Control system and method of flexible interconnection device based on back-to-back converter

Abstract

The invention discloses a control system and method of a flexible interconnection device based on a back-to-back converter. The method comprises the following steps: establishing a nonlinear model of a BTB-VSC according to a topological structure of the BTB-VSC; the nonlinear model of the BTB-VSC is linearized, and a linear model of the BTB-VSC is obtained; designing a controller according to the linear model of the BTB-VSC; meanwhile, dynamic changes of alternating-current side inductance and direct-current side capacitance are considered, an augmented matrix K of state feedback control in a controller is calculated, it is guaranteed that all poles in the system are distributed in corresponding areas of a complex plane, and the system operates stably under the condition that bidirectional power flow and power grid equivalent impedance are uncertain. According to the method, good control performance can be achieved under the nondeterminacy of bidirectional power flow and power grid equivalent impedance, and the controlled variable has small overshoot on the step change of the reference value and the sudden change of the power grid equivalent inductance value.

Description

Technical Field

[0001] The invention relates to a control system and method for a flexible interconnection device based on back-to-back converters, belonging to the technical field of power electronics. Background Art

[0002] At present, with the increasing proportion of renewable energy power generation, the distribution network presents the "double high" characteristics of high proportion of renewable energy access and high proportion of power electronic equipment application. Since the flow direction of the power flow is no longer single, there will be uneven distribution of the power flow. In order to control the power flow in the power system, a large number of solutions based on power electronics technology have been proposed, such as static synchronous compensator (STATCOM), unified power flow controller (UPFC) and controllable network transformer (CNT). However, since the back-to-back converter (BTB-VSC) can not only control the power flow, but also control the active power and reactive power separately, and can also suppress the system harmonics, it has been widely studied. Among them, the flexible switch device is a new type of flexible primary device that can replace the traditional tie switch at several key nodes of the distribution network. Compared with the traditional tie switch, it not only has two states of on and off, but also has no limit on the number of traditional mechanical switch actions, increases the power continuous controllable state, and has the characteristics of flexible switching of operation mode and flexible and diverse control methods. The common connection point is also called PCC point (Point of Common Coupling), which is the connection point of more than one user load in the power system. A static synchronous compensator (STATCOM) is a parallel type reactive power compensation FACTS device that can generate or absorb reactive power, and its output can be changed to control specific parameters in the power system. A unified power flow controller (UPFC) can control the power flow distribution of the line and effectively improve the stability of the power system.

[0003] In the existing technical solutions, there is direct current control in the strategy of realizing the bidirectional flow control of power flow, whose goal is to make the current output by the converter change according to the current waveform set by the controller. According to the different methods of obtaining and calculating the set value, it is divided into current hysteresis control and predictive current control. Figure 1 As shown in the figure, the advantages of direct current control are fast dynamic response speed and simple controller structure, while the disadvantages are that it requires a higher switching frequency and a precise current sensor, resulting in higher losses and costs. In general high-voltage and high-capacity applications, the switching frequency of the converter cannot be very high, so direct current control is rarely used in high-voltage and high-capacity fields.

[0004] In addition, the phase adjustment control, such as Figure 2As shown in the figure, the initial state of the system is point B. When the DC side load suddenly changes, the amplitude of RU will be affected by the DC capacitor voltage before adjustment, and the current RI will change. Therefore, the phase RU may move along the trajectory of B →C. In order to make the system return to the stable point D, the phase adjustment method will gradually reduce the adjustment step and adjust to the stable point D according to the trajectory of C →E →F →D. If the initial point is P, the phase adjustment method will also follow a similar trajectory to make the system return to the new stable point B. It can be seen that the phase adjustment control requires accurate calculation of each voltage phasor, so the adjustment process depends on the accurate observation of R and L.

[0005] There is also decoupling control under dq coordinates. Starting from the dq-axis state equation of the converter, different state quantities and controller designs are selected, or the dq-axis component of the converter output current or the dq-axis component of the converter output voltage is used as the control quantity, thereby realizing the decoupling control of the dq axis.

[0006] In the existing research on the control method of BTB-VSC, the linear working area of ​​VSC is analyzed and discussed, the selected power operating point of independent VSC is considered, the active and reactive current components are analyzed and discussed, and the approximation describing the performance of BTB-VSC in the linear working area of ​​the converter is introduced, but the results are limited to showing active power transmission and DC bus regulation, and the performance of reactive power has not been verified in the study. A unified multivariable control strategy based on full state feedback control is proposed to control BTB-VSC with LCL output filter. The proposed state feedback strategy can handle the transient mismatch problem of power flow well, but when the equivalent impedance in PCC is uncertain, the system stability is not high. Summary of the invention

[0007] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a control method for a flexible interconnection device based on a back-to-back converter. First, a nonlinear model of the system is established according to the voltage and power flow of the BTB-VSC system. Then, general variables are written as a combination of steady-state components and small-signal change components to linearize the nonlinear model. Then, based on the method of configuring pole distribution, a linear matrix inequality (LMI) system is obtained. The relevant parameters of the controller can be calculated by solving the system.

[0008] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0009] A control method for a flexible interconnection device based on back-to-back converters comprises the following steps:

[0010] Step 1, establishing a nonlinear model of BTB-VSC according to the topological structure of BTB-VSC;

[0011] Step 2, linearize the nonlinear model of BTB-VSC to obtain a linear model of BTB-VSC;

[0012] Step 3, design a controller based on the linear model of BTB-VSC; consider the dynamic changes of the AC side inductance and the DC side capacitance at the same time, and calculate the augmented matrix K of the state feedback control in the controller to ensure that all poles in the system are distributed in the corresponding area of ​​the complex plane, so that the system can operate stably under the conditions of uncertain bidirectional power flow and grid equivalent impedance.

[0013] Optimum: The nonlinear model of BTB-VSC is as follows:

[0014]

[0015] in, Indicates the grid-side equivalent inductance of VSC1, Indicates the grid-side equivalent inductance of VSC2, represents the d-axis component of the VSC1 input current, represents the d-axis component of the VSC2 input current, represents the q-axis component of the VSC1 input current, represents the q-axis component of the VSC2 input current, Indicates the grid-side frequency of VSC1, Indicates the grid-side frequency of VSC2, represents the d-axis component of the VSC1 modulation function, represents the d-axis component of the VSC2 modulation function, represents the q-axis disturbance component of the VSC1 modulation function, represents the q-axis disturbance component of the VSC2 modulation function, Indicates the DC side voltage value, It represents the d-axis component of the AC voltage measured by VSC1, It represents the d-axis component of the AC voltage measured by VSC2, represents the q-axis component of the VSC1 AC voltage measurement, represents the q-axis component of the VSC2 AC voltage measurement, Represents the DC side voltage stabilizing capacitor, Indicates time.

[0016] Optimum: The controller formula is as follows:

[0017]

[0018] Among them, the superscript (*) indicates the reference value. Combined with the small signal model, the augmented matrix is ​​obtained:

[0019]

[0020] The state feedback controller is expressed as:

[0021]

[0022] The linear system of control is described by the equation:

[0023]

[0024] in, Represents the error integration output matrix of voltage and current, represents the coefficient matrix of the state variables, represents the state variable disturbance value matrix, represents the four-dimensional identity matrix, represents the voltage and current reference difference matrix, express The error integral output, express The error integral output, express The error integral output, express The error integral output, represents the system modulation function matrix, Represents the relationship matrix between the modulation function and the state variables, represents the state variables and their error integral matrices, represents the state variables of the linear system, represents the coefficient matrix of the state variable augmentation matrix, Represents the system modulation function coefficient matrix.

[0025] Preferred: The method for finding the augmented matrix K: Assume that the system power is The grid resistance varies within the range of The grid inductance varies within the range of There are eight cases. For each case, it is necessary to calculate matrices A and B so that the closed-loop poles of the entire system must be located in region D. The following conditions must be met:

[0026]

[0027] in:

[0028]

[0029] in: represents the lateral extent of the complex plane, represents the sector angle of the complex plane, represents the radius of the sector in the complex plane, , , Represents the calculated matrix.

[0030] Preferred: Use matrices A and B to evaluate whether the system is stable. If there are positive definite matrices P and Satisfied:

[0031]

[0032] This indicates that the system is stable; represents the coefficient matrix of the state variable augmentation matrix, represents a positive definite matrix, represents the augmented matrix of the system modulation function coefficients, The matrix representing the multiplication of the modulation function state variables and the positive definite matrix, A matrix representing the relationship between the modulation function and the state variables.

[0033] Preferably, the method for linearizing the nonlinear model of BTB-VSC is as follows: when the system is in a steady state, the derivative terms are all zero; through the phase-locked loop system, the AC system and The q-axis components of are all zero, the d-axis components are all voltage peaks, and the steady-state values ​​of the remaining variables are as follows:

[0034]

[0035] Use the state equation to represent the small signal model of the entire system:

[0036]

[0037] in:

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044] in, represents the output power of VSC1, Represents the equivalent resistance on the VSC1 side, represents the d-axis component of the VSC1 modulation function, represents the q-axis component of the VSC1 modulation function, represents the d-axis component of the VSC2 modulation function, represents the state variable disturbance value matrix, represents the coefficient matrix of the state variables, The coefficient matrix representing the system modulation function coefficients, represents the system modulation function matrix, The coefficient matrix representing the voltage disturbance value, represents the voltage disturbance value matrix, represents the disturbance value of the d-axis component of the VSC1 input current, represents the disturbance value of the q-axis component of the VSC1 input current, represents the disturbance value of the d-axis component of the VSC2 output current, represents the disturbance value of the q-axis component of the VSC2 output current, Indicates the DC side voltage disturbance value, Represents the DC side voltage stabilizing capacitor, represents the d-axis disturbance component of the VSC1 modulation function, represents the q-axis disturbance component of the VSC1 modulation function, represents the d-axis disturbance component of the VSC2 modulation function, represents the q-axis disturbance component of the VSC2 modulation function, represents the d-axis disturbance component of the VSC1 AC voltage measurement, represents the q-axis disturbance component of the VSC1 AC voltage measurement, represents the d-axis disturbance component of the VSC2 AC voltage measurement, Represents the q-axis disturbance component of the VSC2 AC measured voltage.

[0045] Another object of the present invention is to provide a control system based on a flexible interconnection device of a back-to-back converter, and the control method of the flexible interconnection device based on the back-to-back converter includes a linear model unit of a BTB-VSC and a controller. The linear model unit of the BTB-VSC is used to linearize the nonlinear model of the BTB-VSC established according to the topological structure of the BTB-VSC to obtain a linear model of the BTB-VSC; the controller is used to simultaneously consider the dynamic changes of the AC side inductance and the DC side capacitance, and by calculating the augmented matrix K of the state feedback control in the controller, ensure that all poles in the system are distributed in the corresponding area of ​​the complex plane, so that the system can operate stably under the condition of uncertainty of the bidirectional power flow and the equivalent impedance of the power grid.

[0046] Another object of the present invention is to provide an electronic device, comprising: at least one processor, at least one memory and a communication interface; the processor, memory and communication interface communicate with each other; the memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the control method of the flexible interconnection device based on back-to-back converters.

[0047] Another object of the present invention is to provide a non-transitory computer-readable storage medium, wherein the non-transitory computer-readable storage medium stores computer instructions, wherein the computer instructions enable the computer to execute the control method of the flexible interconnection device based on back-to-back converters.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention establishes a state space model of BTB-VSC connecting two AC systems, and on this basis, establishes a BTB-VSC control strategy model based on robust pole configuration. According to the voltage and power flow of the BTB-VSC system, a nonlinear model of the system is established, and then the general variables are written as a combination of steady-state components and small signal change components, and the nonlinear model is linearized. Then, based on the method of configuring pole distribution, a linear matrix inequality (LMI) system is obtained, and the relevant parameters of the controller can be calculated by solving it.

[0050] The advantages of the present invention are that the designed control strategy can have good control performance under the uncertainty of bidirectional power flow and equivalent impedance of power grid, and the controlled variable has a small overshoot for the step change of reference value and the sudden change of equivalent inductance value of power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of direct current control.

[0052] Figure 2 Schematic diagram of the phasor relationship under phase regulation control.

[0053] Figure 3 This is the topology of BTB-VSC.

[0054] Figure 4 is the equivalent circuit of a single VSC.

[0055] Figure 5 Schematic diagram of the power flow of BTB-VSC.

[0056] Figure 6 This is the system control structure diagram.

[0057] Figure 7 This is a schematic diagram of area D.

[0058] Figure 8 is the area D and the pole distribution.

[0059] Fig. 9 is the active power change of VSC1.

[0060] Fig.10 is the injected current of AC system 2.

[0061] Fig.11 is the capacitor overvoltage on the DC side. DETAILED DESCRIPTION

[0062] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0063] The indirect current control used by the grid-side VSC is a control structure based on a voltage closed loop. It controls the amplitude and phase of the AC-side sinusoidal voltage through PWM to achieve the effect of indirect control of the AC current. However, its dynamic response is slow and the system robustness is poor. The constant voltage-frequency ratio control (V / F) used by the load-side VSC achieves speed control by adjusting the power supply frequency. It has the characteristics of simple control and easy implementation, but its dynamic performance is not good, the power supply voltage utilization rate is low, and it is not obvious when a speed signal is given or a sudden load is added. And direct torque control (DTC), establish a virtual torque and flux observer in the control system, make a difference between the calculated motor flux and torque and the given value, and output a control signal through a hysteresis comparator to achieve direct control of the motor flux and torque. However, the low-speed speed regulation performance of this control method needs to be optimized. At the same time, the direct torque control of the permanent magnet synchronous motor lags far behind that of the asynchronous motor, and there are few application examples. To this end, we provide a control method for a flexible interconnection device based on a back-to-back converter, including the following steps:

[0064] Step 1, establishing a nonlinear model of BTB-VSC according to the topological structure of BTB-VSC;

[0065] First, if Figure 3 As shown in the figure, the topology of BTB-VSC is given. Each VSC is connected to its own AC system through a series inductor L and a resistor R. R1 and L1 are applicable to VSC1, R2 and L2 are applicable to VSC2, and capacitor C dc Used to maintain DC voltage.

[0066] According to the topological structure, a nonlinear model of BTB-VSC is established. VSC1 and VSC2 are Figure 4The equivalent circuit shown is connected to the respective AC system. In the present invention, the voltage source converter VSC is used as the controlled voltage source, and its value is v t For VSC1, R=R1, L=L1, R1 and L1 are filter parameters, for VSC2, R=R2=R f +R g , L=L2=L f +L g Where R f is the filter parameter, R g is the equivalent resistance of the common coupling point, where L f is the filter parameter, L g is the equivalent inductance of the common coupling end, where R g and L g Affected by the uncertainty of the power grid.

[0067] Depend on Figure 4 Here are some voltage equations:

[0068]

[0069] When considering the average operator, the formula can be rewritten as:

[0070]

[0071] The above two equations both represent single-phase voltage equations. The voltage equation of the three-phase system in the dq coordinate system can be expressed as:

[0072]

[0073] like Figure 5 The power flow diagram of the back-to-back converter is shown in Figure 2. Assuming that the power loss of the two VSCs is negligible, the power of the BTB-VSC system should satisfy the condition

[0074]

[0075] in is the power flowing from VSC1 to AC system 1, is the power flowing from VSC2 to AC system 2, is the power flowing to the capacitor, and its value is:

[0076]

[0077] because The resistance is very large, so the power it produces can be ignored.

[0078] To represent the power flow of the three-phase system, it can be expressed in the dq coordinate system as:

[0079]

[0080] Divide this equation by The relationship can be obtained:

[0081]

[0082] Therefore, the nonlinear model of BTB-VSC can be expressed by the following nonlinear equations:

[0083]

[0084] in,

[0085] Indicates the grid-side equivalent inductance of VSC1, Indicates the grid-side equivalent inductance of VSC2, represents the d-axis component of the VSC1 input current, represents the d-axis component of the VSC2 input current, represents the q-axis component of the VSC1 input current, represents the q-axis component of the VSC2 input current, Indicates the grid-side frequency of VSC1, Indicates the grid-side frequency of VSC2, represents the d-axis component of the VSC1 modulation function, represents the d-axis component of the VSC2 modulation function, represents the q-axis disturbance component of the VSC1 modulation function, represents the q-axis disturbance component of the VSC2 modulation function, Indicates the DC side voltage value, It represents the d-axis component of the AC voltage measured by VSC1, It represents the d-axis component of the AC voltage measured by VSC2, represents the q-axis component of the VSC1 AC voltage measurement, represents the q-axis component of the VSC2 AC voltage measurement, Represents the DC side voltage stabilizing capacitor, Indicates time.

[0086] Step 2, linearize the nonlinear model of BTB-VSC to obtain a linear model of BTB-VSC;

[0087] The method for linearizing the nonlinear model of BTB-VSC is as follows: In order to design a linear controller, the equation needs to be linearized. When the system is in steady state, the derivative terms are all zero; therefore, the state, input and disturbance can be calculated using their steady-state values, and through an appropriate phase-locked loop system, the AC system and The q-axis components of ), the d-axis component (i.e. ) are all voltage peaks. The steady-state values ​​of the remaining variables are as follows:

[0088]

[0089] Use the state equation to represent the small signal model of the entire system:

[0090]

[0091] in:

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098] in, represents the output power of VSC1, Represents the equivalent resistance on the VSC1 side, represents the d-axis component of the VSC1 modulation function, represents the q-axis component of the VSC1 modulation function, represents the d-axis component of the VSC2 modulation function, represents the state variable disturbance value matrix, represents the coefficient matrix of the state variables, The coefficient matrix representing the system modulation function coefficients, represents the system modulation function matrix, The coefficient matrix representing the voltage disturbance value, represents the voltage disturbance value matrix, represents the disturbance value of the d-axis component of the VSC1 input current, represents the disturbance value of the q-axis component of the VSC1 input current, represents the disturbance value of the d-axis component of the VSC2 output current, represents the disturbance value of the q-axis component of the VSC2 output current, Indicates the DC side voltage disturbance value, Represents the DC side voltage stabilizing capacitor, represents the d-axis disturbance component of the VSC1 modulation function, represents the q-axis disturbance component of the VSC1 modulation function, represents the d-axis disturbance component of the VSC2 modulation function, represents the q-axis disturbance component of the VSC2 modulation function, represents the d-axis disturbance component of the VSC1 AC voltage measurement, represents the q-axis disturbance component of the VSC1 AC voltage measurement, represents the d-axis disturbance component of the VSC2 AC voltage measurement, Represents the q-axis disturbance component of the VSC2 AC measured voltage.

[0099] Step 3, design a controller based on the linear model of BTB-VSC; consider the dynamic changes of the AC side inductance and the DC side capacitance at the same time, and calculate the augmented matrix K of the state feedback control in the controller to ensure that all poles in the system are distributed in the corresponding area of ​​the complex plane, so that the system can operate stably under the conditions of uncertain bidirectional power flow and grid equivalent impedance.

[0100] In this embodiment, the reactive power of the two VSCs must be kept under ideal conditions. and In addition, during operation, the voltage on the DC side It must be controlled to a constant value and also needs to meet the power requirements on the BTB-VSC side. Therefore, the current Take control.

[0101] If the state variable is taken as the output acting on the integral part of the error, then the controller can be written as:

[0102]

[0103] Among them, the superscript (*) indicates the reference value. Combined with the small signal model, the augmented matrix is ​​obtained:

[0104]

[0105] The state feedback controller is expressed as:

[0106]

[0107] The linear system of control is described by the equation:

[0108]

[0109] in, Represents the error integration output matrix of voltage and current, represents the coefficient matrix of the state variables, represents the state variable disturbance value matrix, represents the four-dimensional identity matrix, represents the voltage and current reference difference matrix, express The error integral output, express The error integral output, express The error integral output, express The error integral output, represents the system modulation function matrix, Represents the relationship matrix between the modulation function and the state variables, represents the state variables and their error integral matrices, represents the state variables of the linear system, represents the coefficient matrix of the state variable augmentation matrix, Represents the system modulation function coefficient matrix.

[0110] In order to check whether the system is stable, we can use matrices A and B to evaluate whether the system is stable. If there are positive definite matrices P and Satisfied:

[0111]

[0112] This indicates that the system is stable; represents the coefficient matrix of the state variable augmentation matrix, represents a positive definite matrix, represents the augmented matrix of the system modulation function coefficients, The matrix representing the multiplication of the modulation function state variables and the positive definite matrix, A matrix representing the relationship between the modulation function and the state variables.

[0113] The key point of this state feedback control is to find the augmented matrix K. In addition to satisfying the system stability, the augmented matrix K must also ensure that all poles are located in the region D of the complex plane (such as Figure 7 ), this can be achieved by combining a set of equations that must be solved simultaneously. Figure 7 It can be seen that region D is defined by three parameters: , and .

[0114] Method for finding the augmented matrix K: The controller designed in this embodiment needs to meet the two conditions of being able to handle bidirectional power flow and uncertainty of the equivalent resistance and inductance of the grid at the common coupling point. Assume that the system power is The grid resistance varies within the range of The grid inductance varies within the range of It varies within a certain range, so there are eight cases. For each case, it is necessary to calculate matrices A and B so that the closed-loop poles of the entire system must be located in region D; the poles are points where the denominator of the transfer function of a linear time-invariant system is zero. For Laplace transforms, the system is stable when the poles are located in the left half plane. For linear discrete-time systems, the system is stable when the poles are located within the unit circle. According to the position of the system's zero poles, the amplitude-frequency characteristics of the system can be analyzed. Therefore, the following conditions need to be met:

[0115]

[0116] in:

[0117]

[0118] in: represents the lateral extent of the complex plane, represents the sector angle of the complex plane, represents the radius of the sector in the complex plane, , , Represents the calculated matrix.

[0119] In another embodiment, a control system for a flexible interconnection device based on a back-to-back converter is provided. The control method for the flexible interconnection device based on the back-to-back converter is adopted, including a linear model unit of a BTB-VSC and a controller. The linear model unit of the BTB-VSC is used to linearize a nonlinear model of the BTB-VSC established according to the topological structure of the BTB-VSC to obtain a linear model of the BTB-VSC; the controller is used to simultaneously consider the dynamic changes of the AC side inductance and the DC side capacitance, and by calculating the augmented matrix K of the state feedback control in the controller, ensure that all poles in the system are distributed in the corresponding area of ​​the complex plane, so that the system can operate stably under the condition of uncertainty of the bidirectional power flow and the equivalent impedance of the power grid.

[0120] In another embodiment, an electronic device is provided, comprising: at least one processor, at least one memory and a communication interface; the processor, memory and communication interface communicate with each other; the memory stores program instructions executable by the processor, and the processor calls the program instructions to execute the control method of the flexible interconnection device based on back-to-back converters.

[0121] In another embodiment, a non-transitory computer-readable storage medium is provided, wherein the non-transitory computer-readable storage medium stores computer instructions, wherein the computer instructions enable the computer to execute the control method of the flexible interconnection device based on back-to-back converters.

[0122] like Figure 8 As shown in the figure, the area D and pole distribution calculated by the proposed closed-loop pole configuration method are as follows: Figure 9-11 As shown in the figure, in order to calculate the relevant parameters of the controller, the designed control strategy can have good control performance under the uncertainty of bidirectional power flow and grid equivalent impedance, and the controlled variable has a small overshoot for the step change of the reference value and the sudden change of the grid equivalent inductance value.

[0123] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A control method for a flexible interconnection device based on back-to-back converters, characterized in that: The following steps are involved: Step 1, establishing a nonlinear model of BTB-VSC according to the topological structure of BTB-VSC; Step 2, linearize the nonlinear model of BTB-VSC to obtain a linear model of BTB-VSC; Step 3, design a controller based on the linear model of BTB-VSC; consider the dynamic changes of the AC side inductance and the DC side capacitance at the same time, and calculate the augmented matrix K of the state feedback control in the controller to ensure that all poles in the system are distributed in the corresponding area of ​​the complex plane, so that the system can operate stably under the conditions of uncertain bidirectional power flow and grid equivalent impedance.

2. The control method of the flexible interconnection device based on back-to-back converters according to claim 1 is characterized in that: The nonlinear model of BTB-VSC is as follows: in, Indicates the grid-side equivalent inductance of VSC1, Indicates the grid-side equivalent inductance of VSC2, represents the d-axis component of the VSC1 input current, represents the d-axis component of the VSC2 input current, represents the q-axis component of the VSC1 input current, represents the q-axis component of the VSC2 input current, Indicates the grid-side frequency of VSC1, Indicates the grid-side frequency of VSC2, represents the d-axis component of the VSC1 modulation function, represents the d-axis component of the VSC2 modulation function, represents the q-axis disturbance component of the VSC1 modulation function, represents the q-axis disturbance component of the VSC2 modulation function, Indicates the DC side voltage value, It represents the d-axis component of the AC voltage measured by VSC1, It represents the d-axis component of the AC voltage measured by VSC2, represents the q-axis component of the VSC1 AC voltage measurement, represents the q-axis component of the VSC2 AC voltage measurement, Represents the DC side voltage stabilizing capacitor, Indicates time.

3. The control method of the flexible interconnection device based on back-to-back converters according to claim 2 is characterized in that: The controller formula is as follows: Among them, the superscript (*) indicates the reference value. Combined with the small signal model, the augmented matrix is ​​obtained: The state feedback controller is expressed as: The linear system of control is described by the equation: in, Represents the error integration output matrix of voltage and current, represents the coefficient matrix of the state variables, represents the state variable disturbance value matrix, represents the four-dimensional identity matrix, represents the voltage and current reference difference matrix, express The error integral output, express The error integral output, express The error integral output, express The error integral output, represents the system modulation function matrix, Represents the relationship matrix between the modulation function and the state variables, represents the state variables and their error integral matrices, represents the state variables of the linear system, represents the coefficient matrix of the state variable augmentation matrix, Represents the system modulation function coefficient matrix.

4. The control method of the flexible interconnection device based on back-to-back converters according to claim 3 is characterized in that: The method of finding the augmented matrix K: Assuming that the system power is The grid resistance varies within the range of The grid inductance varies within the range of There are eight cases. For each case, it is necessary to calculate matrices A and B so that the closed-loop poles of the entire system must be located in region D. The following conditions must be met: in: in: represents the lateral extent of the complex plane, represents the sector angle of the complex plane, represents the radius of the sector in the complex plane, , , Represents the calculated matrix.

5. The control method of the flexible interconnection device based on back-to-back converters according to claim 4 is characterized in that: Use matrices A and B to evaluate whether the system is stable. If there are positive definite matrices P and B, Satisfied: This indicates that the system is stable; represents the coefficient matrix of the state variable augmentation matrix, represents a positive definite matrix, represents the augmented matrix of the system modulation function coefficients, The matrix representing the multiplication of the modulation function state variables and the positive definite matrix, A matrix representing the relationship between the modulation function and the state variables.

6. The control method of the flexible interconnection device based on back-to-back converters according to claim 5 is characterized in that: The method of linearizing the nonlinear model of BTB-VSC is as follows: when the system is in a steady state, the derivative terms are all zero; through the phase-locked loop system, the AC system and The q-axis components of are all zero, the d-axis components are all voltage peaks, and the steady-state values ​​of the remaining variables are as follows: Use the state equation to represent the small signal model of the entire system: in: in, represents the output power of VSC1, Represents the equivalent resistance on the VSC1 side, represents the d-axis component of the VSC1 modulation function, represents the q-axis component of the VSC1 modulation function, represents the d-axis component of the VSC2 modulation function, represents the state variable disturbance value matrix, represents the coefficient matrix of the state variables, The coefficient matrix representing the system modulation function coefficients, represents the system modulation function matrix, The coefficient matrix representing the voltage disturbance value, represents the voltage disturbance value matrix, represents the disturbance value of the d-axis component of the VSC1 input current, represents the disturbance value of the q-axis component of the VSC1 input current, represents the disturbance value of the d-axis component of the VSC2 output current, represents the disturbance value of the q-axis component of the VSC2 output current, Indicates the DC side voltage disturbance value, Represents the DC side voltage stabilizing capacitor, represents the d-axis disturbance component of the VSC1 modulation function, represents the q-axis disturbance component of the VSC1 modulation function, represents the d-axis disturbance component of the VSC2 modulation function, represents the q-axis disturbance component of the VSC2 modulation function, represents the d-axis disturbance component of the VSC1 AC voltage measurement, represents the q-axis disturbance component of the VSC1 AC voltage measurement, represents the d-axis disturbance component of the VSC2 AC voltage measurement, Represents the q-axis disturbance component of the VSC2 AC measured voltage.

7. A control system based on a flexible interconnection device of back-to-back converters, characterized in that: The control method of the flexible interconnection device based on back-to-back converters according to claim 1 includes a linear model unit of BTB-VSC and a controller, wherein the linear model unit of BTB-VSC is used to linearize the nonlinear model of BTB-VSC established according to the topological structure of BTB-VSC to obtain the linear model of BTB-VSC; the controller is used to simultaneously consider the dynamic changes of the AC side inductance and the DC side capacitance, and by calculating the augmented matrix K of the state feedback control in the controller, ensure that all poles in the system are distributed in the corresponding area of ​​the complex plane, so that the system can operate stably under the conditions of uncertain bidirectional power flow and grid equivalent impedance.

8. An electronic device, characterized in that: include: at least one processor, at least one memory, and a communication interface; The processor, memory and communication interface communicate with each other; The memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the control method of the flexible interconnection device based on back-to-back converters according to any one of claims 1-6.

9. A non-transitory computer-readable storage medium, characterized in that: The non-transitory computer-readable storage medium stores computer instructions, and the computer instructions enable the computer to execute the control method of the flexible interconnection device based on back-to-back converters according to any one of claims 1 to 10.

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