Simplified construction method and system of high-frequency impedance theoretical model of flexible direct-current converter station

Abstract

The application discloses a simplification construction method of a high-frequency impedance theoretical model of a flexible DC converter station, and comprises the following steps: obtaining data information of a target flexible DC converter station; calculating positive and negative sequence electrical quantity data information of the target flexible DC converter station; adopting a harmonic state space method to construct an alternating current impedance theoretical model of the target flexible DC converter station; simplifying the constructed model at a high frequency; uniformly performing frequency shift representation on positive and negative sequence impedances of the target flexible DC converter station; and completing the simplification construction of the high-frequency impedance theoretical model of the target flexible DC converter station. The application further discloses a system for realizing the simplification construction method of the high-frequency impedance theoretical model of the flexible DC converter station. The application not only realizes the simplification construction of the high-frequency impedance theoretical model of the flexible DC converter station, but also has better accuracy and higher reliability, and the modeling process is simpler.

Description

Technical Field

[0001] This invention belongs to the field of electrical automation, and specifically relates to a simplified construction method and system for a high-frequency impedance theoretical model of a flexible DC converter station. Background Technology

[0002] With economic and technological development and the improvement of people's living standards, electricity has become an indispensable secondary energy source in people's production and daily life, bringing endless convenience. Therefore, ensuring a stable and reliable supply of electricity has become one of the most important tasks of the power system.

[0003] Flexible direct current (DC) transmission technology, with its advantages of flexible control, ability to supply power to passive systems, and absence of commutation failure issues, has been widely applied in long-distance power transmission, offshore wind power integration, renewable energy grid connection, asynchronous grid interconnection, and isolated platform power supply. Flexible DC transmission technology not only enables independent regulation of active and reactive power, but also features rapid power flow reversal, simple and convenient control, and good grid performance. Therefore, current power systems are conducting research and application of flexible DC transmission technology.

[0004] However, as more and more new energy power generation systems are integrated into the power system and generate electricity, the "high-voltage and high-inertia" characteristics of the current new power system are becoming more prominent, exhibiting features such as "underdamping, weak disturbance rejection, and low inertia," which easily induces instability problems characterized by oscillations. In recent years, oscillation problems have occurred multiple times globally in flexible DC transmission processes, greatly affecting the safe and stable operation of the power system.

[0005] Constructing a high-frequency impedance theoretical model for flexible DC converter stations is one of the fundamental tasks in the research of flexible DC transmission technology. Although current schemes for constructing high-frequency impedance theoretical models for flexible DC converter stations can build relatively accurate theoretical models, these schemes are extremely complex and have poor reliability. Summary of the Invention

[0006] One of the objectives of this invention is to provide a simplified construction method for a high-frequency impedance theoretical model of a flexible DC converter station that is highly reliable, accurate, and relatively simple.

[0007] The second objective of this invention is to provide a system for a simplified construction method of the high-frequency impedance theoretical model of the flexible DC converter station.

[0008] The simplified construction method for the high-frequency impedance theoretical model of the flexible DC converter station provided by this invention includes the following steps:

[0009] S1. Obtain data information of the target flexible DC converter station;

[0010] S2. Based on the data obtained in step S1, calculate the positive and negative sequence electrical quantity data of the target flexible DC converter station;

[0011] S3. Based on the data obtained in step S2, construct the AC impedance theoretical model of the target flexible DC converter station using the harmonic state-space method;

[0012] S4. Perform high-frequency simplification on the model constructed in step S3;

[0013] S5. Based on the simplified model obtained in step S4, perform unified frequency shift characterization of the positive-sequence impedance and negative-sequence impedance of the target flexible DC converter station, and complete the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station.

[0014] Step S1, which involves acquiring data information of the target flexible DC converter station, specifically includes the following steps:

[0015] Acquire data information of the target flexible DC converter station;

[0016] The data information includes the three-phase current data, fundamental frequency period data, and control system data of the target flexible DC converter station.

[0017] Step S2, which involves calculating the positive and negative sequence electrical quantity data of the target flexible DC converter station based on the data information obtained in step S1, specifically includes the following steps:

[0018] The positive and negative sequence electrical quantity data of the target flexible DC converter station are calculated using the following formula:

[0019] In the formula For the delay Shaft voltage; For the delay Shaft voltage; Indicates a delay of one-quarter of a cycle; for Shaft voltage; for Shaft voltage; for Positive sequence voltage; for Positive sequence voltage; for Negative sequence voltage; for Negative sequence voltage.

[0020] Step S3, which involves constructing the AC impedance theoretical model of the target flexible DC converter station using the harmonic state-space method based on the data obtained in step S2, specifically includes the following steps:

[0021] Theoretical model of AC impedance for the target flexible DC converter station considering negative sequence control:

[0022] Using the harmonic state-space method, the internal dynamic harmonic order of the AC impedance theoretical model of the target flexible DC converter station is calculated up to the fourth order, resulting in the impedance theoretical model in the three-phase coordinate system, expressed as:

[0023] In the formula The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the coefficient matrix of the three-phase circulation in the state variable equations; This is the coefficient matrix of the three-phase voltages in the three-phase circulating current equation; This is the coefficient matrix of the three-phase voltages in the state variable equations; It is a 27th order identity matrix; This is the coefficient matrix of the three-phase currents in the state variable equations; This is the coefficient matrix of the three-phase currents in the three-phase circulating current equation; It is a 117th order identity matrix; The state matrix of the harmonic state equation for the electrical side of the converter station; This is the first column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; This is the coefficient matrix of the three-phase current in the inner loop control output of the control system; This is the second column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The coefficient matrix for the three-phase circulating current in the output of the circulating current suppression controller of the control system; This is the coefficient matrix of the three-phase voltage in the inner loop control output of the control system; This is the coefficient matrix of the three-phase voltage in the output of the circulating current suppression controller of the control system; This is the third column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The first intermediate matrix consists of 0 and the identity matrix. The second intermediate matrix is ​​composed of 0 and the identity matrix. ;

[0024] Transforming to the sequence domain, we obtain the positive and negative sequence impedance models, expressed as:

[0025] In the formula The harmonic state space impedance matrix of the flexible DC converter station in the positive and negative sequence coordinate system; This is the transformation matrix for transforming from a three-phase coordinate system to a positive-negative sequence coordinate system; The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the transformation matrix for transforming from the positive and negative sequence coordinate system to the three-phase coordinate system;

[0026] Theoretical model of AC impedance for the target flexible DC converter station without considering negative sequence control:

[0027] Using the harmonic state-space method, the internal dynamic harmonic order of the AC impedance theoretical model of the target flexible DC converter station is calculated up to the fourth order, resulting in the impedance theoretical model in the three-phase coordinate system, expressed as:

[0028] In the formula The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the coefficient matrix of the three-phase circulation in the state variable equations; This is the coefficient matrix of the three-phase voltages in the three-phase circulating current equation; This is the coefficient matrix of the three-phase voltages in the state variable equations; It is a 27th order identity matrix; This is the coefficient matrix of the three-phase currents in the state variable equations; This is the coefficient matrix of the three-phase currents in the three-phase circulating current equation; It is a 117th order identity matrix; The state matrix of the harmonic state equation for the electrical side of the converter station; This is the first column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; This is the coefficient matrix of the three-phase current in the inner loop control output of the control system; This is the second column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The coefficient matrix for the three-phase circulating current in the output of the circulating current suppression controller of the control system; This is the coefficient matrix of the three-phase voltage in the inner loop control output of the control system; This is the coefficient matrix of the three-phase voltage in the output of the circulating current suppression controller of the control system; This is the third column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The first intermediate matrix consists of 0 and the identity matrix. The second intermediate matrix is ​​composed of 0 and the identity matrix. ;

[0029] Transforming to the sequence domain, we obtain the positive and negative sequence impedance models, expressed as:

[0030] In the formula The harmonic state space impedance matrix of the flexible DC converter station in the positive and negative sequence coordinate system; This is the transformation matrix for transforming from a three-phase coordinate system to a positive-negative sequence coordinate system; The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the transformation matrix for converting from the positive and negative order coordinate system to the three-phase coordinate system.

[0031] Considering sequence separation, the final output signal of the inner loop controller is:

[0032] Without considering sequence separation, the final output signal of the inner loop controller is:

[0033] In the formula

[0034] In the formula This is the transformation matrix for transforming positive-sequence three-phase coordinates to dq coordinates. For the delay matrix, The transfer function matrix for the inner-loop positive-sequence PI controller. This is the transformation matrix for transforming positive-order dq coordinates to three-phase coordinates. This is the phase-corresponding coefficient matrix in the expression of the inner-loop positive-sequence output signal. The transfer function of the phase-locked loop is in matrix form. Here is the transfer function matrix of the voltage feedforward filter. It is in matrix form of the power outer loop transfer function. The steady-state voltage values ​​in the positive sequence of the dq coordinate system are in matrix form. This is the matrix form of the positive sequence current steady-state value in the dq coordinate system. This is the transformation matrix for transforming negative-sequence three-phase coordinates to dq coordinates. The transfer function matrix for the inner-loop negative-sequence PI controller. This is the transformation matrix for transforming negative-order dq coordinates to three-phase coordinates. The form of the steady-state value matrix of the negative sequence voltage in the dq coordinate system. The steady-state values ​​of the negative sequence current in the dq coordinate system are in matrix form. This is the phase-corresponding coefficient matrix in the expression of the inner-loop negative-sequence output signal.

[0035] Step S4 involves performing high-frequency simplification on the model constructed in step S3, specifically including the following steps:

[0036] The distribution of impedance elements within the AC-side impedance matrix is ​​expressed as:

[0037] In the formula This is the positive and negative sequence matrix of AC voltage under small disturbance conditions; This is the positive and negative sequence matrix of AC current under small disturbance conditions; for Positive sequence voltage with frequency shift; for Negative sequence voltage with frequency shift; It is a positive-sequence voltage with no frequency shift; It is a negative sequence voltage with no frequency shift; for Positive sequence voltage with frequency shift; for Negative sequence voltage with frequency shift; The perturbation frequency; For power frequency;

[0038] When performing high-frequency impedance analysis, off-diagonal impedance elements are ignored, and only the main diagonal impedance elements are considered and analyzed.

[0039] therefore, It is a diagonal matrix, represented as:

[0040] In the formula for Impedance corresponding to frequency-shifted positive-sequence voltage and current; for Impedance corresponding to frequency-shifted negative sequence voltage and current; The impedance corresponding to the positive-sequence voltage and current without frequency shift; The impedance corresponding to the negative sequence voltage and current without frequency shift; for Impedance corresponding to frequency-shifted positive-sequence voltage and current; for Impedance corresponding to frequency-shifted negative sequence voltage and current;

[0041] Main diagonal positive sequence impedance elements , and The two can be converted through frequency shift, negative sequence impedance element , and The two frequencies can be converted through frequency shifting; the conversion relationship is expressed as:

[0042] In the formula For the Laplace operator; It is the power frequency angular frequency; This is a plural sign;

[0043] Based on satisfying the frequency shift conversion relationship between positive-sequence impedance and negative-sequence impedance, factors whose impact on high-frequency impedance characteristics is less than a set threshold are further ignored, thus completing high-frequency simplification.

[0044] Step S5, based on the simplified model obtained in step S4, involves performing a unified frequency shift characterization of the positive-sequence and negative-sequence impedances of the target flexible DC converter station, thereby completing the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station. This specifically includes the following steps:

[0045] After simplification, a simplified AC impedance frequency shift model for the target flexible DC converter station considering positive and negative sequence separation and negative sequence control is obtained, expressed as:

[0046] In the formula, A is the first intermediate variable; B is the second intermediate variable; and C is the third intermediate variable. To account for the positive sequence impedance with sequence separation and k-th frequency shift; To account for the negative sequence impedance with sequence separation and k-th frequency shift; The equivalent impedance on the AC side of the converter station is given by the k-th frequency shift. Let be the delay parameter for the k-1th frequency shift; The inner loop d-axis control parameters are for the k-1th frequency shift; Let be the delay parameter for the (k+1)th frequency shift; The inner loop d-axis control parameters are for the k+1th frequency shift. The equivalent inductance on the AC side of the converter station; Let be the sequence separation delay parameter for k frequency shifts; For voltage feedforward at frequency shift k-1; For voltage feedforward at frequency shift k+1;

[0047] After simplification, a simplified AC impedance frequency shift model for the target flexible DC converter station, neglecting positive-negative sequence separation and negative sequence control, is obtained, expressed as:

[0048] In the formula The positive-sequence impedance with k-th frequency shift and without considering sequence separation; For voltage feedforward at frequency shift k-1; For voltage feedforward at frequency shift k+1;

[0049] A simplified theoretical model of the high-frequency impedance of the target flexible DC converter station was constructed.

[0050] This invention also provides a system for simplifying the construction of a high-frequency impedance theoretical model for a flexible DC converter station, comprising a data acquisition module, a data calculation module, a model construction module, a high-frequency simplification module, and a simplified modeling module; the data acquisition module, data calculation module, model construction module, high-frequency simplification module, and simplified modeling module are connected in series; the data acquisition module acquires data information of the target flexible DC converter station and uploads the data information to the data calculation module; the data calculation module calculates the positive and negative sequence electrical quantity data of the target flexible DC converter station based on the received data information and the acquired data information, and uploads the data information to the model construction module; the model construction module constructs an AC impedance theoretical model of the target flexible DC converter station using the harmonic state-space method based on the received data information, and uploads the data information to the high-frequency simplification module; the high-frequency simplification module performs high-frequency simplification on the constructed model based on the received data information, and uploads the data information to the simplified modeling module; the simplified modeling module performs unified frequency shift characterization of the positive and negative sequence impedances of the target flexible DC converter station based on the received data information and the simplified model, thus completing the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station.

[0051] The present invention provides a simplified construction method and system for the high-frequency impedance theoretical model of a flexible DC converter station. By acquiring and calculating the data information of the target flexible DC converter station, the theoretical model is constructed. Based on high-frequency simplification and unified frequency shift characterization, not only is the high-frequency impedance theoretical model of the flexible DC converter station simplified, but the model also has better accuracy, higher reliability, and a simpler modeling process. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0053] Figure 2 This is a schematic diagram of the control structure of a flexible DC converter station considering the negative sequence control loop in the method of the present invention.

[0054] Figure 3 This is a schematic diagram comparing the AC impedance amplitude of a flexible DC converter station with and without negative sequence control according to the method of the present invention.

[0055] Figure 4This is a simplified model verification diagram for the method of the present invention when positive and negative order control is taken into account and when positive and negative order control is not taken into account.

[0056] Figure 5 This is a schematic diagram of the functional modules of the system of the present invention. Detailed Implementation

[0057] like Figure 1 The diagram shown is a flowchart of the method of the present invention: The simplified construction method of the high-frequency impedance theoretical model of the flexible DC converter station disclosed in this invention includes the following steps:

[0058] S1. Obtain data information of the target flexible DC converter station; specifically including the following steps:

[0059] Acquire data information of the target flexible DC converter station;

[0060] The data information includes the three-phase current data, fundamental frequency period data, and control system data of the target flexible DC converter station;

[0061] S2. Based on the data obtained in step S1, calculate the positive and negative sequence electrical quantity data of the target flexible DC converter station; specifically including the following steps:

[0062] The positive and negative sequence electrical quantity data of the target flexible DC converter station are calculated using the following formula:

[0063] In the formula For the delay Shaft voltage; For the delay Shaft voltage; Indicates a delay of one-quarter of a cycle; for Shaft voltage; for Shaft voltage; for Positive sequence voltage; for Positive sequence voltage; for Negative sequence voltage; for Negative sequence voltage;

[0064] The specific calculation process is as follows: Figure 2 As shown in (a), Figure 2 (b) is a block diagram of the control system for the target flexible DC converter station;

[0065] S3. Based on the data obtained in step S2, construct the AC impedance theoretical model of the target flexible DC converter station using the harmonic state-space method; specifically including the following steps:

[0066] Theoretical model of AC impedance for the target flexible DC converter station considering negative sequence control:

[0067] Using the harmonic state-space method, the internal dynamic harmonic order of the AC impedance theoretical model of the target flexible DC converter station is calculated up to the fourth order, resulting in the impedance theoretical model in the three-phase coordinate system, expressed as:

[0068] In the formula The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the coefficient matrix of the three-phase circulation in the state variable equations; This is the coefficient matrix of the three-phase voltages in the three-phase circulating current equation; This is the coefficient matrix of the three-phase voltages in the state variable equations; It is a 27th order identity matrix; This is the coefficient matrix of the three-phase currents in the state variable equations; This is the coefficient matrix of the three-phase currents in the three-phase circulating current equation; It is a 117th order identity matrix; The state matrix of the harmonic state equation for the electrical side of the converter station; This is the first column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; This is the coefficient matrix of the three-phase current in the inner loop control output of the control system; This is the second column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The coefficient matrix for the three-phase circulating current in the output of the circulating current suppression controller of the control system; This is the coefficient matrix of the three-phase voltage in the inner loop control output of the control system; This is the coefficient matrix of the three-phase voltage in the output of the circulating current suppression controller of the control system; This is the third column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The first intermediate matrix consists of 0 and the identity matrix. The second intermediate matrix is ​​composed of 0 and the identity matrix. ;

[0069] Transforming to the sequence domain, we obtain the positive and negative sequence impedance models, expressed as:

[0070] In the formula The harmonic state space impedance matrix of the flexible DC converter station in the positive and negative sequence coordinate system; This is the transformation matrix for transforming from a three-phase coordinate system to a positive-negative sequence coordinate system; The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the transformation matrix for transforming from the positive and negative sequence coordinate system to the three-phase coordinate system;

[0071] Theoretical model of AC impedance for the target flexible DC converter station without considering negative sequence control:

[0072] Using the harmonic state-space method, the internal dynamic harmonic order of the AC impedance theoretical model of the target flexible DC converter station is calculated up to the fourth order, resulting in the impedance theoretical model in the three-phase coordinate system, expressed as:

[0073] In the formula The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the coefficient matrix of the three-phase circulation in the state variable equations; This is the coefficient matrix of the three-phase voltages in the three-phase circulating current equation; This is the coefficient matrix of the three-phase voltages in the state variable equations; It is a 27th order identity matrix; This is the coefficient matrix of the three-phase currents in the state variable equations; This is the coefficient matrix of the three-phase currents in the three-phase circulating current equation; It is a 117th order identity matrix; The state matrix of the harmonic state equation for the electrical side of the converter station; This is the first column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; This is the coefficient matrix of the three-phase current in the inner loop control output of the control system; This is the second column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The coefficient matrix for the three-phase circulating current in the output of the circulating current suppression controller of the control system; This is the coefficient matrix of the three-phase voltage in the inner loop control output of the control system; This is the coefficient matrix of the three-phase voltage in the output of the circulating current suppression controller of the control system; This is the third column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The first intermediate matrix consists of 0 and the identity matrix. The second intermediate matrix is ​​composed of 0 and the identity matrix. ;

[0074] Transforming to the sequence domain, we obtain the positive and negative sequence impedance models, expressed as:

[0075] In the formula The harmonic state space impedance matrix of the flexible DC converter station in the positive and negative sequence coordinate system; This is the transformation matrix for transforming from a three-phase coordinate system to a positive-negative sequence coordinate system; The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the transformation matrix for transforming from the positive and negative sequence coordinate system to the three-phase coordinate system;

[0076] Considering sequence separation, the final output signal of the inner loop controller is:

[0077] Without considering sequence separation, the final output signal of the inner loop controller is:

[0078] In the formula

[0079] In the formula This is the transformation matrix for transforming positive-sequence three-phase coordinates to dq coordinates. For the delay matrix, The transfer function matrix for the inner-loop positive-sequence PI controller. This is the transformation matrix for transforming positive-order dq coordinates to three-phase coordinates. This is the phase-corresponding coefficient matrix in the expression of the inner-loop positive-sequence output signal. The transfer function of the phase-locked loop is in matrix form. Here is the transfer function matrix of the voltage feedforward filter. It is in matrix form of the power outer loop transfer function. The steady-state voltage values ​​in the positive sequence of the dq coordinate system are in matrix form. This is the matrix form of the positive sequence current steady-state value in the dq coordinate system. This is the transformation matrix for transforming negative-sequence three-phase coordinates to dq coordinates. The transfer function matrix for the inner-loop negative-sequence PI controller. This is the transformation matrix for transforming negative-order dq coordinates to three-phase coordinates. The form of the steady-state value matrix of the negative sequence voltage in the dq coordinate system. The steady-state values ​​of the negative sequence current in the dq coordinate system are in matrix form. This is the phase-corresponding coefficient matrix in the expression of the inner-loop negative-sequence output signal;

[0080] After plotting only the voltage and current meters and the fourth harmonic, consider the voltage and current harmonic coupling that has a significant impact on impedance, taking into account / not taking into account the negative sequence control converter station impedance, as shown below. Figure 3 As shown;

[0081] S4. Perform high-frequency simplification on the model constructed in step S3; specifically, this includes the following steps:

[0082] The distribution of impedance elements within the AC-side impedance matrix is ​​expressed as:

[0083] In the formula This is the positive and negative sequence matrix of AC voltage under small disturbance conditions; This is the positive and negative sequence matrix of AC current under small disturbance conditions; for Positive sequence voltage with frequency shift; for Negative sequence voltage with frequency shift; It is a positive-sequence voltage with no frequency shift; It is a negative sequence voltage with no frequency shift; for Positive sequence voltage with frequency shift; for Negative sequence voltage with frequency shift; The perturbation frequency; For power frequency;

[0084] Depend on Figure 3 As can be seen, the amplitude of off-diagonal impedance elements is almost zero in the high-frequency range. Therefore, when performing high-frequency impedance analysis, off-diagonal impedance elements are ignored, and only the main diagonal impedance elements are considered and analyzed.

[0085] therefore, It is a diagonal matrix, represented as:

[0086] In the formula for Impedance corresponding to frequency-shifted positive-sequence voltage and current; for Impedance corresponding to frequency-shifted negative sequence voltage and current; The impedance corresponding to the positive-sequence voltage and current without frequency shift; The impedance corresponding to the negative sequence voltage and current without frequency shift; for Impedance corresponding to frequency-shifted positive-sequence voltage and current; for Impedance corresponding to frequency-shifted negative sequence voltage and current;

[0087] Main diagonal positive sequence impedance elements , and The two can be converted through frequency shift, negative sequence impedance element , and The two frequencies can be converted through frequency shifting; the conversion relationship is expressed as:

[0088] In the formula For the Laplace operator; It is the power frequency angular frequency; This is a plural sign;

[0089] Based on satisfying the frequency shift conversion relationship between positive-sequence impedance and negative-sequence impedance, factors with an impact on high-frequency impedance characteristics less than a set threshold are further ignored to complete high-frequency simplification;

[0090] S5. Based on the simplified model obtained in step S4, perform a unified frequency shift characterization of the positive-sequence and negative-sequence impedances of the target flexible DC converter station, thus completing the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station; specifically, this includes the following steps:

[0091] After simplification, a simplified AC impedance frequency shift model for the target flexible DC converter station considering positive and negative sequence separation and negative sequence control is obtained, expressed as:

[0092] In the formula, A is the first intermediate variable; B is the second intermediate variable; and C is the third intermediate variable. To account for the positive sequence impedance with sequence separation and k-th frequency shift; To account for the negative sequence impedance with sequence separation and k-th frequency shift; The equivalent impedance on the AC side of the converter station is given by the k-th frequency shift. Let be the delay parameter for the k-1th frequency shift; The inner loop d-axis control parameters are for the k-1th frequency shift; Let be the delay parameter for the (k+1)th frequency shift; The inner loop d-axis control parameters are for the k+1th frequency shift. The equivalent inductance on the AC side of the converter station; Let be the sequence separation delay parameter for k frequency shifts; For voltage feedforward at frequency shift k-1; For voltage feedforward at frequency shift k+1;

[0093] After simplification, a simplified AC impedance frequency shift model for the target flexible DC converter station, neglecting positive-negative sequence separation and negative sequence control, is obtained, expressed as:

[0094] In the formula The positive-sequence impedance with k-th frequency shift and without considering sequence separation; For voltage feedforward at frequency shift k-1; For voltage feedforward at frequency shift k+1;

[0095] A simplified theoretical model of the high-frequency impedance of the target flexible DC converter station was constructed.

[0096] The present invention was verified, and the verification results are as follows: Figure 4 As shown, the simplified model obtained, regardless of whether negative sequence control is considered or not, exhibits impedance amplitudes that completely overlap with the detailed model in the mid-to-high frequency range. Furthermore, the simplified model considering negative sequence control can accurately fit the fluctuations in the high-frequency range, reflecting the fluctuation characteristics. Therefore, the simplified model constructed by the present invention not only accurately characterizes the impedance fluctuation characteristics in the high-frequency range but also facilitates theoretical analysis.

[0097] This invention, while simplifying the high-frequency impedance model of flexible DC converter stations and completing the unified characterization of positive and negative sequence impedances, boasts advantages such as simple algorithm, ease of implementation, high accuracy of simplified model, clear characterization of high-frequency impedance characteristics, and reduced complexity of high-frequency stability analysis. It effectively improves the efficiency of high-frequency operational stability analysis, lays a solid foundation for revealing high-frequency oscillation mechanisms and designing oscillation suppression schemes, and has good application value.

[0098] like Figure 5The diagram shows the functional modules of the system of the present invention: The system disclosed in this invention, which implements a simplified construction method for the high-frequency impedance theoretical model of the flexible DC converter station, includes a data acquisition module, a data calculation module, a model construction module, a high-frequency simplification module, and a simplified modeling module; these modules are connected in series. The data acquisition module acquires data information of the target flexible DC converter station and uploads it to the data calculation module. The data calculation module calculates the positive and negative sequence electrical quantity data of the target flexible DC converter station based on the received and acquired data information. The system then uploads the received data to the model building module. Based on this data, the model building module constructs a theoretical AC impedance model of the target flexible DC converter station using the harmonic state-space method and uploads the data to the high-frequency simplification module. The high-frequency simplification module performs high-frequency simplification on the constructed model based on the received data and uploads the data to the simplified modeling module. Finally, the simplified modeling module performs a unified frequency shift characterization of the positive-sequence and negative-sequence impedances of the target flexible DC converter station based on the received data and the simplified model, thus completing the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station.

Claims

1. A simplified method for constructing a high-frequency impedance theoretical model for a flexible DC converter station, comprising the following steps: S1. Obtain data information of the target flexible DC converter station; S2. Based on the data obtained in step S1, calculate the positive and negative sequence electrical quantity data of the target flexible DC converter station; S3. Based on the data obtained in step S2, construct the AC impedance theoretical model of the target flexible DC converter station using the harmonic state-space method; S4. Perform high-frequency simplification on the model constructed in step S3; S5. Based on the simplified model obtained in step S4, perform unified frequency shift characterization of the positive-sequence impedance and negative-sequence impedance of the target flexible DC converter station, and complete the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station.

2. The simplified construction method of the high-frequency impedance theoretical model of the flexible DC converter station according to claim 1, characterized in that... Step S1, which involves acquiring data information of the target flexible DC converter station, specifically includes the following steps: Acquire data information of the target flexible DC converter station; The data information includes the three-phase current data, fundamental frequency period data, and control system data of the target flexible DC converter station.

3. The simplified construction method of the high-frequency impedance theoretical model of the flexible DC converter station according to claim 2, characterized in that... Step S2, which involves calculating the positive and negative sequence electrical quantity data of the target flexible DC converter station based on the data information obtained in step S1, specifically includes the following steps: The positive and negative sequence electrical quantity data of the target flexible DC converter station are calculated using the following formula: In the formula For the delay Shaft voltage; For the delay Shaft voltage; Indicates a delay of one-quarter of a cycle; for Shaft voltage; for Shaft voltage; for Positive sequence voltage; for Positive sequence voltage; for Negative sequence voltage; for Negative sequence voltage.

4. The simplified construction method of the high-frequency impedance theoretical model of the flexible DC converter station according to claim 3, characterized in that... Step S3, which involves constructing the AC impedance theoretical model of the target flexible DC converter station based on the data information obtained in step S2 using the harmonic state-space method, specifically includes the following steps: Theoretical model of AC impedance for the target flexible DC converter station considering negative sequence control: Using the harmonic state-space method, the internal dynamic harmonic order of the AC impedance theoretical model of the target flexible DC converter station is calculated up to the fourth order, resulting in the impedance theoretical model in the three-phase coordinate system, expressed as: In the formula The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the coefficient matrix of the three-phase circulation in the state variable equations; This is the coefficient matrix of the three-phase voltages in the three-phase circulating current equation; This is the coefficient matrix of the three-phase voltages in the state variable equations; It is a 27th order identity matrix; This is the coefficient matrix of the three-phase currents in the state variable equations; This is the coefficient matrix corresponding to the three-phase currents in the three-phase circulating current equation; It is a 117th order identity matrix; The state matrix of the harmonic state equation for the electrical side of the converter station; This is the first column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; This is the coefficient matrix of the three-phase current in the inner loop control output of the control system; This is the second column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The coefficient matrix for the three-phase circulating current in the output of the circulating current suppression controller of the control system; This is the coefficient matrix of the three-phase voltage in the inner loop control output of the control system; This is the coefficient matrix of the three-phase voltage in the output of the circulating current suppression controller of the control system; This is the third column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The first intermediate matrix consists of 0 and the identity matrix. The second intermediate matrix is ​​composed of 0 and the identity matrix. ; Transforming to the sequence domain, we obtain the positive and negative sequence impedance models, expressed as: In the formula The harmonic state space impedance matrix of the flexible DC converter station in the positive and negative sequence coordinate system; This is the transformation matrix for transforming from a three-phase coordinate system to a positive-negative sequence coordinate system; The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the transformation matrix for transforming from the positive and negative sequence coordinate system to the three-phase coordinate system; Theoretical model of AC impedance for the target flexible DC converter station without considering negative sequence control: Using the harmonic state-space method, the internal dynamic harmonic order of the AC impedance theoretical model of the target flexible DC converter station is calculated up to the fourth order, resulting in the impedance theoretical model in the three-phase coordinate system, expressed as: In the formula The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the coefficient matrix of the three-phase circulation in the state variable equations; This is the coefficient matrix of the three-phase voltages in the three-phase circulating current equation; This is the coefficient matrix of the three-phase voltages in the state variable equations; It is a 27th order identity matrix; This is the coefficient matrix of the three-phase currents in the state variable equations; This is the coefficient matrix corresponding to the three-phase currents in the three-phase circulating current equation; It is a 117th order identity matrix; The state matrix of the harmonic state equation for the electrical side of the converter station; This is the first column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; This is the coefficient matrix of the three-phase current in the inner loop control output of the control system; This is the second column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The coefficient matrix for the three-phase circulating current in the output of the circulating current suppression controller of the control system; This is the coefficient matrix of the three-phase voltage in the inner loop control output of the control system; This is the coefficient matrix of the three-phase voltage in the output of the circulating current suppression controller of the control system; This is the third column vector of the coefficient matrix of the harmonic state equation on the electrical side of the converter station; The first intermediate matrix consists of 0 and the identity matrix. The second intermediate matrix is ​​composed of 0 and the identity matrix. ; Transforming to the sequence domain, we obtain the positive and negative sequence impedance models, expressed as: In the formula The harmonic state space impedance matrix of the flexible DC converter station in the positive and negative sequence coordinate system; This is the transformation matrix for transforming from a three-phase coordinate system to a positive-negative sequence coordinate system; The harmonic state space impedance matrix of the flexible DC converter station in a three-phase coordinate system; This is the transformation matrix for transforming from the positive and negative sequence coordinate system to the three-phase coordinate system; Considering sequence separation, the final output signal of the inner loop controller is: Without considering sequence separation, the final output signal of the inner loop controller is: In the formula In the formula This is the transformation matrix for transforming positive-sequence three-phase coordinates to dq coordinates. For the delay matrix, The transfer function matrix for the inner-loop positive-sequence PI controller. This is the transformation matrix for transforming positive-order dq coordinates to three-phase coordinates. This is the phase-corresponding coefficient matrix in the expression of the inner-loop positive-sequence output signal. The transfer function of the phase-locked loop is in matrix form. Here is the transfer function matrix of the voltage feedforward filter. It is in matrix form of the power outer loop transfer function. The steady-state voltage values ​​in the positive sequence of the dq coordinate system are in matrix form. This is the matrix form of the positive sequence current steady-state value in the dq coordinate system. This is the transformation matrix for transforming negative-sequence three-phase coordinates to dq coordinates. The transfer function matrix for the inner-loop negative-sequence PI controller. This is the transformation matrix for transforming negative-order dq coordinates to three-phase coordinates. The form of the steady-state value matrix of the negative sequence voltage in the dq coordinate system. The steady-state values ​​of the negative sequence current in the dq coordinate system are in matrix form. This is the phase-corresponding coefficient matrix in the expression of the inner-loop negative-sequence output signal.

5. The simplified construction method of the high-frequency impedance theoretical model of the flexible DC converter station according to claim 4, characterized in that... Step S4 involves performing high-frequency simplification on the model constructed in step S3, specifically including the following steps: The distribution of impedance elements within the AC-side impedance matrix is ​​expressed as: In the formula This is the positive and negative sequence matrix of AC voltage under small disturbance conditions; This is the positive and negative sequence matrix of AC current under small disturbance conditions; for Positive sequence voltage with frequency shift; for Negative sequence voltage with frequency shift; It is a positive-sequence voltage with no frequency shift; It is a negative sequence voltage with no frequency shift; for Positive sequence voltage with frequency shift; for Negative sequence voltage with frequency shift; The perturbation frequency; For power frequency; When performing high-frequency impedance analysis, off-diagonal impedance elements are ignored, and only the main diagonal impedance elements are considered and analyzed. therefore, It is a diagonal matrix, represented as: In the formula for Impedance corresponding to frequency-shifted positive-sequence voltage and current; for Impedance corresponding to frequency-shifted negative sequence voltage and current; The impedance corresponding to the positive-sequence voltage and current without frequency shift; The impedance corresponding to the negative sequence voltage and current without frequency shift; for Impedance corresponding to frequency-shifted positive-sequence voltage and current; for Impedance corresponding to frequency-shifted negative sequence voltage and current; Main diagonal positive sequence impedance elements , and The two can be converted through frequency shift, negative sequence impedance elements , and The two frequencies can be converted through frequency shift; the conversion relationship is expressed as: In the formula For the Laplace operator; It is the power frequency angular frequency; This is a plural sign; Based on satisfying the frequency shift conversion relationship between positive-sequence impedance and negative-sequence impedance, factors whose impact on high-frequency impedance characteristics is less than a set threshold are further ignored, thus completing high-frequency simplification.

6. The simplified construction method of the high-frequency impedance theoretical model of the flexible DC converter station according to claim 5, characterized in that... Step S5, based on the simplified model obtained in step S4, involves performing a unified frequency shift characterization of the positive-sequence and negative-sequence impedances of the target flexible DC converter station, thereby completing the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station. This specifically includes the following steps: After simplification, a simplified AC impedance frequency shift model for the target flexible DC converter station considering positive and negative sequence separation and negative sequence control is obtained, expressed as: In the formula, A is the first intermediate variable; B is the second intermediate variable; and C is the third intermediate variable. To account for the positive sequence impedance with sequence separation and k-th frequency shift; To account for the negative sequence impedance with sequence separation and k-th frequency shift; The equivalent impedance on the AC side of the converter station is given by the k-th frequency shift. Let be the delay parameter for the k-1th frequency shift; The inner loop d-axis control parameters are for the k-1th frequency shift; Let be the delay parameter for the (k+1)th frequency shift; The inner loop d-axis control parameters are for the k+1th frequency shift. The equivalent inductance on the AC side of the converter station; Let be the sequence separation delay parameter for k frequency shifts; For voltage feedforward at frequency shift k-1; For voltage feedforward at frequency shift k+1; After simplification, a simplified AC impedance frequency shift model for the target flexible DC converter station, neglecting positive-negative sequence separation and negative sequence control, is obtained, expressed as: In the formula The positive-sequence impedance with k-th frequency shift and without considering sequence separation; For voltage feedforward at frequency shift k-1; For voltage feedforward at frequency shift k+1; A simplified theoretical model of the high-frequency impedance of the target flexible DC converter station was constructed.

7. A system for implementing a simplified construction method of the high-frequency impedance theoretical model of a flexible DC converter station as described in any one of claims 1 to 6, characterized in that... It includes a data acquisition module, a data calculation module, a model building module, a high-frequency simplification module, and a simplified modeling module; the data acquisition module, data calculation module, model building module, high-frequency simplification module, and simplified modeling module are connected in series; the data acquisition module is used to acquire data information of the target flexible DC converter station and upload the data information to the data calculation module; The data calculation module is used to calculate the positive and negative sequence electrical quantity data of the target flexible DC converter station based on the received data information and the acquired data information, and upload the data information to the model building module; The model building module is used to construct the AC impedance theoretical model of the target flexible DC converter station based on the received data information and using the harmonic state-space method, and uploads the data information to the high-frequency simplification module. The high-frequency simplification module is used to perform high-frequency simplification on the constructed model based on the received data information and uploads the data information to the simplified modeling module. The simplified modeling module is used to perform unified frequency shift characterization of the positive-sequence impedance and negative-sequence impedance of the target flexible DC converter station based on the received data information and the simplified model, thus completing the simplified construction of the high-frequency impedance theoretical model of the target flexible DC converter station.

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