Impedance modeling method, apparatus, and computer device

Abstract

The application relates to an impedance modeling method, device and computer equipment. The method comprises the following steps: injecting a disturbance voltage to an AC side of a main circuit, obtaining a first relationship between a small signal modulation and an AC current small signal through an AC control topology, and determining a second relationship between the small signal modulation and an AC voltage small signal through a phase-locked loop associated with the disturbance voltage and a phase angle small signal; injecting the disturbance voltage to a DC side of the main circuit, determining a third relationship between the small signal modulation and the AC current small signal and a fourth relationship between DC current small signals based on the AC control topology and a DC control topology; and finally, combining a frequency small signal model to perform impedance modeling, so as to accurately reflect self-impedance and coupling impedance characteristics of the AC side and the DC side, and provide a basis for analyzing system stability and optimizing a control strategy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of smart grid control, in particular to an impedance modeling method and device and computer equipment. BACKGROUND

[0002] In power grid control, how to realize stable output of electric energy and grid connection adaptation becomes a core demand. Among them, the two-level voltage source converter can effectively suppress the power fluctuation of new energy generation and ensure that the power quality meets the grid connection standard, due to its precise regulation and control ability of output voltage amplitude, frequency and phase.

[0003] However, the impedance modeling process of traditional two-level voltage source converter (VSC) usually adopts a 2-order transfer function matrix, which only describes the AC side impedance characteristics, and has the following problems: the influence of DC bus voltage fluctuation on the AC side is not considered, especially under weak grid conditions, the error is significant; the coupling is simplified, only assuming that the AC side dq axis is completely decoupled, but the actual high frequency coupling effect is obvious; it cannot analyze the DC side stability, such as the DC bus resonance problem in photovoltaic grid-connected system. SUMMARY

[0004] Based on this, the purpose of the present application is to provide an impedance modeling method, device and computer equipment capable of realizing accurate power control under unbalanced power grid, to solve the technical problems mentioned in the background technology.

[0005] In the first aspect, the present application provides an impedance modeling method. Applied to a two-level voltage source converter, including a main circuit, an AC control topology and a phase-locked loop, wherein:

[0006] When a disturbance voltage is injected into the AC side of the main circuit, a first frequency small signal model in the AC loop is determined;

[0007] Based on the AC control topology, a first relationship between the modulation small signal and the AC current small signal is determined;

[0008] Based on the phase-locked loop, the disturbance voltage and the phase angle small signal are associated, and a second relationship between the modulation small signal and the AC voltage small signal is determined;

[0009] According to the first relationship, the second relationship and the first frequency small signal model, impedance modeling is performed.

[0010] In one embodiment, the AC control topology comprises a proportional-integral regulator and a decoupling module; the modulation small signal comprises a first modulation small signal; the first relationship between the modulation small signal and the AC current small signal is determined based on the AC control topology, comprising: performing a Park transformation on the AC current small signal according to the fundamental voltage phase; processing the transformed AC current small signal through the proportional-integral regulator and the decoupling module to obtain an initial modulation small signal; performing an inverse Park transformation on the initial modulation small signal to obtain the first modulation small signal, and converting the first relationship between the first modulation small signal and the AC current small signal.

[0011] In one embodiment, the disturbance voltage and the phase angle small signal are associated based on the phase-locked loop, comprising: determining an AC voltage after the disturbance voltage is subjected to a Park transformation; determining a relationship between the AC voltage and the phase angle small signal according to the fundamental voltage amplitude and the fundamental voltage phase; and associating the disturbance voltage and the phase angle small signal according to a transfer function of the phase-locked loop and the relationship between the AC voltage and the phase angle small signal.

[0012] In one embodiment, the modulation small signal comprises a second modulation small signal; the second relationship between the modulation small signal and the AC voltage small signal is determined, comprising: superimposing the phase angle small signal associated with the disturbance voltage into the AC control topology; performing a Park transformation on the AC current small signal superimposed with the phase angle small signal until a candidate modulation small signal is determined through the proportional-integral regulator and the decoupling module in the AC control topology; performing an inverse Park transformation on the candidate modulation small signal superimposed with the phase angle small signal to obtain the second modulation small signal, and converting the second relationship between the second modulation small signal and the AC voltage small signal.

[0013] In one embodiment, the two-level voltage source converter further comprises a DC control topology, and the method further comprises: determining a second frequency small signal model in the AC loop when the disturbance voltage is injected into the DC side of the main circuit; determining a third relationship between the modulation small signal and the AC current small signal based on the AC control topology; determining a fourth relationship between the modulation small signal and the DC voltage small signal based on the DC control topology; and performing impedance modeling according to the third relationship, the fourth relationship, and the second frequency small signal model.

[0014] In one embodiment, the modulation small signal further comprises a third modulation small signal; the fourth relationship between the modulation small signal and the DC voltage small signal is determined based on the DC control topology, comprising: determining an initial current according to the DC voltage small signal and a transfer function of the DC control topology; determining a target modulation small signal according to the initial current and a transfer function of the AC control topology; performing an inverse Park transformation on the target modulation small signal to obtain the third modulation small signal, and converting the fourth relationship between the third modulation small signal and the DC current small signal.

[0015] In a second aspect, the present application also provides an impedance modeling device. The device is applied to a two-level voltage source converter, and comprises a main circuit, an AC control topology, and a phase-locked loop, wherein:

[0016] A first relationship determining module is configured to determine a first frequency small signal model in an AC loop when a disturbance voltage is injected into an AC side of the main circuit, and determine a first relationship between a modulation small signal and an AC current small signal based on the AC control topology;

[0017] A second relationship determining module is configured to associate the disturbance voltage and a phase angle small signal based on the phase-locked loop, and determine a second relationship between the modulation small signal and an AC voltage small signal, and perform impedance modeling according to the first relationship, the second relationship, and the first frequency small signal model.

[0018] In an embodiment, the two-level voltage source converter further comprises a DC control topology, and the device further comprises:

[0019] A third relationship determining module is configured to determine a second frequency small signal model in the AC loop when the disturbance voltage is injected into a DC side of the main circuit, and determine a third relationship between the modulation small signal and the AC current small signal based on the AC control topology;

[0020] A fourth relationship determining module is configured to determine a fourth relationship between the modulation small signal and a DC current small signal based on the DC control topology, and perform impedance modeling according to the third relationship, the fourth relationship, and the second frequency small signal model.

[0021] In a third aspect, the present application also provides a computer device. The computer device comprises a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above impedance modeling method when executing the computer program.

[0022] In a fourth aspect, the present application also provides a computer readable storage medium. The computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the steps of the above impedance modeling method.

[0023] The above impedance modeling method, device, computer device, and readable storage medium inject a disturbance voltage into an AC side of a main circuit, determine a first frequency small signal model in an AC loop, determine a first relationship between a modulation small signal and an AC current small signal based on an AC control topology, associate a disturbance voltage and a phase angle small signal based on a phase-locked loop, determine a second relationship between the modulation small signal and an AC voltage small signal, and perform impedance modeling according to the three relationships. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1A main circuit topology of a two-level voltage source converter in one embodiment;

[0025] Figure 2 A flow chart of an impedance modeling method in one embodiment;

[0026] Figure 3 An AC control topology in one embodiment;

[0027] Figure 4 A PLL control topology in one embodiment;

[0028] Figure 5 A flow chart of an impedance modeling method in another embodiment;

[0029] Figure 6 A DC control topology in one embodiment;

[0030] Figure 7 An impedance definition and distribution in one embodiment;

[0031] Figure 8 A flow chart of an impedance modeling method in another embodiment;

[0032] Figure 9 An internal structure of a computer device in one embodiment;

[0033] Figure 1 In one embodiment, represents three-phase AC port currents, represents three-phase AC port voltages, represents DC side currents, represents DC port voltages, represents equivalent output currents of converter legs, L represents filter inductances, C dc represents capacitances;

[0034] Figure 3 In one embodiment, represents three-phase AC port currents, represents current components in dq coordinate system after Park transformation, represents modulation signals in dq coordinate system, represents three-phase modulation signals after inverse Park transformation, represents PLL phase angle, represents d-axis reference currents in dq coordinate system, represents q-axis reference currents in dq coordinate system, represents decoupling gains, represents current PI control transfer functions;

[0035] Figure 4 Vd, Vq represent three-phase voltage of AC port, Vd, Vq represent three-phase voltage of AC port, Vd, Vq represent voltage components in dq coordinate system after Park transformation, φ represent phase angle of phase-locked loop, Kp, Ki represent PI control transfer function of phase-locked loop, ω represent angular frequency correction value, ω represent rated angular frequency;

[0036] Figure 6 Vd, Vq represent three-phase voltage of AC port, Vd, Vq represent three-phase voltage of AC port, Vd, Vq represent three-phase voltage of AC port, Id, Iq represent d-axis reference current in dq coordinate system, Kp, Ki represent PI control transfer function of phase-locked loop. DETAILED DESCRIPTION

[0037] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0038] The impedance modeling method provided by the embodiments of the present application can be applied to a two-level voltage source converter, such as Figure 1 as shown in the figure, Figure 1 is a main circuit topology of a two-level voltage source converter. It is composed of a three-phase full-bridge circuit, each phase including two IGBTs with anti-parallel diodes, a total of 6 switching devices; the DC side is supported by a stable voltage provided by a capacitor, and the AC side outputs controllable AC voltage through PWM modulation; it supports decoupled control of active power and reactive power, and is suitable for occasions that require flexible power adjustment. The self-impedance and coupling impedance obtained through impedance modeling are the frequency domain identity cards of the two-level voltage source converter, which can be used in new energy grid-connected inverters, static synchronous compensators, energy storage, high-voltage direct current transmission, etc. They can be used to calculate the wideband stability margin, lock the oscillation source, optimize the PLL and voltage loop gain, and design the feedforward canceller; they can also quantitatively add LC filtering, evaluate the short-circuit ratio of the power grid, set the high-frequency protection threshold, and realize the closed-loop of the whole life cycle of equipment grid-connected design, operation and upgrading.

[0039] In one embodiment, as shown in the figure, Figure 2 a kind of impedance modeling method is provided, applied to two-level voltage source converter, including main circuit, AC control topology and phase-locked loop, including the following steps:

[0040] Step S202, when a disturbance voltage is injected into the AC side of the main circuit, a first frequency small signal model in the AC circuit is determined.

[0041] In this application, the small-signal representation only retains the small perturbation amount that deviates from the steady-state operating point, and does not consider the signal quantity when higher-order nonlinear terms are not considered.

[0042] Specifically, when a disturbance voltage is injected at the AC side port of the main circuit and there is no disturbance voltage at the DC side port, the current response data sequence is simultaneously acquired. At this time, the time-domain model of the main circuit is transformed into a first frequency-domain small-signal model under the AC loop. For example, using... Figure 1 Taking phase a as an example, the small-signal model of the first frequency is determined as follows: .in, This represents the small-signal component of the phase a current in the three-phase AC current. Indicates the DC bus voltage. This represents the small signal component modulated by phase a. Y represents the small-signal component of phase a voltage. lp This represents a diagonal admittance matrix.

[0043] In one embodiment, the determination is made based on the AC side port response data sequence at the disturbance frequency. At this point, all three phase responses are zero sequence. The diagonal element at the corresponding position is 0, as shown below:

[0044] ;

[0045] in, L Indicates the filter inductance. The imaginary unit, , , , , This is the fundamental frequency.

[0046] Step S204: Determine the first relationship between the modulated small signal and the AC current small signal based on the AC control topology.

[0047] Specifically, such as Figure 3 The AC control topology diagram is shown. After the small AC current signal is input to the AC control topology, it undergoes Parker transformation and small-signal linearization to obtain the small current signal in dq coordinates. Then, this small current signal in dq coordinates is passed through a regulator and decoupling circuit to obtain the initial modulated small signal (m). d m q Finally, the initial modulation signal is subjected to an inverse Parker transform to obtain the modulation signal (m) in the three-phase stationary coordinate system. a m b m cThis leads to the determination of the first relationship Q between the modulation small signal and the AC current small signal. The Q matrix represents the dependence of the modulation signal on the AC side port current, determined by the current control of the two-level voltage source converter.

[0048] Step S206: Based on the phase-locked loop correlation of disturbance voltage and phase angle small signal, determine the second relationship between modulation small signal and AC voltage small signal.

[0049] Specifically, such as Figure 4 The diagram shows a phase-locked loop (PLL) control topology. When a disturbance voltage is input to the PLL, it undergoes Parker transformation and PLL transfer function processing sequentially, yielding the harmonic vector relationship between the input disturbance voltage and the output phase angle small signal. However, when considering the effects of a non-ideal PLL, the grid current in the AC control topology, after coordinate transformation, interacts with the harmonic vector of the phase angle small signal, generating additional harmonic components. Therefore, refer to... Figure 3 As shown, the phase angle small signal also needs to be... This is superimposed onto the AC control topology to further consider the second relationship P between the modulated small signal and the AC voltage small signal corresponding to the disturbance voltage. The P matrix represents the dependence of the modulated small signal on the AC side port voltage, and is jointly determined by the phase-locked loop and the current control of the two-level voltage source converter.

[0050] Step S208: Impedance modeling is performed based on the first relation, the second relation, and the first frequency small-signal model.

[0051] When a positive sequence voltage disturbance is applied to the AC side port At that time, the AC side port of the two-level voltage source converter generates a frequency of The positive sequence current, the positive sequence self-admittance is The DC-side port generates a frequency of... The current, i.e., the coupling admittance. The frequency generated by the AC side port is The negative sequence current, i.e., the coupling admittance. When a negative sequence voltage disturbance is applied to the AC side port At that time, the AC side port of the two-level voltage source converter generates a frequency of The negative sequence current, the negative sequence self-admittance is The DC-side port generates a frequency of... The current, i.e., the coupling admittance. The frequency generated by the AC side port is The positive sequence current, i.e., the coupling admittance. .

[0052] Specifically, the first relationship between the modulation small signal and the alternating current small signal and the second relationship between the modulation small signal and the alternating voltage small signal are determined to determine the modulation small signal m a The first target relationship between the alternating current small signal i a and the alternating voltage small signal v a is: The first target relationship is substituted into the first frequency small signal model and is moved to simplify to obtain a harmonic component relationship between the alternating current small signal and the alternating voltage small signal, so that the self-inductance and the coupling inductance corresponding to different disturbances are determined according to the harmonic component relationship.

[0053] In the above impedance modeling method, the disturbance voltage is injected into the alternating side of the main circuit to determine the first frequency small signal model of the alternating loop; the first relationship between the modulation and the alternating current small signal is determined through the alternating control topology, and the second relationship between the modulation and the alternating voltage small signal is determined by associating the disturbance voltage and the phase angle small signal through the phase-locked loop; the three are combined to model to accurately reflect the impedance characteristics of the alternating side, and provide a basis for analyzing system stability and optimizing control strategy.

[0054] In one embodiment, as shown in Figure 5 , the flowchart of the impedance modeling method when the disturbance voltage is injected into the alternating side is shown in Figure 5 . The method includes: converting the time domain model of the main circuit into the first frequency domain small signal model under the alternating loop; determining the first relationship between the modulation small signal and the alternating current small signal based on the alternating port current control and calculating the expression of the modulation small signal about the alternating current small signal; determining the second relationship between the modulation small signal and the alternating voltage small signal based on the phase-locked loop and the alternating port current control and calculating the expression of the modulation small signal about the alternating voltage small signal; and substituting the expression related to the modulation small signal into the first frequency domain small signal model to obtain the impedance modeling result of the alternating side.

[0055] Among them, the related parameters mentioned in the present application include the fundamental frequency current amplitude , the fundamental frequency current amplitude , the fundamental wave voltage phase (for example, 30°), the fundamental wave current phase (for example, 15°), the DC bus voltage , the current PI control integral coefficient , the phase-locked loop PI control proportional coefficient and the integral coefficient , the voltage PI control proportional coefficient and the integral coefficient , the decoupling gain , the modulator gain , the disturbance frequency , and the fundamental frequency .

[0056] In one embodiment, determining the first relationship between the modulation small signal and the alternating current small signal based on the alternating current control topology comprises: performing a Park transformation on the alternating current small signal according to a fundamental voltage phase; processing the transformed alternating current small signal through a proportional-integral regulator and a decoupling module to obtain an initial modulation small signal; performing an inverse Park transformation on the initial modulation small signal to obtain a first modulation small signal, and converting the first modulation small signal into the first relationship between the first modulation small signal and the alternating current small signal.

[0057] The alternating current control topology comprises the proportional-integral regulator and the decoupling module; and the modulation small signal comprises the first modulation small signal.

[0058] Specifically, referring to FIG. 1, after the Park transformation is performed on the alternating current small signal, the current small signal in the dq coordinate system is obtained as follows: Figure 3

[0059]

[0060] wherein, , is a fundamental voltage phase, represents an alternating current port three-phase current small signal component, represents a dq coordinate system d-axis and q-axis current small signal component. The coordinate conversion matrix is:

[0061]

[0062] Then, when the current small signal in the dq coordinate system passes through the proportional-integral regulator and the decoupling module, the obtained initial modulation small signal is as follows:

[0063]

[0064] wherein, represents a proportional-integral regulator transfer function, represents a decoupling gain. Finally, after the inverse Park transformation is performed to the three-phase stationary coordinate system, the harmonic vector expression of the first modulation small signal is as follows:

[0065]

[0066] The first relationship Q between the first modulation small signal and the alternating current small signal is simplified as follows:

[0067]

[0068] wherein represents a modulator gain.

[0069] ​​​​​​In the embodiment, first, the AC current small signal is subjected to a Park transformation according to the fundamental voltage phase, to realize AC to DC conversion; then, the initial modulation small signal is obtained through a proportional-integral regulator and a decoupling module; finally, the first modulation small signal is obtained through an inverse Park transformation, and the first relationship between the first modulation small signal and the original AC current small signal is determined, to avoid the problem of excessively simplified coupling, lay a foundation for accurate current control, and improve the regulation efficiency and accuracy.

[0070] In one embodiment, when a positive sequence voltage disturbance is injected:

[0071] ;

[0072] wherein:

[0073] ;

[0074] In one embodiment, the disturbance voltage and the phase angle small signal are associated based on a phase-locked loop, including: determining the AC voltage after the Park transformation of the disturbance voltage; determining the relationship between the AC voltage and the phase angle small signal according to the fundamental voltage amplitude and the fundamental voltage phase; and associating the disturbance voltage and the phase angle small signal according to the transfer function of the phase-locked loop and the relationship between the AC voltage and the phase angle small signal.

[0075] Specifically, when the phase angle small signal existing in the phase-locked loop is considered, the new coordinate conversion matrix is:

[0076] ;

[0077] After the disturbance voltage is subjected to the Park transformation through the new coordinate conversion matrix, the output AC voltage in the dq coordinate system is:

[0078] ;

[0079] After simplification, the relationship between the AC voltage and the phase angle small signal is: ;

[0080] wherein, is a 5x5 matrix, the elements in positions (2, 1), (2, 3), and (5, 4) are , and , and the elements in other positions are 0. In combination with the transfer function in the control block diagram of the phase-locked loop, the harmonic vector expression of the phase-locked loop output phase angle small signal when the positive sequence voltage disturbance is input is as follows:

[0081] ;

[0082] In the embodiment, the AC voltage after the perturbation voltage is determined by the Park transformation, which provides a basis for the subsequent correlation; the relationship between the AC voltage and the phase angle small signal is determined by combining the fundamental voltage amplitude and the fundamental voltage phase; and finally, the perturbation voltage and the phase angle small signal are correlated by using the phase-locked loop transfer function, which provides a basis for accurately analyzing the influence of the perturbation on the phase angle and optimizing the phase-locked loop control.

[0083] In one embodiment, the second relationship between the modulation small signal and the AC voltage small signal can be obtained after the relationship between the AC voltage and the phase angle small signal is determined.

[0084] ;

[0085] wherein the AC voltage small signal is , ;

[0086] In one embodiment, the second relationship between the modulation small signal and the AC voltage small signal is determined by: superimposing the phase angle small signal correlated with the perturbation voltage into the AC control topology; performing the Park transformation on the AC current small signal superimposed with the phase angle small signal until the candidate modulation small signal is determined by passing through the proportional-integral regulator and the decoupling module in the AC control topology; performing the inverse Park transformation on the candidate modulation small signal superimposed with the phase angle small signal to obtain the second modulation small signal, and converting the second modulation small signal into the second relationship between the second modulation small signal and the AC voltage small signal.

[0087] wherein the modulation small signal includes the second modulation small signal.

[0088] Specifically, referring to the phase angle small signal Figure 3 has been input into the AC control topology in , therefore, the new current small signal without the steady-state term is obtained after the Park transformation on the AC current small signal superimposed with the phase angle small signal as follows:

[0089] ;

[0090] Then, the candidate modulation small signal is obtained after the new current small signal in the dq coordinate system passes through the proportional-integral regulator and the decoupling module; the second modulation small signal without the steady-state term is obtained after the inverse Park transformation on the candidate modulation small signal superimposed with the phase angle small signal in the three-phase stationary coordinate system as follows:

[0091] ;

[0092] Finally, the second relationship P between the second modulation small signal and the AC voltage small signal is converted as follows:

[0093] ;

[0094] ;​

[0095] In this matrix, all elements except those in (1, 3) and (3, 3) are 0. , Indicates the phase of the modulated signal. This represents the decoupling gain.

[0096] In this embodiment, the phase angle small signal is superimposed on the AC control topology, and a candidate modulation small signal is obtained through Parker transformation, regulator and decoupling module; then the candidate signal superimposed with the phase angle small signal is inversely Parker transformed to obtain the second modulation small signal and determine its second relationship with the AC voltage small signal, which provides a basis for analyzing the impact of disturbances and optimizing control, and improves the system's disturbance immunity.

[0097] In one embodiment, the method further includes: when injecting a disturbance voltage to the DC side of the main circuit, determining a second frequency small-signal model in the AC loop; determining a third relationship between the modulation small signal and the AC current small signal based on the AC control topology; determining a fourth relationship between the modulation small signal and the DC voltage small signal based on the DC control topology; and performing impedance modeling based on the third relationship, the fourth relationship, and the second frequency small-signal model.

[0098] Among them, the two-level voltage source converter also includes a DC control topology, which allows for the application of voltage disturbances to the DC side port. At that time, the DC-side port of the two-level voltage source converter generates a frequency of... The current, the self-admittance is The frequency generated by the AC side port is The positive sequence current, i.e., the coupling admittance. The frequency generated by the AC side port is The negative sequence current, i.e., the coupling admittance. The specific impedance definition and distribution are as follows: Figure 7 As shown.

[0099] Specifically, when a disturbance voltage is injected at the DC side port of the main circuit and there is no disturbance voltage at the AC side port, the current response data sequence is simultaneously acquired. At this time, the time-domain model of the main circuit is transformed into a second frequency-domain small-signal model under the AC loop. For example, using... Figure 1 Taking phase a as an example, the small-signal model of the second frequency is determined as follows: Similarly, referring to step S204 above, a third relationship Q between the modulation small signal and the AC current small signal can be determined based on the AC control topology. Then, the DC voltage small signal corresponding to the disturbance voltage is input to the DC control topology to obtain the initial current. After the initial current is further input to the AC control topology, a fourth relationship E between the modulation small signal and the DC voltage small signal is obtained. Here, the E matrix represents the dependence of the modulation small signal on the DC bus voltage, which is determined by the DC bus voltage control.

[0100] Finally, based on the third relationship between the modulation small signal and the AC current small signal, and the fourth relationship between the modulation small signal and the DC voltage small signal, the modulation small model m is determined. a With alternating current small signal i a DC voltage small signal v dc The second objective relationship is: Substituting the second objective relationship into the second frequency small-signal model and simplifying by rearranging terms, the harmonic component relationship between the AC current small-signal and the DC voltage small-signal is obtained. Based on the harmonic component relationship, the self-admittance and coupling admittance under the applied disturbance voltage at the DC side port are determined.

[0101] In this embodiment, after injecting a disturbance voltage to the DC side of the main circuit, the second frequency small-signal model of the AC loop is determined, providing a basis for impedance modeling. The influence of DC bus voltage fluctuations on the AC side is fully considered. The third relationship between modulation and AC current small-signal is determined by the AC control topology, and the fourth relationship between the two is determined by the DC control topology. Finally, the modeling is performed by combining the third and fourth relationships with the second frequency small-signal model, which can accurately reflect the system impedance characteristics and provide a basis for analyzing DC side stability and optimizing control strategies.

[0102] In one embodiment, the determination is made based on the AC side port response data sequence at the disturbance frequency. At this point, all three phase responses are zero sequence. The corresponding diagonal element is 0, as shown below:

[0103] ;

[0104] In one embodiment, such as Figure 8 As shown, Figure 8 A flowchart illustrating the impedance modeling method when injecting disturbance voltage into the DC side is shown. It includes: transforming the time-domain model of the main circuit into a second-frequency-domain small-signal model under AC loop conditions; calculating the expression of the modulation small signal with respect to the AC current small signal based on AC port current control, i.e., determining the third relationship between the modulation small signal and the AC current small signal; calculating the expression of the modulation small signal with respect to the DC voltage small signal based on DC control topology control, i.e., determining the fourth relationship between the modulation small signal and the DC voltage small signal; and substituting the expression related to the modulation small signal into the second-frequency-domain small-signal model to obtain the impedance modeling result on the DC side.

[0105] therefore, Figure 5 and Figure 8 The impedance modeling process can accurately reflect the self-impedance and coupling impedance characteristics of the AC and DC sides, providing a basis for analyzing system stability and optimizing control strategies.

[0106] In one embodiment, determining the fourth relationship between the modulation small signal and the DC current small signal based on the DC control topology includes: determining the initial current based on the DC voltage small signal and the transfer function of the DC control topology; determining the target modulation small signal based on the initial current and the transfer function of the AC control topology; performing an inverse Park transform on the target modulation small signal to obtain a third modulation small signal, and converting it into the fourth relationship between the third modulation small signal and the DC current small signal.

[0107] The modulated small signal also includes a third modulated small signal.

[0108] Specifically, DC-side port voltage disturbances do not generate small-signal harmonic components of the phase-locked loop (PLL), but only cause disturbances in the d-axis reference current, thereby affecting the target modulation small-signal. At the same frequency The following disturbance is generated:

[0109] ;

[0110] in This represents the transfer function of the DC control topology. Therefore, after determining the initial current based on the small DC voltage signal corresponding to the disturbance voltage and the transfer function of the DC control topology, the target modulation signal can be determined based on the initial current and the transfer function of the AC control topology. Finally, the target modulation signal is transformed by inverse dq coordinates to obtain the third modulation signal, which is then converted into a fourth relationship E between the third modulation signal and the DC current signal:

[0111] ;

[0112] In this embodiment, the initial current is first determined by the disturbance voltage and the DC control topology transfer function; then, the target modulation small signal is obtained by combining the AC control topology transfer function; the third modulation small signal is obtained by inverse Park transform, and then the fourth relationship between it and the DC current small signal is determined, which provides a basis for analyzing the AC-DC side coupling characteristics and optimizing system control.

[0113] In one embodiment, the frequency domain small-signal model of the DC bus in the DC control topology is as follows:

[0114] ;

[0115] in, This indicates the three-phase current at the AC side port. Indicates the amplitude of the three-phase current. This indicates the three-phase voltage at the AC side port. This indicates a three-phase modulated small signal. This indicates the amplitude of the three-phase modulated signal. Indicates the DC side current. denotes the common-mode voltage, usually under positive sequence disturbance:

[0116] The cross product of two vectors is converted into the dot product of a Toeplitz matrix and a vector, 、 The Toeplitz matrix of:

[0117] ;

[0118] wherein, , denotes the phase of the modulation signal. , denotes the phase of the phase current. The asterisk denotes the complex conjugate.

[0119] In one embodiment, after the first target relationship is substituted into the first frequency small signal model and moved to simplify, the harmonic component relationship between the alternating current small signal and the alternating voltage small signal is obtained as:

[0120] ;

[0121] From the above, the impedance modeling result in the:

[0122] ;

[0123] ;

[0124] wherein , . Further, based on a negative sequence current compensator can be designed to achieve accurate power control under unbalanced power grid. Combined with the frequency domain small signal model of the DC bus, the coupling admittance of the DC side under the alternating voltage disturbance of the positive sequence of the alternating side , which will not be repeated here.

[0125] Through the self-admittance and transfer admittance relationship related to the positive sequence and the negative sequence, the self-admittance of the alternating side when the negative sequence disturbance is injected into the alternating side , the coupling admittance and the coupling admittance of the DC side .

[0126] ;

[0127] In one embodiment, after the second target relationship is substituted into the second frequency small signal model and moved to simplify, the harmonic component relationship between the alternating current small signal and the DC voltage small signal is obtained as:

[0128] ;

[0129] The following impedance modeling results can be determined from the above formula:

[0130] ;

[0131] ;

[0132] wherein , Further, the self-admittance can be calculated based on the combination of the DC bus frequency domain small signal model, and the DC bus resonance point is identified, and the resonance frequency domain point is identified by stability analysis and other methods to suppress oscillation by path blocking, enhanced damping and other methods.

[0133] In summary, based on the frequency domain small signal model of the main circuit, when the disturbance voltage is injected at the AC side port, the current response of the AC port and the current response of the DC port are derived by frequency domain small signal modeling of the AC control topology and the phase-locked loop. When the disturbance voltage is injected at the DC side port, the current response of the DC port and the current response of the AC port are derived by frequency domain small signal modeling of the AC control topology and the DC control topology. Therefore, compared with the traditional impedance model which ignores the influence of AC side voltage disturbance on the DC side current response, the coupling admittance of AC side voltage disturbance corresponding to DC side current response and DC side voltage disturbance corresponding to AC side current response is established, and the stability analysis accuracy is improved. And compared with the traditional impedance model based on dq coordinate system modeling, without considering the negative sequence voltage disturbance, the self-admittance and coupling admittance of current response under positive sequence and negative sequence voltage disturbance are considered at the same time.

[0134] It should be understood that, although each step in the flowchart involved in each of the above embodiments is shown in sequence according to the arrow, these steps are not necessarily executed in the order indicated by the arrow. Unless otherwise specified herein, the execution of these steps is not strictly limited in sequence, and these steps can be executed in other orders. Moreover, at least part of the steps in the flowchart involved in each of the above embodiments can include multiple steps or stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of these steps or stages is not necessarily sequential, but can be executed alternately or alternately with at least part of other steps or steps or stages in other steps.

[0135] Based on the same inventive concept, the embodiments of the present application also provide an impedance modeling device for implementing the above-mentioned impedance modeling method. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme described in the above method, and therefore the specific limitations in one or more impedance modeling device embodiments provided below can refer to the limitations of the impedance modeling method described above, which will not be described here again.

[0136] In one embodiment, an impedance modeling device is provided, applied to a two-level voltage source converter, including a main circuit, an AC control topology and a phase-locked loop, comprising: a first relationship determining module and a second relationship determining module, wherein:

[0137] The first relationship determining module is configured to inject a disturbance voltage to the AC side of the main circuit, determine a first frequency small signal model in the AC loop, and determine a first relationship between the modulation small signal and the AC current small signal based on the AC control topology.

[0138] The second relationship determining module is configured to associate the disturbance voltage and the phase angle small signal based on the phase-locked loop, determine a second relationship between the modulation small signal and the AC voltage small signal, and perform impedance modeling according to the first relationship, the second relationship and the first frequency small signal model.

[0139] In one embodiment, the two-level voltage source converter further includes a DC control topology, and the above device further includes a third relationship determining module and a fourth relationship determining module, wherein:

[0140] The third relationship determining module is configured to inject a disturbance voltage to the DC side of the main circuit, determine a second frequency small signal model in the AC loop, and determine a third relationship between the modulation small signal and the AC current small signal based on the AC control topology.

[0141] The fourth relationship determining module is configured to determine a fourth relationship between the modulation small signal and the DC current small signal based on the DC control topology, and perform impedance modeling according to the third relationship, the fourth relationship and the second frequency small signal model.

[0142] Each module in the above impedance modeling can be realized by software, hardware and a combination thereof, in whole or in part. Each module can be embedded in or independent of the processor in the computer device in hardware form, or can be stored in the memory in the computer device in software form, so as to be called and executed by the processor to perform the operations corresponding to each module.

[0143] In one embodiment, a computer device is provided, which can be a server, and the internal structure diagram thereof can be as shown in Figure 9As shown in the figure. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. Among them, the processor, the memory and the input / output interface are connected through the system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capability. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store the time domain equation and the frequency domain small signal equation. The input / output interface of the computer device is used to exchange information between the processor and the external device. The communication interface of the computer device is used to communicate with the terminal outside through the network connection. The computer program is executed by the processor to realize an impedance modeling method.

[0144] Those skilled in the art can understand that, Figure 9 The structure shown in the figure is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. The specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different component arrangement.

[0145] In one embodiment, a computer device is also provided, including a memory and a processor, the memory storing a computer program, and the processor executing the computer program to realize the steps in each of the above method embodiments.

[0146] In one embodiment, a computer readable storage medium is provided, storing a computer program, which is executed by a processor to realize the steps in each of the above method embodiments.

[0147] In one embodiment, a computer program product or computer program is provided, which includes computer instructions stored in a computer readable storage medium. The processor of the computer device reads the computer instructions from the computer readable storage medium, and the processor executes the computer instructions, so that the computer device executes the steps in each of the above method embodiments.

[0148] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when the computer program is executed, the processes of the above-mentioned embodiments of the methods can be included. Any reference to memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. The non-volatile memory can include read-only memory (Read-Only Memory, ROM), magnetic tape, floppy disk, flash memory, optical storage, high-density embedded non-volatile memory, resistive memory (ReRAM), magnetoresistive random access memory (Magnetoresistive Random Access Memory, MRAM), ferroelectric memory (Ferroelectric Random Access Memory, FRAM), phase change memory (Phase Change Memory, PCM), graphene memory, etc. The volatile memory can include random access memory (Random Access Memory, RAM) or external cache memory, etc. As an illustration but not limitation, the RAM can be in various forms, such as static random access memory (Static Random Access Memory, SRAM) or dynamic random access memory (Dynamic Random Access Memory, DRAM), etc. The database involved in the embodiments provided in the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a block chain, etc., without being limited thereto. The processor involved in the embodiments provided in the present application can be a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., without being limited thereto.

[0149] Any combination of the technical features of the above embodiments can be made. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0150] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent of the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method of impedance modeling, characterized by, The application is applied to a two-level voltage source converter, comprising a main circuit, an AC control topology and a phase-locked loop, wherein: When a disturbance voltage is injected into the AC side of the main circuit, a first frequency small signal model in the AC loop is determined; A first relationship between a modulation small signal and an AC current small signal is determined based on the AC control topology; The disturbance voltage and a phase angle small signal are associated based on the phase-locked loop, and a second relationship between the modulation small signal and an AC voltage small signal is determined; Impedance modeling is performed according to the first relationship, the second relationship and the first frequency small signal model; The AC control topology comprises a proportional-integral regulator and a decoupling module; and the modulation small signal comprises a first modulation small signal; The first relationship between the modulation small signal and the AC current small signal is determined based on the AC control topology, comprising: performing a Park transformation on the AC current small signal according to a fundamental voltage phase; processing the transformed AC current small signal through the proportional-integral regulator and the decoupling module to obtain an initial modulation small signal; performing an inverse Park transformation on the initial modulation small signal to obtain the first modulation small signal, and converting the first relationship between the first modulation small signal and the AC current small signal; The disturbance voltage and the phase angle small signal are associated based on the phase-locked loop, comprising: determining an AC voltage after the disturbance voltage is subjected to the Park transformation; determining a relationship between the AC voltage and the phase angle small signal according to a fundamental voltage amplitude and the fundamental voltage phase; and associating the disturbance voltage and the phase angle small signal according to a transfer function of the phase-locked loop and the relationship between the AC voltage and the phase angle small signal; The modulation small signal comprises a second modulation small signal; and the second relationship between the modulation small signal and the AC voltage small signal is determined, comprising: superimposing the phase angle small signal associated with the disturbance voltage into the AC control topology; performing a Park transformation on the AC current small signal superimposed with the phase angle small signal until a candidate modulation small signal is determined through the proportional-integral regulator and the decoupling module in the AC control topology; performing an inverse Park transformation on the candidate modulation small signal superimposed with the phase angle small signal to obtain the second modulation small signal, and converting the second relationship between the second modulation small signal and the AC voltage small signal.

2. The method of claim 1, wherein, The two-level voltage source converter further comprises a DC control topology, and the method further comprises: When a disturbance voltage is injected into the DC side of the main circuit, a second frequency small signal model in the AC loop is determined; A third relationship between the modulation small signal and the AC current small signal is determined based on the AC control topology; A fourth relationship between the modulation small signal and a DC voltage small signal is determined based on the DC control topology; Impedance modeling is performed according to the third relationship, the fourth relationship and the second frequency small signal model.

3. The method of claim 2, wherein, The modulation small signal further comprises a third modulation small signal; and the fourth relationship between the modulation small signal and the DC voltage small signal is determined based on the DC control topology, comprising: An initial current is determined according to the DC voltage small signal and a transfer function of the DC control topology; A target modulation small signal is determined according to the initial current and a transfer function of the AC control topology; and The target modulation small signal is subjected to inverse Park transformation to obtain a third modulation small signal, and is converted into a fourth relationship between the third modulation small signal and a direct-current voltage small signal.

4. Impedance modeling apparatus for implementing the method of any one of claims 1 to 3, characterized by The application is applied to a two-level voltage source converter, and the two-level voltage source converter comprises a main circuit, an AC control topology and a phase-locked loop, wherein: The first relationship determining module is configured to determine a first frequency small signal model in an AC loop when a disturbance voltage is injected into an AC side of the main circuit; and determine a first relationship between a modulation small signal and an AC current small signal based on the AC control topology. The second relationship determining module is configured to associate the disturbance voltage and a phase angle small signal based on the phase-locked loop, and determine a second relationship between the modulation small signal and an AC voltage small signal; and perform impedance modeling according to the first relationship, the second relationship and the first frequency small signal model.

5. The apparatus of claim 4, wherein, The two-level voltage source converter further comprises a DC control topology, and the device further comprises: The third relationship determining module is configured to determine a second frequency small signal model in the AC loop when the disturbance voltage is injected into a DC side of the main circuit; and determine a third relationship between the modulation small signal and the AC current small signal based on the AC control topology. The fourth relationship determining module is configured to determine a fourth relationship between the modulation small signal and a DC current small signal based on the DC control topology; and perform impedance modeling according to the third relationship, the fourth relationship and the second frequency small signal model. 6.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-5 when the computer program is executed by the processor. The processor executes the computer program to implement the steps of the method in any one of claims 1 to 3.

7. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the method in any one of claims 1 to 3.

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