A method and system for suppressing overvoltage of submodules of a modular multilevel converter

Abstract

The present invention discloses a method and system for suppressing overvoltage of submodules of a modular multilevel converter, and relates to the field of direct current transmission technology. The submodule overvoltage suppression method performs dual-loop decoupling control and three-phase coordinate transformation based on the operating data of the modular multilevel converter to generate a three-phase modulation ratio; when no submodule overvoltage occurs, the modulation wave of the bridge arm in the modular multilevel converter is modulated using the three-phase modulation ratio to generate bridge arm modulation data; when a submodule overvoltage occurs, the modulation wave adjustment coefficient is calculated based on the submodule operating voltage to generate the modulation wave adjustment coefficient; the modulation wave of the bridge arm in the modular multilevel converter is modulated using the three-phase modulation ratio and the modulation wave adjustment coefficient, and the submodule in the modular multilevel converter is suppressed from overvoltage by the modulation signal. The present invention can timely put the corresponding submodule into operation without control switching, thereby achieving submodule overvoltage suppression, and has good stability while achieving a control effect.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current transmission, and in particular to a method and system for suppressing overvoltage of submodules of a modular multi-level converter. Background Art

[0002] Flexible DC transmission technology is a long-distance, high-capacity DC transmission method. Particularly for centralized renewable energy transmission in the desertified region, flexible DC transmission, due to its high controllability, has become one of the most effective technologies. As a sending-end converter, a flexible DC converter provides a stable access voltage and required reactive power for renewable energy stations. As a receiving-end converter, a flexible DC converter mitigates commutation failures associated with conventional DC. A modular multilevel converter (MMC) is a topology for flexible DC converters. Currently, half-bridge MMCs and full-half hybrid MMCs are the two mainstream types of DC transmission.

[0003] Submodule overvoltage in a modular multilevel converter (MMC) occurs when a fault occurs on the AC or DC side of the MMC, causing a sudden interruption in power transmission, resulting in the complete flow of energy into the MMC's submodules. Submodule overvoltage can cause the converter to lock out, leading to fault ride-through failure and, in severe cases, threatening system safety, necessitating control. Existing methods for suppressing submodule overvoltage in modular multilevel converters have high hardware costs, cumbersome calculations for switching control strategies during faults, and are prone to control instability, resulting in poor submodule overvoltage suppression in modular multilevel converters. Summary of the Invention

[0004] The present invention provides a method and system for suppressing overvoltage of submodules in a modular multi-level converter, which solves the technical problems that the existing submodule overvoltage suppression method adopts a cumbersome calculation method for switching the control strategy and is prone to control instability, resulting in poor overvoltage suppression effect of the submodule.

[0005] The present invention provides a method for suppressing overvoltage of submodules of a modular multi-level converter, comprising:

[0006] Acquiring operating data of a modular multilevel converter and operating voltages of multiple submodules, performing dual-loop decoupling control and three-phase coordinate transformation based on the operating data, and generating a three-phase modulation ratio;

[0007] When no submodule overvoltage occurs in the modular multilevel converter, modulating the modulation wave of the bridge arm in the modular multilevel converter using the three-phase modulation ratio to generate bridge arm modulation data;

[0008] When a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the operating voltage of the submodule to generate the modulation wave adjustment coefficient;

[0009] The modulation wave of the bridge arm in the modular multilevel converter is modulated using the three-phase modulation ratio and the modulation wave adjustment coefficient, and overvoltage suppression is performed on the submodules in the modular multilevel converter through the modulation signal.

[0010] Optionally, the step of performing dual-loop decoupling control and three-phase coordinate transformation based on the operating data to generate a three-phase modulation ratio includes:

[0011] Performing active outer loop control based on the active outer loop data in the operating data to generate an initial d-axis current loop reference value;

[0012] The initial d-axis current loop reference value is used to perform active inner loop control and generate a target d-axis current loop reference value;

[0013] Performing reactive outer loop control based on reactive outer loop data in the operating data to generate an initial q-axis current loop reference value;

[0014] The initial q-axis current loop reference value is used to perform reactive inner loop control and generate a target q-axis current loop reference value;

[0015] The target d-axis current loop reference value and the target q-axis current loop reference value are used to perform three-phase coordinate transformation to generate a three-phase modulation ratio.

[0016] Optionally, the active outer loop data includes a measured value of a DC side current, a measured value of a DC side voltage, and a measured value of an AC side active power; and the step of performing active outer loop control based on the active outer loop data in the operating data to generate an initial d-axis current loop reference value includes:

[0017] Determining whether the system demand data corresponding to the active outer loop data is first preset system demand data;

[0018] If the system requirement data is the first preset system requirement data, calculating a multiplication value between the DC side current and a first preset resistance adjustment coefficient to generate a DC side voltage;

[0019] Subtracting the DC link voltage from a DC link voltage reference value corresponding to the DC link voltage actual value to generate a first DC link voltage difference value;

[0020] Subtracting the first DC link voltage difference from the DC link voltage measured value to generate a second DC link voltage difference;

[0021] Inputting the second DC side voltage difference into a first PI controller for parameter adjustment to generate a first initial d-axis current loop reference value;

[0022] If the system demand data is not the first preset system demand data, subtracting the AC side active power reference value corresponding to the AC side active power actual measurement value from the AC side active power actual measurement value to generate a first AC side power difference value;

[0023] The first AC side power difference is input into a second PI controller for parameter adjustment to generate a second initial d-axis current loop reference value.

[0024] Optionally, the reactive outer loop data includes an AC side current, an AC side voltage measured value, and an AC side reactive power measured value; and the step of performing reactive outer loop control based on the reactive outer loop data in the operating data to generate an initial q-axis current loop reference value includes:

[0025] Determining whether the system demand data corresponding to the reactive outer loop data is second preset system demand data;

[0026] If the system demand data is the second preset system demand data, calculating the product of the AC side current and the second preset resistance adjustment coefficient to generate the AC side voltage;

[0027] Subtracting the AC side voltage from the AC side voltage reference value corresponding to the AC side voltage measured value to generate a first AC side voltage difference;

[0028] Subtracting the first AC side voltage difference from the AC side voltage measured value to generate a second AC side voltage difference;

[0029] Inputting the second AC side voltage difference into a third PI controller for parameter adjustment to generate a first initial q-axis current loop reference value;

[0030] If the system demand data is not the second preset system demand data, subtracting the AC side reactive power reference value corresponding to the AC side reactive power actual measurement value from the AC side reactive power actual measurement value to generate a second AC side power difference value;

[0031] The second AC side power difference is input into a fourth PI controller for parameter adjustment to generate a second initial q-axis current loop reference value.

[0032] Optionally, when a submodule overvoltage occurs in the modular multilevel converter, the step of calculating a modulation wave adjustment coefficient based on the submodule operating voltage to generate the modulation wave adjustment coefficient includes:

[0033] Calculating an average value of the operating voltages of all the submodules to generate an average submodule voltage value;

[0034] Subtracting a submodule voltage average value reference value corresponding to the submodule voltage average value from the submodule voltage average value to generate an average value difference;

[0035] Determining whether the submodule type corresponding to the submodule operating voltage is a preset type;

[0036] If the submodule type is a preset type, when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated according to the average value difference and the DC modulation degree corresponding to the average value of the submodule voltage to generate a first modulation wave adjustment coefficient;

[0037] If the submodule type is not a preset type, when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated according to the average value difference and the DC current control loop output value corresponding to the submodule voltage average value to generate a second modulation wave adjustment coefficient.

[0038] Optionally, when a submodule overvoltage occurs in the modular multilevel converter, the step of calculating a modulation wave adjustment coefficient according to the average value difference and a DC modulation degree corresponding to the average value of the submodule voltage to generate a first modulation wave adjustment coefficient includes:

[0039] Inputting the mean value difference into a third PI controller for parameter adjustment to generate adjustment parameters of the first submodule;

[0040] When a submodule overvoltage occurs in the modular multilevel converter, a sum of the first submodule adjustment parameter and the DC modulation index corresponding to the average value of the submodule voltage is calculated to generate a first modulation wave adjustment coefficient.

[0041] Optionally, when a submodule overvoltage occurs in the modular multilevel converter, the step of calculating a modulation wave adjustment coefficient according to the average value difference and a DC current control loop output value corresponding to the submodule voltage average value to generate a second modulation wave adjustment coefficient includes:

[0042] Inputting the DC current control loop output value corresponding to the average voltage value of the submodule into a fourth PI controller for parameter adjustment and amplitude limiting processing to generate DC control data;

[0043] Calculate the ratio of the submodule voltage average value reference value corresponding to the submodule voltage average value and the submodule voltage average value difference to generate a second submodule adjustment parameter;

[0044] When a submodule overvoltage occurs in the modular multilevel converter, a sum of the second submodule adjustment parameter and the DC control data is calculated to generate a second modulation wave adjustment coefficient.

[0045] The present invention also provides a submodule overvoltage suppression system for a modular multilevel converter, comprising:

[0046] A three-phase modulation ratio generation module is used to obtain operating data of the modular multilevel converter and operating voltages of multiple submodules, perform dual-loop decoupling control and three-phase coordinate transformation based on the operating data, and generate a three-phase modulation ratio;

[0047] a bridge arm modulation data generating module, configured to modulate the modulation wave of the bridge arm in the modular multilevel converter using the three-phase modulation ratio to generate bridge arm modulation data when no submodule overvoltage occurs in the modular multilevel converter;

[0048] a modulation wave adjustment coefficient generating module, configured to calculate the modulation wave adjustment coefficient based on the operating voltage of the submodule when a submodule overvoltage occurs in the modular multilevel converter, and generate the modulation wave adjustment coefficient;

[0049] The submodule overvoltage suppression module is used to modulate the modulation wave of the bridge arm in the modular multilevel converter by using the three-phase modulation ratio and the modulation wave adjustment coefficient, and suppress overvoltage of the submodule in the modular multilevel converter through the modulation signal.

[0050] The present invention also provides an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of implementing any of the above-mentioned methods for suppressing overvoltage of a sub-module of a modular multilevel converter.

[0051] The present invention also provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed, the method for suppressing overvoltage of a submodule of a modular multi-level converter as described above is implemented.

[0052] It can be seen from the above technical solutions that the present invention has the following advantages:

[0053] The present invention calculates the three-phase modulation ratio and the modulation wave adjustment coefficient. When a submodule overvoltage occurs in a modular multi-level converter, the three-phase modulation ratio and the modulation wave adjustment coefficient can be promptly transferred to the modulation wave, so that more submodules are put into the modulation link, thereby reducing the average value of the voltage of all submodules. The present invention optimizes the existing voltage reduction method by adopting the control strategy of the three-phase modulation ratio and the modulation wave adjustment coefficient to suppress the overvoltage of the submodule, and has better economy and feasibility. Without the need for control switching, the corresponding submodule can be put into use in a timely manner to achieve submodule overvoltage suppression, and the stability is good while achieving the control effect. It solves the technical problem that the calculation method used by the existing submodule overvoltage suppression method to switch the control strategy is cumbersome and prone to control instability, resulting in poor submodule overvoltage suppression effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 A flowchart of the steps of the method for suppressing overvoltage of submodules of a modular multilevel converter provided in the first embodiment of the present invention;

[0056] Figure 2 A flowchart of the steps of a method for suppressing overvoltage of submodules of a modular multilevel converter provided in the second embodiment of the present invention;

[0057] Figure 3 A control strategy diagram of a half-bridge MMC submodule overvoltage suppression method provided in the second embodiment of the present invention;

[0058] Figure 4 A control strategy diagram of a full-half-bridge hybrid MMC submodule overvoltage suppression method provided in the second embodiment of the present invention;

[0059] Figure 5 A structural block diagram of a sub-module overvoltage suppression system for a modular multi-level converter provided in a third embodiment of the present invention;

[0060] Figure 6 This is a structural block diagram of an electronic device provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0061] Application No. 202310667896.8 discloses a method for suppressing freewheeling overvoltage in a flexible DC transmission system and its submodules. The method proposes that after a fault, DC energy dissipation devices already configured in the control system continue to operate to absorb redundant power and reduce the overvoltage level in the submodules of the faulty converter valve. This method utilizes hardware, which is expensive due to the hardware cost.

[0062] Application number 202211625691.5 discloses a new energy island power grid transmission system optimization control method, which switches the outer loop in the event of a fault to achieve overvoltage control. This patent requires switching the control strategy in the event of a fault. The switching method first requires running two parallel control loops simultaneously, which wastes computing resources. At the same time, the switching method has high requirements for the parameter design of the control loop and is prone to control instability. The actual control system is relatively complex.

[0063] In order to solve the above problems, an embodiment of the present invention provides a sub-module overvoltage suppression method and system for a modular multi-level converter, which is used to solve the technical problems that the existing sub-module overvoltage suppression method uses a cumbersome calculation method to switch the control strategy, is prone to control instability, and results in poor sub-module overvoltage suppression effect.

[0064] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0065] Example 1

[0066] See also Figure 1 , Figure 1 This is a flowchart of the steps of the method for suppressing overvoltage of submodules of a modular multilevel converter provided in the first embodiment of the present invention.

[0067] A method for suppressing overvoltage of a submodule of a modular multi-level converter provided in Example 1 of the present invention includes:

[0068] Step 101: Acquire operating data of a modular multilevel converter and operating voltages of multiple submodules, perform dual-loop decoupling control and three-phase coordinate transformation based on the operating data, and generate a three-phase modulation ratio.

[0069] In an embodiment of the present invention, operating data and submodule operating voltages corresponding to a modular multilevel converter are obtained. The operating data includes active operating data and reactive operating data. Active operating data includes, for example, the DC side current, the DC side voltage measured value, and the AC side active power measured value. Reactive operating data includes, for example, the AC side current, the AC side voltage measured value, and the AC side reactive power measured value. By acquiring the operating data and operating voltages of multiple submodules of the modular multilevel converter in real time, and using these data to perform dual-loop decoupling control and calculate the three-phase modulation ratio and modulation wave adjustment coefficient, when a submodule overvoltage occurs in the modular multilevel converter, it can be quickly transmitted to the modulation wave, allowing the modulation link to engage more submodules, thereby reducing the average voltage of all submodules.

[0070] Specifically, active power outer loop control is performed based on active power outer loop data in the operating data to generate an initial d-axis current loop reference value. Active power inner loop control is performed using the initial d-axis current loop reference value to generate a target d-axis current loop reference value. Reactive power outer loop control is performed based on reactive power outer loop data in the operating data to generate an initial q-axis current loop reference value. Reactive power inner loop control is performed using the initial q-axis current loop reference value to generate a target q-axis current loop reference value. Three-phase coordinate transformation is performed using the target d-axis current loop reference value and the target q-axis current loop reference value to generate a three-phase modulation ratio.

[0071] Step 102: When no submodule overvoltage occurs in the modular multilevel converter, a modulation wave of a bridge arm in the modular multilevel converter is modulated using a three-phase modulation ratio to generate bridge arm modulation data.

[0072] In the embodiment of the present invention, when the modular multilevel converter does not have a submodule overvoltage, the three-phase modulation ratio calculated by the dual-loop decoupling control method can be directly used as The modulation wave is sent to the bridge arm for modulation to generate the bridge arm modulation data. When the modular multilevel converter has a submodule overvoltage, the modulation wave adjustment coefficient corresponding to the overvoltage of the submodule needs to be superimposed when sending the modulation wave to the bridge arm. .

[0073] Step 103: When a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the submodule operating voltage to generate the modulation wave adjustment coefficient.

[0074] In an embodiment of the present invention, an average value is calculated using the operating voltages of all submodules to generate an average value of the submodule voltages. A submodule voltage average value reference value corresponding to the submodule voltage average value is subtracted from the submodule voltage average value to generate an average value difference. It is determined whether the submodule type corresponding to the submodule operating voltage is a preset type. If the submodule type is a preset type, then when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the average value difference and the DC modulation index corresponding to the submodule voltage average value to generate a first modulation wave adjustment coefficient. If the submodule type is not a preset type, then when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the average value difference and the DC current control loop output value corresponding to the submodule voltage average value to generate a second modulation wave adjustment coefficient.

[0075] Step 104 : modulate the modulation wave of the bridge arm in the modular multilevel converter using the three-phase modulation ratio and the modulation wave adjustment coefficient, and suppress overvoltage of the submodule in the modular multilevel converter through the modulation signal.

[0076] In an embodiment of the present invention, when a submodule overvoltage occurs in a modular multilevel converter, the control loop transmits the calculated modulation wave adjustment coefficient to the modulation link, and modulates the modulation wave of the corresponding bridge arm of the modular multilevel converter in combination with the three-phase modulation ratio, determines the number of submodules that need to be put into operation, generates a modulation signal, and uses the modulation signal to trigger and control the corresponding submodules of the modular multilevel converter. This allows the modulation link to promptly put more submodules into operation, thereby reducing the average voltage of all submodules and completing submodule overvoltage suppression.

[0077] In an embodiment of the present invention, operating data of a modular multilevel converter and the operating voltages of multiple submodules are obtained. Dual-loop decoupling control and three-phase coordinate transformation are performed based on the operating data to generate a three-phase modulation ratio. When no submodule overvoltage occurs in the modular multilevel converter, the modulation wave of the bridge arm within the modular multilevel converter is modulated using the three-phase modulation ratio to generate bridge arm modulation data. When a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the submodule operating voltage to generate the modulation wave adjustment coefficient. The modulation wave of the bridge arm within the modular multilevel converter is modulated using the three-phase modulation ratio and the modulation wave adjustment coefficient, and overvoltage suppression is performed on the submodules within the modular multilevel converter using the modulation signal. The present invention utilizes a voltage reduction method with optimized control strategy, resulting in improved cost-effectiveness and feasibility. The corresponding submodules can be put into operation in a timely manner to achieve submodule overvoltage suppression, while maintaining good control stability. This method addresses the technical issues of existing submodule overvoltage suppression methods, which employ cumbersome calculation methods for switching control strategies and are prone to control instability, resulting in poor submodule overvoltage suppression.

[0078] Example 2

[0079] See also Figure 2 , Figure 2 This is a flowchart of the steps of a method for suppressing overvoltage of submodules of a modular multilevel converter provided in the second embodiment of the present invention.

[0080] Another method for suppressing overvoltage of a submodule of a modular multilevel converter provided in Example 2 of the present invention includes:

[0081] Step 201: Acquire operating data of a modular multilevel converter and operating voltages of multiple submodules, perform dual-loop decoupling control and three-phase coordinate transformation based on the operating data, and generate a three-phase modulation ratio.

[0082] Furthermore, step S202 may include the following sub-steps S11-S15:

[0083] S11 . Perform active outer loop control based on active outer loop data in the operating data to generate an initial d-axis current loop reference value.

[0084] S12. Use the initial d-axis current loop reference value to perform active inner loop control to generate a target d-axis current loop reference value.

[0085] S13. Perform reactive outer loop control based on reactive outer loop data in the operating data to generate an initial q-axis current loop reference value.

[0086] S14: Use the initial q-axis current loop reference value to perform reactive inner loop control to generate a target q-axis current loop reference value.

[0087] S15 , performing three-phase coordinate transformation using the target d-axis current loop reference value and the target q-axis current loop reference value to generate a three-phase modulation ratio.

[0088] In an embodiment of the present invention, the active outer loop data is first used to perform active outer loop control to generate an initial d-axis current loop reference value. The initial d-axis current loop reference value is then used to perform active inner loop control to obtain a target d-axis current loop reference value, wherein the active inner loop control can be any active inner loop control method in a conventional inner loop control link. Reactive outer loop control is first performed based on the reactive outer loop data in the operating data to generate an initial q-axis current loop reference value. The initial q-axis current loop reference value is then used to perform reactive inner loop control to obtain a target q-axis current loop reference value, wherein the reactive inner loop control can be any reactive inner loop control method in a conventional inner loop control link. Finally, the target d-axis current loop reference value and the target q-axis current loop reference value are compared. The three-phase modulation ratio is obtained by transformation .

[0089] Furthermore, the active outer loop data includes the measured values ​​of the DC side current, the DC side voltage, and the AC side active power. Step S11 may include the following sub-steps S111-S117:

[0090] S111 , determining whether the system demand data corresponding to the active outer loop data is the first preset system demand data; if so, executing step S112 ; if not, executing step S116 .

[0091] S112 : Calculate the product of the DC side current and the first preset resistance adjustment coefficient to generate a DC side voltage.

[0092] S113 . Subtract the DC link voltage from the DC link voltage reference value corresponding to the DC link voltage actual measurement value to generate a first DC link voltage difference value.

[0093] S114 , subtracting the first DC side voltage difference from the actually measured DC side voltage to generate a second DC side voltage difference.

[0094] S115 , inputting the second DC side voltage difference into the first PI controller for parameter adjustment to generate a first initial d-axis current loop reference value.

[0095] S116 . Subtract the AC side active power reference value corresponding to the AC side active power actual measurement value from the AC side active power actual measurement value to generate a first AC side power difference value.

[0096] S17 , inputting the first AC side power difference into a second PI controller for parameter adjustment to generate a second initial d-axis current loop reference value.

[0097] The first preset system demand data is that the active power outer loop control mode corresponding to the system demand data is DC voltage outer loop control.

[0098] In the embodiment of the present invention, Figure 3 and Figure 4 As shown, is the DC side current; R is the first preset resistance adjustment coefficient, and its value is set based on actual needs; is the measured value of DC side voltage; is the DC side voltage reference value; P is the measured value of the AC side active power of the MMC; The reference value of the active power on the AC side of the MMC; is the d-axis current loop reference value, which is also the value output by the active power / voltage outer loop; is the reference value of the q-axis current loop, which is also the output value of the reactive power / AC voltage outer loop. Due to its commonness, the reactive power / AC voltage outer loop is not drawn in the figure; is the average value of the submodule voltage measured value, that is, the average value of the submodule voltage; The reference value of the average submodule voltage is the average module voltage reference value; is the DC modulation index; is the modulation wave adjustment coefficient; is the three-phase modulation ratio; For the general Coordinate conversion to coordinate.

[0099] When the active outer loop control mode corresponding to the system demand data is the DC voltage outer loop control, that is, when the system demand data corresponding to the active outer loop data is the first preset system demand data, the active outer loop selects the DC voltage outer loop control. First, by calculating the DC side current The multiplication value between the first preset resistance adjustment coefficient R and the DC side voltage is generated. Then, the DC side voltage actual value is calculated. Corresponding DC side voltage reference value The difference between the DC side voltage and the DC side voltage is used to generate a first DC side voltage difference. Then, the first DC side voltage difference is calculated and the DC side voltage actual value is calculated. Finally, the second DC side voltage difference is input into the first PI controller for parameter adjustment to generate a first initial d-axis current loop reference value.

[0100] When the active outer loop control mode corresponding to the system demand data is active power control, that is, when the system demand data corresponding to the active outer loop data is not the first preset system demand data, the active outer loop selects active power control, and calculates the AC side active power reference value corresponding to the AC side active power measured value P The difference between the AC side active power measured value P and the AC side active power measured value P is used to generate a first AC side power difference value. Then, the first AC side power difference value is input into the second PI controller for parameter adjustment to generate a second initial d-axis current loop reference value.

[0101] Furthermore, the reactive outer loop data includes the AC side current, the AC side voltage measured value, and the AC side reactive power measured value. Step S13 may include the following sub-steps S132-S137:

[0102] S131 , determining whether the system demand data corresponding to the reactive outer loop data is the second preset system demand data; if so, executing step S132 ; if not, executing step S136 .

[0103] S132: Calculate the product of the AC side current and the second preset resistance adjustment coefficient to generate an AC side voltage.

[0104] S133 . Subtract the AC side voltage from the AC side voltage reference value corresponding to the AC side voltage actual measurement value to generate a first AC side voltage difference.

[0105] S134 . Subtract the first AC side voltage difference from the AC side voltage measured value to generate a second AC side voltage difference.

[0106] S135 , inputting the second AC side voltage difference into a third PI controller for parameter adjustment to generate a first initial q-axis current loop reference value.

[0107] S136 . Subtract the AC side reactive power reference value corresponding to the AC side reactive power actual measurement value from the AC side reactive power actual measurement value to generate a second AC side power difference value.

[0108] S137 : Input the second AC side power difference into the fourth PI controller for parameter adjustment to generate a second initial q-axis current loop reference value.

[0109] The second preset system demand data is that the reactive outer loop control mode corresponding to the system demand data is AC voltage control.

[0110] In the embodiment of the present invention, the active outer loop selects DC voltage outer loop control or active power control according to system requirements; the reactive outer loop selects reactive power control or AC voltage control according to system requirements (this part is in Figure 3 The active outer loop is obtained (The reference value of the d-axis current loop, which is also the value output by the active power / voltage outer loop) and the reactive outer loop are obtained (q-axis current loop reference value, also the value of reactive power / AC voltage outer loop output), through The coordinate transformation gives the three-phase modulation ratio .

[0111] When the reactive outer loop control mode corresponding to the system demand data is AC voltage outer loop control, that is, when the system demand data corresponding to the reactive outer loop data is the second preset system demand data, the reactive outer loop selects AC voltage control. First, by calculating the DC side current The DC side voltage is obtained by multiplying the AC side current by the first preset resistance adjustment coefficient R. Then, the AC side voltage is generated by multiplying the AC side current by the second preset resistance adjustment coefficient. Next, the AC side voltage is subtracted from the AC side voltage reference value corresponding to the measured AC side voltage to obtain a first AC side voltage difference. The first AC side voltage difference is then subtracted from the measured AC side voltage to obtain a second AC side voltage difference. Finally, the second AC side voltage difference is input into a third PI controller for parameter adjustment to obtain a first initial q-axis current loop reference value.

[0112] When the reactive outer loop control mode corresponding to the system demand data is reactive power control, that is, when the system demand data corresponding to the reactive outer loop data is not the first preset system demand data, the reactive outer loop selects reactive power control. A second AC side power difference is generated by subtracting an AC side reactive power reference value corresponding to the actual AC side reactive power value from the actual AC side reactive power value. This second AC side power difference is then input into a fourth PI controller for parameter adjustment to generate a second initial q-axis current loop reference value.

[0113] Step 202: When no submodule overvoltage occurs in the modular multilevel converter, a modulation wave of a bridge arm in the modular multilevel converter is modulated using a three-phase modulation ratio to generate bridge arm modulation data.

[0114] In the embodiment of the present invention, the specific implementation process of step 202 is similar to that of step 102 and will not be repeated here.

[0115] 203. Calculate the average value of the operating voltages of all submodules to generate an average submodule voltage value.

[0116] In the embodiment of the present invention, the average operating voltage of all submodules corresponding to the modular multilevel converter at the current moment is calculated to obtain the average submodule voltage of the modular multilevel converter at the current moment. .

[0117] 204 . Subtract the submodule voltage average value reference value corresponding to the submodule voltage average value from the submodule voltage average value to generate an average value difference.

[0118] In the embodiment of the present invention, the average value difference corresponding to the average submodule voltage is obtained by calculating the difference between the submodule voltage average value reference value corresponding to the average submodule voltage value and the average submodule voltage value.

[0119] 205. Determine whether the submodule type corresponding to the submodule operating voltage is a preset type. If so, execute step S206; if not, execute step S207.

[0120] In the embodiment of the present invention, the preset type refers to the type of the submodule corresponding to the half-bridge MMC submodule. , the average submodule voltage Corresponding submodule voltage average reference value The average voltage of the submodule Perform the difference calculation to obtain the average value difference. Then, according to the submodule type, determine the calculation method of the modulation wave adjustment coefficient when the submodule is overvoltage. If the submodule type corresponding to the submodule operating voltage is a half-bridge MMC submodule, that is, the preset type, then when the modular multilevel converter has a submodule overvoltage, according to the average value difference and the submodule voltage average value The modulation wave adjustment coefficient is calculated based on the corresponding DC modulation index to generate the first modulation wave adjustment coefficient. If the submodule type corresponding to the submodule operating voltage is a full-half-bridge hybrid MMC submodule, then when the modular multilevel converter has a submodule overvoltage, the average value difference and the submodule voltage average value are used. The modulation wave adjustment coefficient is calculated based on the corresponding DC current control loop output value to generate a second modulation wave adjustment coefficient.

[0121] 206. When a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated according to the average value difference and a DC modulation index corresponding to the submodule voltage average value to generate a first modulation wave adjustment coefficient.

[0122] Furthermore, step 206 may include the following sub-steps S21-S22:

[0123] S21 , inputting the average value difference into a third PI controller for parameter adjustment to generate adjustment parameters of the first submodule.

[0124] S22. When a submodule overvoltage occurs in the modular multilevel converter, calculate the sum of the first submodule adjustment parameter and the DC modulation index corresponding to the average value of the submodule voltage to generate a first modulation wave adjustment coefficient.

[0125] In the embodiment of the present invention, Figure 3 As shown in the figure, the dotted box part is the half-bridge MMC submodule control loop. and the average voltage of the submodule The difference is made through the third PI controller, and its value passes through a hysteresis loop (the value reaches a certain threshold before output is allowed, that is, the modular multilevel converter has a sub-module overvoltage), and is increased to the DC modulation index corresponding to the average value of the sub-module voltage. The first modulation wave adjustment coefficient is obtained The advantage of this approach is that the control loop within the dashed box can quickly transmit submodule overvoltage information to the modulation wave, allowing more submodules to be deployed in the modulation process, thereby reducing the average voltage of all submodules. The remaining parts outside the dashed line need to be replaced with a conventional fault ride-through strategy based on the actual fault conditions.

[0126] 207. When a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated according to the average value difference and a DC current control loop output value corresponding to the submodule voltage average value to generate a second modulation wave adjustment coefficient.

[0127] Furthermore, step 207 may include the following sub-steps S31-S33:

[0128] S31 , inputting the DC current control loop output value corresponding to the average submodule voltage into the fourth PI controller for parameter adjustment and amplitude limiting processing to generate DC control data.

[0129] S32 , performing a ratio calculation on a submodule voltage average value reference value corresponding to the submodule voltage average value and a submodule voltage average value difference to generate a second submodule adjustment parameter.

[0130] S33. When a submodule overvoltage occurs in the modular multilevel converter, a sum of the second submodule adjustment parameter and the DC control data is calculated to generate a second modulation wave adjustment coefficient.

[0131] In the embodiment of the present invention, Figure 4 As shown in the figure, the dotted box part is the full-half bridge hybrid MMC submodule control loop. The DC current control loop output value corresponding to the average voltage of the submodule is determined by the d-axis current loop reference value corresponding to the submodule. and DC side current The DC current control loop output value is input into the fourth PI controller for parameter adjustment and amplitude limiting processing to obtain DC control data. Then the submodule voltage average value reference value corresponding to the submodule voltage average value is calculated as a ratio with the difference between the submodule voltage average value to obtain the corresponding current value, i.e., the second submodule adjustment parameter. When a submodule overvoltage occurs in the modular multi-level converter, the hysteresis loop outputs the second submodule adjustment parameter, which is added to the DC control data obtained by inputting the DC current control loop output value corresponding to the submodule voltage average value into the fourth PI controller for parameter adjustment and amplitude limiting processing to obtain the second modulation wave adjustment coefficient. The advantage of this approach is that the control loop within the dashed box can quickly transmit submodule overvoltage information to the modulation wave, allowing more submodules to be deployed in the modulation process, thereby reducing the average voltage of all submodules. The remaining parts outside the dashed line need to be replaced with a conventional fault ride-through strategy based on the actual fault conditions.

[0132] Step 208: modulate the modulation wave of the bridge arm in the modular multilevel converter using the three-phase modulation ratio and the modulation wave adjustment coefficient, and suppress overvoltage of the submodule in the modular multilevel converter through the modulation signal.

[0133] In the embodiment of the present invention, the specific implementation process of step 208 is similar to that of step 104 and will not be repeated here.

[0134] In an embodiment of the present invention, operating data of a modular multilevel converter and operating voltages of multiple submodules are obtained. Dual-loop decoupling control and three-phase coordinate transformation are performed based on the operating data to generate a three-phase modulation ratio. When no submodule overvoltage occurs in the modular multilevel converter, a modulation wave of a bridge arm within the modular multilevel converter is modulated using the three-phase modulation ratio to generate bridge arm modulation data. An average value is calculated using the operating voltages of all submodules to generate a submodule voltage average value. A submodule voltage average value reference value corresponding to the submodule voltage average value is subtracted from the submodule voltage average value to generate an average value difference. A determination is made as to whether the submodule type corresponding to the submodule operating voltage is a preset type. If the submodule type is the preset type, then when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the average value difference and the DC modulation index corresponding to the submodule voltage average value to generate a first modulation wave adjustment coefficient. If the submodule type is not the preset type, then when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the average value difference and the DC current control loop output value corresponding to the submodule voltage average value to generate a second modulation wave adjustment coefficient. When a submodule of a modular multilevel converter experiences overvoltage, the modulation wave of the bridge arm within the converter is modulated using a three-phase modulation ratio and a corresponding modulation wave adjustment coefficient. This modulation signal suppresses overvoltage in the submodules within the converter. This method optimizes existing voltage reduction methods by using a three-phase modulation ratio and a modulation wave adjustment coefficient. It achieves better economic efficiency and feasibility, suppresses submodule overvoltage without requiring control switching, and achieves effective control while maintaining excellent stability.

[0135] Example 3

[0136] See also Figure 5 , Figure 5 This is a structural block diagram of a sub-module overvoltage suppression system of a modular multi-level converter provided in Embodiment 3 of the present invention.

[0137] A third embodiment of the present invention provides a submodule overvoltage suppression system for a modular multilevel converter, comprising:

[0138] The three-phase modulation ratio generating module 501 is configured to obtain operating data of the modular multilevel converter and operating voltages of multiple submodules, perform dual-loop decoupling control and three-phase coordinate transformation based on the operating data, and generate a three-phase modulation ratio.

[0139] The bridge arm modulation data generating module 502 is configured to modulate the modulation wave of the bridge arm in the modular multilevel converter using a three-phase modulation ratio to generate bridge arm modulation data when no submodule overvoltage occurs in the modular multilevel converter.

[0140] The modulation wave adjustment coefficient generating module 503 is configured to calculate the modulation wave adjustment coefficient based on the submodule operating voltage to generate the modulation wave adjustment coefficient when a submodule overvoltage occurs in the modular multilevel converter.

[0141] The submodule overvoltage suppression module 504 is configured to modulate the modulation wave of the bridge arm in the modular multilevel converter using a three-phase modulation ratio and a modulation wave adjustment coefficient, and suppress overvoltage of the submodule in the modular multilevel converter through the modulation signal.

[0142] Optionally, the three-phase modulation ratio generating module 501 includes:

[0143] The initial d-axis current loop reference value generation module is used to perform active outer loop control based on active outer loop data in the operating data and generate an initial d-axis current loop reference value.

[0144] The target d-axis current loop reference value generation module is used to use the initial d-axis current loop reference value to perform active inner loop control and generate a target d-axis current loop reference value.

[0145] The initial q-axis current loop reference value generation module is used to perform reactive outer loop control based on reactive outer loop data in the operating data and generate an initial q-axis current loop reference value.

[0146] The target q-axis current loop reference value generation module is used to use the initial q-axis current loop reference value to perform reactive inner loop control and generate a target q-axis current loop reference value.

[0147] The three-phase modulation ratio generation submodule is used to perform three-phase coordinate transformation using the target d-axis current loop reference value and the target q-axis current loop reference value to generate the three-phase modulation ratio.

[0148] Optionally, the active outer loop data includes the DC side current, the DC side voltage measured value and the AC side active power measured value. The initial D-axis current loop reference value generation module can perform the following steps:

[0149] Determining whether the system demand data corresponding to the active outer loop data is the first preset system demand data;

[0150] If the system demand data is the first preset system demand data, calculating the product of the DC side current and the first preset resistance adjustment coefficient to generate the DC side voltage;

[0151] Subtracting the DC link voltage reference value corresponding to the DC link voltage measured value from the DC link voltage to generate a first DC link voltage difference value;

[0152] Subtracting the first DC side voltage difference from the actual DC side voltage measurement value to generate a second DC side voltage difference;

[0153] Inputting the second DC side voltage difference into the first PI controller for parameter adjustment to generate a first initial d-axis current loop reference value;

[0154] If the system demand data is not the first preset system demand data, subtracting the AC side active power reference value corresponding to the AC side active power actual measurement value from the AC side active power actual measurement value to generate a first AC side power difference value;

[0155] The first AC side power difference is input into the second PI controller for parameter adjustment to generate a second initial d-axis current loop reference value.

[0156] Optionally, the reactive outer loop data includes the AC side current, the AC side voltage measured value and the AC side reactive power measured value. The initial q-axis current loop reference value generation module can perform the following steps:

[0157] Determining whether the system demand data corresponding to the reactive outer loop data is the second preset system demand data;

[0158] If the system demand data is the second preset system demand data, calculating the product of the AC side current and the second preset resistance adjustment coefficient to generate the AC side voltage;

[0159] Subtracting the AC side voltage reference value corresponding to the AC side voltage measured value from the AC side voltage to generate a first AC side voltage difference value;

[0160] Subtracting the first AC side voltage difference from the AC side voltage measured value to generate a second AC side voltage difference;

[0161] Inputting the second AC side voltage difference into a third PI controller for parameter adjustment to generate a first initial q-axis current loop reference value;

[0162] If the system demand data is not the second preset system demand data, subtracting the AC side reactive power reference value corresponding to the AC side reactive power actual value from the AC side reactive power actual value to generate a second AC side power difference value;

[0163] The second AC side power difference is input into the fourth PI controller for parameter adjustment to generate a second initial q-axis current loop reference value.

[0164] Optionally, the modulation wave adjustment coefficient generating module 503 includes:

[0165] The submodule voltage average value generating module is used to calculate the average value of the operating voltages of all submodules to generate the submodule voltage average value.

[0166] The average value difference generating module is used to generate an average value difference by performing a sub-module voltage average value reference value corresponding to the sub-module voltage average value and the sub-module voltage average value.

[0167] The submodule type judgment module is used to judge whether the submodule type corresponding to the submodule operating voltage is a preset type.

[0168] The first modulation wave adjustment coefficient generating module is used to calculate the modulation wave adjustment coefficient according to the DC modulation index corresponding to the average value difference and the average value of the submodule voltage when a submodule overvoltage occurs in the modular multilevel converter if the submodule type is a preset type, and generate the first modulation wave adjustment coefficient.

[0169] The second modulation wave adjustment coefficient generation module is used to calculate the modulation wave adjustment coefficient based on the average value difference and the DC current control loop output value corresponding to the submodule voltage average value when the submodule overvoltage occurs in the modular multilevel converter if the submodule type is not a preset type, and generate the second modulation wave adjustment coefficient.

[0170] Optionally, the first modulation wave adjustment coefficient generating module may perform the following steps:

[0171] The average value difference is input into the third PI controller for parameter adjustment to generate the adjustment parameters of the first submodule;

[0172] When a submodule overvoltage occurs in the modular multilevel converter, a sum of a first submodule adjustment parameter and a DC modulation index corresponding to an average value of the submodule voltage is calculated to generate a first modulation wave adjustment coefficient.

[0173] Optionally, the second modulation wave adjustment coefficient generating module may perform the following steps:

[0174] Inputting the DC current control loop output value corresponding to the average value of the submodule voltage into the fourth PI controller for parameter adjustment and amplitude limiting processing to generate DC control data;

[0175] Calculate the ratio of the submodule voltage average value reference value corresponding to the submodule voltage average value and the submodule voltage average value difference to generate the second submodule adjustment parameter;

[0176] When a submodule overvoltage occurs in the modular multilevel converter, a sum of a second submodule adjustment parameter and DC control data is calculated to generate a second modulation wave adjustment coefficient.

[0177] Example 4

[0178] Figure 6 This is a structural block diagram of an electronic device provided in Example 4 of the present invention.

[0179] An electronic device according to an embodiment of the present invention includes: a memory 601 and a processor 602, wherein the memory 601 stores a computer program; when the computer program is executed by the processor 602, the processor 602 executes the sub-module overvoltage suppression method of the modular multilevel converter as described in any of the above embodiments.

[0180] The memory 601 can be an electronic memory such as a flash memory, an EEPROM (Electrically Erasable Programmable Read-Only Memory), an EPROM, a hard disk, or a ROM. The memory 601 has storage space 603 for program code 613 for executing any of the method steps described above. For example, the program code storage space 603 can include individual program codes 613 for implementing various steps in the method described above. These program codes can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards, or floppy disks. The program codes can be compressed, for example, in a suitable format. When executed by a processing device, these codes cause the processing device to execute the various steps of the method for overvoltage suppression in submodules of a modular multilevel converter described above.

[0181] An embodiment of the present invention further provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the method for suppressing overvoltage of a submodule of a modular multilevel converter according to any of the above embodiments is implemented.

[0182] 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.

[0183] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interface, device or unit, which can be electrical, mechanical or other forms.

[0184] Units described as separate components may or may not be physically separate, and 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 these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0185] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0186] 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, or the portion 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 for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the various embodiments of the method of the present invention. The aforementioned storage medium includes various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical disks.

[0187] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for suppressing overvoltage of submodules of a modular multilevel converter, characterized in that: include: Acquiring operating data of a modular multilevel converter and operating voltages of multiple submodules, performing dual-loop decoupling control and three-phase coordinate transformation based on the operating data, and generating a three-phase modulation ratio; When no submodule overvoltage occurs in the modular multilevel converter, modulating the modulation wave of the bridge arm in the modular multilevel converter using the three-phase modulation ratio to generate bridge arm modulation data; When a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated based on the operating voltage of the submodule to generate the modulation wave adjustment coefficient; The modulation wave of the bridge arm in the modular multilevel converter is modulated using the three-phase modulation ratio and the modulation wave adjustment coefficient, and overvoltage suppression is performed on the submodules in the modular multilevel converter through the modulation signal.

2. The method for suppressing overvoltage of submodules of a modular multilevel converter according to claim 1, characterized in that: The step of performing dual-loop decoupling control and three-phase coordinate transformation based on the operating data to generate a three-phase modulation ratio includes: Performing active outer loop control based on the active outer loop data in the operating data to generate an initial d-axis current loop reference value; The initial d-axis current loop reference value is used to perform active inner loop control and generate a target d-axis current loop reference value; Performing reactive outer loop control based on reactive outer loop data in the operating data to generate an initial q-axis current loop reference value; The initial q-axis current loop reference value is used to perform reactive inner loop control and generate a target q-axis current loop reference value; The target d-axis current loop reference value and the target q-axis current loop reference value are used to perform three-phase coordinate transformation to generate a three-phase modulation ratio.

3. The method for suppressing overvoltage of submodules of a modular multilevel converter according to claim 2, characterized in that: The active outer loop data includes the DC side current, DC side voltage measured value and AC side active power measured value; The step of performing active outer loop control based on the active outer loop data in the operating data to generate an initial d-axis current loop reference value includes: Determining whether the system demand data corresponding to the active outer loop data is first preset system demand data; If the system requirement data is the first preset system requirement data, calculating a multiplication value between the DC side current and a first preset resistance adjustment coefficient to generate a DC side voltage; Subtracting the DC link voltage from a DC link voltage reference value corresponding to the DC link voltage actual value to generate a first DC link voltage difference value; Subtracting the first DC link voltage difference from the actual DC link voltage value to generate a second DC link voltage difference; Inputting the second DC side voltage difference into a first PI controller for parameter adjustment to generate a first initial d-axis current loop reference value; If the system demand data is not the first preset system demand data, subtracting the AC side active power reference value corresponding to the AC side active power actual measurement value from the AC side active power actual measurement value to generate a first AC side power difference value; Inputting the first AC side power difference into a second PI controller for parameter adjustment to generate a second initial d-axis current loop reference value; The first preset system requirement data is system requirement data corresponding to the DC voltage outer loop control.

4. The method for suppressing overvoltage of submodules of a modular multilevel converter according to claim 2, wherein: The reactive outer loop data includes the AC side current, the AC side voltage measured value, and the AC side reactive power measured value; the step of performing reactive outer loop control based on the reactive outer loop data in the operating data to generate an initial q-axis current loop reference value includes: Determining whether the system demand data corresponding to the reactive outer loop data is second preset system demand data; If the system demand data is the second preset system demand data, calculating the product of the AC side current and the second preset resistance adjustment coefficient to generate the AC side voltage; Subtracting the AC side voltage from the AC side voltage reference value corresponding to the AC side voltage measured value to generate a first AC side voltage difference; Subtracting the first AC side voltage difference from the AC side voltage measured value to generate a second AC side voltage difference; Inputting the second AC side voltage difference into a third PI controller for parameter adjustment to generate a first initial q-axis current loop reference value; If the system demand data is not the second preset system demand data, subtracting the AC side reactive power reference value corresponding to the AC side reactive power actual measurement value from the AC side reactive power actual measurement value to generate a second AC side power difference value; Inputting the second AC side power difference into a fourth PI controller for parameter adjustment to generate a second initial q-axis current loop reference value; The second preset system requirement data is system requirement data corresponding to AC voltage control.

5. The method for suppressing overvoltage of submodules of a modular multilevel converter according to claim 1, characterized in that: The step of calculating a modulation wave adjustment coefficient based on the operating voltage of the submodule to generate the modulation wave adjustment coefficient when a submodule overvoltage occurs in the modular multilevel converter includes: Calculating an average value of the operating voltages of all the submodules to generate an average submodule voltage value; Subtracting a submodule voltage average value reference value corresponding to the submodule voltage average value from the submodule voltage average value to generate an average value difference; Determining whether the submodule type corresponding to the submodule operating voltage is a preset type; If the submodule type is a preset type, when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated according to the average value difference and the DC modulation degree corresponding to the average value of the submodule voltage to generate a first modulation wave adjustment coefficient; If the submodule type is not a preset type, when a submodule overvoltage occurs in the modular multilevel converter, a modulation wave adjustment coefficient is calculated according to the average value difference and the DC current control loop output value corresponding to the submodule voltage average value to generate a second modulation wave adjustment coefficient; The preset type is a half-bridge MMC submodule.

6. The method for suppressing overvoltage of submodules of a modular multilevel converter according to claim 5, characterized in that: The step of calculating a modulation wave adjustment coefficient according to the average value difference and a DC modulation degree corresponding to the average value of the submodule voltage to generate a first modulation wave adjustment coefficient when a submodule overvoltage occurs in the modular multilevel converter includes: Inputting the mean value difference into a third PI controller for parameter adjustment to generate adjustment parameters of the first submodule; When a submodule overvoltage occurs in the modular multilevel converter, a sum of the first submodule adjustment parameter and the DC modulation index corresponding to the average value of the submodule voltage is calculated to generate a first modulation wave adjustment coefficient.

7. The method for suppressing overvoltage of submodules of a modular multilevel converter according to claim 5, characterized in that: The step of calculating a modulation wave adjustment coefficient according to the average value difference and a DC current control loop output value corresponding to the average value of the submodule voltage to generate a second modulation wave adjustment coefficient when a submodule overvoltage occurs in the modular multilevel converter includes: Inputting the DC current control loop output value corresponding to the average voltage value of the submodule into a fourth PI controller for parameter adjustment and amplitude limiting processing to generate DC control data; Calculate the ratio of the submodule voltage average value reference value corresponding to the submodule voltage average value and the submodule voltage average value difference to generate a second submodule adjustment parameter; When a submodule overvoltage occurs in the modular multilevel converter, a sum of the second submodule adjustment parameter and the DC control data is calculated to generate a second modulation wave adjustment coefficient.

8. A submodule overvoltage suppression system for a modular multilevel converter, characterized in that: include: A three-phase modulation ratio generation module is used to obtain operating data of the modular multilevel converter and operating voltages of multiple submodules, perform dual-loop decoupling control and three-phase coordinate transformation based on the operating data, and generate a three-phase modulation ratio; a bridge arm modulation data generating module, configured to modulate the modulation wave of the bridge arm in the modular multilevel converter using the three-phase modulation ratio to generate bridge arm modulation data when no submodule overvoltage occurs in the modular multilevel converter; a modulation wave adjustment coefficient generating module, configured to calculate the modulation wave adjustment coefficient based on the operating voltage of the submodule when a submodule overvoltage occurs in the modular multilevel converter, and generate the modulation wave adjustment coefficient; The submodule overvoltage suppression module is used to modulate the modulation wave of the bridge arm in the modular multilevel converter by using the three-phase modulation ratio and the modulation wave adjustment coefficient, and suppress overvoltage of the submodule in the modular multilevel converter through the modulation signal.

9. An electronic device, characterized in that: The method comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor performs the steps of the method for suppressing overvoltage of a submodule of a modular multilevel converter according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the method for suppressing overvoltage of a submodule of a modular multilevel converter is implemented.

Images