Loss optimization method and system for modular multilevel converter

Abstract

The invention discloses a loss optimization method and system for a modular multilevel converter, and the method comprises the steps: obtaining the target output voltage of a bridge arm according to an output voltage instruction value of the modular multilevel converter, calculating the number of to-be-input common sub-modules of the bridge arm at the current moment and the output voltage state of the bridge arm in combination with a carrier parameter; the carrier parameters comprise a carrier frequency, a modulation frequency and a phase angle; judging whether the output voltage state of the bridge arm is a positive pulse width modulation (PWM) state or not, and updating the number of common sub-modules to be input and the number of adjusting sub-modules of the bridge arm in different states; and completing loss optimization of the modular multilevel converter according to the updated number of the common sub-modules to be input and the number of the adjusted sub-modules of the bridge arm in combination with a voltage balancing strategy. The waveform quality of the target output voltage is improved, the switching frequency is reduced, the switching loss is reduced, and the working performance of the modular multilevel converter is improved.

Description

Technical Field

[0001] This invention relates to the field of energy-saving optimization technology, and in particular to a loss optimization method and system for modular multilevel converters. Background Technology

[0002] Modular multilevel converters (MMCs) are increasingly being widely used in medium-voltage DC power grids due to their high degree of modularity, good output waveform quality, ease of expansion, and low switching frequency of electronic components.

[0003] In medium-voltage DC grids, when MMC is used for power conversion, the required submodules are significantly reduced compared to high-voltage DC transmission. Using Nearest Level Modulation (NLM) affects the waveform quality of the output sine wave. While multi-carrier modulation can improve waveform quality, it increases switching losses. Pulse modulation is a key control technology for ensuring MMC characteristics, playing a decisive role in output waveform quality and power device switching losses. It is also an effective method for optimizing MMC losses without significantly increasing hardware investment. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the aforementioned existing problems, the present invention is proposed.

[0006] Therefore, the present invention provides a loss optimization method and system for modular multilevel converters, which can solve the problems mentioned in the background art.

[0007] To address the aforementioned technical problems, this invention provides the following technical solution: a loss optimization method for modular multilevel converters, comprising:

[0008] The target output voltage of the bridge arm is obtained based on the output voltage command value of the modular multilevel converter. The number of ordinary sub-modules to be put into the bridge arm and the output voltage status of the bridge arm at the current moment are calculated in combination with the carrier parameters. The carrier parameters include carrier frequency, modulation frequency and phase angle.

[0009] Determine whether the output voltage state of the bridge arm is in positive pulse width modulation (PWM) state, and update the number of ordinary sub-modules and adjustment sub-modules to be put into the bridge arm under different states;

[0010] Based on the number of ordinary sub-modules and regulating sub-modules to be put into operation in the bridge arm after the update, and combined with the voltage balancing strategy, the loss optimization of the modular multilevel converter is completed.

[0011] As a preferred embodiment of the loss optimization method for modular multilevel converters described in this invention, the step of obtaining the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter, and calculating the number of ordinary sub-modules to be put into operation in the bridge arm at the current moment and the output voltage state of the bridge arm in combination with carrier parameters includes:

[0012] The number of ordinary sub-modules waiting to be deployed in the bridge arm at the current moment is expressed as follows:

[0013]

[0014] The round function returns an integer value after rounding, F1 is the carrier frequency, F2 is the modulation frequency, α is the phase angle, U is the target output voltage of the bridge arm, and N is a positive integer not less than 4, where N represents the sum of the number of ordinary submodules and regulating submodules in each bridge arm.

[0015] As a preferred embodiment of the loss optimization method for modular multilevel converters described in this invention, the step of obtaining the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter, and calculating the number of ordinary sub-modules to be put into operation in the bridge arm at the current moment and the output voltage status of the bridge arm in combination with carrier parameters, further includes:

[0016] The output voltage state of the bridge arm is represented as follows:

[0017]

[0018] The mod function is a remainder function that returns the remainder after dividing two numerical expressions. The ceiling function is a rounding function that rounds the decimal part of the input parameter upwards. F1 is the carrier frequency, F2 is the modulation frequency, α is the phase angle, N is a positive integer not less than 4, and N represents the sum of the number of ordinary submodules and regulation submodules in each bridge arm.

[0019] As a preferred embodiment of the loss optimization method for modular multilevel converters described in this invention, the modular multilevel converter includes three phase units, each phase unit is divided into upper and lower bridge arms, each bridge arm is composed of N ordinary sub-modules and 1 reactor cascaded, each ordinary sub-module includes 2 insulated gate bipolar transistors and a freewheeling diode group, and 1 energy storage capacitor, the operating state of the ordinary sub-module can be divided into three types according to the on / off state of the two insulated gate bipolar transistor devices inside it: on, off, and blocked;

[0020] Each arm of the updated and optimized modular multilevel converter contains N-1 ordinary submodules and 1 regulating submodule, where N is a positive integer not less than 4, and the capacitor voltage of the regulating submodule is controlled to be 1 / 2 of the voltage of the ordinary submodule, and the number of output levels of the regulating submodule is twice the voltage of the ordinary submodule.

[0021] As a preferred embodiment of the loss optimization method for modular multilevel converters described in this invention, it further includes:

[0022] When the target output voltage of the bridge arm is an integer multiple of the capacitor voltage of the ordinary submodule, the adjustment submodule is not invoked to participate in the voltage synthesis, and the control adjustment submodule is in the disconnected state.

[0023] When the target output voltage of the bridge arm is an integer multiple of the capacitor voltage of the regulating submodule, the regulating submodule is invoked to participate in the voltage synthesis, and the regulating submodule is in the activated state at this time.

[0024] The adjustment submodule is in an engaged state, including a forward engaged state and a reverse engaged state;

[0025] Let the capacitor voltage of the ordinary submodule be a, then the capacitor voltage of the regulating submodule is a / 2, the target output voltage of the bridge arm is A, and k is a positive integer;

[0026] When A = k*a, the regulating submodule is not invoked to participate in the voltage synthesis, and the regulating submodule is in the cut-off state at this time;

[0027] When A = k*a + a / 2, the adjustment submodule is invoked to participate in the voltage synthesis. At this time, k ordinary submodules and one adjustment submodule are put into operation, and the adjustment submodule is put into operation in the positive direction.

[0028] When A = k*aa / 2, the regulating submodule is not called to participate in the voltage synthesis. At this time, k ordinary submodules and one regulating submodule are put into operation, and the regulating submodule is put into operation in reverse.

[0029] As a preferred embodiment of the loss optimization method for modular multilevel converters described in this invention, the voltage balancing strategy includes a capacitor voltage sorting method, which involves sorting the capacitor voltages of the bridge arm sub-modules according to the current capacitor voltage of the current ordinary sub-module and the current direction of the bridge arm, and locating an ordinary sub-module corresponding to a regulated capacitor that is in operation to participate in PWM waveform modulation.

[0030] As a preferred embodiment of the loss optimization method for modular multilevel converters described in this invention, the step of updating the number of ordinary sub-modules and the number of regulating sub-modules to be put into operation in different states of the bridge arm includes:

[0031] If the output voltage of the bridge arm is zero, then the number of ordinary sub-modules n to be put into the bridge arm is reduced by 1.

[0032] If the output voltage of the bridge arm is not zero, then increment the number of ordinary submodules n that the bridge arm needs to be put into operation by 1.

[0033] A loss optimization system for modular multilevel converters, characterized by comprising a calculation module, a judgment module, and an optimization module.

[0034] The calculation module is used to obtain the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter, and calculate the number of ordinary sub-modules to be put into the bridge arm and the output voltage status of the bridge arm at the current moment in combination with the carrier parameters. The carrier parameters include carrier frequency, modulation frequency and phase angle.

[0035] The judgment module is used to determine whether the output voltage state of the bridge arm is in positive pulse width modulation (PWM) state, and update the number of ordinary sub-modules and adjustment sub-modules to be put into the bridge arm under different states.

[0036] The optimization module is used to optimize the losses of the modular multilevel converter by combining the number of ordinary sub-modules and the number of regulating sub-modules to be put into operation in the bridge arm after the update, and in conjunction with the voltage balancing strategy.

[0037] A computer device includes a memory and a processor, the memory storing a computer program, characterized in that the processor executes the computer program to implement the steps of the method described above.

[0038] A computer-readable storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the steps of the method described above.

[0039] The beneficial effects of this invention are as follows: This invention proposes a loss optimization method and system for modular multilevel converters. The method obtains the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter. It then calculates the number of ordinary submodules to be put into operation in the bridge arm at the current moment and the output voltage state of the bridge arm, combined with carrier parameters including carrier frequency, modulation frequency, and phase angle. The method determines whether the output voltage state of the bridge arm is in a positive pulse width modulation (PWM) state and updates the number of ordinary submodules and regulating submodules to be put into operation in the bridge arm under different states. Based on the updated number of ordinary submodules and regulating submodules to be put into operation in the bridge arm, and combined with a voltage balancing strategy, the loss optimization of the modular multilevel converter is completed. The Nth submodule on each bridge arm is improved into an adjustment submodule. The capacitor voltage of the adjustment submodule is controlled to a specific value lower than that of the ordinary submodule, in order to increase the maximum output level of the bridge arm voltage. By improving the pulse modulation strategy of the control method of the bridge arm of the MMC, at most only one adjustment submodule and the ordinary submodule are in a PWM state of frequent switching at any time in a phase unit. This improves the target output voltage waveform quality, reduces the number of switching, reduces switching losses, and improves the working performance of the modular multilevel converter. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0041] Figure 1 A flowchart of a loss optimization method and system for a modular multilevel converter provided in one embodiment of the present invention;

[0042] Figure 2 A schematic diagram of the topology of a modular multilevel converter for a loss optimization method and system for a modular multilevel converter, provided as an embodiment of the present invention;

[0043] Figure 3 A schematic diagram of the topology of a modular multilevel converter, including an adjustment submodule, is provided for a loss optimization method and system for a modular multilevel converter according to an embodiment of the present invention.

[0044] Figure 4 This is an internal structural diagram of a computer device for a loss optimization method and system for a modular multilevel converter, provided as an embodiment of the present invention. Detailed Implementation

[0045] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0046] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0047] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0048] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0049] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0050] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0051] Example 1

[0052] Reference Figure 1-4This is the first embodiment of the present invention, which provides a loss optimization method and system for a modular multilevel converter, comprising:

[0053] The target output voltage of the bridge arm is obtained based on the output voltage command value of the modular multilevel converter. The number of ordinary sub-modules to be put into the bridge arm and the output voltage status of the bridge arm at the current moment are calculated in combination with the carrier parameters. The carrier parameters include carrier frequency, modulation frequency and phase angle.

[0054] The number of ordinary sub-modules to be deployed in the bridge arm at the current moment is represented as follows:

[0055]

[0056] The round function returns an integer value after rounding, F1 is the carrier frequency, F2 is the modulation frequency, α is the phase angle, U is the target output voltage of the bridge arm, and N is a positive integer not less than 4, where N represents the sum of the number of ordinary submodules and regulating submodules in each bridge arm.

[0057] Furthermore, the bridge arm output voltage state is represented as follows:

[0058]

[0059] The mod function is a remainder function that returns the remainder after dividing two numerical expressions. The ceiling function is a rounding function that rounds the decimal part of the input parameter upwards. F1 is the carrier frequency, F2 is the modulation frequency, α is the phase angle, N is a positive integer not less than 4, and N represents the sum of the number of ordinary submodules and regulation submodules in each bridge arm.

[0060] Furthermore, determine whether the output voltage state of the bridge arm is in positive pulse width modulation (PWM) state, and update the number of ordinary sub-modules and adjustment sub-modules to be put into the bridge arm under different states;

[0061] The updating of the number of ordinary sub-modules and adjustment sub-modules to be put into operation in different states of the bridge arm includes:

[0062] If the output voltage of the bridge arm is zero, then the number of ordinary sub-modules n to be put into the bridge arm is reduced by 1.

[0063] If the output voltage of the bridge arm is not zero, then increment the number of ordinary submodules n that the bridge arm needs to be put into operation by 1.

[0064] It should be noted that the modular multilevel converter includes 3 phase units, each phase unit is divided into upper and lower bridge arms, each bridge arm is composed of N ordinary sub-modules and 1 reactor cascaded. Each ordinary sub-module contains 2 insulated gate bipolar transistors and a freewheeling diode group, and 1 energy storage capacitor. The operating state of the ordinary sub-module can be divided into 3 types according to the on and off state of the 2 insulated gate bipolar transistor devices inside it: on, off, and blocked.

[0065] Furthermore, each arm of the updated and optimized modular multilevel converter contains N-1 ordinary submodules and 1 regulating submodule, where N is a positive integer not less than 4, and the capacitor voltage of the regulating submodule is controlled to be 1 / 2 of the voltage of the ordinary submodule, and the number of output levels of the regulating submodule is twice the voltage of the ordinary submodule.

[0066] It should be noted that when the target output voltage of the bridge arm is an integer multiple of the capacitor voltage of the ordinary submodule, the adjustment submodule is not invoked to participate in the voltage synthesis, and the control adjustment submodule is in the disconnected state at this time.

[0067] It should be noted that when the target output voltage of the bridge arm is an integer multiple of the capacitor voltage of the regulating submodule, the regulating submodule is invoked to participate in the voltage synthesis, and the regulating submodule is in the activated state at this time.

[0068] It should be noted that the adjustment submodule being in operation includes both forward operation and reverse operation.

[0069] In this embodiment of the application, the capacitor voltage of the ordinary submodule is denoted as a, then the capacitor voltage of the regulating submodule is a / 2, the target output voltage of the bridge arm is A, and k is a positive integer;

[0070] When A = k*a, the regulating submodule is not invoked to participate in the voltage synthesis, and the regulating submodule is in the cut-off state at this time;

[0071] When A = k*a + a / 2, the regulating submodule is called to participate in the voltage synthesis. At this time, k ordinary submodules and one regulating submodule are put into operation, and the regulating submodule is put into operation in the positive direction.

[0072] When A = k*aa / 2, the regulating submodule is not called to participate in the voltage synthesis. At this time, k ordinary submodules and one regulating submodule are put into operation, and the regulating submodule is put into operation in reverse.

[0073] It should be noted that the voltage balancing strategy includes the use of a capacitor voltage sorting method. The capacitor voltage sorting method involves sorting the capacitor voltages of the bridge arm sub-modules according to the current capacitor voltage of the current ordinary sub-module and the current direction of the bridge arm, and locating an ordinary sub-module corresponding to a regulated capacitor that is in the working state to participate in PWM waveform modulation.

[0074] Furthermore, based on the number of ordinary sub-modules and regulating sub-modules to be put into operation in the bridge arm after the update, and combined with the voltage balancing strategy, the loss optimization of the modular multilevel converter is completed.

[0075] In a preferred embodiment, a loss optimization system for a modular multilevel converter includes a calculation module, a judgment module, and an optimization module.

[0076] The calculation module is used to obtain the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter, and calculate the number of ordinary sub-modules to be put into the bridge arm at the current moment and the output voltage status of the bridge arm in combination with the carrier parameters. The carrier parameters include carrier frequency, modulation frequency and phase angle.

[0077] The judgment module is used to determine whether the output voltage state of the bridge arm is in positive pulse width modulation (PWM) state, and to update the number of ordinary sub-modules and adjustment sub-modules to be put into the bridge arm under different states.

[0078] The optimization module is used to optimize the losses of the modular multilevel converter based on the number of ordinary sub-modules and regulating sub-modules to be put into operation in the bridge arm after the update, combined with the voltage balancing strategy.

[0079] The above-mentioned unit modules can be embedded in the processor of the computer device in hardware form or independent of it, or they can be stored in the memory of the computer device in software form, so that the processor can call and execute the corresponding operations of the above modules.

[0080] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 4 As shown, the computer device includes a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. When executed by the processor, the computer program implements a loss optimization method for modular multilevel converters. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device casing, or an external keyboard, touchpad, or mouse.

[0081] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0082] The target output voltage of the bridge arm is obtained based on the output voltage command value of the modular multilevel converter. The number of ordinary sub-modules to be put into the bridge arm and the output voltage status of the bridge arm at the current moment are calculated in combination with the carrier parameters. The carrier parameters include carrier frequency, modulation frequency and phase angle.

[0083] Determine whether the output voltage state of the bridge arm is in positive pulse width modulation (PWM) state, and update the number of ordinary sub-modules and adjustment sub-modules to be put into the bridge arm under different states;

[0084] Based on the number of ordinary sub-modules and regulating sub-modules to be put into operation in the bridge arm after the update, and combined with the voltage balancing strategy, the loss optimization of the modular multilevel converter is completed.

[0085] Example 2

[0086] Reference Figure 2-3 As an embodiment of the present invention, a loss optimization method and system for modular multilevel converters are provided. To verify the beneficial effects of the present invention, scientific demonstration is carried out through experiments.

[0087] Figure 2 This is a schematic diagram of the topology of a modular multilevel converter. Figure 2 As shown, the Modular Multilevel Converter (MMC) has three phase units, each divided into upper and lower arms. Each arm consists of N sub-modules and one cascaded reactor. Each sub-module contains two Insulated Gate Bipolar Transistors (IGBTs), a freewheeling diode group, and one energy storage capacitor. The sub-module's operating state can be categorized into three types based on the on / off state of its two internal IGBT devices: engaged, disconnected, and latched. The engagement and disengagement of each sub-module within each arm are controlled according to a specific strategy. Each phase unit generates an internal electromotive force on the AC side, realizing energy conversion between the AC and DC sides.

[0088] Figure 2 The dashed box in the text represents the sub-module structure, I SM and U SM These represent the current and voltage of the submodule, respectively. C0 is the internal capacitor of the submodule, and K0 and K1 are switching transistors. When K0 is on and K1 is off, the submodule SM is in the on state, and the submodule output voltage is equal to the submodule capacitor voltage. When switching transistor K0 is off and K1 is on, the submodule is in the off state, and the submodule output voltage is equal to 0. a U b U c U is the AC input phase voltage, P is the positive terminal, N is the negative terminal, and U is the negative terminal.dc / 2 is the DC side voltage, I dc is the DC side current, and O is the equivalent neutral point.

[0089] like Figure 3 As shown, this invention improves the Nth submodule on each bridge arm into an adjustment submodule. The capacitor voltage of the adjustment submodule is controlled to a specific value lower than that of the ordinary submodule, thereby increasing the maximum output level of the bridge arm voltage. The structure of the ordinary submodule is as follows: Figure 2 As shown in the top left corner (SM), the structure of the adjustment submodule is as follows: Figure 3 As shown in the upper left corner (SMN). Preferably, the specific value mentioned above is such that the capacitor voltage of the regulating submodule is controlled to be half the voltage of the ordinary submodule, thereby increasing the number of output levels by nearly two times. When the target output voltage U of the bridge arm is a multiple of the capacitor voltage of the ordinary submodule, the regulating submodule does not need to participate in the voltage synthesis, and the regulating submodule is controlled in the off state. When the target output voltage U of the bridge arm is a multiple of the capacitor voltage of the regulating submodule, the regulating submodule needs to participate in the voltage synthesis, and the regulating submodule is controlled in the on state. The regulating submodule being in the on state is divided into a forward on state and a reverse on state.

[0090] For example, if the capacitor voltage of the ordinary submodule is u / 4, then the capacitor voltage of the regulating submodule can be u / 8. When the target output voltage U of the bridge arm is 5u / 8, there are two ways to synthesize this target output voltage U. One is to have 2 ordinary submodules engaged, with the regulating submodule in a forward-engaged state; the other is to have 3 ordinary submodules engaged, with the regulating submodule in a reverse-engaged state. Regarding the control of the regulating submodule's state, when K0 and K3 are on and K1 and K2 are off, the regulating submodule is in a forward-engaged state; when K1 and K2 are on and K0 and K3 are off, the regulating submodule is in a reverse-engaged state; when K0 and K1 are on, or K3 and K4 are on, the regulating submodule is in a disconnected state.

[0091] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

[0092] 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 implemented 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. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0093] 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 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0094] 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.

[0095] 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.

[0096] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0097] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A loss optimization method for modular multilevel converters, characterized in that, include: The target output voltage of the bridge arm is obtained based on the output voltage command value of the modular multilevel converter. The number of ordinary sub-modules to be put into the bridge arm and the output voltage status of the bridge arm at the current moment are calculated in combination with the carrier parameters. The carrier parameters include carrier frequency, modulation frequency and phase angle. Determine whether the output voltage state of the bridge arm is in positive pulse width modulation (PWM) state, and update the number of ordinary sub-modules and adjustment sub-modules to be put into the bridge arm under different states; Based on the number of ordinary sub-modules and regulating sub-modules to be put into operation in the bridge arm after the update, and combined with the voltage balancing strategy, the loss optimization of the modular multilevel converter is completed.

2. The loss optimization method for modular multilevel converters as described in claim 1, characterized in that, The process of obtaining the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter, and calculating the number of ordinary sub-modules to be put into operation in the bridge arm at the current moment and the output voltage status of the bridge arm in combination with carrier parameters includes: The number of ordinary sub-modules waiting to be deployed in the bridge arm at the current moment is expressed as follows: The round function returns an integer value after rounding, F1 is the carrier frequency, F2 is the modulation frequency, α is the phase angle, U is the target output voltage of the bridge arm, and N is a positive integer not less than 4, where N represents the sum of the number of ordinary submodules and regulating submodules in each bridge arm.

3. The loss optimization method for modular multilevel converters as described in claim 2, characterized in that, The process of obtaining the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter, and calculating the number of ordinary sub-modules to be put into operation in the bridge arm at the current moment and the output voltage status of the bridge arm in combination with carrier parameters, also includes: The output voltage state of the bridge arm is represented as follows: The mod function is a remainder function that returns the remainder after dividing two numerical expressions. The ceiling function is a rounding function that rounds the decimal part of the input parameter upwards. F1 is the carrier frequency, F2 is the modulation frequency, α is the phase angle, N is a positive integer not less than 4, and N represents the sum of the number of ordinary submodules and regulation submodules in each bridge arm.

4. The loss optimization method for modular multilevel converters as described in claim 3, characterized in that, The modular multilevel converter includes three phase units, each phase unit is divided into upper and lower bridge arms, each bridge arm is composed of N ordinary sub-modules and 1 reactor cascaded together, each ordinary sub-module contains 2 insulated gate bipolar transistors and a freewheeling diode group, and 1 energy storage capacitor. The operating state of the ordinary sub-module can be divided into three types according to the on and off state of the two insulated gate bipolar transistor devices inside it: on, off, and locked. Each arm of the updated and optimized modular multilevel converter contains N-1 ordinary submodules and 1 regulating submodule, where N is a positive integer not less than 4, and the capacitor voltage of the regulating submodule is controlled to be 1 / 2 of the voltage of the ordinary submodule, and the number of output levels of the regulating submodule is twice the voltage of the ordinary submodule.

5. The loss optimization method for modular multilevel converters as described in claim 4, characterized in that, Also includes: When the target output voltage of the bridge arm is an integer multiple of the capacitor voltage of the ordinary submodule, the adjustment submodule is not invoked to participate in the voltage synthesis, and the control adjustment submodule is in the disconnected state. When the target output voltage of the bridge arm is an integer multiple of the capacitor voltage of the regulating submodule, the regulating submodule is invoked to participate in the voltage synthesis, and the regulating submodule is in the activated state at this time. The adjustment submodule is in an engaged state, including a forward engaged state and a reverse engaged state; Let the capacitor voltage of the ordinary submodule be a, then the capacitor voltage of the regulating submodule is a / 2, the target output voltage of the bridge arm is A, and k is a positive integer; When A = k*a, the regulating submodule is not invoked to participate in the voltage synthesis, and the regulating submodule is in the cut-off state at this time; When A = k*a + a / 2, the adjustment submodule is invoked to participate in the voltage synthesis. At this time, k ordinary submodules and one adjustment submodule are put into operation, and the adjustment submodule is put into operation in the positive direction. When A = k*aa / 2, the regulating submodule is not called to participate in the voltage synthesis. At this time, k ordinary submodules and one regulating submodule are put into operation, and the regulating submodule is put into operation in reverse.

6. The loss optimization method for modular multilevel converters as described in claim 5, characterized in that, The voltage balancing strategy includes using a capacitor voltage sorting method. This method involves sorting the capacitor voltages of the bridge arm sub-modules according to the current capacitor voltage of the current ordinary sub-module and the current direction of the bridge arm, and then locating an ordinary sub-module corresponding to a regulated capacitor that is in operation to participate in PWM waveform modulation.

7. The loss optimization method for modular multilevel converters as described in claim 6, characterized in that, The method of updating the number of ordinary sub-modules and adjustment sub-modules to be put into operation in different states of the bridge arm includes: If the output voltage of the bridge arm is zero, then the number of ordinary sub-modules n to be put into the bridge arm is reduced by 1. If the output voltage of the bridge arm is not zero, then increment the number of ordinary submodules n that the bridge arm needs to be put into operation by 1.

8. A loss optimization system for a modular multilevel converter, characterized in that, It includes a calculation module, a judgment module, and an optimization module. The calculation module is used to obtain the target output voltage of the bridge arm based on the output voltage command value of the modular multilevel converter, and calculate the number of ordinary sub-modules to be put into the bridge arm and the output voltage status of the bridge arm at the current moment in combination with the carrier parameters. The carrier parameters include carrier frequency, modulation frequency and phase angle. The judgment module is used to determine whether the output voltage state of the bridge arm is in positive pulse width modulation (PWM) state, and update the number of ordinary sub-modules and adjustment sub-modules to be put into the bridge arm under different states. The optimization module is used to optimize the losses of the modular multilevel converter by combining the number of ordinary sub-modules and the number of regulating sub-modules to be put into operation in the bridge arm after the update, and in conjunction with the voltage balancing strategy.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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