Sub-module derating control method, device and equipment for modular multilevel converter

Abstract

The present application relates to a sub-module derating control method, device and equipment for a modular multilevel converter. The method includes: obtaining harmonic modulation voltages corresponding to multiple harmonic components existing under the excitation of a fundamental frequency modulation voltage of a target sub-module, where the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are harmonic components of different types; allocating the arm modulation voltage obtained by jointly fusing each of the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module; and performing derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage. The use of this method improves the derating control effect of the sub-module of the modular multilevel converter.

Description

Technical Field

[0001] The present application relates to the technical field of modular multi-level converters, and in particular to a method and apparatus for controlling sub-module capacity reduction of a modular multi-level converter, a power conversion device, and a computer-readable storage medium. Background Art

[0002] With the continuous development of science and technology, power conversion equipment is also gradually iterating. Among them, the modular multilevel converter (MMC) is gradually replacing the traditional two-level voltage source converter due to its advantages such as modularity, low switching frequency and good harmonic performance. It has been widely used in fields such as large-scale centralized renewable energy power generation and high-voltage flexible direct current transmission.

[0003] At present, in order to reduce the problem of capacitor voltage fluctuations in MMC sub-modules, capacity reduction control is usually achieved by injecting or eliminating the current or voltage of harmonic components. However, in modular multi-level converters, since the generation of harmonic components is interfered with by multiple factors such as modular structure, operating conditions and modulation strategy, the harmonic components controlled by the injection control strategy are difficult to match the harmonic components that actually cause the sub-module capacitor voltage fluctuations, which makes it easy for the sub-module capacitor voltage fluctuations to still be large. Therefore, the current capacity reduction control effect of the sub-modules of modular multi-level converters is poor. Summary of the Invention

[0004] Based on this, it is necessary to provide a method, device, power conversion equipment and computer-readable storage medium for controlling the sub-module capacity reduction of a modular multilevel converter to improve the capacity reduction control effect of the sub-modules of the modular multilevel converter in order to address the above technical problems.

[0005] In a first aspect, the present application provides a method for controlling capacity reduction of submodules of a modular multilevel converter, comprising:

[0006] When the bus voltage of a current substation in the voltage coordination area exceeds a limit, obtaining a first compensation performance indicator corresponding to the current substation;

[0007] Obtaining harmonic modulation voltages corresponding to respective multiple harmonic components existing in a target submodule under excitation of a fundamental frequency modulation voltage, wherein the target submodule is any standard submodule of a modular multilevel converter, and the multiple harmonic components are harmonic components of different types;

[0008] Distributing the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule;

[0009] Perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage.

[0010] In one embodiment, the multiple harmonic components include a first harmonic component and a second harmonic component, and the harmonic modulation voltage includes a first modulation voltage of the first harmonic component and a second modulation voltage of the second harmonic component; the obtaining of the harmonic modulation voltages corresponding to the multiple harmonic components existing under the excitation of the fundamental frequency modulation voltage of the target sub-module includes:

[0011] Convert a first voltage parameter of the fundamental frequency modulation voltage into a second voltage parameter according to a first correspondence between the first harmonic component and a first fundamental frequency component of the fundamental frequency modulation voltage;

[0012] Generate the first modulation voltage according to the second voltage parameter;

[0013] Extract a harmonic component voltage corresponding to the second harmonic component from the capacitor voltage of the target sub-module;

[0014] Determine a harmonic component current of the target sub-module in the bridge arm where it is located;

[0015] Convert the harmonic component current into the second modulation voltage according to a second correspondence between the harmonic component voltage and the second harmonic component.

[0016] In one embodiment, the generating the first modulation voltage according to the second voltage parameter includes:

[0017] Generate a harmonic modulation voltage corresponding to the first harmonic component according to the second voltage parameter;

[0018] Generate the first modulation voltage according to the harmonic modulation voltage and the switching bridge arm where the target sub-module is located.

[0019] In one embodiment, the determining the harmonic component current of the target sub-module in the bridge arm where it is located includes:

[0020] Extract a fundamental frequency component voltage corresponding to a second fundamental frequency component from the capacitor voltage of the target sub-module;

[0021] Determine a current parameter of the target sub-module in the bridge arm where it is located according to the fundamental frequency component voltage and the harmonic component voltage;

[0022] Generate the harmonic component current according to the current parameter.

[0023] In one embodiment, converting the harmonic component current into the second modulation voltage according to the second correspondence between the harmonic component voltage and the second harmonic component includes:

[0024] Performing a coordinate transformation on the harmonic component voltage according to the common-mode voltage component of the arm of the modular multilevel converter to obtain a direct-axis harmonic component voltage and a quadrature-axis harmonic component voltage in a preset coordinate system;

[0025] Converting the direct-axis harmonic component voltage into a direct-axis harmonic modulation reference current according to the direct-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system, and converting the quadrature-axis harmonic component voltage into a quadrature-axis harmonic modulation reference current according to the quadrature-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system;

[0026] Performing a coordinate transformation on the harmonic component current to obtain a direct-axis harmonic component current and a quadrature-axis harmonic component current in the preset coordinate system;

[0027] Converting the direct-axis harmonic component current and the direct-axis harmonic modulation reference current into a direct-axis harmonic modulation voltage according to the second correspondence, and converting the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current, and the direct-axis harmonic modulation reference current into a quadrature-axis harmonic modulation voltage according to the second correspondence;

[0028] Generating the second modulation voltage according to the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage.

[0029] In one embodiment, before distributing the arm modulation voltage obtained by jointly fusing the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module, the method further includes:

[0030] Determining the arm where the target sub-module is located;

[0031] Fusing the harmonic modulation voltages and the fundamental frequency modulation voltage according to the arm where the target sub-module is located to obtain an arm modulation voltage.

[0032] In one embodiment, the step of performing derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage includes:

[0033] Modulating the target modulation voltage to a preset carrier signal to obtain an initial voltage modulation signal;

[0034] Performing a normalization process on the initial voltage modulation signal to obtain the voltage modulation signal;

[0035] Perform derating control on the target sub-module according to the voltage modulation signal.

[0036] In a second aspect, the present application further provides a derating control device for a sub-module of a modular multilevel converter, including:

[0037] An acquisition module, configured to acquire harmonic modulation voltages corresponding to multiple harmonic components existing under the excitation of a fundamental frequency modulation voltage of a target sub-module, where the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are harmonic components of different types;

[0038] An allocation module, configured to allocate the arm modulation voltage obtained by jointly fusing the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module;

[0039] A derating control module, configured to perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage.

[0040] In a third aspect, the present application further provides a power conversion device, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0041] Acquire harmonic modulation voltages corresponding to multiple harmonic components existing under the excitation of a fundamental frequency modulation voltage of a target sub-module, where the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are harmonic components of different types; allocate the arm modulation voltage obtained by jointly fusing the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module; perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage.

[0042] In a fourth aspect, the present application further provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the following steps are implemented:

[0043] Acquire harmonic modulation voltages corresponding to multiple harmonic components existing under the excitation of a fundamental frequency modulation voltage of a target sub-module, where the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are harmonic components of different types; allocate the arm modulation voltage obtained by jointly fusing the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module; perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage.

[0044] In a fifth aspect, the present application further provides a computer program product, including a computer program, and when the computer program is executed by a processor, the following steps are implemented:

[0045] Obtain harmonic modulation voltages corresponding to multiple harmonic components existing under the excitation of the fundamental frequency modulation voltage for a target sub-module, where the target sub-module is any standard sub-module of a modular multilevel converter, and the multiple harmonic components are harmonic components of different types; allocate the arm modulation voltage obtained by jointly fusing the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module; perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage.

[0046] The above-mentioned sub-module derating control method, device, power conversion equipment and computer-readable storage medium of the modular multilevel converter first obtain corresponding harmonic modulation voltages for multiple harmonic components existing under the excitation of the fundamental frequency modulation voltage for the target sub-module. Since the target sub-module is any standard sub-module of the modular multilevel converter and the multiple harmonic components are also harmonic components of different types, that is, for any standard sub-module in the modular multilevel converter, for different types of harmonic components generated under the excitation of the fundamental frequency modulation voltage, the harmonic modulation voltage corresponding to this harmonic component can be obtained. Furthermore, the arm modulation voltage obtained by fusing the harmonic modulation voltages is allocated to obtain a target modulation voltage acting on the target sub-module, so as to achieve the purpose of allocating target modulation signals for different types of harmonic components for the target sub-module from the structural perspective of the modular multilevel converter. Finally, through the voltage modulation signal corresponding to the target modulation signal, derating control is performed on the target sub-module, that is, the capacitor voltage of the target sub-module can be directly derated with the voltage modulation signal as the reference. Since the target modulation voltage is allocated based on the overall structure of the modular multilevel converter on the premise of considering multiple harmonic components existing under the excitation of the fundamental frequency modulation voltage for the target sub-module, the voltage modulation signal acting on the target sub-module can completely match the harmonic components causing the capacitor voltage fluctuation of the target sub-module, and finally the purpose of precisely controlling the harmonic components affecting the capacitor voltage fluctuation of the target sub-module is achieved. Therefore, it overcomes the technical defect that in the modular multilevel converter, due to the generation of harmonic components being interfered by multiple factors such as the modular structure, operating conditions, and control strategies, it is difficult for the harmonic components controlled under the injection control strategy to match the harmonic components actually causing the capacitor voltage fluctuation of the sub-module, and thus it is easy to have a relatively large capacitor voltage fluctuation of the sub-module. Therefore, the derating control effect of the sub-module of the modular multilevel converter is improved. Description of the Drawings

[0047] To more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the related art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0048] Figure 1 It is a schematic flowchart of the sub-module derating control method for a modular multilevel converter in an embodiment.

[0049] Figure 2 It is a schematic diagram of the circuit topology of a three-phase half-bridge modular multilevel converter for the sub-module derating control method of a modular multilevel converter in an embodiment.

[0050] Figure 3 It is a schematic flowchart of the sub-module derating control method for a modular multilevel converter in another embodiment.

[0051] Figure 4 It is a control flowchart of the modulated voltage for the sub-module derating control method of a modular multilevel converter in an embodiment.

[0052] Figure 5 It is a control flowchart of the harmonic component voltage controller for the sub-module derating control method of a modular multilevel converter in an embodiment.

[0053] Figure 6 It is a control flowchart of the circulating current controller for the sub-module derating control method of a modular multilevel converter in an embodiment.

[0054] Figure 7 It is a schematic diagram of the overall structure for derating control of the target sub-module in the sub-module derating control method of a modular multilevel converter in an embodiment.

[0055] Figure 8 It is a structural block diagram of the sub-module derating control device for a modular multilevel converter in an embodiment.

[0056] Figure 9 It is an internal structure diagram of a power conversion device in an embodiment. Detailed implementation manners

[0057] In order to make the purpose, technical solutions and advantages of the present application more clear, the following further details the present application in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0058] First of all, it should be understood that there are many standard sub-modules in the MMC. The capacitors in the standard sub-modules replace the large DC-side capacitors used in the traditional flexible DC transmission system to support the DC voltage. The distributed standard sub-modules inside the MMC will also bring many problems. For example, the coupling of the electric quantity inside the MMC will cause the circulating current and voltage fluctuation of the capacitors in the standard sub-modules. And the problem of the capacitor voltage fluctuation of any standard sub-module will affect the stable operation of the MMC. Therefore, usually, the capacitor voltage fluctuation of the standard sub-module is suppressed by selecting an appropriate sub-module capacitor value. Although selecting an appropriate sub-module capacitor value can significantly suppress the capacitor voltage fluctuation of the sub-module, increasing the sub-module capacitance value will cause a large increase in the volume and cost of the MMC. Even, in the MMC converter, the cost of the sub-module capacitor accounts for 1 / 3 of the total cost, and the capacitor volume accounts for 1 / 2 of the total volume. Therefore, considering the cost and volume of the MMC, the capacity reduction control is also carried out through the injection control strategy. For example, in order to suppress or eliminate the second harmonic current in the MMC arm current, an appropriate second harmonic circulating current is injected to suppress or eliminate the second harmonic component in the capacitor voltage of the MMC sub-module. Another example is to change the waveform of the MMC arm voltage by injecting the third harmonic voltage, so as to reduce the peak-to-peak value of the capacitor voltage fluctuation of the sub-module, and it is also an effective strategy to reduce the capacitor voltage fluctuation of the MMC sub-module. However, in the process of reducing the capacitor voltage of the MMC sub-module by the above injection control strategies, there are certain shortcomings. Injecting an appropriate second harmonic circulating current requires a large amount of calculation or look-up table work with the change of working conditions to obtain the current parameters of the second harmonic circulating current. And the injected second harmonic circulating current and the second harmonic circulating current originally existing in the arm current will be superimposed in the arm, so that the effective value of the arm current will increase. After the effective value of the arm current increases, problems such as accelerated device damage, increased cost and reduced system stability will occur due to temperature rise. And injecting the third harmonic voltage will also cause limited capacity reduction control effect due to reasons such as harmonic superposition effect and nonlinear load influence. At the same time, the harmonic components existing in the MMC sub-module under the excitation of the fundamental frequency modulation voltage are very complex, and the harmonic components existing in the MMC during the working process are the main reasons for the capacitor voltage fluctuation of the MMC sub-module. However, the above methods only carry out capacity reduction control on the MMC sub-module from different angles, and the controlled harmonic components after control do not match the harmonic components actually causing the capacitor voltage fluctuation of the sub-module. Therefore, there is an urgent need for a capacity reduction control method that can improve the capacity reduction control effect of the sub-module of the modular multilevel converter.

[0059] In one embodiment, as Figure 1As shown, a sub-module derating control method for a modular multilevel converter is provided. In this embodiment, this method is exemplified by its application to a power conversion device, which includes but is not limited to DC-DC converters, AC-AC converters, DC-AC inverters, AC-DC rectifiers, etc. The power conversion device includes a modular multilevel converter and an upper control system of the modular multilevel converter, etc. The upper control system is composed of a central controller, sensors, actuators, communication interfaces, and a human-machine interface, etc. The upper control system includes an acquisition module, a distribution module, and a derating control module. The acquisition module is used to acquire the harmonic modulation voltages corresponding to multiple harmonic components existing under the fundamental frequency modulation voltage excitation of the target sub-module. Herein, the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are different types of harmonic components. The distribution module is used to distribute the arm modulation voltage obtained by fusing each harmonic modulation voltage to obtain the target modulation voltage acting on the target sub-module. The derating control module is used to perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage. Through the cooperation among the acquisition module, the distribution module, and the derating control module, it is possible to modulate multiple harmonic components existing under the fundamental frequency modulation voltage excitation of the target sub-module by means of the voltage modulation signal corresponding to the target modulation voltage, thereby reducing the harmonic voltage generated across the capacitor of the target sub-module during the charge and discharge process of the target sub-module. That is, by applying the voltage modulation signal to the target sub-module, the matching between the controlled harmonic components and the harmonic components causing the voltage fluctuation of the target sub-module capacitor is achieved, thereby realizing the purpose of reducing the voltage fluctuation of the target sub-module capacitor. Therefore, the derating control effect of the sub-module of the modular multilevel converter can be improved. It can be understood that this method can also be applied to a server connected to the power conversion device, and can also be applied to a system including the power conversion device and the server, and is realized through the interaction between the power conversion device and the server. In this embodiment, the method includes the following steps:

[0060] Step 202: Acquire the harmonic modulation voltages corresponding to multiple harmonic components existing under the fundamental frequency modulation voltage excitation of the target sub-module, where the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are different types of harmonic components.

[0061] It should be noted that the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are harmonic components of different types. Specifically, the multiple harmonic components can be a combination of harmonic components such as the second harmonic component, the third harmonic component, and the fourth harmonic component. Among them, the harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage can be either the harmonic components generated by the target sub-module under the excitation of the fundamental frequency voltage or the harmonic components actively introduced by the fundamental frequency modulation voltage when exciting the target sub-module. For example, in an implementable manner, the capacitor voltage of the target sub-module is mainly divided into the double-frequency component and the fundamental frequency component. If the fundamental frequency modulation voltage injects the third harmonic voltage, the multiple harmonic components are specifically the double-frequency component (second harmonic component) and the third harmonic component (introduced by the third harmonic voltage). By controlling the multiple harmonic components, the capacitor voltage fluctuation of the target sub-module can be reduced.

[0062] It should be noted that the harmonic modulation voltage is used to modulate the multiple harmonic components existing under the excitation of the fundamental frequency modulation voltage. Specifically, it can be used to suppress the harmonic components existing under the excitation of the fundamental frequency modulation voltage or to control the generation of the harmonic components under the excitation of the fundamental frequency modulation voltage. For example, in an implementable manner, the harmonic modulation voltage includes the second harmonic modulation voltage and the third harmonic modulation voltage. Among them, the second harmonic modulation voltage is used to eliminate or suppress the second harmonic circulating current in the MMC arm current, and the third harmonic modulation voltage is used to inject the third harmonic component generated by the fundamental frequency modulation voltage to reduce the amplitude of the capacitor voltage of the target sub-module. That is, by using the combined control method of injecting the third harmonic modulation voltage and injecting the second harmonic circulating current, the multiple harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage are co-modulated, and the effect of reducing the capacitor voltage fluctuation of the target sub-module can be achieved without significantly increasing the effective value of the MMC arm current.

[0063] It should be noted that the harmonic modulation voltage varies with the different circuit topologies of the modular multilevel converter. For example, referring to Figure 2 , Figure 2 is a schematic diagram showing the circuit topology of the three-phase half-bridge modular multilevel converter. Specifically, it may include a DC source, an AC grid, a three-phase half-bridge modular multilevel converter, an arm inductor, an arm resistor, and a transformer equivalent inductor, etc. As Figure 2 shown, each phase of the three-phase half-bridge modular multilevel converter contains two arms, and each arm is serially connected with N standard sub-modules of the bridge plate. That is, are N half-bridge standard sub-modules, and any half-bridge standard sub-module can be understood as the target sub-module. is the DC bus voltage. is the arm inductor of the three-phase half-bridge modular multilevel converter. is the arm resistor of the three-phase half-bridge modular multilevel converter. is the equivalent inductance of the transformer, is the current of the upper arm of the three-phase half-bridge modular multilevel converter, where specifically can be , is the current of the upper arm of phase A, is the current of the upper arm of phase B, is the current of the upper arm of phase C, is the current of the lower arm of the three-phase half-bridge modular multilevel converter, where specifically can be , is the current of the lower arm of phase A, is the current of the lower arm of phase B, is the current of the lower arm of phase C, is the output voltage of the half-bridge standard sub-module, is the capacitor current of the half-bridge standard sub-module, is the capacitor voltage of the half-bridge standard sub-module, C is the capacitor, is the AC current on the grid side of phase A, is the AC current on the grid side of phase B, is the AC current on the grid side of phase C, is the AC voltage on the grid side of phase A, is the AC voltage on the grid side of phase B, is the AC voltage on the grid side of phase C, S is the transmission capacity of the three-phase half-bridge modular multilevel converter, o is the neutral point of the grid, is the power factor angle.

[0064] As an example, step 202 includes: extracting multiple harmonic components generated by the target sub-module under the excitation of the fundamental frequency modulation voltage from the capacitor voltage of the target sub-module, and generating corresponding harmonic components for each harmonic component. For example, in an implementable manner, the second harmonic component and the third harmonic component existing in the capacitor voltage of the target sub-module are jointly used as multiple harmonic components.

[0065] As another example, step 202 includes: jointly using the harmonic components generated by the fundamental frequency modulation voltage and the harmonic components generated by the target sub-module under the excitation of the fundamental frequency modulation voltage as multiple harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage, and obtaining the corresponding harmonic modulation voltages for each harmonic component. For example, in an implementable manner, the third harmonic component generated by the fundamental frequency modulation voltage injecting the third harmonic voltage and the second harmonic component existing in the capacitor voltage of the target sub-module are jointly used as multiple harmonic components.

[0066] Step 204, distributing the arm modulation voltage obtained by jointly fusing each harmonic modulation voltage to obtain the target modulation voltage acting on the target sub-module.

[0067] It should be noted that since the modular multilevel converter is composed of multiple standard sub-modules, when determining the target modulation voltage of the target sub-module, the problem of the arm modulation voltage distribution of the modular multilevel converter is involved. Among them, the target modulation voltage is used to control multiple harmonic components existing under the excitation of the fundamental frequency modulation voltage. The distribution method of the arm modulation voltage can specifically be an equal distribution method or a method of distribution using an equal voltage control algorithm. The embodiments of the present application do not limit this.

[0068] As an example, step 204 includes: injecting each harmonic modulation voltage into the fundamental frequency modulation voltage to obtain the arm modulation voltage of the arm where the target sub-module is located, and evenly distributing the arm modulation voltage to obtain the target modulation voltage acting on the target sub-module.

[0069] It can be understood that affected by the circuit topology of the modular multilevel converter, the arm modulation voltage of the target sub-module changes with the change of the arm where it is located, that is, the arm modulation voltage of the target sub-module in the upper arm is different from that of the target sub-module in the lower arm.

[0070] Step 206, perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage.

[0071] It should be noted that by modulating the target modulation voltage to a preset carrier signal, the voltage modulation signal for performing derating control on the target sub-module can be obtained. Specifically, the voltage modulation signal can be obtained by adjusting the amplitude, phase or frequency of the signal, and the voltage modulation signal is applied to the target sub-module of the modular multilevel converter. For example, in an implementable manner, the voltage modulation signal can be used to control the on / off of the IGBT (Insulated Gate Bipolar Transistor) of the target sub-module, so as to greatly reduce the capacitor voltage fluctuation of the target sub-module and achieve derating of the target sub-module.

[0072] As an example, step 206 includes: modulating the amplitude of the preset carrier signal according to the target modulation voltage to obtain a voltage modulation signal, and performing on / off control on the insulated gate bipolar transistor of the target sub-module according to the voltage modulation signal.

[0073] In the above-mentioned sub-module capacity reduction control method of the modular multi-level converter, first, multiple different types of harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage are determined, and the harmonic modulation voltage corresponding to each harmonic component is obtained, and then the bridge arm modulation voltage is obtained by injecting each harmonic modulation voltage into the fundamental frequency modulation voltage, and the bridge arm modulation voltage is evenly distributed to obtain the target modulation voltage acting on the target sub-module, and finally the signal parameters of the preset carrier signal are modulated by the target modulation voltage to obtain a voltage modulation signal, and based on the voltage modulation signal, the insulated gate transistor of the target sub-module is controlled to be on and off to achieve capacity reduction control of the target sub-module. Since the voltage modulation signal fully takes into account the multiple harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage during the modulation process, the voltage modulation signal is applied to the target sub-module. When the insulated gate transistor of the target sub-module is controlled to be on and off, the harmonic components that cause the capacitor voltage fluctuation of the target sub-module can be completely controlled. That is, the purpose of accurately controlling the harmonic components that affect the capacitor voltage fluctuation of the target sub-module is achieved. Therefore, various types of harmonic components are fully considered and corresponding harmonic modulation voltages are generated to modulate the voltage modulation signal acting on the target sub-module. This can overcome the technical defect that in the modular multilevel converter, the generation of harmonic components is interfered by multiple factors such as modular structure, operating conditions and control strategy, resulting in the harmonic components controlled under the injection control strategy being difficult to match the harmonic components that actually cause the capacitor voltage fluctuation of the sub-module, thereby making it easy for the capacitor voltage fluctuation of the sub-module to still be large. Therefore, the capacity reduction control effect of the sub-module of the modular multilevel converter is improved.

[0074] In one embodiment, Figure 3 As shown, the multiple harmonic components include a first harmonic component and a second harmonic component, and the harmonic modulation voltage includes a first modulation voltage of the first harmonic component and a second modulation voltage of the second harmonic component; obtaining the harmonic modulation voltages corresponding to the multiple harmonic components existing in the target submodule under the excitation of the fundamental frequency modulation voltage includes:

[0075] Step 302 : Convert a first voltage parameter of the fundamental frequency modulation voltage into a second voltage parameter according to a first corresponding relationship between the first harmonic component and the first fundamental frequency component of the fundamental frequency modulation voltage.

[0076] It should be noted that in order to reduce the capacitance voltage fluctuation of the target sub-module, different derating control methods may be adopted. In some derating control methods, the processing of the fundamental frequency modulation signal is involved, which leads to the active introduction of harmonic components. That is, multiple different types of harmonic components may include both the different harmonic components passively generated by the target sub-module under the excitation of the fundamental frequency modulation voltage and the harmonic components actively injected when modulating the fundamental frequency modulation signal. For the actively injected harmonic components and the passively generated harmonic components, there are differences in the way of generating the harmonic modulation voltage. Therefore, the first harmonic component refers to the harmonic component actively injected to reduce the capacitance voltage fluctuation of the target sub-module, such as the third harmonic component generated by the fundamental frequency modulation voltage, and the second harmonic component refers to the harmonic component that affects the capacitance voltage of the target sub-module and is passively generated, such as the second harmonic component of the capacitance voltage of the target sub-module.

[0077] It should be noted that the harmonic modulation voltage includes the first modulation voltage of the first harmonic component and the second modulation voltage of the second harmonic component. For the first modulation voltage, since it is obtained by active injection, the first modulation voltage can be finally determined directly based on the linear relationship between the voltage parameters of the fundamental frequency modulation voltage and the first modulation voltage. Among them, the first modulation voltage can specifically be the third harmonic modulation voltage. For example, in an implementable manner, the first correspondence between the third harmonic component of the third harmonic modulation voltage and the first fundamental component of the fundamental frequency modulation voltage is as follows:

[0078]

[0079] Among them, is the amplitude of the fundamental frequency modulation voltage, is the amplitude of the third harmonic modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the phase angle of the third harmonic modulation voltage, that is, and are the first voltage parameters, and are the second voltage parameters.

[0080] As an example, step 302 includes: analyzing the fundamental frequency modulation voltage to obtain the first correspondence between the first harmonic component and the first fundamental component of the fundamental frequency modulation voltage, and based on the first correspondence, converting the first voltage parameter of the fundamental frequency modulation voltage to obtain the second voltage parameter.

[0081] In an implementable manner, referring to Figure 4 , Figure 4 is the control flow chart representing the first modulation voltage, where is the trigger signal for amplitude detection and phase angle detection, is the amplitude of the fundamental frequency modulation voltage, is the amplitude of the third harmonic modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the phase angle of the third harmonic modulation voltage.

[0082] Step 304: Generate a first modulation voltage according to the second voltage parameter.

[0083] It should be noted that after determining the voltage parameter of a certain voltage, the corresponding modulation voltage can be generated. For example, in an implementable manner, assuming that the first correspondence between the first harmonic component and the fundamental frequency modulation voltage is as stated above, the expressions of the fundamental frequency modulation voltage and the third harmonic modulation voltage are as follows:

[0084]

[0085] Among them, is the fundamental frequency modulation voltage, is the third harmonic modulation voltage, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, is the period. If only injecting the third harmonic modulation voltage into the fundamental frequency modulation voltage is used as a method to reduce the capacitor voltage fluctuation of the target sub-module, the expression of the bridge arm modulation voltage can be as follows:

[0086]

[0087] Among them, is the bridge arm modulation voltage of the upper bridge arm of phase A, is the DC bus voltage of the modular multilevel sub-module, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, is the period.

[0088] As an example, step 304 includes: modulating the initial modulation voltage according to the amplitude and phase angle of the first modulation voltage to obtain the first modulation voltage.

[0089] Step 306: Extract the harmonic component voltage corresponding to the second harmonic component from the capacitor voltage of the target sub-module.

[0090] It should be noted that the waveforms of different frequencies in the capacitor voltage represent different voltage components. Therefore, by analyzing the waveform of the capacitor voltage, the harmonic component voltage corresponding to the second harmonic component can be extracted. Among them, the second harmonic component can be one or more, and the second harmonic component and the harmonic component voltage are in one-to-one correspondence.

[0091] As an example, step 306 includes: extracting a harmonic component voltage corresponding to a second harmonic component from the capacitor voltage of the target sub-module.

[0092] Step 308, determining the harmonic component current of the target sub-module in the arm where it is located.

[0093] As an example, step 308 includes: using a preset harmonic component current as the harmonic component current of the target sub-module in the arm where it is located.

[0094] Step 310, converting the harmonic component current into a second modulation voltage according to a second correspondence between the harmonic component voltage and the second harmonic component.

[0095] It should be noted that after a second harmonic component exists in the capacitor voltage, an opposite harmonic current needs to be injected to suppress the second harmonic component, so as to change the arm current of the modular multilevel converter. Among them, the second correspondence can be as follows:

[0096] [ u c ] = 1 4 wC [ i c ] + mI m 96 wC [ − sin φ cos φ ] − mI m 16 wC [ sin φ cos φ ]

[0097] Among them, is the harmonic component voltage, is the harmonic component voltage, is the angular frequency, is the period, is the power factor angle, C is the capacitance value of the capacitor of the target sub-module, is the amplitude of the alternating current, and m is the fundamental frequency modulation ratio of the modular multilevel converter.

[0098] As an example, step 310 includes: converting the harmonic component current into a second modulation voltage based on the second correspondence.

[0099] It can be understood that in order not to generate triplen harmonic currents in the modular multilevel converter and on the grid side, the AC side of the modular multilevel converter needs to be connected to a transformer and then to the AC grid. The transformer adopts the yd11 or yd1 connection method. At the same time, in order to improve the modulation ratio of the modular multilevel converter, compared with the case where no triplen harmonic voltage is injected, after injecting the triplen harmonic voltage, the valve side voltage of the modular multilevel converter can be increased by 1.15 times through the transformer.

[0100] In this embodiment, for different types of first harmonic components and second harmonic components, different solving methods are used to obtain the first modulation voltage and the second modulation voltage. Among them, when solving the first modulation voltage of the actively injected first harmonic component, it depends on the correspondence between the first fundamental component of the fundamental frequency modulation voltage and the first harmonic component to confirm the conversion relationship of voltage parameters. After converting the first voltage parameter of the fundamental frequency modulation voltage into the second voltage parameter, the first modulation voltage is directly generated based on the second voltage parameter. When solving the second modulation voltage of the passively generated second harmonic component, the second harmonic component is determined through the capacitor voltage of the target sub-module, and based on the conversion relationship between voltage and current, the second modulation voltage corresponding to injecting an appropriate harmonic component current is obtained to suppress the second harmonic component. Taking the first harmonic component as the third harmonic voltage and the second harmonic component as the second harmonic circulating current as an example, in the process of implementing the sub-module derating control method of the modular multilevel converter in this embodiment, a collaborative injection strategy is designed, combining the injection control of the third harmonic voltage and the second harmonic circulating current. The second harmonic circulating current and the third harmonic voltage can be automatically injected under various operating conditions. Compared with the traditional single derating control method, due to the adoption of the collaborative injection control strategy in this embodiment, while improving the derating effect of the target sub-module of the modular multilevel converter, that is, while achieving more significant effective derating, the operating loss of the modular multilevel converter is not increased. Therefore, while achieving precise control of the harmonic components affecting the capacitor voltage fluctuation of the target sub-module, it has less operating loss of the modular multilevel converter. Therefore, while improving the derating control effect of the sub-module of the modular multilevel converter, the operating cost of the modular multilevel converter is reduced.

[0101] In one embodiment, generating the first modulation voltage according to the second voltage parameter includes:

[0102] Generating a harmonic modulation voltage corresponding to the first harmonic component according to the second voltage parameter; generating the first modulation voltage according to the harmonic modulation voltage and the switching bridge arm where the target sub-module is located.

[0103] It should be noted that when the target sub-module is located at different positions of the bridge arm of the modular multilevel converter, the first modulation voltage is different, which is determined by the circuit topology of the modular multilevel converter. For example, in an implementable manner, if the circuit topology of the modular multilevel converter is as Figure 2 shown, the expression of the first modulation voltage (third harmonic voltage) is as follows:

[0104]

[0105] Wherein, is the first modulation voltage of the target sub-module in the upper arm of phase A of the modular multilevel converter, is the third harmonic modulation voltage of the target sub-module in the lower arm of phase A of the modular multilevel converter, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, is the period. If only injecting the third harmonic modulation voltage into the fundamental frequency modulation voltage is used as a method to reduce the capacitor voltage fluctuation of the target sub-module, the expression of the arm modulation voltage can be shown as follows:

[0106]

[0107] is the arm modulation voltage in the upper arm of phase A, is the arm modulation voltage in the lower arm of phase A, is the DC bus voltage of the modular multilevel sub-module, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, is the period.

[0108] As an example, according to the amplitude and phase angle of the harmonic modulation voltage, the preset modulation voltage is modulated to obtain the harmonic modulation voltage corresponding to the first harmonic component; determine the specific position of the switch arm where the target sub-module is located in the modular multilevel converter, and adjust the harmonic modulation voltage to the first modulation voltage. Since different types of first modulation voltages will be generated specifically for the positional relationship between the target sub-module and the modular multilevel converter, and thus the first modulation voltage for controlling the first harmonic component can be generated when the target sub-module is located at any position in the modular multilevel converter. Therefore, while improving the sub-module derating control effect of the modular multilevel converter, the control flexibility of the sub-module derating control of the modular multilevel converter is improved.

[0109] In one embodiment, determining the harmonic component current of the target sub-module in the arm where it is located includes:

[0110] Extracting the fundamental component voltage corresponding to the second fundamental component from the capacitor voltage of the target sub-module; determining the current parameters of the target sub-module in the arm where it is located according to the fundamental component voltage and the harmonic component voltage; generating the harmonic component current according to the current parameters.

[0111] It should be noted that in a modular multilevel converter, the relative relationship between the harmonic component current and the harmonic component current changes in real time and is affected by multiple factors. Therefore, the current parameters (amplitude and phase angle) corresponding to the second harmonic component can be calculated or queried multiple times. For example, in an implementable manner, assuming that the main components in the target sub-module include the fundamental frequency component voltage and the double frequency component voltage, then the double frequency component voltage is the harmonic component voltage. Considering that the initial phase angle of the modulation voltage is 0, based on the coupling relationship between the internal electrical quantities of the target sub-module, the expressions of the fundamental frequency component voltage and the double frequency component voltage are as follows:

[0112]

[0113] Wherein, is the fundamental frequency component voltage, is the double frequency component voltage, is the DC side current of the modular multilevel converter, is the AC current amplitude, is the amplitude of the harmonic component current, is the phase angle of the harmonic component current, is the angular frequency, is the period, is the power factor angle, C is the capacitance value of the target sub-module, m is the fundamental frequency modulation ratio of the modular multilevel converter, and the expression of m is as follows:

[0114]

[0115] Wherein, is the amplitude of the fundamental frequency modulation voltage, is the DC bus voltage of the modular multilevel sub-module, and the expression of the harmonic component current is as follows:

[0116]

[0117] Wherein, is the harmonic component current, is the amplitude of the harmonic component current, is the phase angle of the harmonic component current, is the angular frequency, is the period. It can be understood that when and are known, and can be calculated by means of the above expressions, while when and When it is known, the harmonic component current can be further calculated based on the above expression. That is, when determining the harmonic component current, a suitable second harmonic circulating current can be injected to suppress the double-frequency component voltage in the target sub-module capacitor voltage to 0. Thus, when the fundamental frequency component and the harmonic component voltage are known, the amplitude and phase angle of the harmonic component voltage can be obtained. That is, the amplitude and phase angle of the harmonic component current are calculated multiple times, and then the harmonic component current (second harmonic circulating current) can be determined. If injecting the second harmonic circulating current is used as a method to reduce the fluctuation of the target sub-module capacitor voltage, the expression of the bridge arm modulation current can be as follows:

[0118]

[0119] Wherein, is the current of the upper bridge arm of phase A of the modular multilevel converter, is the current of the lower bridge arm of phase A of the modular multilevel converter, is the angular frequency, is the period, is the direct current side current of the modular multilevel converter, is the amplitude of the alternating current, is the amplitude of the harmonic component voltage, is the phase angle of the harmonic component voltage, is the power factor angle.

[0120] As an example, the fundamental frequency component voltage corresponding to the second fundamental frequency component is extracted from the capacitor voltage of the target sub-module; according to the harmonic component voltage and the fundamental frequency component voltage extracted from the capacitor voltage of the target sub-module, the amplitude and phase angle of the harmonic component voltage are calculated. Then, by substituting the amplitude and phase angle of the harmonic component voltage into a preset expression, the harmonic component current of the target sub-module in the corresponding bridge arm is calculated. When determining the harmonic component current of the target sub-module in the corresponding bridge arm, the amplitude and phase angle of the harmonic component current are calculated through the fundamental frequency component voltage and the harmonic component voltage in the capacitor voltage of the target sub-module under the real-time working condition. Then, the harmonic component current is calculated through the amplitude and phase angle, so as to avoid the error of the second modulation voltage caused by the determination of the harmonic component current not conforming to the real-time working condition in the process of generating the second modulation voltage for the second harmonic component. For example, if the second harmonic modulation voltage corresponding to the second harmonic circulating current generated by the modular multilevel converter under the actual working condition is not determined, the control effect of the second harmonic modulation voltage on the second harmonic circulating current will be poor. Therefore, adopting the above embodiment can further improve the effect of reducing the capacity of the sub-module of the modular multilevel converter.

[0121] In one embodiment, converting the harmonic component current into a second modulation voltage according to a second corresponding relationship between the harmonic component voltage and the second harmonic component includes:

[0122] Based on the common-mode voltage component of the arm of the modular multilevel converter, perform a coordinate transformation on the harmonic component voltage to obtain the direct-axis harmonic component voltage and the quadrature-axis harmonic component voltage in a preset coordinate system; according to the direct-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system, convert the direct-axis harmonic component voltage into a direct-axis harmonic modulation reference current, and according to the quadrature-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system, convert the quadrature-axis harmonic component voltage into a quadrature-axis harmonic modulation reference current; perform a coordinate transformation on the harmonic component current to obtain the direct-axis harmonic component current and the quadrature-axis harmonic component current in the preset coordinate system; according to the second correspondence, jointly convert the direct-axis harmonic component current and the direct-axis harmonic modulation reference current into a direct-axis harmonic modulation voltage, and according to the second correspondence, jointly convert the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current, and the direct-axis harmonic modulation reference current into a quadrature-axis harmonic modulation voltage; generate a second modulation voltage according to the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage.

[0123] It should be noted that considering factors such as the convenience of collecting the modulation voltage and the accuracy of generating the modulation signal under the circuit topology of the modular multilevel circulator, the harmonic component voltage and the harmonic component current in the abc coordinate system are both converted to the negative-sequence coordinate system according to a preset angle, and the second correspondence between the harmonic component voltage and the second harmonic component is also transformed accordingly in the coordinate system. At the same time, to reduce the large amount of calculation process for determining the harmonic component current, a harmonic component voltage controller is designed. Through PI control, the voltage-current conversion is directly completed, and a circulating current controller is designed to directly complete the current-voltage conversion to achieve the final output of the second modulation voltage. For example, in an implementable manner, assuming that the second harmonic component is the second harmonic circulating current, the negative-sequence coordinate system is specifically the double-frequency coordinate system, where d is the direct axis and q is the quadrature axis. The preset angle for the coordinate transformation from the three-phase coordinate system to the double-frequency coordinate is , w is the angular frequency, t is the period, and the harmonic component voltage controller is a double-frequency voltage controller. Then the expressions for the direct-axis harmonic component voltage (i.e., the voltage component of the double-frequency component voltage of the target sub-module capacitor voltage on the d axis) and the quadrature-axis harmonic component voltage (i.e., the voltage component of the double-frequency component voltage of the target sub-module capacitor voltage on the q axis) are as follows:

[0124] [ u c 2 d u c 2 q ] = I 2 m 4 wC [ cos θ sin θ ] + mI m 96 wC [ − sin φ cos φ ] − mI m 16 wC [ sin φ cos φ ]

[0125] Among them, is the amplitude of the harmonic component current, is the phase angle of the harmonic component current, is the angular frequency, is the period, is the direct-axis harmonic component voltage, is the quadrature-axis harmonic component voltage, is the amplitude of the alternating current, is the power factor angle, C is the capacitance value of the target sub-module, m is the fundamental frequency modulation ratio of the modular multilevel converter. The expressions for the direct-axis harmonic component current (the current component of the harmonic component current on the d-axis) and the quadrature-axis harmonic component current (the current component of the harmonic component current on the q-axis) are as follows:

[0126] [ i cird i cirq ] =− I 2 m [ sin θ cos θ ]

[0127] Among them, is the direct-axis harmonic component current, is the quadrature-axis harmonic component current, is the amplitude of the harmonic component current, is the phase angle of the harmonic component current. Thus, the expression for the second corresponding relationship is as follows:

[0128] [ u c 2 d u c 2 q ] = 1 4 wC [ i cird i cirq ] + mI m 96 wC [ − sin φ cos φ ] − mI m 16 wC [ sin φ cos φ ]

[0129] Among them, under the control of the double-frequency voltage controller, since the direct-axis harmonic component voltage and the quadrature-axis harmonic component voltage are known, then through the above second corresponding relationship, and after setting the capacitor voltage component of the target sub-module to the target value (that is, presetting the direct-axis harmonic modulation reference voltage and the quadrature-axis harmonic modulation reference voltage), the direct-axis harmonic modulation reference current and the quadrature-axis harmonic modulation reference current are output by the double-frequency voltage controller. The expressions for the direct-axis harmonic modulation reference current and the quadrature-axis harmonic modulation reference current are as follows:

[0130]

[0131] Among them, is the direct-axis harmonic modulation reference current, is the quadrature-axis harmonic modulation reference current, is the direct-axis harmonic modulation reference voltage, is the quadrature-axis harmonic modulation reference voltage. For example, by setting and both to 0, and can be solved through the above expressions. is the proportional coefficient of the double-frequency voltage controller, is the integral coefficient of the double-frequency voltage controller in the integral link, is the integral link. Among them, the solution processes for the direct-axis harmonic component voltage and the quadrature-axis harmonic component voltage can be referred to the following expressions:

[0132]

[0133]

[0134]

[0135] Among them, is the common-mode voltage component (average capacitor voltage) of the A-phase bridge arm, is the average capacitor voltage of the upper bridge arm of phase A, is the average capacitor voltage of the lower bridge arm of phase A, is the average capacitor voltage of the B-phase bridge arm, is the common-mode voltage component (average capacitor voltage) of the upper bridge arm of phase B, is the average capacitor voltage of the lower bridge arm of phase B, is the common-mode voltage component (average capacitor voltage) of the C-phase bridge arm, is the average capacitor voltage of the upper bridge arm of phase C, is the average capacitor voltage of the lower bridge arm of phase C. Then, substitute the common-mode voltage components of each phase bridge arm into the coordinate transformation matrix to transform from the abc three-phase stationary coordinate system to the negative-sequence double-frequency dq rotating coordinate system, and obtain the d-axis and q-axis components of the double-frequency components of the capacitor voltage. .

[0136] As an example, the average capacitor voltages of the upper and lower arms of each phase of the modular multilevel converter are obtained respectively. Based on the average capacitor voltages of the upper and lower arms of each phase, the common-mode voltage component of the converter arm is calculated. The common-mode voltage component of the converter arm is substituted into the coordinate transformation matrix for converting the three-phase coordinate system to the negative-sequence coordinate system, and the harmonic component voltage is converted into the direct-axis harmonic component voltage and the quadrature-axis harmonic component voltage in the negative-sequence coordinate system; the direct-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system is input into the harmonic component voltage controller, and the direct-axis harmonic component voltage is converted into the direct-axis harmonic modulation reference current, and the quadrature-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system is input into the harmonic component voltage controller, and the quadrature-axis harmonic component voltage is converted into the quadrature-axis harmonic modulation reference current; the harmonic component current is subjected to coordinate transformation to obtain the direct-axis harmonic component current and the quadrature-axis harmonic component current in the preset coordinate system; according to the second correspondence, the direct-axis harmonic component current and the direct-axis harmonic modulation reference current are jointly converted into the direct-axis harmonic modulation voltage, and according to the second correspondence, the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current and the direct-axis harmonic modulation reference current are jointly converted into the quadrature-axis harmonic modulation voltage; according to the coordinate transformation matrix, the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage are jointly converted into the second modulation voltage. By performing coordinate transformation on the harmonic component voltage and the harmonic component voltage, it is more suitable for the actual control scenario of the modular multilevel converter. At the same time, the design of the harmonic component voltage controller can directly and automatically generate the harmonic modulation reference current without the need for back-and-forth calculation and query, thus improving the acquisition efficiency of the second modulation voltage, and the setting of the circulating current controller is more convenient for outputting the appropriate second modulation voltage for suppressing the second harmonic component, that is, by generating the circulating current for suppressing the second harmonic component in the modular multilevel controller through the second modulation voltage. Generally speaking, it lays a foundation for improving the derating effect of the sub-modules of the modular multilevel converter.

[0137] In an implementable manner, referring to Figure 5 , Figure 5 is the control flow chart of the harmonic component voltage controller, specifically, it can be , or , is the direct-axis harmonic modulation reference voltage, is the quadrature-axis harmonic modulation reference voltage, is the direct-axis harmonic modulation reference current, is the quadrature-axis harmonic modulation reference current, is the direct-axis harmonic component voltage, is the quadrature-axis harmonic component voltage, is the preset angle.

[0138] In an implementable manner, referring to Figure 6 , Figure 6 is the control flowchart of the circulating current controller, is the direct-axis harmonic modulation reference current, is the quadrature-axis harmonic modulation reference current, is the direct-axis harmonic component current, is the quadrature-axis harmonic component current, is the arm inductor of the three-phase half-bridge modular multilevel converter, is the angular frequency, is the preset angle, is the direct-axis harmonic modulation voltage, is the quadrature-axis harmonic modulation voltage, is the second modulation voltage, specifically it can be , or , where is the second modulation voltage of phase A, is the second modulation voltage of phase B, is the second modulation voltage of phase C.

[0139] In one embodiment, before distributing the arm modulation voltage obtained by jointly fusing each harmonic modulation voltage to obtain the target modulation voltage acting on the target sub-module, the method further includes:

[0140] Determine the arm where the target sub-module is located; according to the arm where the target sub-module is located, fuse each harmonic modulation voltage and the fundamental frequency modulation voltage to obtain the arm modulation voltage.

[0141] It should be noted that when fusing to obtain the arm modulation voltage, different arms where the target sub-module is located will fuse to obtain different arm modulation voltages. For example, in an implementable manner, the expression of the arm modulation voltage is as follows:

[0142]

[0143] where is the arm modulation voltage of the target sub-module in the upper arm of phase A, is the arm modulation voltage of the target sub-module in the lower arm of phase A, is the DC bus voltage of the modular multilevel sub-module, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, is the period, is the second modulation voltage of the arm of phase A, is the first modulation voltage of the upper arm of phase A, The first modulation voltage of the lower arm of phase A.

[0144] As an example, according to the positional relationship between the target sub-module and the modular multilevel converter, determine the arm where the target sub-module is located; according to the arm where the target sub-module is located, fuse each harmonic modulation voltage and the fundamental frequency modulation voltage to obtain the arm modulation voltage. Since different arm modulation voltages will be generated specifically for the positional relationship between the target sub-module and the modular multilevel converter, and thus arm modulation voltages for controlling different harmonic components can be generated when the target sub-module is located at any position of the modular multilevel converter, therefore, while improving the sub-module derating control effect of the modular multilevel converter, the control flexibility of the sub-module derating control of the modular multilevel converter is improved.

[0145] In one embodiment, derating control of the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage includes:

[0146] Modulate the target modulation voltage to a preset carrier signal to obtain an initial voltage modulation signal; perform normalization processing on the initial voltage modulation signal to obtain a voltage modulation signal; perform derating control on the target sub-module according to the voltage modulation signal.

[0147] As an example, modulate the signal parameters of the preset carrier signal through the target modulation voltage to obtain an initial voltage modulation signal; perform normalization processing on the initial voltage modulation signal to obtain a voltage modulation signal, where the expression of the voltage modulation signal can be as follows:

[0148]

[0149] Where is the voltage modulation signal of the upper arm of phase A, is the voltage modulation signal of the lower arm of phase A, is the DC bus voltage of the modular multilevel sub-module, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, is the period, is the second modulation voltage of the arm of phase A, is the first modulation voltage of the upper arm of phase A, The first modulation voltage of the lower arm of phase A; perform derating control on the target sub-module according to the voltage modulation signal. By converting the voltage modulation signals of different arms of the modular multilevel converter to a unified standard for control, the modulation logic can be simplified, which is convenient for improving the derating control efficiency.

[0150] In an implementable manner, referring toFigure 7 , Figure 7 is a general structural schematic diagram for representing the derating control of the target sub-module. During the process of derating control by coordinating two different harmonic components, namely the secondary harmonic circulation and the third harmonic voltage, first, a trigger signal for amplitude detection and phase angle detection is output via the current inner-loop controller through power control , where the power outer-loop control of the modular multilevel converter controls the output power of the modular multilevel converter and generates the inner-loop current reference value of the current inner-loop controller and , and then, after the conversion of the first voltage parameter, the first modulation voltage is output by the third harmonic voltage controller, and the direct-axis harmonic modulation reference current and the quadrature-axis harmonic modulation reference current are output by the capacitor voltage double-frequency component controller. The direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage are output by the circulation controller based on the second corresponding relationship. Finally, the second modulation voltage is jointly converted from the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage. Finally, the fundamental frequency modulation voltage, the first modulation voltage, and the second modulation voltage are combined to perform modulation and voltage equalization control to output a drive signal, that is, an output voltage modulation signal is used to perform derating control on the target sub-module.

[0151] Therefore, in the process of implementing the derating control method for the sub-module of the modular multilevel converter in this embodiment, a coordinated injection strategy is designed, which combines the injection control of the third harmonic voltage and the secondary harmonic circulation. The secondary harmonic circulation and the third harmonic voltage can be automatically injected under various operating conditions. Compared with the traditional single derating control method, since the coordinated injection control strategy is adopted in this embodiment, while improving the derating effect of the target sub-module of the modular multilevel converter, that is, while more significantly and effectively derating, the operating loss of the modular multilevel converter is not increased. Therefore, while achieving precise control of the harmonic components affecting the capacitor voltage fluctuation of the target sub-module, it has less operating loss of the modular multilevel converter. Therefore, while improving the derating control effect of the sub-module of the modular multilevel converter, the operating cost of the modular multilevel converter is reduced.

[0152] It should be understood that although the steps in the flowcharts involved in the above embodiments are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear description in this article, there is no strict order limit for the execution of these steps, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be executed alternately or in turn with at least a part of other steps or steps or stages in other steps.

[0153] Based on the same inventive concept, an embodiment of the present application further provides a sub-module derating control device for a modular multilevel converter for implementing the sub-module derating control method of the modular multilevel converter involved above. The solution provided by this device to solve the problem is similar to the solution described in the above method. Therefore, the specific limitations in one or more embodiments of the sub-module derating control device of the modular multilevel converter provided below can refer to the limitations on the sub-module derating control method of the modular multilevel converter in the above text, and will not be repeated here.

[0154] In an exemplary embodiment, as Figure 8 shown, a sub-module derating control device for a modular multilevel converter is provided, including: an acquisition module 401, a distribution module 402, and a derating control module 403, where:

[0155] The acquisition module 401 is configured to acquire harmonic modulation voltages corresponding to multiple harmonic components existing under the fundamental frequency modulation voltage excitation of a target sub-module, where the target sub-module is any standard sub-module of the modular multilevel converter, and the multiple harmonic components are harmonic components of different types;

[0156] The distribution module 402 is configured to distribute the arm modulation voltage obtained by jointly fusing the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module;

[0157] The derating control module 403 is configured to perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage.

[0158] In one of the embodiments, the multiple harmonic components include a first harmonic component and a second harmonic component, and the harmonic modulation voltages include a first modulation voltage of the first harmonic component and a second modulation voltage of the second harmonic component; the acquisition module 401 is further configured to:

[0159] Convert the first voltage parameter of the fundamental frequency modulation voltage into a second voltage parameter according to a first correspondence between the first harmonic component and the first fundamental frequency component of the fundamental frequency modulation voltage; generate the first modulation voltage according to the second voltage parameter; extract a harmonic component voltage corresponding to the second harmonic component from the capacitor voltage of the target sub-module; determine a harmonic component current of the target sub-module in the bridge arm where it is located; convert the harmonic component current into the second modulation voltage according to a second correspondence between the harmonic component voltage and the second harmonic component.

[0160] In one embodiment, the obtaining module 401 is further configured to:

[0161] Generate a harmonic modulation voltage corresponding to the first harmonic component according to the second voltage parameter; generate the first modulation voltage according to the harmonic modulation voltage and the switching bridge arm where the target sub-module is located.

[0162] In one embodiment, the obtaining module 401 is further configured to:

[0163] Extract a fundamental frequency component voltage corresponding to a second fundamental frequency component from the capacitor voltage of the target sub-module; determine a current parameter of the target sub-module in the bridge arm where it is located according to the fundamental frequency component voltage and the harmonic component voltage; generate the harmonic component current according to the current parameter.

[0164] In one embodiment, the obtaining module 401 is further configured to:

[0165] Perform a coordinate transformation on the harmonic component voltage according to a common-mode voltage component of a bridge arm of the modular multilevel converter to obtain a direct-axis harmonic component voltage and a quadrature-axis harmonic component voltage in a preset coordinate system; convert the direct-axis harmonic component voltage into a direct-axis harmonic modulation reference current according to a direct-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system, and convert the quadrature-axis harmonic component voltage into a quadrature-axis harmonic modulation reference current according to a quadrature-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system; perform a coordinate transformation on the harmonic component current to obtain a direct-axis harmonic component current and a quadrature-axis harmonic component current in the preset coordinate system; convert the direct-axis harmonic component current and the direct-axis harmonic modulation reference current into a direct-axis harmonic modulation voltage according to the second correspondence, and convert the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current, and the direct-axis harmonic modulation reference current into a quadrature-axis harmonic modulation voltage according to the second correspondence; generate the second modulation voltage according to the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage.

[0166] In one embodiment, the sub-module derating control device of the modular multilevel converter is further configured to:

[0167] Determine the arm where the target sub-module is located; according to the arm where the target sub-module is located, fuse each of the harmonic modulation voltages and the fundamental frequency modulation voltage to obtain an arm modulation voltage.

[0168] In one embodiment, the derating control module 403 is further configured to:

[0169] Modulate the target modulation voltage to a preset carrier signal to obtain an initial voltage modulation signal; perform normalization processing on the initial voltage modulation signal to obtain the voltage modulation signal; perform derating control on the target sub-module according to the voltage modulation signal.

[0170] Each module in the above-mentioned sub-module derating control device of the modular multilevel converter can be implemented in whole or in part by software, hardware, and their combination. The above-mentioned modules can be embedded in the processor of the power conversion device in hardware form or be independent of it, or can be stored in the memory of the power conversion device in software form, so that the processor can call and execute the operations corresponding to the above-mentioned each module.

[0171] In an exemplary embodiment, a power conversion device is provided. The power conversion device can be a terminal, and its internal structure diagram can be as Figure 9 shown. The power conversion device includes a processor, a memory, an input / output interface, a communication interface, a display unit, and an input device. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface, the display unit, and the input device are connected to the system bus through the input / output interface. Among them, the processor of the power conversion device is used to provide computing and control capabilities. The memory of the power conversion device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the power conversion device is used for exchanging information between the processor and external devices. The communication interface of the power conversion device is used for communicating with external terminals in a wired or wireless manner, and the wireless manner can be implemented through WIFI, a mobile cellular network, NFC (Near Field Communication), or other technologies. When the computer program is executed by the processor, it implements a method for controlling the derating of sub-modules of a modular multilevel converter. Those skilled in the art can understand that Figure 9 the structure shown in

[0172] In one embodiment, a power conversion device is further provided, which includes a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, the steps in the above method embodiments are implemented.

[0173] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0174] In one embodiment, a computer program product is provided, which includes a computer program. When the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0175] Those of ordinary skill in the art can understand that all or part of the processes of implementing the above method embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the above method embodiments. Among them, any reference to a memory, database, or other medium provided in the embodiments of the present application can include at least one of non-volatile and volatile memories. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The databases involved in the embodiments of the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments of the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logic devices, data processing logics based on quantum computing, etc., without limitation.

[0176] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0177] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A sub-module derating control method for a modular multilevel converter, characterized in that The method comprises: Obtaining harmonic modulation voltages corresponding to respective multiple harmonic components present in a target submodule under excitation of a fundamental frequency modulation voltage, wherein the harmonic modulation voltages vary depending on the circuit topology of a modular multilevel converter, wherein each phase of the modular multilevel converter includes two bridge arms, and each bridge arm is connected in series with multiple half-bridge standard submodules, wherein the target submodule is any half-bridge standard submodule, and wherein the multiple harmonic components are harmonic components of different types; Distributing the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule; The target submodule is subjected to capacity reduction control according to the voltage modulation signal corresponding to the target modulation voltage, wherein the multiple harmonic components include a first harmonic component and a second harmonic component, the harmonic modulation voltage includes a first modulation voltage for controlling the first harmonic component and a second modulation voltage for suppressing the second harmonic component, the first harmonic component refers to a harmonic component actively injected to reduce the capacitor voltage fluctuation of the target submodule, and the second harmonic component refers to a harmonic component that affects the capacitor voltage of the target submodule and is passively generated; the step of obtaining the harmonic modulation voltages corresponding to the multiple harmonic components existing in the target submodule under the excitation of the fundamental frequency modulation voltage includes: converting a first voltage parameter of the fundamental frequency modulation voltage into a second voltage parameter according to a first corresponding relationship between the first harmonic component and the first fundamental frequency component of the fundamental frequency modulation voltage; modulating a preset modulation voltage according to the second voltage parameter to obtain a harmonic modulation voltage corresponding to the first harmonic component, and adjusting the harmonic modulation voltage to the first modulation voltage by determining a specific position of the switch bridge arm where the target submodule is located in the modular multilevel converter; Determining the harmonic component current of the target submodule in the bridge arm where it is located; The harmonic component current is converted into the second modulation voltage according to a second corresponding relationship between the harmonic component voltage and the second harmonic component.

2. The method according to claim 1, characterized in that The determining of the harmonic component current of the target submodule in the bridge arm includes: extracting a fundamental frequency component voltage corresponding to the second fundamental frequency component from the capacitor voltage of the target submodule; Determining a current parameter of the target submodule in the bridge arm according to the fundamental frequency component voltage and the harmonic component voltage; The harmonic component current is generated according to the current parameter.

3. The method according to claim 1, characterized in that, The converting the harmonic component current into the second modulation voltage according to the second corresponding relationship between the harmonic component voltage and the second harmonic component includes: performing coordinate transformation on the harmonic component voltage according to the common-mode voltage component of the bridge arm of the modular multilevel converter to obtain a direct-axis harmonic component voltage and a quadrature-axis harmonic component voltage in a preset coordinate system; Convert the direct-axis harmonic component voltage into a direct-axis harmonic modulation reference current according to the direct-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system, and convert the quadrature-axis harmonic component voltage into a quadrature-axis harmonic modulation reference current according to the quadrature-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system; Perform coordinate transformation on the harmonic component current to obtain the direct-axis harmonic component current and the quadrature-axis harmonic component current in the preset coordinate system; Convert the direct-axis harmonic component current and the direct-axis harmonic modulation reference current into a direct-axis harmonic modulation voltage according to the second correspondence, and convert the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current, and the direct-axis harmonic modulation reference current into a quadrature-axis harmonic modulation voltage according to the second correspondence; Generate the second modulation voltage according to the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage.

4. The method according to claim 1, characterized in that, Before distributing the arm modulation voltage obtained by fusing each of the harmonic modulation voltages to obtain the target modulation voltage acting on the target sub-module, the method further includes: Determine the arm where the target sub-module is located; Fuse each of the harmonic modulation voltages and the fundamental frequency modulation voltage according to the arm where the target sub-module is located to obtain an arm modulation voltage.

5. The method according to claim 1, wherein The step of performing derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage includes: Modulate the target modulation voltage to a preset carrier signal to obtain an initial voltage modulation signal; Perform normalization processing on the initial voltage modulation signal to obtain the voltage modulation signal; Perform derating control on the target sub-module according to the voltage modulation signal.

6. A submodule capacity reduction control device for a modular multilevel converter, characterized in that: The device includes: An acquisition module, configured to acquire harmonic modulation voltages corresponding to a plurality of harmonic components existing under the excitation of a fundamental frequency modulation voltage of a target sub-module, where the harmonic modulation voltages are different due to different circuit topologies of a modular multilevel converter, each phase of the modular multilevel converter includes two arms, a plurality of half-bridge standard sub-modules are connected in series on each arm, the target sub-module is any one of the bridge standard sub-modules, and the plurality of harmonic components are harmonic components of different types; A distribution module, configured to distribute the arm modulation voltage obtained by fusing each of the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module; A derating control module, configured to perform derating control on the target sub-module according to the voltage modulation signal corresponding to the target modulation voltage, where the plurality of harmonic components include a first harmonic component and a second harmonic component, the harmonic modulation voltages include a first modulation voltage for controlling the first harmonic component and a second modulation voltage for suppressing the second harmonic component, the first harmonic component is a harmonic component actively injected to reduce the capacitor voltage fluctuation of the target sub-module, and the second harmonic component is a harmonic component that affects the capacitor voltage of the target sub-module and is generated passively; the acquisition module is further configured to: Convert the first voltage parameter of the fundamental-frequency modulation voltage into a second voltage parameter according to the first correspondence between the first harmonic component and the first fundamental-frequency component of the fundamental-frequency modulation voltage; modulate a preset modulation voltage according to the second voltage parameter to obtain a harmonic modulation voltage corresponding to the first harmonic component, and adjust the harmonic modulation voltage to the first modulation voltage by determining the specific position of the switching bridge arm where the target sub-module is located in the modular multilevel converter; determine the harmonic component current of the target sub-module in the arm where it is located; and convert the harmonic component current into the second modulation voltage according to the second correspondence between the harmonic component voltage and the second harmonic component.

7. The device according to claim 6, characterized in that The obtaining module is further configured to: Extract a fundamental-frequency component voltage corresponding to a second fundamental-frequency component from the capacitor voltage of the target sub-module; and determine the current parameter of the target sub-module in the arm where it is located according to the fundamental-frequency component voltage and the harmonic component voltage. Generate the harmonic component current according to the current parameter.

8. The device according to claim 6, characterized in that, The obtaining module is further configured to: Perform a coordinate transformation on the harmonic component voltage according to the common-mode voltage component of the arm of the modular multilevel converter to obtain a direct-axis harmonic component voltage and a quadrature-axis harmonic component voltage in a preset coordinate system; convert the direct-axis harmonic component voltage into a direct-axis harmonic modulation reference current according to the direct-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system, and convert the quadrature-axis harmonic component voltage into a quadrature-axis harmonic modulation reference current according to the quadrature-axis harmonic modulation reference voltage of the second harmonic component in the preset coordinate system. Perform a coordinate transformation on the harmonic component current to obtain a direct-axis harmonic component current and a quadrature-axis harmonic component current in the preset coordinate system; convert the direct-axis harmonic component current and the direct-axis harmonic modulation reference current into a direct-axis harmonic modulation voltage according to the second correspondence, and convert the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current, and the direct-axis harmonic modulation reference current into a quadrature-axis harmonic modulation voltage according to the second correspondence. Generate the second modulation voltage according to the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage.

9. A power conversion device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method according to any one of claims 1 to 5.

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