Full-bridge sub-module voltage bias balance control method and device

Abstract

The invention discloses a full-bridge sub-module voltage bias balance control method and device, which are used for solving the technical problem that the voltage of a full-bridge sub-module and the voltage of a half-bridge sub-module in an MMC (Modular Multilevel Converter) are unbalanced under the voltage reduction operation condition of a flexible direct-current power transmission system at present. The method comprises the following steps: acquiring sub-module voltage data of any bridge arm in the MMC converter, and calculating full-half bridge voltage unbalance degree of the bridge arm according to the sub-module voltage data; when the full-half-bridge voltage unbalance degree exceeds a preset threshold value, obtaining operation data, and calculating a power factor angle and a voltage deviation angle between the valve side voltage and the network side voltage based on the operation data; calculating a control reference value of the secondary circulating current based on the power factor angle and the voltage deviation angle; and carrying out circulating current suppression according to the control reference value so as to balance the voltage bias of the full-bridge sub-module in the bridge arm.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, and in particular to a full-bridge submodule voltage bias balance control method, a full-bridge submodule voltage bias balance control device, an electronic device, and a storage medium. Background Technology

[0002] In high-voltage direct current (HVDC) engineering, converter valves typically employ an MMC (Modular Multilevel Converter) topology, composed of a hybrid of full-bridge and half-bridge submodules, known as a flexible DC converter valve. During normal operation of the MMC converter, for submodule safety, it is generally required that the voltage of all submodules remain consistent. The MMC converter valve control system includes a corresponding sequencing unit to maintain voltage stability among the submodules.

[0003] like Figure 1 The diagram shows a typical MMC topology. It consists of six bridge arms, each composed of a full-bridge submodule and a half-bridge submodule connected in series. Each submodule consists of switching devices and capacitors. Different switching states determine the charging and discharging direction of the capacitors, thus controlling the capacitor voltage.

[0004] In the special scenario of transmitting ultra-long-distance renewable energy via flexible DC transmission, the voltage drop across the line is significant due to the extremely long transmission distance. Furthermore, flexible DC transmission systems also operate under conditions such as step-down operation. Particularly in step-down operation, the DC-side voltage of the receiving-end MMC converter is low, resulting in an excessively large negative level region in the modulation waveform. For example... Figure 2 The figure shows the arm voltage u in a typical receiving-end MMC converter. pa and bridge arm current i pa The waveform diagram. Combined with... Figure 2 The lower the DC voltage, the greater the distance between θ1 and θ2.

[0005] According to the basic operating principle of MMC converters, when the arm voltage is negative, only the full-bridge submodule can be in a "negative input" state, achieving negative voltage output. Therefore, when the DC voltage is too low, the arm voltage between θ1 and θ2 can only be output by the full-bridge submodule. Simultaneously, considering the operating principle of the full-bridge submodule, when it is in a "negative input" state and the current is positive, the capacitors in the submodule can only discharge. Therefore, if conventional control methods are used, the full-bridge submodule capacitors can only discharge between θ1 and θ2, charge between θ2 and θ3, and the selected full-bridge submodule between θ3 and θ4 will again be in a "discharging" state. Overall, if the θ1 and θ2 range is too large, the overall discharge time of the full-bridge submodule will be much longer than its charging time. This will lead to voltage bias in the full-bridge submodule, causing voltage inconsistencies between the full-bridge and half-bridge submodules within the same arm, which is detrimental to the healthy operation of the flexible DC system.

[0006] Currently, there is no effective solution for the problem of low DC-side voltage of the receiving-end MMC in long-distance power transmission scenarios, which leads to excessively long discharge time of the full-bridge submodule and thus an imbalance between the voltage of the full-bridge submodule and the half-bridge submodule. Summary of the Invention

[0007] This invention provides a full-bridge submodule voltage bias balance control method, a full-bridge submodule voltage bias balance control device, an electronic device, and a storage medium, which are used to solve or partially solve the technical problem of voltage imbalance between full-bridge submodules and half-bridge submodules in MMC converters under the current step-down operation conditions of flexible DC transmission systems.

[0008] This invention provides a method for voltage bias balance control of a full-bridge submodule, the method comprising:

[0009] Collect submodule voltage data of any arm in the MMC converter, and calculate the full-half-bridge voltage imbalance of the arm based on the submodule voltage data.

[0010] When the full-bridge voltage imbalance exceeds a preset threshold, operating data is acquired, and the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage are calculated based on the operating data.

[0011] Based on the power factor angle and the voltage deviation angle, calculate the control reference value of the secondary circulating current;

[0012] Circulating current suppression is performed based on the control reference value to balance the voltage bias of the full-bridge submodules in the bridge arm.

[0013] Optionally, the submodule voltage data includes the voltage of each full-bridge submodule and the voltage of each half-bridge submodule in the bridge arm; the step of calculating the full-to-half-bridge voltage imbalance of the bridge arm based on the submodule voltage data includes:

[0014] Calculate the overall average voltage based on the voltage of all sub-modules in the bridge arm;

[0015] Calculate the average voltage of the full-bridge submodule based on the voltage of each full-bridge submodule, and calculate the average voltage of the half-bridge submodule based on the voltage of each half-bridge submodule.

[0016] Based on the overall average voltage, the average voltage of the full-bridge submodule, and the average voltage of the half-bridge submodule, the full-to-half-bridge voltage imbalance of the bridge arm is calculated.

[0017] Optionally, the operating data includes the current output active power and output reactive power of the MMC converter, the rated phase voltage on the secondary side of the transformer, the effective value of the phase current on the valve side of the MMC converter, and the equivalent connection reactance between the MMC converter and the AC grid; the calculation of the power factor angle and the voltage deviation angle between the valve side voltage and the grid side voltage based on the operating data includes:

[0018] Based on the output active power and the output reactive power, calculate the power factor angle on the valve side of the MMC converter;

[0019] Based on the power factor angle, combined with the rated phase voltage, the effective value of the phase current, and the equivalent connection reactance, the voltage deviation angle between the valve-side voltage and the AC grid-side voltage of the MMC converter is calculated.

[0020] Optionally, the formula for calculating the power factor angle is as follows:

[0021]

[0022] in, Indicates the power factor angle; Indicates the output active power; This indicates the output reactive power.

[0023] Optionally, the formula for calculating the voltage deviation angle is as follows:

[0024]

[0025] in, Indicates the voltage deviation angle; Indicates the rated value of the phase voltage; Indicates the effective value of the phase current; This represents the equivalent connection reactance.

[0026] Optionally, calculating the control reference value of the secondary circulating current based on the power factor angle and the voltage deviation angle includes:

[0027] Based on the different directions of the output active power and the output reactive power, and using the power factor angle and the voltage deviation angle, along with the preset injection circulating current ratio, the control reference value of the secondary circulating current is calculated.

[0028] Optionally, the step of suppressing circulating current according to the control reference value to balance the voltage bias of the full-bridge submodule in the bridge arm includes:

[0029] Based on the control reference value, the modulation voltage of the secondary circulating current is obtained through circulating current suppression loop control;

[0030] The voltage of the full-bridge submodule in the bridge arm is modulated according to the modulation voltage to achieve voltage bias balance of the full-bridge submodule.

[0031] The present invention also provides a full-bridge submodule voltage bias balance control device, comprising:

[0032] The voltage imbalance calculation unit is used to collect the submodule voltage data of any arm in the MMC converter, and calculate the full-half-bridge voltage imbalance of the arm based on the submodule voltage data.

[0033] An angle calculation unit is used to acquire operating data when the full-half-bridge voltage imbalance exceeds a preset threshold, and to calculate the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage based on the operating data.

[0034] The control reference value calculation unit is used to calculate the control reference value of the secondary circulating current based on the power factor angle and the voltage deviation angle.

[0035] A circulating current suppression unit is used to suppress circulating current according to the control reference value in order to balance the voltage bias of the full-bridge submodule in the bridge arm.

[0036] The present invention also provides an electronic device, the device comprising a processor and a memory:

[0037] The memory is used to store program code and transmit the program code to the processor;

[0038] The processor is configured to execute the full-bridge submodule voltage bias balance control method as described above, according to instructions in the program code.

[0039] The present invention also provides a computer-readable storage medium for storing program code for executing the full-bridge submodule voltage bias balance control method as described in any of the preceding claims.

[0040] As can be seen from the above technical solutions, the present invention has the following advantages:

[0041] A method for balancing the voltage bias of full-bridge submodules is provided. First, voltage data of submodules in any arm of the MMC converter is collected, and the full-to-half-bridge voltage imbalance of the arm is calculated based on this data. This allows for the calculation of the voltage imbalance based on the submodule voltage data, thus measuring the voltage difference between the full-bridge and half-bridge submodules in the current arm. When the full-to-half-bridge voltage imbalance exceeds a preset threshold, operating data is acquired, and the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage are calculated based on this data. Therefore, when the voltage difference between the full-bridge and half-bridge submodules is large, valuable evaluation indicators can be calculated based on the current operating data, providing a valid data basis for subsequent control reference value calculations. Next, based on the power factor angle and voltage deviation angle, a control reference value for the secondary circulating current is calculated; circulating current suppression is then performed based on the control reference value to balance the voltage bias of the full-bridge submodules in the arm. By injecting a secondary circulating current, the negative voltage range of the bridge arm voltage is reduced, allowing more charging time for the full-bridge submodule. This avoids excessive DC bias in the full-bridge submodule and achieves voltage balance with the half-bridge submodule. Furthermore, the technical solution provided by this invention does not require additional additions or modifications to existing circulating current suppressors. Voltage bias balance of the full-bridge submodule can be achieved simply by calculating and adjusting the command value according to different operating conditions, making it more suitable for engineering implementation. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of a typical MMC topology;

[0044] Figure 2 This is a waveform diagram of the arm voltage and arm current in a receiving-end MMC converter;

[0045] Figure 3 A flowchart illustrating the steps of a full-bridge submodule voltage bias balance control method;

[0046] Figure 4This is a schematic diagram of the control principle of a circulating current suppression controller;

[0047] Figure 5 This is a schematic diagram of the overall process of a full-bridge submodule voltage bias balance control method.

[0048] Figure 6 This is a structural block diagram of a full-bridge submodule voltage bias balance control device. Detailed Implementation

[0049] This invention provides a full-bridge submodule voltage bias balance control method, a full-bridge submodule voltage bias balance control device, an electronic device, and a storage medium, which are used to solve or partially solve the technical problem of voltage imbalance between full-bridge submodules and half-bridge submodules in MMC converters under the current step-down operation condition of flexible DC transmission systems.

[0050] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0051] As an example, in the special scenario of transmitting ultra-long-distance renewable energy via flexible DC transmission, the voltage drop across the line is significant due to the extremely long transmission distance. Furthermore, flexible DC transmission systems also operate under conditions such as step-down operation. Especially in step-down operation, the DC-side voltage of the receiving-end MMC converter is low, resulting in an excessively large negative level region in the modulation waveform. For example... Figure 2 The figure shows the arm voltage u in a typical receiving-end MMC converter. pa and bridge arm current i pa The waveform diagram. Combined with... Figure 2 The lower the DC voltage, the greater the distance between θ1 and θ2. θ1 represents the bridge arm voltage u. pa The angle of the grid-side voltage vector when entering the "negative input" state; θ2 represents the arm voltage u. pa The angle of the grid-side voltage vector when exiting the "negative input" state.

[0052] According to the basic operating principle of MMC converters, when the arm voltage is negative, only the full-bridge submodule can be in a "negative input" state, achieving negative voltage output. Therefore, when the DC voltage is too low, the arm voltage between θ1 and θ2 can only be output by the full-bridge submodule. Simultaneously, considering the operating principle of the full-bridge submodule, when it is in a "negative input" state and the current is positive, the capacitor in the submodule can only discharge. Therefore, if conventional control methods are used, the full-bridge submodule capacitor can only discharge between θ1 and θ2, charge between θ2 and θ3, and the selected full-bridge submodule between θ3 and θ4 will again be in a "discharging" state. Overall, if the θ1 and θ2 regions are too large, the overall discharge time of the full-bridge submodule will be much longer than its charging time. This will lead to voltage bias in the full-bridge submodule, causing voltage inconsistencies between the full-bridge and half-bridge submodules within the same arm, which is detrimental to the healthy operation of the flexible DC system. θ3 represents the arm current i. pa The grid-side voltage vector angle when entering the "negative input" state; θ4 represents the arm current i pa The angle of the grid-side voltage vector when exiting the "negative input" state.

[0053] Currently, there is no effective solution for the problem of low DC-side voltage of the receiving-end MMC in long-distance power transmission scenarios, which leads to excessively long discharge time of the full-bridge submodule and thus an imbalance between the voltage of the full-bridge submodule and the half-bridge submodule.

[0054] Therefore, one of the core inventive points of this invention is to propose a control method for improving the DC voltage bias of a full-bridge submodule using secondary circulating current injection. The core idea is to reduce the negative voltage range of the bridge arm voltage through secondary circulating current injection, allowing more charging time for the full-bridge submodule, thereby avoiding excessive DC bias and achieving voltage balance between the full-bridge submodule and the half-bridge submodule. The technical solution provided by this invention does not require additional additions or modifications to existing circulating current suppressors; it only requires calculations based on different operating conditions and adjustment of the command value to achieve voltage bias balance of the full-bridge submodule, making it more suitable for engineering implementation.

[0055] Reference Figure 3 The diagram illustrates a flowchart of a full-bridge submodule voltage bias balance control method provided by an embodiment of the present invention, which may specifically include the following steps:

[0056] Step 301: Collect the submodule voltage data of any bridge arm in the MMC converter, and calculate the full-half bridge voltage imbalance of the bridge arm based on the submodule voltage data.

[0057] The embodiments of this invention mainly improve upon existing circulating current suppression controllers. In practical applications, the voltage bias of the full-bridge submodule can be balanced simply by calculating and adjusting the command values ​​according to different operating conditions.

[0058] For example, Figure 4 This paper illustrates a circulating flow suppression controller that is currently widely used in flexible DC converter valves. Figure 4 middle, This refers to the current in the upper arm of the three-phase bridge. This refers to the current in the lower arm of the three-phase bridge. and The control reference value for the secondary circulation is generally set to 0; The angle of the grid-side voltage vector; and All are transformation matrices; and These are the d-axis and q-axis components of the circulating current in the bridge arm. Through the control action of the PI controller, the circulating current in the bridge arm is controlled to its reference value, i.e., 0.

[0059] The control method provided in this embodiment of the invention only needs to determine the imbalance of the capacitor voltage and calculate the corresponding result based on the current state. and This achieves a balance in the voltage bias of the full-bridge submodules. Compared to other control methods, it is easier to implement in engineering.

[0060] First, the voltage values ​​of the full-bridge submodules and half-bridge submodules in the bridge arm are collected, and their average values ​​are calculated. If the voltage imbalance between the two (i.e., the full-to-half-bridge voltage imbalance of the bridge arm) exceeds 10%, the circulating current injection value is calculated and adjusted using the method provided in this embodiment of the invention.

[0061] Here, the imbalance refers to the ratio of the absolute value of the difference between the average value of the full-bridge submodule and the average value of the half-bridge submodule of the bridge arm at the current moment, to the average value of all submodules of the bridge arm (i.e., the average value of the voltage of all modules in a bridge arm, including the full-bridge and half-bridge), expressed as a percentage.

[0062] In some embodiments, the submodule voltage data may include the voltages of each full-bridge submodule and each half-bridge submodule in any arm of the MMC converter. In a specific implementation, calculating the full-to-half-bridge voltage imbalance of the arm based on the submodule voltage data can be achieved by: calculating the overall average voltage based on the voltages of all submodules in the arm; calculating the average voltage of the full-bridge submodules based on the voltages of each full-bridge submodule; calculating the average voltage of the half-bridge submodules based on the voltages of each half-bridge submodule; and calculating the full-to-half-bridge voltage imbalance of the arm based on the overall average voltage, the average voltage of the full-bridge submodules, and the average voltage of the half-bridge submodules.

[0063] Furthermore, when the voltage imbalance between the full-bridge and half-bridge submodules in the bridge arm is less than or equal to 10%, it can be controlled using conventional methods. For example, a dual-loop voltage and current control plus a circulating current suppression loop can be used, and the obtained value can be fed into NLM modulation (Nearest Level Modulation). The difference between the technical solution provided in this invention and current methods is that when the voltage imbalance between the full-bridge submodule and the half-bridge submodule in the bridge arm exceeds a certain threshold (e.g., 10%), the circulating current suppression loop is modified so that its reference value is the value calculated based on the method provided in this invention.

[0064] Step 302: When the full-bridge voltage imbalance exceeds a preset threshold, obtain operating data and calculate the power factor angle and the voltage deviation angle between the valve side voltage and the grid side voltage based on the operating data;

[0065] In some embodiments, operating data may include the current output active power of the MMC converter, the output reactive power, the rated phase voltage on the secondary side of the transformer, the effective value of the phase current on the valve side of the MMC converter, and the equivalent connection reactance between the MMC converter and the AC grid.

[0066] Assume that the current MMC converter output active and reactive power are respectively and (Output power is in the positive direction) and The value is an absolute value); the rated value of the secondary phase voltage of the transformer is... The effective value of the phase current on the MMC valve side is The power factor angle on the MMC valve side is... The deviation angle between the MMC valve-side voltage and the grid-side voltage is... The equivalent connection reactance between the MMC and the AC grid, including the sum of the line reactance, transformer leakage reactance, and bridge arm reactance between the AC grid connection point and the MMC, is: .

[0067] In the specific implementation, the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage are calculated based on the operating data, which can be:

[0068] First, based on the output active power and output reactive power, the power factor angle on the valve side of the MMC converter is calculated. The formula for calculating the power factor angle is shown below:

[0069]

[0070] in, Indicates the power factor angle; Indicates the output active power; This indicates the output reactive power.

[0071] Next, based on the power factor angle, and combining the rated phase voltage, effective phase current, and equivalent connection reactance, the voltage deviation angle between the valve-side voltage of the MMC converter and the AC grid-side voltage is calculated. The formula for calculating the voltage deviation angle is shown below:

[0072]

[0073] in, Indicates the voltage deviation angle; Indicates the rated value of the phase voltage; Indicates the effective value of the phase current; This represents the equivalent connection reactance.

[0074] Step 303: Calculate the control reference value of the secondary circulating current based on the power factor angle and the voltage deviation angle;

[0075] In some embodiments, the control reference value of the secondary circulating current is calculated based on the power factor angle and the voltage deviation angle. Specifically, the control reference value of the secondary circulating current can be calculated based on the different directions of the output active power and the output reactive power, the power factor angle and the voltage deviation angle, and in combination with the preset injection circulating current ratio.

[0076] Based on the output active power With output reactive power In different directions, assuming the proportion of injected circulation is... (Typical value can be 0.3, a reference value in a per-unit control system). and The calculation methods for the different values ​​are shown in Table 1 below:

[0077] Table 1: Calculation methods for secondary circulation control reference values ​​under different scenarios

[0078]

[0079] Referring to Table 1, the direction of power flow out of the AC side of the converter is defined as the positive direction, i.e., active power in the inverter state is positive, and active power in the rectification state is negative. Reactive power output is positive, and reactive power absorption is negative. Different control reference values ​​can be obtained based on the different directions of active and reactive power, according to the calculation formulas provided in Table 1.

[0080] Step 304: Perform circulating current suppression based on the control reference value to balance the voltage bias of the full-bridge submodule in the bridge arm.

[0081] When the control reference value of the secondary circulation is obtained through calculation and Then, based on the control reference value and Circulating current suppression is performed to balance the voltage bias of the full-bridge submodules in the bridge arm. Combined with... Figure 4 Specifically, this process can be based on control reference values. and The modulation voltage of the secondary circulating current is obtained through circulating current suppression loop control. According to the modulation voltage Voltage modulation is applied to the full-bridge submodules in the bridge arm to achieve voltage bias balance of the full-bridge submodules.

[0082] In this embodiment of the invention, a control method for improving the DC voltage bias of a full-bridge submodule using secondary circulating current injection is proposed. First, submodule voltage data of any arm in the MMC converter is collected, and the full-to-half-bridge voltage imbalance of the arm is calculated based on the submodule voltage data. This allows for the calculation of voltage imbalance based on the arm submodule voltage data, measuring the voltage difference between the full-bridge and half-bridge submodules in the current arm. When the full-to-half-bridge voltage imbalance exceeds a preset threshold, operating data is acquired, and the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage are calculated based on the operating data. Thus, when the voltage difference between the full-bridge and half-bridge submodules is large, a valuable evaluation index can be calculated based on the current operating data, providing an effective data basis for subsequent control reference value calculations. Next, based on the power factor angle and voltage deviation angle, a control reference value for the secondary circulating current is calculated; circulating current suppression is then performed based on the control reference value to balance the voltage bias of the full-bridge submodules in the arm. By injecting a secondary circulating current, the negative voltage range of the bridge arm voltage is reduced, allowing more charging time for the full-bridge submodule. This avoids excessive DC bias in the full-bridge submodule and achieves voltage balance with the half-bridge submodule. Furthermore, the technical solution provided by this invention does not require additional additions or modifications to existing circulating current suppressors. Voltage bias balance of the full-bridge submodule can be achieved simply by calculating and adjusting the command value according to different operating conditions, making it more suitable for engineering implementation.

[0083] For better explanation, refer to Figure 5 This diagram illustrates the overall flow of a full-bridge submodule voltage bias balance control method provided by an embodiment of the present invention. It should be noted that this embodiment only provides a brief description of the general flow of the full-bridge submodule voltage bias balance control. The specific implementation process of each step can be understood by referring to the relevant content in the foregoing embodiments, and will not be elaborated here. It is understood that the present invention does not impose any limitations on this.

[0084] Step 501: Collect the submodule voltage data of any arm in the MMC converter, and calculate the full-half bridge voltage imbalance of the arm based on the submodule voltage data.

[0085] Step 502: When the full-half bridge voltage imbalance exceeds 10%, acquire the operating data and calculate the power factor angle on the valve side of the MMC converter based on the operating data;

[0086] Step 503: Based on the power factor angle and combined with the operating data, calculate the voltage deviation angle between the valve-side voltage of the MMC converter and the AC grid-side voltage;

[0087] Step 504: Based on the different directions of the output active power and output reactive power, and taking into account the power factor angle and voltage deviation angle, and in conjunction with the preset injection circulating current ratio, calculate the control reference value of the secondary circulating current.

[0088] Step 505: Based on the control reference value, the modulation voltage of the secondary circulating current is obtained through the circulating current suppression loop control, and the voltage of the full-bridge submodule in the bridge arm is modulated according to the modulation voltage to achieve voltage bias balance of the full-bridge submodule.

[0089] Reference Figure 6 The diagram illustrates a structural block diagram of a full-bridge submodule voltage bias balance control device provided in an embodiment of the present invention, which may specifically include:

[0090] The voltage imbalance calculation unit 601 is used to collect the submodule voltage data of any bridge arm in the MMC converter, and calculate the full-half bridge voltage imbalance of the bridge arm based on the submodule voltage data.

[0091] Angle calculation unit 602 is used to acquire operating data when the full-half-bridge voltage imbalance exceeds a preset threshold, and to calculate the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage based on the operating data.

[0092] The control reference value calculation unit 603 is used to calculate the control reference value of the secondary circulating current based on the power factor angle and the voltage deviation angle.

[0093] The circulating current suppression unit 604 is used to suppress circulating current according to the control reference value in order to balance the voltage bias of the full-bridge submodule in the bridge arm.

[0094] In one optional embodiment, the submodule voltage data includes the voltage of each full-bridge submodule and the voltage of each half-bridge submodule in the bridge arm; the voltage imbalance calculation unit 601 includes:

[0095] The overall average voltage calculation unit is used to calculate the overall average voltage based on the voltages of all sub-modules in the bridge arm.

[0096] The submodule average voltage calculation unit is used to calculate the average voltage of the full-bridge submodule based on the voltage of each full-bridge submodule, and to calculate the average voltage of the half-bridge submodule based on the voltage of each half-bridge submodule.

[0097] The full-half-bridge voltage imbalance calculation subunit is used to calculate the full-half-bridge voltage imbalance of the bridge arm based on the overall average voltage, the average voltage of the full-bridge submodule, and the average voltage of the half-bridge submodule.

[0098] In one optional embodiment, the operating data includes the current output active power and output reactive power of the MMC converter, the rated phase voltage on the secondary side of the transformer, the effective value of the phase current on the valve side of the MMC converter, and the equivalent connection reactance between the MMC converter and the AC grid; the angle calculation unit 602 includes:

[0099] The power factor angle calculation unit is used to calculate the power factor angle of the MMC converter valve side based on the output active power and the output reactive power.

[0100] The voltage deviation angle calculation unit is used to calculate the voltage deviation angle between the valve-side voltage of the MMC converter and the AC grid-side voltage based on the power factor angle, combined with the rated value of the phase voltage, the effective value of the phase current and the equivalent connection reactance.

[0101] In one alternative embodiment, the formula for calculating the power factor angle is as follows:

[0102]

[0103] in, Indicates the power factor angle; Indicates the output active power; This indicates the output reactive power.

[0104] In one alternative embodiment, the voltage deviation angle is calculated as follows:

[0105]

[0106] in, Indicates the voltage deviation angle; Indicates the rated value of the phase voltage; Indicates the effective value of the phase current; This represents the equivalent connection reactance.

[0107] In one optional embodiment, the control reference value calculation unit 603 is specifically used for:

[0108] Based on the different directions of the output active power and the output reactive power, and using the power factor angle and the voltage deviation angle, along with the preset injection circulating current ratio, the control reference value of the secondary circulating current is calculated.

[0109] In one alternative embodiment, the circulating suppression unit 604 includes:

[0110] A modulation voltage generation unit is used to obtain the modulation voltage of the secondary circulating current based on the control reference value through circulating current suppression loop control;

[0111] A voltage modulation unit is used to modulate the voltage of the full-bridge submodule in the bridge arm according to the modulation voltage, so as to achieve voltage bias balance of the full-bridge submodule.

[0112] As the device embodiment is basically similar to the method embodiment, it is described in a relatively simple way. For relevant details, please refer to the description of the method embodiment above.

[0113] This invention also provides an electronic device, which includes a processor and a memory:

[0114] The memory is used to store program code and transfer the program code to the processor;

[0115] The processor is used to execute the full-bridge submodule voltage bias balance control method of any embodiment of the present invention according to the instructions in the program code.

[0116] This invention also provides a computer-readable storage medium for storing program code for executing the full-bridge submodule voltage bias balance control method of any embodiment of the invention.

[0117] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0118] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0119] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0120] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0121] If the integrated unit is implemented as 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 the present invention, in essence, or the part that contributes to the prior art, or all or part of the 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 to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0122] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for voltage bias balance control of a full-bridge submodule, characterized in that, include: Collect submodule voltage data of any arm in the MMC converter, and calculate the full-half-bridge voltage imbalance of the arm based on the submodule voltage data. When the full-bridge voltage imbalance exceeds a preset threshold, operating data is acquired, and the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage are calculated based on the operating data. Based on the power factor angle and the voltage deviation angle, calculate the control reference value of the secondary circulating current; Circulating current suppression is performed based on the control reference value to balance the voltage bias of the full-bridge submodules in the bridge arm.

2. The full-bridge submodule voltage bias balance control method according to claim 1, characterized in that, The submodule voltage data includes the voltage of each full-bridge submodule and the voltage of each half-bridge submodule in the bridge arm; The step of calculating the full-to-half bridge voltage imbalance of the bridge arm based on the submodule voltage data includes: Calculate the overall average voltage based on the voltage of all sub-modules in the bridge arm; Calculate the average voltage of the full-bridge submodule based on the voltage of each full-bridge submodule, and calculate the average voltage of the half-bridge submodule based on the voltage of each half-bridge submodule. Based on the overall average voltage, the average voltage of the full-bridge submodule, and the average voltage of the half-bridge submodule, the full-to-half-bridge voltage imbalance of the bridge arm is calculated.

3. The full-bridge submodule voltage bias balance control method according to claim 1, characterized in that, The operating data includes the current output active power and reactive power of the MMC converter, the rated phase voltage on the secondary side of the transformer, the effective value of the phase current on the valve side of the MMC converter, and the equivalent connection reactance between the MMC converter and the AC grid; the calculation of the power factor angle and the voltage deviation angle between the valve side voltage and the grid side voltage based on the operating data includes: Based on the output active power and the output reactive power, calculate the power factor angle on the valve side of the MMC converter; Based on the power factor angle, combined with the rated phase voltage, the effective value of the phase current, and the equivalent connection reactance, the voltage deviation angle between the valve-side voltage and the AC grid-side voltage of the MMC converter is calculated.

4. The full-bridge submodule voltage bias balance control method according to claim 3, characterized in that, The formula for calculating the power factor angle is as follows: in, Indicates the power factor angle; Indicates the output active power; This indicates the output reactive power.

5. The full-bridge submodule voltage bias balance control method according to claim 4, characterized in that, The formula for calculating the voltage deviation angle is as follows: in, Indicates the voltage deviation angle; Indicates the rated value of the phase voltage; Indicates the effective value of the phase current; This represents the equivalent connection reactance.

6. The full-bridge submodule voltage bias balance control method according to any one of claims 3 to 5, characterized in that, The calculation of the control reference value for the secondary circulating current based on the power factor angle and the voltage deviation angle includes: Based on the different directions of the output active power and the output reactive power, and using the power factor angle and the voltage deviation angle, along with the preset injection circulating current ratio, the control reference value of the secondary circulating current is calculated.

7. The full-bridge submodule voltage bias balance control method according to claim 1, characterized in that, The step of suppressing circulating current according to the control reference value to balance the voltage bias of the full-bridge submodule in the bridge arm includes: Based on the control reference value, the modulation voltage of the secondary circulating current is obtained through circulating current suppression loop control; The voltage of the full-bridge submodule in the bridge arm is modulated according to the modulation voltage to achieve voltage bias balance of the full-bridge submodule.

8. A full-bridge submodule voltage bias balance control device, characterized in that, include: The voltage imbalance calculation unit is used to collect the submodule voltage data of any arm in the MMC converter, and calculate the full-half-bridge voltage imbalance of the arm based on the submodule voltage data. An angle calculation unit is used to acquire operating data when the full-half-bridge voltage imbalance exceeds a preset threshold, and to calculate the power factor angle and the voltage deviation angle between the valve-side voltage and the grid-side voltage based on the operating data. The control reference value calculation unit is used to calculate the control reference value of the secondary circulating current based on the power factor angle and the voltage deviation angle. A circulating current suppression unit is used to suppress circulating current according to the control reference value in order to balance the voltage bias of the full-bridge submodule in the bridge arm.

9. An electronic device, characterized in that, The device includes a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the full-bridge submodule voltage bias balance control method according to any one of claims 1-7, based on 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 code for executing the full-bridge submodule voltage bias balance control method according to any one of claims 1-7.

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