Dc power flow controller damping reshaping and stabilizing method based on bilateral droop characteristics

Abstract

The application provides a DC power flow controller damping reshaping and stabilizing method based on bilateral droop characteristics, comprising the following steps: step 1: establishing an open-loop small signal state equation of a single-stage current source type DC power flow controller in a complex frequency domain, and adopting a double closed-loop control; after substituting the control law, defining and calculating a closed-loop state conversion matrix and a closed-loop input vector; step 2: deducing key two-port parameters of the power flow controller, and obtaining equivalent source impedance and equivalent load impedance converted to an interface of the single-stage current source type DC power flow controller; step 3: extending a control operator from a pure proportion to a first-order low-pass filter form, based on the angle-preserving mapping characteristics of a bilinear transformation, driving an equivalent output impedance vector to rotate through phase lag introduced by the first-order low-pass filter at a resonance frequency, and inversely solving a theoretical minimum time constant required for eliminating oscillation.

Description

Technical Field

[0001] This invention relates to the field of power electronic converters and their control technology, specifically to a method for damping reshaping and stabilization of a DC power flow controller based on bilateral droop characteristics. Background Technology

[0002] With the widespread application of DC power distribution technology in microgrids, ship power supply, data centers, and other fields, the power flow control problem of multi-bus DC systems is becoming increasingly prominent. The single-stage current source DC power flow controller (SCS-DCPFC), due to its topology of parallel connection at one end and series connection at the other, can achieve independent regulation of line power flow at the cost of handling a smaller portion of the power, and has extremely high engineering application value.

[0003] In practical engineering applications, SCS-DCPFC is often cascaded with upstream and downstream DC-DC converters (such as Buck converters, LC filters, etc.). When SCS-DCPFC uses bilateral droop current inner loop pure proportional control, the reference current is obtained from the voltage difference between the two bus sides via a fixed proportional coefficient. generate( When the controller is in a state of flux, harmful interactions can easily occur between the controller and the system impedance. This interaction can manifest as a "negative damping" characteristic in certain frequency bands, meaning that the controller's equivalent output impedance falls into the left half-plane in the complex plane, which can lead to low-frequency oscillations or even system instability and collapse.

[0004] Existing stability solutions largely rely on blind parameter trial and error or the use of external passive dampers, lacking analytical guidance based on impedance complex plane mapping mechanisms. Since SCS-DCPFC is a two-port network with complex input-output coupling, conventional Bode plots or Nyquist criteria can only passively determine system stability, failing to actively synthesize controller parameters that ensure absolute system stability. Revealing the underlying mechanism of the mapping between control parameters and port impedances in the complex plane, and actively reshaping the impedance to a stable region through extremely low-cost control strategies, is a pressing technical challenge for multi-bus DC systems.

[0005] Reference 1 (J. Yang et al., "On the Impedance and Stability Analysis of Dual-Active-Bridge-Based Input-Series Output-Parallel Converters in DCSystems," IEEE Transactions on Power Electronics, 2023.) proposes an impedance modeling and stability analysis method for ISOP converters, establishes the system's input / output impedance model, and performs stability assessment based on the Nyquist criterion. This reference (and most existing impedance modeling techniques) only stays at the level of "impedance measurement and stability assessment," passively determining whether the system is stable; while this invention advances the research depth to the stage of "active stability synthesis."

[0006] Reference 2 (L. Yao, Hongfen Cui, Jun Zhuang, Guanjun Li, Bo Yang and Zhibing Wang, "A DC power flow controller and its control strategy in the DCgrid," 2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), Hefei, 2016.) analyzes the working principle of a DC power flow controller in a DC grid and studies the influence of DC voltage and line equivalent resistance on DC power flow. Based on the above research, a novel DC power flow controller based on a dual active bridge (DAB) topology is proposed. This controller can achieve bidirectional power flow control of DC transmission lines without the need for an external power supply. This reference uses traditional constant current control, with a preset constant as the current reference value, passively following commands. It lacks the adaptive capability to dynamically adjust power according to bus voltage, and the port equivalent impedance tends to infinity (open circuit), lacking the dynamic support capability for changes in grid-side conditions.

[0007] Patent application CN121124532A discloses a converter grid control method with low-frequency impedance reshaping function, including a grid control module, a virtual impedance control module, a first coordinate transformation module, a second coordinate transformation module, a third coordinate transformation module, a current control module, a voltage filtering module, a low-frequency impedance reshaping module, and a coordinate inverse transformation module. This method achieves positive impedance in the low-frequency band, improving the stability of the power electronic converter in weak grid environments. Its modular design facilitates integration into existing converter systems, completely eliminating the oscillation risk caused by fundamental frequency negative impedance, providing wide-band compatibility covering the 0–200Hz harmonic range, and optimizing performance through an adjustable reshaping coefficient kz. However, this patent cannot completely solve the existing technical problems, nor can it meet the needs of this invention. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for damping reshaping and stabilization of DC power flow controllers based on bilateral droop characteristics.

[0009] The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics provided by the present invention includes the following steps: Step 1: Establish the open-loop small-signal state equation of a single-stage current source DC power flow controller in the complex frequency domain, and adopt dual closed-loop control; after substituting the control law, define and calculate the closed-loop state transition matrix and the closed-loop input vector; Step 2: Derive the key two-port parameters of the power flow controller and calculate the equivalent source impedance and equivalent load impedance referred to the interface of the single-stage current source type DC power flow controller. Step 3: Extend the control operator from a pure proportional form to a first-order low-pass filter. Based on the conformal mapping characteristics of the bilinear transformation, drive the equivalent output impedance vector to rotate by the phase lag introduced at the resonant frequency through the first-order low-pass filter; solve for the theoretical minimum time constant required to eliminate oscillation.

[0010] Preferably, the open-loop small-signal state equation is:

[0011] Where s is the Laplace complex frequency domain operator; This refers to the line current disturbance. This represents the voltage disturbance of the clamping capacitor. , These are the voltage disturbances at the beginning and end of the bus, respectively. The main bridge duty cycle disturbance; This represents the proportional disturbance of the phase shift angle of the high-frequency transformer. This represents the steady-state duty cycle. This represents the steady-state phase shift angle ratio; This is the steady-state clamping capacitor voltage; This represents the steady-state head-end bus voltage. This refers to the steady-state line current. For AC side filter inductance; For clamping capacitors; The equivalent resistance of the line; For switching cycles; This refers to the primary and secondary turns ratio of the transformer. This refers to the leakage inductance of the transformer.

[0012] Preferably, the dual closed-loop control includes frequency domain control law equations and input port current. Constraints:

[0013]

[0014]

[0015] in, It is a current inner-loop PI controller. , These are the proportional and integral gains, respectively. It is a voltage outer loop PI controller. , These are the proportional and integral gains, respectively. These are the impedance reshaping control law coefficients; It is the current disturbance at the source-side input port of a single-stage current source type DC power flow controller; , The input is the equivalent feedforward constant. , .

[0016] Preferably, the closed-loop state transition matrix and the closed-loop input vector are defined and calculated in the following manner:

[0017]

[0018]

[0019] in, It is a closed-loop state transition matrix that integrates the poles of the physical circuit and the zeros and poles of the PI controller for the entire system; , It includes physical voltage feedforward and based on The closed-loop input vector of the control loop active feedback; Here is the open-loop state pole matrix. , This is the voltage perturbation input matrix. The input matrix is ​​used to control the disturbance.

[0020] Preferably, let the matrix inversion operation be performed. The first row is a row vector The second row is a row vector. ,extract The linear polynomial structure is defined. , Control mapping items Derive the key two-port parameters of the power flow controller:

[0021]

[0022]

[0023]

[0024] in, These are respectively the bus voltage disturbance amount to line current disturbance The closed-loop transfer function; The closed-loop transfer functions from voltage to line current are given, and the self-admittance and mutual admittance parameters of the source-side port of the single-stage current source DC power flow controller are obtained after combining the input constraints. It is separated from the control law The background ground state complex constant; It is the separated adjoint control law The complex constant of the varying linear gain.

[0025] Preferably, the equivalent source impedance and equivalent load impedance are obtained in the following manner:

[0026]

[0027]

[0028] in, It is the equivalent physical output impedance on the power supply side; For DC-side filter capacitors, This is the equivalent load resistance; , , , These are the elements of the two-port closed-loop G-parameter matrix of the preceding DAB converter; This is the equivalent physical output impedance on the power supply side; , , , These are the elements of the two-port closed-loop G-parameter matrix of the subsequent DAB converter; This is the equivalent physical output impedance on the power supply side of the subsequent stage; It is the equivalent source-side Thevenin impedance and equivalent load-side impedance of the entire link network referred to the interface of the single-stage current source type DC power flow controller.

[0029] Preferably, the bilinear transformation includes: converting the load-side equivalent admittance... Connect to the power flow controller and derive its equivalent output impedance. Regarding the control law The fully analytical expression, after finding a common denominator and expanding the numerator, with the quadratic terms completely canceled out mathematically, yields the following bilinear transformation formula:

[0030] Find a common denominator and expand the numerator, where the quadratic term... coefficient The quadratic terms are completely canceled out mathematically, ultimately yielding a rigorous bilinear transformation formula:

[0031] in, It is the overall equivalent output impedance of a single-stage current source type DC power flow controller, which includes its own closed-loop control characteristics and the network characteristics of the subsequent system. This is the equivalent admittance on the load side; These are the basis coefficients of the bilinear transformation in the complex plane, whose values ​​are constant and determined by the system hardware parameters and internal PI parameters. , , , ; , , These are parameters related to the system's closed-loop characteristic matrix; These are the impedance reshaping control law coefficients; , , These are coefficients related to the system's two-port admittance parameters.

[0032] Preferably, for the purpose of Rotate to the positive damping region, extending the control operator from a purely proportional form to a first-order low-pass filter:

[0033] in, This is a traditional pure proportional droop control gain. The filtering time constant; The angular frequency at which low-frequency resonance occurs in the cascaded system. At the location, filter The frequency characteristics introduce a definite phase lag:

[0034] in, Indicates the filter at angular frequency The phase angle at the point, The imaginary unit; Based on the geometric mapping mechanism of the complex plane, under pure proportional control Located in the negative half-plane, after introducing a low-pass filter, the control vector A clockwise rotation occurs on the complex plane starting from the negative real axis, with a rotation angle of... ; Impedance mapping model It belongs to the bilinear transformation and has conformal mapping characteristics. The phase deflection is proportionally and conformally transmitted to the impedance complex plane, directly driving the vector. Slide clockwise along the mapped arc and rotate by an angle This allows them to escape the negative damping danger zone of the left half-plane.

[0035] Preferably, before solving for the theoretical minimum time constant, the method further includes: setting the target safe point that the equivalent output impedance of the single-stage current source type DC power flow controller needs to reach on the complex plane as... By performing an algebraic inverse solution based on the impedance bilinear mapping model, the required target control vector in the complex plane can be obtained. :

[0036]

[0037] in, This represents the imaginary part of the original system impedance when oscillation occurs. The minimum forward virtual resistance is set by the user. For the set engineering safety margin, This represents the real part of the original system impedance when oscillation occurs.

[0038] Preferably, the theoretical minimum time constant required to eliminate oscillations is obtained by inverse solving, including: The first-order low-pass filter control law used is Simplify it by separating the real and imaginary parts:

[0039] The analytical relationship for the ratio of the imaginary part to the real part of a filter is:

[0040] make The theoretical minimum time constant required to eliminate oscillations can be obtained by inverse solving. :

[0041] The final filter time constant written to the controller is selected to be 1.2 to 2 times the theoretical value, that is... .

[0042] Compared with the prior art, the present invention has the following beneficial effects: (1) Through precise algebraic derivation, this invention rigorously proves for the first time that the cascaded impedance of the power flow controller strictly conforms to the first-order bilinear transformation law, transforming the control reshaping from an analytical geometric mapping problem; (2) The present invention only needs to be upgraded to a first-order low-pass filter in the control code, and relies on phase deflection to drive impedance rotation to achieve stabilization effect, without any hardware consumables or additional losses; (3) This invention cleverly utilizes the mathematical properties of the ratio of the real and imaginary parts of the filter to derive the absolute closed-form solution of the filter time constant, directly locking the optimal parameters and shortening the research and development and on-site debugging cycle. Attached Figure Description

[0043] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 System architecture diagram; Figure 2 for Z oL Theoretical and Measurement Bode Plots; Figure 3 for Z out2 Theoretical and Measurement Bode Plots; Figure 4 for k When = -0.2, T m (s) Nyquist plot; Figure 5 for k When = -0.2 / (0.01s+1), T m (s) Nyquist plot; Figure 6 The simulation results are shown in the figure. Figure 7 for Z out Trajectory change diagram. Detailed Implementation

[0044] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0045] Example The purpose of this invention is to address the shortcomings of existing technologies by providing a method for damping reshaping and stabilization of DC power flow controllers based on bilateral droop characteristics. The specific objectives are as follows: 1. Solving the problem of negative damping instability caused by traditional constant current control: In adopting... Based on bilateral droop control, and addressing the issue of low-frequency oscillations easily induced in cascaded systems by SCS-DCPFC, a method with a time constant is proposed. low-pass filter Control laws actively reshape the impedance of the system from a control perspective.

[0046] 2. Revealing the underlying geometric mapping mechanism of impedance reshaping: For the first time, the Möbius Transformation is introduced into the impedance modeling of DC power flow controllers, and it is analytically proven how the phase angle deflection of the control parameters is accurately mapped to the arc trajectory sliding of the port impedance on the complex plane.

[0047] 3. Provides a visual basis for parameter design: Utilizing the conformal mapping principle of "straight lines becoming circles, circles becoming circles," it provides a basis for controlling parameters (especially the time constant). The design provides intuitive complex-plane geometry guidance, ensuring that the system impedance crosses from the "instability region" of the left half-plane to the "stability region" of the right half-plane, thereby achieving an absolute enhancement of system stability.

[0048] This invention addresses application scenarios such as DC microgrids, providing a damping reshaping and stabilization method for single-stage current source DC power flow controllers based on bilateral droop characteristics. The core idea is to upgrade the traditional pure proportional power flow control law k to a frequency domain control law k(s), and utilize the bilinear transformation mechanism to guide parameter design. The specific implementation steps are as follows: The following text is in the format of Figure 1 Taking the system shown as an example, we will explain its specific technical implementation scheme.

[0049] I. SCS-DCPFC Closed-Loop State Space Modeling; Based on Kirchhoff's laws of circuits, the open-loop small-signal state equation of SCS-DCPFC in the complex frequency domain is established as follows: (1) Where s is the Laplace complex frequency domain operator; This refers to the line current disturbance. This represents the voltage disturbance of the clamping capacitor. , These are the voltage disturbances at the beginning and end of the bus, respectively. The main bridge duty cycle disturbance; This represents the proportional disturbance of the phase shift angle of the high-frequency transformer. This represents the steady-state duty cycle. This represents the steady-state phase shift angle ratio; This is the steady-state clamping capacitor voltage; This represents the steady-state head-end bus voltage. This refers to the steady-state line current. For AC side filter inductance; For clamping capacitors; The equivalent resistance of the line; For switching cycles; This refers to the primary and secondary turns ratio of the transformer. This refers to the leakage inductance of the transformer.

[0050] SCS-DCPFC employs dual closed-loop control, and its frequency domain control law equation and input port current... The constraint relationships are as follows: (2) (3) (4) in, It is a current inner-loop PI controller. , These are the proportional and integral gains, respectively. It is a voltage outer loop PI controller. , These are the proportional and integral gains, respectively. k(s) These are the impedance reshaping control law coefficients; It is the current disturbance at the source-side input port of a single-stage current source type DC power flow controller; , The input is the equivalent feedforward constant. , .

[0051] Define the coefficient matrices on both sides of the equality in the open-loop state equation as the background matrix: the open-loop state pole matrix. Voltage perturbation input matrix , Control perturbation input matrix (The specific elements correspond to the matrix blocks in formula (1) respectively). After substituting into the control law, define and calculate the closed-loop state transition matrix. and closed-loop input vector , : (5) (6) (7) in: It is a closed-loop characteristic matrix of the entire system that integrates the poles of the physical circuit and the zeros and poles of the PI controller; , It includes physical voltage feedforward and based on The integrated input excitation vector of the control loop active feedback.

[0052] II. Derivation of system-level equivalent impedance; Let matrix inversion operation The first row is a row vector The second row is a row vector. .extract The linear polynomial structure is defined. , Control mapping items Derivation of the key two-port parameters of the power flow controller: (8) (9) (10) (11) in: From voltage respectively to line current The closed-loop transfer function; The self-admittance and mutual admittance parameters of the source port of SCS-DCPFC are obtained by combining the input constraint formula (4); It is separated from the control law The background ground state complex constant; It is the separated adjoint control law The complex constant of the varying linear gain.

[0053] For the external network consisting of the power supplies at the beginning and end points and the front / rear DAB converters, calculate the equivalent source impedance and load impedance referred to the SCS-DCPFC interface: (12) (13) (14) in, It is the equivalent physical output impedance on the power supply side; For DC-side filter capacitors, This is the equivalent load resistance; , , , These are the elements of the two-port closed-loop G-parameter matrix of the preceding DAB converter; This is the equivalent physical output impedance on the power supply side; , , , These are the elements of the two-port closed-loop G-parameter matrix of the subsequent DAB converter; This is the equivalent physical output impedance on the power supply side of the subsequent stage; It is the equivalent source-side Thevenin impedance and equivalent load-side impedance of the entire link network referred to the interface of the single-stage current source type DC power flow controller.

[0054] III. Derivation of Impedance Reshaping Based on Bilinear Transformation; Equivalent admittance on the load side Connect to the power flow controller and derive its equivalent output impedance. Regarding the control law The fully analytical expression. Substituting the linear parameters from Module 2: (15) Find a common denominator and expand the numerator, where the quadratic term... coefficient The quadratic terms are completely canceled out mathematically. This leads to the rigorous formula for the bilinear transformation (Möbius transform): (16) in, It is the overall equivalent output impedance of a single-stage current source type DC power flow controller, which includes its own closed-loop control characteristics and the network characteristics of the subsequent system. This is the equivalent admittance on the load side; These are the basis coefficients of the bilinear transformation in the complex plane, whose values ​​are constant and determined by the system hardware parameters and internal PI parameters. , , , ; , , These are parameters related to the system's closed-loop characteristic matrix; These are the impedance reshaping control law coefficients; , , These are coefficients related to the system's two-port admittance parameters.

[0055] To be Rotating to the positive damping region, this invention proposes to extend the control operator from a purely proportional form to a first-order low-pass filter form: (17) in, This is a traditional pure proportional droop control gain. The filtering time constant; The angular frequency at which low-frequency resonance occurs in the cascaded system. At the location, filter The frequency characteristics introduce a definite phase lag: (18) in, Indicates the filter at angular frequency The phase angle at the point, The imaginary unit; From the perspective of the geometric mapping mechanism of the complex plane, under pure proportional control Located in the negative half-plane. After introducing a low-pass filter, the control vector... A clockwise rotation occurred on the complex plane starting from the negative real axis, with a rotation angle of... .

[0056] Due to the impedance mapping model derived above Belonging to the bilinear transformation, it possesses strictly conformal mapping characteristics. The phase deflection is proportionally and conformally transmitted to the impedance complex plane, directly driving... The vector also slides clockwise along the mapped arc, rotating by an angle. This allows them to escape the negative damping danger zone of the left half-plane.

[0057] In the complex plane, the target safe point that the equivalent output impedance of the SCS-DCPFC needs to reach is set as follows: To ensure it escapes the negative damping region, it must satisfy the following: (19) in, This represents the imaginary part of the original system impedance when oscillation occurs. The minimum forward virtual resistance is set by the user. For the set engineering safety margin, This represents the real part of the original system impedance when oscillation occurs.

[0058] Based on the aforementioned derived impedance bilinear mapping model When the target impedance is determined to be At this time, an inverse algebraic solution can be performed to obtain the target control vector required on the complex plane. : (20) In the formula, All are at the oscillation frequency The fixed complex constant can be accurately calculated from the system parameters, therefore A uniquely determined complex number can be represented as , , These are the target control vectors. The real and imaginary parts.

[0059] The first-order low-pass filter control law used in this invention is: Simplify it by separating its real and imaginary components: (twenty one) Observing formula (21), it can be seen that the ratio of the imaginary part to the real part of the filter has a very simple analytical relationship: (twenty two) Due to the target control vector It must be generated by this filter, let This allows us to solve for the theoretical minimum time constant required to eliminate oscillations. : (twenty three) In practical engineering implementation, to balance the system's dynamic response speed with ample damping margin, the filter time constant ultimately written into the controller is selected to be 1.2 to 2 times the theoretical value, i.e. .

[0060] For the sake of simplicity, the proposed technical solution is illustrated using a cascaded system of "DC power supply 1 - LC filter - DAB1 - SCS - DCPFC - DAB2 - LC filter - DC power supply 2" as an example.

[0061] Application scenario: Line power flow control and stability enhancement in multi-bus AC / DC hybrid microgrids; The circuit parameters, steady-state operating point parameters, and controller parameters of the full-link cascaded system are shown below, with the core system circuit parameters shown in Table 1.

[0062] Table 1 Simulation Circuit Parameters

[0063] Steady-state operating point parameters: Bus input voltage U g1 =4000V, U g2 =4000V, SCS bus input voltage V grid1 =900V, V grid2 =890V, line currentI line =-5A, capacitor clamping voltage V cc =45V.

[0064] According to the method of this invention, the system parameters in Table 1 are first substituted into the two-port closed-loop state equation to calculate the equivalent source-side output impedance at the SCS-DCPFC interface. Z oL With equivalent load-side input impedance Z oR Subsequently, the SCS-DCPFC parameters are imported into the closed-loop state transition matrix. The equivalent output impedance, including the characteristics of the subsequent network, is analyzed. Z out2 The theoretical transfer function was compared with the experimental frequency sweep results extracted from Excel. Figure 2 and Figure 3 As shown, its amplitude-frequency and phase-frequency characteristics are in perfect agreement, confirming the accuracy of the impedance analytical model.

[0065] Based on this, the system back ratio function is calculated for the following two control strategies respectively. T m (s)= Z oL (s) / Z out2 Nyquist verification of (s): 1. Employs traditional pure proportional droop control (real gain) k When =-0.5): Calculations show that the system's hysteresis function at this time T m (s) There exists a right half-plane (RHP) pole, such as Figure 4 As shown, the Nyquist curve encircles the point (-1, j0) in the complex plane clockwise. SCS-DCPFC interface impedance. Z out2 (s) exhibits significant negative damping characteristics in the low-frequency range within the left half-plane. For example... Figure 6 The time-domain simulation waveforms show that the waveform before 1.2s is under traditional proportional control. V grid 1. Voltage waveform: The system bus voltage experienced severe low-frequency divergent oscillations, making stable operation impossible.

[0066] 2. Impedance reshaping control (filter) of the present invention )hour: time constant The first-order low-pass filter is embedded in the current reference generation algorithm. Based on the physical mechanism revealed by this invention, the filter introduces a target hysteresis phase angle at the 40Hz resonant frequency, and according to the bilinear conformal mapping characteristic, drives the impedance vector Z... out2 Rotating clockwise, it successfully crossed the imaginary axis and entered the positive damping safe region. The rotation process is as follows: Figure 7 As shown.

[0067] Redraw the back ratio function T m (s) Nyquist plot, such as Figure 5 As shown, the curve no longer encircles the point (-1, j0), and the number of poles in the right half-plane has been cleared to zero. Based on the criterion, the reshaped cascaded system possesses ample stability margin. Figure 6 As shown, at 1.2s, the control is changed from traditional proportional droop control to impedance reshaping control. The time-domain simulation waveform clearly confirms that the line current converges smoothly and accurately tracks the command under all operating conditions, and the low-frequency oscillation is completely eliminated, thus successfully achieving the engineering objective of enhancing stability of this invention.

[0068] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0069] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for damping reshaping and stabilization of a DC power flow controller based on bilateral droop characteristics, characterized in that, Includes the following steps: Step 1: Establish the open-loop small-signal state equation of a single-stage current source DC power flow controller in the complex frequency domain, and adopt dual closed-loop control; after substituting the control law, define and calculate the closed-loop state transition matrix and the closed-loop input vector; Step 2: Derive the key two-port parameters of the power flow controller and calculate the equivalent source impedance and equivalent load impedance referred to the interface of the single-stage current source type DC power flow controller. Step 3: Extend the control operator from a pure proportional form to a first-order low-pass filter. Based on the conformal mapping characteristics of the bilinear transformation, drive the equivalent output impedance vector to rotate by the phase lag introduced at the resonant frequency through the first-order low-pass filter; solve for the theoretical minimum time constant required to eliminate oscillation.

2. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 1, characterized in that, The open-loop small-signal state equation is: Where s is the Laplace complex frequency domain operator; This refers to the line current disturbance. This represents the voltage disturbance of the clamping capacitor. , These are the voltage disturbances at the beginning and end of the bus, respectively. The main bridge duty cycle disturbance; This represents the proportional disturbance of the phase shift angle of the high-frequency transformer. This represents the steady-state duty cycle. This represents the steady-state phase shift angle ratio; This is the steady-state clamping capacitor voltage; This represents the steady-state head-end bus voltage. This refers to the steady-state line current. For AC side filter inductance; For clamping capacitors; The equivalent resistance of the line; For switching cycles; This refers to the primary and secondary turns ratio of the transformer. This refers to the leakage inductance of the transformer.

3. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 2, characterized in that, The dual closed-loop control includes frequency domain control law equations and input port current. Constraints: in, It is a current inner-loop PI controller. , These are the proportional and integral gains, respectively. It is a voltage outer loop PI controller. , These are the proportional and integral gains, respectively. k(s) These are the impedance reshaping control law coefficients; It is the current disturbance at the source-side input port of a single-stage current source type DC power flow controller; , The input is the equivalent feedforward constant. , .

4. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 3, characterized in that, The closed-loop state transition matrix and the closed-loop input vector are defined and calculated in the following manner: in, It is a closed-loop state transition matrix that integrates the poles of the physical circuit and the zeros and poles of the PI controller for the entire system; , These include physical voltage feedforward and based on The closed-loop input vector of the control loop active feedback; Here is the open-loop state pole matrix. , This is the voltage perturbation input matrix. The input matrix is ​​used to control the disturbance.

5. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 4, characterized in that, Let matrix inversion operation The first row is a row vector The second row is a row vector. ,extract The linear polynomial structure is defined. , Control mapping items Derive the key two-port parameters of the power flow controller: in, These are respectively the bus voltage disturbance amount to line current disturbance The closed-loop transfer function; The closed-loop transfer functions from voltage to line current are given, and the self-admittance and mutual admittance parameters of the source-side port of the single-stage current source DC power flow controller are obtained after combining the input constraints. It is separated from the control law The background ground state complex constant; It is the separated adjoint control law The complex constant of the varying linear gain.

6. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 5, characterized in that, The equivalent source impedance and equivalent load impedance are obtained in the following way: in, It is the equivalent physical output impedance on the power supply side; For DC-side filter capacitors, This is the equivalent load resistance; , , , These are the elements of the two-port closed-loop G-parameter matrix of the preceding DAB converter; This is the equivalent physical output impedance on the power supply side; , , , These are the elements of the two-port closed-loop G-parameter matrix of the subsequent DAB converter; This is the equivalent physical output impedance on the power supply side of the subsequent stage; It is the equivalent source-side Thevenin impedance and equivalent load-side impedance of the entire link network referred to the interface of the single-stage current source type DC power flow controller.

7. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 6, characterized in that, The bilinear transformation includes: converting the load-side equivalent admittance... Connect to the power flow controller and derive its equivalent output impedance. Regarding the control law The fully analytical expression, after finding a common denominator and expanding the numerator, with the quadratic terms completely canceled out mathematically, yields the following bilinear transformation formula: Find a common denominator and expand the numerator, where the quadratic term... coefficient The quadratic terms are completely canceled out mathematically, ultimately yielding a rigorous bilinear transformation formula: in, It is the overall equivalent output impedance of a single-stage current source type DC power flow controller, which includes its own closed-loop control characteristics and the network characteristics of the subsequent system. This is the equivalent admittance on the load side; These are the basis coefficients of the bilinear transformation in the complex plane, whose values ​​are constant and determined by the system hardware parameters and internal PI parameters. , , , ; , , These are parameters related to the system's closed-loop characteristic matrix; These are the impedance reshaping control law coefficients; , , These are coefficients related to the system's two-port admittance parameters.

8. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 7, characterized in that, To be Rotate to the positive damping region, extending the control operator from a purely proportional form to a first-order low-pass filter: in, This is a traditional pure proportional droop control gain. The filtering time constant; The angular frequency at which low-frequency resonance occurs in the cascaded system. At the location, filter The frequency characteristics introduce a definite phase lag: in, Indicates the filter at angular frequency The phase angle at the point, The imaginary unit; Based on the geometric mapping mechanism of the complex plane, under pure proportional control Located in the negative half-plane, after introducing a low-pass filter, the control vector A clockwise rotation occurs on the complex plane starting from the negative real axis, with a rotation angle of... ; Impedance mapping model It belongs to the bilinear transformation and has conformal mapping characteristics. The phase deflection is proportionally and conformally transmitted to the impedance complex plane, directly driving the vector. Slide clockwise along the mapped arc and rotate by an angle This allows them to escape the negative damping danger zone of the left half-plane.

9. The DC power flow controller damping reshaping and stabilization method based on bilateral droop characteristics according to claim 8, characterized in that, Before solving for the theoretical minimum time constant, the following steps are also included: setting the target safe point that the equivalent output impedance of the single-stage current source DC power flow controller needs to reach on the complex plane is... By performing an algebraic inverse solution based on the impedance bilinear mapping model, the required target control vector in the complex plane can be obtained. : in, This represents the imaginary part of the original system impedance when oscillation occurs. The minimum forward virtual resistance is set by the user. For the set engineering safety margin, This represents the real part of the original system impedance when oscillation occurs.

10. The method for damping reshaping and stabilization of DC power flow controller based on bilateral droop characteristics according to claim 9, characterized in that, The theoretical minimum time constant required to eliminate oscillations, obtained by inverse solving, includes: The first-order low-pass filter control law used is Simplify it by separating the real and imaginary parts: The analytical relationship for the ratio of the imaginary part to the real part of a filter is: make The theoretical minimum time constant required to eliminate oscillations can be obtained by inverse solving. : The final filter time constant written to the controller is selected to be 1.2 to 2 times the theoretical value, that is... .

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