Novel modular multilevel converter system bridge arm controller separation control method, system, device and medium

Abstract

The invention relates to the technical field of power electronic converter control, and discloses a novel modular multilevel converter system bridge arm controller separation control method, system, device and medium, and the method comprises the steps: respectively obtaining the current directions of an upper bridge arm and a lower bridge arm, calculating the capacitor voltage average value of each bridge arm sub-module, and calculating the capacitor voltage average value of each bridge arm sub-module; generating sub-module input quantity distribution parameters through proportional-integral adjustment based on the capacitor voltage average value difference between the upper bridge arm and the third bridge arm and the capacitor voltage average value difference between the lower bridge arm and the third bridge arm; determining the input number of the sub-modules of the upper bridge arm, the lower bridge arm and the third bridge arm by combining the combined operation state mark of the third bridge arm, the current direction and the total input demand of the sub-modules; and each bridge arm controller independently sorts the capacitor voltage of the corresponding bridge arm sub-module, selects a corresponding number of sub-modules for switching according to a sorting result, generates respective pulse width modulation signals, and realizes separation control of complete decoupling of the three bridge arm controllers.

Description

A novel modular multilevel converter system arm controller separation control method, system, equipment and medium Technical Field

[0001] This invention relates to the field of power electronic converter control technology, and in particular to a novel modular multilevel converter system arm controller separation control method, system, equipment and medium. Background Technology

[0002] Modular multilevel converters (MMCs), with their modular structure, high scalability, low harmonic output, and flexible power control capabilities, have become core equipment in the field of flexible high-voltage direct current (HVDC) transmission. Their core advantage lies in achieving high-voltage output through cascaded submodules while reducing voltage stress and losses in switching devices. In recent years, MMC technology has rapidly developed from low-voltage demonstration projects to high-voltage, high-capacity applications. With the advancement of the "dual-carbon" goal, the supporting role of MMCs in building new power systems is becoming increasingly significant.

[0003] Despite the significant advantages of MMC technology, its large number of submodules in high-voltage, high-capacity scenarios (such as the Zhoushan Five-Terminal Project which contains tens of thousands of modules) results in high converter station size, weight, and investment costs, especially limiting its application in space-constrained scenarios such as offshore wind power. To address this, researchers have proposed a new type of MMC that uses a "time-division combined" bridge arm structure to reduce the number of submodules per phase unit by 25%, while increasing the submodule utilization rate from 50% to 66.7%, significantly reducing equipment size and cost.

[0004] The new MMC (Multi-Module Control) reconfigures the phase unit into a three-arm structure of "upper arm - third arm - lower arm," and combines this with a dynamic switching strategy to achieve efficient integration of submodules. Its advantages lie in significantly reducing equipment size and cost while retaining the DC fault ride-through capability of the MMC. For example, hybrid new MMCs (such as FHF and HFH topologies) can reduce the proportion of fault-limiting submodules by 50% by configuring full-bridge submodules (FBSM), balancing economy and reliability. In terms of application scenarios, the new MMC is particularly suitable for fields with high requirements for equipment compactness, such as offshore wind power transmission and urban power distribution network expansion.

[0005] However, the combined characteristics of the bridge arms also bring new control challenges. Traditional control methods require time-sharing transmission of the submodule capacitor voltage data of the third bridge arm to the upper and lower bridge arm controllers, and dynamic switching of control signals. This increases the complexity of the control system, raises link latency, and makes it difficult to ensure the voltage balance of each bridge arm submodule. For example, during startup, if the control strategy is inappropriate when the third bridge arm switches, it may cause inconsistencies in the submodule capacitor voltages, thus affecting system stability. In addition, existing methods lack the ability to dynamically coordinate power distribution between bridge arms, limiting the application potential of the new MMC under high-frequency operating conditions. Summary of the Invention

[0006] In view of the aforementioned existing problems, the present invention is proposed.

[0007] Therefore, the present invention provides a novel modular multilevel converter system arm controller separation control method, system, device and medium, which can solve the problems of increased link delay and difficulty in ensuring voltage balance of arm sub-modules in the prior art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a novel modular multilevel converter system arm controller separation control method, comprising: acquiring the current direction of the upper arm and the current direction of the lower arm; calculating the average value of the capacitor voltage of all sub-modules in the upper arm, the average value of the capacitor voltage of all sub-modules in the lower arm, and the average value of the capacitor voltage of all sub-modules in the third arm, respectively; generating a sub-module allocation parameter for the combined operation of the upper arm and the third arm based on the difference between the average value of the capacitor voltage of the upper arm sub-modules and the average value of the capacitor voltage of the third arm sub-modules through proportional-integral adjustment; and generating a parameter for the combined operation of the lower arm and the third arm based on the difference between the average value of the capacitor voltage of the lower arm sub-modules and the average value of the capacitor voltage of the third arm sub-modules through proportional-integral adjustment. The submodule deployment quantity allocation parameters are obtained; the joint operation status flag of the third bridge arm is obtained, which indicates whether the third bridge arm is in conjunction with the upper bridge arm, in conjunction with the lower bridge arm, or in a bridge arm switching state; based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of submodules required for the upper bridge arm and the third bridge arm to be in conjunction, the total number of submodules required for the lower bridge arm and the third bridge arm to be in conjunction, and the submodule deployment quantity allocation parameters, the number of submodules to be deployed for the upper bridge arm, the lower bridge arm, and the third bridge arm are determined respectively; based on the number of submodules to be deployed for each, the capacitor voltages of all submodules in the upper bridge arm, the lower bridge arm, and the third bridge arm are sorted respectively, and the corresponding number of submodules are selected for deployment or removal according to the sorting results, generating their respective pulse width modulation signals.

[0009] As a preferred embodiment of the novel modular multilevel converter system arm controller separation control method described in this invention, the step of obtaining the upper arm current direction and the lower arm current direction includes: when the upper arm current is flowing in the forward direction, determining that the upper arm current direction is the charging direction; when the upper arm current is flowing in the reverse direction, determining that the upper arm current direction is the discharging direction; when the lower arm current is flowing in the forward direction, determining that the lower arm current direction is the charging direction; and when the lower arm current is flowing in the reverse direction, determining that the lower arm current direction is the discharging direction.

[0010] As a preferred embodiment of the novel modular multilevel converter system arm controller separation control method described in this invention, the step of determining the number of sub-modules required for each of the upper arm, lower arm, and third arm based on the joint operation status flag of the third arm, the current direction of the upper arm, the current direction of the lower arm, the total number of sub-modules required for the joint operation of the upper arm and the third arm, the total number of sub-modules required for the joint operation of the lower arm and the third arm, and the sub-module allocation parameters, includes: when the joint operation status flag of the third arm indicates the third arm... When the bridge arm and the upper bridge arm are combined, if the current direction of the upper bridge arm is the charging direction, the total number of sub-modules required for the combination of the upper bridge arm and the third bridge arm is allocated to the third bridge arm according to the sub-module allocation parameters, and the remaining number is allocated to the upper bridge arm; if the current direction of the upper bridge arm is the discharging direction, the total number of sub-modules required for the combination of the upper bridge arm and the third bridge arm is allocated to the upper bridge arm according to the sub-module allocation parameters, and the remaining number is allocated to the third bridge arm; the number of sub-modules in the lower bridge arm is equal to the total number of sub-modules required for the combination of the lower bridge arm and the third bridge arm.

[0011] As a preferred embodiment of the novel modular multilevel converter system arm controller separation control method described in this invention, the method further includes: determining the number of sub-modules required for each of the upper arm, lower arm, and third arm based on the joint operation status flag of the third arm, the current direction of the upper arm, the current direction of the lower arm, the total number of sub-modules required for the joint operation of the upper arm and the third arm, the total number of sub-modules required for the joint operation of the lower arm and the third arm, and the sub-module allocation parameters; and further includes: when the joint operation status flag of the third arm indicates the third arm... When the bridge arm and the lower bridge arm are combined, if the current direction of the lower bridge arm is the charging direction, the total number of sub-modules required for the lower bridge arm and the third bridge arm to be combined is allocated to the third bridge arm according to the sub-module allocation parameters, and the remaining number is allocated to the lower bridge arm; if the current direction of the lower bridge arm is the discharging direction, the total number of sub-modules required for the lower bridge arm and the third bridge arm to be combined is allocated to the lower bridge arm according to the sub-module allocation parameters, and the remaining number is allocated to the third bridge arm; the number of sub-modules invested in the upper bridge arm is equal to the total number of sub-modules required for the upper bridge arm and the third bridge arm to be combined.

[0012] As a preferred embodiment of the novel modular multilevel converter system arm controller separation control method described in this invention, the method further includes: determining the number of sub-modules required for each of the upper arm, lower arm, and third arm based on the joint operation status flag of the third arm, the current direction of the upper arm, the current direction of the lower arm, the total number of sub-modules required for the joint operation of the upper arm and the third arm, the total number of sub-modules required for the joint operation of the lower arm and the third arm, and the sub-module allocation parameters; and further includes: when the joint operation status flag of the third arm indicates that the third arm is in the arm switching state, setting the number of sub-modules required for the upper arm to be the total number of sub-modules contained in the upper arm, setting the number of sub-modules required for the lower arm to be the total number of sub-modules contained in the lower arm, and setting the number of sub-modules required for the third arm to zero.

[0013] As a preferred embodiment of the novel modular multilevel converter system arm controller separation control method described in this invention, it further includes: during the arm switching state of the third arm, sending a switching command to two sets of arm status control switches, causing the third arm to disconnect from the currently connected arm and connect to another arm, thereby completing the conversion of the joint operation mode.

[0014] As a preferred embodiment of the novel modular multilevel converter system bridge arm controller separation control method described in this invention, the generation of their respective pulse width modulation signals includes: the upper bridge arm controller, the lower bridge arm controller, and the third bridge arm controller do not exchange their sub-module switching commands or pulse width modulation signals during the generation of pulse width modulation signals.

[0015] Secondly, this invention provides a novel modular multilevel converter system arm controller separation control system, comprising: a three-phase unit, each phase unit including an upper arm, a lower arm, a third arm, two arm reactors, and two sets of arm status control switches, each arm being composed of multiple cascaded half-bridge submodules; an upper arm controller, used to acquire the current direction of the upper arm, calculate the average value of the capacitor voltage of the upper arm submodule, receive the average value of the capacitor voltage of the third arm submodule, generate submodule allocation parameters for joint operation of the upper and third arms, determine the number of upper arm submodules to be engaged based on the joint operation status flag and the submodule allocation parameters, and generate an upper arm pulse width modulation signal after sorting the capacitor voltages of the upper arm submodules; and a lower arm controller, used to acquire the current direction of the lower arm, calculate the average value of the capacitor voltage of the lower arm submodule, receive the average value of the capacitor voltage of the third arm submodule, and generate submodule pulse width modulation signals; and a lower arm controller, used to acquire the current direction of the lower arm, calculate the average value of the capacitor voltage of the lower arm submodule, receive the average value of the capacitor voltage of the third arm submodule, and generate submodule allocation parameters for joint operation of the upper and third arms, determine the number of upper arm submodules to be engaged based on the joint operation status flag and the submodule allocation parameters, and generate an upper arm pulse width modulation signal after sorting the capacitor voltages of the upper arm submodules; and a lower arm controller, used to acquire the current direction of the lower arm, calculate the average value of the capacitor voltage of the lower arm submodule, receive the average value of the capacitor voltage of the third arm submodule, and generate submodule allocation parameters for joint operation of the upper and third arms. The system calculates the average voltage of the lower and third bridge arms, generates submodule allocation parameters for joint operation of the lower and third bridge arms, determines the number of lower bridge arm submodules to be deployed based on the joint operation status flag and the submodule deployment allocation parameters, and generates a lower bridge arm pulse width modulation signal after sorting the capacitor voltages of the lower bridge arm submodules. The third bridge arm controller calculates the average voltage of the capacitors of the third bridge arm submodules, receives the average voltage of the capacitors of the upper and lower bridge arm submodules, receives the joint operation status flag, the current direction of the upper and lower bridge arms, the submodule deployment allocation parameters, and the total number of submodules deployed, determines the number of third bridge arm submodules to be deployed, and generates a third bridge arm pulse width modulation signal after sorting the capacitor voltages of the third bridge arm submodules. The upper, lower, and third bridge arm controllers operate independently and do not exchange submodule switching commands or pulse width modulation signals.

[0016] Thirdly, the present invention provides an electronic device including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method described above.

[0017] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described above.

[0018] Compared with existing technologies, the beneficial effect of this invention is that it proposes a novel modular multilevel converter system arm controller separation control method. This method obtains the current direction of the upper and lower arms, calculates the average capacitor voltage of each arm sub-module, and generates sub-module allocation parameters based on the difference between the average capacitor voltages of the upper and third arms, and the lower and third arms, through proportional-integral adjustment. Combining the joint operating status flag of the third arm, the current direction, and the total sub-module allocation requirements, the number of sub-modules to be allocated for each of the upper, lower, and third arms is determined. Each arm controller independently sorts the capacitor voltages of its own arm sub-modules and selects the corresponding number of sub-modules for switching based on the sorting results, generating its own pulse width modulation signal, thus achieving completely decoupled separation control of the three arm controllers. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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.

[0020] Figure 1 is a schematic diagram of the topology of a novel modular multilevel converter system arm controller separation control method provided by an embodiment of the present invention.

[0021] Figure 2 is a schematic diagram of the structure of a novel MMC arm state control switch in a novel modular multilevel converter system arm controller separation control method provided by an embodiment of the present invention.

[0022] Figure 3 is a schematic diagram of the structure of a novel MMC valve control system described in this invention, which provides a novel modular multilevel converter system arm controller separation control method according to an embodiment of the invention.

[0023] Figure 4 is a flowchart of the novel MMC system arm controller separation control method described in this invention, which is based on an embodiment of the present invention.

[0024] Figure 5 is a diagram illustrating the effect of the separation control of the arm controller in a novel modular multilevel converter system according to an embodiment of the present invention.

[0025] Figure 6 is an internal structure diagram of an electronic device for a novel modular multilevel converter system arm controller separation control method provided in an embodiment of the present invention. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0027] It should be noted in advance that the system mentioned in the embodiments as the subject of real-time operation refers to any system configured with this method.

[0028] Example 1, the first embodiment of the present invention, provides a novel modular multilevel converter system arm controller separation control method, including: S101, obtaining the upper arm current direction and the lower arm current direction; in this embodiment of the present invention, obtaining the upper arm current direction and the lower arm current direction includes: when the upper arm current is flowing in the forward direction, determining that the upper arm current direction is the charging direction; when the upper arm current is flowing in the reverse direction, determining that the upper arm current direction is the discharging direction; when the lower arm current is flowing in the forward direction, determining that the lower arm current direction is the charging direction; when the lower arm current is flowing in the reverse direction, determining that the lower arm current direction is the discharging direction.

[0029] It should be noted that in actual operation, the current direction of the upper and lower arms of the modular multilevel converter system directly determines whether the submodule capacitor is in a charging or discharging state, and this state has a decisive impact on the voltage balance of the submodule capacitor.

[0030] For example, when the current in the upper arm is flowing in the positive direction, the current flows from the DC side to the AC side. At this time, the capacitors in the sub-modules in the upper arm are charged, and the capacitor voltage rises. If the current direction is incorrectly determined to be the discharge direction, the controller will allocate the number of sub-modules to be put into operation based on the incorrect power flow direction, resulting in some sub-modules being overcharged while others are not fully involved in energy exchange, which in turn causes capacitor voltage imbalance or even overvoltage fault.

[0031] For example, when the current in the lower bridge arm flows in the reverse direction, the current flows back from the AC side to the DC side. At this time, the capacitor in the submodule of the lower bridge arm is in a discharging state, and the capacitor voltage drops. If the discharge direction is not accurately identified, the controller may continue to assign tasks to the submodule that is already in a low voltage state, causing the voltage to drop further. In severe cases, it may trigger the undervoltage protection and cause the system to shut down.

[0032] If a fixed direction assumption is used or the dynamic changes in current direction are ignored for submodule switching control, the actual power flow path cannot be matched. This will cause the average deviation of the capacitor voltage between the third bridge arm and the upper or lower bridge arm to continue to increase during joint operation, thereby destroying the voltage balance capability of the entire phase unit.

[0033] Therefore, the direction of charging or discharging can be determined by whether the current in the upper arm is flowing in the forward direction, and the direction of charging or discharging can be determined by whether the current in the lower arm is flowing in the forward direction. This provides an accurate basis for the subsequent allocation of the number of sub-modules based on the current direction, ensuring that the capacitor voltage of each arm sub-module is always maintained within a balanced and controllable range under different power flow conditions.

[0034] S102, calculate the average value of the capacitor voltage of all sub-modules in the upper bridge arm, the average value of the capacitor voltage of all sub-modules in the lower bridge arm, and the average value of the capacitor voltage of all sub-modules in the third bridge arm, respectively; S103, based on the difference between the average value of the capacitor voltage of the upper bridge arm sub-modules and the average value of the capacitor voltage of the third bridge arm sub-modules, generate the sub-module deployment allocation parameters for the joint operation of the upper and third bridge arms through proportional-integral adjustment; S104, based on the difference between the average value of the capacitor voltage of the lower bridge arm sub-modules and the average value of the capacitor voltage of the third bridge arm sub-modules, generate the sub-module deployment allocation parameters for the joint operation of the lower and third bridge arms through proportional-integral adjustment; S105, obtain the joint operation status flag of the third bridge arm, which indicates whether the third bridge arm is in conjunction with the upper bridge arm, in conjunction with the lower bridge arm, or in a bridge arm switching state; S106, based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of sub-modules required for the joint operation of the upper and third bridge arms, the total number of sub-modules required for the joint operation of the lower and third bridge arms, and the number of sub-modules deployed. The quantity allocation parameters determine the number of submodules required for each of the upper arm, lower arm, and third arm. In this embodiment of the invention, the number of submodules required for each of the upper arm, lower arm, and third arm is determined based on the joint operation status flag of the third arm, the current direction of the upper arm, the current direction of the lower arm, the total number of submodules required for the upper arm and third arm to be combined, the total number of submodules required for the lower arm and third arm to be combined, and the submodule allocation parameters. This includes: when the joint operation status flag of the third arm indicates the number of submodules required for the upper arm, lower arm, and third arm to be combined, the number of submodules required for the upper arm, lower arm, and third arm to be combined is determined. When the third bridge arm is combined with the upper bridge arm, if the current direction of the upper bridge arm is the charging direction, the total number of sub-modules required for the combination of the upper bridge arm and the third bridge arm is allocated to the third bridge arm according to the sub-module allocation parameters, and the remaining number is allocated to the upper bridge arm; if the current direction of the upper bridge arm is the discharging direction, the total number of sub-modules required for the combination of the upper bridge arm and the third bridge arm is allocated to the upper bridge arm according to the sub-module allocation parameters, and the remaining number is allocated to the third bridge arm; the number of sub-modules in the lower bridge arm is equal to the total number of sub-modules required for the combination of the lower bridge arm and the third bridge arm.

[0035] It should be understood that when the joint operation status indicator of the third bridge arm indicates that the third bridge arm is combined with the upper bridge arm and the current direction of the upper bridge arm is the charging direction, if the total number of sub-modules required for the combination of the upper bridge arm and the third bridge arm is directly allocated to the upper bridge arm, the third bridge arm will be unable to participate in energy absorption, resulting in a decrease in the DC side voltage support capability, which in turn will cause voltage fluctuations or control instability.

[0036] If most of the sub-modules are still allocated to the third bridge arm when the current direction of the upper bridge arm is the discharge direction, it will weaken the upper bridge arm's ability to release energy to the AC side, causing the sub-module capacitor voltage to rise continuously. In severe cases, it may trigger overvoltage protection and interrupt normal power transmission.

[0037] After obtaining the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of sub-modules required for the joint operation of the upper and third bridge arms, the total number of sub-modules required for the joint operation of the lower and third bridge arms, and the sub-module allocation parameters, this invention initiates a dynamic sub-module allocation mechanism based on the collaborative determination of current direction and joint status. The sub-module allocation ratio between the upper and third bridge arms is accurately divided according to the actual current flow direction, and the total number of sub-modules required for the joint operation of the lower and third bridge arms is fixedly allocated to the lower bridge arm to maintain voltage stability in the independent operation state of the lower bridge arm.

[0038] The aforementioned submodule allocation parameter can be understood as a proportional coefficient used in this invention to characterize the number of submodules required to prioritize the energy absorption or release path based on the current direction when the third bridge arm and the upper bridge arm are operating together.

[0039] In this embodiment of the invention, the number of submodules required for each of the upper, lower, and third bridge arms is determined based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of submodules required for the joint operation of the upper and third bridge arms, the total number of submodules required for the joint operation of the lower and third bridge arms, and the submodule allocation parameters. The method further includes: when the joint operation status flag of the third bridge arm indicates that the third and lower bridge arms are in conjunction, if the current direction of the lower bridge arm is the charging direction, the total number of submodules required for the joint operation of the lower and third bridge arms is allocated to the third bridge arm according to the submodule allocation parameters, and the remaining number is allocated to the lower bridge arm; if the current direction of the lower bridge arm is the discharging direction, the total number of submodules required for the joint operation of the lower and third bridge arms is allocated to the lower bridge arm according to the submodule allocation parameters, and the remaining number is allocated to the third bridge arm; the number of submodules required for the upper bridge arm is equal to the total number of submodules required for the joint operation of the upper and third bridge arms.

[0040] It should be noted that when the joint operation status indicator of the third bridge arm indicates that the third bridge arm is combined with the lower bridge arm and the current direction of the lower bridge arm is the charging direction, if the total number of sub-modules required for the combination of the lower bridge arm and the third bridge arm is directly allocated to the lower bridge arm, the third bridge arm will not be able to effectively participate in DC side energy absorption, weaken the system's dynamic support capability for DC voltage, and thus cause DC bus voltage fluctuations or control response lag.

[0041] If most of the sub-modules are still allocated to the third bridge arm when the current direction of the lower bridge arm is the discharge direction, it will limit the ability of the lower bridge arm to release energy to the AC side, causing the capacitor voltage of the lower bridge arm sub-module to continuously accumulate and rise. In severe cases, it may trigger overvoltage protection and interrupt power output.

[0042] Therefore, after obtaining the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of sub-modules required for the joint operation of the upper and third bridge arms, the total number of sub-modules required for the joint operation of the lower and third bridge arms, and the sub-module allocation parameters, this invention initiates a dynamic sub-module allocation mechanism based on the joint determination of the current direction of the lower bridge arm and the joint status. When the current direction of the lower bridge arm is the charging direction, the sub-modules are preferentially allocated to the third bridge arm to enhance the energy absorption capacity. When the current direction of the lower bridge arm is the discharging direction, the sub-modules are preferentially allocated to the lower bridge arm to ensure energy release efficiency. The total number of sub-modules required for the joint operation of the upper and third bridge arms is fixedly allocated to the upper bridge arm to maintain voltage stability in the independent operation state of the upper bridge arm.

[0043] The aforementioned submodule allocation parameter can be understood as a proportional coefficient used in this invention to characterize the number of submodules required to prioritize the energy absorption or release path based on the current direction when the third bridge arm and the lower bridge arm are operating together.

[0044] In this embodiment of the invention, based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of sub-modules required for the joint operation of the upper and third bridge arms, the total number of sub-modules required for the joint operation of the lower and third bridge arms, and the sub-module allocation parameters, the number of sub-modules required for the upper, lower, and third bridge arms to be deployed is determined respectively. The method further includes: when the joint operation status flag of the third bridge arm indicates that the third bridge arm is in a bridge arm switching state, setting the number of sub-modules deployed in the upper bridge arm to the total number of sub-modules contained in the upper bridge arm, setting the number of sub-modules deployed in the lower bridge arm to the total number of sub-modules contained in the lower bridge arm, and setting the number of sub-modules deployed in the third bridge arm to zero.

[0045] In an embodiment of the present invention, during the period when the third bridge arm is in the bridge arm switching state, a switching command is sent to two sets of bridge arm status control switches to disconnect the third bridge arm from the currently connected bridge arm and connect it to another bridge arm, thereby completing the conversion of the joint operation mode.

[0046] S107: Based on the number of sub-modules that need to be put into operation, sort the capacitor voltages of all sub-modules in the upper arm, lower arm and third arm respectively, and select the corresponding number of sub-modules to be put into operation or cut off according to the sorting results, and generate their respective pulse width modulation signals.

[0047] In this embodiment of the invention, the generation of their respective pulse width modulation signals includes: the upper arm controller, the lower arm controller, and the third arm controller do not exchange submodule switching commands or pulse width modulation signals with each other during the generation of pulse width modulation signals.

[0048] It is understandable that when the upper arm controller, lower arm controller, and third arm controller attempt to exchange their submodule switching commands or pulse width modulation signals during the generation of pulse width modulation signals, if they directly rely on the real-time control information of other arms for synchronous modulation, it will lead to the superposition of communication delays between controllers, destroy the independence and response speed of the local control loops of each arm, and thus cause submodule switching timing disorder or voltage imbalance.

[0049] If the three-arm controllers are required to share the complete pulse width modulation waveform to achieve unified modulation, it will significantly increase the communication bandwidth burden. Under high switching frequency conditions, it is very easy to cause data packet loss or instruction lag. In severe cases, it may induce a surge in circulating current between the arms or DC side voltage oscillation.

[0050] Therefore, when generating their respective pulse width modulation signals, the present invention initiates a decentralized independent modulation mechanism, enabling the upper arm controller, lower arm controller, and third arm controller to generate pulse width modulation signals based solely on the number of sub-modules they are allocated and the local current direction information. They do not exchange sub-module switching commands or pulse width modulation signals with each other throughout the process, thereby ensuring that the control logic of each arm is decoupled, responds quickly, and does not interfere with each other.

[0051] The decentralized independent modulation mechanism mentioned above can be understood as the core execution method used in this invention to enable the three bridge arms to complete the precise switching and voltage equalization control of sub-modules based on local decisions without mutual communication dependence.

[0052] Example 2, referring to Figures 1 to 5, provides a further detailed description of the specific embodiments of the present invention.

[0053] Figure 1 shows a schematic diagram of the novel MMC topology applicable to the present invention. Each phase unit includes three bridge arms: an upper bridge arm, a third bridge arm, and a lower bridge arm; two bridge arm reactors; and two sets of state control switches. Each bridge arm contains N half-bridge sub-modules.

[0054] Figure 2 shows a schematic diagram of the bridge arm state control switch. Each group of state control switches consists of IGCT devices with anti-parallel diodes connected in series in the same direction.

[0055] Figure 3 shows a schematic diagram of the novel MMC valve control system described in this invention. The upper, third, and lower bridge arms each have their own independent controllers, wherein N u N m and N d The number of sub-modules to be deployed for each of the three bridge arms is pre-allocated and distributed from the valve control function block, avoiding the interaction of PWM control signals between the bridge arms and reducing the complexity of the control system.

[0056] Figure 4 shows the flowchart of the separate control of the bridge arm controller in the novel MMC system described in this invention. Where AM is the joint status flag of the third bridge arm, U... au_ave U am_av e and U ad_ave The average values ​​of the submodule capacitor voltages for the upper arm, third arm, and lower arm, respectively, n u and n d I represents the allocation coefficient for the number of submodules deployed in the combined upper and lower bridge arms, respectively. u and I d The current directions for the upper and lower bridge arms are respectively, N. p N n N represents the number of sub-modules deployed for the upper arm (or combined upper arm) and the combined lower arm (or lower arm), respectively. u N m and N d The number of sub-modules deployed for the upper, third, and lower bridge arms, respectively.

[0057] Figure 5 shows the effect of separate control of the bridge arm controller of the novel MMC system described in this invention. From top to bottom, the instantaneous values ​​of the sub-module capacitor voltages of the upper bridge arm, the third bridge arm, and the lower bridge arm are shown.

[0058] It should be noted that, due to the structural characteristics of the new MMC, the third bridge arm has a "time-division joint" characteristic. Therefore, the AM flag is set to indicate the joint state of the third bridge arm.

[0059] Taking phase A as an example, when N pa When N > N, the third bridge arm and the upper bridge arm form a combined upper bridge arm, at which point AM = 1; when N na When N > N, the third bridge arm and the lower bridge arm form a combined lower bridge arm, at which point AM = 0; when N pa =N na When =N, the moment when the third bridge arm switches from the upper (lower) bridge arm joint to the lower (upper) bridge arm joint is set to AM=2.

[0060] 1) Determine the direction of the bridge arm current: Determine the current direction of the upper / lower bridge arm. When the bridge arm current is positive, the bridge arm submodule capacitor is in a charging state; when the bridge arm current is negative, the bridge arm submodule capacitor is in a discharging state. Set the current direction flag bits of the upper and lower bridge arms to I and I, respectively. u and I d When the current direction of the upper bridge arm is positive, I u =1, when I is negative u =-1; when the current direction of the current in the current arm is positive, I d =1, when I is negative d =-1.

[0061] 2) Calculate the average capacitor voltage of each bridge arm submodule: Taking phase A as an example, calculate the average capacitor voltage of the upper, lower, and third bridge arm submodules as U... au_ave、 U ad_ave U am_ave .

[0062] 3) Perform closed-loop control on the average difference of capacitor voltage between each bridge arm submodule: Taking phase A as an example, calculate the average difference U between the capacitor voltage of the upper bridge arm and the third bridge arm submodule. diffu Calculate the average difference U between the capacitor voltages of the lower bridge arm and the third bridge arm submodule. diffd .

[0063] U respectively diffu and U diffd As the input to the closed-loop controller, the output of the PI controller is the submodule allocation coefficient n when AM=1 and AM=0, respectively. u and n d .

[0064] 4) Submodule allocation in bridge arm joint mode: Under the system bridge arm controller separation control strategy, the allocation of submodules for each bridge arm in the new MMC is shown in Table 1, where round() represents the nearest integer function.

[0065] Table 1. Allocation of Submodule Quantities for Different Bridge Arm Joint Modes

[0066] When AM=1, the third bridge arm and the upper bridge arm together form a combined upper bridge arm, and the number of combined upper bridge arm sub-modules deployed at this time is N. p The number of lower bridge arm sub-modules deployed is N. n , will N p According to the allocation coefficient n u and the direction of the current in the upper bridge arm I u The current is allocated to the upper arm and the third arm respectively. Specifically, when the arm current is positive (I... u When =1), the capacitor voltage of the bridge arm submodule is in a charging state. Let N be the number of submodules engaged in the third bridge arm at this time. m =round(N p *n u The number of upper bridge arm sub-modules deployed, N u =N p -N m The number of N lower bridge arm sub-modules deployed d =N n When the bridge arm current is negative (I) u =-1), the capacitor voltage of the bridge arm submodule is in a discharging state, let N be the number of submodules engaged in the upper bridge arm at this time. u=round(N p *n u The number of N third bridge arm sub-modules deployed. m =N p -N u The number of N lower bridge arm sub-modules deployed d =N n , where round() is the nearest integer function.

[0067] When AM=0, the third bridge arm and the lower bridge arm together form a combined lower bridge arm, and the number of combined lower bridge arm sub-modules deployed at this time is N. n The number of upper bridge arm sub-modules deployed is N. p , will N n According to the allocation coefficient n d and the direction of the lower bridge arm current I d These are respectively allocated to the lower bridge arm and the third bridge arm. Specifically, when the bridge arm current is positive (I... d =1), the capacitor voltage of the bridge arm submodule is in a charging state, let N be the number of submodules engaged in the third bridge arm at this time. m =round(N n *n d The number of N lower bridge arm sub-modules deployed. d =N n -N m The number of N upper bridge arm sub-modules deployed u =N p When the bridge arm current is negative (I) d =-1), the capacitor voltage of the lower bridge arm submodule is in a discharging state, let N be the number of submodules engaged in the lower bridge arm at this time. d =round(N n *n d The number of N third bridge arm sub-modules deployed. m =N n -N d The number of N upper bridge arm sub-modules deployed u =N p , where round() is the nearest integer function.

[0068] When AM=2, the third arm is in switching mode. To ensure the safety of the arm status control switch's on / off action when the arm joint mode changes, when N... pa =N na When N = N, all upper and lower bridge arm sub-modules are engaged, and all third bridge arm sub-modules are disengaged. When the number of third bridge arm sub-modules engaged is 0, an action command is issued to the bridge arm status control switch to change the bridge arm joint mode, where N is the number of sub-modules of a bridge arm.

[0069] Under the control method proposed in this invention, by separating the control units of the upper, lower, and third bridge arms, the individual sorting and switching decisions of the capacitor voltages of each bridge arm sub-module are realized, reducing control link interaction; based on the bridge arm current direction and joint state, the sub-module allocation coefficient is calculated in real time, and the average difference of capacitor voltage is adjusted through closed-loop control to ensure power balance; when the bridge arm joint state is switched, a zero-voltage switching strategy is adopted to avoid dynamic voltage equalization problems.

[0070] Example 3, referring to Figure 6, also provides a novel modular multilevel converter system arm controller separation control system, including: a three-phase unit, each phase unit comprising an upper arm, a lower arm, a third arm, two arm reactors, and two sets of arm status control switches, each arm being composed of multiple cascaded half-bridge sub-modules; an upper arm controller, used to acquire the current direction of the upper arm, calculate the average value of the capacitor voltage of the upper arm sub-module, receive the average value of the capacitor voltage of the third arm sub-module, generate sub-module allocation parameters for joint operation of the upper arm and the third arm, determine the number of upper arm sub-modules to be engaged based on the joint operation status flag and the sub-module allocation parameters, and generate an upper arm pulse width modulation signal after sorting the capacitor voltages of the upper arm sub-modules; and a lower arm controller, used to acquire the current direction of the lower arm, calculate the average value of the capacitor voltage of the lower arm sub-module, receive the average value of the capacitor voltage of the third arm sub-module, generate sub-module allocation parameters for joint operation of the upper arm and the third arm, determine the number of upper arm sub-modules to be engaged based on the joint operation status flag and the sub-module allocation parameters, and generate an upper arm pulse width modulation signal after sorting the capacitor voltages of the upper arm sub-modules; and a lower arm controller, used to acquire the current direction of the lower arm, calculate the average value of the capacitor voltage of the lower arm sub-module, receive the average value of the capacitor voltage of the third arm sub-module, and generate sub-module allocation parameters for joint operation of the upper arm and the third arm. The average voltage of the block capacitor is used to generate the submodule deployment allocation parameters for the joint operation of the lower and third bridge arms. Based on the joint operation status flag and the submodule deployment allocation parameters, the deployment quantity of the lower bridge arm submodules is determined, and the lower bridge arm pulse width modulation signal is generated after sorting the capacitor voltages of the lower bridge arm submodules. The third bridge arm controller is used to calculate the average voltage of the third bridge arm submodule capacitors, receive the average voltage of the upper and lower bridge arm submodule capacitors, receive the joint operation status flag, the current direction of the upper and lower bridge arms, the submodule deployment allocation parameters, and the total deployment quantity of submodules, determine the deployment quantity of the third bridge arm submodules, and generate the third bridge arm pulse width modulation signal after sorting the capacitor voltages of the third bridge arm submodules. The upper, lower, and third bridge arm controllers are independent of each other and do not exchange submodule switching commands or pulse width modulation signals.

[0071] The above-mentioned unit modules can be embedded in the processor of the electronic device in hardware form or independent of it, or they can be stored in the memory of the electronic device in software form, so that the processor can call and execute the corresponding operations of the above modules.

[0072] This embodiment also provides an electronic device, which can be a terminal, and its internal structure diagram is shown in Figure 6. The electronic device includes a processor, memory, communication interface, display screen, and input device connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The communication interface is used for wired or wireless communication with external terminals. Wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. When the computer program is executed by the processor, it implements a novel modular multilevel converter system arm controller separation control method. The display screen can be a liquid crystal display (LCD) or an e-ink display. The input device can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the electronic device's casing, or an external keyboard, touchpad, or mouse.

[0073] This embodiment also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it performs the following steps: obtaining the current direction of the upper bridge arm and the current direction of the lower bridge arm; calculating the average value of the capacitor voltage of all sub-modules in the upper bridge arm, the average value of the capacitor voltage of all sub-modules in the lower bridge arm, and the average value of the capacitor voltage of all sub-modules in the third bridge arm; generating sub-module deployment allocation parameters for the combined operation of the upper and third bridge arms based on the difference between the average value of the capacitor voltage of the upper bridge arm sub-modules and the average value of the capacitor voltage of the third bridge arm sub-modules through proportional-integral adjustment; and generating sub-module deployment parameters for the combined operation of the lower and third bridge arms based on the difference between the average value of the capacitor voltage of the lower bridge arm sub-modules and the average value of the capacitor voltage of the third bridge arm sub-modules through proportional-integral adjustment. The system allocates input parameters; it obtains the joint operation status flag of the third bridge arm, which indicates whether the third bridge arm is in conjunction with the upper bridge arm, the lower bridge arm, or is in a bridge arm switching state; based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of sub-modules required for the upper and third bridge arms to be in conjunction, the total number of sub-modules required for the lower and third bridge arms to be in conjunction, and the sub-module input quantity allocation parameters, it determines the number of sub-modules that need to be input for each of the upper, lower, and third bridge arms; based on the number of sub-modules that need to be input for each, it sorts the capacitor voltages of all sub-modules in the upper, lower, and third bridge arms, and selects the corresponding number of sub-modules to be input or removed according to the sorting results, generating their respective pulse width modulation signals.

[0074] It should be noted that the above 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

[0075] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0076] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A novel modular multilevel converter system arm controller separation control method, characterized in that, include: Obtain the current direction of the upper bridge arm and the current direction of the lower bridge arm; Calculate the average capacitor voltage of all submodules in the upper arm, the lower arm, and the third arm respectively. Based on the difference between the average capacitor voltage of the upper arm and the third arm, generate submodule deployment allocation parameters for joint operation of the upper and third arms using proportional-integral (PI) adjustment. Similarly, based on the difference between the average capacitor voltage of the lower arm and the third arm, generate submodule deployment allocation parameters for joint operation of the lower and third arms using PI adjustment. Obtain the joint operation status flag of the third arm, which is used for... The system indicates whether the third bridge arm is in conjunction with the upper bridge arm, the lower bridge arm, or is in a bridge arm switching state. Based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of sub-modules required for the upper and third bridge arms to be in conjunction, the total number of sub-modules required for the lower and third bridge arms to be in conjunction, and the sub-module allocation parameters, the system determines the number of sub-modules required for each of the upper, lower, and third bridge arms. Based on the number of sub-modules required for each, the system sorts the capacitor voltages of all sub-modules in the upper, lower, and third bridge arms, and selects the corresponding number of sub-modules to be in or out according to the sorting results, generating their respective pulse width modulation signals.

2. The novel modular multilevel converter system arm controller separation control method as described in claim 1, characterized in that, The process of obtaining the current direction of the upper bridge arm and the current direction of the lower bridge arm includes: when the current of the upper bridge arm is flowing in the forward direction, determining that the current direction of the upper bridge arm is the charging direction; when the current of the upper bridge arm is flowing in the reverse direction, determining that the current direction of the upper bridge arm is the discharging direction; when the current of the lower bridge arm is flowing in the forward direction, determining that the current direction of the lower bridge arm is the charging direction; and when the current of the lower bridge arm is flowing in the reverse direction, determining that the current direction of the lower bridge arm is the discharging direction.

3. The novel modular multilevel converter system arm controller separation control method as described in claim 2, characterized in that, The method of determining the number of submodules required for each of the upper, lower, and third bridge arms based on the joint operation status indicator of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of submodules required for the joint operation of the upper and third bridge arms, the total number of submodules required for the joint operation of the lower and third bridge arms, and the submodule allocation parameters, includes: when the joint operation status indicator of the third bridge arm indicates that the third bridge arm is in conjunction with the upper bridge arm, if the current direction of the upper bridge arm is the charging direction, the total number of submodules required for the joint operation of the upper and third bridge arms is allocated to the third bridge arm according to the submodule allocation parameters, and the remaining number is allocated to the upper bridge arm; if the current direction of the upper bridge arm is the discharging direction, the total number of submodules required for the joint operation of the upper and third bridge arms is allocated to the upper bridge arm according to the submodule allocation parameters, and the remaining number is allocated to the third bridge arm; the number of submodules required for the lower bridge arm is equal to the total number of submodules required for the joint operation of the lower and third bridge arms.

4. The novel modular multilevel converter system arm controller separation control method as described in claim 3, characterized in that, The method of determining the number of submodules required for each of the upper, lower, and third bridge arms based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of submodules required for the joint operation of the upper and third bridge arms, the total number of submodules required for the joint operation of the lower and third bridge arms, and the submodule allocation parameters, further includes: when the joint operation status flag of the third bridge arm indicates that the third and lower bridge arms are in conjunction, if the current direction of the lower bridge arm is the charging direction, the total number of submodules required for the joint operation of the lower and third bridge arms is allocated to the third bridge arm according to the submodule allocation parameters, and the remaining number is allocated to the lower bridge arm; if the current direction of the lower bridge arm is the discharging direction, the total number of submodules required for the joint operation of the lower and third bridge arms is allocated to the lower bridge arm according to the submodule allocation parameters, and the remaining number is allocated to the third bridge arm; the number of submodules required for the upper bridge arm is equal to the total number of submodules required for the joint operation of the upper and third bridge arms.

5. The novel modular multilevel converter system arm controller separation control method as described in claim 4, characterized in that, The method of determining the number of sub-modules required for each of the upper, lower, and third bridge arms based on the joint operation status flag of the third bridge arm, the current direction of the upper bridge arm, the current direction of the lower bridge arm, the total number of sub-modules required for the joint operation of the upper and third bridge arms, the total number of sub-modules required for the joint operation of the lower and third bridge arms, and the sub-module allocation parameters, further includes: when the joint operation status flag of the third bridge arm indicates that the third bridge arm is in the bridge arm switching state, setting the number of sub-modules required for the upper bridge arm to the total number of sub-modules contained in the upper bridge arm, setting the number of sub-modules required for the lower bridge arm to the total number of sub-modules contained in the lower bridge arm, and setting the number of sub-modules required for the third bridge arm to zero.

6. The novel modular multilevel converter system arm controller separation control method as described in claim 5, characterized in that, Also includes: During the period when the third bridge arm is in the bridge arm switching state, a switching command is sent to the two sets of bridge arm status control switches to disconnect the third bridge arm from the currently connected bridge arm and connect it to another bridge arm, thus completing the conversion of the joint operation mode.

7. The novel modular multilevel converter system arm controller separation control method as described in claim 6, characterized in that, The generation of their respective pulse width modulation signals includes the following: during the generation of pulse width modulation signals, the upper arm controller, the lower arm controller, and the third arm controller do not exchange submodule switching commands or pulse width modulation signals with each other.

8. A novel modular multilevel converter system arm controller separation control system, using the method described in any one of claims 1 to 7, characterized in that, include: The three-phase unit consists of an upper bridge arm, a lower bridge arm, a third bridge arm, two bridge arm reactors, and two sets of bridge arm status control switches. Each bridge arm is composed of multiple cascaded half-bridge sub-modules. The upper bridge arm controller is used to acquire the current direction of the upper bridge arm, calculate the average value of the capacitor voltage of the upper bridge arm sub-module, receive the average value of the capacitor voltage of the third bridge arm sub-module, generate sub-module allocation parameters for the joint operation of the upper and third bridge arms, determine the number of upper bridge arm sub-modules to be engaged based on the joint operation status flag and the sub-module allocation parameters, and generate an upper bridge arm pulse width modulation signal after sorting the capacitor voltage of the upper bridge arm sub-modules. The lower bridge arm controller is used to acquire the current direction of the lower bridge arm, calculate the average value of the capacitor voltage of the lower bridge arm sub-module, receive the average value of the capacitor voltage of the third bridge arm sub-module, generate sub-module allocation parameters for the joint operation of the lower bridge arm and the third bridge arm, determine the number of lower bridge arm sub-modules to be engaged based on the joint operation status flag and the sub-module allocation parameters, and generate a lower bridge arm pulse width modulation signal after sorting the capacitor voltage of the lower bridge arm sub-modules. The third arm controller is used to calculate the average capacitor voltage of the third arm submodule, receive the average capacitor voltage of the upper arm submodule and the lower arm submodule, receive the joint operation status flag, the current direction of the upper arm and the current direction of the lower arm, the submodule deployment quantity allocation parameters and the total number of submodules deployed, determine the number of third arm submodules deployed, and generate the third arm pulse width modulation signal after sorting the capacitor voltage of the third arm submodules. The upper arm controller, the lower arm controller and the third arm controller are independent of each other and do not exchange submodule switching commands or pulse width modulation signals.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the novel modular multilevel converter system arm controller separation control method 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 by the processor, it implements the steps of the novel modular multilevel converter system arm controller separation control method according to any one of claims 1 to 7.

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