A method and device for suppressing circulating current based on hierarchical composite control, equipment and medium

Abstract

The present application relates to the technical field of modular multilevel converter, and discloses a circulating current suppression method and device based on hierarchical composite control, equipment and medium, the circulating current suppression method based on hierarchical composite control comprises the following steps: obtaining a first correction value according to a proportional resonant control method, superimposing the first correction value on a modulation wave, so that the modular multilevel converter operates according to the first modulation wave; obtaining a first fundamental frequency circulating current component and a second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase; obtaining a first voltage fluctuation component and a second voltage fluctuation component according to the first fundamental frequency circulating current component and the second fundamental frequency circulating current component; calculating a second correction value according to the first voltage fluctuation component and the second voltage fluctuation component; superimposing the second correction value on the first modulation wave, so that the modular multilevel converter operates according to the second modulation wave. The present application realizes the suppression of the second harmonic circulating current and the fundamental frequency circulating current, does not need to improve the operating voltage of the sub-module, and is simple to operate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of modular multilevel converter, and particularly relates to a circulating current suppression method and device based on hierarchical composite control, equipment and medium. BACKGROUND

[0002] Compared with the traditional two-level converter, the modular multilevel converter (MMC) has the advantage of modular design, which makes the MMC have good scalability and facilitates the voltage level upgrade.

[0003] When the MMC is normally working, the sub-modules are put in and cut off according to the sine law at the sampling time. As the core component unit of the MMC, the normal or abnormal of the working state of the sub-modules directly affects the safe and stable operation of the converter. In actual power transmission projects, in order to adapt to higher transmission voltage levels, a large number of sub-modules are often cascaded. However, due to some on-site operation and environmental factors, some sub-modules will inevitably fail. When the fault of the sub-modules is controlled, the MMC usually operates asymmetrically, at this time, circulating current will appear, which will disturb the stable operation of the MMC after the sub-modules fail. The method for ensuring the stable operation of the MMC after the sub-modules fail is circulating current suppression.

[0004] In the related art, the common method for realizing circulating current suppression is a multiple frequency proportional resonance circulating current suppression method, and a circulating current suppression method for changing the average switching frequency of the sub-modules. The method can suppress the circulating current caused by the asymmetric operation of the sub-modules after the sub-modules fail. However, the method needs to increase the operating voltage of the sub-modules, which increases the requirements for the device stress, and needs to know the specific number of sub-module fault information, which increases the communication burden of the control system. In addition, in the circulating current suppression process, only the double frequency circulating current can be suppressed. If the non-double frequency circulating current is to be suppressed, the scheme design is difficult. SUMMARY

[0005] Therefore, the present application provides a circulating current suppression method and device based on hierarchical composite control to solve the problem of the need to increase the operating voltage of the sub-modules.

[0006] In a first aspect, the application provides a circulating current suppression method based on hierarchical composite control, comprising: obtaining a first correction value according to a proportional-resonant control method, superimposing the first correction value on a first modulation wave, so that the modular multilevel converter operates according to the first modulation wave, and the first modulation wave is used to suppress the second-order circulating current; obtaining a first fundamental frequency circulating current component and a second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase, the first fundamental frequency circulating current component being a component of the fundamental frequency circulating current on the d-axis, and the second fundamental frequency circulating current component being a component of the fundamental frequency circulating current on the q-axis; inputting the first fundamental frequency circulating current component and the second fundamental frequency circulating current component into a first relationship, to obtain a first voltage fluctuation component and a second voltage fluctuation component, the first relationship being used to represent the relationship between the fundamental frequency circulating current and the voltage fluctuation in the dq coordinate system, the first voltage fluctuation component being a component of the voltage fluctuation on the d-axis, and the second voltage fluctuation component being a component of the voltage fluctuation on the q-axis; calculating a second correction value according to the first voltage fluctuation component and the second voltage fluctuation component; superimposing the second correction value on the first modulation wave, so that the modular multilevel converter operates according to a second modulation wave, and the second modulation wave is used to suppress the fundamental frequency circulating current and the second-order circulating current.

[0007] Beneficial effects: The embodiment of the application obtains a first correction value according to the quasi-proportional resonant control method, superimposes the first correction value on a modulation wave, so that the modular multilevel converter operates according to the first modulation wave, and the first modulation wave is used to suppress the double-frequency circulating current, that is, the double-frequency circulating current is suppressed according to the quasi-proportional resonant control method. The embodiment of the application obtains a first fundamental frequency circulating current component and a second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase, the first fundamental frequency circulating current component is a component of the fundamental frequency circulating current on the d-axis, and the second fundamental frequency circulating current component is a component of the fundamental frequency circulating current on the q-axis. When a sub-module of the modular multilevel converter fails, the modular multilevel converter operates asymmetrically, at this time, the fundamental frequency circulating current appears, which affects the stable operation of the modular multilevel converter. The embodiment of the application processes in the dq coordinate system through virtual synchronous rotating coordinate transformation, and independently obtains the fundamental frequency circulating current of the sub-module fault phase. The embodiment of the application inputs the first fundamental frequency circulating current component and the second fundamental frequency circulating current component into a first relationship to obtain a first voltage fluctuation component and a second voltage fluctuation component. The first relationship is used to represent the relationship between the fundamental frequency circulating current and the voltage fluctuation in the dq coordinate system. The first voltage fluctuation component is a component of the voltage fluctuation on the d-axis, and the second voltage fluctuation component is a component of the voltage fluctuation on the q-axis. The second correction value is calculated according to the first voltage fluctuation component and the second voltage fluctuation component, and the second correction value is superimposed on the first modulation wave, so that the modular multilevel converter operates according to the second modulation wave. Compared with related technologies, the embodiment of the application can suppress the double-frequency circulating current and the fundamental frequency circulating current, does not need to use multiple different frequency resonant controllers in parallel, reduces the complexity of system design, does not need to increase the operating voltage of the sub-module, reduces the requirement for device stress, does not need to know the specific fault number information of the sub-module, and reduces the communication burden of the control system.

[0008] In an optional embodiment, before obtaining the first correction value according to the quasi-proportional resonant control method, the method further includes: obtaining the double-frequency circulating current by using a first band-pass filter combining a direct current integrator and a second-order generalized integrator.

[0009] Beneficial effects: The first band-pass filter combining the direct current integrator and the second-order generalized integrator is used to obtain the double-frequency circulating current, and fast tracking of the double-frequency circulating current is realized.

[0010] In an optional embodiment, obtaining the first fundamental frequency circulating current component and the second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase includes: obtaining the fundamental frequency circulating current; performing weighted processing on the fundamental frequency circulating current to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current; and inputting the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current into a filter to obtain the first fundamental frequency circulating current component and the second fundamental frequency circulating current component.

[0011] In one alternative implementation, the filter's transfer function is:

[0012]

[0013] Among them, G NF (s) represents the output of the filter's transfer function, k is the gain, s is the independent variable, and ω is the angular velocity.

[0014] In one alternative implementation, obtaining the fundamental frequency circulating current includes: obtaining the fundamental frequency circulating current through a second bandpass filter.

[0015] In one alternative implementation, the transfer function of the second bandpass filter is:

[0016]

[0017] Among them, G BPF2 (s) is the output of the transfer function of the second bandpass filter, k is the gain, s is the independent variable, and ω is the angular velocity.

[0018] In one optional implementation, the fundamental frequency circulating current is weighted to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current, including: multiplying the fundamental frequency circulating current by a first weighting value and a second weighting value, respectively, to obtain the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current.

[0019] In one alternative implementation, the first relation is:

[0020]

[0021] Among them, u jz_f_d For the first voltage fluctuation component, u jz_f_q Let L be the inductance and i be the second voltage fluctuation component. jz_f_d i is the first fundamental frequency circulating component. jz_f_q ω represents the second fundamental frequency circulating component, and ω represents the angular velocity.

[0022] In one optional implementation, calculating a first correction value based on a first voltage fluctuation component and a second voltage fluctuation component includes: inputting the first voltage fluctuation component and the second voltage fluctuation component into a second relational expression to obtain a second correction value, wherein the second relational expression is used to characterize the relationship between the second correction value and the first voltage fluctuation component and the second voltage fluctuation component.

[0023] Beneficial effect: After obtaining the first voltage fluctuation component and the second voltage fluctuation component, the first voltage fluctuation component and the second voltage fluctuation component are input into the second relational expression to calculate the second correction value.

[0024] In one alternative implementation, the second relation is:

[0025]

[0026] wherein Δu jz_f is a second correction value, u jz_f_d is a first voltage fluctuation component, u jz_f_q is a second voltage fluctuation component, ω is an angular velocity, and t is time.

[0027] In a second aspect, the present application provides a circulating current suppression device based on hierarchical composite control, comprising: a first operation module, configured to obtain a first correction value according to a quasi-proportional resonant control method, and superimpose the first correction value on a first modulation wave, so that the modular multilevel converter operates according to the first modulation wave, and the first modulation wave is used to suppress the double-frequency circulating current, i.e., the double-frequency circulating current is suppressed according to the quasi-proportional resonant control method; an obtaining module, configured to obtain a first fundamental-frequency circulating current component and a second fundamental-frequency circulating current component of the fundamental-frequency circulating current in the fault phase, the first fundamental-frequency circulating current component being a component of the fundamental-frequency circulating current on a d-axis, and the second fundamental-frequency circulating current component being a component of the fundamental-frequency circulating current on a q-axis; a voltage fluctuation component calculation module, configured to input the first fundamental-frequency circulating current component and the second fundamental-frequency circulating current component into a first relationship, to obtain a first voltage fluctuation component and a second voltage fluctuation component, the first relationship being used to represent a relationship between the fundamental-frequency circulating current and a voltage fluctuation in a dq coordinate system, the first voltage fluctuation component being a component of the voltage fluctuation on the d-axis, and the second voltage fluctuation component being a component of the voltage fluctuation on the q-axis; a correction value calculation module, configured to calculate a second correction value according to the first voltage fluctuation component and the second voltage fluctuation component; and a second operation module, configured to superimpose the second correction value on the first modulation wave, so that the modular multilevel converter operates according to a second modulation wave, and the second modulation wave is used to suppress the fundamental-frequency circulating current and the double-frequency circulating current.

[0028] Beneficial effects: in the embodiment of the present application, the first operation module is used for obtaining a first correction value according to a proportional-resonant control method, and superimposing the first correction value on a modulation wave, so that the modular multilevel converter operates according to the first modulation wave, and the first modulation wave is used for suppressing the double-frequency circulating current; the obtaining module obtains a first fundamental frequency circulating current component and a second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase, the first fundamental frequency circulating current component is a component of the fundamental frequency circulating current on the d-axis, and the second fundamental frequency circulating current component is a component of the fundamental frequency circulating current on the q-axis; when the sub-module of the modular multilevel converter fails, the modular multilevel converter operates asymmetrically, at this time, the fundamental frequency circulating current appears, which affects the stable operation of the modular multilevel converter, and the embodiment of the present application processes the fundamental frequency circulating current in the dq coordinate system through virtual synchronous rotating coordinate transformation, and realizes independent acquisition of the fundamental frequency circulating current in the fault phase of the sub-module. Compared with related technologies, the embodiment of the present application can not only suppress the double-frequency circulating current, but also suppress the fundamental frequency circulating current, without parallel use of multiple different frequency resonant controllers, reducing the complexity of system design, without the need to increase the operating voltage of the sub-module, reducing the requirement for device stress, and without the need to know the specific fault number information of the sub-module, reducing the communication burden of the control system.

[0029] In an optional embodiment, the obtaining module for obtaining the first fundamental frequency circulating current component and the second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase comprises: an obtaining unit for obtaining the fundamental frequency circulating current; a weighting processing unit for weighting processing the fundamental frequency circulating current to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current; and a filter processing unit for inputting the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current into a filter to obtain the first fundamental frequency circulating current component and the second fundamental frequency circulating current component.

[0030] In an optional embodiment, the obtaining unit comprises: a second band-pass filter subunit for obtaining the fundamental frequency circulating current through a second band-pass filter.

[0031] In a third aspect, the present application provides a computer device, comprising: a memory and a processor, which are in communication connection with each other, and the memory stores computer instructions, and the processor executes the computer instructions to perform the layered composite control based circulating current suppression method of the first aspect or any of the corresponding embodiments thereof.

[0032] In a fourth aspect, the present application provides a computer readable storage medium, which stores computer instructions, and the computer instructions are used to make the computer execute the layered composite control based circulating current suppression method of the first aspect or any of the corresponding embodiments thereof. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0034] Figure 1 is a flowchart of a circulating current suppression method based on hierarchical composite control according to an embodiment of the present application;

[0035] Figure 2 is a flowchart of another circulating current suppression method based on hierarchical composite control according to an embodiment of the present application;

[0036] Figure 3 is a schematic diagram of an equivalent model of a bridge arm of a modular multilevel converter according to an embodiment of the present application;

[0037] Figure 4 is a structural block diagram of a circulating current suppression device based on hierarchical composite control according to an embodiment of the present application;

[0038] Figure 5 is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0040] In the related art, there is also a proportional resonant circulating current suppression method based on split-phase control, which can realize suppression of double-frequency circulating current when MMC is in steady state operation or asymmetric operation, but cannot fully realize suppression of circulating current when MMC sub-modules are in fault. There is also a multiple-frequency proportional resonant circulating current suppression method, which can cope with suppression of circulating current at multiple frequencies such as fundamental frequency and double frequency when MMC is in steady state operation or asymmetric operation, but requires parallel use of multiple resonant controllers of different frequencies, which requires special stability design of control parameters, increasing the complexity of system design.

[0041] The embodiments of the present application provide a circulating current suppression method based on hierarchical composite control, which obtains a fundamental frequency circulating current component in a dq coordinate system to achieve the effect of suppressing the fundamental frequency circulating current.

[0042] According to the embodiment of the present application, a layered composite control-based circulating current suppression method is provided. It should be noted that the steps shown in the flowchart can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0043] In the embodiment, a layered composite control-based circulating current suppression method is provided, which can be used in the modular multilevel converter described above. Figure 1 The flowchart of the layered composite control-based circulating current suppression method according to the embodiment of the present application is shown in FIG. 1, which includes the following steps: Figure 1

[0044] In step S101, a first correction value is obtained according to a quasi-proportional-resonant control method, and the first correction value is superimposed on a modulation wave, so that the modular multilevel converter operates according to the first modulation wave, and the first modulation wave is used to suppress the double-frequency circulating current.

[0045] In some optional embodiments, the first band-pass filter combining a direct-current integrator and a second-order generalized integrator is used to obtain the double-frequency circulating current.

[0046] In order to achieve fast tracking of the double-frequency circulating current, the first band-pass filter combining a direct-current integrator and a second-order generalized integrator is used to achieve fast separation of the double-frequency circulating current when the quasi-proportional-resonant control method is used.

[0047] In step S102, a first fundamental-frequency circulating current component and a second fundamental-frequency circulating current component of the fundamental-frequency circulating current in the fault phase are obtained, the first fundamental-frequency circulating current component is a component of the fundamental-frequency circulating current on the d-axis, and the second fundamental-frequency circulating current component is a component of the fundamental-frequency circulating current on the q-axis.

[0048] The d-axis is the d-axis of the dq coordinate system, and the q-axis is the q-axis of the dq coordinate system.

[0049] In the embodiment of the present application, first, the second band-pass filter is used to extract the fundamental-frequency circulating current, then the fundamental-frequency circulating current is multiplied by the first weighting value and the second weighting value respectively, and the two obtained fundamental-frequency circulating currents are filtered, so that the first fundamental-frequency circulating current component and the second fundamental-frequency circulating current component of the fundamental-frequency circulating current are obtained.

[0050] In step S103, the first fundamental-frequency circulating current component and the second fundamental-frequency circulating current component are input into a first relationship, so that a first voltage fluctuation component and a second voltage fluctuation component are obtained, the first relationship is used to represent the relationship between the fundamental-frequency circulating current and the voltage fluctuation in the dq coordinate system, the first voltage fluctuation component is a component of the voltage fluctuation on the d-axis, and the second voltage fluctuation component is a component of the voltage fluctuation on the q-axis.

[0051] ​The dq coordinate system is a coordinate system used for describing three-phase voltage, and is composed of a conversion relationship between the dq coordinate system and the three-phase voltage. The dq coordinate system is a rotating coordinate system, and can convert the three-phase voltage into two components in the dq coordinate system, namely a d-axis component and a q-axis component. Exemplarily, the first voltage fluctuation component is the d-axis component, and the second voltage fluctuation component is the q-axis component.

[0052] In the embodiment of the present application, the first relationship is used to represent the relationship between the fundamental frequency circulating current and the voltage fluctuation in the dq coordinate system. The first fundamental frequency circulating current component and the second fundamental frequency circulating current component are input into the first relationship, and the first voltage fluctuation component and the second voltage fluctuation component can be obtained.

[0053] In step S104, a second correction value is calculated according to the first voltage fluctuation component and the second voltage fluctuation component.

[0054] In an optional embodiment, the calculation formula of the second correction value is used to represent the relationship between the voltage fluctuation component and the correction value. The unknowns in the calculation formula of the second correction value are the first voltage fluctuation component and the second voltage fluctuation component. Therefore, the first voltage fluctuation component and the second voltage fluctuation are input into the calculation formula of the second correction value, and the second correction value can be calculated.

[0055] In step S105, the second correction value is superimposed on the first modulation wave, so that the modular multilevel converter operates according to the second modulation wave. The second modulation wave is used to suppress the fundamental frequency circulating current and the double-frequency circulating current.

[0056] In the embodiment of the present application, the second correction value is superimposed on the first modulation wave to suppress the fundamental frequency circulating current and the double-frequency circulating current. The modulation wave is changed, and the signal recombination between the modulation wave and the carrier wave is also changed, so that the modular multilevel converter operates according to the signal recombination between the modulation wave and the carrier wave after the circulating current is suppressed.

[0057] In the embodiment of the present application, the first correction value is obtained according to the quasi-proportional-resonant control method, and the first correction value is superimposed on the modulation wave, so that the modular multilevel converter operates according to the first modulation wave, and the first modulation wave is used to suppress the double-frequency circulating current, that is, the double-frequency circulating current is suppressed according to the quasi-proportional-resonant control method. In the embodiment of the present application, the first fundamental-frequency circulating current component and the second fundamental-frequency circulating current component of the fundamental-frequency circulating current in the fault phase are obtained, the first fundamental-frequency circulating current component is the component of the fundamental-frequency circulating current on the d-axis, and the second fundamental-frequency circulating current component is the component of the fundamental-frequency circulating current on the q-axis. When the sub-module of the modular multilevel converter fails, the modular multilevel converter operates asymmetrically, at this time, the fundamental-frequency circulating current appears, which affects the stable operation of the modular multilevel converter. In the embodiment of the present application, the virtual synchronous rotating coordinate transformation is used to process in the dq coordinate system, so that the independent acquisition of the fundamental-frequency circulating current in the fault phase of the sub-module is realized. In the embodiment of the present application, the first fundamental-frequency circulating current component and the second fundamental-frequency circulating current component are input into the first relationship, so that the first voltage fluctuation component and the second voltage fluctuation component are obtained, the first relationship is used to represent the relationship between the fundamental-frequency circulating current and the voltage fluctuation in the dq coordinate system, the first voltage fluctuation component is the component of the voltage fluctuation on the d-axis, and the second voltage fluctuation component is the component of the voltage fluctuation on the q-axis. The second correction value is calculated according to the first voltage fluctuation component and the second voltage fluctuation component, and the second correction value is superimposed on the first modulation wave, so that the modular multilevel converter operates according to the second modulation wave. Compared with related technologies, the embodiment of the present application can suppress the double-frequency circulating current and the fundamental-frequency circulating current, does not need to use multiple different frequency resonant controllers in parallel, reduces the complexity of system design, does not need to increase the operating voltage of the sub-module, reduces the requirement for the stress of the device, and does not need to know the specific fault number information of the sub-module, and reduces the communication burden of the control system.

[0058] In the embodiment, a circulating current suppression method based on hierarchical composite control is provided, which can be used for the modular multilevel converter described above, Figure 2 is a flowchart of another circulating current suppression method based on hierarchical composite control according to the embodiment of the present application, as Figure 2 shown, the flowchart includes the following steps:

[0059] In step S201, the first correction value is obtained according to the quasi-proportional-resonant control method, and the first correction value is superimposed on the modulation wave, so that the modular multilevel converter operates according to the first modulation wave, and the first modulation wave is used to suppress the double-frequency circulating current. For details, please refer to step S101 of the embodiment shown in Figure 1 , which will not be described here again.

[0060] In step S202, a first fundamental frequency circulating current component and a second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase are obtained, the first fundamental frequency circulating current component being a component of the fundamental frequency circulating current on the d-axis, and the second fundamental frequency circulating current component being a component of the fundamental frequency circulating current on the q-axis.

[0061] Specifically, step S202 includes:

[0062] In step S2021, the fundamental frequency circulating current is obtained.

[0063] Specifically, the fundamental frequency circulating current is obtained through a second band-pass filter, wherein the band-pass filter refers to a filter capable of passing frequency components within a certain frequency range but attenuating frequency components in other ranges to a very low level, and the fundamental frequency circulating current of the fault phase of the modular multilevel converter is extracted through the second band-pass filter.

[0064] The transfer function of the second band-pass filter is:

[0065]

[0066] wherein G BPF2 (s) is the output of the transfer function of the second band-pass filter, k is a gain, s is an independent variable, and ω is an angular velocity.

[0067] In step S2022, the fundamental frequency circulating current is subjected to weighting processing to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current.

[0068] In some optional embodiments, the fundamental frequency circulating current is multiplied by a first weighting value and a second weighting value respectively to obtain the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current.

[0069] For example, the first weighting value is 2sin(ωt), and the second weighting value is 2cos(ωt), wherein ω is an angular velocity, and t is time.

[0070] In step S2023, the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current are input into a filter to obtain the first fundamental frequency circulating current component and the second fundamental frequency circulating current component.

[0071] wherein the filter is a noise filter, which can pass useful signals as much as possible without attenuation, and reflect useless signals as much as possible, and the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current are input into the filter, and the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current are filtered through the filter to obtain the first fundamental frequency circulating current component and the second fundamental frequency circulating current component.

[0072] In some optional embodiments, the transfer function of the filter is:

[0073]

[0074] wherein GNF (s) represents the output of the filter's transfer function, k is the gain, s is the independent variable, and ω is the angular velocity.

[0075] Step S203: Input the first fundamental frequency circulating current component and the second fundamental frequency circulating current component into the first relational expression to obtain the first voltage fluctuation component and the second voltage fluctuation component. The first relational expression is used to characterize the relationship between the fundamental frequency circulating current and the voltage fluctuation in the dq coordinate system. The first voltage fluctuation component is the component of the voltage fluctuation in the d-axis, and the second voltage fluctuation component is the component of the voltage fluctuation in the q-axis. For details, please refer to [link to relevant documentation]. Figure 1 Step S103 of the illustrated embodiment will not be described again here.

[0076] In some alternative implementations, the first relation is:

[0077]

[0078] Among them, u jz_f_d For the first voltage fluctuation component, u jz_f_q Let L be the inductance and i be the second voltage fluctuation component. jz_f_d i is the first fundamental frequency circulating component. jz_f_q ω represents the second fundamental frequency circulating component, and ω represents the angular velocity.

[0079] Specifically, such as Figure 3 The diagram shows the equivalent model of a modular multilevel converter bridge arm, including an upper bridge arm and a lower bridge arm, as well as a resistor R and an inductor L. The voltage of the upper bridge arm is u. jp The current is i jp The voltage of the lower bridge arm is u. j1 The current is i j1 The voltage across the equivalent resistance R section is u. j The current is i j Since the equivalent resistance of the bridge arms of the modular multilevel converter is very small, the equivalent resistance of the bridge arms can be ignored. Figure 3 The influence of R in the middle, therefore, Figure 3 The total voltage in is:

[0080]

[0081] Among them, U dc For the total voltage, u jp For the upper bridge arm voltage, u j1 This is the voltage of the lower bridge arm. Let L be the inductor voltage, and i be the inductance. jz This represents the inductor current.

[0082] Therefore, the voltage fluctuation component caused by the fundamental frequency circulating current is:

[0083]

[0084] wherein, U jz_f is the voltage fluctuation component caused by the fundamental circulating current, L is the inductance, i jz_f is the inductance current.

[0085] The first relationship can be obtained by converting the above voltage fluctuation component formula into the dq coordinate system.

[0086] In step S204, the second correction value is calculated according to the first voltage fluctuation component and the second voltage fluctuation component. For details, please refer to step S104 of the embodiment shown in Figure 1 In step S104 of the embodiment shown in

[0087] In some optional embodiments, the first voltage fluctuation component and the second voltage fluctuation component are input into the second relationship to obtain the second correction value, and the second relationship is used to represent the relationship between the second correction value and the first voltage fluctuation component and the second voltage fluctuation component.

[0088] In some optional embodiments, the second relationship is:

[0089]

[0090] wherein, Δu jz_f is the second correction value, u jz_f_d is the first voltage fluctuation component, u jz_f_q is the second voltage fluctuation component, ω is the angular velocity, and t is the time.

[0091] In step S205, the second correction value is superimposed on the first modulation wave, so that the modular multilevel converter operates according to the second modulation wave, and the second modulation wave is used to suppress the fundamental circulating current and the double-frequency circulating current. For details, please refer to step S105 of the embodiment shown in Figure 1 In step S105 of the embodiment shown in

[0092] In this embodiment, a circulating current suppression device based on hierarchical composite control is also provided, which is used to implement the above embodiments and preferred embodiments, and has been described above. As used below, the term "module" can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware, or a combination of software and hardware is also possible and is contemplated.

[0093] The embodiment provides a circulating current suppression device based on hierarchical composite control, as shown in Figure 4 comprises:

[0094] The first operation module 401 is configured to obtain a first correction value according to a proportional-resonant control method, and superimpose the first correction value on a modulation wave, so that the modular multilevel converter operates according to a first modulation wave, and the first modulation wave is used to suppress a double-frequency circulating current.

[0095] The obtaining module 402 is configured to obtain a first fundamental-frequency circulating current component and a second fundamental-frequency circulating current component of the fundamental-frequency circulating current in the fault phase, the first fundamental-frequency circulating current component being a component of the fundamental-frequency circulating current on a d-axis, and the second fundamental-frequency circulating current component being a component of the fundamental-frequency circulating current on a q-axis.

[0096] The voltage fluctuation component calculation module 403 is configured to input the first fundamental-frequency circulating current component and the second fundamental-frequency circulating current component into a first relationship formula to obtain a first voltage fluctuation component and a second voltage fluctuation component, the first relationship formula being used to represent a relationship between the fundamental-frequency circulating current and a voltage fluctuation in a dq coordinate system, the first voltage fluctuation component being a component of the voltage fluctuation on the d-axis, and the second voltage fluctuation component being a component of the voltage fluctuation on the q-axis.

[0097] The correction value calculation module 404 is configured to calculate a second correction value according to the first voltage fluctuation component and the second voltage fluctuation component.

[0098] The operation module 405 is configured to superimpose the second correction value on the first modulation wave, so that the modular multilevel converter operates according to a second modulation wave, and the second modulation wave is used to suppress the fundamental-frequency circulating current and the double-frequency circulating current.

[0099] Specifically, the obtaining module 402 includes:

[0100] The obtaining unit is configured to obtain the fundamental-frequency circulating current.

[0101] The weighting processing unit is configured to perform weighting processing on the fundamental-frequency circulating current to obtain a first weighted fundamental-frequency circulating current and a second weighted fundamental-frequency circulating current.

[0102] The filter processing unit is configured to input the first weighted fundamental-frequency circulating current and the second weighted fundamental-frequency circulating current into a filter to obtain the first fundamental-frequency circulating current component and the second fundamental-frequency circulating current component.

[0103] Specifically, the obtaining unit includes:

[0104] The second band-pass filter subunit is configured to obtain the fundamental-frequency circulating current through a second band-pass filter.

[0105] Further function descriptions of the above modules and units are the same as those of the above corresponding embodiments, and will not be described here.

[0106] In this embodiment, the circulating current suppression device based on hierarchical composite control is presented in the form of a functional unit. Here, a unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that execute one or more software or fixed programs, and / or other devices that can provide the above functions.

[0107] This invention also provides a computer device having the above-described features. Figure 4 The circulating flow suppression device shown is based on hierarchical composite control.

[0108] Please see Figure 5 , Figure 5 This is a schematic diagram of the structure of a computer device provided in an optional embodiment of the present invention, such as... Figure 5 As shown, the computer device includes one or more processors 10, memory 20, and interfaces for connecting the components, including high-speed interfaces and low-speed interfaces. The components communicate with each other via different buses and can be mounted on a common motherboard or otherwise installed as needed. The processors can process instructions executed within the computer device, including instructions stored in or on memory to display graphical information of a GUI on external input / output devices (such as display devices coupled to the interfaces). In some alternative implementations, multiple processors and / or multiple buses can be used with multiple memories and multiple memory modules, if desired. Similarly, multiple computer devices can be connected, each providing some of the necessary operations (e.g., as a server array, a group of blade servers, or a multiprocessor system). Figure 5 Take a processor 10 as an example.

[0109] Processor 10 may be a central processing unit, a network processor, or a combination thereof. Processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The programmable logic device may be a complex programmable logic device (CAMP), a field-programmable gate array (FPGA), a general-purpose array logic (GPA), or any combination thereof.

[0110] The memory 20 stores instructions executable by at least one processor 10 to cause the at least one processor 10 to perform the method shown in the above embodiments.

[0111] The memory 20 can include a program storage area and a data storage area. The program storage area can store an operating system, application programs required for at least one function, and the like. The data storage area can store data created according to the use of the computer device, and the like. In addition, the memory 20 can include a high-speed random access memory, and can further include a non-transitory memory such as at least one of a magnetic disk storage device, a flash memory device, or other non-transitory solid state memory device. In some alternative embodiments, the memory 20 can optionally include a memory disposed remotely from the processor 10, which can be connected to the computer device through a network. Examples of the network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof.

[0112] The memory 20 can include a volatile memory such as a random access memory, and can further include a non-volatile memory such as a flash memory, a hard disk, or a solid state disk, and a combination thereof.

[0113] The computer device further includes a communication interface 30 for communication of the computer device with other devices or communication networks.

[0114] The embodiments of the present application also provide a computer readable storage medium. The method according to the embodiments of the present application can be implemented in hardware, firmware, or as software code to be recorded in a storage medium, or originally stored in a remote storage medium or a non-transitory machine readable storage medium to be downloaded through a network and stored in a local storage medium, so that the method described herein can be processed by such software using a general purpose computer, a special purpose processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, an optical disk, a read-only memory, a random access memory, a flash memory, a hard disk, or a solid state disk, and the like. Further, the storage medium can include a combination of the above-mentioned storage media. It can be understood that the computer, the processor, the microprocessor controller, or the programmable hardware includes a storage component that can store or receive software or computer code, which, when accessed and executed by the computer, the processor, or the hardware, implements the method shown in the above embodiments.

[0115] Although the embodiments of the present application have been described with reference to the accompanying drawings, various modifications and changes can be suggested to one skilled in the art, and it is intended that the present application encompass such modifications and changes as fall within the scope of the appended claims.

Claims

1. A circulating current suppression method based on hierarchical composite control, characterized in that, The method includes: A first correction value is obtained according to the quasi-proportional resonance control method, and the first correction value is superimposed on the modulation wave so that the modular multilevel converter operates according to the first modulation wave, which is used to suppress the second harmonic circulating current. Obtain the first fundamental frequency circulating current component and the second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase. The first fundamental frequency circulating current component is the component of the fundamental frequency circulating current on the d-axis, and the second fundamental frequency circulating current component is the component of the fundamental frequency circulating current on the q-axis. The first fundamental frequency circulating current component and the second fundamental frequency circulating current component are input into the first relational expression to obtain the first voltage fluctuation component and the second voltage fluctuation component. The first relational expression is used to characterize the relationship between the fundamental frequency circulating current and the voltage fluctuation in the dq coordinate system. The first voltage fluctuation component is the component of the voltage fluctuation in the d-axis, and the second voltage fluctuation component is the component of the voltage fluctuation in the q-axis. Calculate the second correction value based on the first voltage fluctuation component and the second voltage fluctuation component; The second correction value is superimposed on the first modulation wave so that the modular multilevel converter operates according to the second modulation wave, which is used to suppress the fundamental frequency circulating current and the second harmonic frequency circulating current. The step of calculating the second correction value based on the first voltage fluctuation component and the second voltage fluctuation component includes: inputting the first voltage fluctuation component and the second voltage fluctuation component into a second relational expression to obtain the second correction value, wherein the second relational expression is used to characterize the relationship between the second correction value and the first voltage fluctuation component and the second voltage fluctuation component; The second relation is: in, This is the second correction value. This is the first voltage fluctuation component. This is the second voltage fluctuation component. Angular velocity, t For time.

2. The method according to claim 1, characterized in that, Before obtaining the first correction value according to the quasi-proportional resonance control method, the method further includes: The second harmonic circulating current is obtained by using a first bandpass filter that combines a DC integrator and a second-order generalized integrator.

3. The method according to claim 1 or 2, characterized in that, The acquisition of the first and second fundamental frequency circulating components of the fundamental frequency circulating current in the fault phase includes: Obtain the fundamental frequency circulating current; The fundamental frequency circulating current is weighted to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current; The first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current are input into the filter to obtain the first fundamental frequency circulating current component and the second fundamental frequency circulating current component.

4. The method according to claim 3, characterized in that, The transfer function of the filter is: in, The output of the filter's transfer function. For gain, As the independent variable, ω is the angular velocity.

5. The method according to claim 3, characterized in that, The acquisition of the fundamental frequency circulating current includes: The fundamental frequency circulating current is obtained through a second bandpass filter.

6. The method according to claim 5, characterized in that, The transfer function of the second bandpass filter is: in, The output of the transfer function of the second bandpass filter. For gain, As the independent variable, ω is the angular velocity.

7. The method according to claim 3, characterized in that, The weighting process of the fundamental frequency circulating current to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current includes: The fundamental frequency circulating current is multiplied by a first weighting value and a second weighting value to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current.

8. The method according to claim 1 or 2, characterized in that, The first relation is: in, This is the first voltage fluctuation component. This is the second voltage fluctuation component. For inductance, This is the first fundamental frequency circulating component. This is the second fundamental frequency circulating component. ω is the angular velocity.

9. A circulating current suppression device based on hierarchical composite control, characterized in that, The device includes: The first operating module is used to obtain a first correction value according to the quasi-proportional resonance control method, and to superimpose the first correction value onto the modulation wave so that the modular multilevel converter operates according to the first modulation wave, the first modulation wave being used to suppress the second harmonic circulating current. The acquisition module is used to acquire the first fundamental frequency circulating current component and the second fundamental frequency circulating current component of the fundamental frequency circulating current in the fault phase. The first fundamental frequency circulating current component is the component of the fundamental frequency circulating current on the d-axis, and the second fundamental frequency circulating current component is the component of the fundamental frequency circulating current on the q-axis. The voltage fluctuation component calculation module is used to input the first fundamental frequency circulating current component and the second fundamental frequency circulating current component into the first relational expression to obtain the first voltage fluctuation component and the second voltage fluctuation component. The first relational expression is used to characterize the relationship between the fundamental frequency circulating current and the voltage fluctuation in the dq coordinate system. The first voltage fluctuation component is the component of the voltage fluctuation in the d-axis, and the second voltage fluctuation component is the component of the voltage fluctuation in the q-axis. The correction value calculation module is used to calculate a second correction value based on the first voltage fluctuation component and the second voltage fluctuation component; The second operating module is used to superimpose the second correction value onto the first modulation wave so that the modular multilevel converter operates according to the second modulation wave, which is used to suppress the fundamental frequency circulating current and the second harmonic frequency circulating current. The step of calculating the second correction value based on the first voltage fluctuation component and the second voltage fluctuation component includes: inputting the first voltage fluctuation component and the second voltage fluctuation component into a second relational expression to obtain the second correction value, wherein the second relational expression is used to characterize the relationship between the second correction value and the first voltage fluctuation component and the second voltage fluctuation component; The second relation is: in, This is the second correction value. This is the first voltage fluctuation component. This is the second voltage fluctuation component. Angular velocity, t For time.

10. The apparatus according to claim 9, characterized in that, The acquisition module is used to acquire the first fundamental frequency circulating current component and the second fundamental frequency circulating current component in the fault phase, including: Acquisition unit, used to acquire fundamental frequency circulating current; A weighted processing unit is used to perform weighted processing on the fundamental frequency circulating current to obtain a first weighted fundamental frequency circulating current and a second weighted fundamental frequency circulating current; The filter processing unit is used to input the first weighted fundamental frequency circulating current and the second weighted fundamental frequency circulating current into the filter to obtain the first fundamental frequency circulating current component and the second fundamental frequency circulating current component.

11. The apparatus according to claim 10, characterized in that, The acquisition unit includes: The second bandpass filter subunit is used to obtain the fundamental frequency circulating current through the second bandpass filter.

12. A computer device, characterized in that, include: A memory and a processor are interconnected, the memory storing computer instructions, and the processor executing the computer instructions to perform the circulating current suppression method based on hierarchical composite control as described in any one of claims 1 to 8.

13. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing a computer to execute the circulation suppression method based on hierarchical composite control as described in any one of claims 1 to 8.

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