A method and system for improving transient stability of a grid-following-inverter hybrid system

Abstract

The application discloses a network-keeping variable converter hybrid system transient stability promotion method and system, relates to the power electronic technology field, and solves the problem of the coupling effect between the network-keeping variable converter and the network-keeping variable converter increasing the system instability risk. The method comprises the following steps: constructing a network-keeping variable converter nonlinear state equation based on a network-keeping variable converter hybrid topology; extracting an interactive power item based on the network-keeping variable converter nonlinear state equation; constructing a damping additional item model based on the interactive power item, and calculating an additional damping coefficient through the damping additional item model; forming an additional damping signal based on the additional damping coefficient and a system rated angular frequency, and introducing the additional damping signal into an active power control loop of a virtual synchronous generator of the network-keeping variable converter to jointly act with an original damping item. A feedback is formed by introducing the additional damping signal, the output phase of the network-keeping variable converter is adjusted, and then the output power of the network-keeping variable converter is changed.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a method for improving transient stability in a grid-connected converter hybrid system. Background Technology

[0002] As the proportion of heterogeneous converters in microgrids continues to increase, the hybrid architecture integrating grid-forming (GFM) and grid-following converters has become crucial for supporting a high proportion of renewable energy grid connection. While grid-following converters offer fast dynamic response, they lack voltage-frequency support capabilities, while grid-forming converters, although possessing virtual inertia, require additional energy storage and have a slower dynamic response. Parallel operation of the two has become the mainstream approach in practical engineering.

[0003] However, traditional research largely focuses on designing synchronous control strategies for single-machine connected-to-infinite-bus (SMIB) systems. The understanding of the complex heterogeneous interactions between grid-connected and grid-linked converters and their impact on system transient stability is insufficient, and control methods to improve system transient stability by suppressing undesirable interactions are lacking. Under complex power grid conditions, the coupling effect between grid-connected and grid-linked converters can significantly increase the risk of system instability. Summary of the Invention

[0004] To address the problem that the coupling effect between grid-connected and grid-linked converters in existing technologies can significantly increase the risk of system instability, this invention provides a method and system for improving the transient stability of a hybrid grid-connected converter system. This method can suppress phase interaction oscillations in the hybrid system, ultimately improving the system's transient stability under large disturbances. The specific technical solution is as follows: A method for improving transient stability in a grid-connected converter hybrid system includes the following steps: constructing a nonlinear state equation for the grid-connected converter based on the grid-connected converter hybrid topology; extracting the interactive power term of the grid-connected converter based on the nonlinear state equation; constructing a damping additional term model based on the interactive power term of the grid-connected converter, and calculating the additional damping coefficient through the damping additional term model; forming an additional damping signal based on the additional damping coefficient and the system rated angular frequency, and introducing the additional damping signal into the virtual synchronous generator active power control loop of the grid-connected converter to work together with the original damping term.

[0005] Preferably, constructing the nonlinear state equation of the grid-connected converter based on the grid-connected converter hybrid topology includes: constructing the q-axis voltage component equation of the grid-connected converter at the common connection point; Construct the active power output equation and reactive power equation for the grid-type converter; The dynamic behavior equations of the phase-locked loop of the grid converter and the dynamic behavior equations of the virtual synchronous generator of the grid converter are constructed. The nonlinear state equations of the grid-connected converter are constructed based on the q-axis voltage component equations at the common connection point of the grid-connected converter, the active power output equations and reactive power output equations of the grid-connected converter, the dynamic behavior equations of the phase-locked loop, and the dynamic behavior equations of the virtual synchronous generator.

[0006] Preferably, the nonlinear state equation of the grid-connected converter is: In the formula, J 1 represents the equivalent inertia of the grid-type converter. J 2 represents the equivalent inertia of the grid-type converter. P M1 To match the equivalent mechanical power of the grid converter, P M2 The equivalent mechanical power of the grid-type converter, P E1 To match the equivalent electromagnetic power of the grid converter, P E2 The equivalent electromagnetic power of a grid-type converter. P int1 To compare with the equivalent electromagnetic interaction power of the grid converter, P int2 The equivalent electromagnetic interaction power of a grid-type converter. D 1 represents the equivalent damping coefficient of the grid-connected converter. D 2 represents the equivalent damping coefficient of the grid-type converter. D int1 The equivalent interactive damping coefficient, To match the angular velocity deviation of the grid converter, To match the virtual power angle of the grid converter, For amplitude and phase, To match the virtual power angle of the grid converter, For amplitude and phase, For the angular velocity deviation of the grid-type converter, i e For amplitude and phase, The current reference vector power factor angle of the grid-type converter.

[0007] Preferably, the interactive power term of the grid-connected converter is: P int2 cos( d 2- d 1- ie -π / 2).

[0008] The preferred damping additional term model is: , ,max( oh 2cr ) indicates the stability region oh The maximum frequency value of 2, For the additional damping coefficient, It is a positive adjustable coefficient. It refers to the amplitude and phase.

[0009] Preferably, an additional damping signal is generated based on the additional damping coefficient and the system's rated angular frequency. This additional damping signal is then introduced into the active power control loop of the virtual synchronous generator in the grid-connected converter, working in conjunction with the original damping term. This includes: generating the additional damping signal based on the additional damping coefficient and the system's rated angular frequency; real-time monitoring of the operating data of the grid-connected converter hybrid system; calculating the active power deviation of the grid-connected converter based on the operating data; calculating the real-time angular frequency based on the active power deviation of the grid-connected converter; calculating the frequency deviation based on the real-time angular frequency; calculating the original damping adjustment term based on the frequency deviation; superimposing the original damping term with the additional damping signal to obtain the total damping term; and sending the total damping term to the power deviation comparison loop for feedback adjustment of the power error.

[0010] Preferably, calculating the active power deviation of the grid converter based on operating data includes: calculating the active power output of the grid converter; and calculating the active power deviation of the grid converter based on the active power output.

[0011] Preferably, the calculation of the real-time angular frequency based on the active power deviation of the grid-type converter includes: inputting the active power deviation of the grid-type converter into a preset integrator and outputting the corresponding real-time angular frequency.

[0012] Preferably, the active power output equation for a grid-type converter is: In the formula, The active power output of the grid-type converter. E The output voltage amplitude of the grid-connected converter. V g The voltage amplitude of the power grid. For the virtual power angle of the grid-type converter, For equivalent susceptance, For equivalent amplitude, For equivalent amplitude, This is the current reference value. For amplitude and phase, For amplitude and phase, The power factor angle.

[0013] The present invention also provides a transient stability improvement system for a grid-connected converter hybrid system, which is applied to the above-mentioned transient stability improvement method for a grid-connected converter hybrid system.

[0014] Compared with existing technologies, the beneficial effects of this invention are as follows: by adding an additional damping signal to form feedback, the output phase of the grid-type converter is adjusted, thereby changing the output power of the grid-type converter, suppressing phase interaction oscillations in the hybrid system, and ultimately improving the transient stability of the system under large disturbances. This control method only applies additional damping when the system shows signs of instability, without changing the original steady-state operating point of the system, and will not have any additional impact on the normal operation of the system. At the same time, it can make full use of the damping resources of the grid-type converter itself, without requiring modification to the control structure of the grid-type converter, making it easy to implement and highly adaptable. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0016] Figure 1 This is a schematic diagram of transient stability control of a grid-connected converter hybrid system based on a damping additional term model, as shown in Example 1. Figure 2 This is a flowchart of the method in Example 1; Figure 3 This is a topology diagram of a grid-connected converter hybrid system in Example 2; Figure 4 This is a comparison chart showing the robustness verification of the time delay in Example 2; Figure 5 This is a comparison chart showing the robustness verification of the power angle observation error in Example 2; Figure 6 This is a schematic diagram of the RT-Lab simulation in Example 2; Figure 7 This is a schematic diagram of the experimental results for calculating the additional damping signal based on 1.0 pu Zg in Example 2; Figure 8 This is a schematic diagram of the experimental results for calculating the additional damping signal based on 0.8 pu Zg in Example 2; Figure 9 This is a schematic diagram of the experimental results for calculating the additional damping signal based on 1.2 pu Zg in Example 2; Figure 10 This is a schematic diagram of the experimental results of Example 2 without the addition of an additional damping signal. Detailed Implementation

[0017] The technical solutions of the embodiments of the present 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 the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0019] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0020] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0021] This embodiment provides a method for improving the transient stability of a grid-connected converter hybrid system, which includes the following steps: S1. Construct the nonlinear state equations for the grid-connected converter based on the grid-connected converter hybrid topology. Specifically, step S1 includes the following steps: S11. Construct the q-axis voltage component equations of the grid converter at the point of common coupling.

[0022] In the topology architecture, the grid-connected converter relies on a phase-locked loop (PLL) to achieve synchronization with the AC power network, which is achieved through the grid connection point voltage. V GFL To track the grid phase. Therefore, in the phase-locked loop synchronization coordinate system, it tracks the q-axis voltage component of the grid-type converter at the point of common coupling. V PCC1q The equation can be derived as follows: ,in, , , To reference the d-axis current value on the grid-connected converter side, To reference the q-axis current value on the grid-connected converter side, , , The amplitude coefficient, , , For amplitude and phase, The power angle difference between grid-connected and grid-connected converters, The output voltage amplitude of the grid-connected converter. This refers to the grid voltage. The amplitude coefficient in the expression... to and amplitude and phase to It is given by the following equation: ;in, To match the virtual power angle of the grid converter, d 1= i PLL - i g， i PLL To match the phase of the grid converter, i g The phase of the grid voltage; Z GFL This indicates the line impedance from the grid-connected converter to the parallel connection point; Z GFM This represents the line impedance from the grid converter to the parallel connection point; Z g It represents the equivalent impedance of the AC power grid side.

[0023] S12. Construct the active power output equation and reactive power equation of the grid-type converter. Based on the topology, construct the active power output equation and reactive power output equation of the grid-type converter. The equation for the active power output of the grid-type converter is as follows: The reactive power output equation of the grid-type converter is: ,in, E The output voltage amplitude of the grid-connected converter. V g The voltage amplitude of the power grid. For the virtual power angle of the grid-type converter, d 2= i VSG - i g , i VSG For grid-type converter phase, i g The phase of the grid voltage; The power angle difference between grid-connected and grid-connected converters, The virtual part, This is the grid voltage. For equivalent amplitude, For amplitude and phase, This is the current reference value. For equivalent amplitude, The power angle difference between grid-connected and grid-connected converters, For amplitude and phase, The power factor angle.

[0024] Furthermore, the correlation coefficient m e and phase angle i e , and its part G e virtual part B e The definition is shown in the following equation: ,in, The impedance of the grid-type converter. The admittance of the grid-type converter, This is the equivalent complex admittance on the grid side. Z g Represents the equivalent impedance of the AC power grid side. It is an imaginary number. For equivalent conductance, This is the equivalent susceptance.

[0025] S13. Construct the dynamic behavior equations of the phase-locked loop and the virtual synchronous generator. The dynamic behavior equations of the phase-locked loop are: ,in, The integral coefficient is... The q-axis voltage component at the point of common connection. This is the proportionality coefficient. The dynamic behavior equation of the virtual synchronous generator is: ,in, For reference power, The rated angular frequency, For the active power output of the grid-type converter, The damping coefficient is... This is the equivalent inertia.

[0026] S14. Based on the q-axis voltage component equation of the grid-connected converter at the point of common coupling, the active power output equation and reactive power equation of the grid-connected converter, the dynamic behavior equation of the phase-locked loop, and the dynamic behavior equation of the virtual synchronous generator, construct the nonlinear state equation of the grid-connected converter. The nonlinear state equation of the grid-connected converter is: in, J 1 represents the equivalent inertia of the grid-type converter. J 2 represents the equivalent inertia of the grid-type converter. PM1 To match the equivalent mechanical power of the grid converter, P M2 The equivalent mechanical power of the grid-type converter, P E1 To match the equivalent electromagnetic power of the grid converter, P E2 The equivalent electromagnetic power of a grid-type converter. P int1 To compare with the equivalent electromagnetic interaction power of the grid converter, P int2 The equivalent electromagnetic interaction power of a grid-type converter. D 1 represents the equivalent damping coefficient of the grid-connected converter. D 2 represents the equivalent damping coefficient of the grid-type converter. D int1 The equivalent interactive damping coefficient, To match the angular velocity deviation of the grid converter, To match the virtual power angle of the grid converter, For amplitude and phase, To match the virtual power angle of the configuration converter, For amplitude and phase, This refers to the angular velocity deviation of the grid-type converter.

[0027] Furthermore, the relevant parameter expressions of the nonlinear state equations for the grid-connected converter are as follows: in, For phase coefficients, This is the amplitude coefficient.

[0028] S2. Based on the hybrid topology of grid-connected and grid-connected converters, construct the nonlinear state equation of the grid-connected and grid-connected converters and extract the interaction power term of the grid-connected and grid-connected converters. The interaction power term is: P int2 cos( d 2- d 1- i e -π / 2).

[0029] In a parallel system of grid-connected converters, the grid-connected converter dynamically generates a disturbance to the point of common coupling voltage through a phase-locked loop. This disturbance is transmitted to the grid-connected converter side via the line impedance, forming an interactive power term. P int2 cos( d2- d 1- i e -π / 2). Wherein... P int2 The equivalent electromagnetic interaction power of a grid-type converter. P int2 It exhibits negative characteristics, while cos( d 2- d 1- i e -π / 2) is positive within the stability region, therefore this interaction term is equivalent to an additional increment of mechanical torque in the active power control loop of the grid converter. This increment leads to a virtual power angle in the grid converter. d 2. Further increases. Simultaneously, changes in the output voltage of the grid-connected converter will also affect the input of the grid-connected converter's phase-locked loop through the line impedance, thus increasing the virtual power angle of the grid-connected converter. d 1. Dynamic adjustments are generated, forming a closed-loop interaction between the two. When the system is subjected to a large disturbance, this interaction may cause... d 2 and d If the phase difference between phases exceeds the stability threshold, it can cause the grid-type converter to lose synchronization or the phase-locked loop of the grid-type converter to lose lock, thereby triggering transient instability in the entire hybrid system. Analysis of the interactive power term and damping coefficient in the nonlinear state equation reveals that the amplitude of the interactive power is closely related to the line impedance parameters and converter control parameters, while the equivalent damping coefficient... The magnitude of the value directly affects the system's ability to suppress interactive oscillations.

[0030] From the nonlinear state equation of the grid-connected converter, it can be seen that... P int1 and D int1 All are positive coefficients. Therefore, electromagnetic interaction torque always benefits the relative state of the system. d 12 & oh 12 The transient stability is achieved. Therefore, damping compensation is not required for the grid-connected converter interaction terms in the grid-connected converter.

[0031] Step S3: Construct a damping additional term model based on the interactive power term of the grid-connected converter.

[0032] As analyzed in step S2, the interaction terms between the grid converter and the network converter always have a negative impact on the stability of the grid converter. Therefore, it is necessary to... P int2 cos( d 2- d 1- iCompensation of 5-π / 2) is used to improve the transient stability of the system. To avoid affecting the steady-state operating point of the system, a damping-based compensation strategy is adopted. Considering the physical limitations of the damping capability of the grid-type converter, the compensation damping needs to be divided by the maximum stable frequency max( oh 2cr And multiply by the positive adjustable coefficient 0 < x ≤1.

[0033] The expression for the damping additional term is: In the formula, , where max( oh 2cr ) indicates the stability region oh The maximum frequency value of 2 ensures the additional damping signal. D add oh 2 never exceed P int2 cos( d 2- d 1- i 5-π / 2), For the additional damping coefficient, It is a positive adjustable coefficient. It refers to the amplitude and phase. The adjustable coefficient of the damping compensation term in a grid-type converter. This is a key parameter balancing damping support capacity and hardware constraints, and its optimal value needs to be dynamically adjusted based on the real-time operating status of the system. When the DC-side voltage deviation of the converter is less than 5%, the active power utilization rate is less than 80%, and the peak output current does not exceed 70% of the current limiting threshold, the damping resources can be considered sufficient. It should be set to 1 to maximize the damping effect. Under conditions where DC-side energy is limited or the output current is close to the protection threshold, it needs to be reduced proportionally. The value prioritizes ensuring the safe and stable operation of the converter itself. Engineering practice shows that... The reasonable adjustment range is 0.1~1.0, and it can be reduced to 0.2~0.3 under extreme conditions such as low voltage ride-through. At the same time, the adjustment rate should be limited to avoid secondary disturbances to the system.

[0034] By adding damping coefficient It is used to improve system damping and suppress oscillations in the grid-connected converter hybrid system.

[0035] It should be noted that by using the ReLU activation function, only non-negative damping is retained: that is, the additional damping signal is only applied when the system shows signs of instability / oscillation. During normal operation, the additional damping signal is 0 and will not affect the steady-state characteristics.

[0036] S4. An additional damping signal is generated based on the additional damping coefficient and the system's rated angular frequency. This additional damping signal is then introduced into the active power control loop of the virtual synchronous generator in the grid-type converter, where it works in conjunction with the original damping term.

[0037] For details, please refer to Figure 1 , Figure 1 This diagram illustrates transient stability control of a grid-connected converter hybrid system based on a damping-added-term model. The transient stability control equations in the diagram are: in, This refers to the phase of a grid-type converter.

[0038] Specifically, step S4 includes the following sub-steps: S41. An additional damping signal is generated based on the additional damping coefficient and the system's rated angular frequency. Its expression is as follows: .

[0039] S42. Real-time monitoring of the operating data of the grid-connected converter hybrid system, and calculation of the active power deviation of the grid-connected converter based on the operating data. Real-time acquisition of the virtual power angle of the grid-connected converter. Virtual angular velocity Virtual power angle of grid converter This includes key electrical quantities such as voltage and current at the system's common connection point. These data are acquired using high-precision sensors and data acquisition modules, with a sampling frequency that meets the requirements for transient process analysis, typically no less than 1kHz, to ensure the capture of details of the system's dynamic changes.

[0040] Specifically, calculating the active power deviation of a grid-type converter based on operating data includes: calculating the active power output of the grid-type converter based on operating data, and then calculating the active power deviation based on the active power output. The equation for calculating the active power deviation is: ,in, For reference power, For the active power output of the grid converter, This is the rated angular velocity.

[0041] The active power output of the grid-type converter is: In the formula, The active power output of the grid-type converter. E The output voltage amplitude of the grid-connected converter. V g The voltage amplitude of the power grid. For the virtual power angle of the grid-type converter, For equivalent susceptance, For equivalent amplitude, For equivalent amplitude, This is the current reference value. For amplitude and phase, For amplitude and phase, The power factor angle, This is the relative virtual power angle difference.

[0042] S43. Calculate the real-time angular frequency based on the active power deviation of the grid-type converter. Input the active power deviation of the grid-type converter into the preset integrator. Then, output the real-time angular frequency. .

[0043] S44. Calculate the frequency deviation based on the real-time angular frequency, and calculate the original damping adjustment term based on the frequency deviation. The original damping adjustment item is: .

[0044] S45. The original damping term is superimposed with the additional damping signal to obtain the total damping term, and the total damping term is sent to the power deviation comparison circuit to provide feedback and adjust the power error.

[0045] Furthermore, Thus, by adding an additional damping signal to form feedback, the output phase of the grid-type converter is adjusted, thereby changing the output power of the grid-type converter, suppressing the phase interaction oscillation of the hybrid system, and ultimately improving the transient stability of the system under large disturbances. This control method only applies additional damping when the system shows signs of instability, without changing the original steady-state operating point of the system, and will not have any additional impact on the normal operation of the system. At the same time, it can make full use of the damping resources of the grid-type converter itself, without requiring modification to the control structure of the grid-type converter, making it easy to implement and highly adaptable.

[0046] Example 2 In this embodiment, a simulation experiment is conducted based on the transient stability improvement method for the grid-connected converter hybrid system described in Embodiment 1. In this embodiment, the grid-connected converter hybrid topology is constructed using MATLAB / Simulink simulation software; please refer to [reference needed]. Figure 2 , Figure 2 The diagram shows the hybrid topology of the grid-connected converter and the grid-connected converter. The circuit and controller parameters of the hybrid topology are adjusted, and the specific parameters are shown in Table 1. The fault depth is uniformly set to 80% of the grid voltage sag.

[0047] Table 1 The proposed transient stability improvement control of the grid-connected converter hybrid system addresses time delay, parameter errors (line impedance measurement deviation), and phase errors (which are negligible). L dI gd / d t The stability enhancement capability is maintained even under conditions caused by fast-scale voltage drops. Although only a 10-microsecond algorithm delay and 1% observation error are mentioned, the simulation verification in this step uses more stringent test conditions to ensure rigor: 100-millisecond delay, 10% parameter bias, and 0.2 rad error. The control parameters are configured as follows: x =0.8 and max( oh 2cr =8 rad / s. The disturbance is set to 80% grid voltage sag, and the Fault Clearing Time (FCT) is 500 milliseconds.

[0048] Please refer to Figure 3-Figure 5 , Figure 3 This is a comparison chart to verify the robustness of time delay. Figure 4 A comparison chart showing the robustness verification of line parameter estimation errors. Figure 5 This is a comparison chart to verify the robustness of the observation error of the power angle. Figure 3 In the diagram, the blue line represents the ideal case with no time delay error, the green line represents the case with a time delay error of τ_d = 100 ms, and the red line represents the case without additional damping control (without additional D). a The simulation results show that, in both the ideal and the case with a 100ms time delay, the phase trajectories eventually converge inward to the origin (0,0), indicating system stability. However, without added damping, the phase trajectories continue to diverge, and the deviations in power angle and angular velocity increase continuously, leading to system instability. This demonstrates the effectiveness of damped control and its robustness to time delay errors on the order of 100ms.

[0049] Figure 4 In the diagram, the blue line represents the ideal case with no power estimation error; the green line represents the case where the power estimation is +10% (estimated value is 10% larger than the actual value); and the red line represents the case where the power estimation is -10% (estimated value is 10% smaller than the actual value). Simulation results show that the phase trajectories in all three cases eventually converge to the origin. Even with a ±10% power gain estimation error, the system remains stable, indicating that the control scheme has good robustness to power measurement / estimation errors. Similarly, under the second row with a large control cycle, although the trajectory divergence range is larger, it still converges, verifying the robustness. It should be noted that the line parameter error is directly measured by the equivalent electromagnetic interaction power in the grid-type converter. P int2 Simplify the estimates by introducing bias, since different types of impedance measurement errors ultimately manifest in the equivalent electromagnetic interaction power of the grid converter. P int2 In the estimates.

[0050] Figure 5 In the middle, the blue line represents phaselessness. d 1. The ideal case of estimation error; the green line represents the case where the phase estimation is off by -0.2 rad (approximately 11.5 degrees underestimation); the red line represents the case where the phase estimation is off by +0.2 rad (approximately 11.5 degrees overestimation). Simulation results show that both the ideal and negative deviation cases can converge stably; for a positive phase error of +0.2 rad, the trajectory diverges in the first row of small plots, but convergence is still achieved in the second row of large control cycle scenarios. Overall, this indicates that the control maintains acceptable robustness to phase estimation errors within 0.2 rad.

[0051] It should be noted that, due to the additional damping signal D add Virtual power angle only with grid-type converters d 1. Virtual power angle of grid-type converter d The difference between 2 and 3 is related, therefore it is only necessary to consider the virtual power angle of the grid converter. d 1. Apply positive and negative errors to the observations.

[0052] The simulation results above show that the ReLU function in the proposed grid-connected converter hybrid system transient stability enhancement control ensures the additional damping coefficient. D add The nonnegativity of the proposed grid-connected converter hybrid system ensures that it always outperforms the system without additional damping, regardless of the form and degree of estimation error.

[0053] Furthermore, hardware-in-the-loop experimental verification based on RT-Lab simulation software was conducted. Please refer to [link / reference]. Figure 6 , Figure 6 This is a schematic diagram based on RT-Lab simulation, such as... Figure 6 As shown. The controller sections of GFMC and GFLC are deployed in DSP1 and DSP2 respectively, while the circuitry is implemented in RT-Lab. The DSP obtains sampled analog signal inputs from the virtual power grid running in RT-Lab and outputs the digital signals generated according to the control law back to RT-Lab. Some measurement values ​​are output to an oscilloscope via RT-Lab for observation.

[0054] Observation results as follows Figure 7-Figure 10 As shown, where, Figure 7 This is a schematic diagram of the experimental results for calculating the additional damping signal based on 1.0 pu Zg; Figure 8 This is a schematic diagram of the experimental results for calculating the additional damping signal based on 0.8 pu Zg; Figure 9 This is a schematic diagram of the experimental results for calculating the additional damping signal based on 1.2 pu Zg; Figure 10This is a schematic diagram of the experimental results without the addition of an additional damping signal. It should be noted that... Figure 7-Figure 10 In the image, the left half is a zoomed-out view, and the right half is a zoomed-in view.

[0055] pass Figure 7-Figure 9 It can be seen that the disturbance was cleared within the set 600ms disturbance clearing time, and the system eventually returned to stability: power angle difference d 12 Eventually converges to a new steady state, frequency difference ,Voltage power The oscillations gradually subsided and the market returned to a stable state. Figure 10 It can be seen that without the addition of additional damping control, the disturbance clearing time was shortened to 462ms (shorter than the 600ms of the first three groups), but the system still lost stability: power angle difference. d 12 Continuous divergence without convergence, frequency difference The voltage continues to increase. Output power Both exhibited significant oscillations followed by instability, ultimately maintaining power and voltage in an unstable state after divergence. This verifies the practical effectiveness and robustness to parameter errors of the proposed control method, and is in complete agreement with theoretical analysis and simulation results.

[0056] Example 3 The present invention also provides a transient stability improvement system for a grid-connected converter hybrid system, which is applied to the above-mentioned transient stability improvement method for a grid-connected converter hybrid system.

[0057] 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for improving transient stability in a grid-connected converter hybrid system, characterized in that, Includes the following steps: Constructing the nonlinear state equations of the grid-connected converter based on the hybrid topology of grid-connected converters; Extracting the interactive power term of the grid-connected converter based on the nonlinear state equation of the grid-connected converter; A damping additional term model is constructed based on the interactive power term of the grid-connected converter, and the additional damping coefficient is calculated through the damping additional term model; An additional damping signal is generated based on the additional damping coefficient and the system rated angular frequency. This additional damping signal is then introduced into the virtual synchronous generator active power control loop of the grid-type converter, where it works in conjunction with the original damping term.

2. The transient stability improvement method for a grid-connected converter hybrid system according to claim 1, characterized in that, The nonlinear state equations of the grid-connected converter based on the grid-connected converter hybrid topology include: Construct the q-axis voltage component equations for the grid-type converter at the point of common coupling; Construct the active power output equation and reactive power output equation for the grid-type converter; The dynamic behavior equations of the phase-locked loop of the grid converter and the dynamic behavior equations of the virtual synchronous generator of the grid converter are constructed. The nonlinear state equations of the grid-connected converter are constructed based on the q-axis voltage component equations at the common connection point of the grid-connected converter, the active power output equations and reactive power output equations of the grid-connected converter, the dynamic behavior equations of the phase-locked loop, and the dynamic behavior equations of the virtual synchronous generator.

3. The transient stability improvement method for a grid-connected converter hybrid system according to claim 1, characterized in that, The nonlinear state equation of the grid-connected converter is: In the formula, J 1 represents the equivalent inertia of the grid-type converter. J 2 represents the equivalent inertia of the grid-type converter. P M1 To match the equivalent mechanical power of the grid converter, P M2 The equivalent mechanical power of the grid-type converter, P E1 To match the equivalent electromagnetic power of the grid converter, P E2 The equivalent electromagnetic power of a grid-type converter. P int1 To compare with the equivalent electromagnetic interaction power of the grid converter, P int2 The equivalent electromagnetic interaction power of a grid-type converter. D 1 represents the equivalent damping coefficient of the grid-connected converter. D 2 represents the equivalent damping coefficient of the grid-type converter. D int1 The equivalent interactive damping coefficient, To match the angular velocity deviation of the grid converter, To match the virtual power angle of the grid converter, For amplitude and phase, To match the virtual power angle of the grid converter, For amplitude and phase, For the angular velocity deviation of the grid-type converter, θ e For amplitude and phase, The current reference vector power factor angle of the grid-type converter.

4. The transient stability improvement method for a grid-connected converter hybrid system according to claim 3, characterized in that, The interactive power term of the grid-connected converter is: P int2 cos( δ 2- δ 1- θ e -π / 2).

5. The transient stability improvement method for a grid-connected converter hybrid system according to claim 4, characterized in that, The damping additional term model is as follows: , ,max( ω 2cr ) indicates the stability region ω The maximum frequency value of 2, For the additional damping coefficient, It is a positive adjustable coefficient. It refers to the amplitude and phase.

6. The transient stability improvement method for a grid-connected converter hybrid system according to claim 1, characterized in that, An additional damping signal is generated based on the additional damping coefficient and the system's rated angular frequency. This additional damping signal is introduced into the virtual synchronous generator active power control loop of the grid-type converter, where it works in conjunction with the original damping term, including: An additional damping signal is generated based on the additional damping coefficient and the system's rated angular frequency; Real-time monitoring of the operating data of the grid-connected converter hybrid system, and calculation of the active power deviation of the grid-connected converter based on the operating data; Calculate the real-time angular frequency based on the active power deviation of the grid-type converter; Calculate the frequency deviation based on the real-time angular frequency, and then calculate the original damping adjustment term based on the frequency deviation. The original damping term is superimposed with the additional damping signal to obtain the total damping term, which is then fed into the power deviation comparison circuit to provide feedback and adjust the power error.

7. The transient stability improvement method for a grid-connected converter hybrid system according to claim 6, characterized in that, The calculation of the active power deviation of the grid-type converter based on operating data includes: Calculate the active power output of the grid-type converter based on the operating data; The active power deviation of the grid converter is calculated based on the active power output.

8. The transient stability improvement method for a grid-connected converter hybrid system according to claim 6, characterized in that, The calculation of real-time angular frequency based on the active power deviation of the grid-type converter includes: The active power deviation of the grid-type converter is input into a preset integrator, which outputs the corresponding real-time angular frequency.

9. The transient stability improvement method for a grid-connected converter hybrid system according to claim 3, characterized in that, The active power output of the grid-type converter is: ； In the formula, The active power output of the grid-type converter. E The output voltage amplitude of the grid-connected converter. V g The voltage amplitude of the power grid. For the virtual power angle of the grid-type converter, For equivalent susceptance, For equivalent amplitude, For equivalent amplitude, This is the current reference value. For amplitude and phase, For amplitude and phase, The power factor angle, This is the relative virtual power angle difference.

10. A transient stability improvement system for a grid-connected converter hybrid system, characterized in that, The transient stability improvement method is applied to any one of the grid-connected converter hybrid systems as described in claims 1-9.

Images