Method for controlling inter-arm capacitor voltage balance of modular multilevel matrix converter

Abstract

The application discloses a control method for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter, which comprises the following steps: defining relevant electrical quantities related to the modular multilevel matrix converter; defining positive and negative sequence cyclic component forms of low and high frequencies of the modular multilevel matrix converter and control strategies of the cyclic components based on the relevant electrical quantities; adding module capacitor voltages of nine bridge arms of the modular multilevel matrix converter and filtering the added voltages by using a low-pass filter to obtain direct current components of the capacitor voltages of the nine bridge arms; performing double alpha beta 0 transformation on the direct current components of the capacitor voltages of the nine bridge arms to obtain eight u Cαβ0 / αβ0 components; controlling the eight u Cαβ0 / αβ0 components based on the positive and negative sequence cyclic component forms of low and high frequencies and the control strategies of the cyclic components to obtain four groups of sequence cyclic components of the nine bridge arms, and then adding the four groups of sequence cyclic components to obtain voltage modulation waveforms of the cyclic components of the nine bridge arms.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible low-frequency power transmission, and more particularly, to a control method for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter. BACKGROUND

[0002] Flexible low-frequency power transmission technology is a beneficial supplement to power frequency AC power transmission and DC power transmission by reducing power transmission frequency to improve AC power transmission capacity, while having the characteristics of AC electromagnetic transformation and zero-crossing breaking. A high-voltage and high-capacity modular multilevel matrix converter (M3C) bears important functions such as frequency conversion, power transmission, and flexible regulation, and is a core device in a flexible low-frequency power transmission system. A large number of floating capacitors are included in the M3C, and maintaining the voltage balance of these capacitors is a prerequisite for normal operation of the M3C. The capacitor voltage balance of the M3C can be divided into three levels, namely, total capacitor voltage balance, capacitor voltage balance between bridge arms, and capacitor voltage balance of each sub-module within a bridge arm. The capacitor voltage balance between bridge arms as an intermediate level has multiple control dimensions and is difficult to control, and is the focus of capacitor voltage balance control of the bridge arm.

[0003] However, the existing control method for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter cannot perform full decoupling control in horizontal, vertical, and diagonal dimensions. SUMMARY

[0004] To solve the problems of the prior art, the present application provides a control method for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter.

[0005] According to one aspect of the present application, a control method for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter is provided, comprising:

[0006] In a flexible low-frequency power transmission system, a modular multilevel matrix converter is connected to a power frequency system and a low-frequency system on both sides, and then related electrical quantities related to the modular multilevel matrix converter are defined. The related electrical quantities include three-phase voltage and three-phase current on the power frequency side, and three-phase voltage and three-phase current on the low-frequency side.

[0007] Based on the related electrical quantities related to the modular multilevel matrix converter, a power frequency positive and negative sequence circular component form and a low-frequency positive and negative sequence circular component form of the modular multilevel matrix converter are defined.

[0008] A control strategy for each circular component of the modular multilevel matrix converter is determined.

[0009] The module capacitor voltages of nine bridge arms of the modular multilevel matrix converter are added and filtered by a low-pass filter to obtain DC components of the capacitor voltages of the nine bridge arms;

[0010] The DC components of the capacitor voltages of the nine bridge arms are double-alpha-beta-0 transformed to obtain eight u Cαβ0 / αβ0 components;

[0011] Based on the defined power frequency positive and negative sequence cyclic component forms and low frequency positive and negative sequence cyclic component forms and the control strategies of the cyclic components, the eight u Cαβ0 / αβ0 components are controlled to obtain four groups of sequence cyclic components of the nine bridge arms;

[0012] The four groups of sequence cyclic components are added to obtain voltage modulation waveforms of the cyclic components of the nine bridge arms.

[0013] Optionally, the power frequency positive and negative sequence cyclic component forms include a power frequency positive sequence cyclic component form and a power frequency negative sequence cyclic component form, wherein

[0014] The power frequency positive sequence cyclic component form is:

[0015]

[0016] In the formula, u scirp1 , u scirp2 , u scirp3 constitute a group of power frequency positive sequence AC components, ω s is a power frequency angular frequency, is a power frequency positive sequence cyclic component phase angle;

[0017] The power frequency negative sequence cyclic component form is:

[0018]

[0019] In the formula, u scirn1 , u scirn2 , u scirn3 constitute a group of power frequency negative sequence AC components, ω s is a power frequency angular frequency, is a power frequency negative sequence cyclic component phase angle.

[0020] Optionally, the low frequency positive and negative sequence cyclic component forms include a low frequency positive sequence cyclic component form and a low frequency negative sequence cyclic component form, wherein

[0021] The low frequency positive sequence cyclic component form is:

[0022]

[0023] In the formula, u mcirp1 , umcirp2 ,u mcirp3 constitute a group of low-frequency positive-sequence alternating components, ω m is a low-frequency angular frequency, is a low-frequency positive-sequence cyclic component phase angle;

[0024] The low-frequency negative-sequence cyclic component has two forms:

[0025]

[0026] In the formula, u mcirn1 ,u mcirn2 ,u mcirn3 constitute a group of low-frequency negative-sequence alternating components, ω m is a low-frequency angular frequency, is a low-frequency negative-sequence cyclic component phase angle.

[0027] Optionally, each cyclic component of the modular multilevel matrix converter includes a bridge-arm capacitor voltage component u Cα0 and u Cβ0 based on a power-frequency positive-sequence cyclic component, a bridge-arm capacitor voltage component u C0α and u C0β based on a low-frequency positive-sequence cyclic component, a bridge-arm capacitor voltage component u Cαα and u Cαβ based on a power-frequency negative-sequence cyclic component, and a bridge-arm capacitor voltage component u Cβα and u Cββ based on a low-frequency negative-sequence cyclic component; wherein

[0028] u Cα0 , u Cβ0 , u C0α and u C0β are controlled by two groups of positive-sequence cyclic components, including a group of power-frequency positive-sequence cyclic components and a group of low-frequency positive-sequence cyclic components.

[0029] u Cαα , u Cαβ , u Cβα and u Cββ are controlled by two groups of negative-sequence cyclic components, including a group of power-frequency negative-sequence cyclic components and a group of low-frequency negative-sequence cyclic components, the power-frequency negative-sequence cyclic components having two forms, and the low-frequency negative-sequence cyclic components having two forms.

[0030] According to still another aspect of the present application, there is provided a control device for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter, comprising:

[0031] The first definition module is configured to connect a power frequency system and a low frequency system on both sides of the modular multilevel matrix converter of the flexible low frequency power transmission system, and then define relevant electrical quantities related to the modular multilevel matrix converter; wherein the relevant electrical quantities include three-phase voltage and three-phase current on the power frequency side, and three-phase voltage and three-phase current on the low frequency side.

[0032] The second definition module is configured to define a power frequency positive and negative sequence circular component form and a low frequency positive and negative sequence circular component form of the modular multilevel matrix converter based on the relevant electrical quantities related to the modular multilevel matrix converter.

[0033] The control strategy determination module is configured to determine a control strategy of each circular component of the modular multilevel matrix converter.

[0034] The DC component acquisition module is configured to add the module capacitor voltages of the nine bridge arms of the modular multilevel matrix converter, and filter the sum by using a low pass filter to obtain a DC component of the capacitor voltages of the nine bridge arms.

[0035] The transformation module is configured to perform double αβ0 transformation on the DC component of the capacitor voltages of the nine bridge arms to obtain eight u Cαβ0 / αβ0 components.

[0036] The control module is configured to control the eight u Cαβ0 / αβ0 components based on the defined power frequency positive and negative sequence circular component form and the low frequency positive and negative sequence circular component form and the control strategy of each circular component to obtain four groups of sequence circular components of the nine bridge arms.

[0037] The component addition module is configured to add the four groups of sequence circular components to obtain voltage modulation waveforms of the circular components of the nine bridge arms.

[0038] Optionally, the power frequency positive and negative sequence circular component form includes a power frequency positive sequence circular component form and a power frequency negative sequence circular component form, wherein

[0039] The power frequency positive sequence circular component form is:

[0040]

[0041] In the formula, u scirp1 , u scirp2 , u scirp3 constitute a group of power frequency positive sequence alternating current components, ω s is a power frequency angular frequency, is a power frequency positive sequence circular component phase angle.

[0042] The power frequency negative sequence circular component form is:

[0043]

[0044] wherein u scirn1 scirn2 scirn3 constitute a set of power frequency negative sequence AC components, ω s is a power frequency angular frequency, is a power frequency negative sequence circulating component phase angle.

[0045] Optionally, the low frequency positive and negative sequence circulating component forms include a low frequency positive sequence circulating component form and a low frequency negative sequence circulating component form, wherein

[0046] The low frequency positive sequence circulating component form is:

[0047]

[0048] wherein u mcirp1 mcirp2 mcirp3 constitute a set of low frequency positive sequence AC components, ω m is a low frequency angular frequency, is a low frequency positive sequence circulating component phase angle.

[0049] The low frequency negative sequence circulating component form is:

[0050]

[0051] wherein u mcirn1 mcirn2 mcirn3 constitute a set of low frequency negative sequence AC components, ω m is a low frequency angular frequency, is a low frequency negative sequence circulating component phase angle.

[0052] Optionally, each circulating component of the modular multilevel matrix converter includes a bridge arm capacitor voltage component u Cα0 and u Cβ0 based on the power frequency positive sequence circulating component, a bridge arm capacitor voltage component u C0α and u C0β based on the low frequency positive sequence circulating component, a bridge arm capacitor voltage component u Cαα and u Cαβ based on the power frequency negative sequence circulating component, and a bridge arm capacitor voltage component u Cβα and u Cββ based on the low frequency negative sequence circulating component; wherein

[0053] u Cα0 , u Cβ0 , u C0α and u C0β are controlled by two sets of positive sequence circulating components, including a set of power frequency positive sequence circulating components and a set of low frequency positive sequence circulating components.​​​​​​

[0054] u Cαα u Cαβ u Cβα and u Cββ It is controlled by two sets of negative sequence cyclic components, including a set of power frequency negative sequence cyclic components and a set of low frequency negative sequence cyclic components. The power frequency negative sequence cyclic components have two forms, and the low frequency negative sequence cyclic components have two forms.

[0055] According to another aspect of the present invention, a computer-readable storage medium is provided, the storage medium storing a computer program for performing the methods described in any of the above aspects of the present invention.

[0056] According to another aspect of the present invention, an electronic device is provided, the electronic device comprising: a processor; a memory for storing executable instructions of the processor; the processor being configured to read the executable instructions from the memory and execute the instructions to implement the method described in any of the preceding aspects of the present invention.

[0057] This invention utilizes the sequential cyclic components of the frequencies on both sides to achieve fully decoupled control of the inter-arm capacitor voltage in three dimensions: horizontal, vertical, and diagonal. This invention also decouples the influence of the power generated by the cyclic voltage and current on the inter-arm capacitor voltage, effectively controlling the balanced stability of the high-voltage, high-capacity M3C bridge arm capacitor voltage. This avoids excessively high or low individual bridge arm capacitor voltages caused by poor bridge arm parameter uniformity or asymmetrical faults in the two systems, as well as potential protection action blocking and system malfunction. Attached Figure Description

[0058] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0059] Figure 1 This is a schematic diagram of the converter topology of a flexible low-frequency power transmission system according to an embodiment of the present invention;

[0060] Figure 2 This is a basic control block diagram of M3C in a flexible low-frequency power transmission system according to an embodiment of the present invention;

[0061] Figure 3 This is a flowchart illustrating a control method for balancing capacitor voltage between bridge arms of a modular multilevel matrix converter according to an embodiment of the present invention.

[0062] Figure 4 This is a block diagram of bridge arm capacitor voltage control based on power frequency positive sequence cyclic components in one embodiment of the present invention;

[0063] Figure 5is a bridge arm capacitor voltage component control block diagram based on a low-frequency positive sequence cyclic component in an embodiment of the present application;

[0064] Figure 6 is a bridge arm capacitor voltage component control block diagram based on a low-frequency negative sequence cyclic component in an embodiment of the present application;

[0065] Figure 7 is a bridge arm capacitor voltage component control block diagram based on a power frequency negative sequence cyclic component in an embodiment of the present application;

[0066] Figure 8 is an M3C bridge arm inter-capacitor voltage balance control block diagram based on a sequence cyclic component in an embodiment of the present application;

[0067] Figure 9 is a typical system schematic diagram in an embodiment of the present application;

[0068] Figure 10 is a control effect comparison diagram in an embodiment of the present application;

[0069] Figure 11 is a structural schematic diagram of an electronic device in an embodiment of the present application. DETAILED DESCRIPTION

[0070] The embodiments of the present application will be described in detail below, and the following description refers to the accompanying drawings, in which the same numbers in different drawings represent the same or similar elements unless otherwise indicated. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0071] It should be understood that, in the description of all embodiments of the present application, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0072] Figure 1 is a flexible low-frequency power transmission system converter topology schematic diagram, Figure 2 is a basic control block diagram of M3C in a flexible low-frequency power transmission system. As Figure 1 and Figure 2As shown, the modulation voltage of the bridge arm of M3C is the sum of the modulation voltage of the low-frequency side control output and the modulation voltage of the bridge arm inter-capacitance voltage balance control output. On this basis, combined with the modulation voltage of the module capacitance voltage balance control output in the bridge arm, the modulation voltage of each module in M3C can be obtained to achieve the control effect of M3C.

[0073] Figure 3 The flowchart of the control method of the inter-bridge arm capacitance voltage balance of the modular multilevel matrix converter provided by the application is shown. As shown in the figure, Figure 3 The control method of the inter-bridge arm capacitance voltage balance of the modular multilevel matrix converter comprises the following steps:

[0074] Step S1: connecting the power frequency system and the low-frequency system on both sides of the modular multilevel matrix converter of the flexible low-frequency power transmission system, and then defining the related electrical quantities involved in the modular multilevel matrix converter; wherein the related electrical quantities include the three-phase voltage and the three-phase current on the power frequency side, and the three-phase voltage and the three-phase current on the low-frequency side.

[0075] In the embodiment of the application, as shown in the figure, Figure 1 In the embodiment of the application, as shown in the figure,

[0076] 1) define the three-phase voltage and current on the power frequency side as:

[0077]

[0078] wherein, u u , u v , u w are the three-phase voltage on the power frequency side, U s is the power frequency voltage amplitude, ω s is the power frequency; i u , i v , i w are the three-phase current on the power frequency side, I s is the power frequency current amplitude, is the power frequency current phase angle.

[0079] 2) define the three-phase voltage and current on the low-frequency side as:

[0080]

[0081] wherein, u a , u b , u c are the three-phase voltage on the low-frequency side, U m is the low-frequency voltage amplitude, ω m is the low-frequency frequency; ia b c is the low-frequency three-phase current, I m is the low-frequency current amplitude, is the low-frequency current phase angle.

[0082] The relationship between the 9 bridge arm capacitor voltages of M3C and the bridge arm power can be obtained as follows

[0083]

[0084] wherein u Cxy is the DC component of the bridge arm capacitor voltage, p xy is the bridge arm instantaneous power (x = a, b, c, y = u, v, w), C is the module capacitance value, is the control reference value of the capacitor voltage, and n is the number of modules per bridge arm.

[0085] After double αβ transformation, we can obtain:

[0086]

[0087] For M3C bridge arm voltage bridge arm capacitor voltage balance, mainly aiming at the eight components of p αα , p αβ , p βα , p ββ , p α0 , p β0 , p 0α , p 0β , the control effect of capacitor voltage is achieved.

[0088] Step S2: Based on the related electrical quantities involved in the modular multilevel matrix converter, define the positive and negative sequence cyclic component form of the modular multilevel matrix converter at power frequency and the low-frequency positive and negative sequence cyclic component form;

[0089] Optionally, the positive and negative sequence cyclic component form at power frequency includes a positive sequence cyclic component form at power frequency and a negative sequence cyclic component form at power frequency, wherein

[0090] The positive sequence cyclic component form at power frequency is:

[0091]

[0092] In the formula, u scirp1 , u scirp2 , u scirp3 constitute a group of positive sequence alternating current components at power frequency, ω s is the power frequency angular frequency, is the positive sequence cyclic component phase angle at power frequency; ​​

[0093] The form of the power frequency negative sequence alternating component is:

[0094]

[0095] In the formula, u scirn1 ,u scirn2 ,u scirn3 constitute a group of power frequency positive sequence alternating components, ω s is a power frequency angular frequency, is a power frequency negative sequence alternating component phase angle.

[0096] Optionally, the form of the low frequency positive and negative sequence alternating component includes a low frequency positive sequence alternating component form and a low frequency negative sequence alternating component form, wherein

[0097] The form of the low frequency positive sequence alternating component is:

[0098]

[0099] In the formula, u mcirp1 ,u mcirp2 ,u mcirp3 constitute a group of low frequency positive sequence alternating components, ω m is a low frequency angular frequency, is a low frequency positive sequence alternating component phase angle.

[0100] The form of the low frequency negative sequence alternating component is:

[0101]

[0102] In the formula, u mcirn1 ,u mcirn2 ,u mcirn3 constitute a group of low frequency negative sequence alternating components, ω m is a low frequency angular frequency, is a low frequency negative sequence alternating component phase angle.

[0103] In the embodiments of the present application, the form of the power low frequency positive and negative sequence alternating component is defined by the following steps:

[0104] 1) defining the form of the power frequency positive sequence alternating component

[0105]

[0106] In the formula, u scirp1 ,u scirp2 ,u scirp3 constitute a group of power frequency positive sequence alternating components,

[0107]

[0108]

[0109]

[0110] where ω = 2πf s is the power frequency angular frequency, is the power frequency positive sequence rotating component phase angle

[0111] 2) Define the power frequency negative sequence rotating component form

[0112]

[0113] where ω = 2πf scirn1 is the power frequency angular frequency, scirn2 is the power frequency angular frequency, scirn3 forms a set of power frequency negative sequence alternating components

[0114]

[0115]

[0116]

[0117] where ω = 2πf is the low frequency angular frequency, is the low frequency positive sequence rotating component phase angle

[0118] 3) Define the low frequency positive sequence rotating component form

[0119]

[0120] where ω = 2πf mcirp1 is the low frequency angular frequency, mcirp2 is the low frequency angular frequency, mcirp3 forms a set of low frequency positive sequence alternating components

[0121]

[0122]

[0123]

[0124] where ω = 2πf m is the low frequency angular frequency, is the low frequency negative sequence rotating component phase angle

[0125] 4) Define the low frequency negative sequence rotating component form

[0126]

[0127] where ω = 2πf mcirn1 is the low frequency angular frequency, mcirn2 is the low frequency angular frequency, mcirn3 forms a set of low frequency negative sequence alternating components

[0128]

[0129]

[0130]

[0131] In the formula: The phase angle is for the low-frequency negative sequence cyclic component.

[0132] Step S3: Determine the control strategy for each cyclic component of the modular multilevel matrix converter;

[0133] Optionally, each cyclic component of the modular multilevel matrix converter includes the bridge arm capacitor voltage component u based on the power frequency positive sequence cyclic component. Cα0 and u Cβ0 Bridge arm capacitor voltage component u based on low-frequency positive sequence cyclic component C0α and u C0β Bridge arm capacitor voltage component u based on power frequency negative sequence cyclic component Cαα and u Cαβ Bridge arm capacitor voltage component u based on low-frequency negative sequence cyclic component Cβα and u Cββ ;where u Cα0 u Cβ0 u C0α and u C0β Controlled by two sets of positive-sequence cyclic components, including one set of power frequency positive-sequence cyclic components and one set of low-frequency positive-sequence cyclic components; u Cαα u Cαβ u Cβα and u Cββ It is controlled by two sets of negative sequence cyclic components, including a set of power frequency negative sequence cyclic components and a set of low frequency negative sequence cyclic components. The power frequency negative sequence cyclic components have two forms, and the low frequency negative sequence cyclic components have two forms.

[0134] In this embodiment of the invention, the control strategy for each cyclic component is determined through the following steps:

[0135] 1) Bridge arm capacitor voltage component u based on power frequency positive sequence cyclic component Cα0 u Cβ0 and the bridge arm capacitor voltage component u based on the low-frequency positive sequence cyclic component C0α u C0β It is controlled by two sets of positive sequence cyclic components, including a set of power frequency positive sequence cyclic components and a set of low frequency positive sequence cyclic components.

[0136] In order to control u Cα0 and u Cβ0 It is necessary to inject a positive-sequence cyclic component of the power frequency into the bridge arm. Taking the first type of positive-sequence cyclic component of the power frequency as an example, p α0 and pβ0 The relationship between the positive-sequence cyclic component of the power frequency and its components in the dq coordinate system is as follows:

[0137]

[0138]

[0139] In the formula: L is the inductance value of the bridge arm;

[0140] but

[0141] U scirp_d =k1u Cα0 -k2u Cβ0

[0142] U scirp_q =k2u Cα0 +k1u Cβ0

[0143] In the formula

[0144]

[0145]

[0146] In the formula: U sd and U sq Let I be the component of the power frequency system voltage in the dq coordinate system. sd and I sq Let be the component of the power frequency system current in the dq coordinate system.

[0147] Bridge arm capacitor voltage component u based on power frequency positive sequence cyclic component Cα0 u Cβ0 Control such as Figure 4 As shown, a cross-decoupling control was designed to eliminate u in the dq axis. Cα0 and u Cβ0 The coupling is achieved by subtracting the voltage of the cross-decoupled bridge arm capacitor from the reference value. This difference, after passing through a proportional-integral (PI) regulator, yields the two components U of the positive-sequence cyclic voltage in the dq axis. scirp_d U scirp_q Then, through the inverse Parker transform based on the power frequency phase, the two components in the dq coordinate system are transformed into three power frequency components in the abc coordinate system.

[0148] In order to control u C0α and u C0β This requires injecting low-frequency positive-sequence cyclic components into the bridge arm. Taking the first type of low-frequency positive-sequence cyclic component as an example, p 0α and p 0β The relationship between the low-frequency positive-sequence cyclic component and its components in the dq coordinate system is as follows:

[0149]

[0150]

[0151] wherein: then

[0152] U mcirp_d = k3u C0α + k4u C0β

[0153] U mcirp_q = -k4u C0α + k3u C0β

[0154] wherein

[0155]

[0156]

[0157] wherein: U md and U mq are the components of the low-frequency system voltage in the dq coordinate system, I md and I mq are the components of the low-frequency system current in the dq coordinate system.

[0158] The control of the bridge-arm capacitor voltage components u C0α , u C0β based on the low-frequency positive-sequence circulating components is shown in Fig. Figure 5 A cross-decoupling control is designed to eliminate the coupling of u C0α and u C0β in the dq axis. After the cross-decoupling of the bridge-arm capacitor voltage, the difference between the decoupled voltage and the reference value is obtained, and after the proportional-integral (PI) regulator, two components of the positive-sequence circulating voltage in the dq axis, U mcirp_d , U mcirp_q are obtained. Then, by means of the inverse Park transformation based on the low-frequency phase, the two components in the dq coordinate system are converted into three low-frequency components in the abc coordinate system.

[0159] 2) The bridge-arm capacitor voltage components u Cαα , u Cαβ , u Cβα and u Cββ based on the low-frequency negative-sequence circulating components are controlled by two groups of negative-sequence circulating components. The first form of the fundamental-frequency negative-sequence component and the low-frequency negative-sequence component have the same control effect on p αα and p ββ . The second form of the fundamental-frequency negative-sequence component and the second form of the low-frequency negative-sequence component have the same control effect on p αβ and pβα have the same control effect. Therefore, there are four feasible schemes to meet the requirement of control freedom:

[0160] Scheme 1: the first form of power frequency negative sequence component and the second form of low frequency negative sequence component

[0161] Scheme 2: the second form of power frequency negative sequence component and the first form of low frequency negative sequence component

[0162] Scheme 3: the first form of power frequency negative sequence component and the second form of power frequency negative sequence component

[0163] Scheme 4: the first form of low frequency negative sequence component and the second form of low frequency negative sequence component

[0164] Taking Scheme 1 as an example to design the control method.

[0165] For the first form of power frequency negative sequence component, the relationship between the sequence circular component in dq axis and the bridge arm capacitor voltage component u Cαα , u Cαβ , u Cβα and u Cββ is expressed as:

[0166]

[0167]

[0168] In the formula: then

[0169] U scirn_d = k5(u Cαα + u Cββ ) - k6(u Cαβ - u Cβα )

[0170] U scirn_q = k6(u Cαα + u Cββ ) + k5(u Cαβ - u Cβα )

[0171] In the formula:

[0172] For the second form of low frequency negative sequence component, the relationship between the sequence circular component in dq axis and the bridge arm capacitor voltage component u Cαα , u Cαβ , u Cβα and u Cββ is expressed as:

[0173]

[0174]

[0175] In the formula: but

[0176] U mcirn_d =k7(u Cαα -u Cββ )+k8(u Cαβ +u Cβα )

[0177] U mcirn_q =-k8(u Cαα -u Cββ )+k7(u Cαβ +u Cβα )

[0178] In the formula:

[0179] Bridge arm capacitor voltage component u based on high-frequency and low-frequency negative sequence cyclic components. Cαα u Cαβ u Cβα and u Cββ The control is as follows Figure 6 and 7 As shown. Among them, Figure 6 The design incorporates cross-decoupling control to eliminate u-axis interference in the dq axis. Cαα +u Cββ and u Cαβ -u Cβα The coupling is achieved by subtracting the voltage of the cross-decoupled bridge arm capacitor from the reference value. This difference, after passing through a proportional-integral (PI) regulator, yields the two components U of the positive-sequence cyclic voltage in the dq axis. scirn_d U scirn_q Then, through the inverse Parker transform based on the power frequency phase, the two components in the dq coordinate system are transformed into three power frequency components in the abc coordinate system.

[0180] Figure 7 The design incorporates cross-decoupling control to eliminate u-axis interference in the dq axis. Cαα -u Cββ and u Cαβ +u Cβα The coupling is achieved by subtracting the voltage of the cross-decoupled bridge arm capacitor from the reference value. This difference, after passing through a proportional-integral (PI) regulator, yields the two components U of the positive-sequence cyclic voltage in the dq axis. mcirn_d U mcirn_q Then, by using the inverse Parker transform based on the low-frequency phase, the two components in the dq coordinate system are transformed into three low-frequency components in the abc coordinate system.

[0181] Step S4: sum the module capacitor voltages of the nine bridge arms of the modular multilevel matrix converter, and filter with a low-pass filter to obtain the DC components of the capacitor voltages of the nine bridge arms;

[0182] Step S5: double αβ0 transform the DC components of the capacitor voltages of the nine bridge arms to obtain eight u Cαβ0 / αβ0 components;

[0183] Step S6: control the eight u Cαβ0 / αβ0 components based on the defined positive and negative sequence cyclic component forms of power frequency and low frequency and the control strategies of the cyclic components to obtain four sets of sequence cyclic components of the nine bridge arms;

[0184] Step S7: sum the four sets of sequence cyclic components to obtain the voltage modulation waveforms of the cyclic components of the nine bridge arms.

[0185] In the embodiment of the application, the M3C bridge arm inter-capacitor voltage balance control based on sequence cyclic components is as shown in Figure 8 The module capacitor voltages of the bridge arms are summed, filtered with a low-pass filter (LPF) to obtain the DC components of the capacitor voltages, and double αβ0 transform the DC components of the capacitor voltages of the nine bridge arms to obtain eight u Cαβ0 / αβ0 components. Based on the control diagrams of the sequence cyclic components and the defined sequence cyclic component forms, four sets of sequence cyclic components of the nine bridge arms are obtained respectively. By summing the four sets, the voltage modulation waveforms of the cyclic components of the nine bridge arms are obtained. Figure 8 The module capacitor voltages of the bridge arms are summed, filtered with a low-pass filter (LPF) to obtain the DC components of the capacitor voltages, and double αβ0 transform the DC components of the capacitor voltages of the nine bridge arms to obtain eight u Cαβ0 / αβ0 components. Based on the control diagrams of the sequence cyclic components and the defined sequence cyclic component forms, four sets of sequence cyclic components of the nine bridge arms are obtained respectively. By summing the four sets, the voltage modulation waveforms of the cyclic components of the nine bridge arms are obtained.

[0186] The control method is verified for a typical system as shown in Figure 9 The control method is verified for a typical system as shown in Figure 9 The control method is verified for a typical system as shown in Figure 10Compared with the conventional control method, the control performance of the proposed control method is improved by 60.3% and 81.6% in terms of standard deviation in the case of uneven parameters and unbalanced power system. Without considering the circulating voltage, the control performance of the proposed control method is improved by 49.3% and 74.4%. Compared with the proposed control method, the control performance in the two cases is reduced by 11% and 7.2% without considering the circulating voltage. When the transmitting power of M3C increases, the advantage of the proposed control method will be more obvious.

[0187] In summary, the application can achieve full decoupling control of the horizontal, vertical and diagonal three dimensions of the capacitor voltage between the bridge arms of the M3C by using the sequence circulating components of the two sides frequencies. The application decouples the influence of the circulating voltage and current generated power on the capacitor voltage between the bridge arms through feedforward control, which can effectively control the balance and stability of the high-voltage and large-capacity M3C bridge arm capacitor voltage, avoid the over-high or over-low of the single bridge arm capacitor voltage caused by the poor uniformity of the bridge arm parameters or the asymmetric fault of the two sides systems, and the problem that the system cannot run normally due to the protection action lockout.

[0188] Exemplary Apparatus

[0189] The application also provides a control device for balancing capacitor voltage between bridge arms of a modular multilevel matrix converter, comprising:

[0190] A first definition module is configured to connect a power frequency system and a low frequency system on two sides of a modular multilevel matrix converter of a flexible low frequency power transmission system, and then define relevant electrical quantities related to the modular multilevel matrix converter; wherein the relevant electrical quantities include three-phase voltage and three-phase current on the power frequency side, and three-phase voltage and three-phase current on the low frequency side.

[0191] A second definition module is configured to define positive and negative sequence circulating component forms of the power frequency side and the low frequency side of the modular multilevel matrix converter based on the relevant electrical quantities related to the modular multilevel matrix converter.

[0192] A control strategy determination module is configured to determine control strategies of each circulating component of the modular multilevel matrix converter.

[0193] A direct current component acquisition module is configured to add module capacitor voltages of nine bridge arms of the modular multilevel matrix converter, and filter the sum by using a low-pass filter to obtain direct current components of the capacitor voltages of the nine bridge arms.

[0194] A transformation module is configured to perform double alpha beta zero transformation on the direct current components of the capacitor voltages of the nine bridge arms to obtain eight u Cαβ0 / αβ0 components.

[0195] a control module, configured to control eight u Cαβ0 / αβ0 components based on the defined power frequency positive and negative sequence cyclic component forms and the low frequency positive and negative sequence cyclic component forms and the control strategy of each cyclic component, to obtain four groups of sequence cyclic components of nine bridge arms;

[0196] a component adding module, configured to add the four groups of sequence cyclic components to obtain the voltage modulation waveform of the cyclic components of the nine bridge arms.

[0197] Optionally, the power frequency positive and negative sequence cyclic component forms include a power frequency positive sequence cyclic component form and a power frequency negative sequence cyclic component form, wherein

[0198] the power frequency positive sequence cyclic component form is:

[0199]

[0200] wherein, u scirp1 , u scirp2 , u scirp3 constitutes a group of power frequency positive sequence alternating current components, ω s is a power frequency angular frequency, is a power frequency positive sequence cyclic component phase angle;

[0201] the power frequency negative sequence cyclic component form is:

[0202]

[0203] wherein, u scirn1 , u scirn2 , u scirn3 constitutes a group of power frequency negative sequence alternating current components, ω s is a power frequency angular frequency, is a power frequency negative sequence cyclic component phase angle.

[0204] Optionally, the low frequency positive and negative sequence cyclic component forms include a low frequency positive sequence cyclic component form and a low frequency negative sequence cyclic component form, wherein

[0205] the low frequency positive sequence cyclic component form is:

[0206]

[0207] wherein, u mcirp1 , u mcirp2 , u mcirp3 constitutes a group of low frequency positive sequence alternating current components, ω m is a low frequency angular frequency, is a low frequency positive sequence cyclic component phase angle;

[0208] the low frequency negative sequence cyclic component form is:

[0209]

[0210] wherein u mcirn1 , u mcirn2 , u mcirn3 constitute a set of low-frequency negative-sequence AC components, ω m is a low-frequency angular frequency, is a low-frequency negative-sequence cyclic component phase angle.

[0211] Optionally, each cyclic component of the modular multilevel matrix converter comprises a bridge-arm capacitor voltage component u Cα0 and u Cβ0 based on a power-frequency positive-sequence cyclic component, C0α and u C0β based on a low-frequency positive-sequence cyclic component, Cαα and u Cαβ based on a power-frequency negative-sequence cyclic component, Cβα and u Cββ based on a low-frequency negative-sequence cyclic component; wherein

[0212] u Cα0 , u Cβ0 , u C0α and u C0β are controlled by two sets of positive-sequence cyclic components, comprising a set of power-frequency positive-sequence cyclic components and a set of low-frequency positive-sequence cyclic components.

[0213] u Cαα , u Cαβ , u Cβα and u Cββ are controlled by two sets of negative-sequence cyclic components, comprising a set of power-frequency negative-sequence cyclic components and a set of low-frequency negative-sequence cyclic components, the power-frequency negative-sequence cyclic components having two forms, and the low-frequency negative-sequence cyclic components having two forms.

[0214] The control device for balancing the capacitor voltages between the bridge arms of the modular multilevel matrix converter of the embodiments of the present application corresponds to the control method for balancing the capacitor voltages between the bridge arms of the modular multilevel matrix converter of another embodiment of the present application, and will not be described here again.

[0215] Exemplary Electronic Device

[0216] Figure 11 is a structure of an electronic device provided by an exemplary embodiment of the present application. As shown in Figure 11 , the electronic device 110 includes one or more processors 111 and a memory 112.

[0217] The processor 111 can be a central processing unit (CPU) or other form of processing unit having data processing and / or instruction execution capabilities and can control other components in the electronic device to perform desired functions.

[0218] The memory 112 can include one or more computer program products that can include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory, for example, can include random access memory (RAM), cache memory, and / or the like. The non-volatile memory, for example, can include read only memory (ROM), hard disk, flash memory, and / or the like. One or more computer program instructions can be stored on the computer-readable storage media, which the processor 111 can execute to implement the method of performing information mining on the history change record of the software program of the various embodiments of the present application and / or other desired functions described above. In one example, the electronic device can further include an input device 113 and an output device 114, which are interconnected through a bus system and / or other form of connection mechanism (not shown).

[0219] In addition, the input device 113 can further include, for example, a keyboard, a mouse, and / or the like.

[0220] The output device 114 can output various information to the outside. The output device 114 can include, for example, a display, a speaker, a printer, a communication network and a remote output device connected thereto, and / or the like.

[0221] Of course, in order to simplify, Figure 11 Only some of the components related to the present application among the components in the electronic device are shown in FIG. 1, and components such as a bus, an input / output interface, and / or the like are omitted. In addition, the electronic device can further include any other appropriate components according to a specific application.

[0222] Exemplary Computer Program Product and Computer-Readable Storage Medium

[0223] In addition to the above-described method and device, an embodiment of the present application can be a computer program product including computer program instructions that, when executed by a processor, cause the processor to perform steps of the method according to various embodiments of the present application described in the above "Exemplary Method" section of the specification.

[0224] The computer program product can be written in any combination of one or more programming languages, including an object oriented programming language such as Java, C++ or the like, and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code can execute entirely on the user's computing device, partly on the user's device, as a stand-alone software package, partly on the user's computing device and partly on a remote computing device or entirely on the remote computing device or server.

[0225] Furthermore, embodiments of the present application can also be a computer readable storage medium, having stored thereon, computer program instructions which, when executed by a processor, cause the processor to perform the steps described in the above "Exemplary Method" section of the present specification for the method of information mining on historical change records according to various embodiments of the present application.

[0226] The computer readable storage medium can be a combination of one or more computer readable media. The computer readable media can be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium can include, for example, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium include an electrical connection having one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0227] The above description sets forth numerous specific details regarding the described embodiments. However, it is understood that the foregoing description and examples are intended to be illustrative only and are not intended to limit the scope of the application as set forth in the appended claims. Various modifications and changes can be made thereto by those skilled in the art which fall within the scope of the application as outlined in the appended claims. Moreover, other implementations of the application will be apparent from consideration of the specification and the examples as contained herem. Therefore, the true scope of the application is not to be limited to the foregoing description but is to be accorded the full scope including equivalents and equivalent combinations thereof.

[0228] Each embodiment described in the specification is illustrated by way of progression, each embodiment highlighting a different aspect of the application. The same or similar parts between embodiments are mutually referred to. For system embodiments, since they are basically corresponding to the method embodiments, the description is relatively simple, and the relevant parts are referred to the part of the method embodiments.

[0229] The block diagrams of the devices, systems, apparatuses, systems referred to in this disclosure are only meant to be illustrative examples and are not intended to require or imply that the connections, arrangements, configurations shown in the block diagrams are required. These devices, systems, apparatuses, systems can be connected, arranged, configured in any manner as will be appreciated by those skilled in the art. Words such as "including," "containing," "comprising," and the like are to be construed in an inclusive fashion, meaning that "consisting of" is to be read into each of such terms, and that "consisting of" and "consisting essentially of" are each permissible claim limitations. The terms "or," "and," and "and / or" as used herein are to be interpreted as an inclusive or meaning any one or any combination of the listed possible options so that, for example, "A or B" means "A or B or both." The terms "and," "and / or" as used herein are to be interpreted as an inclusive or meaning any one or any combination of the listed possible options so that, for example, "A and B" means "A and B or A or B." The term "such as" is to be read as meaning "such as but not limited to."

[0230] The methods and systems of the present application can be implemented in a number of ways. For example, the methods and systems of the present application can be implemented via software, hardware, firmware, or any combination of software, hardware, and firmware. The above described order of steps for the methods is merely illustrative and the steps of the methods of the present application are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, the present application can also be implemented as a program recorded on a recording medium, which includes machine readable instructions for implementing the methods according to the present application. Thus, the present application also covers recording media storing programs for executing the methods according to the present application.

[0231] It is also to be noted that in the systems, apparatuses, and methods of the present application, various components or steps can be decomposed and / or recombined. These decompositions and / or recombinations are to be considered as equivalent to the present application. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other aspects without departing from the scope of the application. Thus, the present application is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0232] The above description has been given for the purpose of illustration and description. Furthermore, this description is not intended to limit embodiments of the present application to the forms disclosed herein. Although several example aspects and embodiments have been discussed above, those of ordinary skill in the art will appreciate a variety of modifications, alternatives, permutations, additions, and sub-combinations, which fall within the scope of the application.

Claims

1. A control method for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter, characterized in that, include: The modular multilevel matrix converter of the flexible low-frequency power transmission system is connected to the power frequency system and the low-frequency system on both sides. Then, the relevant electrical quantities involved in the modular multilevel matrix converter are defined. Among them, the relevant electrical quantities include the three-phase voltage and three-phase current on the power frequency side and the three-phase voltage and three-phase current on the low-frequency side. Based on the relevant electrical quantities involved in the modular multilevel matrix converter, the power frequency positive and negative sequence cyclic component form and the low frequency positive and negative sequence cyclic component form of the modular multilevel matrix converter are defined. Determine the control strategy for each cyclic component of the modular multilevel matrix converter; The module capacitor voltages of the nine bridge arms of the modular multilevel matrix converter are summed and filtered by a low-pass filter to obtain the DC component of the capacitor voltages of the nine bridge arms. By performing a double αβ0 transform on the DC components of the capacitor voltages of the nine bridge arms, eight u values ​​were obtained. Cαβ0 / αβ0 Quantity; Based on the defined power frequency positive and negative sequence cyclic component forms and low frequency positive and negative sequence cyclic component forms, as well as the control strategies for each cyclic component, eight u Cαβ0 / αβ0 The components are controlled to obtain four sets of sequential cyclic components for the nine bridge arms; The four sets of sequential cyclic components are added together to obtain the voltage modulation waveform of the cyclic components of the nine bridge arms.

2. The method according to claim 1, characterized in that, The power frequency positive and negative sequence cyclic component forms include power frequency positive sequence cyclic component forms and power frequency negative sequence cyclic component forms, wherein... The positive-sequence cyclic component of power frequency is in the form of: In the formula, u scirp1 ,u scirp2 ,u scirp3 This constitutes a set of positive-sequence AC components at the power frequency. ω s It is the power frequency angular frequency. The phase angle of the positive sequence cyclic component of the power frequency; The form of the negative sequence cyclic component of power frequency is: In the formula, u scirn1 ,u scirn2 ,u scirn3 This constitutes a set of negative-sequence AC components at the power frequency. ω s It is the power frequency angular frequency. The phase angle is the negative sequence cyclic component of the power frequency.

3. The method according to claim 1, characterized in that, The low-frequency positive and negative sequence cyclic component forms include low-frequency positive sequence cyclic component forms and low-frequency negative sequence cyclic component forms, wherein... The low-frequency positive-sequence cyclic component is in the form of: In the formula, u mcirp1 ,u mcirp2 ,u mcirp3 This constitutes a set of low-frequency positive-sequence AC components. ω m It is a low-frequency angular frequency. The phase angle of the low-frequency positive-sequence cyclic component; The low-frequency negative-sequence cyclic component is in the form of: In the formula, u mcirn1 ,u mcirn2 ,u mcirn3 This constitutes a set of low-frequency negative-sequence AC components, ω m It is a low-frequency angular frequency. The phase angle is for the low-frequency negative sequence cyclic component.

4. The method according to claim 1, characterized in that, Each cyclic component of the modular multilevel matrix converter includes the bridge arm capacitor voltage component u based on the power frequency positive sequence cyclic component. Cα0 and u Cβ0 Bridge arm capacitor voltage component u based on low-frequency positive sequence cyclic component C0α and u C0β Bridge arm capacitor voltage component u based on power frequency negative sequence cyclic component Cαα and u Cαβ Bridge arm capacitor voltage component u based on low-frequency negative sequence cyclic component Cβα and u Cββ ;in u Cα0 u Cβ0 u C0α and u C0β It is controlled by two sets of positive sequence cyclic components, including one set of power frequency positive sequence cyclic components and one set of low frequency positive sequence cyclic components; u Cαα u Cαβ u Cβα and u Cββ It is controlled by two sets of negative sequence cyclic components, including a set of power frequency negative sequence cyclic components and a set of low frequency negative sequence cyclic components. The power frequency negative sequence cyclic components have two forms, and the low frequency negative sequence cyclic components have two forms.

5. A control system for balancing capacitor voltages between bridge arms of a modular multilevel matrix converter, characterized in that, include: The first definition module is used to connect the power frequency system and the low frequency system on both sides of the modular multilevel matrix converter of the flexible low frequency transmission system. Then, it defines the relevant electrical quantities involved in the modular multilevel matrix converter. Among them, the relevant electrical quantities include the three-phase voltage and three-phase current on the power frequency side and the three-phase voltage and three-phase current on the low frequency side. The second definition module is used to define the power frequency positive and negative sequence cyclic component form and the low frequency positive and negative sequence cyclic component form of the modular multilevel matrix converter based on the relevant electrical quantities involved in the modular multilevel matrix converter; The control strategy determination module is used to determine the control strategy for each cyclic component of the modular multilevel matrix converter. The DC component acquisition module is used to sum the module capacitor voltages of the nine bridge arms of the modular multilevel matrix converter and filter them with a low-pass filter to obtain the DC component of the capacitor voltages of the nine bridge arms. The transformation module performs a double αβ0 transformation on the DC components of the capacitor voltages of the nine bridge arms, resulting in eight u... Cαβ0 / αβ0 Quantity; The control module is used to control eight u based on the defined power frequency positive and negative sequence cyclic component forms and low frequency positive and negative sequence cyclic component forms, as well as the control strategy for each cyclic component. Cαβ0 / αβ0 The components are controlled to obtain four sets of sequential cyclic components for the nine bridge arms; The component summing module is used to sum the four sets of sequential cyclic components to obtain the voltage modulation waveform of the cyclic components of the nine bridge arms.

6. The system according to claim 5, characterized in that, The power frequency positive and negative sequence cyclic component forms include power frequency positive sequence cyclic component forms and power frequency negative sequence cyclic component forms, wherein... The positive-sequence cyclic component of power frequency is in the form of: In the formula, u scirp1 ,u scirp2 ,u scirp3 This constitutes a set of positive-sequence AC components at the power frequency. ω s It is the power frequency angular frequency. The phase angle of the positive sequence cyclic component of the power frequency; The form of the negative sequence cyclic component of power frequency is: In the formula, u scirn1 ,u scirn2 ,u scirn3 This constitutes a set of negative-sequence AC components at the power frequency. ω s It is the power frequency angular frequency. The phase angle is the negative sequence cyclic component of the power frequency.

7. The system according to claim 5, characterized in that, The low-frequency positive and negative sequence cyclic component forms include low-frequency positive sequence cyclic component forms and low-frequency negative sequence cyclic component forms, wherein... The low-frequency positive-sequence cyclic component is in the form of: In the formula, u mcirp1 ,u mcirp2 ,u mcirp3 This constitutes a set of low-frequency positive-sequence AC components. ω m It is a low-frequency angular frequency. The phase angle of the low-frequency positive-sequence cyclic component; The low-frequency negative-sequence cyclic component is in the form of: In the formula, u mcirn1 ,u mcirn2 ,u mcirn3 This constitutes a set of low-frequency negative-sequence AC components, ω m It is a low-frequency angular frequency. The phase angle is for the low-frequency negative sequence cyclic component.

8. The system according to claim 5, characterized in that, Each cyclic component of the modular multilevel matrix converter includes the bridge arm capacitor voltage component u based on the power frequency positive sequence cyclic component. Cα0 and u Cβ0 Bridge arm capacitor voltage component u based on low-frequency positive sequence cyclic component C0α and u C0β Bridge arm capacitor voltage component u based on power frequency negative sequence cyclic component Cαα and u Cαβ Bridge arm capacitor voltage component u based on low-frequency negative sequence cyclic component Cβα and u Cββ ;in u Cα0 u Cβ0 u C0α and u C0β It is controlled by two sets of positive sequence cyclic components, including one set of power frequency positive sequence cyclic components and one set of low frequency positive sequence cyclic components; u Cαα u Cαβ u Cβα and u Cββ It is controlled by two sets of negative sequence cyclic components, including a set of power frequency negative sequence cyclic components and a set of low frequency negative sequence cyclic components. The power frequency negative sequence cyclic components have two forms, and the low frequency negative sequence cyclic components have two forms.

9. A computer-readable storage medium, characterized in that, The storage medium stores a computer program for performing the method described in any one of claims 1-4.

10. An electronic device, characterized in that, The electronic device includes: processor; Memory used to store the processor's executable instructions; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method described in any one of claims 1-4.

Images