CN114337343A

CN114337343A - Method and device for establishing MMC broadband three-port frequency coupling impedance model

Info

Publication number: CN114337343A
Application number: CN202210022449.2A
Authority: CN
Inventors: 谢小荣; 满九方
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2022-01-10
Filing date: 2022-01-10
Publication date: 2022-04-12

Abstract

The application relates to the technical field of power system modeling and analysis, in particular to a method and a device for establishing an MMC broadband three-port frequency coupling impedance model, wherein the method comprises the following steps: establishing a three-dimensional transfer function matrix of an MMC internal control link to determine a reference voltage generated by the MMC internal control link; performing secondary iteration solution of bridge arm dynamics inside the MMC based on the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain actual output voltages of an upper bridge arm and a lower bridge arm of the MMC; and calculating differential mode voltage and common mode voltage of the MMC according to the actual output voltage of the upper bridge arm and the lower bridge arm, and establishing a broadband three-port frequency coupling impedance model of the MMC for outputting the stability of the broadband oscillation of the flexible-direct system by utilizing a differential mode voltage loop and a common mode voltage loop. Therefore, the problems that the applicable frequency range of the impedance model established in the related technology is narrow, the accuracy is low, the requirement of broadband oscillation stability analysis cannot be met and the like are solved.

Description

Method and device for establishing MMC broadband three-port frequency coupling impedance model

Technical Field

The present disclosure relates to the field of modeling and analyzing power systems, and in particular, to a method and an apparatus for establishing a wideband three-port frequency-coupled impedance model of an MMC (modular multilevel converter).

Background

In recent years, many novel power system broadband oscillation events appear in a flexible direct-current transmission system based on an MMC, in order to explore a mechanism of the flexible direct-current system broadband oscillation, an impedance model suitable for the flexible direct-current system broadband oscillation stability analysis needs to be built urgently, and the difficulty of the flexible direct-current system impedance modeling lies in modeling of a modular multilevel converter.

The MMC is formed by cascading a plurality of sub-modules with the same structure, and compared with a traditional two-level converter or a three-level converter, the MMC has the particularity. Firstly, the MMC is often used in a high-voltage and high-capacity scene, and compared with a two-level converter used in a low-voltage and low-capacity scene, the control delay of the MMC is often larger; secondly, the MMC has a characteristic internal bridge arm submodule dynamic state, and internal circulation and circulation suppression control have an influence on the impedance characteristic of the MMC, which is difficult to ignore. The inner bridge arm dynamic of the MMC mainly influences the impedance characteristic in a low-frequency range, and the control and modulation delay of the MMC mainly influences the high-frequency range of the impedance characteristic of the MMC.

However, in the related art, the impedance modeling work of the MMC mostly continues to use the modeling method of the conventional two-level converter, the influence of the bridge arm dynamics and the delay of the MMC is not considered, and the obtained impedance model is applicable to a narrow frequency range and low in precision, and cannot meet the requirement of broadband oscillation stability analysis.

Disclosure of Invention

The application provides an MMC broadband three-port frequency coupling impedance model establishing method, an MMC broadband three-port frequency coupling impedance model establishing device, electronic equipment and a storage medium, and aims to solve the problems that in the related technology, the MMC impedance modeling work mostly continues to use a traditional two-level converter modeling method, the established impedance model is applicable to a narrow frequency range and low in precision, cannot meet the requirement of broadband oscillation stability analysis and the like.

An embodiment of a first aspect of the present application provides a method for establishing an MMC broadband three-port frequency coupling impedance model, including the following steps: establishing a three-dimensional transfer function matrix of an MMC internal control link, and determining a reference voltage generated by the MMC internal control link based on the three-dimensional transfer function matrix; performing secondary iteration solution of the dynamic of an inner bridge arm of the MMC on the basis of the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain actual output voltages of an upper bridge arm and a lower bridge arm of the MMC; calculating differential mode voltage and common mode voltage of the MMC according to actual output voltage of an upper bridge arm and actual output voltage of a lower bridge arm of the MMC, establishing a differential mode voltage loop and a common mode voltage loop respectively based on the differential mode voltage and the common mode voltage, and establishing a broadband three-port frequency coupling impedance model of the MMC, wherein the broadband three-port frequency coupling impedance model is used for outputting the broadband oscillation stability of a flexible-straight system, and the broadband three-port frequency coupling impedance model is established by utilizing the differential mode voltage loop and the common mode voltage loop.

Further, the broadband three-port frequency coupling impedance model is:

wherein Z represents a three-port frequency coupling impedance matrix, Z11, Z22 and Z33 are self-impedances and respectively represent impedances at two coupling frequencies at an alternating current side and at a direct current harmonic frequency; the other matrix elements are mutual impedance and represent impedance between different frequencies of an alternating current side or between alternating current and direct current; vp and Vp2 respectively represent harmonic voltage components of two frequency couplings at the alternating current side, and Δ Vdc represents harmonic voltage components at the direct current side; ip and Ip2 represent harmonic current components of two frequency couplings on the alternating current side, and Δ Idc represents a harmonic current component on the direct current side; the frequency coupling represents that the sum of the frequencies of two harmonic voltage or harmonic current components is 2 times of the power frequency, namely fp + fp2 is 2f1, f1 is the frequency of the fundamental component, and the conjugate is taken.

Further, the establishing of the three-dimensional transfer function matrix of the MMC internal control link includes: acquiring the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state in a control link; and establishing the three-dimensional transfer function matrix according to the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state.

Further, the performing secondary iteration solution on the dynamic of the bridge arm inside the MMC based on the reference voltage and the disturbance components of the ac side and the dc side of the MMC to obtain the actual output voltages of the upper bridge arm and the lower bridge arm of the MMC includes: performing first iteration solution on the basis of the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain a harmonic circulating current component; and carrying out second iteration solution on the dynamic state of the bridge arm based on the harmonic circulating current component to generate actual output voltages of an upper bridge arm and a lower bridge arm of the MMC.

Further, before performing a second iteration solution of the MMC internal bridge arm dynamics based on the reference voltage and disturbance components of the ac side and the dc side of the MMC, the method further includes: and injecting preset signal harmonic disturbance into the AC side and the DC side of the MMC simultaneously to generate disturbance components of the AC side and the DC side of the MMC.

An embodiment of a second aspect of the present application provides an apparatus for establishing a wideband three-port frequency-coupled impedance model of an MMC, including: the device comprises a derivation module, a conversion module and a control module, wherein the derivation module is used for establishing a three-dimensional transfer function matrix of an MMC internal control link and determining a reference voltage generated by the MMC internal control link based on the three-dimensional transfer function matrix; the solving module is used for carrying out secondary iteration solving on the dynamic state of an inner bridge arm of the MMC on the basis of the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain actual output voltages of an upper bridge arm and a lower bridge arm of the MMC; the modeling module is used for calculating the differential mode voltage and the common mode voltage of the MMC according to the actual output voltage of the upper bridge arm and the actual output voltage of the lower bridge arm of the MMC, establishing a differential mode voltage loop and a common mode voltage loop respectively based on the differential mode voltage and the common mode voltage, establishing the broadband three-port frequency coupling impedance model of the MMC by utilizing the differential mode voltage loop and the common mode voltage loop, and establishing the broadband three-port frequency coupling impedance model of the MMC for outputting the stability of the broadband oscillation of the flexible-direct system by utilizing the differential mode voltage loop and the common mode voltage loop.

Further, the broadband three-port frequency coupling impedance model is:

Furthermore, the derivation module is further configured to obtain a phase-locked loop dynamic state, an outer loop control dynamic state, a positive sequence current inner loop control dynamic state, and a negative sequence current inner loop control dynamic state in the control link; and establishing the three-dimensional transfer function matrix according to the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state.

Further, the solving module is further configured to perform a first iterative solution based on the reference voltage and disturbance components on the ac side and the dc side of the MMC to obtain a harmonic circulating current component; and carrying out second iteration solution on the dynamic state of the bridge arm based on the harmonic circulating current component to generate actual output voltages of an upper bridge arm and a lower bridge arm of the MMC.

Further, still include: and the injection module is used for injecting preset signal harmonic disturbance to the alternating current side and the direct current side of the MMC simultaneously to generate disturbance components of the alternating current side and the direct current side of the MMC before carrying out secondary iteration solution on the dynamic of a bridge arm in the MMC on the basis of the reference voltage and the disturbance components of the alternating current side and the direct current side of the MMC.

An embodiment of a third aspect of the present application provides an electronic device, including: the MMC broadband three-port frequency-coupled impedance model establishing method comprises the steps of storing a first parameter value, storing a second parameter value, storing a third parameter value, and storing a third parameter value.

A fourth aspect of the present application provides a computer-readable storage medium, on which a computer program is stored, where the computer program is executed by a processor to implement the method for establishing the MMC broadband three-port frequency-coupled impedance model according to the foregoing embodiments.

Therefore, the application has at least the following beneficial effects:

through the derivation of an MMC control link, the dynamic state of an internal bridge arm and an external circuit, a broadband three-port frequency coupling impedance model of the MMC is finally formed, due to the fact that all aspects of factors such as MMC control delay, signal transmission and calculation delay in simulation software, MMC internal circulation and circulation suppression control and the like are considered, the accuracy of the obtained model in a broadband range can be guaranteed, meanwhile, the model establishes a coupling relation between an AC side and a DC side of a current converter, and a foundation is laid for stability analysis of a flexible direct-current system. Therefore, the technical problems that the impedance modeling work of the MMC in the related technology mostly continues to use the modeling method of the traditional two-level converter, the established impedance model is applicable to a narrow frequency range and low in precision, the requirement of broadband oscillation stability analysis cannot be met and the like are solved.

Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.

Drawings

The foregoing and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a flowchart of a method for establishing a wideband three-port frequency-coupled impedance model of an MMC according to an embodiment of the present disclosure;

fig. 2 is a single-phase topology structure diagram of a modular multilevel converter provided according to an embodiment of the present application;

fig. 3 is a flowchart of a method for establishing a wideband three-port frequency-coupled impedance model of an MMC according to an embodiment of the present disclosure;

fig. 4 is a diagram illustrating an apparatus for establishing a wideband three-port frequency-coupled impedance model of an MMC according to an embodiment of the present disclosure;

fig. 5 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

Detailed Description

Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary and intended to be used for explaining the present application and should not be construed as limiting the present application.

The broadband oscillation of the flexible-straight system occurs under multiple scenes: if the large-scale new energy station is sent out flexibly and directly, high-frequency oscillation may occur between the sending end converter and the offshore wind farm; during back-to-back dc transmission, high frequency oscillations may also occur between the inverter-side converter and the ac grid. Therefore, in order to analyze the broadband oscillation phenomenon in multiple scenarios, it is necessary to establish an impedance model considering the characteristics of the MMC alternating current port and the characteristics of the direct current port at the same time. The MMC has an alternating current port and a direct current port, and different converters are connected with each other through a direct current power grid; however, the current impedance modeling work usually splits the whole ac-dc-ac system, and only the MMC impedance model looking into the ac port or only the MMC impedance model looking into the dc port is established assuming that the dc side or the ac side is constant. The impedance model cannot consider the influence of an alternating current system or a direct current system on the impedance characteristic of the impedance model, has limitation in the application of broadband oscillation of the flexible direct current system under multiple scenes, and lacks an impedance model capable of simultaneously representing the characteristics of alternating current and direct current ports of an MMC.

The MMC under the high-voltage and high-capacity scenes is limited by a modeling method and a mathematical theory, and the stability research of the flexible-direct system in the broadband oscillation field is severely restricted. Therefore, the invention provides a broadband three-port frequency coupling impedance modeling method considering dynamic of a bridge arm in an MMC, a coupling relation between AC and DC sides of the MMC is constructed through a three-port frequency coupling impedance model, and the proposed model has important theoretical and engineering significance in the aspects of researching a broadband oscillation mechanism of a flexible DC power transmission system and improving the stability of the flexible DC power transmission system.

In order to study the stability of an electric power system, in particular to stability analysis of broadband oscillation of a flexible-direct system, the embodiment of the application provides a broadband three-port frequency coupling impedance modeling method and device considering the dynamic state of an internal bridge arm of an MMC, an electronic device and a storage medium.

The method, the apparatus, the electronic device and the storage medium for establishing the MMC broadband three-port frequency-coupled impedance model according to the embodiments of the present application are described below with reference to the accompanying drawings. Aiming at the problems that the impedance modeling work of MMC in the related technology mentioned in the background technology mostly adopts the modeling method of the traditional two-level converter, the applicable frequency range of the established impedance model is narrow, the precision is low, and the requirement of broadband oscillation stability analysis cannot be met, the application provides the establishing method of the MMC broadband three-port frequency coupling impedance model, in the method, the broadband three-port frequency coupling impedance model of the MMC is finally formed through the derivation of an MMC control link, the dynamic state of an internal bridge arm and an external circuit, because the comprehensive factors of MMC control delay, signal transmission and calculation delay in simulation software, MMC internal circulation and circulation suppression control and the like are considered, the obtained model can ensure the accuracy in a broadband range, and meanwhile, the model establishes the coupling relation between the AC side and the DC side of the converter, and a foundation is laid for the stability analysis of the flexible and straight system. Therefore, the technical problems that the impedance modeling work of the MMC in the related technology mostly continues to use the modeling method of the traditional two-level converter, the established impedance model is applicable to a narrow frequency range and low in precision, the requirement of broadband oscillation stability analysis cannot be met and the like are solved.

Specifically, fig. 1 is a schematic flowchart of a method for establishing a wideband three-port frequency-coupled impedance model of an MMC according to an embodiment of the present disclosure.

As shown in fig. 1, the method for establishing the MMC broadband three-port frequency-coupled impedance model includes the following steps:

in step S101, a three-dimensional transfer function matrix of the MMC internal control link is established, and a reference voltage generated by the MMC internal control link is determined based on the three-dimensional transfer function matrix.

In this embodiment, establishing a three-dimensional transfer function matrix of an MMC internal control link includes: acquiring the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state in a control link; and establishing a three-dimensional transfer function matrix according to the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state.

It can be understood that, in the embodiment of the present application, a three-dimensional transfer function matrix of an MMC control link is established, and control links such as park transformation, phase-locked loop, various outer loop controls, positive sequence current inner loop control, negative sequence current inner loop control, park inverse transformation, and the like are considered, and reference voltage generated by an MMC internal control link is derived and obtained, including a fundamental component and two frequency-coupled harmonic components.

In step S102, based on the reference voltage and the disturbance components on the ac side and the dc side of the MMC, performing a second iteration solution of the MMC internal bridge arm dynamics to obtain actual output voltages of the upper bridge arm and the lower bridge arm of the MMC.

It can be understood that the voltage actually output by the upper bridge arm and the lower bridge arm of the MMC can be dynamically derived through the MMC bridge arm based on the reference voltage, the circulating current and the current components at the ac side and the dc side.

In this embodiment, performing a second iteration solution of the dynamic state of the bridge arm inside the MMC based on the reference voltage and the disturbance components of the ac side and the dc side of the MMC to obtain the actual output voltages of the upper bridge arm and the lower bridge arm of the MMC includes: performing first iteration solution on the basis of reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain a harmonic circulating current component; and carrying out second iteration solution on the dynamic state of the bridge arm based on the harmonic circulating current component to generate actual output voltages of an upper bridge arm and a lower bridge arm of the MMC.

It can be understood that, in the embodiment of the present application, the harmonic circulating current component can be obtained through dynamic derivation of the MMC bridge arm based on the reference voltage obtained through the derivation and the harmonic disturbance components at the ac and dc sides; and then, after the harmonic circulating current component is considered, the second iteration of the bridge arm dynamic is carried out, and the upper and lower bridge arm voltages are obtained through derivation.

It should be noted that the circulation suppression control is closely related to the dynamic state inside the bridge arm, and the solution is performed by dividing the circulation suppression control into two cases according to whether the circulation suppression control is put into operation or not; when the circulation restraining control is not considered, the bridge arm modulation wave does not contain a double-frequency negative sequence circulation component, but the circulation component of the double-frequency negative sequence is stored; when the loop suppression control is considered, the double-frequency negative sequence loop component is not considered any more, but the double-frequency negative sequence loop component in the modulated wave is considered.

Specifically, the single-phase topology of the MMC is shown in fig. 2, where j ═ a, B, and C. Each bridge arm is provided with a bridge arm reactance L₀One bridge arm resistor R₀And N sub-modules are connected in series. As can be seen from fig. 1, the bridge arm current will include both ac side current and dc side current; in addition, however, the bridge arm current will also contain internal circulating currents due to the disparity in the sum of the upper and lower bridge arm voltages of each phase. Thus, the MMC bridge arm current can be represented as:

wherein i_Tj(t)，i_Bj(t) represents the upper and lower bridge arm currents of a certain phase, i_cirj(t) denotes a circulating current component, i 'of a certain phase'_j(t) represents the converter transformer valve side current of a certain phase.

And assuming that the dynamic responses of the bridge arm submodules in the MMC are consistent, the modulation wave of each bridge arm is the arithmetic average value of the switching function of each submodule in the bridge arm. The modulated waves of the upper and lower bridge arms of the MMC are related to the reference voltage generated by the control link, and the reference voltage is obtained by the calculation of the preorder control link, so that the bridge arm voltage is calculated by advancing one simulation step length, the calculation delay of the preorder control link is compensated, and the calculation delay can be expressed as follows:

wherein m is_Tj(t)，m_Bj(t) are the modulated waves of the upper and lower bridge arms of a certain phase of the converter respectively,

reference voltage, T, representing the generation of the MMC control link_dAnd representing the simulation step size of the electromagnetic transient simulation software.

The same electric quantity of the upper bridge arm and the lower bridge arm of each phase of the MMC are symmetrical, the electric quantities are different from each other by T/2 in the time domain, and T represents the period of a fundamental wave. Therefore, the same electric quantity of the lower arm can be directly obtained from the electric quantity of the upper arm. Furthermore, the same electrical quantities of the three phases of the MMC will be successively delayed by T/3 in the time domain. Therefore, the dynamics of all 6 bridge arms can be deduced according to the dynamics of a certain bridge arm. Taking the phase a upper bridge arm as an example, since the modulation wave of each bridge arm is the arithmetic average of the switching functions of each submodule in the bridge arm, the arithmetic average of the capacitance currents of the submodules can be directly calculated from the modulation wave of the bridge arm and the bridge arm current, and can be expressed as:

wherein the content of the first and second substances,

representing the capacitive current of the sub-module of the bridge arm on the a phase, i_Ta(t) represents the bridge arm current on the A phase, m_Ta(t) represents a modulated wave of the upper arm of the A phase.

In steady-state operation, the dc component of the sub-module capacitor current should be zero, otherwise the capacitor voltage will increase continuously. Therefore, the dc component in the sub-module capacitance current in formula 3 should be ignored and then substituted into the subsequent calculation. The arithmetic mean value of the sub-module capacitor voltage can be further obtained according to the capacitance value of the sub-module capacitor and the arithmetic mean value of the sub-module capacitor current, and can be expressed as:

wherein the content of the first and second substances,

representing the capacitor voltage of the bridge arm submodule on phase A, C₀The sub-module dc capacitance is represented.

The sub-module capacitor voltage is coupled to the bridge arm through the sub-module switch action, so that the bridge arm voltage can be calculated by the sub-module capacitor voltage average value and the bridge arm modulation wave. Considering the time delay of the internal calculation of the simulation software, the sub-module capacitance voltage obtained by the calculation of the formula needs to be delayed by one simulation step length and then substituted into the calculation, and the voltage of an A-phase upper bridge arm of the MMC can be obtained as follows:

wherein u is_TaAnd (t) is the bridge arm voltage on the phase A, and N is the number of the bridge arm submodules.

Because the same electric quantity of each phase of the upper bridge arm and the lower bridge arm is symmetrical, the same phase of the lower bridge arm voltage u can be directly obtained from the upper bridge arm voltage_Ba(t) of (d). Considering the time delay calculated in the simulation software, the calculated bridge arm voltage also needs to be delayed by one simulation step length to obtain the accurate bridge arm voltage. The MMC common mode voltage obtained by calculating the arithmetic mean value of the corrected upper and lower bridge arm voltages is as follows:

wherein u is_comaAnd (t) is the common mode voltage of the A phase.

Due to the injection of harmonic disturbance components at the AC side and the DC side, new harmonic components appear in the circulation current inside the MMC. Therefore, the bridge arm voltage and the common-mode voltage are obtained through the first iteration according to the steps, and then the harmonic circulating current component is solved according to the common-mode voltage loop. Subsequently, the loop current and the reference voltage are corrected, and the bridge arm voltage is solved through secondary iteration. After two times of iteration process, relatively accurate upper and lower bridge arm voltages can be obtained.

In this embodiment, before performing a second iteration solution of the MMC internal bridge arm dynamics based on a reference voltage and disturbance components on an ac side and a dc side of the MMC, the method further includes: and injecting preset signal harmonic disturbance at the AC side and the DC side of the MMC simultaneously to generate disturbance components of the AC side and the DC side of the MMC.

Specifically, the embodiment of the application derives the three-port frequency coupling impedance based on a multi-harmonic linearization modeling method, wherein the harmonic linearization method is to add small-signal harmonic disturbance to a steady-state working point of a target object, extract harmonic signals under corresponding frequencies in the response of the harmonic disturbance, and further obtain the equivalent impedance of the target object. In order to establish a three-port frequency coupling impedance model capable of uniformly representing the alternating current and direct current dynamic characteristics of the MMC, small-signal harmonic disturbance needs to be injected into the alternating current side and the direct current side of the MMC at the same time. The MMC has a frequency coupling effect due to coordinate transformation and phase-locked loop dynamic in internal control, so that two harmonic disturbances with frequency coupling need to be added to a steady-state power frequency voltage signal at an AC side of the MMC at the same time, and the A-phase power grid voltage after the small-signal harmonic disturbance is added can be represented as follows:

u_a(t)＝V₁ cos(ω₁t)+V_p cos(ω_pt+φ_p)+V_p2 cos(ω_p2t+φ_p2) (7)

wherein, V₁Is the amplitude of the fundamental voltage, ω₁Is the angular frequency, omega, of the fundamental voltage₁＝2πf₁，f₁Is the frequency of the fundamental voltage; v_pIs the amplitude of the harmonic voltage, ω_pIs the angular frequency, omega, of the harmonic voltage_p＝2πf_p，f_pIs the frequency of the harmonic voltage, phi_pIs the initial phase angle of the harmonic voltage; v_p2Is the amplitude, omega, of the harmonic voltage at the coupling frequency_p2Is the angular frequency, omega, of the harmonic voltage at the coupling frequency_p2＝2πf_p2，f_p2Is the frequency of the harmonic voltage at the coupling frequency, phi_p2Is the initial phase angle of the harmonic voltage at the coupling frequency.

After two frequency-coupled harmonic disturbances are added to the steady-state power frequency voltage signal on the MMC alternating current side, the A-phase power grid current can be represented as follows:

wherein, I₁Is the amplitude of the fundamental current and,

is the initial phase angle of the fundamental current; i is_pIs the magnitude of the harmonic current and,

is the initial phase angle of the harmonic current; i is_p2Is the magnitude of the harmonic current at the coupling frequency,

is the initial phase angle of the harmonic current at the coupling frequency.

It should be noted that since the injected harmonic disturbance component is an ac signal, the positive and negative sequence phase angles of the ac signal have different representations. In order to simplify the derivation process, the embodiments of the present application may use all the ac signals to be represented in the form of phase angles of positive sequence components, distinguish the positive sequence components from the negative sequence components by the positive and negative frequency, and do not need to distinguish the positive sequence components from the negative sequence components to be represented separately.

In addition, in order to represent the direct current dynamic state of the MMC, a harmonic disturbance needs to be additionally added to a steady-state direct current voltage signal on the direct current side of the MMC, and the frequency of the harmonic disturbance of the small signal on the direct current side is related to the frequency of the harmonic disturbance injected on the alternating current side. According to the instantaneous power formula, the active power output by the MMC can be represented as:

P＝u_a(t)i_a(t)+u_b(t)i_b(t)+u_c(t)i_c(t) (9)

after considering the harmonic disturbance of two frequency couplings injected at the AC side of the MMC, the active power of the MMC contains the frequency f_p-f₁The harmonic component of (a). According to the conservation of active power, the following can be obtained:

P＝u_dc(t)i_dc(t) (10)

wherein u is_dcRepresenting a direct voltage, i_dcRepresenting a direct current.

From the above formula, after considering the harmonic disturbance injected from the AC side of the MMC, the frequency f will be generated in the DC voltage and DC current_p-f₁The harmonic component of (a). Therefore, the frequency of the harmonic disturbance of the small signal on the direct current side is f_p-f₁And the direct current dynamic of the MMC can be conveniently deduced subsequently. The dc voltage after the additional small signal harmonic disturbance can be expressed as follows:

u_dc(t)＝V_dc0+ΔV_dccos[(ω_p-ω₁)t+φ_dc] (11)

wherein, V_dc0Is the amplitude of the DC steady-state voltage, Δ V_dcIs the amplitude of the harmonic voltage on the DC side, phi_dcIs the initial phase angle of the harmonic voltage on the DC side. Based on the three harmonic disturbances injected from the alternating current side and the direct current side, the embodiment of the application establishes an MMC broadband three-port frequency coupling impedance model.

In step S103, a differential mode voltage and a common mode voltage of the MMC are calculated according to actual output voltages of an upper bridge arm and a lower bridge arm of the MMC, a differential mode voltage loop and a common mode voltage loop are respectively established based on the differential mode voltage and the common mode voltage, and a broadband three-port frequency coupling impedance model of the MMC for outputting the stability of broadband oscillation of the flexible-direct system is established by using the differential mode voltage loop and the common mode voltage loop.

It can be understood that the differential mode voltage and the common mode voltage of the MMC can be calculated through the upper and lower bridge arm voltages obtained through derivation, and the relationship between the MMC and an external circuit is established by using the differential mode voltage loop and the common mode voltage loop of the MMC to obtain the broadband three-port frequency coupling impedance model of the MMC.

Specifically, the differential mode voltage and the common mode voltage of the MMC can be further calculated through the bridge arm voltage, the differential mode voltage is actually the output voltage of the AC side of the MMC, and an expression between harmonic waves injected into the AC side can be established through the relationship between the differential mode loop and the electric quantities on the two sides of the converter transformer; the common mode voltage may be combined with a common mode loop to establish an expression between the harmonics injected on the dc side. Furthermore, a broadband three-port frequency coupling impedance model of the MMC can be established. Wherein the three-port frequency-coupled impedance model: a three-dimensional matrix containing self-impedance and transimpedance values can be represented as:

The method for establishing the MMC broadband three-port frequency-coupled impedance model according to an embodiment is described as shown in fig. 3, and includes the following steps:

step 1: deducing the phase-locked loop dynamics in the control link to obtain a frequency domain expression of harmonic components in the phase-locked loop output phase angle.

Step 2: deriving outer loop control dynamics

The outer loop control comprises active control, reactive control, direct current voltage control, alternating current voltage control and the like, derivation methods of the different controls are basically the same, and reference currents of a d axis and a q axis are finally generated.

The embodiment of the application provides the transfer function matrix of the outer ring control in the form of the modular matrix, and when different control schemes are adopted, the transfer function matrix can be replaced without deducing the whole control link again.

And step 3: deriving positive sequence current inner loop control dynamics

The positive sequence current inner loop control can adopt the current on the network side of the transformer as the input quantity, and can also adopt the current on the valve side of the transformer as the input quantity. After considering park transformation and positive sequence current inner loop PI control, the dq axis voltage reference value comprises a direct current component and a frequency f_p-f₁The harmonic component of (a).

Further, after park inverse transformation, the finally obtained three-phase voltage reference value will contain the frequency f_pAnd 2f₁-f_pThe harmonic component of (a). To unify the form of harmonic voltage disturbances, the formula at the coupling frequency is conjugated.

And 4, step 4: deriving negative sequence current inner loop control dynamics

The phase angle used by the park transformation in the negative sequence current inner loop control is obtained by inverting the phase angle of the park transformation of the positive sequence current inner loop. Considering park transformation and negative sequence current inner loop PI control, the dq axis voltage reference value includes a frequency doubling component and a frequency f_p+f₁And f_p-3f₁The harmonic component of (a). Wherein the second harmonic component is generated by the positive sequence fundamental component. In order to avoid the influence of the positive sequence fundamental component on the negative sequence current inner loop control, a link for eliminating the positive sequence fundamental component is added after park transformation.

Further, after park inverse transformation, the contained frequency of the three-phase voltage reference value is f_p、2f₁-f_p、-f_p-2f₁And f_p-4f₁The harmonic component of (a). Since the PI parameters used for the dq-axis control of the current inner loop are generally the same after the voltage and the current are unified, the following relationship holds between the dq-axis voltage reference values of different frequency components:

wherein the content of the first and second substances,

represents the d-axis voltage reference generated by the negative-sequence current inner loop,

representing the q-axis voltage reference generated by the negative-sequence current inner loop.

After the formula (12) is substituted, the frequency in the three-phase voltage reference value is f_p-4f₁And-f_p-2f₁The harmonic components of (a) are all zero. Therefore, the negative-sequence current inner loop control only outputs the frequency f finally_pAnd 2f₁-f_pThe harmonic component of (a). To unify the form of harmonic voltage disturbances, the formula at the coupling frequency is conjugated.

And 5: converter transformer broadband modeling

The positive sequence current inner loop and the negative sequence current inner loop control select the current on the valve side of the transformer as input quantity, and the dq axis current component obtained by park transformation of the input quantity is related to harmonic disturbance on the valve side. Therefore, it is necessary to derive the relationship between the transformer valve side electrical quantity and the grid side electrical quantity.

Considering the excitation reactance, the relationships between the converter transformer valve side voltage and current and the network side voltage and current phasor at the harmonic frequency and the coupling frequency can be written as follows. In order to unify the representation of the harmonic voltage and the harmonic current, the formula at the coupling frequency is conjugated.

Wherein, V'_pAnd V'_p2Respectively represent harmonic voltage components, I ', of two frequency couplings at the valve side of the transformer'_pAnd l'_p2Respectively representing harmonic current components coupled at two frequencies on the valve side of the transformer.

Step 6: deducing the overall transfer function of the control link

According to the derivation results of step 2, step 3 and step 5, the reference value of the phase-a voltage generated by the positive sequence current inner loop control can be expressed as:

wherein the content of the first and second substances,

representing the reference value of the a-phase voltage generated by the positive sequence current inner loop control.

According to the derivation results of the step 4 and the step 5, the reference value of the A-phase voltage generated by the negative sequence current inner loop control is obtained by arranging:

wherein the content of the first and second substances,

and represents the reference value of the A-phase voltage generated by the negative-sequence current inner loop control.

And superposing the voltage reference values generated by the positive sequence current inner loop control and the negative sequence current inner loop control, and obtaining the total reference voltage finally generated by the control link after a modulation ratio link. Considering the modulation ratio and the controller delay, the harmonic component in the total reference voltage can be expressed as:

wherein the content of the first and second substances,

representing the total reference voltage generated by the control element at two coupled frequencies.

And 7: MMC internal double-frequency negative sequence circulation derivation

In the steady state, in addition to the fundamental component on the ac side and the dc component on the dc side, there are two in the leg of the MMCFrequency doubling negative sequence circulation. In order to avoid the increase of the model complexity, the invention dynamically deduces the frequency doubling negative sequence circulating current component I through the bridge arm_cirThe circulation is represented by known electrical quantities and element parameters, so that the introduction of new variables is avoided, and the complexity of the model is reduced.

And 8: MMC bridge arm dynamic derivation

Based on the reference voltage obtained by derivation in the step 6, the double-frequency negative-sequence circulating current obtained by derivation in the step 7 and harmonic disturbance components at the alternating current side and the direct current side, the bridge arm output voltage of the MMC after harmonic injection can be obtained through dynamic derivation of the bridge arm of the MMC. However, the harmonic disturbance components injected from the alternating current side and the direct current side cause new harmonic components to appear in the inner circulation of the MMC, so that the dynamic state of a bridge arm needs to be solved by a secondary iteration method; and determining the component of the harmonic circulation in the first iteration, and completing the solution of the harmonic circulation and the bridge arm voltage in the second iteration. In addition, because the bridge arm dynamics involve internal circulation, the solution needs to be carried out according to two conditions of whether circulation suppression control is put into operation or not.

(1) Circulation suppression control without operation

1) First iteration

As can be seen from the single-phase topology structure diagram 1 of the MMC, the bridge arm current includes an ac side current, a dc side current, and an internal circulating current. Thus, the MMC upper arm current can be represented as:

when the circulation suppression control is not in operation, i_cira(t) contains only the frequency-doubled negative-sequence circulating current component, i'_a(t) comprises a fundamental component and has a frequency f_pAnd 2f₁-f_pOf two coupled harmonic components, i_dc(t) contains a DC component and has a frequency f_p-f₁The harmonic component of (a).

The MMC upper bridge arm modulation wave is related to reference voltage generated by a control link, and comprises a fundamental component and two harmonic components with frequency coupling under the condition that the circulation current suppression control is not operated. Because the reference voltage is calculated by the preamble control link, a simulation step length is advanced when the bridge arm voltage is calculated, the calculation delay of the preamble control link is compensated, and the calculation delay can be expressed as:

wherein the content of the first and second substances,

comprising a fundamental component and two frequency-coupled harmonic components, V₁ ^pu-r、

And

the magnitudes of the fundamental component and the two frequency-coupled harmonic components in the reference voltage,

and

the initial phase angles of the fundamental component and the two harmonic components are respectively.

Because the modulation wave of each bridge arm is the arithmetic mean value of the switching function of each submodule in the bridge arm, the arithmetic mean value of the capacitance current of the submodule can be directly calculated by the modulation wave of the bridge arm and the current of the bridge arm, and can be expressed as:

further, after the direct current component in the sub-module capacitance current is ignored, the arithmetic mean value of the sub-module capacitance voltage can be further obtained according to the capacitance value of the sub-module capacitance and the arithmetic mean value of the sub-module capacitance current, which can be expressed as:

considering the time delay of the internal calculation of the simulation software, the sub-module capacitance voltage obtained by the calculation of the formula needs to be delayed by one simulation step length and then substituted into the calculation, and the voltage of an A-phase upper bridge arm of the MMC can be obtained as follows:

as the same electric quantity of each phase of the MMC upper and lower bridge arms is symmetrical, the same phase lower bridge arm voltage u can be directly obtained from the upper bridge arm voltage_Ba(t) of (d). Considering the time delay calculated in the simulation software, the accurate bridge arm voltage can be obtained only after the bridge arm voltage obtained by the calculation is delayed by one simulation step length.

According to the expansion result of the formula 23, after considering the harmonic disturbance injected from the ac side and the dc side, the frequency-f will be coupled out from the common mode voltage of the MMC_p-f₁，f_p-3f₁，f_p+3f₁And 5f₁-f_pThe harmonic component of (a). However, the DC side of the MMC contains only a DC component and has a frequency f_p-f₁The harmonic disturbance component in the common mode voltage can be known by combining with the common mode loop, and the harmonic component in the common mode voltage can generate a harmonic component with the same frequency in the internal circulation of the MMC. Under the condition that the circulation current suppression control is not input, the bridge arm modulation wave is not changed, and the circulation current in the MMC can be rewritten as follows:

wherein, I_cirRepresenting the magnitude, phi, of a double frequency negative sequence circulating component_cirRepresenting the initial phase angle of the double frequency negative sequence circulation component; i is_cir2To representFrequency of-f_p-f₁Amplitude of harmonic circulating current component, phi_cir2Representing a frequency of-f_p-f₁Initial phase angle of harmonic circulating current component; i is_cir3Representing a frequency f_p-3f₁Amplitude of harmonic circulating current component, phi_cir3Representing a frequency f_p-3f₁Initial phase angle of harmonic circulating current component; i is_cir4Representing a frequency f_p+3f₁Amplitude of harmonic circulating current component, phi_cir4Representing a frequency f_p+3f₁Initial phase angle of harmonic circulating current component; i is_cir5Representing a frequency of 5f₁-f_pAmplitude of harmonic circulating current component, phi_cir5Representing a frequency of 5f₁-f_pInitial phase angle of the harmonic circulating current component.

2) Second iteration

According to the above derivation, the MMC internal loop current includes a frequency of-f in addition to the frequency-doubled negative sequence component_p-f₁，f_p-3f₁，f_p+3f₁And 5f₁-f_pThe harmonic component of (a). Therefore, after the loop current needs to be corrected, the secondary iteration is performed on the bridge arm dynamic state.

Calculating to obtain the arithmetic average value of the sub-module capacitance current according to the corrected bridge arm current and the bridge arm modulation wave:

after the direct current component in the sub-module capacitance current is ignored, the arithmetic mean value of the sub-module capacitance voltage can be obtained:

considering the time delay of the internal calculation of simulation software, the sub-module capacitance voltage obtained by the calculation of the formula is delayed by one simulation step length and then is substituted into the calculation, and the A-phase upper bridge arm voltage of the MMC can be obtained as follows:

because the same electric quantity of each phase of the upper bridge arm and the lower bridge arm is symmetrical, the same phase of the lower bridge arm voltage u can be directly obtained from the upper bridge arm voltage_Ba(t) of (d). Considering the time delay calculated in the simulation software, the calculated bridge arm voltage also needs to be delayed by one simulation step length to obtain the accurate bridge arm voltage.

(2) Circulation suppression control commissioning

1) First iteration

In the case of the operation of the circulation suppression control, the double-frequency negative sequence circulation is no longer present, and the reference voltage generated by the control element additionally comprises the double-frequency negative sequence component generated by the circulation control. Because the reference voltage is calculated by the preamble control link, a simulation step length is advanced when the bridge arm voltage is calculated, the calculation delay of the preamble control link is compensated, and the calculation delay can be expressed as:

wherein the content of the first and second substances,

comprising a fundamental component, a double-frequency negative sequence component and two frequency-coupled harmonic components, V_cirRepresenting the amplitude, phi, of a double-frequency negative sequence component in a reference voltage_cirVThe initial phase angle of the double-frequency negative sequence component in the reference voltage is shown.

And (3) calculating to obtain an arithmetic average value of the sub-module capacitance current by the bridge arm modulation wave and the bridge arm current:

further, after the direct current component in the sub-module capacitance current is ignored, the arithmetic mean value of the sub-module capacitance voltage can be obtained according to the capacitance value of the sub-module capacitance and the arithmetic mean value of the sub-module capacitance current:

According to the expansion result of the formula 32, after the harmonic disturbance injected from the ac side and the dc side is considered, the frequency-f will be coupled out from the common mode voltage of the MMC_p-f₁And f_p-3f₁The harmonic component of (a). However, the DC side of the MMC contains only a DC component and has a frequency f_p-f₁The harmonic disturbance component in the common-mode voltage can be known by combining with the common-mode loop, the harmonic component in the common-mode voltage will generate a harmonic component with the same frequency in the internal circulating current of the MMC, and the internal circulating current of the MMC can be expressed as:

i_cira(t)＝I_cir2 cos[-(ω_p+ω₁)t+φ_cir2]+I_cir3 cos[(ω_p-3ω₁)t+φ_cir3] (33)

further, according to the circulation-current suppression control structure, the above-mentioned harmonic circulation current will generate a frequency of-f in the output of the circulation-current control_p-f₁And f_p-3f₁Of the reference voltage component. Thus, can beThe bridge arm modulated wave can be rewritten as:

wherein, V_cir2、V_cir3Respectively indicating the frequencies-f in the reference voltages generated by the circulating current suppression control_p-f₁And f_p-3f₁Of the two harmonic components of phi_cirV2、φ_cirV3Respectively representing the initial phase angles of the two harmonic components.

2) Second iteration

According to the derivation, the MMC inner circulation additionally comprises the frequency of-f_p-f₁And f_p-3f₁Will additionally include a harmonic component of frequency-f in the reference voltage_p-f₁And f_p-3f₁The harmonic component of (a). Therefore, after the internal circulating current and the reference voltage need to be corrected, the secondary iteration is carried out on the bridge arm dynamic state. And calculating the arithmetic average value of the sub-module capacitance current by the corrected bridge arm modulation wave and the bridge arm current, wherein the arithmetic average value can be expressed as:

after the direct current component in the sub-module capacitance current is ignored, the sub-module capacitance voltage can be further obtained:

Therefore, after two iteration processes, relatively accurate upper and lower bridge arm voltages can be obtained;

the differential mode voltage and the common mode voltage of the MMC can be further calculated by the bridge arm voltage, the differential mode voltage is actually the output voltage of the AC side of the MMC, and an expression between harmonic waves injected into the AC side can be established through the relation between the differential mode loop and the electric quantities at two sides of the converter transformer; the common mode voltage can be combined with a common mode loop, and an expression between the common mode voltage and the harmonic wave injected by the direct current side can be established.

And step 9: bulk impedance model derivation

According to the single-phase topology structure diagram of the MMC, a common-mode loop of the MMC can be established as follows:

according to the common-mode loop formula, the same-frequency components on both sides of the equation are still equal. And (4) obtaining a harmonic component newly appearing in the MMC internal circulation by using the common-mode voltage obtained in the step 8, and representing each harmonic circulation component by using known electrical quantities and parameters.

Because the direct current voltage only contains direct current component and has the frequency of f_p-f₁Is derived for the purpose of obtaining a three-port frequency-coupled impedance model, and therefore only concerns the frequency f in the common-mode voltage_p-f₁Part (c) of (a). According to the bridge arm voltage deduced in the step 8, the frequency f in the common mode voltage can be obtained_p-f₁The component (c). Further combining with the common mode voltage loop, we can obtain:

according to the single-phase topological structure diagram of the MMC, a differential mode loop of the MMC can be established as follows:

wherein the content of the first and second substances,

the differential mode voltage of the MMC is represented and is also the potential of a virtual point between an upper bridge arm and a lower bridge arm of the MMC

Referred to as the output voltage on the ac side of the MMC.

Since the MMC alternating current side contains only the fundamental component and the two frequency-coupled harmonic disturbance components. In order to facilitate subsequent derivation of the three-port frequency-coupled impedance model, the frequency f in the differential mode voltage is focused_pAnd f_p2Part (c) of (a). Further, substituting the derivation result of the harmonic circulation, the frequency can be f_pIs expressed as:

wherein the content of the first and second substances,

representing a frequency f_pThe MMC AC side of (1) outputs voltage phasor.

From the derivation, a frequency of 2f can be obtained₁-f_pThe differential mode voltage component of (a) and injected harmonic perturbations. To unify the representation of harmonic voltage and harmonic current, the frequency is 2f₁-f_pThe differential mode voltage of (d) takes the conjugate and is represented as:

wherein the content of the first and second substances,

representing a frequency of 2f₁-f_pThe output voltage phasor at the ac side of the MMC.

By combining the formula 39, the formulas 41 and 42, a three-dimensional transfer function matrix of the output voltage at the ac side and the dc harmonic voltage of the MMC can be obtained as follows:

wherein the content of the first and second substances,

substituting the voltage and current relationship between the network side and the valve side of the converter transformer obtained in the step 5 into a differential mode loop shown in a formula 40 to obtain the relationship between the output voltage of the MMC alternating current side and the injected harmonic disturbance; further considering the dynamic state of the direct current port, the three-dimensional transfer function matrix of the MMC with the external alternating current and direct current characteristics can be obtained as follows:

by combining equations 43 and 44, we can obtain:

wherein the content of the first and second substances,

from the above formula, it is possible to obtain:

in conclusion, through the derivation of the MMC control link, the internal bridge arm dynamics and the external circuit, the broadband three-port frequency coupling impedance model of the MMC is finally formed. Due to the fact that all aspects of factors such as MMC control delay, signal transmission and calculation delay in simulation software, MMC internal circulation and circulation suppression control and the like are considered, the accuracy of the obtained model in a wide frequency range can be guaranteed. In addition, the model establishes the coupling relation between the AC side and the DC side of the converter, and lays a foundation for the stability analysis of the flexible direct current system.

Next, an apparatus for establishing a wideband three-port frequency-coupled impedance model of an MMC according to an embodiment of the present application is described with reference to the drawings.

Fig. 4 is a block diagram illustrating an apparatus for establishing a wideband three-port frequency-coupled impedance model of an MMC according to an embodiment of the present disclosure.

As shown in fig. 4, the apparatus 10 for establishing the MMC broadband three-port frequency-coupled impedance model includes: derivation module 100, solution module 200, and modeling module 300.

The derivation module 100 is configured to establish a three-dimensional transfer function matrix of an MMC internal control link, and determine a reference voltage generated by the MMC internal control link based on the three-dimensional transfer function matrix; the solving module 200 is used for performing secondary iteration solving on the dynamic of an inner bridge arm of the MMC based on the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain actual output voltages of an upper bridge arm and a lower bridge arm of the MMC; the modeling module 300 is configured to calculate a differential mode voltage and a common mode voltage of the MMC according to actual output voltages of an upper bridge arm and a lower bridge arm of the MMC, respectively establish a differential mode voltage loop and a common mode voltage loop based on the differential mode voltage and the common mode voltage, respectively establish a broadband three-port frequency coupling impedance model of the MMC by using the differential mode voltage loop and the common mode voltage loop, and establish a broadband three-port frequency coupling impedance model of the MMC, which is used for outputting stability of broadband oscillation of the flexible-direct system, by using the differential mode voltage loop and the common mode voltage loop.

Further, the broadband three-port frequency coupling impedance model is as follows:

Furthermore, the derivation module is further used for acquiring phase-locked loop dynamics, outer loop control dynamics, positive sequence current inner loop control dynamics and negative sequence current inner loop control dynamics in the control link; and establishing a three-dimensional transfer function matrix according to the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state.

Further, the solving module is further used for carrying out first iteration solving on the basis of the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain a harmonic circulating current component; and carrying out second iteration solution on the dynamic state of the bridge arm based on the harmonic circulating current component to generate actual output voltages of an upper bridge arm and a lower bridge arm of the MMC.

Further, still include: and the injection module is used for simultaneously injecting preset signal harmonic disturbance at the alternating current side and the direct current side of the MMC to generate disturbance components of the alternating current side and the direct current side of the MMC before carrying out secondary iteration solution of bridge arm dynamics inside the MMC on the basis of reference voltage and the disturbance components of the alternating current side and the direct current side of the MMC.

It should be noted that the explanation of the aforementioned embodiment of the method for establishing the MMC broadband three-port frequency-coupled impedance model is also applicable to the apparatus for establishing the MMC broadband three-port frequency-coupled impedance model of the embodiment, and details are not repeated herein.

According to the device for establishing the MMC broadband three-port frequency coupling impedance model, the broadband three-port frequency coupling impedance model of the MMC is finally formed through the derivation of an MMC control link, the dynamic state of an internal bridge arm and an external circuit, the accuracy of the obtained model in a broadband range can be ensured due to the fact that all aspects of factors such as MMC control delay, signal transmission and calculation delay in simulation software, MMC internal circulation and circulation suppression control and the like are considered, meanwhile, the model establishes the coupling relation between the AC side and the DC side of the converter, and a foundation is laid for the stability analysis of a flexible-direct system.

Fig. 5 is a schematic structural diagram of an electronic device according to an embodiment of the present application. The electronic device may include:

a memory 501, a processor 502, and a computer program stored on the memory 501 and executable on the processor 502.

The processor 502 executes the program to implement the method for establishing the MMC broadband three-port frequency-coupled impedance model provided in the above embodiments.

Further, the electronic device further includes:

a communication interface 503 for communication between the memory 501 and the processor 502.

A memory 501 for storing computer programs that can be run on the processor 502.

The Memory 501 may include a high-speed RAM (Random Access Memory) Memory, and may also include a nonvolatile Memory, such as at least one disk Memory.

If the memory 501, the processor 502 and the communication interface 503 are implemented independently, the communication interface 503, the memory 501 and the processor 502 may be connected to each other through a bus and perform communication with each other. The bus may be an ISA (Industry Standard Architecture) bus, a PCI (Peripheral Component interconnect) bus, an EISA (Extended Industry Standard Architecture) bus, or the like. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, only one thick line is shown in FIG. 5, but this is not intended to represent only one bus or type of bus.

Optionally, in a specific implementation, if the memory 501, the processor 502, and the communication interface 503 are integrated on a chip, the memory 501, the processor 502, and the communication interface 503 may complete communication with each other through an internal interface.

The processor 502 may be a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), or one or more Integrated circuits configured to implement embodiments of the present Application.

An embodiment of the present application further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the method for establishing the MMC broadband three-port frequency-coupled impedance model as described above.

In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or N embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "N" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more N executable instructions for implementing steps of a custom logic function or process, and alternate implementations are included within the scope of the preferred embodiment of the present application in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of implementing the embodiments of the present application.

It should be understood that portions of the present application may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. If implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a programmable gate array, a field programmable gate array, or the like.

It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.

Although embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present application, and that variations, modifications, substitutions and alterations may be made to the above embodiments by those of ordinary skill in the art within the scope of the present application.

Claims

1. A method for establishing an MMC broadband three-port frequency coupling impedance model is characterized by comprising the following steps of:

establishing a three-dimensional transfer function matrix of an MMC internal control link, and determining a reference voltage generated by the MMC internal control link based on the three-dimensional transfer function matrix;

performing secondary iteration solution of the dynamic of an inner bridge arm of the MMC on the basis of the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain actual output voltages of an upper bridge arm and a lower bridge arm of the MMC; and

calculating differential mode voltage and common mode voltage of the MMC according to actual output voltage of an upper bridge arm and actual output voltage of a lower bridge arm of the MMC, establishing a differential mode voltage loop and a common mode voltage loop respectively based on the differential mode voltage and the common mode voltage, and establishing a broadband three-port frequency coupling impedance model of the MMC, wherein the broadband three-port frequency coupling impedance model is used for outputting the broadband oscillation stability of a flexible-straight system, and the broadband three-port frequency coupling impedance model is established by utilizing the differential mode voltage loop and the common mode voltage loop.

2. The method of claim 1, wherein the broadband three-port frequency-coupled impedance model is:

3. The method of claim 1, wherein establishing a three-dimensional transfer function matrix of an MMC internal control element comprises:

acquiring the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state in a control link;

and establishing the three-dimensional transfer function matrix according to the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state.

4. The method according to claim 1, wherein the obtaining of the actual output voltages of the upper bridge arm and the lower bridge arm of the MMC by performing a second iteration solution of the MMC internal bridge arm dynamics based on the reference voltage and disturbance components of the ac side and the dc side of the MMC comprises:

performing first iteration solution on the basis of the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain a harmonic circulating current component;

and carrying out second iteration solution on the dynamic state of the bridge arm based on the harmonic circulating current component to generate actual output voltages of an upper bridge arm and a lower bridge arm of the MMC.

5. The method according to claim 1 or 4, wherein before performing the quadratic iterative solution of the MMC internal bridge arm dynamics based on the reference voltage and disturbance components of the AC side and DC side of the MMC, further comprising:

and injecting preset signal harmonic disturbance into the AC side and the DC side of the MMC simultaneously to generate disturbance components of the AC side and the DC side of the MMC.

6. The utility model provides a device for establishing MMC wide band three-port frequency coupling impedance model which characterized in that includes:

the device comprises a derivation module, a conversion module and a control module, wherein the derivation module is used for establishing a three-dimensional transfer function matrix of an MMC internal control link and determining a reference voltage generated by the MMC internal control link based on the three-dimensional transfer function matrix;

the solving module is used for carrying out secondary iteration solving on the dynamic state of an inner bridge arm of the MMC on the basis of the reference voltage and disturbance components of an alternating current side and a direct current side of the MMC to obtain actual output voltages of an upper bridge arm and a lower bridge arm of the MMC; and

the modeling module is used for calculating the differential mode voltage and the common mode voltage of the MMC according to the actual output voltage of the upper bridge arm and the actual output voltage of the lower bridge arm of the MMC, establishing a differential mode voltage loop and a common mode voltage loop respectively based on the differential mode voltage and the common mode voltage, establishing the broadband three-port frequency coupling impedance model of the MMC by utilizing the differential mode voltage loop and the common mode voltage loop, and establishing the broadband three-port frequency coupling impedance model of the MMC for outputting the stability of the broadband oscillation of the flexible-direct system by utilizing the differential mode voltage loop and the common mode voltage loop.

7. The apparatus of claim 6, wherein the broadband three-port frequency-coupled impedance model is:

8. The apparatus of claim 6, wherein the derivation module is further configured to obtain a phase-locked loop dynamic state, an outer loop control dynamic state, a positive sequence current inner loop control dynamic state, and a negative sequence current inner loop control dynamic state in the control link; and establishing the three-dimensional transfer function matrix according to the phase-locked loop dynamic state, the outer loop control dynamic state, the positive sequence current inner loop control dynamic state and the negative sequence current inner loop control dynamic state.

9. The apparatus according to claim 6, wherein the solving module is further configured to perform a first iterative solution based on the reference voltage and disturbance components on the ac side and the dc side of the MMC to obtain a harmonic circulating current component; and carrying out second iteration solution on the dynamic state of the bridge arm based on the harmonic circulating current component to generate actual output voltages of an upper bridge arm and a lower bridge arm of the MMC.

10. The apparatus of claim 6 or 9, further comprising:

and the injection module is used for injecting preset signal harmonic disturbance to the alternating current side and the direct current side of the MMC simultaneously to generate disturbance components of the alternating current side and the direct current side of the MMC before carrying out secondary iteration solution on the dynamic of a bridge arm in the MMC on the basis of the reference voltage and the disturbance components of the alternating current side and the direct current side of the MMC.

11. An electronic device, comprising: memory, processor and computer program stored on the memory and executable on the processor, the processor executing the program to implement the method of establishing the MMC broadband three-port frequency-coupled impedance model according to any of claims 1-5.

12. A computer-readable storage medium, on which a computer program is stored, the program being executed by a processor for implementing the method of establishing the MMC broadband three-port frequency-coupled impedance model according to any of claims 1-5.