltages in the current switching period based on the preset difference calculation formula to obtain the bus voltage difference;

[0019] Conduct difference judgment and analysis based on the bus voltage difference and the preset initial difference, and update to obtain the target updated difference and the target zero-sequence component.

[0020] Preferably, the difference judgment and analysis are performed based on the bus voltage difference and the preset initial difference, and the target updated difference and the target zero-sequence component are updated, including:

[0021] If the bus voltage difference is less than the preset initial difference, the candidate zero-sequence component is updated to the target zero-sequence component, and the bus voltage difference is updated to the target updated difference;

[0022] The candidate zero-sequence component includes the three-phase reference maximum value, the three-phase reference intermediate value, the three-phase reference minimum value, the zero-sequence component maximum value, and the zero-sequence component minimum value.

[0023] The second aspect of the present application provides a zero-sequence component device for controlling the potential balance of a converter, including:

[0024] A zero-sequence analysis unit, configured to determine whether the calculated zero-sequence component based on a preset zero-sequence calculation formula is within the zero-sequence limit range. If so, it enters the sign judgment process, and the zero-sequence limit range includes the zero-sequence component minimum value and the zero-sequence component maximum value;

[0025] The sign judgment process is as follows:

[0026] A first judgment unit, configured to, if the voltage sign of the three-phase reference voltage is of the first type, determine whether the calculated zero-sequence component is less than or equal to the negative value of the three-phase reference maximum value. If so, the calculated zero-sequence component is used as the target zero-sequence component;

[0027] A second judgment unit, configured to, if the voltage sign of the three-phase reference voltage is of the second type, determine whether the calculated zero-sequence component is between the negative value of the three-phase reference maximum value and the negative value of the three-phase reference intermediate value and less than the initial zero-sequence setting value. If so, the calculated zero-sequence component is used as the target zero-sequence component;

[0028] A third judgment unit, configured to, if the voltage sign of the three-phase reference voltage is of the third type, determine whether the calculated zero-sequence component is between the negative value of the three-phase reference intermediate value and the negative value of the three-phase reference minimum value and less than the initial zero-sequence setting value. If so, the calculated zero-sequence component is used as the target zero-sequence component;

[0029] A fourth judgment unit, configured to, if the voltage sign of the three-phase reference voltage is of the fourth type, determine whether the calculated zero-sequence component is greater than or equal to the negative value of the three-phase reference minimum value. If so, the calculated zero-sequence component is used as the target zero-sequence component.

[0030] Preferably, it further includes:

[0031] A voltage determination unit, configured to determine the three-phase reference voltage by means of voltage limiting based on the positive and negative half-bus voltages of the converter;

[0032] A voltage sorting unit, configured to sort the three-phase reference voltages in descending order of voltage value to obtain a three-phase reference maximum value, a three-phase reference intermediate value, and a three-phase reference minimum value;

[0033] A limit calculation unit, configured to calculate a maximum zero-sequence component and a minimum zero-sequence component according to the three-phase reference maximum value and the three-phase reference minimum value.

[0034] Preferably, it further includes:

[0035] A difference calculation unit, configured to, if the calculated zero-sequence component is greater than the maximum zero-sequence component, calculate the difference between the positive and negative half-bus voltages in the current switching period based on a preset difference calculation formula to obtain a bus voltage difference;

[0036] A component update unit, configured to perform difference judgment analysis based on the bus voltage difference and a preset initial difference, and update to obtain a target update difference and a target zero-sequence component.

[0037] Preferably, the component update unit is specifically configured to:

[0038] If the bus voltage difference is less than the preset initial difference, update the candidate zero-sequence component to the target zero-sequence component and update the bus voltage difference to the target update difference;

[0039] The candidate zero-sequence component includes the three-phase reference maximum value, the three-phase reference intermediate value, the three-phase reference minimum value, the maximum zero-sequence component, and the minimum zero-sequence component.

[0040] The third aspect of the present application provides a zero-sequence component calculation device for controlling the potential balance of a converter, and the device includes a processor and a memory;

[0041] The memory is configured to store program code and transmit the program code to the processor;

[0042] The processor is configured to execute the zero-sequence component calculation method for controlling the potential balance of the converter according to the instructions in the program code in the first aspect.

[0043] The fourth aspect of the present application provides a computer-readable storage medium, and the computer-readable storage medium is configured to store program code, and the program code is used to execute the zero-sequence component calculation method for controlling the potential balance of the converter in the first aspect.

[0044] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0045] In this application, a zero-sequence component calculation method for controlling the potential balance of a converter is provided, including: determining whether the zero-sequence calculation component calculated based on a preset zero-sequence calculation formula is within the zero-sequence limit range. If so, enter the sign judgment process. The zero-sequence limit range includes the minimum zero-sequence component and the maximum zero-sequence component. The sign judgment process is as follows: If the voltage signs of the three-phase reference voltages are of the first type, determine whether the zero-sequence calculation component is less than or equal to the negative value of the maximum three-phase reference value. If so, use the zero-sequence calculation component as the target zero-sequence component. If the voltage signs of the three-phase reference voltages are of the second type, determine whether the zero-sequence calculation component is between the negative value of the maximum three-phase reference value and the negative value of the intermediate three-phase reference value, and less than the initial zero-sequence setting value. If so, use the zero-sequence calculation component as the target zero-sequence component. If the voltage signs of the three-phase reference voltages are of the third type, determine whether the zero-sequence calculation component is between the negative value of the intermediate three-phase reference value and the negative value of the minimum three-phase reference value, and less than the initial zero-sequence setting value. If so, use the zero-sequence calculation component as the target zero-sequence component. If the voltage signs of the three-phase reference voltages are of the fourth type, determine whether the zero-sequence calculation component is greater than or equal to the negative value of the minimum three-phase reference value. If so, use the zero-sequence calculation component as the target zero-sequence component.

[0046] The zero-sequence component calculation method for controlling the potential balance of the converter provided in this application determines the target zero-sequence component without relying on the positive-sequence reference voltage in the calculation process, so it will not affect the accuracy of the result. Moreover, the voltage signs of the three-phase reference voltages are divided into four cases for clear limit range judgment and analysis. Not only can the target zero-sequence component be accurately obtained, but also no more trial judgments or calculation processes are required. The overall process is not complicated, which can ensure the efficiency of obtaining the zero-sequence component and meet the requirements of the neutral point potential balance control of the actual three-level converter. Therefore, this application can solve the technical problems that the existing zero-sequence component determination methods rely on the positive-sequence reference voltage or trial calculations, resulting in inaccurate results and low efficiency. Brief Description of the Drawings

[0047] Figure 1 It is a schematic flowchart of the zero-sequence component calculation method for controlling the potential balance of the converter provided in the embodiment of this application;

[0048] Figure 2 It is a schematic structural diagram of the zero-sequence component calculation device for controlling the potential balance of the converter provided in the embodiment of this application. Detailed Embodiments

[0049] To enable those skilled in the art to better understand the solution of this application, the following will clearly and completely describe the technical solution in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0050] For ease of understanding, please refer to Figure 1 , an embodiment of the zero-sequence component calculation method for controlling the potential balance of a converter, including:

[0051] Step 101: Determine whether the calculated zero-sequence calculation component based on a preset zero-sequence calculation formula is within the zero-sequence limit range. If so, enter the sign judgment process. The zero-sequence limit range includes the minimum zero-sequence component and the maximum zero-sequence component.

[0052] Further, before step 101, it also includes:

[0053] Determine the three-phase reference voltage by means of voltage limiting based on the positive and negative half-bus voltages of the converter;

[0054] Sort the three-phase reference voltages in descending order of voltage value to obtain the three-phase reference maximum value, the three-phase reference intermediate value, and the three-phase reference minimum value;

[0055] Calculate the maximum zero-sequence component and the minimum zero-sequence component based on the three-phase reference maximum value and the three-phase reference minimum value.

[0056] It should be noted that in this embodiment, the three-phase reference voltage can be pre-limited according to the positive half-bus voltage and the negative half-bus voltage of the three-level converter. The determined three-phase reference voltage is expressed as , , ; then perform a descending order sorting process on it, and the obtained three-phase reference voltage sequence is denoted as , specifically including the three-phase reference maximum value , the three-phase reference intermediate value and the three-phase reference minimum value . And according to the three-phase reference maximum value and the three-phase reference minimum value , the limit value of the zero-sequence voltage component that can be implemented can be calculated, that is, the maximum zero-sequence component and the minimum zero-sequence component . The zero-sequence component to be updated can be denoted as , and an initial value can be set at the beginning, defined as the zero-sequence initial preset value , and then perform numerical update based on the subsequent judgment update process to obtain a more accurate and reliable target zero-sequence component.

[0057] Zero-sequence calculation component As the name implies, it is the component value calculated by presetting the zero-sequence calculation formula. To analyze whether this value is suitable as the target zero-sequence component, a series of judgment and analysis are required. The preset zero-sequence calculation formula is expressed as:

[0058]

[0059] Among them, is the capacitance value of the DC capacitor of the converter, is the control period of the converter, is the input current of the corresponding item in, for example represents the input current of the corresponding phase of the first item element; is the symbol of the element in, including three elements; represents the value of the corresponding item element in.

[0060] Since the subsequent judgment process of the voltage symbols of the three-phase reference voltages is a deep judgment and analysis carried out when the zero-sequence calculation component falls within the zero-sequence limit range, in this embodiment, a threshold judgment is first made on the zero-sequence calculation component, that is, to judge whether the zero-sequence calculation component is greater than or equal to the minimum value of the zero-sequence component , and less than or equal to the maximum value of the zero-sequence component , that is ; if so, it meets the judgment conditions of the voltage symbol judgment process, and can enter the specific symbol judgment process for deeper judgment and analysis to determine a more accurate target zero-sequence component; if not, other methods need to be used to determine the target zero-sequence component.

[0061] Furthermore, step 101 further includes:

[0062] If the zero-sequence calculation component is greater than the maximum value of the zero-sequence component, calculate the difference between the positive and negative half-bus voltages in this switching period based on the preset difference calculation formula to obtain the bus voltage difference;

[0063] Perform difference judgment and analysis based on the bus voltage difference and the preset initial difference, and update to obtain the target updated difference and the target zero-sequence component.

[0064] Furthermore, the performing difference judgment and analysis based on the bus voltage difference and the preset initial difference, and updating to obtain the target updated difference and the target zero-sequence component includes:

[0065] If the difference in bus voltages is less than the preset initial difference, update the candidate zero-sequence component to the target zero-sequence component and update the difference in bus voltages to the target update difference;

[0066] The candidate zero-sequence component includes the three-phase reference maximum value, the three-phase reference intermediate value, the three-phase reference minimum value, the zero-sequence component maximum value, and the zero-sequence component minimum value.

[0067] This embodiment considers the zero-sequence calculation component greater than the zero-sequence component maximum value In this case, if it exceeds the zero-sequence component maximum value, the symbol judgment analysis cannot continue, and other methods need to be used to determine the target zero-sequence component. This embodiment proposes that the target zero-sequence component can be determined based on the difference in bus voltages, and the difference in bus voltages can be obtained based on a preset difference calculation formula:

[0068]

[0069] According to the difference in bus voltages and the preset initial difference The difference judgment analysis process is as follows:

[0070] Assume that the zero-sequence component is updated to the zero-sequence component maximum value , and then judge whether the difference in bus voltages is less than the preset initial difference . If so, take the updated zero-sequence component maximum value as the target zero-sequence component and take the difference in bus voltages as the target update difference.

[0071] Assume that the zero-sequence component is updated to the zero-sequence component minimum value , and then judge whether the difference in bus voltages is less than the preset initial difference . If so, take the updated zero-sequence component minimum value as the target zero-sequence component and take the difference in bus voltages as the target update difference.

[0072] Similarly, it can also be assumed that the zero-sequence component is the three-phase reference maximum value , the three-phase reference intermediate value , and the three-phase reference minimum value . The judgment method is as above and will not be elaborated here. That is, through the enumeration method, hypothetical difference analysis is carried out. If the analysis meets the conditions, these extreme values can be used as the target zero-sequence component. If the target zero-sequence component is determined, then its superimposed value on the three-phase reference voltages , , can be used to obtain the required output reference voltage.

[0073] The symbol judgment process is as follows:

[0074] Step 102: If the voltage symbol of the three-phase reference voltage is of the first type, determine whether the zero-sequence calculation component is less than or equal to the negative value of the maximum value of the three-phase reference. If so, use the zero-sequence calculation component as the target zero-sequence component.

[0075] Step 103: If the voltage symbol of the three-phase reference voltage is of the second type, determine whether the zero-sequence calculation component is between the negative value of the maximum value of the three-phase reference and the negative value of the intermediate value of the three-phase reference, and less than the initial zero-sequence setting value. If so, use the zero-sequence calculation component as the target zero-sequence component;

[0076] Step 104: If the voltage symbol of the three-phase reference voltage is of the third type, determine whether the zero-sequence calculation component is between the negative value of the intermediate value of the three-phase reference and the negative value of the minimum value of the three-phase reference, and less than the initial zero-sequence setting value. If so, use the zero-sequence calculation component as the target zero-sequence component;

[0077] Step 105: If the voltage symbol of the three-phase reference voltage is of the fourth type, determine whether the zero-sequence calculation component is greater than or equal to the negative value of the minimum value of the three-phase reference. If so, use the zero-sequence calculation component as the target zero-sequence component.

[0078] It should be noted that the voltage symbols of the three-phase reference voltage in this embodiment are , and the symbols of different phases may be different. Therefore, the voltage symbols of the three-phase reference voltage can be expressed as , the first type in this embodiment is , the second type is , the third type is , and the fourth type is .

[0079] If the voltage symbol of the three-phase reference voltage is , then continue to determine whether the zero-sequence calculation component is less than or equal to the negative value of the maximum value of the three-phase reference, that is , which means it exceeds the value range of the three-phase reference value; if so, use the zero-sequence calculation component as the target zero-sequence component.

[0080] If the voltage symbol of the three-phase reference voltage is , then continue to determine whether the zero-sequence calculation component is greater than the negative value of the maximum value of the three-phase reference, less than or equal to the negative value of the intermediate value of the three-phase reference, that is, between the negative value of the maximum value of the three-phase reference and the negative value of the intermediate value of the three-phase reference, expressed as ; and , that is, less than the initial zero-sequence preset value ; then use the zero-sequence calculation component As the target zero-sequence component.

[0081] If the voltage signs of the three-phase reference voltages are , then continue to judge whether the zero-sequence calculation component is greater than the negative value of the three-phase reference middle value and less than or equal to the negative value of the three-phase reference minimum value, that is, between the negative value of the three-phase reference middle value and the negative value of the three-phase reference minimum value, expressed as , and ; then use the zero-sequence calculation component as the target zero-sequence component.

[0082] If the voltage signs of the three-phase reference voltages are , then continue to judge whether the zero-sequence calculation component is , that is, outside the value range of the three-phase reference values, and ; then use the zero-sequence calculation component as the target zero-sequence component.

[0083] So far, the judgment and analysis of the four cases of the three-phase reference voltages are completed. Based on this judgment strategy, the accurate and reliable target zero-sequence component can be obtained more efficiently. And it can be understood that if the conditions are not met during the judgment process, there is no need to update the zero-sequence component, and the initial preset value of the zero-sequence can be used as the target zero-sequence component, and the details will not be elaborated here.

[0084] The zero-sequence component calculation method for controlling the potential balance of the converter provided by the embodiment of the present application determines the target zero-sequence component without relying on the positive-sequence reference voltage during the judgment and calculation process, so it will not affect the accuracy of the result; moreover, the voltage signs of the three-phase reference voltages are divided into four cases for clear limit range judgment and analysis. Not only can the target zero-sequence component be accurately obtained, but also no more tentative judgments or calculation processes are required. The overall process is not complicated, which can ensure the efficiency of obtaining the zero-sequence component and can meet the requirements of the actual neutral point potential balance control of the three-level converter. Therefore, the embodiment of the present application can solve the technical problems that the existing zero-sequence component determination method depends on the positive-sequence reference voltage or tentative calculation, resulting in inaccurate results and low efficiency.

[0085] For easy understanding, please refer to Figure 2 , the embodiment of the zero-sequence component device for controlling the potential balance of the converter provided by the present application includes:

[0086] The zero-sequence analysis unit 201 is used to judge whether the zero-sequence calculation component calculated based on the preset zero-sequence calculation formula is within the zero-sequence limit range. If so, enter the symbol judgment process. The zero-sequence limit range includes the zero-sequence component minimum value and the zero-sequence component maximum value;

[0087] The symbol judgment process is as follows:

[0088] The first judgment unit 202 is configured to, if the voltage symbol of the three-phase reference voltage is of the first type, determine whether the zero-sequence calculation component is less than or equal to the negative value of the three-phase reference maximum value. If so, use the zero-sequence calculation component as the target zero-sequence component;

[0089] The second judgment unit 203 is configured to, if the voltage symbol of the three-phase reference voltage is of the second type, determine whether the zero-sequence calculation component is between the negative value of the three-phase reference maximum value and the negative value of the three-phase reference intermediate value, and less than the initial zero-sequence setting value. If so, use the zero-sequence calculation component as the target zero-sequence component;

[0090] The third judgment unit 204 is configured to, if the voltage symbol of the three-phase reference voltage is of the third type, determine whether the zero-sequence calculation component is between the negative value of the three-phase reference intermediate value and the negative value of the three-phase reference minimum value, and less than the initial zero-sequence setting value. If so, use the zero-sequence calculation component as the target zero-sequence component;

[0091] The fourth judgment unit 205 is configured to, if the voltage symbol of the three-phase reference voltage is of the fourth type, determine whether the zero-sequence calculation component is greater than or equal to the negative value of the three-phase reference minimum value. If so, use the zero-sequence calculation component as the target zero-sequence component.

[0092] Furthermore, it further includes:

[0093] The voltage determination unit 206 is configured to determine the three-phase reference voltage based on the positive and negative half-bus voltages of the converter through voltage limiting;

[0094] The voltage sorting unit 207 is configured to sort the three-phase reference voltages in descending order of voltage value to obtain the three-phase reference maximum value, the three-phase reference intermediate value, and the three-phase reference minimum value;

[0095] The limit calculation unit 208 is configured to calculate the maximum zero-sequence component and the minimum zero-sequence component based on the three-phase reference maximum value and the three-phase reference minimum value.

[0096] Furthermore, it further includes:

[0097] The difference calculation unit 209 is configured to, if the zero-sequence calculation component is greater than the maximum zero-sequence component, calculate the difference between the positive and negative half-bus voltages in the current switching period based on a preset difference calculation formula to obtain the bus voltage difference;

[0098] The component update unit 210 is configured to perform difference judgment and analysis based on the bus voltage difference and the preset initial difference, and update to obtain the target updated difference and the target zero-sequence component.

[0099] Furthermore, the component update unit 210 is specifically configured to:

[0100] If the bus voltage difference is less than a preset initial difference, update the candidate zero-sequence component to the target zero-sequence component and update the bus voltage difference to the target update difference;

[0101] The candidate zero-sequence component includes the three-phase reference maximum value, the three-phase reference intermediate value, the three-phase reference minimum value, the zero-sequence component maximum value, and the zero-sequence component minimum value.

[0102] This application also provides a zero-sequence component calculation device for controlling the potential balance of a converter. The device includes a processor and a memory;

[0103] The memory is used to store program code and transmit the program code to the processor;

[0104] The processor is used to execute the zero-sequence component calculation method for controlling the potential balance of the converter in the above method embodiments according to the instructions in the program code.

[0105] This application also provides a computer-readable storage medium. The computer-readable storage medium is used to store program code, and the program code is used to execute the zero-sequence component calculation method for controlling the potential balance of the converter in the above method embodiments.

[0106] In several embodiments provided by this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point, the displayed or discussed coupling or direct coupling or communication connection between each other can be through some interfaces. The indirect coupling or communication connection of the device or unit can be in an electrical, mechanical or other form.

[0107] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place, or they can be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0108] In addition, in each embodiment of this application, the functional units can be integrated in one processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above integrated units can be implemented in the form of hardware or in the form of software functional units.

[0109] When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of this application. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (English full name: Read-Only Memory, English abbreviation: ROM), random access memories (English full name: Random Access Memory, English abbreviation: RAM), magnetic disks, or optical discs.

[0110] As described above, the above embodiments are only used to illustrate the technical solution of this application, rather than to limit it; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of various embodiments of this application.

Claims

1. A method for calculating the zero-sequence component of a control converter potential balance, characterized in that: include: Determine whether the zero-sequence calculation component calculated based on the preset zero-sequence calculation formula is within the zero-sequence limit range, and if so, enter the sign judgment process, wherein the zero-sequence limit range includes the minimum value of the zero-sequence component and the maximum value of the zero-sequence component; The symbol judgment process is: If the voltage sign of the three-phase reference voltage is of the first type, determining whether the zero-sequence calculation component is less than or equal to the negative value of the three-phase reference maximum value, and if so, taking the zero-sequence calculation component as the target zero-sequence component; If the voltage sign of the three-phase reference voltage is of the second type, it is determined whether the zero-sequence calculation component is between the negative value of the three-phase reference maximum value and the negative value of the three-phase reference intermediate value, and is less than the initial zero-sequence setting value, and the zero-sequence calculation component is used as the target zero-sequence component; If the voltage sign of the three-phase reference voltage is of the third type, it is determined whether the zero-sequence calculation component is between the negative value of the three-phase reference intermediate value and the negative value of the three-phase reference minimum value, and is less than the initial zero-sequence setting value, and the zero-sequence calculation component is used as the target zero-sequence component; If the voltage sign of the three-phase reference voltage is of the fourth type, it is determined whether the zero-sequence calculated component is greater than or equal to the negative value of the three-phase reference minimum value. If so, the zero-sequence calculated component is used as the target zero-sequence component.

2. The method for calculating the zero-sequence component of the control converter potential balance according to claim 1, characterized in that: The process of judging whether the zero-sequence calculation component obtained by the preset zero-sequence calculation formula is within the zero-sequence limit range, if so, entering the sign judgment process, which also includes: Determine the three-phase reference voltage by voltage limiting based on the positive and negative half bus voltages of the converter; The three-phase reference voltages are sorted in descending order of voltage values ​​to obtain a three-phase reference maximum value, a three-phase reference intermediate value, and a three-phase reference minimum value; The zero-sequence component maximum value and the zero-sequence component minimum value are calculated according to the three-phase reference maximum value and the three-phase reference minimum value.

3. The method for calculating the zero-sequence component of the control converter potential balance according to claim 1, characterized in that: The process of judging whether the zero-sequence calculation component obtained by calculating based on the preset zero-sequence calculation formula is within the zero-sequence limit range, and if so, entering the symbol judgment process, further includes: If the zero-sequence calculated component is greater than the zero-sequence component maximum value, the difference between the positive and negative half-bus voltages in the current switching cycle is calculated based on a preset difference calculation formula to obtain a bus voltage difference; A difference judgment analysis is performed based on the bus voltage difference and the preset initial difference, and a target updated difference and a target zero-sequence component are updated.

4. The method for calculating the zero-sequence component of the control converter potential balance according to claim 3, characterized in that: The performing difference judgment and analysis based on the bus voltage difference and the preset initial difference, and updating to obtain a target updated difference and a target zero-sequence component, includes: If the bus voltage difference is less than the preset initial difference, the to-be-selected zero-sequence component is updated to the target zero-sequence component, and the bus voltage difference is updated to the target updated difference; The zero-sequence component to be selected includes the three-phase reference maximum value, the three-phase reference middle value, the three-phase reference minimum value, the zero-sequence component maximum value and the zero-sequence component minimum value.

5. A zero-sequence component calculation device for controlling the potential balance of a current transformer, characterized in that: include: A zero-sequence analysis unit is used to determine whether the zero-sequence calculation component calculated based on a preset zero-sequence calculation formula is within a zero-sequence limit range. If so, a sign determination process is entered, wherein the zero-sequence limit range includes a minimum zero-sequence component and a maximum zero-sequence component. The symbol judgment process is: a first judgment unit, configured to judge whether the zero-sequence calculation component is less than or equal to the negative value of the three-phase reference maximum value if the voltage sign of the three-phase reference voltage is of the first type, and if so, use the zero-sequence calculation component as the target zero-sequence component; A second judgment unit is used to judge whether the zero-sequence calculation component is between the negative value of the three-phase reference maximum value and the negative value of the three-phase reference intermediate value and is less than the initial zero-sequence setting value if the voltage sign of the three-phase reference voltage is of the second type, and use the zero-sequence calculation component as the target zero-sequence component; a third judging unit, configured to judge whether the zero-sequence calculation component is between the negative value of the three-phase reference intermediate value and the negative value of the three-phase reference minimum value and is less than the initial zero-sequence setting value if the voltage sign of the three-phase reference voltage is of the third type, and use the zero-sequence calculation component as the target zero-sequence component; The fourth judgment unit is used to judge whether the zero-sequence calculation component is greater than or equal to the negative value of the three-phase reference minimum value if the voltage sign of the three-phase reference voltage is of the fourth type, and if so, use the zero-sequence calculation component as the target zero-sequence component.

6. The zero-sequence component calculation device for controlling the potential balance of a current transformer according to claim 5, characterized in that: Also includes: A voltage determination unit, used for determining a three-phase reference voltage by voltage limiting based on the positive and negative half-bus voltages of the converter; A voltage sorting unit, used to sort the three-phase reference voltages in descending order of voltage values ​​to obtain a three-phase reference maximum value, a three-phase reference intermediate value, and a three-phase reference minimum value; The limit value calculation unit is used to calculate the zero-sequence component maximum value and the zero-sequence component minimum value according to the three-phase reference maximum value and the three-phase reference minimum value.

7. The zero-sequence component calculation device for controlling the potential balance of a current transformer according to claim 5, characterized in that: Also includes: A difference calculation unit, configured to calculate the difference between the positive and negative half bus voltages in the current switching cycle based on a preset difference calculation formula to obtain a bus voltage difference if the zero-sequence calculation component is greater than the zero-sequence component maximum value; The component updating unit is used to perform difference judgment and analysis based on the bus voltage difference and the preset initial difference, and to update and obtain a target updated difference and a target zero-sequence component.

8. The zero-sequence component calculation device for controlling the potential balance of a current transformer according to claim 7, characterized in that: The component updating unit is specifically used for: If the bus voltage difference is less than the preset initial difference, the to-be-selected zero-sequence component is updated to the target zero-sequence component, and the bus voltage difference is updated to the target updated difference; The zero-sequence component to be selected includes the three-phase reference maximum value, the three-phase reference middle value, the three-phase reference minimum value, the zero-sequence component maximum value and the zero-sequence component minimum value.

9. A zero-sequence component calculation device for controlling the potential balance of a current transformer, characterized in that: The device comprises a processor and a memory; The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the zero-sequence component calculation method for controlling the potential balance of the converter according to any one of claims 1 to 4 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program codes, and the program codes are used to execute the zero-sequence component calculation method for controlling the potential balance of a current transformer as described in any one of claims 1 to 4.

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