Method and device for analyzing additional frequency control stability of grid-following type grid-connected converter

Abstract

The invention provides a method and a device for analyzing additional frequency control stability of a grid-following type grid-connected converter. The method comprises the following steps of: acquiring a current running state of a system for representing dynamic interaction between a voltage source type converter and a power grid; determining an active power phase coupling channel transfer function and a reactive power phase coupling channel transfer function according to the current operation state of the system in combination with the converter model; wherein the current converter model is firstly constructed based on a voltage source type current converter in the system; according to the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, the influence of additional frequency control on damping is determined in combination with a small signal model, and an additional disturbance stability evaluation result is obtained; wherein the small signal model is firstly constructed based on a system. According to the method, the complex system is dynamically decoupled, so that the influence of the additional frequency control on the damping characteristic of the system is efficiently and accurately quantitatively evaluated.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a method and apparatus for analyzing the stability of additional frequency control in a grid-connected converter. Background Technology

[0002] With the large-scale application of new energy power generation technologies in power systems, the penetration rate of power electronic devices, such as voltage source converters (VSCs), continues to rise. However, these devices achieve power conversion through power electronic components, and their rotor inertia is almost zero, resulting in a significant reduction in the overall physical inertia of the power system, posing new challenges to frequency stability.

[0003] Traditional synchronous generators, relying on the inherent kinetic energy of their rotating mass, can spontaneously respond to power imbalances in the power grid, thus effectively suppressing frequency fluctuations. In contrast, renewable energy grid-connected systems lack this natural physical inertia, exhibiting rapid frequency changes and large fluctuations when faced with disturbances, posing a severe challenge to system frequency stability. Therefore, renewable energy grid-connected systems need to employ additional control strategies, such as virtual inertia control and droop control, to simulate the frequency regulation characteristics of synchronous machines through additional frequency control, providing rapid frequency support to the power grid.

[0004] However, the aforementioned additional control strategies fail to fully consider the complex dynamic characteristics of the phase-locked loop (PLL) in the VSC. The PLL is a closed-loop dynamic system containing a proportional-integral (PI) controller. Its dynamic response is not only related to the system frequency, but also closely related to its own PI parameters, phase-locked point voltage, and strong coupling with the current loop. When the complex torque coefficient method is used for analysis, the dynamic characteristics of the PLL will make the final calculated equivalent damping coefficient highly coupled with the synchronization coefficient, making it difficult to separate them accurately. This coupling may mislead the determination of system stability and make it impossible to accurately identify the subsynchronous oscillation boundary dominated by the PLL, thus limiting the effectiveness and reliability of this method in the small disturbance stability analysis of high-proportion new energy power systems. Summary of the Invention

[0005] This invention provides a method and apparatus for stability analysis of additional frequency control in grid-connected converters, which solves the defect in the prior art where the equivalent damping coefficient and synchronization coefficient are highly coupled, leading to misleading judgments of system stability. It can dynamically decouple complex systems and efficiently and accurately quantify the impact of additional frequency control on system damping characteristics.

[0006] This invention provides a method for stability analysis of additional frequency control in grid-connected converters, comprising: obtaining the current operating state of a system characterizing the dynamic interaction between a voltage source converter and the power grid; determining the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model; wherein the converter model is constructed based on the voltage source converter in the system; determining the impact of additional frequency control on damping based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function and the small-signal model, and obtaining the stability assessment result of the additional disturbance; wherein the small-signal model is constructed based on the system.

[0007] According to the present invention, a method for stability analysis of additional frequency control in a grid-connected converter includes the following steps before determining the active power phase coupling channel transfer function and reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model: constructing a phase-locked loop (PLL) sub-model based on the PLL in the voltage source converter; constructing an active power control outer loop based on a proportional-integral (PI) controller, using the difference between the active power command value and the output active power of the voltage source converter as input and the outer loop output d-axis current as output; and constructing a reactive power control outer loop based on a PLL controller, using the difference between the reactive power command value and the output reactive power of the voltage source converter as input and the outer loop output q-axis current as output; and constructing a reactive power control outer loop based on the PLL... The sub-model, active power outer loop, and reactive power outer loop, combined with the impedance of the filter line between the voltage source converter and the common coupling point obtained in advance, simulate the d-axis and q-axis current control in the rotating coordinate system of the voltage source converter under feedforward decoupling, and construct the current control inner loop. Based on the phase-locked loop sub-model, active power control outer loop, reactive power control outer loop, and current control inner loop, combined with the Kirchhoff voltage law (KVL) constraint of the internal potential, the converter model is obtained. Among them, the KVL constraint of the internal potential is constructed in advance based on the equivalent resistance of the transmission line between the common coupling point and the grid, the impedance of the transmission line, the impedance of the filter line, the grid voltage and grid current, combined with the phase-locked loop frequency generated by the phase-locked loop sub-model and the corresponding d-axis current component and q-axis current component of the common coupling point.

[0008] According to the present invention, a stability analysis method for additional frequency control of a grid-connected converter is provided. Based on the current operating state of the system and combined with the converter model, the transfer functions of the active power phase coupling channel and the reactive power phase coupling channel are determined. This includes: determining the current command value of reactive power, current reactive power, current command value of active power, current active power, current voltage and current of the common coupling point, and current voltage and current of the grid, based on the current operating state of the system; wherein, the common coupling point is used to characterize the coupling point between the voltage source converter and the grid in the system; and inputting the current current and current voltage of the common coupling point into the phase-locked loop (PLL) sub-model to obtain the PLL phase, PLL frequency, and current d-axis phase. The current and q-axis current, along with the system operating state at the equilibrium point, are linearized to obtain the phase-locked loop (PLL) phase disturbance. The equilibrium point characterizes the stable operating point of the system after grid connection. The PLL frequency, the current active power command value of the voltage source converter, and the current active power are input into the active power control outer loop to obtain the outer loop output d-axis current. The current reactive power command value and the current reactive power of the voltage source converter are input into the reactive power control outer loop to obtain the outer loop output q-axis current. The current d-axis current, current q-axis current, outer loop output d-axis current, and outer loop output q-axis current are input into the current control inner loop and linearized using the system operating state at the equilibrium point to obtain the first... The d-axis internal potential disturbance and the first q-axis internal potential disturbance are obtained. Based on the current voltage and current of the power grid, combined with the KVL constraints of the internal potential, and using the system operating state at the equilibrium point for linearization, the second d-axis internal potential disturbance and the second q-axis internal potential disturbance are obtained. Based on the first d-axis internal potential disturbance, the first q-axis internal potential disturbance, and the first q-axis internal potential disturbance, the first outer loop output d-axis current disturbance and the first outer loop output q-axis current disturbance are obtained. Based on the active power control outer loop and the reactive power control outer loop, linearization is performed using the system operating state at the equilibrium point, combined with the phase-locked loop phase disturbance, the frequency change principle within the disturbance target time, and the active power of the voltage source converter. The principles of power and reactive power output determine the d-axis current disturbance and q-axis current disturbance of the second outer loop output. The frequency change principle within the disturbance target time is used to suppress the rate of frequency change, reduce the maximum frequency deviation, and help the frequency quickly recover to a new stable point when power disturbances occur in the power grid. The active and reactive power output principles of the voltage source converter are used to determine the corresponding actual output active and reactive power based on the measured voltage and current. Based on the d-axis current disturbance, q-axis current disturbance, and d-axis current disturbance of the first outer loop output, the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function are obtained.

[0009] According to the present invention, a method for analyzing the stability of additional frequency control in a grid-connected converter is provided. Based on the phase-locked loop (PLL) in a voltage source converter, a PLL sub-model is constructed, including: determining the corresponding common coupling point voltage and current based on the operating state of the common coupling point, and simulating the zero-q-axis voltage principle at the input terminal of the corresponding PLL in the voltage source converter to construct the PLL sub-model; wherein, the zero-q-axis voltage principle is used to: determine the q-axis voltage component, q-axis current component, and d-axis current component corresponding to the common coupling point based on the common coupling point voltage and current, combined with the previously generated PLL phase; using the q-axis voltage component as an error signal, the generated PLL frequency and phase are adjusted through a first proportional-integral (PI) controller and an integrator to ensure that the generated PLL frequency and phase are consistent with the grid frequency and phase.

[0010] According to the present invention, a method for stability analysis of additional frequency control in a grid-connected converter is provided. Based on a proportional-integral controller, the method uses the difference between the active power command value and the output active power of the voltage source converter as input, and the outer loop output d-axis current as output. The method includes: obtaining the corresponding active power command value and output active power of the voltage source converter, as well as the phase-locked loop (PLL) frequency obtained from the PLL sub-model, based on the PLL frequency obtained from the PLL sub-model; performing differentiation using a first-order inertial element combined with additional inertial control coefficients, and proportional integration using additional droop control coefficients, based on the PLL frequency obtained from the PLL sub-model, to determine a first output result; and performing proportional integration using a first-order inertial element combined with additional droop control coefficients, based on the PLL frequency obtained from the PLL sub-model, to determine a second output result; and determining the outer loop output d-axis current using a second PI controller, based on the first and second output results, combined with the active power output and active power command value of the voltage source converter, to construct an active power control outer loop.

[0011] According to the present invention, a method for analyzing the stability of additional frequency control in a grid-connected converter is provided. Based on a proportional-integral controller, the method uses the difference between the reactive power command value and the output reactive power of the voltage source converter as input, and the outer loop output q-axis current as output to construct a reactive power control outer loop. The method includes: obtaining the reactive power command value and the output reactive power of the corresponding voltage source converter; using the difference between the reactive power command value and the output reactive power of the voltage source converter as input, and utilizing a third PI controller to determine the outer loop output q-axis current to construct the reactive power control outer loop.

[0012] According to the present invention, a method for analyzing the stability of additional frequency control in a grid-connected converter is provided. Based on a phase-locked loop (PLL) sub-model, an active power outer loop, and a reactive power outer loop, and combined with the impedance of the filter line between the voltage source converter and the common coupling point (CCP), the method simulates the d-axis and q-axis current control in a rotating coordinate system with feedforward decoupling of the voltage source converter, constructing a current control inner loop. This includes: based on the d-axis current component corresponding to the CCP output from the PLL sub-model and the actual d-axis current value output from the active power control outer loop, and combined with a fourth PI controller, simulating the adjustment process of the excitation system on the active power-related components; and based on the output of the fourth PI controller, combined with the q-axis current component corresponding to the CCP output from the PLL sub-model and the impedance of the filter line between the voltage source converter and the common coupling point, simulating the adjustment process of the excitation system on the active power-related components, and based on the output of the fourth PI controller, combined with the q-axis current component corresponding to the CCP output from the PLL sub-model and the impedance of the filter line between the voltage source converter and the common coupling point (CCP), simulating the adjustment process of the excitation system on the active power-related components, and simulating the adjustment process of the excitation system on the active power-related components, and based on the output of the fourth PI controller, combined with the q-axis current component corresponding to the common coupling point output from the PLL sub-model and the impedance of the filter line between the voltage source converter and the common coupling point (CCP), simulating the adjustment process of the voltage source converter on the excitation system with the active power-related components ... First, the impedance of the filter line between the voltage source converter and the common coupling point is obtained. Then, the d-axis current feedforward decoupling compensation is simulated to construct the d-axis control sub-model. Based on the q-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model and the actual q-axis current output by the reactive power control outer loop, the adjustment process of the excitation system on the reactive power related components is simulated in conjunction with the fifth PI controller. Based on the output of the fifth PI controller, the d-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model, and the impedance of the filter line between the voltage source converter and the common coupling point obtained in advance, the q-axis current feedforward decoupling compensation is simulated to construct the q-axis control sub-model. Based on the constructed d-axis control sub-model and q-axis control sub-model, the current control inner loop is obtained.

[0013] According to the present invention, a method for analyzing the stability of additional frequency control in a grid-connected converter includes the following steps before determining the impact of additional frequency control on damping and obtaining the stability assessment result of additional disturbances based on the transfer functions of the active power phase coupling channel and the reactive power phase coupling channel, combined with a small-signal model: First, based on the first PI controller and integrator in the phase-locked loop (PLL) sub-model, and combined with the impedance of the transmission line, a forward transmission sub-model is constructed for the forward channel; wherein, the forward channel is used to characterize the active control path that converts the power command input by the controller into the power output of the voltage source converter; Second, based on the grid voltage, the equivalent resistance of the transmission line, the impedance of the transmission line, and the PLL equilibrium point phase and grid frequency obtained from the equilibrium point in the PLL sub-model, combined with the active power and reactive power phase coupling channel transfer functions previously determined based on the system operating state and the converter model, a feedback transmission sub-model is constructed for the feedback channel; wherein, the feedback channel is used to characterize the sensing path that transmits the actual state of the voltage source converter and the grid back to the controller input; Third, based on the forward transmission sub-model and the feedback transmission sub-model, a small-signal model is obtained.

[0014] According to the present invention, a stability analysis method for additional frequency control of a grid-connected converter is provided. Based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with a small-signal model, the method determines the impact of additional frequency control on damping and obtains the stability assessment result of the additional disturbance. The method includes: determining the corrected synchronization coefficient and the corrected damping coefficient using the modified preset complex torque coefficient method based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with a small-signal model; wherein, the synchronization coefficient is used to characterize the active power output of the voltage source converter. The steady-state relationship between the rate and its common angle is established. The damping coefficient is used to characterize the ability of a voltage source converter to suppress power oscillations when the frequency fluctuates. The positive preset complex torque coefficient method is used to change the complex torque decomposition method by utilizing the decomposition coordinate axis of the rotating complex torque. Based on the forward transfer sub-model and the synchronization coefficient, the closed-loop transfer sub-model is determined. Based on the closed-loop transfer sub-model and the feedback transfer sub-model, the damping is determined and corrected using the corrected synchronization coefficient and the corrected damping coefficient to obtain the corrected damping coefficient. Based on the corrected damping coefficient, the influence of additional frequency control on damping is determined, and the additional disturbance stability assessment result is obtained.

[0015] This invention also provides a stability analysis device for additional frequency control of a grid-connected converter, comprising: a state acquisition module for acquiring the current operating state of a system characterizing the dynamic interaction between a voltage source converter and the power grid; a coefficient determination module for determining the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model; wherein the converter model is constructed based on the voltage source converter in the system; and a stability assessment module for determining the impact of additional frequency control on damping based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function and a small-signal model, thereby obtaining the stability assessment result of the additional disturbance; wherein the small-signal model is constructed based on the system.

[0016] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-described method for analyzing the stability of additional frequency control of a grid-connected converter.

[0017] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method for analyzing the stability of additional frequency control of a grid-connected converter.

[0018] The present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method for analyzing the stability of additional frequency control for grid-connected converters.

[0019] The present invention provides a method and apparatus for stability analysis of additional frequency control in grid-connected converters. By acquiring the current operating state of the system, it is easier to capture the trend of the system evolving from a stable state to an unstable state during subsequent evaluation. Combined with the converter model, the complex system is dynamically decoupled into active power phase coupling channels and reactive power phase coupling channels. This bypasses a large number of secondary and non-critical dynamic links in the system, directly focusing on the core contradiction that causes oscillations and quantifying its transfer function. This clarifies how the control strategy of the voltage source converter and the power grid jointly affect these coupling strengths. Furthermore, by combining a small-signal model, the damping characteristics of the system under additional disturbances are quantitatively evaluated, so as to efficiently and accurately quantify the impact of additional frequency control on the system damping characteristics and determine the stability evaluation results of the additional disturbance. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating the stability analysis method for additional frequency control in grid-connected converters provided by the present invention. Figure 2 This is a schematic diagram of the system structure of the stability analysis method for additional frequency control of grid-connected converters provided by the present invention. Figure 3 This is a schematic diagram of the converter control model provided by the present invention; Figure 4 This is a schematic diagram of the small signal model provided by the present invention; Figure 5 This is a schematic diagram illustrating the variation trend of the modified damping coefficient with the additional frequency control coefficient provided by the present invention. Figure 6 This is a schematic diagram illustrating the effect of changes in the additional frequency control parameters provided by this invention on phase angle oscillation; Figure 7 The different droop control coefficients (k) provided by this invention p Schematic diagram of phase oscillation curves under perturbation when (=0, 0.5, 1.5); Figure 8 The different droop control coefficients (k) provided by this inventionp Schematic diagram of the rotational speed oscillation curves under disturbances when the values ​​are 0, 0.5, and 1.5. Figure 9 The different droop control coefficients (k) provided by this invention p A schematic diagram of the output active power oscillation curve under disturbances of 0, 0.5, and 1.5. Figure 10 The different inertia control coefficients (k) provided by this invention d Schematic diagram of phase oscillation curves under perturbation when =0, 0.005, 0.01); Figure 11 The different inertia control coefficients provided by this invention are relatively small (k) d Schematic diagram of the rotational speed oscillation curve under disturbance (=0, 0.005, 0.01); Figure 12 The present invention provides a larger inertia control coefficient (k) d A schematic diagram of the output active power oscillation curve under disturbances of 0, 0.005, and 0.01. Figure 13 This is a schematic diagram of the structure of the frequency control stability analysis device for grid-connected converters provided by the present invention. Figure 14 This is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] Figure 1 This is a flowchart illustrating the stability analysis method for additional frequency control in grid-connected converters provided by this invention, as shown below. Figure 1 As shown, the method includes: S11, obtain the current operating state of the system characterizing the dynamic interaction between the voltage source converter and the power grid; wherein, the system is used to characterize the system characterizing the dynamic interaction between the voltage source converter and the power grid; S12, Based on the current operating status of the system and combined with the converter model, determine the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function; wherein, the converter model is constructed based on the voltage source converter in the system; S13. Based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with the small-signal model, the influence of additional frequency control on damping is determined, and the stability assessment results of the additional disturbance are obtained; among them, the small-signal model is constructed based on the system first.

[0024] It should be noted that the step number "S1N" in this manual does not represent the order of the frequency control stability analysis methods for grid-connected converters. The following details will explain the specific steps. Figures 2-12 This invention describes the stability analysis method for additional frequency control in grid-connected converters.

[0025] Step S11: Obtain the current operating status of the system that characterizes the dynamic interaction between the voltage source converter and the power grid.

[0026] It should be added that, for reference Figure 2 The system includes a controller, a voltage source converter (VSC), and a power grid. A point of common coupling (PCC) is established between the VSC and the power grid. A filter line connects the PCC and the VSC, and a transmission line connects the PCC and the power grid. Accordingly, the current operating status of the system includes the current status of the VSC, the current status of the PCC, and the current status of the power grid. The current status of the VSC includes the current active power, current reactive power, and corresponding current active power and reactive power commands output by the VSC. The current status of the PCC includes the current voltage and current of the PCC, and the current status of the power grid includes the current voltage and current of the power grid.

[0027] In an optional embodiment, before determining the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model, the process includes: SA1, construct a phase-locked loop sub-model based on the phase-locked loop in the voltage source converter.

[0028] Specifically, based on the phase-locked loop (PLL) in the voltage source converter, a PLL sub-model is constructed, including: determining the corresponding common coupling point voltage and common coupling point current based on the operating state of the common coupling point, and simulating the zero-q-axis voltage principle at the input terminal of the corresponding PLL of the voltage source converter to construct the PLL sub-model; wherein, the zero-q-axis voltage principle is used to: determine the q-axis voltage component, q-axis current component, and d-axis current component corresponding to the common coupling point based on the common coupling point voltage and common coupling point current, combined with the previously generated PLL phase; using the q-axis voltage component as an error signal, the generated PLL frequency and PLL phase are adjusted through a first proportional-integral (PI) controller and an integrator to ensure that the generated PLL frequency and PLL phase are consistent with the grid frequency and phase.

[0029] It should be noted that the PLL tracks the PCC voltage U t q-axis component U q To provide synchronization phase, U t Equivalent grid voltage U g and the equivalent impedance between VSC and the mains voltage U z The vector sum, U gq and U zq satisfy: in, Indicates grid voltage Voltage component on the q-axis; Indicates the phase of the phase-locked loop; This represents the impedance and voltage U between the transmission line and the power grid. z Components on the q-axis; Represents the equivalent resistance of the transmission line; This indicates the q-axis current component corresponding to the PCC current; Indicates the reactance of the transmission line; This indicates the d-axis current component corresponding to the PCC current; Indicates the phase-locked loop frequency; Indicates the power grid frequency.

[0030] Correspondingly, the voltage component of the grid voltage on the q-axis is expressed as: Furthermore, the phase-locked loop sub-model is represented as follows: in, Indicates the phase of the phase-locked loop The derivative; This represents the gain coefficient of the first PI controller; This represents the scaling factor of the first integrator; This represents the state variable introduced by the first PI controller, which is... The decision is Time integration is used to eliminate steady-state errors, ensuring that the PLL can function even with fixed deviations. Approaching 0; express The derivative; This indicates the q-axis voltage component corresponding to the PCC voltage.

[0031] SA2, based on the proportional-integral controller, uses the difference between the active power command value and the output active power of the voltage source converter as input, and the d-axis current of the outer loop output as output to construct an active power control outer loop; and, based on the proportional-integral controller, uses the difference between the reactive power command value and the output reactive power of the voltage source converter as input, and the q-axis current of the outer loop output as output to construct a reactive power control outer loop.

[0032] In this embodiment, according to the proportional-integral controller, the difference between the active power command value and the output active power of the voltage source converter is used as input, and the outer loop output d-axis current is used as output. This includes: obtaining the corresponding active power command value and output active power of the voltage source converter, as well as the phase-locked loop frequency obtained from the phase-locked loop sub-model, based on the voltage source converter; determining a first output result by using a first-order inertial element combined with additional inertial control coefficients to differentiate the phase-locked loop frequency obtained from the phase-locked loop sub-model, and by using a proportional-integral controller combined with additional droop control coefficients; determining a second output result by using a first-order inertial element combined with additional droop control coefficients to proportional-integrate the phase-locked loop frequency obtained from the phase-locked loop sub-model; and determining the outer loop output d-axis current using a second PI controller based on the first and second output results, combined with the active power output and active power command value of the voltage source converter, to construct an active power control outer loop.

[0033] It should be added that the active power control outer loop is represented as: in, This indicates the d-axis current output from the outer loop; Indicates the gain and proportional coefficient of the second PI controller; This represents the active power command value output by the voltage source converter; This indicates the active power output of the voltage source converter; The state variables of the second PI controller are represented by... Decide; express The derivative of .

[0034] Furthermore, when the VSC performs additional frequency control based on the frequency measurement signal from the PLL, the active power command value will change with the frequency, therefore... , Among them, the additional droop control simulates the primary frequency regulation of the synchronous generator. By introducing the difference between the frequency and the rated frequency, it provides power support and responds to changes in the grid frequency. Its output is proportional to the frequency deviation and is essentially a proportional element. The additional inertial control simulates the rotor inertia of the synchronous generator. By introducing the frequency change rate, it simulates the inertial response of the synchronous machine. Its output is proportional to the frequency change rate and is essentially a differential element, which suppresses rapid frequency changes in a very short time after a disturbance occurs.

[0035] Furthermore, according to the proportional-integral controller, the difference between the reactive power command value and the output reactive power of the voltage source converter is used as input, and the outer loop output q-axis current is used as output to construct a reactive power control outer loop. This includes: obtaining the reactive power command value and the output reactive power of the corresponding voltage source converter; using the difference between the reactive power command value and the output reactive power of the voltage source converter as input, and using a third PI controller to determine the outer loop output q-axis current to construct the reactive power control outer loop.

[0036] Furthermore, the reactive power control outer loop is represented as: in, This indicates the outer loop output q-axis current; Indicates the gain and proportional coefficient of the third PI controller; This indicates the reactive power output of the voltage source converter; This represents the reactive power command value output by the voltage source converter; This represents the state variables of the third PI controller, which are... Decide; express Differentiate it.

[0037] SA3, based on the phase-locked loop sub-model, active power outer loop and reactive optical power outer loop, combined with the impedance of the filter line between the voltage source converter and the common coupling point obtained in advance, simulates the d-axis and q-axis current control in the rotating coordinate system of the voltage source converter under feedforward decoupling, and constructs the current control inner loop.

[0038] Specifically, based on the phase-locked loop (PLL) sub-model, the active power outer loop, and the reactive power outer loop, and combined with the impedance of the filter line between the voltage source converter and the common coupling point obtained earlier, the d-axis and q-axis current control in the rotating coordinate system of the voltage source converter with feedforward decoupling is simulated to construct the current control inner loop. This includes: based on the d-axis current component corresponding to the common coupling point output by the PLL sub-model and the actual d-axis current value output by the active power control outer loop, combined with the fourth PI controller, simulating the adjustment process of the excitation system on the active power-related components, and based on the output of the fourth PI controller, combined with the q-axis current component corresponding to the common coupling point output by the PLL sub-model and the impedance of the filter line between the voltage source converter and the common coupling point obtained earlier. The impedance of the filter line between coupling points is used to simulate d-axis current feedforward decoupling compensation, and a d-axis control sub-model is constructed. Based on the q-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model and the actual q-axis current output by the reactive power control outer loop, combined with the fifth PI controller, the adjustment process of the excitation system on the reactive power related components is simulated. Based on the output of the fifth PI controller, combined with the d-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model and the impedance of the filter line between the voltage source converter and the common coupling point obtained earlier, the q-axis current feedforward decoupling compensation is simulated, and a q-axis control sub-model is constructed. Based on the constructed d-axis control sub-model and q-axis control sub-model, the current control inner loop is obtained.

[0039] It should be added that the current control inner loop is represented as: in, This represents the d-axis potential obtained based on the d-axis control sub-model; This indicates the gain and proportional coefficient of the fourth PI controller; This represents the d-axis current component of the outer loop output of the active power control outer loop. This represents the d-axis current component output by the phase-locked loop sub-model; The state variables of the fourth PI controller are represented by... Decide; Indicates the impedance of the filter line; This represents the q-axis current component output by the phase-locked loop sub-model; This indicates the gain and proportional coefficient of the fifth PI controller; This represents the q-axis current component of the outer loop output for reactive power control. The state variables of the fifth PI controller are represented by... Decide; express The derivative; express The derivative of .

[0040] SA4, based on the phase-locked loop sub-model, active power control outer loop, reactive power control outer loop, and current control inner loop, combined with Kirchhoff's voltage law (KVL) constraint on the internal electromotive force, yields the converter model. The KVL constraint on the internal electromotive force is constructed first based on the equivalent resistance of the transmission line between the common coupling point and the grid, the impedance of the transmission line, the impedance of the filter line, the grid voltage, and the grid current, combined with the phase-locked loop frequency generated by the phase-locked loop sub-model and the corresponding d-axis and q-axis current components at the common coupling point.

[0041] It should be added that the KVL constraint on the internal potential is expressed as: Where s represents the Laplace operator.

[0042] Step S12: Based on the current operating state of the system and the converter model, determine the transfer function of the active power phase coupling channel and the transfer function of the reactive power phase coupling channel; wherein, the converter model is constructed based on the voltage source converter in the system.

[0043] In this embodiment, based on the current operating state of the system and the converter model, the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function are determined, including: SB1 determines the current command value of reactive power, current reactive power, current command value of active power, current active power, current voltage and current of the common coupling point, and current voltage and current of the power grid based on the current operating status of the system; wherein, the common coupling point is used to characterize the coupling point between the voltage source converter and the power grid in the system.

[0044] SB2 inputs the current current and current voltage of the common coupling point into the phase-locked loop sub-model to obtain the phase-locked loop phase, phase-locked loop frequency, current current on the d-axis and current current on the q-axis, and linearizes the phase-locked loop sub-model using the system operating state at the equilibrium point to obtain the phase-locked loop phase disturbance; where the equilibrium point is used to characterize the operating point of the system's stable operation after grid connection.

[0045] It should be added that, for reference Figure 3The current current and voltage at the common coupling point are input into the phase-locked loop (PLL) sub-model. Combined with the PLL phase generated earlier, the current voltage and current of the PCC in the stationary coordinate system are converted to the rotating coordinate system, and the corresponding current voltage, current d-axis, and current q-axis are determined. The current current d-axis and current q-axis are input into the current control inner loop, and the current voltage q-axis is input into the first PI controller for proportional gain integration to obtain the PLL frequency. The PLL frequency is then input into the active power control outer loop and the integrator. The integrator differentiates the PLL frequency to obtain the PLL phase, which is used as the phase for the next calculation of the q-axis voltage component, d-axis current component, and q-axis current component.

[0046] In addition, the phase disturbance of the phase-locked loop is expressed as: in, This indicates the phase disturbance of the phase-locked loop; This represents the frequency disturbance of the phase-locked loop.

[0047] Furthermore, at the equilibrium point, the voltage component of the grid voltage on the q-axis is linearized to obtain the disturbance of the voltage component of the grid voltage on the q-axis, expressed as: This indicates the amount of disturbance in the current q-axis voltage at PCC; Indicates the current voltage of the power grid; The phase of the phase-locked loop at the equilibrium point; This indicates the phase disturbance of the phase-locked loop; Represents the equivalent resistance of the transmission line; This indicates the amount of disturbance to the current q-axis current at PCC; This indicates the amount of disturbance to the current d-axis current at PCC; Indicates the reactance of the transmission line; This indicates the grid frequency at the equilibrium point; This represents the d-axis current component at the equilibrium point PCC; This represents the frequency disturbance of the phase-locked loop.

[0048] It is worth noting that the equilibrium point is used to characterize the stable operating point of the system after grid connection. Additionally, because... It is the rotational speed relative to the synchronous rotating coordinate system, and its steady-state value is 0. Therefore The penultimate term in There is no This item has a value of 0.

[0049] SB3 inputs the phase-locked loop frequency, the current command value of the active power of the voltage source converter, and the current active power into the active power control outer loop to obtain the outer loop output d-axis current.

[0050] It should be added that you should continue to refer to this. Figure 3 The phase-locked loop frequency, the current active power command value of the voltage source converter, and the current active power are input into the active power control outer loop. Based on the phase-locked loop frequency, the first-order inertial element 1 / (T) is used to control the active power. d Simulate the delayed response (s+1) and differentiate it (s) to incorporate the differential result with the additional inertial control coefficient K. D Determine the corresponding first output result, and based on the phase-locked loop frequency, utilize the first-order inertial element 1 / (T) d s+1) simulates the delayed response, combined with an additional droop control coefficient K P The corresponding second output result is determined, and the first and second output results are added together. This sum, combined with the difference between the active power command value and the output active power of the voltage source converter, is then input into the second PI controller to obtain the outer loop output d-axis current of the second PI controller. .

[0051] SB4 inputs the current reactive power command value and the current reactive power of the voltage source converter into the reactive power control outer loop to obtain the outer loop output q-axis current.

[0052] Further reference Figure 3 The current reactive power command value and the current reactive power of the voltage source converter are input into the reactive power control outer loop to subtract the current reactive power command value from the current reactive power of the voltage source converter. The result is then input into the third PI controller to obtain the outer loop output q-axis current of the third PI controller. .

[0053] SB5 inputs the current d-axis current, the current q-axis current, the outer loop output d-axis current, and the outer loop output q-axis current into the current control inner loop, and performs linearization processing using the system operating state at the equilibrium point to obtain the first d-axis internal potential disturbance and the first q-axis internal potential disturbance.

[0054] Specifically, the potential disturbance in the first d-axis and the potential disturbance in the first q-axis are expressed as follows: in, This represents the potential disturbance within the first d-axis; This indicates the disturbance of the outer loop output d-axis current; This represents the potential disturbance within the first q-axis; This represents the disturbance of the q-axis current output of the outer loop.

[0055] SB6, based on the current voltage and current of the power grid, combined with the KVL constraint of the internal potential, and using the system operating state at the equilibrium point for linearization processing, obtains the internal potential disturbance of the second d-axis and the internal potential disturbance of the second q-axis.

[0056] Specifically, the potential disturbance in the second d-axis and the potential disturbance in the second q-axis are expressed as: SB7, based on the potential disturbance in the first d-axis, the potential disturbance in the first q-axis, and the potential disturbance in the first d-axis, the first outer loop output d-axis current disturbance and the first outer loop output q-axis current disturbance are obtained.

[0057] It should be noted that, based on the potential disturbances within the first d-axis, the first q-axis, and the first q-axis, the following can be eliminated: and The disturbance quantities of the first outer loop output d-axis current and the first outer loop output q-axis current are obtained and expressed as: in, This indicates the d-axis current disturbance of the first outer loop output; This indicates the q-axis current disturbance of the first outer loop output; Indicates the total impedance. .

[0058] Furthermore, let , , and Let represent the droop proportional coefficient and integral coefficient of the inner loop of the current control, respectively, and let: The d-axis current disturbance and the q-axis current disturbance of the first outer loop output can be further expressed as: SB8, based on the active power control outer loop and the reactive power control outer loop, performs linearization processing using the system operating state at the equilibrium point, and combines the phase-locked loop phase disturbance, the frequency change principle within the disturbance target time, and the active and reactive power output principles of the voltage source converter to determine the d-axis current disturbance of the second outer loop output and the q-axis current disturbance of the second outer loop output.

[0059] In this embodiment, determining the d-axis current disturbance of the second outer loop output and the q-axis current disturbance of the second outer loop output includes: linearizing the system operating state at the equilibrium point based on the active power control outer loop and the reactive power control outer loop to determine the corresponding d-axis current disturbance of the outer loop output and the q-axis current disturbance of the outer loop output; linearizing the system at the equilibrium point based on the frequency change principle within the disturbance target time, and combining it with the phase-locked loop phase disturbance to determine the active power command value disturbance; linearizing the active power and reactive power output principles of the voltage source converter at the equilibrium point, and combining it with the phase-locked loop phase disturbance to obtain the active power disturbance and reactive power disturbance; and determining the d-axis current disturbance of the second outer loop output and the q-axis current disturbance of the second outer loop output based on the d-axis current disturbance of the outer loop output and the q-axis current disturbance, combined with the active power command value disturbance, the active power disturbance, and the reactive power disturbance.

[0060] It should be added that, based on the active power control outer loop and the reactive power control outer loop, linearization is performed using the system operating state at the equilibrium point to determine the corresponding outer loop output d-axis current disturbance. and outer loop output q-axis current disturbance Specifically, it is expressed as: Furthermore, the frequency change principle within the target disturbance time is used to suppress the rate of frequency change, reduce the maximum frequency deviation (frequency minimum / maximum point), and help the frequency quickly recover to a new stable point when power disturbances occur in the power grid (such as sudden increases or decreases in load). Accordingly, the frequency change principle within the target disturbance time is expressed as: in, This indicates the active power command value without additional frequency control. This indicates an additional droop control factor; Indicates the phase-locked loop frequency; Indicates the rated angular frequency of the power grid; This represents the additional inertial control coefficient. It is worth noting that... The frequency control loop is added to facilitate subsequent research on the impact of changes in these two coefficients on small disturbances. When considering uncertainties such as signal measurement and control response delay, a first-order inertial element needs to be added to the control equation. The larger the time constant of this element, the weaker the frequency support effect. The smaller the time constant, the better it helps to improve the frequency dynamic response characteristics. Ignoring the first-order inertial element is equivalent to taking the time constant to 0.

[0061] Furthermore, linearization is performed at the equilibrium point to obtain the disturbance of the active power command value. , represented as: Furthermore, the active and reactive power output principles of voltage source converters are used to determine the corresponding actual output active and reactive power based on the measured voltage and current. Accordingly, the active and reactive power output principles of voltage source converters are expressed as follows: Furthermore, linearization is performed at the equilibrium point to obtain the active power disturbance. and reactive power disturbance , represented as: in, This indicates the phase of the phase-locked loop at the equilibrium point; This represents the q-axis current component at the equilibrium point PCC.

[0062] Furthermore, the d-axis current disturbance of the second outer loop output and the q-axis current disturbance of the second outer loop output are expressed as follows: Furthermore, let , , and Let represent the droop proportionality coefficient and integral coefficient of the outer ring, respectively, and let: The disturbance of the d-axis current and the disturbance of the q-axis current of the second outer loop output can be further expressed as: SB9, based on the d-axis current disturbance of the first outer loop output, the q-axis current disturbance of the first outer loop output, the d-axis current disturbance of the second outer loop output, and the q-axis current disturbance of the second outer loop output, the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function are obtained.

[0063] It should be added that, based on the d-axis current disturbance of the first outer loop output, the q-axis current disturbance of the first outer loop output, the d-axis current disturbance of the second outer loop output, and the q-axis current disturbance of the second outer loop output, the disturbance is eliminated. and The result is: Next, the order is: Therefore, we get: Will and use This means that we can solve for: in, This represents the active power phase coupling channel transfer function; This represents the reactive power phase coupling channel transfer function.

[0064] In one alternative embodiment, reference Figure 4 Before determining the impact of additional frequency control on damping and obtaining the additional disturbance stability assessment results based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with the small-signal model, the process includes: constructing a forward transfer sub-model of the forward channel based on the first PI controller and integrator in the phase-locked loop sub-model, combined with the impedance of the transmission line; wherein, the forward channel is used to characterize the active control path that converts the power command input by the controller into the power output of the voltage source converter; constructing a feedback transfer sub-model of the feedback channel based on the grid voltage, the equivalent resistance of the transmission line, the impedance of the transmission line, and the phase-locked loop equilibrium point phase and the grid frequency at the equilibrium point obtained by the phase-locked loop sub-model based on the equilibrium point, combined with the active power and reactive power phase coupling channel transfer functions determined earlier based on the system operating state and the converter model; wherein, the feedback channel is used to characterize the sensing path that transmits the actual state of the voltage source converter and the grid back to the controller input; and obtaining the small-signal model based on the forward transfer sub-model and the feedback transfer sub-model.

[0065] The forward pass sub-model is represented as follows: The feedback propagation sub-model is represented as: Step S13: Based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, and combined with the small-signal model, determine the impact of additional frequency control on damping, and obtain the additional disturbance stability assessment result; wherein, the small-signal model is constructed based on the system in advance.

[0066] In this embodiment, based on the active power phase-coupled channel transfer function and the reactive power phase-coupled channel transfer function, combined with the small-signal model, the influence of additional frequency control on damping is determined, and the additional disturbance stability assessment result is obtained. This includes: determining the corrected synchronization coefficient and the corrected damping coefficient using the modified preset complex torque coefficient method based on the active power phase-coupled channel transfer function and the reactive power phase-coupled channel transfer function, combined with the small-signal model; wherein, the synchronization coefficient is used to characterize the steady-state relationship between the active power output of the voltage source converter and its common angle, the damping coefficient is used to characterize the ability of the voltage source converter to suppress power oscillations when the frequency fluctuates, and the positive preset complex torque coefficient method is used to change the complex torque decomposition method using the decomposition coordinate axis of the rotating complex torque; determining the closed-loop transmission sub-model based on the forward transmission sub-model and the synchronization coefficient; determining the damping based on the closed-loop transmission sub-model and the feedback transmission sub-model, and correcting it using the corrected synchronization coefficient and the corrected damping coefficient to obtain the corrected damping coefficient; and determining the influence of additional frequency control on damping based on the corrected damping coefficient to obtain the additional disturbance stability assessment result.

[0067] It should be noted that, inspired by the traditional complex torque coefficient method, the small-signal model is determined based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, and the corresponding negative feedback channel is decomposed into synchronization coefficient and damping coefficient. Substituting this into the feedback propagation sub-model, where j represents the imaginary unit, Indicates the subsynchronous oscillation frequency, which will be compared with... The in-phase component is defined as the synchronization coefficient. ,and The in-phase component is defined as the damping coefficient. The feedback propagation sub-model is obtained, which is represented as: At this point, the forward transit submodel satisfies: Furthermore, the closed-loop transitive sub-model is represented as: Where M(s) represents the synchronization coefficient.

[0068] Accordingly, based on the closed-loop transfer sub-model and the feedback transfer sub-model, the characteristic equation and characteristic roots of the second-order system are determined, and the damping is obtained. The characteristic equation and characteristic roots of the second-order system are expressed as follows: Damping is expressed as: It is worth noting that the necessary and sufficient condition for the system's small disturbance stability is that all poles of the transfer sub-model are located on the left side of the complex plane. Based on this condition, it can be found that small disturbance stability of the VSC requires the synchronization coefficient MS > 0, while the damping coefficient MD can be positive or negative. This is because the proportional term of the PI control in the VSC has a significant impact on the small-signal stability characteristics, unlike the small-signal stability condition of a synchronous generator (where both MS and MD must be greater than 0). The proportional term of the first PI controller "converts" a portion of the synchronous torque into a damping effect; therefore, even when the damping torque is negative and the synchronous torque is positive, it is still possible to satisfy the small disturbance stability constraint.

[0069] Furthermore, using the modified pre-defined complex torque coefficient method, the modified synchronization coefficient and the modified damping coefficient are determined, expressed as follows: Accordingly, damping is expressed as: As can be seen from the damping expression, when the system's corrected damping coefficient... When positive, damping When the value is positive, all poles of the transfer sub-model lie in the left half of the complex plane, and the system exhibits small-signal stability. The larger the modified damping coefficient, the stronger the modified damping. For the system to be stable under small disturbances, the following constraints must be satisfied: By combining modified damping and constraint conditions, the effect of additional frequency control on damping is determined, and the stability assessment results of the additional disturbance are obtained.

[0070] Furthermore, after obtaining the stability assessment results of the additional disturbance, the process also includes: adjusting the additional inertial control coefficient K within a preset correction range based on the stability assessment results of the additional disturbance. D and additional droop control coefficient K P .

[0071] In an optional embodiment, when considering additional frequency control, the trend of the modified damping coefficient change when the additional frequency control coefficient is changed is as follows: Figure 5 As shown in the figure. From the figure, it can be seen that the corrected damping coefficient... Follow It increases with the increase of, and with It decreases as it increases.

[0072] In an alternative embodiment, based on the verification of the above-mentioned conclusion regarding the effect of additional frequency control on the stability of small disturbances, a 12th-order single-machine infinite bus system was built in MATLAB for simulation verification of the above system. The simulation parameter settings are shown in Table 1, with a frequency disturbance applied at 0.1s.

[0073] Table 1 System Parameters Add active frequency support control to the system to maintain Keep it unchanged, change the additional frequency droop control coefficient The result is as follows Figure 6 As shown by the red dashed line in the figure, frequency droop control has a positive effect on the damping of the dominant oscillation of the phase-locked loop. Increase, and damping increases.

[0074] Furthermore, maintain Keep it unchanged, change the additional inertial control coefficient The result is as follows Figure 6 As shown by the blue dashed line in the figure, virtual inertia control also has a certain impact on damping. As the damping increases, the damping decreases, but ultimately the damping will not decrease to a negative value.

[0075] Keep Different additional droop control coefficients The simulation results are as follows Figure 7-9 As shown, Figure 7 No additional droop control factor (k) p Phase oscillation curve under perturbation when =0). Figure 8 To add a smaller droop control coefficient (k) p Phase oscillation curve when (=0.5), Figure 9 To add a large droop control coefficient (k) p The phase oscillation curve is shown when (=1.5). As can be seen from the figure, when... When the value of is 0, 0.5, and 1.5, the system oscillates and converges after frequency disturbances. As the frequency increases, the output power decreases to suppress frequency oscillations. As the value increases, the phase oscillation amplitude of the PLL decreases significantly, indicating that... Increasing the damping will increase the damping.

[0076] Keep Different virtual inertia coefficients The simulation results are as follows Figure 10-12 As shown, Figure 10 For the no-additional-inertia control coefficient (k) d Phase oscillation curve under perturbation when =0). Figure 11 The additional inertia control coefficient is relatively small (k) d Phase oscillation curve when (=0.005), Figure 12 The additional inertia control coefficient is relatively large (k) d The phase oscillation curve when =0.01). As shown in the figure, when... When the value is 0.005, the waveform oscillation amplitude increases compared to when there is no virtual inertia control.

[0077] In summary, this invention, by acquiring the current operating state of the system, facilitates subsequent evaluation by capturing the trend of the system evolving from a stable state to an unstable state. Combined with a converter model, the complex system is dynamically decoupled into active power phase coupling channels and reactive power phase coupling channels. This bypasses numerous secondary, non-critical dynamic links in the system, directly focusing on the core contradictions causing oscillations and quantifying their transfer functions. This clarifies how the control strategy of the voltage source converter and the power grid jointly influence these coupling strengths. Furthermore, by combining a small-signal model, the damping characteristics of the system under additional disturbances are quantitatively evaluated, efficiently and accurately quantifying the impact of additional frequency control on the system's damping characteristics and determining the stability evaluation results of the additional disturbance.

[0078] The following describes the frequency control stability analysis device for grid-connected converters provided by the present invention. The frequency control stability analysis device for grid-connected converters described below can be referred to in correspondence with the frequency control stability analysis method for grid-connected converters described above.

[0079] Figure 14 A schematic diagram of a frequency control stability analysis device for a grid-connected converter is shown. The device includes: The status acquisition module 131 acquires the current operating status of the system representing the dynamic interaction between the voltage source converter and the power grid; The coefficient determination module 132 determines the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model; wherein, the converter model is constructed based on the voltage source converter in the system. The stability assessment module 133, based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with the small-signal model, determines the impact of additional frequency control on damping and obtains the stability assessment results of the additional disturbance; wherein, the small-signal model is constructed based on the system in advance.

[0080] It should be noted that the specific principles of the embodiments of the present invention are the same as those of the method embodiments described above. For details, please refer to the method embodiments above. More detailed explanations will not be repeated here.

[0081] Figure 14 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 14As shown, the electronic device may include: a processor 1410, a communication interface 1420, a memory 1430, and a communication bus 1440. The processor 1410, communication interface 1420, and memory 1430 communicate with each other via the communication bus 1440. The processor 1410 can call logic instructions in the memory 1430 to execute a stability analysis method for additional frequency control of a grid-connected converter. This method includes: obtaining the current operating state of the system characterizing the dynamic interaction between the voltage source converter and the power grid; determining the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model; wherein the converter model is constructed based on the voltage source converter in the system; and determining the impact of additional frequency control on damping based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with a small-signal model, to obtain the stability assessment result of the additional disturbance; wherein the small-signal model is constructed based on the system.

[0082] Furthermore, the logical instructions in the aforementioned memory 1430 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0083] On the other hand, the present invention also provides a computer program product, which includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the stability analysis method for additional frequency control of grid-connected converters provided by the above methods. This method includes: obtaining the current operating state of a system characterizing the dynamic interaction between a voltage source converter and the power grid; determining the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and in conjunction with the converter model; wherein the converter model is constructed based on the voltage source converter in the system; determining the impact of additional frequency control on damping based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, in conjunction with a small-signal model, and obtaining the stability assessment result of the additional disturbance; wherein the small-signal model is constructed based on the system.

[0084] In another aspect, the present invention also provides a non-transitory computer-readable storage medium storing a computer program thereon. When executed by a processor, the computer program performs the above-described method for analyzing the stability of additional frequency control in a grid-connected converter. This method includes: obtaining the current operating state of a system characterizing the dynamic interaction between a voltage source converter and the power grid; determining the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and a converter model; wherein the converter model is constructed prior to the voltage source converter in the system; and determining the impact of additional frequency control on damping based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with a small-signal model, to obtain an additional disturbance stability assessment result; wherein the small-signal model is constructed prior to the system.

[0085] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0086] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing the stability of an additional frequency control in a grid-connected converter, characterized in that, include: Obtain the current operating status of the system that represents the dynamic interaction between the voltage source converter and the power grid; Based on the current operating state of the system and in conjunction with the converter model, the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function are determined; wherein, the converter model is constructed based on the voltage source converter in the system. Based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with the small-signal model, the influence of additional frequency control on damping is determined, and the additional disturbance stability assessment result is obtained; wherein, the small-signal model is constructed based on the system.

2. The stability analysis method for additional frequency control of grid-connected converters according to claim 1, characterized in that, Before determining the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model, the following steps are included: Based on the phase-locked loop in the voltage source converter, construct a phase-locked loop sub-model; According to the proportional-integral controller, the difference between the active power command value and the output active power of the voltage source converter is used as input, and the d-axis current of the outer loop output is used as output to construct an active power control outer loop; and according to the proportional-integral controller, the difference between the reactive power command value and the output reactive power of the voltage source converter is used as input, and the q-axis current of the outer loop output is used as output to construct a reactive power control outer loop. Based on the phase-locked loop sub-model, the active power outer loop, and the reactive optical power outer loop, and combined with the impedance of the filter line between the voltage source converter and the common coupling point obtained earlier, the d-axis and q-axis current control in the rotating coordinate system of the voltage source converter under feedforward decoupling is simulated to construct the current control inner loop. Based on the phase-locked loop sub-model, the active power control outer loop, the reactive power control outer loop, and the current control inner loop, and combined with the Kirchhoff voltage law (KVL) constraint of the internal potential, the converter model is obtained. The KVL constraint of the internal potential is constructed first based on the equivalent resistance of the transmission line between the common coupling point and the power grid, the impedance of the transmission line, the impedance of the filter line, the grid voltage, and the grid current, combined with the phase-locked loop frequency generated by the phase-locked loop sub-model and the d-axis and q-axis current components corresponding to the common coupling point.

3. The method for analyzing the stability of additional frequency control in a grid-connected converter according to claim 2, characterized in that, Based on the current operating state of the system and the converter model, the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function are determined, including: Based on the current operating status of the system, determine the current command value of reactive power, current reactive power, current command value of active power, current active power, current voltage and current of the common coupling point, and current voltage and current of the power grid of the voltage source converter; wherein, the common coupling point is used to characterize the coupling point between the voltage source converter and the power grid in the system; The current current and current voltage of the common coupling point are input into the phase-locked loop sub-model to obtain the phase-locked loop phase, phase-locked loop frequency, current current on the d-axis and current current on the q-axis. The phase-locked loop sub-model is linearized using the system operating state at the equilibrium point to obtain the phase-locked loop phase disturbance. The equilibrium point is used to characterize the operating point of the system after grid connection for stable operation. The phase-locked loop frequency, the current active power command value of the voltage source converter, and the current active power are input into the active power control outer loop to obtain the outer loop output d-axis current; The current reactive power command value and current reactive power of the voltage source converter are input into the reactive power control outer loop to obtain the outer loop output q-axis current. The current current of the d-axis, the current current of the q-axis, the output d-axis current of the outer loop, and the output q-axis current of the outer loop are input into the current control inner loop, and linearized using the system operating state at the equilibrium point to obtain the first d-axis internal potential disturbance and the first q-axis internal potential disturbance. Based on the current voltage and current of the power grid, combined with the KVL constraints of the internal potential, and using the system operating state at the equilibrium point for linearization processing, the second d-axis internal potential disturbance and the second q-axis internal potential disturbance are obtained. Based on the first d-axis internal potential disturbance, the first q-axis internal potential disturbance, the first d-axis internal potential disturbance, and the first q-axis internal potential disturbance, the first outer loop output d-axis current disturbance and the first outer loop output q-axis current disturbance are obtained. Based on the active power control outer loop and the reactive power control outer loop, linearization is performed using the system operating state at the equilibrium point. Combined with the phase-locked loop phase disturbance, the frequency change principle within the disturbance target time, and the active and reactive power output principles of the voltage source converter, the d-axis current disturbance and q-axis current disturbance of the second outer loop output are determined. The frequency change principle within the disturbance target time is used to suppress the rate of frequency change, reduce the maximum frequency deviation, and help the frequency quickly recover to a new stable point when power disturbances occur in the power grid. The active and reactive power output principles of the voltage source converter are used to determine the corresponding actual output active and reactive power based on the measured voltage and current. Based on the first outer loop output d-axis current disturbance, the first outer loop output q-axis current disturbance, the second outer loop output d-axis current disturbance, and the second outer loop output q-axis current disturbance, the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function are obtained.

4. The stability analysis method for additional frequency control of grid-connected converters according to claim 2, characterized in that, Based on the phase-locked loop (PLL) in the voltage source converter, a PLL sub-model is constructed, including: Based on the operating state of the common coupling point, the corresponding common coupling point voltage and common coupling point current are determined, and the q-axis voltage zeroing principle at the input terminal of the corresponding phase-locked loop of the voltage source converter is simulated to construct a phase-locked loop sub-model; wherein, the q-axis voltage zeroing principle is used for: Based on the common coupling point voltage and the common coupling point current, and combined with the phase of the previously generated phase-locked loop, determine the q-axis voltage component, q-axis current component, and d-axis current component corresponding to the common coupling point; The q-axis voltage component is used as an error signal. The generated phase-locked loop frequency and phase are adjusted by the first proportional-integral (PI) controller and integrator to ensure that the generated phase-locked loop frequency and phase are consistent with the grid frequency and phase.

5. The method for analyzing the stability of additional frequency control in a grid-connected converter according to claim 2, characterized in that, According to the proportional-integral controller, the difference between the active power command value and the output active power of the voltage source converter is used as input, and the outer loop output d-axis current is used as output, including: Based on the voltage source converter, obtain the corresponding active power command value and output active power of the voltage source converter, as well as the phase-locked loop frequency obtained from the phase-locked loop sub-model; Based on the phase-locked loop frequency obtained from the phase-locked loop sub-model, a first output result is determined by using a first-order inertial element and combining it with an additional inertial control coefficient for differentiation, and by using an additional droop control coefficient for proportional integration; and a second output result is determined by using a first-order inertial element and combining it with an additional droop control coefficient for proportional integration based on the phase-locked loop frequency obtained from the phase-locked loop sub-model. Based on the first output result and the second output result, and combined with the active power output and active power command value of the voltage source converter, the outer loop output d-axis current is determined using the second PI controller to construct the active power control outer loop.

6. The stability analysis method for additional frequency control of grid-connected converters according to claim 2, characterized in that, According to the proportional-integral controller, the difference between the reactive power command value and the output reactive power of the voltage source converter is used as input, and the outer loop output q-axis current is used as output to construct a reactive power control outer loop, including: Based on the voltage source converter, obtain the reactive power command value and the output reactive power of the corresponding voltage source converter; The difference between the reactive power command value and the output reactive power of the voltage source converter is used as input, and the outer loop output q-axis current is determined by the third PI controller to construct the reactive power control outer loop.

7. The method for analyzing the stability of additional frequency control in a grid-connected converter according to claim 2, characterized in that, Based on the phase-locked loop sub-model, the active power outer loop, and the reactive optical power outer loop, and combined with the previously obtained impedance of the filter line between the voltage source converter and the common coupling point, the d-axis and q-axis current control in the rotating coordinate system of the voltage source converter under feedforward decoupling is simulated to construct the current control inner loop, including: Based on the d-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model and the actual d-axis current value output by the active power control outer loop, combined with the fourth PI controller, the adjustment process of the excitation system on the active power related components is simulated. Based on the output of the fourth PI controller, combined with the q-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model and the impedance of the filter line between the voltage source converter and the common coupling point obtained in advance, the d-axis current feedforward decoupling compensation is simulated, and the d-axis control sub-model is constructed. Based on the q-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model and the actual q-axis current output by the reactive power control outer loop, combined with the fifth PI controller, the adjustment process of the excitation system on the reactive power related components is simulated. Based on the output of the fifth PI controller, combined with the d-axis current component corresponding to the common coupling point output by the phase-locked loop sub-model and the impedance of the filter line between the voltage source converter and the common coupling point obtained in advance, the q-axis current feedforward decoupling compensation is simulated, and the q-axis control sub-model is constructed. Based on the constructed d-axis control sub-model and the constructed q-axis control sub-model, the current control inner loop is obtained.

8. The method for analyzing the stability of additional frequency control in a grid-connected converter according to claim 4, characterized in that, Before determining the impact of additional frequency control on damping and obtaining the additional disturbance stability assessment results based on the active power phase-coupled channel transfer function and the reactive power phase-coupled channel transfer function, combined with the small-signal model, the following steps are included: Based on the first PI controller and integrator in the phase-locked loop sub-model, and combined with the impedance of the transmission line, a forward transmission sub-model of the forward channel is constructed; wherein, the forward channel is used to characterize the active control path that converts the power command input by the controller into the power output of the voltage source converter; Based on the grid voltage, the equivalent resistance of the transmission line, the impedance of the transmission line, and the phase-locked loop (PLL) equilibrium point phase and grid frequency obtained from the equilibrium point in the PLL sub-model, combined with the active and reactive power phase coupling channel transfer functions previously determined based on the system operating state and the converter model, a feedback transfer sub-model for the feedback channel is constructed. The feedback channel characterizes the sensing path that transmits the actual states of the voltage source converter and the grid back to the controller input. Based on the forward transit sub-model and the feedback transit sub-model, the small signal model is obtained.

9. The method for analyzing the stability of additional frequency control in a grid-connected converter according to claim 8, characterized in that, Based on the active power phase-coupled channel transfer function and the reactive power phase-coupled channel transfer function, and combined with the small-signal model, the impact of additional frequency control on damping is determined, and the additional disturbance stability assessment results are obtained, including: Based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with the small-signal model, the corrected synchronization coefficient and the corrected damping coefficient are determined using the modified preset complex torque coefficient method. The synchronization coefficient characterizes the steady-state relationship between the active power output of the voltage source converter and its common angle; the damping coefficient characterizes the ability of the voltage source converter to suppress power oscillations when the frequency fluctuates; and the positive preset complex torque coefficient method is used to change the complex torque decomposition method by utilizing the decomposition coordinate axis of the rotating complex torque. Based on the forward transfer sub-model and the synchronization coefficient, the closed-loop transfer sub-model is determined; Based on the closed-loop transfer sub-model and the feedback transfer sub-model, the damping is determined, and then corrected using the corrected synchronization coefficient and the corrected damping coefficient to obtain the corrected damping coefficient. Based on the modified damping coefficient, the effect of additional frequency control on damping is determined, and the results of the additional disturbance stability assessment are obtained.

10. A frequency control stability analysis device for a grid-connected converter, characterized in that, include: The status acquisition module acquires the current operating status of the system, which represents the dynamic interaction between the voltage source converter and the power grid. The coefficient determination module determines the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function based on the current operating state of the system and the converter model; wherein, the converter model is constructed based on the voltage source converter in the system. The stability assessment module, based on the active power phase coupling channel transfer function and the reactive power phase coupling channel transfer function, combined with the small-signal model, determines the impact of additional frequency control on damping and obtains the stability assessment result of the additional disturbance; wherein, the small-signal model is constructed based on the system in advance.

Images