Modeling and stability analysis method for structure and network hybrid system
By constructing two-port networks for grid-connected and grid-connected converters and combining them with grid impedance admittance, a stability criterion for three-port networks is established. This solves the problem of high computational complexity in traditional methods and improves the stability of grid-connected/grid-connected hybrid systems under weak grid conditions.
Patent Information
- Application Number
- CN202511340580.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-19
- Publication Date
- 2026-01-06
AI Technical Summary
Under weak grid conditions with a high proportion of renewable energy and a high proportion of power electronic equipment, grid-connected converters that adopt grid-following control or grid-connection control alone cannot simultaneously meet the requirements of system stability, operating economy and grid support capacity. Traditional modeling methods have high computational complexity and are difficult to adapt to the rapid analysis of grid-connected/grid-connected hybrid systems.
By adopting the stability criterion of three-port networks, and by constructing two-port networks of grid-connected and grid-connected converters, and combining the grid impedance admittance, a three-port network of the grid-connected hybrid system is established, the stability criterion is determined, and the computational complexity is reduced.
It improves the efficiency of stability analysis of the grid-connected system, reduces computational complexity, effectively suppresses system oscillations, and enhances stability under weak grid conditions.
Smart Images
Figure CN121282940A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of converter modeling and stability analysis technology, specifically relating to a method for modeling and stability analysis of a hybrid grid-connected system. Background Technology
[0002] With the development of power electronics technology, grid-connected and grid-linked converters have each formed mature technical systems. However, in the new power system scenario of "high proportion of renewable energy and high proportion of power electronic equipment," especially under weak grid conditions, grid-connected converters that solely adopt grid-linked or grid-connected control cannot simultaneously meet the requirements of system stability, operational economy, and grid support capacity. Therefore, hybrid grid-connected / grid-linked systems have become a research hotspot in academia.
[0003] In existing research, some scholars have used impedance modeling methods to deeply analyze the differences in impedance characteristics between grid-type and follow-grid-type converters and the resulting oscillation risks. They have also proposed stability criteria for grid-type converters to suppress power oscillations in follow-grid-type converters, revealing the underlying mechanism for oscillation suppression from a theoretical perspective. Other scholars have established sequence impedance models for grid / follow-grid hybrid systems, demonstrating that the positive resistance characteristics of grid-type converters can effectively offset the negative resistance effect of follow-grid-type converters, significantly improving the oscillation stability in the mid-frequency range under follow-grid control mode, thereby suppressing system oscillations.
[0004] Currently, the mainstream modeling and stability analysis methods for grid-connected and grid-coupled converters mainly include impedance modeling and state-space models. While these traditional methods can accurately characterize various operating states of the system, they have significant limitations: the modeling process requires comprehensive consideration of numerous factors, leading to high implementation difficulty. Taking state-space models as an example, once inverter parameters change, a complete re-analysis of all system state variables is necessary, greatly increasing computational complexity. For grid-connected / grid-coupled systems, as the number of connected inverters increases, the size of the state-space matrix grows exponentially when using traditional modeling methods, further exacerbating the computational burden of system analysis. Therefore, it is urgent to break through existing approaches and explore innovative modeling methods to provide more efficient and applicable solutions for the stability analysis of grid-connected / grid-coupled systems. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modeling and stability analysis method for hybrid network systems. It proposes a stability criterion for three-port networks, providing a more efficient and applicable solution for the stability analysis of hybrid network systems and reducing computational complexity.
[0006] The objective of this invention is achieved as follows: a method for modeling and stability analysis of a hybrid network system, comprising the following steps:
[0007] S1. Based on the small-signal model of the grid converter, define the rotor mechanical admittance Y of the grid converter. 1GFM (s) and dynamic electrical admittance Y 2GFM (s), constructing a two-port network for a grid-type converter;
[0008] S2. Considering the small-signal disturbance of the phase-locked loop, define the rotor mechanical admittance Y of the grid converter. 1GFL (s) and dynamic electrical admittance Y 2GFL (s), constructing a two-port network for the grid-type converter;
[0009] S3, Considering grid impedance admittance Y g The influence of (s) determines the expression for the stability margin of the grid-type converter;
[0010] S4. Establish a three-port network that is connected to the network and determine the stability criteria of the three-port network.
[0011] Furthermore, the small-signal model of the grid-type converter described in step S1 satisfies the following formula:
[0012]
[0013] Where L is the filter inductance, L v R is a virtual inductance, and R is the resistance of the line. v Z is a virtual resistance. o (s) is the equivalent output impedance of the voltage and current inner loop, ω s U is the rated angular frequency of the power grid, E is the virtual internal potential amplitude of the grid-connected converter, and U is the voltage level of the grid-connected converter. g δ is the grid voltage, s is the power angle of the grid-connected converter, and P is the Laplace operator. GFM (s) represents the output active power of the grid-connected converter, Q. GFM (s) represents the reactive power output of the grid-type converter, ΔP GFM (s), ΔQ GFM (s), Δδ, and ΔE are the disturbance components of the active power, reactive power, power angle, and virtual internal potential amplitude of the grid converter, respectively.
[0014] Furthermore, the rotor mechanical admittance Y of the grid-type converter described in step S1... 1GFM (s) and dynamic electrical admittance Y 2GFM (s) satisfies the following formula:
[0015]
[0016] Where, ΔP ref_GFM(s) represents the small disturbance of the reference active power of the grid-connected converter, Δω represents the small disturbance of the output angular frequency of the grid-connected converter, and J and D p These are the virtual inertia coefficient and damping coefficient, Δω. c This refers to small disturbances in the power grid frequency.
[0017] Furthermore, when considering small-signal disturbances of the phase-locked loop in step S2, the output of the phase-locked loop satisfies the following formula:
[0018]
[0019] Where, ΔP ref_GFL (s) represents a small disturbance to the reference active power of the grid-connected converter, ΔP GFL (s) represents the small disturbance to the active power output of the grid-connected converter, ΔP d_GFL (s) Small disturbances in the damping power of the grid converter.
[0020] The rotor mechanical admittance Y of the grid converter mentioned in step S2 1GFL (s) and dynamic electrical admittance Y 2GFL (s) satisfies the following formula:
[0021]
[0022] Furthermore, the grid impedance admittance Y mentioned in step S3 g (s) satisfies the following formula:
[0023]
[0024] Among them, L g R is the grid-side inductance. g For grid-side resistance, δ g0 Let be the initial phase angle difference between the grid voltage and the PCC point voltage, and s be the Laplace operator;
[0025] The stability margin of the grid-connected converter in step S3 satisfies the following formula:
[0026] PM GFL =180°-(Y pGFL (jω GFLkg )-Y g (jω GFLkg (16)
[0027] Among them, PM GFL To maintain the stability margin of the grid converter, ω GFLkg For Y pGFL (s) and Y g The angular frequency at the intersection of the Bode plot of (s), where j is the imaginary unit.
[0028] Furthermore, the stability criterion for the three-port network with hybrid connection described in step S4 satisfies the following formula:
[0029] PM GFL-GFM =180°-(Y pGFL (jω GFL-GFMkx )-Y x (jω GFL-GFMkx )) (twenty three)
[0030] Among them, PM GFL-GFM For the stability margin of a three-port network, ω GFL-GFMkx For Y pGFL (s) and Y x Angular frequency at the intersection of the Bode plots of (s);
[0031] In equation (14), Y x The expression for (s) satisfies the following equation:
[0032]
[0033] The beneficial effects of the present invention: The present invention provides a modeling and stability analysis method for a hybrid grid-connected system, including step S1: defining the rotor mechanical admittance Y of the grid-connected converter based on the small-signal model of the grid-connected converter. 1GFM (s) and dynamic electrical admittance Y 2GFM (s), constructing a two-port network for a grid-type converter;
[0034] S2. Considering the small-signal disturbance of the phase-locked loop, define the rotor mechanical admittance Y of the grid converter. 1GFL (s) and dynamic electrical admittance Y 2GFL (s) Construct the two-port network of the grid-connected converter; S3, Consider the grid impedance admittance Y g (s) influences, determine the expression for the stability margin of the grid-connected converter; S4, establish a three-port network for grid-connected hybrid system, and determine the stability criterion of the three-port network; through the above steps, the present invention provides a more efficient and applicable solution for the stability analysis of grid-connected hybrid systems, reducing the computational complexity. Attached Figure Description
[0035] To more clearly illustrate the technical solutions in the embodiments of the present 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0036] Figure 1 This is a schematic diagram of the main circuit topology and control structure of a grid-type converter.
[0037] Figure 2 A schematic diagram of the equivalent circuit for grid-connected operation of a grid-type converter.
[0038] Figure 3 This is a schematic diagram of a small-signal model for a grid-type converter.
[0039] Figure 4 This is a schematic diagram of a two-port network for a grid-type converter.
[0040] Figure 5 This is a schematic diagram of the main circuit topology and control structure of a grid-type converter.
[0041] Figure 6 This is a control block diagram of the phase-locked loop in a grid converter.
[0042] Figure 7 The voltage U at the point of common coupling (PCC) PCC Phase-locked loop q-axis voltage u q With grid voltage U g A diagram illustrating the relationship between the two.
[0043] Figure 8 This is a schematic diagram of a small-signal model of a grid-type converter.
[0044] Figure 9 This is a schematic diagram of a two-port network for a grid-type converter.
[0045] Figure 10 This is the equivalent transformation diagram of a two-port network for a grid-type converter.
[0046] Figure 11 For the Y-type converter pGFL (s) and Y g A schematic diagram of the phase margin at the intersection of (s) and the phase margin at the intersection point.
[0047] Figure 12 The output power response diagram of the grid-type converter.
[0048] Figure 13 The output current response diagram of the grid-connected converter.
[0049] Figure 14 For equivalent voltage source ω s With admittance Y pGFM (s) Schematic diagram of a two-port network in series.
[0050] Figure 15 A schematic diagram of a three-port network that is connected to the network.
[0051] Figure 16Phase margin diagram of the system when the converter is connected to the grid in a hybrid grid connection and when the converter is connected to the grid independently.
[0052] Figure 17 A schematic diagram of the main circuit experimental model for a hybrid grid system.
[0053] Figure 18 This is a schematic diagram of the output current response of the grid-type converter under operating condition 1.
[0054] Figure 19 This is a schematic diagram of the output power response of the grid converter under operating condition 1.
[0055] Figure 20 This is a schematic diagram of the response of the grid converter when the reference power increases under operating condition 1.
[0056] Figure 21 This is a schematic diagram of the output current response of the grid-type converter under operating condition 2.
[0057] Figure 22 This is a schematic diagram of the output power response of the grid converter under operating condition 2.
[0058] Figure 23 This is a schematic diagram of the response of the grid converter when the reference power increases under operating condition 2. Detailed Implementation
[0059] The present invention will now be further described with reference to the accompanying drawings.
[0060] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.
[0061] 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 a part of the embodiments of the present invention, and not all of them. 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.
[0062] It should be noted that in the embodiments of the present invention, all directional indications (such as up-down-left-right-forward-backward...) are only used to explain the relative positional relationship and movement between the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly. The connection can be a direct connection or an indirect connection.
[0063] The present invention provides a method for modeling and stability analysis of a hybrid network system, comprising the following steps:
[0064] S1. Based on the small-signal model of the grid converter, define the rotor mechanical admittance Y of the grid converter. 1GFM (s) and dynamic electrical admittance Y 2GFM (s), constructing a two-port network for a grid-type converter;
[0065] S2. Considering the small-signal disturbance of the phase-locked loop, define the rotor mechanical admittance Y of the grid converter. 1GFL (s) and dynamic electrical admittance Y 2GFL (s), constructing a two-port network for the grid-type converter;
[0066] S3, Considering grid impedance admittance Y g The influence of (s) determines the expression for the stability margin of the grid-type converter;
[0067] S4. Establish a three-port network that is connected to the network and determine the stability criteria of the three-port network.
[0068] like Figure 1 The diagram shows the main circuit topology and control structure of the grid-type converter in an embodiment of the present invention. Figure 2 The equivalent circuit diagram for grid-connected operation of a grid-type converter is shown below. Figure 2 It can be seen that the small-signal model of the grid-type converter described in step S1 satisfies the following formula:
[0069]
[0070]
[0071] Where L is the filter inductance, L v R is a virtual inductance, and R is the resistance of the line. v Z is a virtual resistance. o (s) is the equivalent output impedance of the voltage and current inner loop, ω s U is the rated angular frequency of the power grid, E is the virtual internal potential amplitude of the grid-connected converter, and U is the voltage level of the grid-connected converter. g δ is the grid voltage, s is the power angle of the grid-connected converter, and P is the Laplace operator. GFM (s) represents the output active power of the grid-connected converter, Q. GFM (s) represents the reactive power output of the grid-type converter, ΔP GFM (s), ΔQ GFM (s), Δδ, and ΔE are the disturbance components of the active power, reactive power, power angle, and virtual internal potential amplitude of the grid converter, respectively.
[0072] in:
[0073]
[0074] Ignoring the power coupling term, the small-signal model of the grid converter described in S1 can be obtained according to equation (3) as follows: Figure 3 As shown, according to Figure 3 Therefore, the rotor mechanical admittance Y of the grid-type converter described in step S1 is... 1GFM (s) and dynamic electrical admittance Y 2GFM (s) satisfies the following formula:
[0075]
[0076] Where, ΔP ref_GFM (s) represents the small disturbance of the reference active power of the grid-connected converter, Δω represents the small disturbance of the output angular frequency of the grid-connected converter, and J and D p These are the virtual inertia coefficient and damping coefficient, Δω. c This refers to small disturbances in the power grid frequency.
[0077] According to equation (4), the two-port network of the grid-type converter in S1 can be constructed as follows: Figure 4 As shown.
[0078] Figure 5 The diagram shows the main circuit topology and control structure of the grid converter in an embodiment of the present invention. Figure 6 To match the control block diagram of the phase-locked loop in the grid converter, based on Figure 6 When considering small-signal disturbances in the phase-locked loop (PLL) in S2, the PLL output satisfies the following equation:
[0079]
[0080] Where J is the virtual inertia coefficient of the phase-locked loop analog synchronous machine, and k ppll k ipll These are the proportional and integral coefficients of the PI controller, respectively; θ is the output angle of the phase-locked loop; and ω is the output angular velocity of the phase-locked loop.
[0081] When considering small-signal disturbances in the phase-locked loop, the voltage U at the point of common coupling (PCC) PCC Phase-locked loop q-axis voltage u q With grid voltage U g Relationship such as Figure 7 As shown, let the output angle θ of the phase-locked loop satisfy θ=θ0+Δθ, and the current angle δ i =δ i0 +Δδ i , where θ0 and δ i0 Let Δ represent the steady-state component and the small perturbation. They satisfy the following equation:
[0082]
[0083] Where I is the current flowing through the circuit. For the power factor angle, ω s This is the rated angular frequency of the power grid.
[0084] Further combining equations (5), (6), and (7), we obtain:
[0085]
[0086] Further small-signal analysis of equation (8) reveals that, considering small-signal disturbances in the phase-locked loop, the output of the phase-locked loop satisfies the following formula:
[0087]
[0088] Where, ΔP ref_GFL (s) represents a small disturbance to the reference active power of the grid-connected converter, ΔP GFL (s) represents the small disturbance to the active power output of the grid-connected converter, ΔP d_GFL (s) Small disturbances in the damping power of the grid converter.
[0089] According to equation (9), the small-signal model of the grid converter considering the small-signal disturbance of the phase-locked loop in S2 can be obtained as follows: Figure 8 As shown, then according to Figure 8 The rotor mechanical admittance Y of the grid-type converter described in step S2 can be derived. 1GFL (s) and dynamic electrical admittance Y 2GFL (s) satisfies the following formula:
[0090]
[0091] According to equation (10), the two-port network of the grid converter in S2 can be constructed as follows: Figure 9 As shown.
[0092] Considering the grid impedance admittance Y g After the influence of (s), Figure 9 The two-port network of the grid-type converter shown is equivalently transformed into Figure 10 As shown, where G(s) and Y pGFL (s) and the grid impedance admittance Y mentioned in step S3 g (s) satisfies the following formula:
[0093]
[0094] Among them, L g R is the grid-side inductance. g For grid-side resistance, δ g0 Let be the initial phase angle difference between the grid voltage and the PCC point voltage, and s be the Laplace operator.
[0095] according to Figure 10 Combining the superposition theorem in circuit theory, consider the equivalent current source ΔP respectively. ref_GFL (s)*G(s) and equivalent voltage source Δω c The function of (s) is used to calculate the power ΔP input to the grid from the grid-connected converter. GFL (s) satisfies the following formula:
[0096]
[0097] For equation (14), the right side of the equation can be regarded as the product of two closed-loop transfer functions, which can be denoted as:
[0098]
[0099] For TF1, assuming stable operation of the grid-connected converter under an ideal power grid, ΔP ref_GFL (s)*G(s), Y pGFL (s) Since all poles are located in the left half-plane, TF1 is stable. The stability of the grid converter then depends on TF2, and TF2 can be considered as having a forward transfer function of 1 and a feedback loop transfer function of Y. pGFL (s) / Y g (s) is a unity negative feedback system, therefore, the stability of the grid converter is related to Y pGFL (s) and Y g It relates to the interaction of (s), i.e., Y pGFL (s) and Y g (s) There is a sufficiently large phase margin at the intersection point, at which point it can be considered that the system is stable when connected to the grid with the grid-type converter.
[0100] At this point, it can be deduced that the grid impedance admittance Y considered in step S3 can be derived. g The stability margin of the grid-connected converter described in (s) satisfies the following formula:
[0101] PM GFL =180°-(Y pGFL (jω GFLkg )-Y g (jω GFLkg (16)
[0102] Among them, PM GFL To maintain the stability margin of the grid converter, ω GFLkg For Y pGFL (s) and Y g The angular frequency at the intersection of the Bode plot of (s), where j is the imaginary unit.
[0103] Figure 11The power grid impedance admittance Y is given as the power grid impedance increases. g When (s) decreases, the Y in the grid-connected converter obtained from equation (16) pGFL (s) and Y g (s) and the phase margin diagram at the intersection point, from Figure 11 It can be seen that as the grid impedance increases, the phase margin at the entire junction decreases, indicating that the stability of the grid-type converter is getting worse and worse and it is prone to instability, which is consistent with the conclusion that the grid-type converter is prone to instability under weak grid conditions.
[0104] Figure 12-13 The operating condition is given, which will change the grid impedance L in 0.5s. g The output power and output current response diagram of a 100kW grid-connected converter is shown when the grid impedance increases from 0.5mH to 1mH, and then further to 2mH at 1 second. When the grid impedance L... g At a current of 0.5mH, the grid strength is considered a strong grid, and the output power of the grid-connected converter can reach a stable value; however, as the grid impedance L... g As the voltage increases from 0.5mH to 1.5mH, and then to 2mH, the grid strength gradually weakens, and the output power gradually begins to oscillate. At this point, the output current also gradually becomes unstable until the grid impedance L... g When the output current is increased to 2mH, the output power oscillates violently, cannot track the commanded power value, and the output current quality is poor, failing to meet grid connection requirements. The above simulation results are consistent with... Figure 11 This is consistent with the theoretical analysis results.
[0105] The above derivation of the two-port networks of grid-connected converters and grid-connected converters is presented. To establish a three-port network in S4 that integrates grid and network connections, the first step is to... Figure 4 Equivalent current source ΔP ref_GFM (s) and rotor mechanical admittance Y 1GFM (s) Parallel two-port network transformed into Figure 14 The equivalent voltage source ω shown s With admittance Y pGFM (s) A two-port network in series, where ω s and Y pGFM The expression for (s) satisfies the following equation:
[0106]
[0107] The grid-connected system of a hybrid power station with grid-connected converters can be equivalently represented by a two-port network of grid-connected converters, a two-port network of grid-connected converters, and the grid impedance admittance Y. g (s) constitute. Combined Figure 10 and Figure 14 It can be deduced that a three-port network with a complex structure and network connection is like this. Figure 15As shown, where ΔP GFL (s) represents the output power of the grid-connected converter, ΔP GFM (s) represents the output power of the grid-type converter, ΔP g (s) represents the active power flowing into the grid from the hybrid system, and numerically it is ΔP. g (s)=ΔP GFM (s)+ΔP GFL (s).
[0108] according to Figure 15 The voltage source ω that can be equivalent to a grid-type converter s and grid voltage Δω c (s) can be considered as a single equivalent voltage source ω x The equivalent voltage ω x The expression satisfies the following formula:
[0109]
[0110] Where, ω x This is the equivalent voltage at the grid connection point when a grid-connected converter is connected to a weak grid. When a grid-connected converter is stable, its poles are located in the left half-plane, therefore the system is stable.
[0111] The equivalent admittance Y of the grid converter pGFM (s) and grid impedance admittance Y g (s) is considered as a whole, and its equivalent admittance Y x (s) satisfies the following equation:
[0112]
[0113] Substituting equations (19) and (20) into equation (14), we obtain the following expression for the output power of the grid-connected unit in the hybrid grid-connected system:
[0114]
[0115] For equation (21), the right side of the equation can be regarded as the product of two closed-loop transfer functions, which can be denoted as:
[0116]
[0117] Equation (22) shows that the stability of the hybrid grid system depends on TF3 and TF4: the entire system is stable if and only if the poles of TF3 and TF4 are both located in the left half-plane. Under an ideal grid, ΔP ref_GFL (s)*G(s), Y pGFL (s) All poles are located in the left half-plane, therefore the stability of TF3 depends on ω. xAs analyzed earlier, ω x When a grid-connected converter is connected to a weak grid, the equivalent voltage at the grid connection point is given. When a grid-connected converter is stable, its poles are located in the left half-plane, therefore TF3 can be considered stable overall. For TF4, when the open-loop transfer function Y... pGFL (s) and Y x (s) When the phase margin is large, it can be assumed that all poles of TF4 are located in the left half-plane, thus the system is stable. In this case, the phase margin of the entire system when the hybrid grid-connected system is connected to the grid satisfies the following formula:
[0118] PM GFL-GFM =180°-(Y pGFL (jω GFL-GFMkx )-Y x (jω GFL-GFMkx )) (twenty three)
[0119] Among them, PM GFL-GFM For the stability margin of a three-port network, ω GFL-GFMkx For Y pGFL (s) and Y x The angular frequency at the intersection of the Bode plots of (s); at this point, the PM at the intersection is calculated. GFL-GFM The size of the signal indicates whether the system is stable.
[0120] Figure 16 The phase margin diagrams of the system are given for both grid-connected and grid-connected converters, as well as for individual grid-connected converters. After adding the grid-connected converter, the entire system at the intersection frequency ω... GFL-GFMkX The phase margin at the point increased from the original 7.03° to 23.06°, indicating that the overall stability of the system has been improved. This shows that the three-port network of the hybrid grid-connected system established by this invention can analyze the access of the grid-connected converter, which helps to suppress the power oscillation problem that is prone to occur in the grid-connected converter under weak grid conditions.
[0121] To further verify the correctness of the above theoretical analysis, an experimental model of the main circuit of the grid-connected system was built, such as... Figure 17 As shown in Table 1, the parameters of grid-type and grid-connected converters are as follows.
[0122] Table 1 Parameters of Grid-type and Grid-connected Converters
[0123]
[0124]
[0125] The grid-connected converter has a power rating of 100kW, and the network-connected converter has a power rating of 10kW. The following experimental conditions are now being tested:
[0126] Operating Condition 1: First, connect the grid-connected converter to the grid independently, i.e., only close the circuit. Figure 17 The switch Breaker1 is shown. Then, when the grid impedance is increased from 0.5mH to 2mH, a 50kW power step disturbance is applied to the grid converter, and the grid converter outputs a response.
[0127] Operating condition 2: Connect to a grid-type converter, i.e., simultaneously close... Figure 17 The switches Breaker1 and Breaker2 shown above were used to repeat the above experimental conditions, that is, when the grid impedance was increased from 0.5mH to 2mH, a power step disturbance of 50kW was applied to the grid-connected converter, and the output response of the grid-connected converter was observed.
[0128] Figure 18-20 These are, respectively, the output current response, output power response, and response to a step change in the reference power of the grid-connected converter under operating condition 1 in this invention.
[0129] Figure 21-23 These are the output current response, output power response, and reference power step response of the grid-connected converter, respectively, corresponding to operating condition 2 in this invention.
[0130] Figure 18-20 This indicates that before the grid-connected converter was added, as the grid impedance increased from 0.5mH to 2mH, the grid strength continuously changed from a strong grid to a weak grid. The output power and current of the grid-connected converter oscillated, and the THD of the output current was 19.6%, which did not meet the grid connection requirements.
[0131] Figure 21-23 The results show that after adding the grid-connected converter, regardless of whether the grid strength is weakened or the reference power of the grid-connected converter jumps from 100kW to 150kW, the output power and current of the grid-connected converter do not oscillate, and the THD of the output current is less than 5%, which meets the grid connection requirements. This further illustrates the correctness of the three-port network theory analysis proposed in this invention.
Claims
1. A method for modeling and stability analysis of a combined construction and web weaving system, characterized in that The method comprises the following steps: S1, defining a rotor mechanical admittance Y of the grid-forming converter from a small-signal model of the grid-forming converter 1GFM (s) and a dynamic electrical admittance Y 2GFM (s) of the grid-forming converter, building a two-port network of the grid-forming converter; S2, considering small signal perturbation of phase-locked loop, define rotor mechanical admittance Y of grid-following converter 1GFL (s) and dynamic electrical admittance Y 2GFL (s), construct two-port network of grid-following converter; S3, considering the grid impedance admittance Y g (s) and determine the expression of the grid-connected converter stability margin; S4, a three-port network of grid-connected hybrid connection is established, and a stability criterion of the three-port network is determined.
2. The method of claim 1, wherein the system is a hybrid system. The small signal model of the network type converter in the step S1 satisfies the following formula: where L is the filter inductance, L v is the virtual inductance, R is the line resistance, R v is the virtual resistance, Z o (s) is the inner loop equivalent output impedance, ω s is the grid rated angular frequency, E is the virtual internal voltage magnitude of grid forming converter, U g is the grid voltage, δ is the grid forming converter power angle, s is the Laplace operator, P GFM (s) is the grid forming converter output active power, Q GFM (s) is the grid forming converter output reactive power, ΔP GFM (s), ΔQ GFM (s), Δδ, and ΔE are the disturbance components of the grid forming converter active power, reactive power, power angle, and virtual internal voltage magnitude of grid forming converter, respectively.
3. The method of claim 1, wherein the system is a hybrid system. the rotor mechanical admittance Y of the network-forming converter in step S1 1GFM (s) and the dynamic electrical admittance Y 2GFM (s) satisfy the following equation: where ΔP ref_GFM (s) is a small perturbation of the grid-forming converter reference active power, Δω is a small perturbation of the grid-forming converter output angular frequency, J and D p are the virtual inertia coefficient and the damping coefficient, respectively, and Δω c is a small perturbation of the grid frequency.
4. The method of claim 1, wherein the system is a hybrid system. When the small signal disturbance of the phase-locked loop is considered in the step S2, the output of the phase-locked loop satisfies the following formula: sΔδ i =Δω where ΔP ref_GFL (s) is a small perturbation of the grid-following converter reference active power, ΔP GFL (s) is a small perturbation of the grid-following converter output active power, ΔP d_GFL (s) is a small perturbation of the grid-following converter damping power. the rotor mechanical admittance Y of the grid- connected converter of step S2 1GFL (s) and the dynamic electrical admittance Y 2GFL (s) satisfy the following equation:
5. The method for modeling and stability analysis of a hybrid network system as described in claim 1, characterized in that, The grid impedance admittance Y in said step S3 g (s) satisfies the following equation: where L g is the grid-side inductance, R g is the grid-side resistance, δ g0 is the initial phase angle difference between the grid voltage and the PCC point voltage, and s is the Laplace operator; The stability margin of the grid-connected type converter in the step S3 satisfies the following formula: PM GFL = 180° - (Y pGFL (jω GFLkg ) - Y g (jω GFLkg )) (16) Among them, PM GFL To maintain the stability margin of the grid converter, ω GFLkg For Y pGFL (s) and Y g The angular frequency at the intersection of the Bode plot of (s), where j is the imaginary unit.
6. The method of claim 1, wherein the system is a hybrid system. The stability criterion of the three-port network of grid-connected hybrid connection in the step S4 satisfies the following formula: PM GFL-GFM = 180° - (Y pGFL (jω GFL-GFMkx )- Y x (jω GFL-GFMkx )) (23) where PM GFL-GFM is the stability margin of the three-port network, ω GFL-GFMkx is the Bode plot intersection point of Y pGFL (s) and Y x (s); In formula (14), Y x The expression of (s) satisfies the following formula: