Method for establishing impedance model of offshore renewable energy hybrid rectifier DC transmission system

Abstract

The present application proposes a method for establishing an impedance model of an offshore new energy hybrid rectifier type DC transmission system. The method includes: establishing a first small signal transfer function matrix model of DR in the dq coordinate system based on the commutation overlap angle dynamics, and the DC voltage dynamics, DC current dynamics and AC current dynamics of the diode uncontrolled rectifier DR; establishing a second small signal transfer function matrix model of MMC in the dq coordinate system based on the small signal state space model of the electrical part of the modular multilevel converter MMC and the small signal state space model of the control part; adjusting the second small signal transfer function matrix model based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier type DC transmission system to obtain the third small signal transfer function matrix model of MMC in the dq coordinate system; establishing an impedance model of the DR-MMC hybrid rectifier in the dq coordinate system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model.

Description

Technical Field

[0001] The present application relates to the technical field of stability analysis of hybrid rectifier DC transmission systems, and in particular to a method for establishing an impedance model of an offshore renewable energy hybrid rectifier DC transmission system. Background Art

[0002] Offshore renewable energy has been rapidly and widely developed worldwide due to its advantages such as wider space, less impact on the environment and more abundant resources. In order to efficiently and reliably utilize offshore renewable energy, how to transmit it is a very practical issue. In recent years, the DR-MMC hybrid rectifier, which is composed of a diode uncontrolled rectifier (DR) and a modular multilevel converter (MMC) in parallel on the AC side and in series on the DC side, not only has the control capability of MMC to support the offshore AC power grid, but also takes advantage of the low construction cost and reliable technology of DR. Therefore, it has received widespread attention in the field of offshore wind power transmission.

[0003] At present, the research and analysis of offshore renewable energy through DR-MMC hybrid rectifier DC transmission is still in the early stage. The small disturbance stability of the interactive system composed of hybrid rectifier and offshore renewable energy is not yet clear. In view of the convenience and scalability of modeling MMC and DR in the dq coordinate system of offshore renewable energy units and hybrid rectifiers, and considering that the control is usually established based on the dq coordinate system, it is urgent to carry out the research on the impedance model of the hybrid rectifier DC transmission system based on the dq coordinate system, so as to lay the foundation for analyzing the small disturbance stability of its interaction with the offshore renewable energy system. Summary of the invention

[0004] In order to solve the above problems, the present application provides a method for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system.

[0005] According to a first aspect of an embodiment of the present application, a method for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system is provided, comprising:

[0006] Based on the commutation overlap angle dynamics, as well as the DC voltage dynamics, DC current dynamics and AC current dynamics of the diode uncontrolled rectifier DR, the first small signal transfer function matrix model of DR in the dq coordinate system is established;

[0007] Based on the small signal state space model of the electrical part and the small signal state space model of the control part of the modular multilevel converter MMC, the second small signal transfer function matrix model of the MMC in the dq coordinate system is established;

[0008] Based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier DC transmission system, the second small signal transfer function matrix model is adjusted to obtain a third small signal transfer function matrix model of MMC in the dq coordinate system; wherein the third small signal transfer function matrix model has the same input and output as DR;

[0009] An impedance model of the DR-MMC hybrid rectifier in a dq coordinate system is established according to the first small signal transfer function matrix model and the third small signal transfer function matrix model.

[0010] According to a second aspect of an embodiment of the present application, a device for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system is provided, comprising:

[0011] A first establishing module is used to establish a first small signal transfer function matrix model of the DR in a dq coordinate system based on the commutation overlap angle dynamics and the DC voltage dynamics, DC current dynamics and AC current dynamics of the diode uncontrolled rectifier DR;

[0012] The second establishing module is used to establish a second small signal transfer function matrix model of the MMC in the dq coordinate system based on the small signal state space model of the electrical part and the small signal state space model of the control part of the modular multilevel converter MMC;

[0013] A third establishment module is used to adjust the second small signal transfer function matrix model based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier DC transmission system to obtain a third small signal transfer function matrix model of MMC in the dq coordinate system; wherein the third small signal transfer function matrix model has the same input and output as DR;

[0014] The fourth establishing module is used to establish an impedance model of the DR-MMC hybrid rectifier in a dq coordinate system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model.

[0015] According to a third aspect of the present application, an electronic device is provided, comprising: a processor; and a memory for storing executable instructions of the processor; wherein the processor is configured to execute the instructions to implement the method described in the first aspect above.

[0016] According to a fourth aspect of the present application, a computer-readable storage medium is provided. When instructions in the computer-readable storage medium are executed by a processor, the method described in the first aspect is implemented.

[0017] According to the technical solution of the present application, the first small signal transfer function matrix model of DR in the dq coordinate system is established based on the dynamics of the commutation overlap angle, and the dynamics of the DC voltage, DC current and AC current of the diode uncontrolled rectifier DR; the second small signal transfer function matrix model of MMC in the dq coordinate system is established based on the small signal state space model of the electrical part of the modular multilevel converter MMC and the small signal state space model of the control part; based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier type DC transmission system, the second small signal transfer function matrix model is adjusted to obtain the third small signal transfer function matrix model of MMC in the dq coordinate system; according to the first small signal transfer function matrix model and the third small signal transfer function matrix model, the impedance model of the DR-MMC hybrid rectifier in the dq coordinate system is established. This solution can realize the accurate establishment of the dq impedance model of the hybrid rectifier type DC transmission system, and provide a basis for the small signal stability of the offshore new energy hybrid rectifier type DC transmission system.

[0018] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0020] Figure 1 This is a structural block diagram of an offshore new energy hybrid rectification type DC transmission system in an embodiment of the present application;

[0021] Figure 2 A flow chart of a method for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system provided in an embodiment of the present application;

[0022] Figure 3 An example diagram of the dq impedance characteristics and simulation measurement results of the DR-MMC hybrid rectifier of the impedance model constructed in the embodiment of the present application;

[0023] Figure 4 A structural block diagram of a device for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system provided in an embodiment of the present application;

[0024] Figure 5 A structural block diagram of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0026] It should be noted that offshore renewable energy has been rapidly and widely developed worldwide due to its advantages such as wider space, less impact on the environment and more abundant resources. In order to efficiently and reliably utilize offshore renewable energy, how to transmit it is a very practical issue. In recent years, the DR-MMC hybrid rectifier, which is composed of a diode uncontrolled rectifier (DR) and a modular multilevel converter (MMC) in parallel on the AC side and in series on the DC side, not only has the control capability of MMC to support the offshore AC power grid, but also takes advantage of the low construction cost and reliable technology of DR. Therefore, it has received widespread attention in the field of offshore wind power transmission.

[0027] At present, the research and analysis of offshore renewable energy through DR-MMC hybrid rectifier DC transmission is still in the early stage. The small disturbance stability of the interactive system composed of hybrid rectifier and offshore renewable energy is not yet clear. In view of the convenience and scalability of modeling MMC and DR in the dq coordinate system of offshore renewable energy units and hybrid rectifiers, and considering that the control is usually established based on the dq coordinate system, it is urgent to carry out the research on the impedance model of the hybrid rectifier DC transmission system based on the dq coordinate system, so as to lay the foundation for analyzing the small disturbance stability of its interaction with the offshore renewable energy system.

[0028] In order to solve the above problems, the present application provides a method for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system. Figure 1 1 is a structural block diagram of an offshore renewable energy hybrid rectifier DC transmission system in an embodiment of the present application. Figure 1 As shown, taking offshore wind power as an example, the offshore wind farm is composed of permanent magnet direct-drive wind turbines in parallel. The converter voltage of the wind turbine is increased from 690V to 66kV through a step-up transformer and connected to the collection system. The hybrid rectifier DC transmission system rectifier station adopts a hybrid rectifier with DR and MMC in series on the DC side and in parallel on the AC side. DR adopts a 12-pulse rectifier bridge and MMC adopts a half-bridge sub-module. The hybrid rectifier adopts grid-forming control, and the wind turbine adopts grid-following control, using open-loop frequency control to autonomously establish the AC side frequency. In addition, the outer loop control link is AC voltage control, and the d-axis and q-axis components of the AC voltage at the PCC point are controlled by PI controllers respectively. As shown Figure 2 As shown, the method for establishing the impedance model of the offshore renewable energy hybrid rectifier type DC transmission system in the embodiment of the present application may include the following steps:

[0029] Step 201, based on the commutation overlap angle dynamics, and the DC voltage dynamics, DC current dynamics, and AC current dynamics of the DR, a first small signal transfer function matrix model of the DR in the dq coordinate system is established.

[0030] In one embodiment of the present application, when the AC voltage disturbance input Δu d (s) and Δu q (s), DC current disturbance input ΔI dc (s), the first small signal transfer function matrix model of DR in the dq coordinate system is shown in formula (1):

[0031]

[0032] Among them, Δi dDR (s) and Δi qDR (s) is the small signal AC current output of DR; ΔU dcDR (s) is the DR small signal DC voltage; Δu d (s) and Δu q (s) is the small signal AC voltage input of DR; ΔI dc (s) is the small signal DC current input of DR; G DR11 (s) is the input Δu d (s), the output is Δi dDR (s) when the transfer function; G DR12 (s) is the input Δu q (s), the output is Δi dDR (s) when the transfer function; G DR13 (s) is the input ΔI dc (s), the output is Δi dDR (s) when the transfer function; G DR21 (s) is the input Δu d (s), the output is Δi qDR (s) when the transfer function; G DR22 (s) is the input Δu q (s), the output is Δi qDR (s) when the transfer function; G DR23 (s) is the input ΔI dc (s), the output is Δi qDR (s) when the transfer function; G DR31 (s) is the input Δu d (s), output is ΔU dcDR (s) when the transfer function; G DR32 (s) is the input Δu q (s), output is ΔU dcDR (s) when the transfer function; GDR33 (s) is the input ΔI dc (s), output is ΔU dcDR (s); s is the frequency point in the frequency domain.

[0033] In some embodiments, the transfer function G can be determined based on the DC voltage dynamics of the 12-pulse DR. DR31 (s), G DR32 (s) and G DR33 The expression of (s) is shown in the following formula (2):

[0034]

[0035] Among them, Δμ(s) is the commutation overlap angle; μ0 is the initial commutation overlap angle; u d0 and u q0 is the initial AC voltage; ω0 is the initial value of the angular velocity of DR.

[0036] It can be understood that the small signal DC voltage depends on the dynamics of the commutation overlap angle. Based on the dynamics of the commutation overlap angle, the small signal commutation overlap angle Δμ(s) and Δu are derived. d (s), Δu q (s) and ΔI dc (s), and the Laplace transform is performed to obtain the expression shown in formula (3):

[0037]

[0038] In some embodiments, the transfer function G can be determined based on the DC current dynamics of the 12-pulse DR. DR11 (s), G DR12 (s) and G DR13 The expression of (s) is shown in the following formula (4):

[0039]

[0040] The same derivation process can be used to obtain the dynamics of the q-axis AC current, and then the transfer function G DR21 (s), G DR22 (s) and G DR23 The expression of (s) is shown in the following formula (5):

[0041]

[0042] Step 202: Based on the small signal state space model of the MMC electrical part and the small signal state space model of the control part, a second small signal transfer function matrix model of the MMC in the dq coordinate system is established.

[0043] In some embodiments of the present application, the implementation process of step 202 may include: establishing a state space model of the modular multilevel converter MMC based on the small signal state space model of the electrical part and the small signal state space model of the control part; linearizing the state space model of the MMC to obtain a second small signal transfer function matrix model.

[0044] Among them, based on the small signal state space model of the modular multilevel converter MMC electrical part and the small signal state space model of the control part, the implementation process of establishing the state space model of the MMC may include: based on the small signal state space model of the MMC electrical part and the small signal state space model of the control part, establishing the initial state space model of the MMC; removing repeated input quantities in the initial state space model of the MMC to obtain the state space model of the MMC.

[0045] In some embodiments, by mathematically describing the dynamic characteristics of the bridge arm capacitance and bridge arm inductance of the MMC submodule, a state space model of the MMC electrical part can be established. By linearizing the model at the steady-state operating point, the 12th-order small signal state space model of the MMC electrical part can be obtained as shown in the following equation (6):

[0046]

[0047] Among them, Ap is the state matrix of the MMC electrical part 12×12, Bp is the input matrix of the MMC electrical part 12×7, Cp is the output matrix of the MMC electrical part, and Dp is the direct transmission matrix of the MMC electrical part.

[0048] The state variable Δxp of the MMC electrical part in formula (6) is:

[0049]

[0050] Among them, Δu c_dc is the small signal DC component of the submodule capacitor voltage, Δu c_1d , Δu c_1q are the small signal fundamental frequency components of the submodule capacitor voltage under the d-axis and q-axis respectively; Δu c_2d , Δu c_2q are the small signal double frequency components of the submodule capacitor voltage under the d-axis and q-axis respectively; Δu c_3x , Δu c_3y are the small signal triple frequency components of the submodule capacitor voltage under the d-axis and q-axis respectively; ΔI dc is the small signal DC current; ΔI sd , ΔI sq are the d-axis and q-axis small signal components of the AC current respectively; ΔI cird , ΔI cirqThey are the d-axis and q-axis small signal components of the double frequency circulating current respectively.

[0051] The input variable Δup of the MMC electrical part in formula (6) is:

[0052]

[0053] Among them, ΔU cd , ΔU cq is the voltage output by the dq decoupling main controller; ΔU cird , ΔU cirq ΔU is the voltage output by the circulating current suppression controller; sd , ΔU sq is the AC outlet voltage, ΔU dc is a DC voltage.

[0054] In some embodiments, by mathematically describing the MMC network control, inner loop current control, and circulating current suppression control, a state space model of the MMC control part can be established. By linearizing the control model at the steady-state operation point, the small signal state space model of the MMC control part can be obtained as shown in formula (9):

[0055]

[0056] Among them, A c is the 6×6 state matrix of the MMC control part, B c It is the 6×8 input matrix of the MMC control part. c D is the 4×6 output matrix of the MMC control part. c It is the 4×8 direct transmission matrix of the MMC control part.

[0057] In the above formula (9), the state variable Δx of the MMC control part is c As shown in the following formula (10):

[0058]

[0059] Among them, Δf1 and Δf2 are state variables introduced by the circulating current suppression controller, Δx1 and Δx2 are state variables introduced by the inner loop current controller; Δx3 and Δx4 are state variables introduced by the outer loop voltage controller.

[0060] In the above formula (9), the input variable Δu of the MMC control part is c for:

[0061]

[0062] Among them, ΔU dref , ΔU qref are the reference values ​​of the d-axis and q-axis of the outer loop voltage controller respectively.

[0063] The output variable Δy of the control part in the above formula (9) is c for:

[0064]

[0065] Combining the above equations (6) and (9), the initial state space model of MMC can be formed, as shown in the following equation (13):

[0066]

[0067] Since the state quantity of the MMC electrical part overlaps with the input quantity of the control part, and the input quantity of the electrical part overlaps with the output quantity of the control part, the 12×7 input matrix B of the electrical part can be p Divide into 12×4 matrix B p1 and the 12×3 matrix B p2 , input variable Δu p Divide into blocks Δu p1 and Δu p2 , the control part 6×8 input matrix B c Divide into 6×4 matrix B c1 and the 6×4 matrix B c2 , input variable Δu c Divide into blocks Δu c1 and Δu c2 , the above formula (13) can be converted into the following formula (14):

[0068]

[0069] Among them, Δu p1 is Δu p The first four quantities of Δu p2 is Δu p The last three quantities of Δu c1 is Δu c The first four quantities in Δu c2 is Δu c The last four quantities in

[0070] In some embodiments, the 4×8 direct transfer matrix D in formula (9) can be c The matrix D is divided into 4×4 blocks c1 and D c2 , the output equation of MMC control can be shown as follows (15):

[0071]

[0072] Since the output Δy of the control system c is the input variable Δu of the electrical part p1 , the input variable Δu of the control system c1 is the state variable Δu of the MMC electrical part p The last four quantities of , we get the following formula (16):

[0073]

[0074] Among them, the matrix E is a 4-order identity matrix.

[0075] Substituting equation (16) into equation (14) and eliminating the repeated inputs in the state-space equation, the expression of the state-space model of MMC can be obtained as shown in equation (17):

[0076]

[0077] In some embodiments, for a linear time-invariant system, its state space general expression is as follows:

[0078]

[0079] Assuming the initial state is zero, taking the Laplace transform, we get the following equation (19):

[0080]

[0081] Transforming the above formula can get the following formula (20):

[0082]

[0083] The transfer function matrix from input to output is obtained by equation (20) as follows:

[0084]

[0085] To this end, the small signal AC voltage input Δu of the MMC is selected d (s) and Δu q (s), small signal DC voltage input ΔU dcMMC (s), the small signal AC current output Δi dMMC (s) and Δi qMMC (s), small signal DC current output ΔI dc (s) can be expressed as the following formula (22), that is, the second minimum signal transfer function matrix model of MMC in the dq coordinate system:

[0086]

[0087] Among them, Δi dMMC (s) and Δi qMMC (s) is the small signal AC current output of MMC; ΔI dc (s) is the small signal DC current output of MMC; Δu d (s) and Δu q (s) is the small signal AC voltage input of MMC; ΔU dcMMC (s) is the small signal DC voltage input of MMC; G ij (s) is the transfer function of the i-th row and j-th column in the second small signal transfer function matrix; The 4×6 output matrix C of the MMC control part c The transposed matrix of the i-th row in ; I is the identity matrix of the same latitude as A; A is the state matrix in the state space model of MMC, that is, b j is the jth column of the input matrix in the state space model of MMC, that is, The jth column of ij is the output matrix [D c1 D c2 ] in the i-th row and j-th column.

[0088] Step 203, based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier DC transmission system, adjust the second small signal transfer function matrix model to obtain the third small signal transfer function matrix model of MMC in the dq coordinate system; wherein the third small signal transfer function matrix model has the same input and output as DR.

[0089] In some embodiments, in order to realize that DR and MMC are connected in parallel on the AC side and in series on the DC side, it is necessary to combine the first small signal transfer function matrix model of DR in the dq coordinate system and the second small signal transfer function matrix model of MMC in the dq coordinate system, that is, combine formula (1) and formula (22), but ΔI dc For DR, it is an input quantity, and for MMC, it is an output quantity. To this end, the DC voltage ΔU of MMC in the second small signal transfer function matrix model of MMC in the dq coordinate system is dcMMC Adjusted to output, DC current ΔI dc Adjust to the input quantity and obtain the third small signal transfer function matrix model with the same input and output as DR, as shown in the following equation (24):

[0090]

[0091] The expression of the transfer function is as follows:

[0092]

[0093] Step 204: Establish an impedance model of the DR-MMC hybrid rectifier in a dq coordinate system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model.

[0094] In some embodiments of the present application, the implementation process of establishing the impedance model of the DR-MMC hybrid rectifier in the dq coordinate system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model includes: determining the dynamic representation of the DC side when considering the equivalent impedance of the DC network side of the HVDC system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model; establishing the impedance model of the DR-MMC hybrid rectifier in the dq coordinate system according to the first small signal transfer function matrix model, the third small signal transfer function matrix model and the dynamic representation of the DC side.

[0095] As an implementation method, combining the above equation (1) and the above equation (24), when the equivalent impedance of the HVDC system DC network side is considered to be Z dc When (s), the DC side dynamics of the DR-MMC-HVDC system can be expressed as follows (26):

[0096] ΔU dc (s) = ΔU dcDR (s)+ΔU dcMMC (s) = Z dc (s)ΔI dc (s)

[0097] =(G DR31 (s)+G MMC31 (s))Δu d (s)+(G DR32 (s)+G MMC32 (s))Δu q (s)+(G DR33 (s)+G MMC33 (s))ΔI dc (s) (26)

[0098] Combining equations (1), (24) and (26), we can get the small signal AC current Δi of the DR-MMC-HVDC system with the DR-MMC hybrid rectifier: d and Δi q is the output, small signal AC voltage Δu of the DR-MMC hybrid rectifier d and Δu q The small signal transfer function matrix model of the input is shown in the following formula (27), that is, the impedance model of the DR-MMC hybrid rectifier in the dq coordinate system:

[0099]

[0100]

[0101] Among them, Δi d (s) and Δi q (s) is the small signal AC current output of the DR-MMC hybrid rectifier; Δi dMMC (s) and Δi qMMC (s) is the small signal AC current output of MMC in the DR-MMC hybrid rectifier; Δi dDR (s) and Δi qDR (s) is the small signal AC current output of DR in the DR-MMC hybrid rectifier; G Hdd (s) is the input Δu d (s) output is Δi d (s) transfer function; G Hdq (s) is the input Δu q (s) output is Δi d (s) transfer function; G Hqd (s) is the input Δu d (s) output is Δi q (s) transfer function; G Hqq (s) is the input Δu q (s) output is Δi q (s) transfer function.

[0102] In order to verify the accuracy of the impedance model of the DR-MMC hybrid rectifier in the dq coordinate system constructed by the method for establishing the impedance model of the offshore renewable energy hybrid rectifier type DC transmission system in the above embodiment, a model of an offshore renewable energy hybrid rectifier type DC transmission system through DR-MMC is built in the simulation platform, and the system parameters are shown in Table 1. Figure 3 1 is an example diagram of the dq impedance characteristics of the DR-MMC hybrid rectifier and the simulation measurement results of the impedance model constructed in the embodiment of the present application. Figure 3 As shown, the impedance model (solid line) constructed by the impedance model building method of the above embodiment can be well consistent with the impedance measurement result (hollow circles), which proves the accuracy of the dq impedance modeling of the DR-MMC hybrid rectifier.

[0103] Table 1 System parameters of offshore renewable energy DR-MMC hybrid rectifier DC transmission system

[0104]

[0105]

[0106] According to the method for establishing the impedance model of the offshore new energy hybrid rectifier type DC transmission system of the embodiment of the present application, the first small signal transfer function matrix model of DR in the dq coordinate system is established based on the dynamics of the commutation overlap angle, and the dynamics of the DC voltage, DC current and AC current of the diode uncontrolled rectifier DR; based on the small signal state space model of the electrical part of the modular multilevel converter MMC and the small signal state space model of the control part, the second small signal transfer function matrix model of MMC in the dq coordinate system is established; based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier type DC transmission system, the second small signal transfer function matrix model is adjusted to obtain the third small signal transfer function matrix model of MMC in the dq coordinate system; according to the first small signal transfer function matrix model and the third small signal transfer function matrix model, the impedance model of the DR-MMC hybrid rectifier in the dq coordinate system is established. This scheme can realize the accurate establishment of the dq impedance model of the hybrid rectifier type DC transmission system, and provide a basis for the small signal stability of the offshore new energy hybrid rectifier type DC transmission system.

[0107] In order to implement the above-mentioned embodiments, the present application also provides a device for establishing an impedance model of an offshore new energy hybrid rectifier type DC transmission system.

[0108] Figure 4 This is a structural block diagram of a device for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system provided in an embodiment of the present application. Figure 4 As shown, the device comprises:

[0109] A first establishing module 401 is used to establish a first small signal transfer function matrix model of the DR in a dq coordinate system based on the commutation overlap angle dynamics and the DC voltage dynamics, DC current dynamics and AC current dynamics of the diode uncontrolled rectifier DR;

[0110] The second establishing module 402 is used to establish a second small signal transfer function matrix model of the modular multilevel converter MMC in the dq coordinate system based on the small signal state space model of the electrical part and the small signal state space model of the control part of the MMC;

[0111] The third establishing module 403 is used to adjust the second small signal transfer function matrix model based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier DC transmission system to obtain a third small signal transfer function matrix model of MMC in the dq coordinate system; wherein the third small signal transfer function matrix model has the same input and output as DR;

[0112] The fourth establishing module 404 is used to establish an impedance model of the DR-MMC hybrid rectifier in the dq coordinate system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model.

[0113] The expression of the first small signal transfer function matrix model established by the first establishing module 401 is as shown in formulas (1)-(5) in the above method embodiment, and will not be repeated here.

[0114] In some embodiments, the second establishing module 402 is specifically used to:

[0115] Based on the small signal state space model of the electrical part and the small signal state space model of the control part of the modular multilevel converter MMC, a state space model of the MMC is established;

[0116] The state space model of the MMC is linearized to obtain the second small signal transfer function matrix model.

[0117] As an implementation manner, the second establishing module 402 is further used for:

[0118] Based on the small signal state space model of the MMC electrical part and the small signal state space model of the control part, an initial state space model of the MMC is established;

[0119] The repeated input quantities in the initial state space model of the MMC are removed to obtain the state space model of the MMC.

[0120] Among them, the expression of the MMC state control model obtained by the second establishment module 402 is shown in formula (17) in the above embodiment, and the expression of the second small signal transfer function matrix model is shown in formulas (22) and (23) in the above embodiment.

[0121] In some embodiments, the expression of the third small signal transfer function matrix model obtained by the third establishing module 403 is as shown in formula (24) and formula (25) in the above embodiments.

[0122] In some embodiments, the fourth establishing module 404 is specifically used to:

[0123] Determining a DC side dynamic representation when considering an equivalent impedance on a DC network side of an HVDC system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model;

[0124] An impedance model of the DR-MMC hybrid rectifier in a dq coordinate system is established according to the first small signal transfer function matrix model, the third small signal transfer function matrix model and the DC side dynamic representation.

[0125] As an implementation method, the DC side dynamic representation obtained by the fourth establishment module 404 is shown in formula (26) in the above embodiment, and the expression of the impedance model of the DR-MMC hybrid rectifier in the dq coordinate system is shown in formulas (27) and (28) in the above embodiment.

[0126] It should be noted here that the above-mentioned device provided in the embodiment of the present invention can implement all the method steps implemented in the above-mentioned method for establishing the impedance model of the offshore new energy hybrid rectifier type DC transmission system, and can achieve the same technical effect. The same parts and beneficial effects of the method for establishing the impedance model of the offshore new energy hybrid rectifier type DC transmission system in this embodiment will not be described in detail here.

[0127] According to an embodiment of the present application, the present application also provides an electronic device and a readable storage medium.

[0128] like Figure 5 As shown, it is a block diagram of an electronic device according to a method for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system according to an embodiment of the present application. The electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workbenches, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present application described and / or required herein.

[0129] like Figure 5 As shown, the electronic device includes: one or more processors 501, a memory 502, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. The various components are interconnected using different buses and can be installed on a common mainboard or installed in other ways as needed. The processor can process instructions executed in the electronic device, including instructions stored in or on the memory to display the graphical information of the GUI on an external input / output device (such as a display device coupled to the interface). In other embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple electronic devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 5 A processor 501 is taken as an example.

[0130] The memory 502 is a non-transitory computer-readable storage medium provided in the present application. The memory stores instructions executable by at least one processor, so that the at least one processor executes the method for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system provided in the present application. The non-transitory computer-readable storage medium of the present application stores computer instructions, which are used to enable a computer to execute the method for establishing an impedance model of an offshore renewable energy hybrid rectifier type DC transmission system provided in the present application.

[0131] The memory 502, as a non-transient computer-readable storage medium, can be used to store non-transient software programs, non-transient computer executable programs and modules, such as the program instructions / modules corresponding to the method for establishing the impedance model of the offshore renewable energy hybrid rectifier type DC transmission system in the embodiment of the present application. The processor 501 executes various functional applications and data processing of the server by running the non-transient software programs, instructions and modules stored in the memory 502, that is, the method for establishing the impedance model of the offshore renewable energy hybrid rectifier type DC transmission system in the above method embodiment is implemented.

[0132] The memory 502 may include a program storage area and a data storage area, wherein the program storage area may store an operating system and an application required by at least one function; the data storage area may store data created by the use of an electronic device according to a method for establishing an impedance model of an offshore new energy hybrid rectifier type DC transmission system, etc. In addition, the memory 502 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some embodiments, the memory 502 may optionally include a memory remotely arranged relative to the processor 501, and these remote memories may be connected to the electronic device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0133] The electronic device may further include: an input device 503 and an output device 504. The processor 501, the memory 502, the input device 503 and the output device 504 may be connected via a bus or other means. Figure 5 The example of connecting through bus is taken in the following.

[0134] The input device 503 can receive input digital or character information, and generate key signal input related to user settings and function control of the electronic device, such as a touch screen, a keypad, a mouse, a track pad, a touch pad, an indicator bar, one or more mouse buttons, a trackball, a joystick and other input devices. The output device 504 may include a display device, an auxiliary lighting device (e.g., an LED) and a tactile feedback device (e.g., a vibration motor), etc. The display device may include, but is not limited to, a liquid crystal display (LCD), a light emitting diode (LED) display and a plasma display. In some embodiments, the display device may be a touch screen.

[0135] Various implementations of the systems and techniques described herein can be realized in digital electronic circuit systems, integrated circuit systems, dedicated ASICs (application specific integrated circuits), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include: being implemented in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which can be a special purpose or general purpose programmable processor that can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit data and instructions to the storage system, the at least one input device, and the at least one output device.

[0136] These computer programs (also referred to as programs, software, software applications, or code) include machine instructions for programmable processors and can be implemented using high-level procedural and / or object-oriented programming languages, and / or assembly / machine languages. As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any computer program product, device, and / or means (e.g., disk, optical disk, memory, programmable logic device (PLD)) for providing machine instructions and / or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal for providing machine instructions and / or data to a programmable processor.

[0137] To provide interaction with a user, the systems and techniques described herein can be implemented on a computer having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user; and a keyboard and pointing device (e.g., a mouse or trackball) through which the user can provide input to the computer. Other types of devices can also be used to provide interaction with the user; for example, the feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form (including acoustic input, voice input, or tactile input).

[0138] The systems and techniques described herein can be implemented in a computing system that includes backend components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes frontend components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such backend components, middleware components, or frontend components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: a local area network (LAN), a wide area network (WAN), the Internet, and a blockchain network.

[0139] A computer system may include a client and a server. The client and the server are generally remote from each other and usually interact through a communication network. The relationship between the client and the server is generated by computer programs running on the corresponding computers and having a client-server relationship with each other. The server may be a cloud server, also known as a cloud computing server or cloud host, which is a host product in the cloud computing service system to solve the defects of difficult management and weak business scalability in traditional physical hosts and VPS services ("Virtual Private Server", or "VPS" for short). The server may also be a server of a distributed system, or a server combined with a blockchain.

[0140] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this application can be executed in parallel, sequentially or in different orders, as long as the expected results of the technical solution disclosed in this application can be achieved, and this document is not limited here.

[0141] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for establishing an impedance model of an offshore renewable energy hybrid rectifier DC transmission system, characterized in that: include: Based on the commutation overlap angle dynamics, as well as the DC voltage dynamics, DC current dynamics and AC current dynamics of the diode uncontrolled rectifier DR, the first small signal transfer function matrix model of DR in the dq coordinate system is established; Based on the small signal state space model of the electrical part and the small signal state space model of the control part of the modular multilevel converter MMC, the second small signal transfer function matrix model of the MMC in the dq coordinate system is established; Based on the series-parallel relationship between DR and MMC in the offshore new energy hybrid rectifier DC transmission system, the second small signal transfer function matrix model is adjusted to obtain a third small signal transfer function matrix model of MMC in the dq coordinate system; wherein the third small signal transfer function matrix model has the same input and output as DR; Establishing an impedance model of the DR-MMC hybrid rectifier in a dq coordinate system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model; The first small signal transfer function matrix model is shown in formula (1), formula (2) and formula (3): Among them, Δi dDR (s) and Δi qDR (s) is the small signal AC current output of DR; ΔU dcDR (s) is the DR small signal DC voltage; Δu d (s) and Δu q (s) is the small signal AC voltage input of DR; ΔI dc (s) is the small signal DC current input of DR; G DR11 (s) is the input Δu d (s), the output is Δi dDR (s) when the transfer function; G DR12 (s) is the input Δu q (s), the output is Δi dDR (s) when the transfer function; G DR13 (s) is the input ΔI dc (s), the output is Δi dDR (s) when the transfer function; G DR21 (s) is the input Δu d (s), the output is Δi qDR (s) when the transfer function; G DR22 (s) is the input Δu q (s), the output is Δi qDR (s) when the transfer function; G DR23 (s) is the input ΔI dc (s), the output is Δi qDR (s) when the transfer function; G DR31 (s) is the input Δu d (s), output is ΔU dcDR (s) when the transfer function; G DR32 (s) is the input Δu q (s), output is ΔU dcDR (s) when the transfer function; G DR33 (s) is the input ΔI dc (s), output is ΔU dcDR (s); Δμ(s) is the commutation overlap angle; μ0 is the initial commutation overlap angle; u d0 and u q0 is the initial AC voltage; s is the frequency point in the frequency domain; ω0 is the initial value of the angular velocity of DR.

2. The method according to claim 1, characterized in that The method of establishing a second small signal transfer function matrix model of the MMC in the dq coordinate system based on the small signal state space model of the electrical part and the small signal state space model of the control part of the modular multilevel converter MMC includes: Based on the small signal state space model of the electrical part and the small signal state space model of the control part of the modular multilevel converter MMC, a state space model of the MMC is established; The state space model of the MMC is linearized to obtain the second small signal transfer function matrix model.

3. The method according to claim 2, characterized in that The state space model of the MMC is established based on the small signal state space model of the electrical part and the small signal state space model of the control part of the modular multilevel converter MMC, including: Establishing an initial state space model of the MMC based on the small signal state space model of the MMC electrical part and the small signal state space model of the control part; The repeated input quantities in the initial state space model of the MMC are removed to obtain the state space model of the MMC.

4. The method according to claim 2, characterized in that: The expressions of the state space model of the MMC are shown in the following formulas (4) and (5): Among them, A p B is the 12×12 state matrix of the MMC electrical part. p1 and B p2 12×7 input matrix B for the MMC electrical part p The matrix after block division, where B p1 is a 12×4 matrix, B p2 is a 12×3 matrix; A c is the 6×6 state matrix of the MMC control part, B c It is the 6×8 input matrix of the MMC control part; C c D is the 4×6 output matrix of the MMC control part; c1 and D c2 The 4×8 direct transmission matrix D of the MMC control part c The matrix after block division is 4×4 matrix; B c2 For B c The 4×4 matrix obtained after block division; Δu c_dc is the small signal DC component of the submodule capacitor voltage, Δu c_1d , Δu c_1q are the small signal fundamental frequency components of the submodule capacitor voltage under the d-axis and q-axis respectively; Δu c_2d , Δu c_2q are the small signal double frequency components of the submodule capacitor voltage under the d-axis and q-axis respectively; Δu c_3x , Δu c_3y are the small signal triple frequency components of the submodule capacitor voltage under the d-axis and q-axis respectively; ΔI dc is the small signal DC current; ΔI sd , ΔI sq are the d-axis and q-axis small signal components of the AC current respectively; ΔI cird , ΔI cirq are the d-axis and q-axis small signal components of the double frequency circulating current respectively; ΔU sd , ΔU sq is the AC outlet voltage, ΔU dc is the DC voltage; Δf1 and Δf2 are the state variables introduced by the circulating current suppression controller, Δx1 and Δx2 are the state variables introduced by the inner loop current controller; Δx3 and Δx4 are the state variables introduced by the outer loop voltage controller; ΔU dref , ΔU qref are the reference values ​​of the d-axis and q-axis of the outer loop voltage controller respectively; E is the fourth-order unit matrix.

5. The method according to claim 4, characterized in that The expression of the second small signal transfer function matrix model is shown in the following formula (6) and formula (7): Among them, Δi dMMC (s) and Δi qMMC (s) is the small signal AC current output of MMC; ΔI dc (s) is the small signal DC current output of MMC; Δu d (s) and Δu q (s) is the small signal AC voltage input of MMC; ΔU dcMMC (s) is the small signal DC voltage input of MMC; G ij (s) is the transfer function of the i-th row and j-th column in the second small signal transfer function matrix; is the transposed matrix of the i-th row in the 4×6 output matrix of the MMC control part; I is the unit matrix with the same latitude as A; A is the state matrix in the state space model of MMC; b j is the jth column of the input matrix in the state space model of MMC; d ij is the i-th row and j-th column in the output matrix in the control output equation of the MMC.

6. The method according to claim 5, characterized in that The expression of the third small signal transfer function matrix model is shown in the following formula (8) and formula (9):

7. The method according to claim 1, characterized in that The step of establishing an impedance model of the DR-MMC hybrid rectifier in a dq coordinate system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model includes: Determining a DC side dynamic representation when considering an equivalent impedance on a DC network side of an HVDC system according to the first small signal transfer function matrix model and the third small signal transfer function matrix model; An impedance model of the DR-MMC hybrid rectifier in a dq coordinate system is established according to the first small signal transfer function matrix model, the third small signal transfer function matrix model and the DC side dynamic representation.

8. The method according to claim 7, characterized in that The expression of the DC side dynamic representation is shown in the following formula (10): ΔU dc (s)=ΔU dcDR (s)+ΔU dcMMC (s)=Z dc (s)ΔI dc (s)=(G DR31 (s)+G MMC31 (s))Δu d (s)+(G DR32 (s)+G MMC32 (s))Δu q (s)+(G DR33 (s)+G MMC33 (s))ΔI dc (s) (10) Among them, Δu d (s) and Δu q (s) is the small signal AC voltage input of the DR-MMC hybrid rectifier; ΔI dc (s) is the small signal DC current input of the DR-MMC hybrid rectifier; G DR31 (s) is the first small signal transfer function matrix model, and the input is Δu d (s), output is ΔU dcDR (s) when the transfer function; G DR32 (s) is the first small signal transfer function matrix model, and the input is Δu q (s), output is ΔU dcDR (s) when the transfer function; G DR33 (s) is the first small signal transfer function matrix model, and the input is ΔI dc (s), output is ΔU dcDR (s) when the transfer function; G MMC31 (s) is the third small signal transfer function matrix model, and the input is Δu d (s), output is ΔU dcMMC (s) when the transfer function; G MMC32 (s) is the third small signal transfer function matrix model, and the input is Δu q (s), output is ΔU dcMMC (s) when the transfer function; G MMC33 (s) is the third small signal transfer function matrix model, and the input is ΔI dc (s), output is ΔU dcMMC (s) when the transfer function; Z dc (s) is the input impedance on the DC network side of the HVDC system.

9. The method according to claim 8, characterized in that The impedance model of the DR-MMC hybrid rectifier in the dq coordinate system is expressed as shown in the following formulas (11) and (12): Among them, Δi d (s) and Δi q (s) is the small signal AC current output of the DR-MMC hybrid rectifier; Δi dMMC (s) and Δi qMMC (s) is the small signal AC current output of MMC in the DR-MMC hybrid rectifier; Δi dDR (s) and Δi qDR (s) is the small signal AC current output of DR in the DR-MMC hybrid rectifier; G Hdd (s) is the input Δu d (s) output is Δi d (s) transfer function; G Hdq (s) is the input Δu q (s) output is Δi d (s) transfer function; G Hqd (s) is the input Δu d (s) output is Δi q (s) transfer function; G Hqq (s) is the input Δu q (s) output is Δi q (s) transfer function; G DR11 (s) is the first small signal transfer function matrix model, and the input is Δu d (s), the output is Δi dDR (s) when the transfer function; G DR12 (s) is the first small signal transfer function matrix model, and the input is Δu q (s), the output is Δi dDR (s) when the transfer function; G DR13 (s) is the first small signal transfer function matrix model, and the input is ΔI dc (s), the output is Δi dDR (s) when the transfer function; G DR21 (s) is the first small signal transfer function matrix model, and the input is Δu d (s), the output is Δi qDR (s) when the transfer function; G DR22 (s) is the first small signal transfer function matrix model, and the input is Δu q (s), the output is Δi qDR (s) when the transfer function; G DR23 (s) is the first small signal transfer function matrix model, and the input is ΔI dc (s), the output is Δi qDR (s) when the transfer function; G DR31 (s) is the first small signal transfer function matrix model, and the input is Δu d (s), output is ΔU dcDR (s) when the transfer function; G DR32 (s) is the first small signal transfer function matrix model, and the input is Δu q (s), output is ΔU dcDR (s) when the transfer function; G DR33 (s) is the first small signal transfer function matrix model, and the input is ΔI dc (s), output is ΔU dcDR (s) when the transfer function; G MMC11 (s) is the third small signal transfer function matrix model, and the input is Δu d (s), the output is Δi dMMC (s) when the transfer function; G MMC12 (s) is the third small signal transfer function matrix model, and the input is Δu q (s), the output is Δi dMMC (s) when the transfer function; G MMC13 (s) is the third small signal transfer function matrix model, and the input is ΔI dc (s), the output is Δi dMMC (s) when the transfer function; G MMC21 (s) is the third small signal transfer function matrix model, and the input is Δu d (s), the output is Δi qMMC (s) when the transfer function; G MMC22 (s) is the third small signal transfer function matrix model, and the input is Δu q (s), the output is Δi qMMC (s) when the transfer function; G MMC23 (s) is the third small signal transfer function matrix model, and the input is ΔI dc (s), the output is Δi qMMC (s) when the transfer function; G MMC31 (s) is the third small signal transfer function matrix model, and the input is Δu d (s), output is ΔU dcMMC (s) when the transfer function; G MMC32 (s) is the third small signal transfer function matrix model, and the input is Δu q (s), output is ΔU dcMMC (s) when the transfer function; G MMC33 (s) is the third small signal transfer function matrix model, and the input is ΔI dc (s), output is ΔU dcMMC (s) is the transfer function.

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