Submodule capacity reduction control method, device and equipment of modular multilevel converter

Abstract

The invention relates to a submodule capacity reduction control method, device and equipment of a modular multilevel converter. The method comprises the steps that harmonic modulation voltages corresponding to multiple harmonic components existing in a target sub-module under excitation of fundamental frequency modulation voltages are obtained, 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; distributing a bridge arm modulation voltage obtained by jointly fusing the harmonic modulation voltages to obtain a target modulation voltage acting on the target sub-module; and according to a voltage modulation signal corresponding to the target modulation voltage, carrying out capacitance reduction control on the target sub-module. By adopting the method, the capacity reduction control effect of the sub-module of the modular multilevel converter is improved.

Description

Technical Field

[0001] The present application relates to the technical field of modular multilevel converters, and in particular to a method and device for controlling submodule capacity reduction of a modular multilevel 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, MMC (Modular Multilevel Converter) has gradually replaced the traditional two-level voltage source converter due to its advantages of modularity, low switching frequency and good harmonic performance. It has been widely used in large-scale renewable energy centralized power generation and high-voltage flexible direct current transmission.

[0003] At present, in order to reduce the capacitor voltage fluctuation problem of the MMC sub-module, the current or voltage of the harmonic component is usually injected or eliminated to achieve capacity reduction control. However, in the modular multi-level converter, since the generation of harmonic components is interfered by multiple factors such as modular structure, operating conditions and modulation strategy, the harmonic components controlled under the injection control strategy are difficult to match the harmonic components that actually cause the sub-module capacitor voltage fluctuation, which makes it easy for the sub-module capacitor voltage fluctuation to still be large. Therefore, the current capacity reduction control effect of the sub-module of the modular multi-level converter 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 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 solve the above technical problems.

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

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

[0007] Acquire harmonic modulation voltages corresponding to each of a plurality of 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 plurality of 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] The target submodule is controlled to be reduced in capacity 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 step of acquiring 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:

[0011] 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;

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

[0013] Extracting a harmonic component voltage corresponding to the second harmonic component from the capacitor voltage of the target submodule;

[0014] Determining the harmonic component current of the target submodule in the bridge arm where it is located;

[0015] 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.

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

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

[0018] The first modulation voltage is generated according to the harmonic modulation voltage and the switch bridge arm where the target submodule is located.

[0019] In one embodiment, determining the harmonic component current of the target submodule in the bridge arm includes:

[0020] Extracting a fundamental frequency component voltage corresponding to a second fundamental frequency component from the capacitor voltage of the target submodule;

[0021] Determining a current parameter of a target submodule in a bridge arm according to the fundamental frequency component voltage and the harmonic component voltage;

[0022] The harmonic component current is generated according to the current parameter.

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

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

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

[0026] Performing 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] According to the second corresponding relationship, the direct-axis harmonic component current and the direct-axis harmonic modulation reference current are converted into a direct-axis harmonic modulation voltage, and according to the second corresponding relationship, the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current and the direct-axis harmonic modulation reference current are converted into a quadrature-axis harmonic modulation voltage;

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

[0029] In one embodiment, before allocating the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain the target modulation voltage acting on the target submodule, the method further includes:

[0030] Determine the bridge arm where the target submodule is located;

[0031] According to the bridge arm where the target submodule is located, each of the harmonic modulation voltages and the fundamental frequency modulation voltage is fused to obtain a bridge arm modulation voltage.

[0032] In one embodiment, the step of performing capacity reduction control on the target submodule 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] Normalizing the initial voltage modulation signal to obtain the voltage modulation signal;

[0035] The target submodule is controlled to reduce capacity according to the voltage modulation signal.

[0036] In a second aspect, the present application further provides a submodule capacity reduction control device of a modular multilevel converter, comprising:

[0037] An acquisition module, used for acquiring harmonic modulation voltages corresponding to each of a plurality of harmonic components existing in a target submodule under the excitation of a fundamental frequency modulation voltage, wherein the target submodule is any standard submodule of a modular multilevel converter, and the plurality of harmonic components are harmonic components of different types;

[0038] A distribution module, used for distributing the bridge arm modulation voltage obtained by integrating the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule;

[0039] The capacity reduction control module is used to perform capacity reduction control on the target submodule 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, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0041] Obtain harmonic modulation voltages corresponding to multiple harmonic components existing in a target submodule under the 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; distribute the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule; and perform capacity reduction control on the target submodule according to a voltage modulation signal corresponding to the target modulation voltage.

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

[0043] Obtain harmonic modulation voltages corresponding to multiple harmonic components existing in a target submodule under the 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; distribute the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule; and perform capacity reduction control on the target submodule according to a 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, which implements the following steps when executed by a processor:

[0045] Obtain harmonic modulation voltages corresponding to multiple harmonic components existing in a target submodule under the 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; distribute the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule; and perform capacity reduction control on the target submodule according to a voltage modulation signal corresponding to the target modulation voltage.

[0046] The above-mentioned sub-module capacity reduction 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 in the target sub-module under the excitation of the fundamental frequency modulation voltage. Since the target sub-module is any standard sub-module of the modular multilevel converter, the multiple harmonic components are also different harmonic components. That is, for any standard sub-module in the modular multilevel converter, the harmonic modulation voltage corresponding to the harmonic component can be obtained for the different types of harmonic components generated by it under the excitation of the fundamental frequency modulation voltage, and then the bridge arm modulation voltage obtained by fusing the harmonic modulation voltages is distributed to obtain the 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 to the target sub-module from the structural perspective of the modular multilevel converter. Finally, the target sub-module is controlled to be reduced in capacity through the voltage modulation signal corresponding to the target modulation signal, so that the target sub-module can be directly Then, based on the voltage modulation signal, the capacitor voltage of the target submodule is controlled to be reduced in capacity. Since the target modulation voltage is obtained based on the overall structure distribution of the modular multilevel converter under the premise of considering the multiple harmonic components existing in the target submodule under the excitation of the fundamental frequency modulation voltage, the voltage modulation signal acting on the target submodule can completely match the harmonic components causing the capacitor voltage fluctuation of the target submodule, and finally achieves the purpose of accurately controlling the harmonic components affecting the capacitor voltage fluctuation of the target submodule. Therefore, the technical defect that the generation of harmonic components in the modular multilevel converter 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 submodule, which makes it easy for the capacitor voltage fluctuation of the submodule to still be large, is overcome. Therefore, the reduction control effect of the submodule of the modular multilevel converter is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 1 is a flow chart of a method for controlling capacity reduction of a submodule of a modular multilevel converter in one embodiment;

[0049] Figure 2 A schematic diagram of a circuit topology structure of a three-phase half-bridge modular multilevel converter of a sub-module capacity reduction control method of a modular multilevel converter in one embodiment;

[0050] Figure 3 is a schematic flow chart of a method for controlling capacity reduction of a submodule of a modular multilevel converter in another embodiment;

[0051] Figure 4 is a control flow chart of a modulated voltage of a sub-module capacity reduction control method of a modular multi-level converter in one embodiment;

[0052] Figure 5 A control flow chart of a harmonic component voltage controller of a sub-module capacity reduction control method of a modular multi-level converter in one embodiment;

[0053] Figure 6 A control flow chart of a circulating current controller of a sub-module capacity reduction control method of a modular multi-level converter in one embodiment;

[0054] Figure 7 It is a schematic diagram of the overall structure of performing capacity reduction control on a target submodule in a method for controlling capacity reduction of a submodule of a modular multilevel converter in one embodiment;

[0055] Figure 8 It is a structural block diagram of a sub-module capacity reduction control device of a modular multi-level converter in one embodiment;

[0056] Fig. 9 FIG. 1 is a diagram showing the internal structure of a power conversion device in one embodiment. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein 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 MMC. The capacitors in the standard sub-modules replace the large DC side capacitors used in traditional flexible DC transmission systems to support DC voltage. The distributed standard sub-modules inside the MMC will also bring many problems. For example, the coupling of internal electricity in the MMC will cause the circulating current and voltage fluctuations of the capacitors of the standard sub-modules. The capacitance and voltage fluctuation problems of any standard sub-module will affect the stable operation of the MMC. Therefore, under normal circumstances, the capacitance and voltage fluctuations of the standard sub-modules are suppressed by selecting appropriate sub-module capacitance values. Although selecting appropriate sub-module capacitance values ​​can suppress the capacitance and voltage fluctuations of the sub-modules, The above effect is obvious, but increasing the sub-module capacitance will lead to a significant increase in the volume and cost of the MMC. It may even happen that the cost of the sub-module capacitor in the MMC converter accounts for 1 / 3 of the total cost, and the capacitor volume accounts for 1 / 2 of the total volume. In consideration of the cost and volume of the MMC, the injection control strategy will also be used for capacity reduction control. For example, in order to suppress or eliminate the second harmonic current in the MMC bridge arm current, the second harmonic component in the MMC sub-module capacitor voltage is suppressed or eliminated by injecting an appropriate second harmonic circulating current. For another example, the waveform of the MMC bridge arm voltage is changed by injecting a third harmonic voltage, thereby reducing the sub-module capacitor voltage. It is also an effective strategy to reduce the fluctuation peak-to-peak value to reduce the voltage fluctuation of the MMC sub-module capacitor. However, the above injection control strategy has certain shortcomings in reducing the voltage of the MMC sub-module capacitor. Injecting the appropriate second harmonic circulating current requires a lot of calculation or table lookup work as the working conditions change to obtain the current parameters of the second harmonic circulating current. In addition, the injected second harmonic circulating current and the original second harmonic circulating current of the bridge arm current will be superimposed in the bridge arm, thereby increasing the effective value of the bridge arm current. After the effective value of the bridge arm current increases, the device will be damaged faster, the cost will increase, and the system stability will decrease due to the temperature rise. Injecting the third harmonic The ripple voltage will also lead to limited derating control effect due to harmonic superposition effect and nonlinear load influence. At the same time, the harmonic components of 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 operation are the main reason for the fluctuation of the capacitor voltage of the MMC sub-module. However, the above methods only perform derating control on the MMC sub-module from different angles. The harmonic components controlled after control do not match the harmonic components that actually cause the fluctuation of the capacitor voltage of the sub-module. Therefore, there is an urgent need for a derating control method that can improve the derating control effect of the sub-module of the modular multilevel converter.

[0059] In one embodiment, Figure 1As shown, a sub-module capacity reduction control method of a modular multilevel converter is provided. This embodiment takes the method applied to a power conversion device as an example. The power conversion device includes but is not limited to a DC-DC converter, an AC-AC converter, a DC-AC inverter and an AC-DC rectifier, 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, a sensor, an actuator, a communication interface and a human-machine interface, etc. The upper control system includes an acquisition module, a distribution module and a capacity reduction control module. The acquisition module is used to obtain the harmonic modulation voltages corresponding to the multiple harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage, wherein 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. The distribution module is used to distribute the bridge arm modulation voltage obtained by fusing the harmonic modulation voltages to obtain the target modulation voltage acting on the target sub-module. The voltage, capacity reduction control module is used to perform capacity reduction control on the target submodule according to the voltage modulation signal corresponding to the target modulation voltage. Through the collaboration between the acquisition module, the allocation module and the capacity reduction control module, the voltage modulation signal corresponding to the target modulation voltage can be used to modulate the multiple harmonic components existing in the target submodule under the excitation of the fundamental frequency modulation voltage, thereby reducing the harmonic voltage generated at both ends of the target submodule capacitor during the charging and discharging process of the target submodule, that is, by applying the voltage modulation signal to the target submodule, the controlled harmonic component and the harmonic component causing the target submodule capacitor voltage fluctuation are matched, thereby achieving the purpose of reducing the target submodule capacitor voltage fluctuation. Therefore, the capacity reduction control effect of the submodule of the modular multilevel converter can be improved. It can be understood that the method can also be applied to a server connected to a power conversion device, and can also be applied to a system including a power conversion device and a server, and is implemented through the interaction between the power conversion device and the server. In this embodiment, the method includes the following steps:

[0060] Step 202 : obtaining harmonic modulation voltages corresponding to multiple harmonic components existing in a target submodule under fundamental frequency modulation voltage excitation, wherein the target submodule is any standard submodule of a modular multilevel converter, and the multiple harmonic components are harmonic components of different types.

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

[0062] It should be noted that the harmonic modulation voltage is used to modulate multiple harmonic components existing under the excitation of the fundamental frequency modulation voltage. It can be specifically used to suppress the harmonic components existing under the excitation of the fundamental frequency modulation voltage, and can also be used to control the generation of harmonic components under the excitation of the fundamental frequency modulation voltage. For example, in one feasible method, the harmonic modulation voltage includes a second harmonic modulation voltage and a third harmonic modulation voltage, wherein the second harmonic modulation voltage is used to eliminate or suppress the second harmonic circulating current in the MMC bridge arm current, and the third harmonic modulation voltage is used to inject the fundamental frequency modulation voltage to generate the third harmonic component, so as to reduce the capacitor voltage amplitude of the target sub-module, that is, by utilizing a capacity reduction control method combining the third harmonic modulation voltage injection and the second harmonic circulating current injection control, the multiple harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage are collaboratively modulated, which can achieve the effect of reducing the capacitor voltage fluctuation of the target sub-module without significantly increasing the effective value of the MMC bridge arm current.

[0063] It should be noted that the harmonic modulation voltage varies depending on the circuit topology of the modular multilevel converter. Figure 2 , Figure 2 Schematic diagram of a circuit topology structure of a three-phase half-bridge modular multilevel converter, which may specifically include a DC source, an AC grid, a three-phase half-bridge modular multilevel converter, a bridge arm inductor, a bridge arm resistor, and a transformer equivalent inductor, etc. Figure 2 As shown, the three-phase half-bridge modular multilevel converter contains two bridge arms per phase, and each bridge arm is connected in series with N board bridge standard submodules, that is, There are N half-bridge standard sub-modules, any half-bridge standard sub-module can be understood as a target sub-module. is the DC bus voltage, is the bridge arm inductance of the three-phase half-bridge modular multilevel converter. is the bridge arm resistance of the three-phase half-bridge modular multilevel converter, is the transformer equivalent inductance, is the upper arm current of the three-phase half-bridge modular multilevel converter, where Specifically, it can be , is the upper arm current of phase A, is the upper arm current of phase B, is the upper arm current of phase C, is the lower arm current of the three-phase half-bridge modular multilevel converter, where Specifically, it can be , is the lower bridge arm current of phase A, is the lower arm current of phase B, is the lower bridge arm current of phase C, is the output voltage of the half-bridge standard submodule, is the capacitive current of the half-bridge standard submodule, is the capacitor voltage of the half-bridge standard submodule, C is the capacitance, 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 of phase A on the grid side, is the AC voltage on the grid side of phase B, is the grid-side AC voltage 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 submodule under the excitation of the fundamental frequency modulation voltage from the capacitor voltage of the target submodule, and generating harmonic components corresponding to each harmonic component. For example, in an implementable manner, the double frequency component and the triple frequency component existing in the capacitor voltage of the target submodule are collectively used as multiple harmonic components.

[0065] As another example, step 202 includes: taking 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 the multiple harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage, and obtaining the harmonic modulation voltage corresponding to each harmonic component. For example, in one feasible method, the third harmonic component generated by the fundamental frequency modulation voltage injected with the third harmonic voltage and the double frequency component existing in the capacitor voltage of the target sub-module are taken as the multiple harmonic components.

[0066] Step 204 , distributing the bridge arm modulation voltage obtained by integrating the harmonic modulation voltages to obtain a target modulation voltage acting on a target submodule.

[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 bridge arm modulation voltage distribution problem of the modular multilevel converter is involved, wherein the target modulation voltage is used to control the multiple harmonic components existing in the target sub-module under the excitation of the fundamental frequency modulation voltage. The distribution method of the bridge arm modulation voltage can specifically be a balanced distribution method or a distribution method using a voltage equalization control algorithm, which is not limited in the embodiments of the present application.

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

[0069] It is understandable that, affected by the circuit topology of the modular multilevel converter, the bridge arm modulation voltage of the target submodule changes with the change of the bridge arm in which it is located, that is, the bridge arm modulation voltage of the target submodule in the upper bridge arm is different from the bridge arm modulation voltage of the target submodule in the lower bridge arm.

[0070] Step 206 , performing capacity reduction control on the target submodule 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, a voltage modulation signal for controlling the capacity reduction of 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 can be applied to the target sub-module of the modular multi-level converter. For example, in one feasible method, the voltage modulation signal can be used to control the on and off of the IGBT (Insulated Gate Bipolar Transistor) of the target sub-module, thereby significantly reducing the capacitor voltage fluctuation of the target sub-module to achieve capacity reduction of the target sub-module.

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

[0073] In the above-mentioned sub-module capacity reduction control method of the modular multi-level converter, firstly, 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 realize the capacity reduction control of the target sub-module. Since the voltage modulation signal fully considers 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 on and off, the harmonic component causing the capacitor voltage fluctuation of the target sub-module can be completely controlled, that is, the purpose of accurately controlling the harmonic component affecting 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 multi-level 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 actually causing 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 multi-level 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, including:

[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 capacitor voltage fluctuation of the target submodule, different capacity reduction control methods may be used. In some capacity reduction control methods, the processing of the baseband modulation signal is involved, which leads to the active introduction of harmonic components, that is, multiple different types of harmonic components may include different harmonic components passively generated by the target submodule under the excitation of the baseband modulation voltage, and may include harmonic components actively injected when modulating the baseband modulation signal. There is a difference in the way of generating the harmonic modulation voltage for the actively injected harmonic components and the passively generated harmonic components. Therefore, the first harmonic component refers to the harmonic component actively injected to reduce the capacitor voltage fluctuation of the target submodule, such as the third harmonic component generated by the baseband modulation voltage, and the second harmonic component refers to the harmonic component that has an impact on the capacitor voltage of the target submodule and is passively generated, such as the second harmonic component of the capacitor voltage of the target submodule.

[0077] It should be noted that the harmonic modulation voltage includes a first modulation voltage of a first harmonic component and a second modulation voltage of a 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, wherein the first modulation voltage can specifically be a third harmonic modulation voltage. For example, in an implementable manner, the first corresponding relationship between the third harmonic component of the third harmonic modulation voltage and the first fundamental frequency component of the fundamental frequency modulation voltage is as follows:

[0078]

[0079] in, 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 is the first voltage parameter, and is the second voltage parameter.

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

[0081] In one practicable manner, referring to Figure 4 , Figure 4 is a control flow chart representing the first modulation voltage, wherein: It 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 parameters of a certain voltage, the corresponding modulation voltage can be generated. For example, in an implementable manner, assuming that the first corresponding relationship 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] in, 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, If the third harmonic modulation voltage is injected into the fundamental frequency modulation voltage as a method to reduce the voltage fluctuation of the target submodule capacitor, the expression of the bridge arm modulation voltage can be shown as follows:

[0086]

[0087] in, is the bridge arm modulation voltage in the upper bridge arm of phase A, is the DC bus voltage of the modular multi-level submodule, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, For cycle.

[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 : extracting the harmonic component voltage corresponding to the second harmonic component from the capacitor voltage of the target submodule.

[0090] It should be noted that waveforms of different frequencies in the capacitor voltage represent different voltage components, and the harmonic component voltage corresponding to the second harmonic component can be extracted by performing waveform analysis on the capacitor voltage, wherein the second harmonic component can be one or more, and the second harmonic component and the harmonic component voltage correspond one to one.

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

[0092] Step 308: determine the harmonic component current of the target submodule in the bridge 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 submodule in the bridge arm where it is located.

[0094] Step 310: convert 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.

[0095] It should be noted that, when the second harmonic component exists in the capacitor voltage, an opposite harmonic current needs to be injected to suppress the second harmonic component, thereby changing the bridge arm current of the modular multilevel converter, wherein the second corresponding relationship can be as follows:

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

[0097] in, is the harmonic component voltage, is the harmonic component voltage, is the angular frequency, For the cycle, is the power factor angle, C is the capacitance value of the target submodule, is the AC current amplitude, and m is the fundamental frequency modulation ratio of the modular multilevel converter.

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

[0099] It is understandable that in order not to generate third harmonic current in the modular multilevel converter and on the grid side, the AC side of the modular multilevel converter needs to be connected to the 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, the valve side voltage of the modular multilevel converter can be increased by 1.15 times after the third harmonic voltage is injected through the transformer compared with the case without the third harmonic voltage being injected.

[0100] In this embodiment, different solutions are used to obtain the first modulation voltage and the second modulation voltage for different types of first harmonic components and second harmonic components. When solving the first modulation voltage of the actively injected first harmonic component, the conversion relationship of the voltage parameters is confirmed based on the correspondence between the first fundamental frequency component and the first harmonic component of the fundamental frequency modulation voltage, and 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 by the capacitor voltage of the target submodule, and based on the conversion relationship between voltage and current, the second modulation voltage corresponding to the injected appropriate harmonic component current is obtained to suppress the second harmonic component, with the first harmonic component as the third harmonic voltage and the second harmonic component as the second harmonic voltage. Taking the circulating current as an example, in the process of the sub-module capacity reduction control method of the modular multilevel converter, this embodiment designs a coordinated injection strategy, combines the third harmonic voltage and the second harmonic circulating current injection control, and can automatically inject the second harmonic circulating current and the third harmonic voltage under various operating conditions. Compared with the traditional single capacity reduction control method, this embodiment adopts the coordinated injection control strategy, which can improve the capacity reduction effect of the target sub-module of the modular multilevel converter, that is, more significantly and effectively reduce the capacity while not increasing the operating loss of the modular multilevel converter. Therefore, while achieving precise control of the harmonic components that affect the capacitor voltage fluctuation of the target sub-module, it has less operating loss of the modular multilevel converter. Therefore, while improving the capacity reduction 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 a first modulation voltage according to a second voltage parameter includes:

[0102] A harmonic modulation voltage corresponding to the first harmonic component is generated according to the second voltage parameter; and a first modulation voltage is generated according to the harmonic modulation voltage and the switch bridge arm where the target submodule is located.

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

[0104]

[0105] in, is the first modulation voltage of the target submodule in the upper bridge arm of phase A of the modular multilevel converter, is the third harmonic modulation voltage of the target submodule in the lower bridge 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, If the third harmonic modulation voltage is injected into the fundamental frequency modulation voltage as a method to reduce the voltage fluctuation of the target submodule capacitor, the expression of the bridge arm modulation voltage can be shown as follows:

[0106]

[0107] is the bridge arm modulation voltage in the upper bridge arm of phase A, is the bridge arm modulation voltage of the lower bridge arm in phase A, is the DC bus voltage of the modular multi-level submodule, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, For cycle.

[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; the specific position of the switch bridge arm where the target submodule is located in the modular multilevel converter is determined, and the harmonic modulation voltage is adjusted to the first modulation voltage. Due to the positional relationship between the target submodule and the modular multilevel converter, different types of first modulation voltages are generated in a targeted manner, and then the first modulation voltage for controlling the first harmonic component can be generated when the target submodule is located at any position of the modular multilevel converter. Therefore, while improving the submodule capacity reduction control effect of the modular multilevel converter, the control flexibility of the submodule capacity reduction control of the modular multilevel converter is improved.

[0109] In one embodiment, determining the harmonic component current of the target submodule in the bridge arm includes:

[0110] The fundamental frequency component voltage corresponding to the second fundamental frequency component is extracted from the capacitor voltage of the target submodule; the current parameters of the target submodule in the bridge arm are determined according to the fundamental frequency component voltage and the harmonic component voltage; and the harmonic component current is generated 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 submodule include the fundamental frequency component voltage and the double frequency component voltage, 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 electrical quantities inside the target submodule, the expressions of the fundamental frequency component voltage and the double frequency component voltage are as follows:

[0112]

[0113] in, 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, For the cycle, is the power factor angle, C is the capacitance of the target submodule, m is the fundamental frequency modulation ratio of the modular multilevel converter, and the expression of m is as follows:

[0114]

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

[0116]

[0117] in, 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, For the cycle, it is understandable that in and If known, it can be calculated with the help of the above expression and , and in and If the harmonic component current 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 submodule capacitor voltage to 0, so that the amplitude and phase angle of the harmonic component voltage can be obtained when the fundamental frequency component and the harmonic component voltage are known, 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 the injection of the second harmonic circulating current is used as a method to reduce the voltage fluctuation of the target submodule capacitor, the expression of the bridge arm modulation current can be as follows:

[0118]

[0119] in, is the A-phase upper arm current of the modular multilevel converter, is the lower arm current of phase A of the modular multilevel converter, is the angular frequency, For the cycle, is the DC side current of the modular multilevel converter, is the AC current amplitude, 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, a fundamental frequency component voltage corresponding to the second fundamental frequency component is extracted from the capacitor voltage of the target submodule; the amplitude and phase angle of the harmonic component voltage are calculated based on the harmonic component voltage and the fundamental frequency component voltage extracted from the capacitor voltage of the target submodule, and then the harmonic component current of the target submodule in the bridge arm is calculated by substituting the amplitude and phase angle of the harmonic component voltage into a preset expression. When determining the harmonic component current of the target submodule in the bridge arm where it is located, 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 submodule under the real-time working condition, and then the harmonic component current is obtained through the amplitude and phase angle calculation, so that in the process of generating the second modulation voltage for the second harmonic component, the error of the second modulation voltage caused by the determination of the harmonic component current not meeting the real-time working condition is avoided. For example, if the second harmonic circulating current generated by the modular multilevel converter under the actual working condition is not used to determine the corresponding second harmonic modulation voltage, it will lead to the situation that the control effect of the second harmonic modulation voltage on the second harmonic circulating current is not good. Therefore, the above embodiment can further improve the capacity reduction control effect of the submodule of the modular multilevel converter.

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

[0122] According to the common-mode voltage component of the bridge arm of the modular multilevel converter, coordinate transformation is performed 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, the direct-axis harmonic component voltage is converted into the 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, the quadrature-axis harmonic component voltage is converted into the quadrature-axis harmonic modulation reference current; coordinate transformation is performed 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 corresponding relationship, 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 corresponding relationship, 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 direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage, a second modulation voltage is generated.

[0123] It should be noted that, taking into account 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 multi-level circulator, the harmonic component voltage and the harmonic component current in the abc coordinate system are converted to the negative-sequence coordinate system according to a preset angle, and the second corresponding relationship between the harmonic component voltage and the second harmonic component is also correspondingly transformed in the coordinate system. At the same time, in order to reduce the large amount of calculation process for determining the harmonic component current, a harmonic component voltage controller is designed to directly complete the voltage-current conversion through PI control, and a circulating current controller is designed to directly complete the current-voltage conversion, so as to finally output the second modulation voltage. For example, in an implementable manner, assuming that the second harmonic component is a second harmonic circulating current, the negative-sequence coordinate system is specifically a double frequency. Coordinate system, where d is the direct axis, q is the quadrature axis, and the three-phase coordinate system is double frequency The preset angle for coordinate conversion is , w is the angular frequency, t is the period, and the harmonic component voltage controller is a double frequency voltage controller. The expressions of the direct-axis harmonic component voltage (i.e., the double frequency component voltage of the target submodule capacitor voltage on the d-axis) and the quadrature-axis harmonic component voltage (i.e., the double frequency component voltage of the target submodule capacitor voltage on the q-axis) are as follows:

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

[0125] in, is the amplitude of the harmonic component current, is the phase angle of the harmonic component current, is the angular frequency, For the cycle, is the direct-axis harmonic component voltage, is the quadrature-axis harmonic component voltage, is the AC current amplitude, is the power factor angle, C is the capacitance of the target submodule, m is the fundamental frequency modulation ratio of the modular multilevel converter, and the expressions of 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] in, 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, so the expression of the second corresponding relationship is as follows:

[0128] [ u c 2 d u c 2 q ] = 1 4 wxya [ i cird i cirq ] + I m 96 wxya [ − sin φ cos φ ] − I m 16 wxya [ 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, the above-mentioned second corresponding relationship can be used, and after the capacitor voltage component of the target submodule is set at the target value (that is, the direct-axis harmonic modulation reference voltage and the quadrature-axis harmonic modulation reference voltage are pre-set), the double frequency voltage controller outputs the direct-axis harmonic modulation reference current and the quadrature-axis harmonic modulation reference current. The expressions of the direct-axis harmonic modulation reference current and the quadrature-axis harmonic modulation reference current are as follows:

[0130]

[0131] in, is the direct-axis harmonic modulation reference current, is the quadrature-axis harmonic modulation reference current, is the direct-axis harmonic modulation reference voltage, For quadrature-axis harmonic modulation reference voltage, for example, and are all set to 0, and the above expression can be solved to get and , 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 an integral link, in which the solution process of the direct-axis harmonic component voltage and the quadrature-axis harmonic component voltage can refer to the following expressions:

[0132]

[0133]

[0134]

[0135] in, is the common-mode voltage component of the A-phase bridge arm (average value of the capacitor voltage), 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 of the upper bridge arm of phase B (average value of capacitor voltage), is the average capacitor voltage of the lower bridge arm of phase B, is the common-mode voltage component of the C-phase bridge arm (average value of capacitor voltage), is the average capacitor voltage of the upper bridge arm of phase C, is the average value of the capacitor voltage of the bridge arm under phase C, and then the common mode voltage component of each phase bridge arm is substituted into the coordinate conversion matrix to transform from the abc three-phase static coordinate to the negative sequence double frequency dq rotating coordinate, and obtain the d and q axis components of the capacitor voltage double frequency component .

[0136] As an example, the average values ​​of the capacitor voltages of the upper and lower bridge arms of each phase of the modular multilevel converter are obtained respectively, and the common-mode voltage components of the bridge arms of the modular multilevel converter are obtained according to the average values ​​of the capacitor voltages of the upper and lower bridge arms of each phase, and the common-mode voltage components of the bridge arms are substituted into the coordinate transformation matrix of the three-phase coordinate system to transform the three-phase coordinate system into the negative-sequence coordinate system, and the harmonic component voltage is transformed 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 component of the second harmonic component in the preset coordinate system is transformed into the direct-axis harmonic modulation reference current. A quadrature-axis harmonic modulation reference voltage is input into a harmonic component voltage controller to convert the quadrature-axis harmonic component voltage into a quadrature-axis harmonic modulation reference current; coordinate transformation is performed on the harmonic component current to obtain a direct-axis harmonic component current and a quadrature-axis harmonic component current in a preset coordinate system; according to a second corresponding relationship, the direct-axis harmonic component current and the direct-axis harmonic modulation reference current are converted together into a direct-axis harmonic modulation voltage; and according to the second corresponding relationship, the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current and the direct-axis harmonic modulation reference current are converted together into a 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 converted together into a 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, thereby improving the efficiency of obtaining the second modulation voltage. The setting of the circulating current controller is more convenient for outputting a suitable second modulation voltage for suppressing the second harmonic component, that is, the second modulation voltage is used to generate and suppress the circulating current of the second harmonic component in the modular multilevel controller. In general, it lays a foundation for improving the capacity reduction effect of the sub-modules of the modular multilevel converter.

[0137] In one practicable 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 one practicable manner, referring to Figure 6 , Figure 6 is the control flow chart of the circulation 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 bridge arm inductance 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, which can be specifically , or ,in, 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 allocating the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain the target modulation voltage acting on the target submodule, the method further includes:

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

[0141] It should be noted that when the bridge arm modulation voltage is obtained by fusion, different bridge arms where the target submodules are located will be fused to obtain different bridge arm modulation voltages. For example, in an implementable manner, the expression of the bridge arm modulation voltage is as follows:

[0142]

[0143] in, is the bridge arm modulation voltage of the target submodule in the upper bridge arm of phase A, is the bridge arm modulation voltage of the target submodule in the lower bridge arm of phase A, is the DC bus voltage of the modular multi-level submodule, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, For the cycle, is the second modulation voltage of the A-phase bridge arm, is the first modulation voltage of the upper bridge arm of phase A, The first modulation voltage of the lower bridge arm of phase A.

[0144] As an example, according to the positional relationship between the target submodule and the modular multilevel converter, the bridge arm where the target submodule is located is determined; according to the bridge arm where the target submodule is located, each harmonic modulation voltage and the fundamental frequency modulation voltage are merged to obtain the bridge arm modulation voltage. Due to the positional relationship between the target submodule and the modular multilevel converter, different bridge arm modulation voltages are generated in a targeted manner, and then when the target submodule is located at any position of the modular multilevel converter, a bridge arm modulation voltage that controls different harmonic components can be generated. Therefore, while improving the submodule capacity reduction control effect of the modular multilevel converter, the control flexibility of the submodule capacity reduction control of the modular multilevel converter is improved.

[0145] In one embodiment, according to the voltage modulation signal corresponding to the target modulation voltage, the target submodule is controlled to reduce capacity, including:

[0146] The target modulation voltage is modulated to a preset carrier signal to obtain an initial voltage modulation signal; the initial voltage modulation signal is normalized to obtain a voltage modulation signal; and the target submodule is subjected to capacity reduction control according to the voltage modulation signal.

[0147] As an example, the signal parameters of the preset carrier signal are modulated by the target modulation voltage to obtain an initial voltage modulation signal; the initial voltage modulation signal is normalized to obtain a voltage modulation signal, wherein the expression of the voltage modulation signal can be as follows:

[0148]

[0149] in, is the voltage modulation signal of the upper bridge arm of phase A, is the voltage modulation signal of the lower bridge arm of phase A, is the DC bus voltage of the modular multi-level submodule, is the amplitude of the fundamental frequency modulation voltage, is the phase angle of the fundamental frequency modulation voltage, is the angular frequency, For the cycle, is the second modulation voltage of the A-phase bridge arm, is the first modulation voltage of the upper bridge arm of phase A, The first modulation voltage of the lower bridge arm of phase A; according to the voltage modulation signal, the target submodule is controlled to reduce capacity. By converting the voltage modulation signals of different bridge arms of the modular multilevel converter to a unified standard for control, the modulation logic can be simplified and the efficiency of the reduction control can be improved.

[0150] In one practicable manner, referring to Figure 7 , Figure 7 To show the overall structural diagram of the target submodule for capacity reduction control, in the process of coordinating the capacity reduction control of the two different harmonic components of the second harmonic circulating current and the third harmonic voltage, the power control is firstly used to output the trigger signal of the amplitude detection and the phase angle detection through the current inner loop controller. , which includes the power outer loop of the modular multilevel converter to control the output power of the modular multilevel converter and generate the inner loop current reference value of the current inner loop controller and , and then the first modulation voltage is outputted through the third harmonic voltage controller after converting the first voltage parameter, and the direct-axis harmonic modulation reference current and the quadrature-axis harmonic modulation reference current are outputted through the capacitor voltage double frequency component controller, and the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage are outputted based on the second corresponding relationship through the circulating current controller, and finally the second modulation voltage is obtained by converting the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage together, and finally the baseband modulation voltage, the first modulation voltage and the second modulation voltage are combined to perform modulation and voltage balancing control to output a driving signal, that is, the output voltage modulation signal performs capacity reduction control on the target submodule.

[0151] Therefore, in the process of performing the sub-module capacity reduction control method of the modular multilevel converter, this embodiment designs a coordinated injection strategy, combines the third harmonic voltage and the second harmonic circulating current injection control, and can automatically inject the second harmonic circulating current and the third harmonic voltage under various operating conditions. Compared with the traditional single capacity reduction control method, this embodiment adopts the coordinated injection control strategy, which can improve the capacity reduction effect of the target sub-module of the modular multilevel converter, that is, more significantly and effectively reduce the capacity while not increasing the operating loss of the modular multilevel converter. Therefore, while achieving precise control of the harmonic components that affect the capacitor voltage fluctuation of the target sub-module, it has less operating loss of the modular multilevel converter. Therefore, while improving the capacity reduction 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 displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, 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, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0153] Based on the same inventive concept, the embodiment of the present application also provides a modular multilevel converter submodule capacity reduction control device for implementing the modular multilevel converter submodule capacity reduction control method involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiments of the submodule capacity reduction control device for one or more modular multilevel converters provided below can refer to the limitations of the modular multilevel converter submodule capacity reduction control method above, and will not be repeated here.

[0154] In an exemplary embodiment, Figure 8 As shown, a submodule capacity reduction control device of a modular multilevel converter is provided, comprising: an acquisition module 401, an allocation module 402 and a capacity reduction control module 403, wherein:

[0155] An acquisition module 401 is used to acquire harmonic modulation voltages corresponding to multiple harmonic components existing in a target submodule under the 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;

[0156] A distribution module 402 is used to distribute the bridge arm modulation voltage obtained by integrating the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule;

[0157] The capacity reduction control module 403 is used to perform capacity reduction control on the target submodule according to the voltage modulation signal corresponding to the target modulation voltage.

[0158] 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 acquisition module 401 is further used to:

[0159] According to a first corresponding relationship between the first harmonic component and the first fundamental frequency component of the fundamental frequency modulation voltage, a first voltage parameter of the fundamental frequency modulation voltage is converted into a second voltage parameter; according to the second voltage parameter, the first modulation voltage is generated; the harmonic component voltage corresponding to the second harmonic component is extracted from the capacitor voltage of the target submodule; the harmonic component current of the target submodule in the bridge arm is determined; according to a second corresponding relationship between the harmonic component voltage and the second harmonic component, the harmonic component current is converted into the second modulation voltage.

[0160] In one embodiment, the acquisition module 401 is further used for:

[0161] A harmonic modulation voltage corresponding to the first harmonic component is generated according to the second voltage parameter; and the first modulation voltage is generated according to the harmonic modulation voltage and the switch bridge arm where the target submodule is located.

[0162] In one embodiment, the acquisition module 401 is further used for:

[0163] The fundamental frequency component voltage corresponding to the second fundamental frequency component is extracted from the capacitor voltage of the target submodule; the current parameter of the target submodule in the bridge arm is determined according to the fundamental frequency component voltage and the harmonic component voltage; and the harmonic component current is generated according to the current parameter.

[0164] In one embodiment, the acquisition module 401 is further used for:

[0165] According to the common-mode voltage component of the bridge arm of the modular multilevel converter, coordinate transformation is performed on the harmonic component voltage to obtain a direct-axis harmonic component voltage and a 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, the direct-axis harmonic component voltage is converted 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, the quadrature-axis harmonic component voltage is converted into a quadrature-axis harmonic modulation reference current; coordinate transformation is performed 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; according to the second corresponding relationship, the direct-axis harmonic component current and the direct-axis harmonic modulation reference current are jointly converted into a direct-axis harmonic modulation voltage, and according to the second corresponding relationship, 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 a quadrature-axis harmonic modulation voltage; according to the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage, the second modulation voltage is generated.

[0166] In one of the embodiments, the submodule capacity reduction control device of the modular multilevel converter is further used for:

[0167] Determine the bridge arm where the target submodule is located; and according to the bridge arm where the target submodule is located, fuse each of the harmonic modulation voltages and the fundamental frequency modulation voltage to obtain a bridge arm modulation voltage.

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

[0169] The target modulation voltage is modulated to a preset carrier signal to obtain an initial voltage modulation signal; the initial voltage modulation signal is normalized to obtain the voltage modulation signal; and the target submodule is subjected to capacity reduction control according to the voltage modulation signal.

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

[0171] In an exemplary embodiment, a power conversion device is provided. The power conversion device may be a terminal, and its internal structure diagram may be as shown in FIG. Fig. 9 As shown. The power conversion device includes a processor, a memory, an input / output interface, a communication interface, a display unit and an input device. The processor, the memory and the input / output interface are connected via a system bus, and the communication interface, the display unit and the input device are connected to the system bus via the input / output interface. 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 to exchange information between the processor and an external device. The communication interface of the power conversion device is used to communicate with an external terminal 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, a sub-module capacity reduction control method of a modular multi-level converter is implemented. Those skilled in the art can understand that Fig. 9 The structure shown in the figure is only a block diagram of a part of the structure related to the scheme of the present application, and does not constitute a limitation on the power conversion device to which the scheme of the present application is applied. The specific power conversion device may include more or fewer components than shown in the figure, or combine certain components, or have a different arrangement of components.

[0172] In one embodiment, a power conversion device is further provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above-mentioned method embodiments when executing the computer program.

[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-mentioned method embodiments are implemented.

[0174] In one embodiment, a computer program product is provided, including a computer program, which implements the steps in the above method embodiments when executed by a processor.

[0175] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and 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 embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. 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. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0176] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0177] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, 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 attached claims.

Claims

1. A method for controlling submodule capacity reduction of a modular multilevel converter, characterized in that: The method comprises: Acquire harmonic modulation voltages corresponding to each of a plurality of 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 plurality of 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 controlled to be reduced in capacity according to the voltage modulation signal corresponding to the target modulation voltage.

2. The method according to claim 1, characterized in that: The plurality of 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 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 comprises: 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; generating the first modulation voltage according to the second voltage parameter; Extracting a harmonic component voltage corresponding to the second harmonic component from the capacitor voltage of the target submodule; 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.

3. The method according to claim 2, characterized in that Generating the first modulation voltage according to the second voltage parameter includes: generating a harmonic modulation voltage corresponding to the first harmonic component according to the second voltage parameter; The first modulation voltage is generated according to the harmonic modulation voltage and the switch bridge arm where the target submodule is located.

4. The method according to claim 2, 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 a second fundamental frequency component from the capacitor voltage of the target submodule; Determining a current parameter of a target submodule in a 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.

5. The method according to claim 2, 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 comprises: According to the common-mode voltage component of the bridge arm of the modular multilevel converter, coordinate transformation is performed on the harmonic component voltage to obtain a direct-axis harmonic component voltage and a 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, converting 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, converting the quadrature-axis harmonic component voltage into a quadrature-axis harmonic modulation reference current; Performing 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; According to the second corresponding relationship, the direct-axis harmonic component current and the direct-axis harmonic modulation reference current are converted into a direct-axis harmonic modulation voltage, and according to the second corresponding relationship, the quadrature-axis harmonic component current, the quadrature-axis harmonic modulation reference current and the direct-axis harmonic modulation reference current are converted into a quadrature-axis harmonic modulation voltage; The second modulation voltage is generated according to the direct-axis harmonic modulation voltage and the quadrature-axis harmonic modulation voltage.

6. The method according to claim 1, characterized in that Before distributing the bridge arm modulation voltage obtained by merging the harmonic modulation voltages to obtain the target modulation voltage acting on the target submodule, the method further includes: Determine the bridge arm where the target submodule is located; According to the bridge arm where the target submodule is located, each of the harmonic modulation voltages and the fundamental frequency modulation voltage is fused to obtain a bridge arm modulation voltage.

7. The method according to claim 1, characterized in that The step of performing capacity reduction control on the target submodule according to the voltage modulation signal corresponding to the target modulation voltage includes: Modulating the target modulation voltage to a preset carrier signal to obtain an initial voltage modulation signal; Normalizing the initial voltage modulation signal to obtain the voltage modulation signal; The target submodule is controlled to reduce capacity according to the voltage modulation signal.

8. A submodule capacity reduction control device for a modular multilevel converter, characterized in that: The device comprises: An acquisition module, used for acquiring harmonic modulation voltages corresponding to each of a plurality of harmonic components existing in a target submodule under the excitation of a fundamental frequency modulation voltage, wherein the target submodule is any standard submodule of a modular multilevel converter, and the plurality of harmonic components are harmonic components of different types; A distribution module, used for distributing the bridge arm modulation voltage obtained by integrating the harmonic modulation voltages to obtain a target modulation voltage acting on the target submodule; The capacity reduction control module is used to perform capacity reduction control on the target submodule according to the voltage modulation signal corresponding to the target modulation voltage.

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

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

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