An Oscillation Suppression Method and System Based on D-Segmentation Method and New Energy Transmission Ratio and Short-Circuit Ratio

Abstract

This invention provides an oscillation suppression method and system based on the D-segmentation method and considering the renewable energy transmission ratio and short-circuit ratio, relating to the field of power supply systems. The method includes: establishing an impedance model of the sending end of a wind farm-connected grid commutated HVDC transmission system; determining the first feasible region of the constant current controller's parameters based on the structure of the constant current controller at the sending end of the grid commutated HVDC transmission system; determining the second feasible region of the constant current controller's parameters corresponding to the renewable energy transmission ratio constraint based on the parameter stability control region of the constant current controller; and determining the third feasible region of the constant current controller's parameters corresponding to the short-circuit ratio constraint by combining the impedance model of the sending end of the wind farm-connected grid commutated HVDC transmission system and the short-circuit ratio constraint. This method controls the operation of the sending end of the grid commutated HVDC transmission system, achieving the advantage of oscillation suppression in systems with low short-circuit ratios and high renewable energy transmission ratios.

Description

Technical Field

[0001] This invention relates to the field of power supply systems, and in particular to an oscillation suppression method and system based on the D-segmentation method for calculating the transmission ratio and short-circuit ratio of new energy sources. Background Technology

[0002] With the increasing penetration rate of new energy units and the continuous improvement of DC transmission capacity in the power system, grid-commutated high-voltage direct current (LCC-HVDC) transmission systems are exhibiting low inertia and low short-circuit ratio operation characteristics. Furthermore, their dynamic interactions with power electronic equipment such as wind turbine converters and photovoltaic inverters are becoming more frequent. Therefore, ensuring the stable and safe operation of the system under conditions of high new energy transmission ratio and low short-circuit ratio is an urgent problem to be solved.

[0003] Under conditions of high renewable energy transmission ratio and low short-circuit ratio, the dynamic interaction between power electronic equipment such as wind turbine converters and photovoltaic inverters intensifies, leading to system oscillations and, in severe cases, even equipment disconnection from the grid or damage. Existing technologies employ optimization algorithms to optimize the parameters of the constant current controller to suppress system oscillations. However, the process of tuning controller parameters using optimization algorithms involves a massive amount of computation, is prone to getting trapped in the optimal solution, and does not use the short-circuit ratio and renewable energy transmission ratio as performance indicators when tuning controller parameters, thus failing to guarantee the accuracy of the obtained controller parameters.

[0004] Therefore, there is a need to provide an oscillation suppression method and system based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, in order to achieve oscillation suppression in systems with low short-circuit ratio and high new energy transmission ratio. Summary of the Invention

[0005] This invention provides an oscillation suppression method based on the D-segmentation method and considering the renewable energy transmission ratio and short-circuit ratio. It is applied to the sending end of a grid-commutated HVDC transmission system. The rectifier side of the sending end of the grid-commutated HVDC transmission system employs constant current control, and the inverter side employs constant voltage control. The method includes: establishing an impedance model of the sending end of the wind farm-grid-connected HVDC transmission system; determining the first feasible region of the constant current controller's parameters based on the structure of the constant current controller at the sending end of the grid-commutated HVDC transmission system; obtaining the renewable energy transmission ratio constraint; determining the second feasible region of the constant current controller's parameters corresponding to the renewable energy transmission ratio constraint based on the parameter stability control region of the constant current controller; obtaining the short-circuit ratio constraint; determining the third feasible region of the constant current controller's parameters corresponding to the short-circuit ratio constraint based on the second feasible region of the constant current controller's parameters corresponding to the renewable energy transmission ratio constraint, the impedance model of the wind farm-grid-connected HVDC transmission system, and the short-circuit ratio constraint; and controlling the operation of the sending end of the grid-commutated HVDC transmission system based on the third feasible region of the constant current controller's parameters corresponding to the short-circuit ratio constraint.

[0006] Furthermore, based on the structure of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the feasible region of the first parameter of the constant current controller is determined, including: establishing the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system; and determining the feasible region of the first parameter of the constant current controller based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, and a gain-phase margin tester, wherein the gain-phase margin tester is embedded in the constant current control loop.

[0007] Furthermore, based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, and the gain-phase margin tester, the first parameter feasible region of the constant current controller is determined, including: determining the D-segmentation boundary of the constant current control parameters based on the D-segmentation method and the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system; and determining the first parameter feasible region of the constant current controller based on the D-segmentation boundary of the constant current control parameters, the gain-phase margin tester, and the requirements for phase margin, gain margin, and bandwidth.

[0008] Furthermore, based on the parameter stability control domain of the constant current controller, the second parameter feasible domain of the constant current controller corresponding to the renewable energy transmission ratio constraint is determined, including: establishing the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending-end current control loop; and determining the second parameter feasible domain of the constant current controller based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending-end current control loop, the gain-phase margin tester, and the renewable energy transmission ratio constraint.

[0009] Furthermore, a mapping relationship is established between the renewable energy transmission ratio and the current setpoint of the sending-end current control loop, including: obtaining the power balance equation of the LCC converter; taking the partial derivative of both sides of the power balance equation with respect to the renewable energy transmission ratio to obtain the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending-end current control loop.

[0010] Furthermore, based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transfer ratio and the current setpoint of the sending end current control loop, the gain-phase margin tester, and the renewable energy transfer ratio constraint, the first parameter feasible region of the constant current controller is determined, including: determining multiple renewable energy transfer ratios; for each renewable energy transfer ratio, based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transfer ratio and the current setpoint of the sending end current control loop, and the gain-phase margin tester, determining the parameter feasible region of the constant current controller corresponding to the renewable energy transfer ratio; based on the renewable energy transfer ratio constraint, determining multiple target renewable energy transfer ratios; and superimposing the parameter feasible regions of the constant current controllers corresponding to multiple target renewable energy transfer ratios to determine the second parameter feasible region of the constant current controller.

[0011] Furthermore, based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop, and the gain-phase margin tester, the feasible region of the parameters of the constant current controller corresponding to the renewable energy transmission ratio is determined. This includes: determining the current setpoint of the sending end current control loop mapped by the renewable energy transmission ratio based on the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop; determining the D-segmentation boundary of the constant current control parameters corresponding to the renewable energy transmission ratio based on the D-segmentation method, the current setpoint of the sending end current control loop mapped by the renewable energy transmission ratio, and the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system; and determining the feasible region of the parameters of the constant current controller corresponding to the renewable energy transmission ratio based on the D-segmentation boundary of the constant current control parameters, the gain-phase margin tester, and the requirements for phase margin, gain margin, and bandwidth.

[0012] Furthermore, based on the feasible region of the second parameter of the constant current controller corresponding to the renewable energy transmission ratio constraint, the impedance model of the sending end of the wind farm-connected grid commutated HVDC transmission system, and the short-circuit ratio constraint, the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint is determined. This includes: establishing a closed-loop transfer function based on the impedance model of the sending end of the wind farm-connected grid commutated HVDC transmission system to determine the ratio of grid impedance to sending end LCC impedance; determining the boundary corresponding to the short-circuit ratio constraint based on the closed-loop transfer function based on the ratio of grid impedance to sending end LCC impedance; and determining the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint based on the boundary corresponding to the short-circuit ratio constraint and the feasible region of the second parameter of the constant current controller corresponding to the renewable energy transmission ratio constraint.

[0013] Furthermore, based on the boundary corresponding to the short-circuit ratio constraint and the second parameter feasible region of the constant current controller corresponding to the new energy transmission ratio constraint, the third parameter feasible region of the constant current controller corresponding to the short-circuit ratio constraint is determined, including: taking the intersection of the boundary corresponding to the short-circuit ratio constraint and the second parameter feasible region of the constant current controller corresponding to the new energy transmission ratio constraint as the third parameter feasible region of the constant current controller corresponding to the short-circuit ratio constraint.

[0014] This invention provides an oscillation suppression system based on the D-segmentation method for calculating the renewable energy transmission ratio and short-circuit ratio. The oscillation suppression method based on the D-segmentation method for calculating the renewable energy transmission ratio and short-circuit ratio includes: an impedance analysis module for establishing an impedance model of the sending end of a wind farm-connected grid commutated HVDC transmission system; a parameter domain determination module for determining a first feasible domain of the constant current controller's parameters based on the structure of the constant current controller at the sending end of the grid commutated HVDC transmission system; a constraint acquisition module for acquiring renewable energy transmission ratio constraints; the parameter domain determination module is further used to determine a second feasible domain of the constant current controller's parameters corresponding to the renewable energy transmission ratio constraints based on the parameter stability control domain of the constant current controller; the constraint acquisition module is further used to acquire short-circuit ratio constraints; the parameter domain determination module is further used to determine a third feasible domain of the constant current controller's parameters corresponding to the short-circuit ratio constraints based on the second feasible domain of the constant current controller's parameters corresponding to the renewable energy transmission ratio constraints and the short-circuit ratio constraints; and an oscillation suppression module for controlling the operation of the sending end of the grid commutated HVDC transmission system based on the third feasible domain of the constant current controller's parameters corresponding to the short-circuit ratio constraints.

[0015] Compared with existing technologies, the oscillation suppression method and system based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio provided by this invention have at least the following beneficial effects:

[0016] Based on the structure of the constant current controller, the feasible region of the first parameter, the feasible region of the second parameter corresponding to the renewable energy transmission ratio constraint, and the feasible region of the third parameter corresponding to the short-circuit ratio constraint are determined sequentially. This step-by-step method of determining the feasible region of parameters makes the design of controller parameters more scientific and reasonable, and can meet the system stability requirements under different constraints. By accurately determining the feasible region of the constant current controller parameters, precise control of the sending end of the grid-commutated HVDC transmission system can be achieved, improving the system's control performance and response speed, and reducing the occurrence of oscillations and instability. Under extreme conditions of high renewable energy penetration and low short-circuit ratio, this method does not require additional compensation devices or complex control strategies, has strong robustness, and can effectively cope with the complex operating condition changes brought about by renewable energy access, ensuring the stable operation of the system. Attached Figure Description

[0017] This specification will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein:

[0018] Figure 1 This is a flowchart illustrating an oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, according to some embodiments of this specification.

[0019] Figure 2 This is an equivalent block diagram of a wind power transmission system shown in some embodiments of this specification;

[0020] Figure 3 This is a flow graph of a unity negative feedback control signal according to some embodiments of this specification;

[0021] Figure 4 This is a structural diagram of a constant current controller shown according to some embodiments of this specification;

[0022] Figure 5 This is a schematic diagram of the feasible region of the first parameter according to some embodiments of this specification;

[0023] Figure 6 These are system impedance characteristic curves under different wind power transmission ratios as shown in some embodiments of this specification;

[0024] Figure 7 These are DC-side current waveforms under different wind power transmission ratios as shown in some embodiments of this specification;

[0025] Figure 8 This is a schematic diagram of the feasible domain of the second parameter according to some embodiments of this specification;

[0026] Figure 9 These are system impedance characteristic curves under different short-circuit ratios as shown in some embodiments of this specification;

[0027] Figure 10 These are DC-side current waveforms under different short-circuit ratios as shown in some embodiments of this specification;

[0028] Figure 11 This is an equivalent transfer function block diagram shown according to some embodiments of this specification;

[0029] Figure 12 This is a schematic diagram of the feasible region of the third parameter according to some embodiments of this specification;

[0030] Figure 13 This is an enlarged view of the feasible region for the second parameter of 20%-30% wind power transmission ratio, as shown in some embodiments of this specification.

[0031] Figure 14 This is an enlarged view of the feasible region for the second parameter of 30%-40% wind power transmission ratio, as shown in some embodiments of this specification.

[0032] Figure 15 This is a schematic diagram of the simulation verification results of the feasible region of the second parameter when the wind power transmission ratio is 20%-30% and 30%-40% according to some embodiments of this specification;

[0033] Figure 16 This is a DC current waveform diagram showing the change in wind power transmission ratio according to some embodiments of this specification;

[0034] Figure 17 This is an enlarged view of the feasible region of the third parameter according to some embodiments of this specification;

[0035] Figure 18 This is a simulation diagram of the DC-side current waveform shown in some embodiments of this specification;

[0036] Figure 19 This is an enlarged view of the feasible region of the third parameter according to some embodiments of this specification;

[0037] Figure 20 This is a simulation diagram of the DC-side current waveform shown in some embodiments of this specification;

[0038] Figure 21 This is a block diagram of an oscillation suppression system based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, according to some embodiments of this specification. Detailed Implementation

[0039] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0040] Figure 1 This is a flowchart illustrating an oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, according to some embodiments of this specification. Figure 1 As shown, the oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio may include the following steps.

[0041] Step 110: Establish the impedance model of the sending end of the wind farm parallel grid commutated high voltage DC transmission system.

[0042] The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio is applied to the sending end of the grid-commutated HVDC transmission system. The rectifier side of the sending end of the grid-commutated HVDC transmission system adopts constant current control mode, and the inverter side adopts constant voltage control mode.

[0043] Figure 2 This is an equivalent block diagram of a wind power transmission system shown in some embodiments of this specification, such as... Figure 2 As shown, the sending ends of the wind farm and the grid-commutated HVDC transmission can each be equivalently represented as an ideal current source connected in parallel with its output impedance. The grid is equivalently represented as an ideal voltage source connected in series with its equivalent impedance. (See diagram.) I wf ( s ), Z wf ( s () represents the equivalent current source and output impedance of the wind farm; I LCC ( s ), Z LCC ( s Z represents the equivalent current source and output impedance of the sending-end system; g ( s ), U g ( s Here, denoted as grid impedance and grid voltage, respectively. Impedance analysis essentially divides the parallel system into two independent subsystems: source and load. In the frequency domain, it analyzes the stability of the closed-loop system based on the open-loop transfer function of each subsystem. The power grid is considered as one subsystem, and the wind farm parallel LCC-HVDC sending-end system is considered as another subsystem.

[0044] According to Kirchhoff's voltage law Figure 1 The voltage at PCC can be expressed as:

[0045] ,

[0046] If the wind farm operates stably when powered by an ideal voltage source, and is stable under no-load conditions at the LCC-HVDC sending end, then the system is stable if the ratio of the grid impedance to the subsystem impedance (the wind farm parallel LCC-HVDC sending end system) satisfies the generalized Nyquist stability criterion.

[0047] Step 120: Based on the structure of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, determine the first parameter feasible region of the constant current controller.

[0048] Specifically, it includes:

[0049] Establish the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system;

[0050] Based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, and the gain-phase margin tester, the first parameter feasible region of the constant current controller is determined, wherein the gain-phase margin tester is embedded in the constant current control loop.

[0051] In some embodiments, based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, and a gain-phase margin tester, the first feasible region of the constant current controller parameters is determined, including:

[0052] Based on the D-segmentation method and the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, the D-segmentation boundary of the constant current control parameters is determined.

[0053] Based on the D-segmentation boundary of the constant current control parameters, the gain-phase margin tester, and the requirements for phase margin, gain margin, and bandwidth, the first parameter feasible region of the constant current controller is determined.

[0054] Specifically, the D-segmentation method establishes a mapping relationship between the polar plane and the controller parameter space, visually projecting the asymptotically stable region of the linear system on the polar plane onto the parameter space, thereby solving for the parameter surface corresponding to the critical stability condition, and then constructing the first parameter feasible region of the constant current controller.

[0055] Figure 3 This is a unity negative feedback control signal flow diagram shown according to some embodiments of this specification, such as... Figure 3 As shown, for a unity negative feedback system containing a PI controller, the transfer function G of the PI controller is included in the feedforward channel. PI (s), and the transfer function G of the controlled object. P (s), where s represents a complex variable, R(s) is the input, Y(s) is the output, and G is the transfer function of the PI controller. PI (s), and the transfer function G of the controlled object. P The expression for (s) is:

[0056] ,

[0057] Among them, K P K I Let a and b be the proportional and integral coefficients of the PI controller, respectively, and let a and b be the transfer functions of the controlled object G. P (s) Coefficients of the numerator and denominator polynomials.

[0058] Based on the above equation, the closed-loop characteristic equation of the unity negative feedback control system can be derived. for:

[0059] ,

[0060] in, Passing functions to the controlled object The coefficients of the denominator polynomial Passing functions to the controlled object GP ( s The coefficients of the numerator polynomial, K = (K p ,K i The D-partition boundary is the set of controller parameters obtained subsequently. The D-partition boundary can be composed of p(0;k)=0, p(∞;k)=0, and p(±jω;k)=0:

[0061] ,

[0062] in, and It is a singular boundary; For non-singular boundaries, This is the system angular frequency.

[0063] The above expression can be equivalent to:

[0064] ,

[0065] From the first and second equations above, we can obtain the singular boundary as follows:

[0066] ,

[0067] From the third equation above, we can obtain the non-singular boundary, let The controlled object's transfer function is transformed to the complex plane. In the complex plane, the controlled object can therefore be written as... In the form of, , They are respectively By taking the real and imaginary parts, we can obtain:

[0068] ,

[0069] Solving for the given information yields:

[0070] ,

[0071] Figure 4 The diagram shows the structure of a constant current controller according to some embodiments of this specification, such as... Figure 4 As shown, and Given the DC current setting and measured values, respectively, the expression for the open-loop transfer function of the constant current controller is:

[0072] ,

[0073] in, Let be the transfer function of the PI control loop. Let be the transfer function of the commutation stage. For the transfer function of a DC line, The transfer function of the detection system has the following expressions:

[0074] ,

[0075] ,

[0076] ,

[0077] ,

[0078] in, The time constant of the converter; This represents the effective value of the AC side line voltage of the converter. The firing angle for stable operation of the converter. It is a time constant. For proportional gain, This is the equivalent inductance in the circuit. This is the equivalent capacitance in the circuit. This is the equivalent resistance of the circuit. This represents the change in direct current. This represents the change in DC voltage.

[0079] Combining the aforementioned formulas for solving nonsingular boundaries, the nonsingular boundaries of the parameters of the constant current controller can be obtained as follows:

[0080] ,

[0081] in, Represents taking the real part of a complex number; This represents taking the imaginary part of a complex number. The proportional coefficient of the constant current controller, The integral coefficient of the constant current controller is... for exist The value at that location.

[0082] From the above equation, we can obtain the critical stable state of the system corresponding to the D-segment boundary, that is, when the parameter points are located on the boundary curve, the closed-loop characteristic roots are exactly distributed on the imaginary axis. However, in engineering practice, it is necessary to ensure that the control system has sufficient stability margin. Therefore, a gain-phase margin tester is embedded in the constant current control loop to ensure the desired phase margin and gain margin. The controller parameter domain designed based on the gain margin and phase margin may still not meet the requirements of actual engineering. Therefore, based on the definition of bandwidth, a mapping relationship between controller parameters and bandwidth is established, and finally, the first parameter feasible domain that satisfies the phase margin, gain margin, and bandwidth is obtained.

[0083] Figure 5 This is a schematic diagram of the feasible region of the first parameter according to some embodiments of this specification, such as... Figure 5 As shown in the figure, the red line represents the gain-phase margin test with respect to a specific gain margin. Relevant boundaries. Gain margin is a metric for system stability; it indicates how many times the gain can be increased without causing instability when the phase reaches -180°. This straight line defines the range of parameter combinations that meet a certain gain margin requirement. (Blue curve and phase margin) Related. Phase margin is another important stability metric; it indicates the stability of the system when the gain is [value missing]. At that time, the phase can lead or lag by how many degrees without causing system instability. (See diagram) and The curves delineate parameter regions that satisfy different phase margin requirements, as shown in the figure. , The straight line divides the parameter regions that satisfy different bandwidth requirements. The shaded area represents the stability region of the constant current controller parameters that satisfy the phase margin, gain margin, and bandwidth requirements. Within this region... and The combination of parameters can enable the control system to have sufficient stability margin and meet certain bandwidth requirements.

[0084] Step 130: Obtain the constraints on the new energy transmission ratio.

[0085] Specifically, let the real-time output of the wind farm be... The rated transmission power of LCC-HVDC is Define the wind power transmission ratio (i.e., the "new energy transmission ratio"). Changes in wind power and transmission power will both lead to... Changes occur when wind power experiences a step disturbance. hour, Increase When the wind power output is constant, changes in the LCC-HVDC transmission power will also cause a change in λ.

[0086] To investigate the impact of wind power transmission ratio on system stability, and whether adjusting the constant current controller parameters can enhance the system's damping characteristics under high wind power transmission ratios, the system impedance characteristic curves for adjusting the wind power transmission ratio and constant current controller parameters are shown below. Figure 6 As shown, by Figure 6 As can be seen from the red and blue curves, with the increase of the wind power transmission ratio, the wind power transmission ratio has little effect on the impedance characteristic curve of the wind power transmission system in the 1-40Hz frequency band. However, in the 40-70Hz frequency band, the amplitude of the resonant peak increases, and the phase gradually approaches -90° downwards, weakening the system's damping characteristics and making the system more unstable. Therefore, the wind power transmission ratio mainly affects the impedance characteristics in the 40-70Hz range, and the system tends to be unstable with increasing wind power transmission ratio. Under the condition of a 30% wind power transmission ratio, changing the constant current controller parameters reveals that the system's damping characteristics in the 40-70Hz frequency band are close to, almost overlapping with, the damping characteristic curve of a 20% wind power transmission ratio. Therefore, it can be concluded that under high wind power transmission ratios, adjusting the constant current controller parameters can enhance the system's damping characteristics.

[0087] The renewable energy transmission ratio constraint can characterize the range of values ​​for the renewable energy transmission ratio, and can be obtained from external data sources. For example, the renewable energy transmission ratio constraint can be determined by manually specifying the constraint or by analyzing historical data from wind farms.

[0088] Figure 7 These are DC-side current waveforms under different wind power transmission ratios, as shown in some embodiments of this specification. Figure 7 As shown, to further illustrate the issue, this conclusion is analyzed from the perspective of time-domain simulation. In the simulation model, the wind power transmission ratio is adjusted, and the DC current waveform changes are observed. During the first 1-3 seconds, the wind power transmission ratio is 20%, and the constant current controller parameters are (6, 180). At this time, the system maintains stable operation. At 3 seconds, the wind power transmission ratio changes from 20% to 30%, and the DC current oscillates. At 6 seconds, the wind power transmission ratio remains at 30%. Changing the constant current controller parameters then eliminates the DC current oscillations, and the system returns to a stable state. Both simulation results and theory indicate that an increase in the wind power transmission ratio leads to system instability, and adjusting the constant current controller parameters can restore the system to a stable state.

[0089] Step 140: Based on the parameter stability control domain of the constant current controller, determine the second parameter feasible domain of the constant current controller corresponding to the new energy transmission ratio constraint.

[0090] Specifically, it includes:

[0091] Establish a mapping relationship between the new energy transmission ratio and the current setpoint of the sending-end current control loop;

[0092] Based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop, the gain-phase margin tester, and the renewable energy transmission ratio constraint, the feasible region of the second parameter of the constant current controller is determined.

[0093] In some embodiments, establishing a mapping relationship between the new energy transmission ratio and the current setpoint of the sending-end current control loop includes:

[0094] Obtain the power balance equations for the LCC converter;

[0095] By taking the partial derivative of both sides of the power balance equation with respect to the renewable energy transmission ratio, we obtain the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending-end current control loop.

[0096] Specifically, the power balance equation for an LCC converter is:

[0097] ,

[0098] in, V represents the rated power of the LCC converter. ac X is the effective value of the AC line voltage. C For commutation reactance, This is a reference value for DC current. This is the trigger delay angle of the converter.

[0099] When wind power changes, the reference value of the DC current needs to be adjusted. To maintain a constant rated transmission power. Therefore It is an implicit function of λ.

[0100] According to the implicit function theorem, taking the partial derivative of both sides of the power balance equation with respect to λ and simplifying, we can obtain the sensitivity S as follows:

[0101] ,

[0102] As can be seen from the above formula, there is a certain mapping relationship between the wind power transmission ratio and the current setpoint of the sending-end current control loop. By introducing this mapping relationship into the sending-end LCC constant current controller, the stability domain of the controller parameters considering the wind power transmission ratio can be obtained.

[0103] In some embodiments, based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop, the gain-phase margin tester, and the renewable energy transmission ratio constraint, the first parameter feasible region of the constant current controller is determined, including:

[0104] Determine the transmission ratio of multiple new energy sources;

[0105] For each renewable energy transmission ratio, the feasible region of parameters of the constant current controller corresponding to the renewable energy transmission ratio is determined based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the current control link at the sending end, and the gain-phase margin tester.

[0106] Based on the constraint of renewable energy transmission ratio, multiple target renewable energy transmission ratios are determined;

[0107] The second parameter feasible region of the constant current controller is determined by superimposing the feasible regions of the parameters of the constant current controller corresponding to multiple target new energy transmission ratios.

[0108] In some embodiments, based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop, and a gain-phase margin tester, the feasible domain of the parameters of the constant current controller corresponding to the renewable energy transmission ratio is determined, including:

[0109] Based on the mapping relationship between the new energy transmission ratio and the current setpoint of the sending-end current control loop, the current setpoint of the sending-end current control loop mapped by the new energy transmission ratio is determined.

[0110] Based on the D-segmentation method, the current setpoint of the sending-end current control loop of the new energy transmission ratio mapping and the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, the D-segmentation boundary of the constant current control parameters corresponding to the new energy transmission ratio is determined.

[0111] Based on the D-segmentation boundary of constant current control parameters, the gain-phase margin tester, and the requirements for phase margin, gain margin, and bandwidth, the feasible domain of parameters for the constant current controller corresponding to the new energy transmission ratio is determined.

[0112] For example only, Figure 8 This is a schematic diagram illustrating the feasible region of the second parameter according to some embodiments of this specification. Figure 8 The feasible region for the second parameter shown is based on the wind farm's transmission power as the rated power P. windThe transmission design involves varying the transmission power of the LCC-HVDC system (1000MW-500MW), resulting in a wind power transmission ratio ranging from 20% to 40%. Using the method given in step 120, the feasible parameter domains for different transmission powers (i.e., different wind power transmission ratios) can be obtained. Superimposing these feasible parameter domains for different wind power transmission ratios yields a general parameter domain. For example... Figure 8 The gray shaded area represents the feasible region for the second parameter, where the wind power transmission ratio is 20%-40%. Similarly, if... Figure 8 70%-100% P rated By superimposing the corresponding parameter domains, that is, by superimposing the areas enclosed by the green, purple, black, and red lines, we can obtain the second feasible domain of wind power transmission ratio of 20%-30%, and so on. Figure 8 In this context, the general controller parameter domain is the feasible domain of the second parameter.

[0113] Step 150: Obtain the short-circuit ratio constraint.

[0114] Specifically, this study aims to investigate the impact of the short-circuit ratio (SCR) on system stability and the feasibility of improving system damping characteristics by optimizing the constant current controller parameters under low SCR conditions. The system impedance characteristic curves under different SCR conditions are shown below. Figure 9 As shown in the red and blue curves, it can be seen that as the short-circuit ratio decreases, the amplitude of the resonant peak in the 40-80Hz frequency band increases, the phase gradually approaches -90°, the system's damping characteristics weaken, and the system becomes more unstable. Therefore, a decrease in the short-circuit ratio leads to system instability.

[0115] The short-circuit ratio is calculated based on the following formula:

[0116] ,

[0117] in, Short-circuit capacity; Rated power, The equivalent impedance of the AC system; This is the rated voltage.

[0118] To further prove this conclusion, a time-domain simulation analysis was performed to observe the changes in the system's DC current under different short-circuit ratios. Figure 10As shown, the system short-circuit ratio is 5 during the first 1-3 seconds, during which the system can operate stably. At 3 seconds, the constant current controller parameters remain unchanged, but the short-circuit ratio changes to 3. It can be observed that the DC current oscillates at this point, and the system is unstable. At 6 seconds, the controller parameters change from (5, 231) to (7, 230), the DC current oscillation disappears, and the system tends to stabilize. Both simulation results and theory demonstrate that the lower the short-circuit ratio, the more unstable the system tends to be. Adjusting the constant current controller parameters can restore the system to stability.

[0119] The short-circuit ratio constraint may include at least one short-circuit ratio value, which can be obtained from an external data source. For example, at least one short-circuit ratio value can be determined by manually specifying it or by analyzing historical data from the wind farm.

[0120] Step 160: Based on the feasible region of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint, the impedance model of the sending end of the wind farm parallel grid commutated high voltage DC transmission system and the short-circuit ratio constraint, determine the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint.

[0121] Specifically, it includes:

[0122] Based on the mapping relationship between the new energy transmission ratio and the current setpoint of the sending-end current control loop, the current setpoint of the sending-end current control loop mapped by the new energy transmission ratio is determined.

[0123] Based on the D-segmentation method, the current setpoint of the sending-end current control loop of the new energy transmission ratio mapping and the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, the D-segmentation boundary of the constant current control parameters corresponding to the new energy transmission ratio is determined.

[0124] Based on the D-segmentation boundary of constant current control parameters, the gain-phase margin tester, and the requirements for phase margin, gain margin, and bandwidth, the feasible domain of parameters for the constant current controller corresponding to the new energy transmission ratio is determined.

[0125] In some embodiments, based on the feasible region of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint, the impedance model of the sending end of the wind farm parallel grid commutated HVDC transmission system, and the short-circuit ratio constraint, the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint is determined, including:

[0126] Based on the impedance model of the sending end of the commutated high-voltage direct current transmission system connected to the wind farm grid, a closed-loop transfer function is established for the ratio of grid impedance to sending end LCC impedance.

[0127] Based on the closed-loop transfer function of the ratio of grid impedance to sending-end LCC impedance, the boundary corresponding to the short-circuit ratio constraint is determined.

[0128] Based on the boundary conditions corresponding to the short-circuit ratio constraint and the feasible region of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint, the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint is determined.

[0129] Specifically, according to the impedance stability criterion, the system must satisfy two conditions to be stable: (1) 1 / Z LCC (s) stable; (2) Z g (s) / Z LCC (s) satisfies the Nyquist stability criterion. Therefore, the grid impedance Z can be established using the impedance stability criterion. g (s) and the LCC impedance at the sending end Z LCC (s) is the transfer function of the ratio, which can be used to obtain the stability boundary considering SCR. Figure 4 Equivalent transformation is performed to obtain Figure 11 The structural diagram shown is from... Figure 11 The impedance transfer function Z of the sending-end LCC can be obtained. LCC (s) is:

[0130] ,

[0131] At this point, the grid impedance is obtained. Z g ( s ) and the LCC impedance Z at the sending end LCC ( s The ratio is the open-loop transfer function:

[0132] ,

[0133] in, This is the inductance value of the AC power grid.

[0134] Further derivation yields the open-loop transfer function. Corresponding closed-loop transfer function for:

[0135] ,

[0136] From the above equation, we can obtain the closed-loop characteristic equation. Setting the closed-loop characteristic equation to 0, we can derive K. p K i The expression, derived from K p With K i The expression yields the stability domain of the controller parameters considering SCR conditions.

[0137] Figure 12 This is a schematic diagram illustrating the feasible region of the third parameter according to some embodiments of this specification. Figure 12The area marked by the red diagonal line represents the feasible region of the second parameter when the wind power transmission ratio is 20%-30%. The gray shaded area represents the intersection of the feasible region of the second parameter when the wind power transmission ratio is 20%-30% and the boundary determined when the SCR is 3. When the SCR constraint is considered, the stable region of the controller parameters is further reduced. Figure 12 In this context, the general domain when the wind power transmission ratio is 20%-30% is the second parameter feasible domain when the wind power transmission ratio is 20%-30%, and the general parameter domain is the third parameter feasible domain.

[0138] Step 170: Control the sending end operation of the grid-commutated high-voltage direct current transmission system based on the feasible domain of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint.

[0139] The following experiments illustrate the beneficial effects of the oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio. In this experiment, a simulation model of a large-scale wind power transmission system via LCC-HVDC was built in PSCAD electromagnetic transient simulation software to verify the results of the theoretical analysis. By dynamically switching the controller parameter groups within and outside the controller's stability domain, the changes in the DC current response waveform were compared to verify the effectiveness and accuracy of the obtained controller parameter stability domain.

[0140] Will Figure 5 The general controller parameter domain with a wind power transmission ratio of 20%-30% and the second parameter feasible domain of 30%-40% are magnified as follows: Figure 13 and Figure 14 As shown, seven sets of PI control parameters are selected. Four sets are red (controller parameters) and fall within the feasible region of the second parameter, while three sets are green (controller parameters) and fall outside the feasible region of the second parameter. The constant current controller parameters are switched according to the changing patterns of the red, green, and blue arrows in the figure, and the changes in the DC current waveform are observed.

[0141] Figure 15 (a) The figure shows the dynamic response process of the DC-side current waveform with the controller parameters (based on the changes of the green arrows) when the wind power transmission ratio is 30%. The initial control parameters of the current loop in the 2-3 second period are (4,240). At this time, it is found that the DC-side current waveform is in a stable operating state. At 3 seconds, the control parameters are switched from the initial control parameters to control parameters (6,303) that are outside its stable range. At this time, it is found that the DC-side current waveform has obvious oscillations and exhibits obvious periodicity. At t=5s, the controller parameters are readjusted from (6,303) back to the stable range (6,243). After the switch, the regular oscillations in the waveform disappear, and the system recovers and maintains a stable operating state.

[0142] Figure 15(b) The figure shows the dynamic response of the DC current under the controller parameters (based on the changes of the red arrows) when the wind power transmission ratio is 30%. In the 2-3 second interval, the initial control parameters of the current loop are (4,240), and the system maintains stable operation. At 3 seconds, the parameters are switched to the parameters outside the stable region (5,285), showing obvious periodic oscillation waveforms. At t=5s, the parameters are adjusted to the stable region (5,234), the oscillations disappear, and the system recovers and maintains a stable operating state.

[0143] Figure 15 (c) The figure shows the dynamic response of the DC current under the controller parameters (based on the changes of the blue arrows) when the wind power transmission ratio is 40%. In the 2-3 second interval, the initial control parameters of the current loop are (4,240), and the system maintains stable operation. At 3 seconds, the parameters are switched to the parameters outside the stable region (7,180), and the system becomes unstable. At t=5s, the parameters are adjusted to the stable region (7,242), and the system recovers and maintains a stable operating state.

[0144] Simulation results show that when the wind power transmission ratio is between 20% and 30% or 40%, the control parameters within the feasible region of the second parameter can ensure the continuous and stable operation of the DC transmission system. Conversely, controller parameter domains outside this feasible region will cause system instability. Simulation results verify that the corresponding general parameter domains for wind power transmission ratios of 20%, 30%, and 40% are effective.

[0145] Depend on Figure 13 and Figure 14 It can be seen that the control parameter (7,180) is outside the feasible region of the second parameter when the wind power transmission ratio is 40%, but inside the feasible region of the second parameter when the wind power transmission ratio is 30%. Therefore, to further verify the accuracy of the determined feasible region of the second parameter, a simulation experiment was conducted with the wind power transmission ratio changed under the same controller parameters (7,180). The DC current waveform is as follows. Figure 16 As shown, by Figure 16 It can be seen that within 2-3 seconds, when the wind power transmission ratio is 40%, the control parameter (4,240) within the feasible region of the second parameter enables the transmission system to operate stably under the 40% wind power transmission ratio condition. When switching to the external control parameter (7,180) after 3 seconds, the DC current becomes unstable. However, when switching to the 30% wind power transmission ratio condition after 5 seconds, the control parameter (7,180) within the feasible region of the second parameter corresponding to the 30% wind power transmission ratio condition enables the DC current to stabilize. Therefore, it can be proven that the determined feasible region of the second parameter is relatively accurate.

[0146] Will Figure 12 The stability domain of the gray shaded controller parameters is magnified as follows: Figure 17As shown, four sets of PI control parameters are selected, with two sets of red controller parameters within the parameter stability region and two sets of green parameters outside the stability region. The constant current controller parameters are switched according to the pattern of the black arrows in the figure, and the dynamic changes of the DC side current waveform are observed to verify the effectiveness of the parameter domain in the gray shaded area.

[0147] Figure 18 The graph shows the dynamic changes in DC current waveform when the wind power transmission ratio is 30% and the short-circuit ratio is 3. For the wind power transmission system, the SCR is 15 for 2-3 seconds, and the constant current controller parameters (2, 170) maintain stable system operation. At 3 seconds, the system SCR abruptly changes from 15 to 3, while the constant current controller parameters remain unchanged, resulting in significant oscillations in the DC current waveform. From 4.5-6 seconds, the system SCR remains at 3, and the constant current controller parameters change from (2, 170) to (4, 200). At this point, the DC current oscillations disappear and the system gradually returns to a steady state.

[0148] Also by Figure 18 It can be seen that the system becomes unstable when the SCR is 3 and the constant current controller is set to control parameters (1.6, 135) outside the feasible region of the third parameter. However, after switching to parameters (5.5, 210) within the feasible region of the third parameter, the system gradually recovers stability. The simulation results verify the effectiveness of the stability region of the constant current controller PI parameters when the SCR is 3.

[0149] When the SCR is 2.5, the stability region of the constant current controller parameters is obtained as follows: (The values ​​are missing from the provided text.) Figure 19 As shown.

[0150] Depend on Figure 20 It can be seen that the wind power transmission system can stably transmit DC current with an SCR of 15 for 2-3 seconds and constant current controller parameters of (4, 200). At 3 seconds, the SCR suddenly drops to 2.5, while the constant current controller parameters (4, 200) remain unchanged, causing the DC current waveform to oscillate. From 4.5-6 seconds, under the weak grid conditions with an SCR of 2.5, the constant current controller parameters change to (7.3, 126), and the DC current returns to stability. Similarly, from... Figure 20 It can be seen that under a weak power grid with an SCR of 2.5, the system becomes unstable when the constant current controller is set to control parameters (3,210) outside the feasible domain of the third parameter. When the control parameters are switched to those inside the feasible domain of the third parameter, the system gradually returns to stability.

[0151] Understandably, the above experiments established an impedance model for a large-scale wind power transmission system via LCC-HVDC. Based on this model, the impact of the renewable energy transmission ratio and the system short-circuit ratio on the system's sending-end stability was analyzed. An innovative parameter domain tuning method for the LCC-HVDC system's sending-end constant current controller, considering multiple constraints related to the renewable energy transmission ratio and short-circuit ratio, was proposed. Simulation experiments were conducted using the PSCAD electromagnetic transient simulation software model to verify the results. The results confirmed that the oscillation suppression method based on the D-segmentation method, considering the renewable energy transmission ratio and short-circuit ratio, improves system stability. Even under extreme conditions of high renewable energy penetration and low short-circuit ratio, the system can still operate safely and stably without additional compensation devices or complex control strategies.

[0152] Figure 21 This is a block diagram of an oscillation suppression system based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, as shown in some embodiments of this specification. Figure 21 As shown, the oscillation suppression system based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio can include an impedance analysis module, a parameter domain determination module, a constraint acquisition module, and an oscillation suppression module.

[0153] Impedance analysis module is used to establish the impedance model of the sending end of the commutated high-voltage direct current transmission system of wind farm parallel grid;

[0154] The parameter domain determination module is used to determine the first parameter feasible domain of the constant current controller based on the structure of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system.

[0155] The constraint acquisition module is used to acquire the constraints on the new energy transmission ratio;

[0156] The parameter domain determination module is also used to determine the second parameter feasible domain of the constant current controller corresponding to the new energy transmission ratio constraint based on the parameter stability control domain of the constant current controller.

[0157] The constraint acquisition module is also used to acquire the short-circuit ratio constraint condition;

[0158] The parameter domain determination module is also used to determine the third parameter feasible domain of the constant current controller corresponding to the short-circuit ratio constraint condition based on the second parameter feasible domain of the constant current controller corresponding to the new energy transmission ratio constraint condition and the short-circuit ratio constraint condition.

[0159] The oscillation suppression module is used to control the sending-end operation of the grid-commutated high-voltage direct current transmission system based on the feasible domain of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint.

[0160] The oscillation suppression system based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio can be used to implement the oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, which will not be elaborated here.

[0161] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. An oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, characterized in that, This technology is applied to the sending end of a grid-commutated HVDC transmission system. The rectifier side of the sending end employs constant current control, while the inverter side employs constant voltage control. The technology includes: Establish an impedance model for the sending end of a commutated high-voltage direct current transmission system connected to a wind farm and grid. The structure of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system is used to determine the feasible region of the first parameter of the constant current controller. Obtain the constraints for the transmission ratio of new energy sources; Based on the parameter stability control domain of the constant current controller, the second parameter feasible domain of the constant current controller corresponding to the new energy transmission ratio constraint is determined. Obtain the short-circuit ratio constraint; Based on the feasible region of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint, the impedance model of the sending end of the wind farm parallel grid commutated high voltage DC transmission system and the short-circuit ratio constraint, the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint is determined. The third parameter of the current controller corresponding to the short-circuit ratio constraint is used to control the sending-end operation of the grid-commutated high-voltage direct current transmission system.

2. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to claim 1, characterized in that, Based on the structure of the constant current controller at the sending end of a grid-commutated HVDC transmission system, the feasible region of the first parameter of the constant current controller is determined, including: Establish the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system; Based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, and the gain-phase margin tester, the first parameter feasible region of the constant current controller is determined, wherein the gain-phase margin tester is embedded in the constant current control loop.

3. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to claim 2, characterized in that, Based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of a grid-commutated HVDC transmission system, and a gain-phase margin tester, the feasible region of the first parameter of the constant current controller is determined, including: Based on the D-segmentation method and the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, the D-segmentation boundary of the constant current control parameters is determined. Based on the D-segmentation boundary of the constant current control parameters, the gain-phase margin tester, and the requirements for phase margin, gain margin, and bandwidth, the first parameter feasible region of the constant current controller is determined.

4. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to claim 2, characterized in that, Based on the parameter stability control domain of the constant current controller, the feasible domain of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint is determined, including: Establish a mapping relationship between the new energy transmission ratio and the current setpoint of the sending-end current control loop; Based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop, the gain-phase margin tester, and the renewable energy transmission ratio constraint, the feasible region of the second parameter of the constant current controller is determined.

5. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to claim 4, characterized in that, Establish a mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending-end current control loop, including: Obtain the power balance equations for the LCC converter; By taking the partial derivative of both sides of the power balance equation with respect to the renewable energy transmission ratio, we obtain the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending-end current control loop.

6. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to claim 5, characterized in that, Based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of a grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop, the gain-phase margin tester, and the renewable energy transmission ratio constraint, the feasible region of the second parameter of the constant current controller is determined, including: Determine the transmission ratio of multiple new energy sources; For each renewable energy transmission ratio, the feasible region of parameters of the constant current controller corresponding to the renewable energy transmission ratio is determined based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the current control link at the sending end, and the gain-phase margin tester. Based on the constraint of renewable energy transmission ratio, multiple target renewable energy transmission ratios are determined; The second parameter feasible region of the constant current controller is determined by superimposing the feasible regions of the parameters of the constant current controller corresponding to multiple target new energy transmission ratios.

7. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to claim 6, characterized in that, Based on the D-segmentation method, the open-loop transfer function of the constant current controller at the sending end of a grid-commutated HVDC transmission system, the mapping relationship between the renewable energy transmission ratio and the current setpoint of the sending end current control loop, and a gain-phase margin tester, the feasible region of the parameters of the constant current controller corresponding to the renewable energy transmission ratio is determined, including: Based on the mapping relationship between the new energy transmission ratio and the current setpoint of the sending-end current control loop, the current setpoint of the sending-end current control loop mapped by the new energy transmission ratio is determined. Based on the D-segmentation method, the current setpoint of the sending-end current control loop of the new energy transmission ratio mapping and the open-loop transfer function of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system, the D-segmentation boundary of the constant current control parameters corresponding to the new energy transmission ratio is determined. Based on the D-segmentation boundary of constant current control parameters, the gain-phase margin tester, and the requirements for phase margin, gain margin, and bandwidth, the feasible domain of parameters for the constant current controller corresponding to the new energy transmission ratio is determined.

8. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to any one of claims 4-7, characterized in that, Based on the feasible region of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint, the impedance model of the sending end of the commutated HVDC transmission system connected to the wind farm grid, and the short-circuit ratio constraint, the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint is determined, including: Based on the impedance model of the sending end of the commutated high-voltage direct current transmission system connected to the wind farm grid, a closed-loop transfer function is established for the ratio of grid impedance to sending end LCC impedance. Based on the closed-loop transfer function of the ratio of grid impedance to sending-end LCC impedance, the boundary corresponding to the short-circuit ratio constraint is determined. Based on the boundary conditions corresponding to the short-circuit ratio constraint and the feasible region of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint, the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint is determined.

9. The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio according to claim 8, characterized in that, Based on the boundary conditions corresponding to the short-circuit ratio constraint and the feasible region of the second parameter of the constant current controller corresponding to the renewable energy transmission ratio constraint, the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint is determined, including: The intersection of the boundary corresponding to the short-circuit ratio constraint and the feasible region of the second parameter of the constant current controller corresponding to the new energy transmission ratio constraint is taken as the feasible region of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint.

10. An oscillation suppression system based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio, characterized in that, The oscillation suppression method based on the D-segmentation method and considering the new energy transmission ratio and short-circuit ratio as described in any one of claims 1-9 includes: Impedance analysis module is used to establish the impedance model of the sending end of the commutated high-voltage direct current transmission system of wind farm parallel grid; The parameter domain determination module is used to determine the first parameter feasible domain of the constant current controller based on the structure of the constant current controller at the sending end of the grid-commutated high-voltage direct current transmission system. The constraint acquisition module is used to acquire the constraints on the new energy transmission ratio; The parameter domain determination module is also used to determine the second parameter feasible domain of the constant current controller corresponding to the new energy transmission ratio constraint based on the parameter stability control domain of the constant current controller. The constraint acquisition module is also used to acquire the short-circuit ratio constraint condition; The parameter domain determination module is also used to determine the third parameter feasible domain of the constant current controller corresponding to the short-circuit ratio constraint condition based on the second parameter feasible domain of the constant current controller corresponding to the new energy transmission ratio constraint condition and the short-circuit ratio constraint condition. The oscillation suppression module is used to control the sending-end operation of the grid-commutated high-voltage direct current transmission system based on the feasible domain of the third parameter of the constant current controller corresponding to the short-circuit ratio constraint.

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