Energy balance control method and device based on hybrid MMC

Abstract

The invention discloses an energy balance control method and device based on a hybrid MMC, and relates to the technical field of electric power. The method comprises the following steps: acquiring a reference voltage of a bridge arm, a half-bridge sub-module output capability of the bridge arm and a full-bridge sub-module output capability of the bridge arm; dividing the input state of the half-bridge sub-module into active input and passive input according to the reference voltage, the output capability of the half-bridge sub-module and the output capability of the full-bridge sub-module; based on the reference voltage of the bridge arm and the output capability of the full-bridge sub-module, determining a passive input demarcation point of the half-bridge sub-module, and determining the capacitance voltage variation when the half-bridge sub-module is passively input; controlling the half-bridge sub-modules to carry out minimum active input; and determining the input condition of the full-bridge sub-module according to the input condition of the half-bridge sub-module, and performing energy balance control based on the input condition of the half-bridge sub-module and the input condition of the full-bridge sub-module. The hybrid MMC-based energy balance control method is used for realizing the hybrid MMC-based energy balance control function.

Description

Technical Field

[0001] This application relates to the field of power technology, and in particular to an energy balance control method and device based on hybrid MMC. Background Technology

[0002] In the field of power technology, my country's DC transmission technology has developed rapidly in recent years, achieving a leapfrog development from conventional DC transmission to flexible DC transmission. Among them, the Modular Multilevel Converter (MMC) has become the primary choice for flexible DC transmission projects due to its low loss, high output waveform quality, and excellent control flexibility. In MMC, the hybrid MMC, composed of half-bridge submodules (HBSM) and full-bridge submodules (FBSM), possesses DC fault handling capabilities and good economic efficiency, and has broad development prospects. It has already been practically applied in my country's Kunliulong flexible DC transmission project. Unlike conventional MMCs, hybrid MMCs can operate under overmodulation using the negative voltage output capability of the full-bridge submodules. However, the different operating characteristics of half-bridge and full-bridge submodules under overmodulation conditions may lead to energy imbalance between the two types of submodules, threatening the safe and stable operation of the hybrid MMC. Therefore, how to control the energy balance of hybrid MMCs to ensure their stable operation has become a key issue for experts in the field.

[0003] Currently, existing hybrid MMC capacitor voltage balancing control mainly employs methods such as current harmonic injection, voltage harmonic injection, topology modification, and increasing the full-bridge ratio. These methods primarily influence the charging and discharging process of sub-modules by introducing additional control signals or altering the circuit topology, thereby achieving capacitor voltage balancing control. However, in practical applications, existing methods using current and voltage harmonic injection suffer from increased voltage and current stress and harmonic content, severely impacting power parameters. Modifying the topology or increasing the full-bridge ratio obviously leads to increased hardware and higher costs. Therefore, developing a hybrid MMC-based energy balance control method that avoids impacting power parameters while minimizing cost increases has become a pressing issue in this field. Summary of the Invention

[0004] This application provides an energy balance control method and apparatus based on hybrid MMC, with the main objective of implementing an energy balance control method based on hybrid MMC to solve the problems of impacting electrical parameters and increasing costs in the existing energy balance control process of hybrid MMC.

[0005] To address the aforementioned technical problems, this application provides the following technical solutions:

[0006] In a first aspect, this application provides an energy balance control method based on hybrid MMC, the method comprising:

[0007] Obtain the reference voltage of the bridge arm, the half-bridge submodule output capability, and the full-bridge submodule output capability of the bridge arm in the hybrid MMC;

[0008] Based on the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule, the engagement state of the half-bridge submodule is divided into active engagement and passive engagement. Passive engagement characterizes the operational state of the half-bridge submodule in ensuring the basic operating functions of the hybrid MMC to meet the bridge arm reference voltage requirements. Active engagement characterizes the operational state of the half-bridge submodule in actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement.

[0009] Based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule, the passive engagement boundary point of the half-bridge submodule is determined, and the change in capacitor voltage when the half-bridge submodule is passively engaged is determined.

[0010] The half-bridge submodule is controlled to perform minimum active engagement to compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged; wherein, the minimum active engagement is used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged.

[0011] The engagement status of the full-bridge submodule is determined based on the engagement status of the half-bridge submodule, and energy balance control is performed on the hybrid MMC based on the engagement status of the half-bridge submodule and the full-bridge submodule. The engagement status is used to characterize the change of the engagement reference voltage of the half-bridge submodule and the full-bridge submodule when engagement control is performed. The engagement status of the half-bridge submodule is determined based on the minimum active engagement of the half-bridge submodule.

[0012] Secondly, this application also provides an energy balance control device based on a hybrid MMC, comprising:

[0013] The acquisition unit is used to acquire the reference voltage of the bridge arm, the half-bridge submodule output capability, and the full-bridge submodule output capability of the bridge arm in the hybrid MMC.

[0014] The division unit is used to classify the engagement state of the half-bridge submodule into active engagement and passive engagement based on the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule. Passive engagement characterizes the operational state of the half-bridge submodule in ensuring the basic operating functions of the hybrid MMC to meet the bridge arm reference voltage requirements. Active engagement characterizes the operational state of the half-bridge submodule in actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement.

[0015] The determining unit is used to determine the passive engagement boundary point of the half-bridge submodule based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule, and to determine the change in capacitor voltage when the half-bridge submodule is passively engaged.

[0016] The control unit is used to control the half-bridge submodule to perform minimum active engagement to compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged; wherein, the minimum active engagement is used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged.

[0017] An operating unit is used to determine the engagement status of the full-bridge submodule based on the engagement status of the half-bridge submodule, and to perform energy balance control on the hybrid MMC based on the engagement status of the half-bridge submodule and the full-bridge submodule. The engagement status is used to characterize the change of the engagement reference voltage of the half-bridge submodule and the full-bridge submodule when engagement control is performed. The engagement status of the half-bridge submodule is determined based on the minimum active engagement of the half-bridge submodule.

[0018] Thirdly, embodiments of this application provide a storage medium including a stored program, wherein, when the program is executed, it controls the device where the storage medium is located to perform the energy balance control method based on hybrid MMC for the terminal device described in the first aspect.

[0019] Fourthly, embodiments of this application provide an energy balance control device based on hybrid MMC, the device including a storage medium; and one or more processors, the storage medium being coupled to the processors, the processors being configured to execute program instructions stored in the storage medium; the program instructions, when executed, perform the energy balance control method based on hybrid MMC for the terminal device described in the first aspect.

[0020] Fifthly, embodiments of this application also provide a computer program product, including a computer program that, when executed by a processor, implements the steps of the energy balance control method based on hybrid MMC as described in any of the first aspects.

[0021] By employing the above-described technical solution, the technical solution provided in this application has at least the following advantages:

[0022] This application provides an energy balance control method and apparatus based on a hybrid MMC. The method first obtains the reference voltage of the bridge arm, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule in the hybrid MMC. Then, based on the reference voltage, half-bridge submodule output capability, and full-bridge submodule output capability, the engagement state of the half-bridge submodule is divided into active engagement and passive engagement. Passive engagement characterizes the operating state of the half-bridge submodule ensuring the basic operation of the hybrid MMC to meet the bridge arm reference voltage requirements. Active engagement characterizes the operating state of the half-bridge submodule actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement. Finally, based on the bridge arm reference voltage and the full-bridge submodule output capability, the passive engagement boundary point of the half-bridge submodule is determined, and the half-bridge submodule is determined to be in a passive state. The system first determines the capacitor voltage change during activation; then, it controls the half-bridge submodule to perform minimum active activation to compensate for the capacitor voltage change when the half-bridge submodule is passively activated; wherein, the minimum active activation is used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the capacitor voltage change when the half-bridge submodule is passively activated; finally, the activation status of the full-bridge submodule is determined based on the activation status of the half-bridge submodule, and energy balance control is performed on the hybrid MMC based on the activation status of the half-bridge submodule and the full-bridge submodule, wherein, the activation status is used to characterize the change of the activation reference voltage of the half-bridge submodule and the full-bridge submodule during activation control, and the activation status of the half-bridge submodule is determined based on the minimum active activation of the half-bridge submodule, thereby realizing the energy balance control function based on the hybrid MMC. Compared with existing technologies, this application effectively solves the energy imbalance problem during the overmodulation operation of hybrid MMCs by dividing the engagement state of the half-bridge submodules, determining the passive engagement boundary point and capacitor voltage change, and then performing minimum active engagement control. This improves the energy stability of the submodules during overmodulation operation of hybrid MMCs and ensures the safe and stable operation of the system. Simultaneously, it eliminates the need for additional control equipment or changes to the circuit topology, offering advantages such as simple architecture and low cost. While achieving energy balance control, it avoids the increased cost and system complexity caused by adding equipment or changing the topology in existing technologies, demonstrating good economic efficiency and practicality. Furthermore, since the method of this application does not require additional current harmonic injection or voltage harmonic injection during the control process, it does not affect the properties of electrical energy, avoiding the problems of increased voltage and current stress and harmonic content.Furthermore, this application effectively solves the energy imbalance problem during the overmodulation operation of the hybrid MMC by accurately distinguishing the active and passive activation states of the half-bridge submodule and carrying out targeted control. This avoids faults such as submodule capacitor voltage exceeding limits, system oscillation, and even instability caused by energy imbalance, significantly improving the stability and reliability of the hybrid MMC under overmodulation operation conditions and ensuring the uninterrupted and safe operation of the power system.

[0023] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0024] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, with the same or corresponding reference numerals denoteing the same or corresponding parts, wherein:

[0025] Figure 1 This paper presents a flowchart of an energy balance control method based on hybrid MMC according to an embodiment of this application.

[0026] Figure 2 This illustration shows a block diagram of an energy balance control device based on a hybrid MMC according to an embodiment of this application;

[0027] Figure 3 This paper shows a block diagram of another energy balance control device based on a hybrid MMC provided in an embodiment of this application. Detailed Implementation

[0028] Exemplary embodiments of this application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.

[0029] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application pertains.

[0030] This application provides an energy balance control method based on hybrid MMC, specifically as follows: Figure 1 As shown, the method includes:

[0031] 101. Obtain the reference voltage of the bridge arm, the half-bridge submodule output capability, and the full-bridge submodule output capability of the bridge arm in the hybrid MMC.

[0032] In this embodiment, the bridge arm reference voltage can be calculated by the hybrid MMC control system based on grid demand, system operating status, and control strategy, and then distributed to the control units of each bridge arm. For example, during stable operation, if the grid requires an AC voltage of a certain amplitude and frequency, the control system will calculate the reference voltage for each bridge arm accordingly to ensure that the voltage waveform output by the entire MMC system meets the requirements.

[0033] The output capability of a half-bridge submodule can be understood as the overall output capability of all half-bridge submodules on a single bridge arm in a hybrid MMC. That is, firstly, the number of half-bridge submodules within the bridge arm can be determined; this number is a parameter determined during the MMC system design. Then, the rated capacitor voltage of each half-bridge submodule is determined. This rated capacitor voltage is the voltage value maintained by the capacitor of each half-bridge submodule during normal operation, and is usually determined by the hardware configuration and design of the submodule, stored in the control system or obtainable in real time through the submodule's monitoring unit.

[0034] Similarly, the output capability of this full-bridge submodule can be understood as the overall output capability of all full-bridge submodules on a single bridge arm in a hybrid MMC. Here, it is also necessary to first determine the number of full-bridge submodules in the bridge arm, which is also determined during the MMC system design phase. After that, it is necessary to determine the rated capacitor voltage of the full-bridge submodule, which is also an inherent parameter of the submodule. It can be found in the system design file or obtained through real-time monitoring.

[0035] By acquiring the reference voltage of the bridge arm, the output capability of the half-bridge submodule of the bridge arm, and the output capability of the full-bridge submodule, data support can be provided for subsequent related control, thus laying the foundation for the smooth execution of the energy balance control of the hybrid MMC described in this embodiment.

[0036] 102. Based on the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule, the activation state of the half-bridge submodule is divided into active activation and passive activation.

[0037] The passive input is used to characterize the operating state of the half-bridge submodule to ensure the basic operating function of the hybrid MMC when meeting the requirements of the bridge arm reference voltage; the active input is used to characterize the operating state of the half-bridge submodule to actively control the hybrid MMC to prevent energy imbalance caused by passive input.

[0038] In this embodiment, after obtaining the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule in the aforementioned steps, the next step is to analyze the passive and active activation processes of the half-bridge submodule based on these obtained parameters.

[0039] On the one hand, regarding passive switching, when the bridge arm reference voltage exceeds the output capacity of the full-bridge submodule, the output capacity of the full-bridge submodule alone cannot meet the bridge arm reference voltage requirement. To ensure the MMC system can output sufficient voltage to maintain basic operation, the half-bridge submodule must be passively switched on to bear the voltage exceeding the output capacity of the full-bridge submodule. Therefore, in this process, the half-bridge submodule adopts a passive switching mode. For example, during system operation, in the normal operation of a hybrid MMC, if the hybrid MMC bridge arm voltage output capacity is 100kV, and there are 4 half-bridges and 6 full-bridges on the bridge arm, with each submodule voltage being 10kV, the output voltage on the bridge arm during normal operation is a sine wave with a peak value not exceeding 100kV. Then, when the bridge arm output voltage exceeds 60kV, the half-bridge submodule will enter passive switching mode to ensure the normal operation of the hybrid MMC.

[0040] On the other hand, for active activation, within a specific region formed by multiple factors such as the bridge arm reference voltage, the difference between the bridge arm reference voltage and the output capability of the half-bridge submodule, the output capability of the full-bridge submodule, and zero voltage, a control strategy is used to actively activate the half-bridge submodule. The purpose of this active activation is to adjust the energy balance, prevent energy imbalance caused by passive activation, and maintain the stable operation of the entire system. For example, under overmodulation operation conditions, actively activating the half-bridge submodule can optimize the energy distribution among submodules, preventing some submodules from having excessively high or low energy levels.

[0041] In this way, by analyzing the operating modes of the half-bridge submodule, it is possible to determine when the half-bridge submodule will participate in the passive input mode and when it needs to participate in the active input mode in the hybrid MMC. This ensures that the entire hybrid MMC can operate normally and that the subsequent energy balancing process can be controlled based on the normal operation of the hybrid MMC.

[0042] 103. Based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule, determine the passive engagement boundary point of the half-bridge submodule, and determine the change in capacitor voltage when the half-bridge submodule is passively engaged.

[0043] This step mainly consists of two processes: determining the passive engagement boundary point of the half-bridge submodule and determining the change in capacitor voltage during the passive engagement process.

[0044] (1) When determining the passive switching point of the half-bridge submodule, the judgment is mainly based on the bridge arm reference voltage and the output capability of the full-bridge submodule. As can be seen from the aforementioned steps, the passive switching mode is mainly to deal with the situation where the output capability of the full-bridge submodule alone cannot meet the bridge arm reference voltage requirement. Therefore, in this process, a judgment can be made based on the bridge arm voltage reference value and the output capability of the full-bridge submodule to determine whether the output capability of the full-bridge submodule alone can meet the bridge arm reference voltage requirement. For example, assuming the output capability of the full-bridge submodule is 50kV, when the bridge arm reference voltage is 50kV, this is the starting point for the passive switching of the half-bridge submodule.

[0045] (2) When determining the change in capacitor voltage when the half-bridge submodule is passively switched on, the passive switching boundary point has already been determined in step (1). Therefore, the capacitor voltage at the start and end points of the passive switching of the half-bridge submodule can be recorded, and the change in capacitor voltage when the half-bridge submodule is passively switched on can be calculated. For example, if the capacitor voltage at the start point is 10.2kV and the capacitor voltage at the end point is 9.8kV, then the change in capacitor voltage is 0.4kV.

[0046] 104. Control the half-bridge submodule to perform minimum active engagement to compensate for the capacitor voltage change when the half-bridge submodule is passively engaged.

[0047] The minimum active input is used to characterize the minimum control amount of the half-bridge submodule on the half-bridge module while ensuring that it can compensate for the change in capacitor voltage when the half-bridge submodule is passively input.

[0048] During overmodulation operation of a hybrid MMC, passive switching of the half-bridge submodules can cause changes in their capacitor voltage, potentially leading to energy imbalance. Therefore, by actively controlling the half-bridge submodules to a minimum, the capacitor voltage changes generated during passive switching can be precisely compensated, thus achieving energy balance. This compensation is based on the principles of energy conservation and voltage regulation. By controlling the charging and discharging process of the half-bridge submodules, their capacitor voltage is restored to the normal range, ensuring stable system operation. In this embodiment, the goal of minimum active switching is to minimize control actions on the half-bridge submodules while maintaining energy balance, thereby reducing control complexity and improving control efficiency. By real-time monitoring and analysis of capacitor voltage changes, combined with the direction of the bridge arm current, the degree and timing of half-bridge submodule switching can be precisely controlled, achieving fine-grained regulation of energy balance.

[0049] Therefore, in this embodiment, the change in capacitor voltage when the half-bridge submodule is passively engaged must first be determined. This can be achieved by controlling the half-bridge submodule to only passively engage within one cycle after the hybrid MMC has been running stably, recording the capacitor voltage at the start and end of the passive engagement, and then performing calculations.

[0050] Next, the direction of the bridge arm current is determined. Specifically, the direction of the bridge arm current can be detected in real time, which is crucial for determining how to control the active activation of the half-bridge submodule. The direction of the bridge arm current affects the charging and discharging process of the half-bridge submodule, thus affecting the change in capacitor voltage.

[0051] Specifically, the process of minimum active input control based on the above is as follows:

[0052] 1) Determine the sign of the capacitor voltage change: First, determine whether the capacitor voltage change is positive or negative when the half-bridge sub-module is passively engaged. Generally speaking, a positive voltage change indicates an increase in voltage, while a negative voltage change indicates a decrease in voltage.

[0053] 2) Perform corresponding control based on the sign of ΔUch and the direction of the bridge arm current:

[0054] When the change in capacitor voltage is negative:

[0055] If the bridge arm current is positive, the control of the bridge arm half-bridge submodules maximizes output, allowing them to output as much energy as possible, under safe conditions, to compensate for the decrease in capacitor voltage. Simultaneously, the voltage increase is monitored in real time, and when it reaches a certain threshold, active connection is cut off to prevent overcharging. If the bridge arm current is negative, all half-bridge submodules are cut off from active connection. This is because the current direction is unfavorable for capacitor voltage increase, and continued connection would exacerbate energy imbalance; cutting off connection maintains capacitor voltage stability.

[0056] When the change in capacitor voltage is positive:

[0057] Specifically, if the bridge arm current is negative, the output of the half-bridge submodules in the bridge arm is maximized. The voltage drop is monitored in real time in the same manner as described above. When the capacitor voltage change reaches a certain threshold, active connection is cut off to prevent excessive capacitor voltage drop. Conversely, when the bridge arm current is positive, all half-bridge submodules are cut off from active connection to prevent further capacitor voltage increase and maintain capacitor voltage stability.

[0058] 105. Determine the deployment status of the full-bridge submodule based on the deployment status of the half-bridge submodule, and perform energy balance control on the hybrid MMC based on the deployment status of the half-bridge submodule and the full-bridge submodule.

[0059] The "engagement status" is used to characterize the change in the engagement reference voltage of the half-bridge submodule and the full-bridge submodule during engagement control. The engagement status of the half-bridge submodule is determined based on the minimum active engagement of the half-bridge submodule.

[0060] After implementing minimum engagement control for the half-bridge submodule, the engagement status of the half-bridge submodule is effectively determined. This engagement status can be understood as the impact of the half-bridge submodule engagement on the input voltage. Since a hybrid MMC consists of only half-bridge and full-bridge submodules, once the engagement status of the half-bridge submodules is determined, the engagement status of the full-bridge submodules can be deduced. Then, by combining the engagement statuses of both the half-bridge and full-bridge submodules, energy balance control can be performed on the hybrid MMC to ensure the energy stability of the entire system.

[0061] This application provides an energy balance control method based on a hybrid MMC. The embodiments of this application first obtain the reference voltage of the bridge arm, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule in the hybrid MMC. Then, based on the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule, the engagement state of the half-bridge submodule is divided into active engagement and passive engagement. Passive engagement characterizes the operating state of the half-bridge submodule ensuring the basic operation of the hybrid MMC to meet the bridge arm reference voltage requirements. Active engagement characterizes the operating state of the half-bridge submodule actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement. Subsequently, based on the bridge arm reference voltage and the output capability of the full-bridge submodule, the passive engagement boundary point of the half-bridge submodule is determined, and the half-bridge submodule is determined to be in a passive state. The system first determines the capacitor voltage change during activation; then, it controls the half-bridge submodule to perform minimum active activation to compensate for the capacitor voltage change when the half-bridge submodule is passively activated; wherein, the minimum active activation is used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the capacitor voltage change when the half-bridge submodule is passively activated; finally, the activation status of the full-bridge submodule is determined based on the activation status of the half-bridge submodule, and energy balance control is performed on the hybrid MMC based on the activation status of the half-bridge submodule and the full-bridge submodule, wherein, the activation status is used to characterize the change of the activation reference voltage of the half-bridge submodule and the full-bridge submodule during activation control, and the activation status of the half-bridge submodule is determined based on the minimum active activation of the half-bridge submodule, thereby realizing the energy balance control function based on the hybrid MMC. Compared with existing technologies, this application's embodiments effectively solve the energy imbalance problem during the overmodulation operation of hybrid MMCs by dividing the engagement state of the half-bridge submodules, determining the passive engagement boundary point and capacitor voltage change, and then performing minimum active engagement control. This improves the energy stability of the submodules during overmodulation operation of hybrid MMCs and ensures the safe and stable operation of the system. Simultaneously, it eliminates the need for additional control equipment or changes to the circuit topology, offering advantages such as simple architecture and low cost. While achieving energy balance control, it avoids the increased cost and system complexity caused by adding equipment or changing the topology in existing technologies, demonstrating good economic efficiency and practicality. Furthermore, since the method of this application's embodiments does not require additional current harmonic injection or voltage harmonic injection during the control process, it does not affect the properties of electrical energy, avoiding the problem of increased voltage and current stress and harmonic content.Furthermore, the embodiments of this application accurately distinguish between the active and passive engagement states of the half-bridge submodules and perform targeted control, effectively solving the energy imbalance problem during the overmodulation operation of the hybrid MMC. This avoids faults such as submodule capacitor voltage exceeding limits, system oscillation, and even instability caused by energy imbalance, significantly improving the stability and reliability of the hybrid MMC under overmodulation operation conditions, and ensuring the uninterrupted and safe operation of the power system.

[0062] As a further description and refinement of the above embodiments, in some embodiments, the output capability of the half-bridge submodule in step 101 of the aforementioned embodiments is calculated using a first calculation formula, wherein the first calculation formula is:

[0063] A = Nh * Uch;

[0064] Where A is used to characterize the output capability of the half-bridge submodule in the bridge arm, Nh is the number of half-bridge submodules in the bridge arm, and Uch is the rated capacitor voltage of the half-bridge module.

[0065] Furthermore, the output capability of the full-bridge submodule in step 101 of the aforementioned embodiment is calculated based on a second calculation formula, wherein the second calculation formula is:

[0066] B = Nf * Ucf;

[0067] Where B is used to characterize the output capability of the full-bridge submodule within the bridge arm, Nf is the number of full-bridge submodules within the bridge arm, and Ucf is the rated capacitor voltage of the full-bridge submodule.

[0068] The specific process for calculating the output capability of the half-bridge submodule is as follows:

[0069] (1) Obtain the number of half-bridge submodules Nh. During the design phase of a hybrid MMC system, the number of half-bridge submodules Nh within a bridge arm is a known, fixed parameter. For example, in a well-designed hybrid MMC topology, the number of half-bridge submodules within a bridge arm can be determined by reviewing the system's design drawings or configuration files. Assuming a bridge arm contains 5 half-bridge submodules, then Nh = 5.

[0070] (2) Obtain the rated capacitor voltage Uch of the half-bridge submodule. The rated capacitor voltage Uch of the half-bridge submodule is an electrical parameter of each half-bridge submodule itself, usually provided by the manufacturer or specified in the system design document. This parameter represents the voltage value maintained by the capacitor of a single half-bridge submodule during normal operation. For example, assuming the rated capacitor voltage of each half-bridge submodule is 10kV, then Uch = 10kV.

[0071] (3) Calculate the output capability A of the half-bridge submodule based on the first calculation formula. Substitute the number of half-bridge submodules Nh and the rated capacitor voltage Uch into the first calculation formula A = Nh * Uch. Following the example above, the output capability A of the half-bridge submodule is calculated to be 5 × 10kV = 50kV. This value represents the maximum voltage support capability that all half-bridge submodules in the bridge arm can provide under ideal conditions, that is, the total voltage they can output.

[0072] The specific process for calculating the output capability of the full-bridge submodule is as follows:

[0073] (1) Obtain the number of full-bridge submodules Nf. Similarly, the number of full-bridge submodules Nf in a bridge arm can be determined during the design phase of a hybrid MMC system. Assuming there are 3 full-bridge submodules in a certain bridge arm, then Nf = 3.

[0074] (2) Obtain the rated capacitor voltage Ucf of the full-bridge submodule. The rated capacitor voltage Ucf of the full-bridge submodule is also an electrical parameter of each full-bridge submodule itself, which can be obtained by consulting the manufacturer's technical data or system design documents. For example, if the rated capacitor voltage of each full-bridge submodule is 15kV, then Ucf = 15kV.

[0075] (3) Calculate the output capability B of the full-bridge submodule. Substitute the number of full-bridge submodules Nf and the rated capacitor voltage Ucf into the second calculation formula B = Nf * Ucf. Taking the above data as an example, the output capability B of the full-bridge submodule is 3 × 15kV = 45kV. It reflects the maximum voltage output capability that all full-bridge submodules in the bridge arm can provide.

[0076] In this embodiment, these calculations are typically performed based on the system's design parameters. In a hybrid MMC control system, these calculation results can be pre-configured or calculated during system initialization for use in subsequent control processes. These output capability parameters are crucial for the control system because they determine the maximum voltage that the bridge arm can output, affecting the overall operating range and control strategy of the MMC system. By accurately calculating the output capabilities of the half-bridge and full-bridge submodules, accurate data can be provided for the allocation of bridge arm reference voltages and the control of submodule activation, ensuring stable system operation and the achievement of energy balance control.

[0077] As a further description and refinement of the above embodiments, in some embodiments, the reference voltage of the bridge arm includes the bridge arm voltage reference value of the previous control cycle and the bridge arm voltage reference value of the current control cycle.

[0078] Step 103 of the aforementioned embodiment, "Determining the passive engagement boundary point of the half-bridge submodule based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule," includes:

[0079] When it is determined that the reference value of the bridge arm voltage in the previous control cycle is less than the output capability of the full-bridge submodule, and the reference value of the bridge arm voltage in the current control cycle is greater than the output capability of the full-bridge submodule, this moment is determined to be the starting point for the passive activation of the half-bridge submodule.

[0080] When it is determined that the reference value of the bridge arm voltage in the previous control cycle is greater than the output capability of the full-bridge submodule, and the reference value of the bridge arm voltage in the current control cycle is less than the output capability of the full-bridge submodule, the passive engagement termination point of the half-bridge submodule is determined.

[0081] In this embodiment, the first step is to obtain the arm reference voltage. This arm reference voltage is a key parameter used in the hybrid MMC to control the arm output voltage, including the arm voltage reference value of the previous control cycle (denoted as Ur_t-1) and the arm voltage reference value of the current control cycle (denoted as Ur_t). These reference voltage values ​​are calculated and updated by the controller in each control cycle based on the MMC system's control strategy and grid requirements.

[0082] Then, the output capability of the full-bridge submodule is obtained based on the method described in the foregoing embodiment. The output capability of the full-bridge submodule (denoted as B) is calculated based on the number of full-bridge submodules (Nf) within the bridge arm and the rated capacitor voltage (Ucf) of each full-bridge submodule, using the formula B = Nf × Ucf. This parameter reflects the maximum voltage support capability that the full-bridge submodule can provide under the current operating conditions.

[0083] Next, the passive engagement boundary point of the half-bridge submodule is determined. This determination process includes both the starting point and the ending point.

[0084] (1) Determining the passive energization starting point. In each control cycle, the control system compares the bridge arm voltage reference value (Ur_t-1) from the previous control cycle with the output capability (B) of the full-bridge submodule. If Ur_t-1 is less than B, while the bridge arm voltage reference value (Ur_t) of the current control cycle is greater than B, this means the required bridge arm reference voltage exceeds the voltage capability provided by the full-bridge submodule. At this point, the system determines that this is the starting point for the passive energization of the half-bridge submodule. For example, assuming B is 50kV, if Ur_t-1 is 45kV, and Ur_t rises to 55kV, then the half-bridge submodule begins passive energization.

[0085] (2) Determining the end point of passive engagement: In this embodiment, it is necessary to continuously monitor the change of the bridge arm reference voltage. When the bridge arm voltage reference value (Ur_t-1) of the previous control cycle is greater than the output capability (B) of the full-bridge submodule, while the bridge arm voltage reference value (Ur_t) of the current control cycle is less than B, it indicates that the demand for the bridge arm reference voltage is lower than the voltage capability that the full-bridge submodule can provide. At this time, the system will determine that this is the end point of passive engagement of the half-bridge submodule. For example, taking B as 50kV, if Ur_t-1 is 55kV and Ur_t drops to 45kV, then the half-bridge submodule stops passive engagement.

[0086] The method described in this embodiment can accurately determine the timing of passive activation of the half-bridge submodule, providing an accurate basis for subsequent energy balance control and ensuring the stable operation of the hybrid MMC system.

[0087] As a further description and refinement of the above embodiments, in some embodiments, step "104. Controlling the half-bridge submodule to perform minimum active engagement" in the aforementioned embodiments includes:

[0088] If the change in capacitor voltage of a half-bridge submodule when passively connected is negative, then when the bridge arm current is positive, the half-bridge submodule is controlled to maximize output, and the reference voltage for active connection of the half-bridge submodule is controlled according to the first target formula. When the voltage increase caused by the active connection of the half-bridge submodule reaches the change in capacitor voltage when the half-bridge submodule is passively connected, all half-bridge submodules are controlled to disconnect from active connection. Wherein, the first target formula is Urh=max{min{Ur,Nh*Uch},0}, where Urh is the reference voltage when the half-bridge submodule is actively connected; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; Uch is the rated capacitor voltage of the half-bridge submodule.

[0089] If the change in capacitor voltage of a half-bridge submodule is negative when it is passively engaged, then when the bridge arm current is negative, all half-bridge submodules will be controlled to disconnect from active engagement.

[0090] This embodiment mainly describes the control process when the capacitor voltage change (ΔUch) is negative. The above method is implemented as follows:

[0091] When the half-bridge submodule is passively engaged, the change in capacitor voltage ΔUch is negative, indicating that the capacitor voltage of the half-bridge submodule has decreased during the passive engagement phase. This means that it is necessary to actively engage the submodule to replenish energy and increase the capacitor voltage.

[0092] The specific control operation when the bridge arm current is positive is as follows:

[0093] (1) Maximizing the output of the half-bridge submodules. In this case, instructions are issued based on the method of this embodiment to activate as many half-bridge submodules as possible within the bridge arm and to allow them to output voltage at their maximum capacity. This is because when the bridge arm current is positive, the output voltage direction of the half-bridge submodule is consistent with the bridge arm current direction, which helps to transfer energy to the power grid or other loads, thereby increasing the capacitor voltage. For example, in a practical hybrid MMC system, if there are multiple half-bridge submodules, the system will select an appropriate number and location of half-bridge submodules to activate based on the current demand and the status of each submodule, so that their output voltages are added together to achieve the effect of maximizing output.

[0094] (2) Control the reference voltage according to the first target formula. At this time, the reference voltage Urh when the half-bridge submodule is actively engaged is determined according to the first target formula Urh=max{min{Ur,Nh*Uch},0}.

[0095] Where Ur is the bridge arm reference voltage, determined by the overall MMC system control strategy, used to guide the bridge arm to output an appropriate voltage to meet the system's stable operation and power transmission requirements. Nh is the number of half-bridge submodules within the bridge arm, and Uch is the rated capacitor voltage of each half-bridge submodule. For example, assuming the bridge arm reference voltage Ur is 60kV, the number of half-bridge submodules Nh is 5, and the rated capacitor voltage Uch of each half-bridge submodule is 10kV, then NhUch = 5 × 10kV = 50kV. According to the formula, min{Ur, NhUch} is min{60kV, 50kV} = 50kV. Then, taking max{50kV, 0}, we get Urh = 50kV. This Urh is the reference voltage that the half-bridge submodule needs to reach when actively engaged.

[0096] By adjusting the switching state and output duty cycle of the half-bridge sub-modules, their actual output voltage can be made as close as possible to the reference voltage Urh, thereby achieving precise control of the half-bridge sub-module output.

[0097] (3) Monitor voltage increase and promptly disconnect active connection. During the active connection of the half-bridge submodule, the control system monitors the changes in capacitor voltage in real time and calculates its voltage increase. Once this increase reaches ΔUch, meaning the capacitor voltage has returned to the level before passive connection or reached the expected equilibrium state, the control system immediately issues a command to disconnect all half-bridge submodules from active connection. This is to prevent overcharging and avoid excessively high capacitor voltage that could damage the submodule or cause other system problems.

[0098] When the bridge arm current is negative, all half-bridge submodules are switched off from active operation. This is because the direction of the bridge arm current at this time is unfavorable for increasing the capacitor voltage. Continuing to switch on the half-bridge submodules may lead to further energy imbalance, making it difficult for the capacitor voltage to return to normal levels. Therefore, to maintain the stability of the capacitor voltage and avoid ineffective energy flow and potential system instability, active operation is switched off.

[0099] This active switching control, based on capacitor voltage changes and bridge arm current direction, accurately compensates for capacitor voltage variations caused by passive switching, maintaining energy balance between half-bridge and full-bridge submodules and ensuring the stability and reliability of the hybrid MMC during overmodulation operation. It effectively avoids submodule overvoltage and undervoltage faults caused by energy imbalance, extending equipment lifespan. Furthermore, the minimum active switching strategy minimizes control actions on the half-bridge submodules while ensuring energy balance, reducing control complexity and system energy loss. This improves control efficiency, enabling the hybrid MMC to respond to grid demands more quickly and accurately, enhancing the system's grid support and adaptability. In addition, flexibly adjusting the active switching strategy of the half-bridge submodules according to different capacitor voltage changes and bridge arm current directions better adapts to the hybrid MMC's operating requirements under various conditions, improving system flexibility and stability, and ensuring good performance under complex operating conditions.

[0100] As a further description and refinement of the above embodiments, in some embodiments, step "104. Controlling the half-bridge submodule to perform minimum active engagement" in the aforementioned embodiments includes:

[0101] If the change in capacitor voltage of a half-bridge submodule is positive when it is passively switched on, then when the bridge arm current is negative, the half-bridge submodule of the bridge arm is controlled to maximize its output. The half-bridge submodule is controlled according to the second target formula using the reference voltage for active switching. When the voltage drop caused by the active switching of the half-bridge submodule reaches the change in capacitor voltage when the half-bridge submodule is passively switched on, all half-bridge submodules are controlled to disconnect from active switching. The second target formula is Urh = max{min{Ur, Nh*Uch}, 0}, where Urh is the reference voltage when the half-bridge submodule is actively switched on; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; and Uch is the rated capacitor voltage of the half-bridge submodule.

[0102] If the change in capacitor voltage of a half-bridge submodule is positive when it is passively engaged, then when the bridge arm current is positive, all half-bridge submodules will be controlled to disconnect from active engagement.

[0103] This embodiment mainly describes the control process when the capacitor voltage change (ΔUch) is positive. The above method is implemented as follows:

[0104] When the half-bridge submodule is passively engaged, the change in capacitor voltage ΔUch is positive, indicating that the capacitor voltage of the half-bridge submodule has increased during the passive engagement phase. At this time, it is necessary to actively engage the module to consume excess energy and reduce the capacitor voltage.

[0105] Specifically, the control operation when the bridge arm current is negative is as follows:

[0106] (1) Maximize the output of the half-bridge submodules. This involves controlling the number of half-bridge submodules in the bridge arm to be in operation as much as possible and outputting voltage at maximum capacity. When the bridge arm current is negative, the output voltage direction of the half-bridge submodules interacts with the bridge arm current direction, which helps to dissipate excess energy on the submodule capacitors. For example, in MMC, by reasonably selecting the number and position of the half-bridge submodules, their output voltages are added together to maximize the output, thereby effectively releasing energy from the submodule capacitors.

[0107] (2) The reference voltage is controlled according to the first target formula. Similarly, the reference voltage Urh when the half-bridge submodule is actively engaged is determined using the first target formula Urh = max{min{Ur, Nh*Uch}, 0}. The meaning of the parameters and the calculation method are the same as when ΔUch is negative. For example, assuming Ur is 55kV, Nh is 5, and Uch is 10kV, then Nh*Uch = 50kV. min{55kV, 50kV} = 50kV, max{50kV, 0} = 50kV, so Urh = 50kV. The control system will control the output of the half-bridge submodule to be near this reference voltage value.

[0108] (3) Monitor voltage drop and promptly disconnect active switching. During active switching, monitor the capacitor voltage change in real time and calculate the voltage drop. When this drop reaches ΔUch, the control system will immediately control all half-bridge sub-modules to disconnect active switching to prevent excessive capacitor voltage drop from causing system instability or other problems.

[0109] On the other hand, the control operation when the bridge arm current is positive is as follows: when the bridge arm current is positive, all half-bridge submodules are controlled to disconnect from active connection. This is because the direction of the bridge arm current at this time is not conducive to reducing the capacitor voltage, and continued connection may cause the capacitor voltage to rise further. Therefore, disconnecting active connection is chosen to maintain the stability of the capacitor voltage.

[0110] This active switching control, based on capacitor voltage changes and bridge arm current direction, accurately compensates for capacitor voltage variations caused by passive switching, maintaining energy balance between half-bridge and full-bridge submodules and ensuring the stability and reliability of the hybrid MMC during overmodulation operation. It effectively avoids submodule overvoltage and undervoltage faults caused by energy imbalance, extending equipment lifespan. Furthermore, the minimum active switching strategy minimizes control actions on the half-bridge submodules while ensuring energy balance, reducing control complexity and system energy loss. This improves control efficiency, enabling the hybrid MMC to respond to grid demands more quickly and accurately, enhancing the system's grid support and adaptability. In addition, flexibly adjusting the active switching strategy of the half-bridge submodules according to different capacitor voltage changes and bridge arm current directions better adapts to the hybrid MMC's operating requirements under various conditions, improving system flexibility and stability, and ensuring good performance under complex operating conditions.

[0111] As a further description and refinement of the above embodiments, in some embodiments, step "105. Determining the deployment status of the full-bridge submodule based on the deployment status of the half-bridge submodule" in the aforementioned embodiments includes:

[0112] The input reference voltage of the full-bridge submodule is calculated based on a preset formula and the input reference voltage of the half-bridge submodule.

[0113] The preset formula is: Urf = Ur – Urh;

[0114] Urf is used to characterize the reference voltage when the full-bridge submodule is actively engaged, Ur is the bridge arm reference voltage, and Urh is the reference voltage when the half-bridge submodule is actively engaged.

[0115] In this implementation, the specific execution process is as follows:

[0116] (1) Obtaining the input reference voltage of the half-bridge submodule. The input reference voltage (Urh) of the half-bridge submodule is calculated based on the active input control strategy. In a hybrid MMC system, Urh represents the voltage value that the half-bridge submodule needs to reach when actively inputting, which guides the output of the half-bridge submodule to achieve energy balance control. Its calculation involves multiple parameters such as the bridge arm reference voltage (Ur), the number of half-bridge submodules (Nh), and the rated capacitor voltage of the half-bridge submodule (Uch), which are determined by a specific formula (e.g., Urh = max{min{Ur, Nh * Uch}, 0}).

[0117] (2) Obtaining the arm reference voltage. The arm reference voltage (Ur) is a key parameter used to control the arm output voltage in a hybrid MMC system. It is calculated by the system's control strategy based on factors such as grid demand and system operating status. For example, under stable grid operating conditions, if a certain amplitude and frequency of AC voltage needs to be output, the control system will calculate the corresponding arm reference voltage to ensure that the voltage waveform output by the entire MMC system meets the requirements.

[0118] (3) Calculate the input reference voltage of the full-bridge submodule. Based on the preset formula Urf = Ur - Urh, calculate the input reference voltage (Urf) of the full-bridge submodule. Urf represents the reference voltage when the full-bridge submodule is actively engaged. The significance of this formula is to reasonably allocate the voltage portion that the full-bridge submodule needs to bear based on the bridge arm reference voltage (Ur) and the input reference voltage (Urh) of the half-bridge submodule.

[0119] For example, assuming the bridge arm reference voltage Ur is 100kV and the half-bridge submodule's input reference voltage Urh is 60kV, then according to the formula, the full-bridge submodule's input reference voltage Urf = 100kV - 60kV = 40kV. This means that under the current operating conditions, the full-bridge submodule needs to output 40kV to coordinate with the half-bridge module's output and meet the bridge arm reference voltage requirement.

[0120] (4) Determine the activation status based on the activation reference voltage of the full-bridge submodules. Once the activation reference voltage (Urf) of the full-bridge submodules is determined, the activation status of the full-bridge submodules can be determined based on this voltage value. The activation status of the full-bridge submodules includes the number of modules activated and the output voltage of each module. For example, if the rated capacitor voltage (Ucf) of the full-bridge submodule is 10kV and the activation reference voltage Urf is 40kV, then theoretically, four full-bridge submodules (each outputting 10kV) need to be activated to meet the 40kV activation reference voltage requirement. The control system will control the corresponding full-bridge submodules to be activated based on this calculation result, so that their output voltages are added together to reach the value of Urf.

[0121] (5) Execution of Input Control. Based on the determined input status of the full-bridge submodules, the control system sends control signals to the corresponding full-bridge submodules, causing them to operate as required and output the corresponding voltage. Simultaneously, considering the input status of the half-bridge submodules, the system performs overall energy balance control on the hybrid MMC to ensure the stable operation of the entire system. For example, the control system sends trigger signals to the switching devices (such as IGBTs) of the full-bridge submodules to control their on / off states, thereby adjusting the output voltage of the full-bridge submodules to stabilize it near the input reference voltage (Urf). At the same time, the system monitors the actual output voltage and operating status of the full-bridge submodules to ensure their normal operation and meet the system's energy balance requirements.

[0122] Furthermore, as a response to the above Figure 1 In addition to the implementation of the methods shown in the above embodiments, another embodiment of this application provides an energy balance control device based on a hybrid MMC. This embodiment of the energy balance control device based on a hybrid MMC corresponds to the aforementioned method embodiments. For ease of reading, this embodiment of the energy balance control device based on a hybrid MMC will not repeat the details of the aforementioned method embodiments one by one, but it should be clear that the device in this embodiment can correspondingly implement all the contents of the aforementioned method embodiments. Specifically, as follows... Figure 2 As shown, the energy balance control device based on hybrid MMC includes:

[0123] The acquisition unit 21 can be used to acquire the reference voltage of the bridge arm, the half-bridge submodule output capability and the full-bridge submodule output capability of the bridge arm in the hybrid MMC.

[0124] The division unit 22 can be used to divide the engagement state of the half-bridge submodule into active engagement and passive engagement based on the reference voltage, half-bridge submodule output capability, and full-bridge submodule output capability acquired by the acquisition unit 21. The passive engagement can characterize the operating state of the half-bridge submodule ensuring the basic operational functions of the hybrid MMC to meet the bridge arm reference voltage requirements. The active engagement can characterize the operating state of the half-bridge submodule actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement.

[0125] The determining unit 23 can be used to determine the passive engagement boundary point of the half-bridge submodule based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule obtained by the obtaining unit 21, and to determine the change in capacitor voltage when the half-bridge submodule is passively engaged as defined by the dividing unit 22.

[0126] Control unit 24 can be used to control the half-bridge submodule to perform minimum active engagement to compensate for the capacitor voltage change determined by determination unit 23 when the half-bridge submodule is passively engaged; wherein, the minimum active engagement can be used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the capacitor voltage change when the half-bridge submodule is passively engaged.

[0127] The operation unit 25 can be used to determine the engagement status of the full-bridge submodule based on the engagement status of the half-bridge submodule, and to perform energy balance control on the hybrid MMC based on the engagement status of the half-bridge submodule and the full-bridge submodule. The engagement status can be used to characterize the change of the engagement reference voltage of the half-bridge submodule and the full-bridge submodule when engagement control is performed. The engagement status of the half-bridge submodule is determined based on the control unit 24 controlling the half-bridge submodule to perform minimum active engagement.

[0128] Furthermore, such as Figure 3 As shown, the output capability of the half-bridge submodule is calculated using a first calculation formula, wherein the first calculation formula is:

[0129] A = Nh * Uch;

[0130] Where A can be used to characterize the output capability of the half-bridge submodule in the bridge arm, Nh is the number of half-bridge submodules in the bridge arm, and Uch is the rated capacitor voltage of the half-bridge module.

[0131] The output capability of the full-bridge submodule is calculated based on a second calculation formula, wherein the second calculation formula is:

[0132] B = Nf * Ucf;

[0133] Where B can be used to characterize the output capability of the full-bridge submodule within the bridge arm, Nf is the number of full-bridge submodules within the bridge arm, and Ucf is the rated capacitor voltage of the full-bridge submodule.

[0134] Furthermore, such as Figure 3 As shown, the reference voltage of the bridge arm includes the bridge arm voltage reference value of the previous control cycle and the bridge arm voltage reference value of the current control cycle.

[0135] The determining unit 23 includes:

[0136] The first determining module 231 can be used to determine that the moment is the passive activation starting point of the half-bridge submodule when the reference value of the bridge arm voltage in the previous control cycle is less than the output capability of the full-bridge submodule and the reference value of the bridge arm voltage in the current control cycle is greater than the output capability of the full-bridge submodule.

[0137] The second determining module 232 can be used to determine the passive engagement end point of the half-bridge submodule when it is determined that the reference value of the bridge arm voltage in the previous control cycle is greater than the output capability of the full-bridge submodule, and the reference value of the bridge arm voltage in the current control cycle is less than the output capability of the full-bridge submodule.

[0138] Furthermore, such as Figure 3 As shown, the control unit 24 includes:

[0139] The first control module 241 can be used to control the half-bridge submodule to maximize its output when the bridge arm current is positive, if the change in capacitor voltage of the half-bridge submodule when it is passively connected is negative, and the reference voltage for the half-bridge submodule to be actively connected is controlled according to the first target formula. When the voltage increase caused by the active connection of the half-bridge submodule reaches the change in capacitor voltage when the half-bridge submodule is passively connected, the first target formula is Urh=max{min{Ur,Nh*Uch},0}, where Urh is the reference voltage when the half-bridge submodule is actively connected; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; and Uch is the rated capacitor voltage of the half-bridge submodule.

[0140] The second control module 242 can be used to control all half-bridge submodules to cut off active connection when the capacitor voltage change is negative and the bridge arm current is negative.

[0141] Furthermore, such as Figure 3 As shown, the control unit 24 includes:

[0142] The third control module 243 can be used to control the bridge arm half-bridge submodule to maximize output when the capacitor voltage change is positive and the bridge arm current is negative, and the half-bridge submodule is controlled according to the second target formula using the reference voltage for active connection. When the voltage drop caused by the active connection of the half-bridge submodule reaches the capacitor voltage change when the half-bridge submodule is passively connected, all half-bridge submodules are controlled to disconnect from active connection. The second target formula is Urh = max{min{Ur, Nh*Uch}, 0}, where Urh is the reference voltage when the half-bridge submodule is actively connected; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; and Uch is the rated capacitor voltage of the half-bridge submodule.

[0143] The fourth control module 244 can be used to control all half-bridge sub-modules to cut off active connection when the capacitor voltage change is positive and the bridge arm current is positive.

[0144] Furthermore, such as Figure 3As shown, the operation unit 25 can be specifically used to calculate the input reference voltage of the full-bridge submodule based on a preset formula and the input reference voltage of the half-bridge submodule.

[0145] The preset formula is: Urf = Ur – Urh;

[0146] Urf can be used to characterize the reference voltage when the full-bridge submodule is actively engaged, Ur is the bridge arm reference voltage, and Urh is the reference voltage when the half-bridge submodule is actively engaged.

[0147] This application provides an energy balance control method and apparatus based on a hybrid MMC. This embodiment first obtains the reference voltage of the bridge arm, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule in the hybrid MMC. Then, based on the reference voltage, half-bridge submodule output capability, and full-bridge submodule output capability, the engagement state of the half-bridge submodule is divided into active engagement and passive engagement. Passive engagement characterizes the operating state of the half-bridge submodule ensuring the basic operation of the hybrid MMC to meet the bridge arm reference voltage requirements. Active engagement characterizes the operating state of the half-bridge submodule actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement. Subsequently, based on the bridge arm reference voltage and the full-bridge submodule output capability, the passive engagement boundary point of the half-bridge submodule is determined, and the engagement state of the half-bridge submodule is determined. The system first determines the capacitor voltage change when passively switched on; then, it controls the half-bridge submodule to perform minimum active switching to compensate for the capacitor voltage change when the half-bridge submodule is passively switched on; wherein, the minimum active switching is used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the capacitor voltage change when the half-bridge submodule is passively switched on; finally, the system determines the switching status of the full-bridge submodule based on the switching status of the half-bridge submodule, and performs energy balance control on the hybrid MMC based on the switching status of the half-bridge submodule and the full-bridge submodule, wherein, the switching status is used to characterize the change of the switching reference voltage of the half-bridge submodule and the full-bridge submodule when switching on, and the switching status of the half-bridge submodule is determined based on the minimum active switching of the half-bridge submodule, thereby realizing the energy balance control function based on the hybrid MMC. Compared with existing technologies, this application's embodiments effectively solve the energy imbalance problem during the overmodulation operation of hybrid MMCs by dividing the engagement state of the half-bridge submodules, determining the passive engagement boundary point and capacitor voltage change, and then performing minimum active engagement control. This improves the energy stability of the submodules during overmodulation operation of hybrid MMCs and ensures the safe and stable operation of the system. Simultaneously, it eliminates the need for additional control equipment or changes to the circuit topology, offering advantages such as simple architecture and low cost. While achieving energy balance control, it avoids the increased cost and system complexity caused by adding equipment or changing the topology in existing technologies, demonstrating good economic efficiency and practicality. Furthermore, since the method of this application's embodiments does not require additional current harmonic injection or voltage harmonic injection during the control process, it does not affect the properties of electrical energy, avoiding the problem of increased voltage and current stress and harmonic content.Furthermore, the embodiments of this application accurately distinguish between the active and passive engagement states of the half-bridge submodules and perform targeted control, effectively solving the energy imbalance problem during the overmodulation operation of the hybrid MMC. This avoids faults such as submodule capacitor voltage exceeding limits, system oscillation, and even instability caused by energy imbalance, significantly improving the stability and reliability of the hybrid MMC under overmodulation operation conditions, and ensuring the uninterrupted and safe operation of the power system.

[0148] This application provides a storage medium including a stored program, wherein, when the program is executed, it controls the device where the storage medium is located to perform the energy balance control method based on hybrid MMC described above. The storage medium may include non-permanent memory in the form of computer-readable media, random access memory (RAM), and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0149] This application embodiment also provides an energy balance control device based on hybrid MMC, the device including a storage medium; and one or more processors, the storage medium being coupled to the processors, the processors being configured to execute program instructions stored in the storage medium; the program instructions executing the above-described energy balance control method based on hybrid MMC.

[0150] This application provides a device including a processor, a memory, and a program stored in the memory and executable on the processor. When the processor executes the program, it performs the following steps: acquiring the reference voltage of the bridge arm in a hybrid MMC, the output capability of the half-bridge submodule of the bridge arm, and the output capability of the full-bridge submodule; classifying the engagement state of the half-bridge submodule into active engagement and passive engagement based on the reference voltage, the half-bridge submodule output capability, and the full-bridge submodule output capability; wherein, passive engagement characterizes the operating state of the half-bridge submodule ensuring the basic operational functions of the hybrid MMC to meet the bridge arm reference voltage requirements; active engagement characterizes the operating state of the half-bridge submodule actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement; and determining... based on the bridge arm reference voltage and the full-bridge submodule output capability... The passive engagement boundary of the half-bridge submodule is determined, and the capacitor voltage change when the half-bridge submodule is passively engaged is identified. The half-bridge submodule is controlled to perform minimum active engagement to compensate for the capacitor voltage change when passively engaged. The minimum active engagement characterizes the minimum control amount required to maintain the half-bridge submodule's capacitor voltage change while ensuring it can compensate for the passive engagement. The engagement status of the full-bridge submodule is determined based on the engagement status of the half-bridge submodule, and energy balance control is performed on the hybrid MMC based on both the engagement statuses. The engagement status characterizes the change in the engagement reference voltage of the half-bridge and full-bridge submodules during engagement control, and the engagement status of the half-bridge submodule is determined based on its minimum active engagement.

[0151] Furthermore, the output capability of the half-bridge submodule is calculated using a first calculation formula, wherein the first calculation formula is:

[0152] A = Nh * Uch;

[0153] Where A is used to characterize the output capability of the half-bridge submodule in the bridge arm, Nh is the number of half-bridge submodules in the bridge arm, and Uch is the rated capacitor voltage of the half-bridge module.

[0154] The output capability of the full-bridge submodule is calculated based on a second calculation formula, wherein the second calculation formula is:

[0155] B = Nf * Ucf;

[0156] Where B is used to characterize the output capability of the full-bridge submodule within the bridge arm, Nf is the number of full-bridge submodules within the bridge arm, and Ucf is the rated capacitor voltage of the full-bridge submodule.

[0157] Furthermore, the reference voltage of the bridge arm includes the bridge arm voltage reference value of the previous control cycle and the bridge arm voltage reference value of the current control cycle.

[0158] The determination of the passive engagement threshold of the half-bridge submodule based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule includes:

[0159] When it is determined that the reference value of the bridge arm voltage in the previous control cycle is less than the output capability of the full-bridge submodule, and the reference value of the bridge arm voltage in the current control cycle is greater than the output capability of the full-bridge submodule, this moment is determined to be the starting point for the passive activation of the half-bridge submodule.

[0160] When it is determined that the reference value of the bridge arm voltage in the previous control cycle is greater than the output capability of the full-bridge submodule, and the reference value of the bridge arm voltage in the current control cycle is less than the output capability of the full-bridge submodule, the passive engagement termination point of the half-bridge submodule is determined.

[0161] Furthermore, the control half-bridge submodule performs minimal active engagement, including:

[0162] If the change in capacitor voltage of a half-bridge submodule when passively connected is negative, then when the bridge arm current is positive, the half-bridge submodule is controlled to maximize output, and the reference voltage for active connection of the half-bridge submodule is controlled according to the first target formula. When the voltage increase caused by the active connection of the half-bridge submodule reaches the change in capacitor voltage when the half-bridge submodule is passively connected, all half-bridge submodules are controlled to disconnect from active connection. Wherein, the first target formula is Urh=max{min{Ur,Nh*Uch},0}, where Urh is the reference voltage when the half-bridge submodule is actively connected; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; Uch is the rated capacitor voltage of the half-bridge submodule.

[0163] If the change in capacitor voltage of a half-bridge submodule is negative when it is passively engaged, then when the bridge arm current is negative, all half-bridge submodules will be controlled to disconnect from active engagement.

[0164] Furthermore, the control half-bridge submodule performs minimal active engagement, including:

[0165] If the change in capacitor voltage of a half-bridge submodule is positive when it is passively switched on, then when the bridge arm current is negative, the half-bridge submodule of the bridge arm is controlled to maximize its output. The half-bridge submodule is controlled according to the second target formula using the reference voltage for active switching. When the voltage drop caused by the active switching of the half-bridge submodule reaches the change in capacitor voltage when the half-bridge submodule is passively switched on, all half-bridge submodules are controlled to disconnect from active switching. The second target formula is Urh = max{min{Ur, Nh*Uch}, 0}, where Urh is the reference voltage when the half-bridge submodule is actively switched on; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; and Uch is the rated capacitor voltage of the half-bridge submodule.

[0166] If the change in capacitor voltage of a half-bridge submodule is positive when it is passively engaged, then when the bridge arm current is positive, all half-bridge submodules will be controlled to disconnect from active engagement.

[0167] Furthermore, determining the deployment status of the full-bridge submodule based on the deployment status of the half-bridge submodule includes:

[0168] The input reference voltage of the full-bridge submodule is calculated based on a preset formula and the input reference voltage of the half-bridge submodule.

[0169] The preset formula is: Urf = Ur – Urh;

[0170] Urf is used to characterize the reference voltage when the full-bridge submodule is actively engaged, Ur is the bridge arm reference voltage, and Urh is the reference voltage when the half-bridge submodule is actively engaged.

[0171] This application also provides a computer program product, which, when executed on a data processing device, is suitable for executing program code that initializes the following steps: acquiring the reference voltage of the bridge arm in a hybrid MMC, the output capability of the half-bridge submodule of the bridge arm, and the output capability of the full-bridge submodule; classifying the engagement state of the half-bridge submodule into active engagement and passive engagement based on the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule; wherein, the passive engagement is used to characterize the operating state of the half-bridge submodule ensuring the basic operating function of the hybrid MMC when meeting the bridge arm reference voltage requirements; the active engagement is used to characterize the operating state of the half-bridge submodule actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement; and determining the half-bridge submodule being engaged based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule. The system identifies the active engagement boundary point and determines the capacitor voltage change when the half-bridge submodule is passively engaged. It then controls the half-bridge submodule to perform minimum active engagement to compensate for the capacitor voltage change when passively engaged. The minimum active engagement characterizes the minimum control amount required to compensate for the capacitor voltage change when the half-bridge submodule is passively engaged. Based on the engagement status of the half-bridge submodule, the system determines the engagement status of the full-bridge submodule and performs energy balance control on the hybrid MMC based on both engagement statuses. The engagement status characterizes the change in the engagement reference voltage of the half-bridge and full-bridge submodules during engagement control, and the engagement status of the half-bridge submodule is determined based on its minimum active engagement.

[0172] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0173] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0174] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0175] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0176] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0177] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0178] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0179] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0180] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0181] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. An energy balance control method based on hybrid MMC, characterized in that, include: Obtain the reference voltage of the bridge arm, the half-bridge submodule output capability, and the full-bridge submodule output capability of the bridge arm in the hybrid MMC; Based on the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule, the engagement state of the half-bridge submodule is divided into active engagement and passive engagement. Passive engagement characterizes the operational state of the half-bridge submodule in ensuring the basic operating functions of the hybrid MMC to meet the bridge arm reference voltage requirements. Active engagement characterizes the operational state of the half-bridge submodule in actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement. Based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule, the passive engagement boundary point of the half-bridge submodule is determined, and the change in capacitor voltage when the half-bridge submodule is passively engaged is determined. The half-bridge submodule is controlled to perform minimum active engagement to compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged; wherein, the minimum active engagement is used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged. The engagement status of the full-bridge submodule is determined based on the engagement status of the half-bridge submodule, and energy balance control is performed on the hybrid MMC based on the engagement status of the half-bridge submodule and the full-bridge submodule. The engagement status is used to characterize the change of the engagement reference voltage of the half-bridge submodule and the full-bridge submodule when engagement control is performed. The engagement status of the half-bridge submodule is determined based on the minimum active engagement of the half-bridge submodule.

2. The method according to claim 1, characterized in that, The output capability of the half-bridge submodule is calculated using a first calculation formula, wherein the first calculation formula is: A = Nh * Uch; Where A is used to characterize the output capability of the half-bridge submodule in the bridge arm, Nh is the number of half-bridge submodules in the bridge arm, and Uch is the rated capacitor voltage of the half-bridge module. The output capability of the full-bridge submodule is calculated based on a second calculation formula, wherein the second calculation formula is: B = Nf * Ucf; Where B is used to characterize the output capability of the full-bridge submodule within the bridge arm, Nf is the number of full-bridge submodules within the bridge arm, and Ucf is the rated capacitor voltage of the full-bridge submodule.

3. The method according to claim 1, characterized in that, The reference voltage of the bridge arm includes the bridge arm voltage reference value of the previous control cycle and the bridge arm voltage reference value of the current control cycle. The determination of the passive engagement threshold of the half-bridge submodule based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule includes: When it is determined that the reference value of the bridge arm voltage in the previous control cycle is less than the output capability of the full-bridge submodule, and the reference value of the bridge arm voltage in the current control cycle is greater than the output capability of the full-bridge submodule, this moment is determined to be the starting point for the passive activation of the half-bridge submodule. When it is determined that the reference value of the bridge arm voltage in the previous control cycle is greater than the output capability of the full-bridge submodule, and the reference value of the bridge arm voltage in the current control cycle is less than the output capability of the full-bridge submodule, the passive engagement termination point of the half-bridge submodule is determined.

4. The method according to claim 1, characterized in that, The control half-bridge submodule performs minimum active engagement, including: If the change in capacitor voltage of a half-bridge submodule when passively connected is negative, then when the bridge arm current is positive, the half-bridge submodule is controlled to maximize output, and the reference voltage for active connection of the half-bridge submodule is controlled according to the first target formula. When the voltage increase caused by the active connection of the half-bridge submodule reaches the change in capacitor voltage when the half-bridge submodule is passively connected, all half-bridge submodules are controlled to disconnect from active connection. Wherein, the first target formula is Urh=max{min{Ur,Nh*Uch},0}, where Urh is the reference voltage when the half-bridge submodule is actively connected; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; Uch is the rated capacitor voltage of the half-bridge submodule. If the change in capacitor voltage of a half-bridge submodule is negative when it is passively engaged, then when the bridge arm current is negative, all half-bridge submodules will be controlled to disconnect from active engagement.

5. The method according to claim 1, characterized in that, The control half-bridge submodule performs minimum active engagement, including: If the change in capacitor voltage of a half-bridge submodule is positive when it is passively switched on, then when the bridge arm current is negative, the half-bridge submodule of the bridge arm is controlled to maximize its output. The half-bridge submodule is controlled according to the second target formula using the reference voltage for active switching. When the voltage drop caused by the active switching of the half-bridge submodule reaches the change in capacitor voltage when the half-bridge submodule is passively switched on, all half-bridge submodules are controlled to disconnect from active switching. The second target formula is Urh = max{min{Ur, Nh*Uch}, 0}, where Urh is the reference voltage when the half-bridge submodule is actively switched on; Ur is the bridge arm reference voltage; Nh is the number of half-bridge submodules in the bridge arm; and Uch is the rated capacitor voltage of the half-bridge submodule. If the change in capacitor voltage of a half-bridge submodule is positive when it is passively engaged, then when the bridge arm current is positive, all half-bridge submodules will be controlled to disconnect from active engagement.

6. The method according to claim 1, characterized in that, Determining the deployment status of the full-bridge submodule based on the deployment status of the half-bridge submodule includes: The input reference voltage of the full-bridge submodule is calculated based on a preset formula and the input reference voltage of the half-bridge submodule. The preset formula is: Urf = Ur – Urh; Urf is used to characterize the reference voltage when the full-bridge submodule is actively engaged, Ur is the bridge arm reference voltage, and Urh is the reference voltage when the half-bridge submodule is actively engaged.

7. An energy balance control device based on hybrid MMC, characterized in that, include: The acquisition unit is used to acquire the reference voltage of the bridge arm, the half-bridge submodule output capability, and the full-bridge submodule output capability of the bridge arm in the hybrid MMC. The division unit is used to classify the engagement state of the half-bridge submodule into active engagement and passive engagement based on the reference voltage, the output capability of the half-bridge submodule, and the output capability of the full-bridge submodule. Passive engagement characterizes the operational state of the half-bridge submodule in ensuring the basic operating functions of the hybrid MMC to meet the bridge arm reference voltage requirements. Active engagement characterizes the operational state of the half-bridge submodule in actively controlling the hybrid MMC to prevent energy imbalance caused by passive engagement. The determining unit is used to determine the passive engagement boundary point of the half-bridge submodule based on the reference voltage of the bridge arm and the output capability of the full-bridge submodule, and to determine the change in capacitor voltage when the half-bridge submodule is passively engaged. The control unit is used to control the half-bridge submodule to perform minimum active engagement to compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged; wherein, the minimum active engagement is used to characterize the minimum control amount of the half-bridge submodule while ensuring that it can compensate for the change in capacitor voltage when the half-bridge submodule is passively engaged. An operating unit is used to determine the engagement status of the full-bridge submodule based on the engagement status of the half-bridge submodule, and to perform energy balance control on the hybrid MMC based on the engagement status of the half-bridge submodule and the full-bridge submodule. The engagement status is used to characterize the change of the engagement reference voltage of the half-bridge submodule and the full-bridge submodule when engagement control is performed. The engagement status of the half-bridge submodule is determined based on the minimum active engagement of the half-bridge submodule.

8. A storage medium, characterized in that, The storage medium includes a stored program, wherein, when the program is executed, it controls the device where the storage medium is located to perform the energy balance control method based on hybrid MMC as described in any one of claims 1 to 6.

9. An energy balance control device based on hybrid MMC, characterized in that, The device includes a storage medium; and one or more processors, the storage medium being coupled to the processors, the processors being configured to execute program instructions stored in the storage medium; the program instructions, when executed, perform the energy balance control method based on hybrid MMC as described in any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the energy balance control method based on hybrid MMC as described in any one of claims 1 to 6.

Images