Simulation substitution method for multi-network-construction-type virtual synchronous machine grid-connected system

Abstract

The invention discloses a simulation substitution method for a multi-GFVSG grid-connected system. According to the method, a mechanical admittance model of the multi-GFVSG grid-connected system is constructed by using an electromechanical comparison principle. Based on a mechanical admittance model, a transfer function capable of completely describing active instruction input and power grid disturbance response of the multi-GFVSG system is deduced, power frequency response characteristics of the multi-GFVSG grid-connected system are analyzed by using the transfer function, and a circuit replacement simulation model of the multi-GFVSG grid-connected system is built by replacing mechanical elements with circuit system elements. And the power frequency response characteristics of the multi-GFVSG grid-connected system are verified by using a circuit substitution simulation result, so that the feasibility of analyzing the power frequency response characteristics of the multi-GFVSG grid-connected system by using a circuit simulation model is ensured. The multi-GFVSG grid-connected system power frequency response characteristic analysis method has the advantages that the system power frequency response characteristic can be accurately analyzed without establishing a complex multi-GFVSG grid-connected system simulation model, the calculation amount is small, and the multi-GFVSG grid-connected system power frequency response characteristic analysis method can be conveniently applied to research on the aspects of power frequency oscillation characteristic analysis and response performance optimization of the multi-GFVSG grid-connected system.

Description

Technical Field

[0001] The present invention relates to the field of virtual synchronous machine control technology, and in particular to a simulation substitution method for a multi-grid type virtual synchronous machine grid-connected system, which is applicable to the field of multi-grid type virtual synchronous machine grid-connected in power electronics technology and the field of microgrid incorporation of such multi-grid type virtual synchronous machine into distribution network control. Background Art

[0002] When grid-forming Virtual Synchronous Generator (GFVSG) is connected to the grid, it can provide certain voltage and virtual inertia support for the connected grid. However, the grid-connected active power of GFVSG has dynamic oscillation and power overshoot problems under disturbances such as active power instructions and grid frequency. When multiple GFVSGs are connected to the grid through the point of common coupling (PCC), due to the existence of equivalent impedance of the grid, the active power-frequency control loops of multiple GFVSGs will inevitably interact with each other, making the operation characteristics of the multiple GFVSG grid-connected system more complicated. Therefore, it is of great significance to construct a simulation model that can fully describe the power-frequency response characteristics of the multiple GFVSG grid-connected system and to carry out research on related power-frequency oscillation suppression strategies.

[0003] To this end, people have done various studies, such as the article entitled "A robust damping control for virtual synchronous generators based on energy reshaping", Yang ML, WANG YX, XIAO XY, et al., "IEEE Transactions on Energy Conversion", Vol. 38, No. 3, 2023, pp. 2146-2159; This article proposes a method based on energy reshaping, which reveals the physical mechanism of power frequency oscillation of GFVSG grid-connected system from the perspective of circuit energy through equivalent circuit modeling. It has the advantages of clear physical meaning and simple design, but does not consider the applicability of this method in multi-GFVSG grid-connected systems, and requires online detection of grid frequency.

[0004] An article entitled "Analysis of Active Oscillation Characteristics of Energy Storage VSG Parallel Networking System and Its Improvement Strategy" is published in Electric Power Automation Equipment, Vol. 44, No. 5, 2024, pp. 51-57. Based on the establishment of a state space small signal model of the energy storage VSG parallel networking system, this article gives the reasons for the existence of power frequency oscillation in the system and its suppression method. However, the state space equation needs to be re-established when the system structure and parameters change, which makes the system modeling process cumbersome and complicated, and does not consider the applicability and feasibility of this method in a multi-energy storage VSG grid-connected system.

[0005] An article entitled "Analysis on the Mechanism of Low-frequency Power Oscillation in Multi-virtual Synchronous Generator Parallel Systems" is published in Automation of Electric Power Systems, Vol. 48, No. 19, 2024, pp. 89-100. This article proposes a modeling method for multi-GFVSG grid-connected systems based on an equivalent model, derives the mathematical expression of the equivalent model, and analyzes the influence of different system parameters on the power frequency oscillation frequency of the multi-GFVSG grid-connected system. However, it has the problems of limited scope of application and poor application flexibility. In particular, the accuracy of the constructed equivalent model decreases significantly as the difference in oscillation frequencies of the multi-GFVSG grid-connected system becomes larger.

[0006] An article entitled “A unified method of frequency oscillation characteristicanalysis for multi-VSG grid-connected system” by QIN BS, XU YH, YUAN C, et al., IEEE Transactions on Power Delivery, Vol. 37, No. 1, 2022, pp. 279-289, proposes a P / ω “admittance” method based on the principle of electromechanical analogy, which can directly use circuit theory to analyze the power frequency oscillation characteristics of multi-GFVSG grid-connected systems. It has the advantages of easy expansion and wide application range, but only applies the P / ω “admittance” model to the system mathematical modeling and its characteristic analysis level, and does not further study the feasibility and effectiveness of the P / ω “admittance” model in circuit replacement simulation.

[0007] From the above, it can be seen that the existing technology can provide certain solutions and technical support for the complete description of the dynamic response characteristics of the multi-GFVSG system and the theoretical analysis of the control strategy of the multi-machine system. When used for the analysis of the power-frequency response characteristics of the multi-GFVSG grid-connected system and the research on its suppression method, there are still disadvantages such as the need to detect the grid frequency, complex spatial state equations, poor application flexibility and limited scope of application. Summary of the invention

[0008] In order to overcome the limitations of various technical solutions given in the background technology, the present invention provides a simulation substitution method for a multi-configuration virtual synchronous machine (GFVSG) grid-connected system, which still has the problems of needing to detect the grid frequency, complex spatial state equations, poor application flexibility and limited scope of application when studying the power-frequency response characteristics analysis and suppression method of a multi-configuration virtual synchronous machine (GFVSG) grid-connected system. The method uses the electromechanical analogy principle to construct a mechanical "admittance" model of a multi-GFVSG grid-connected system. Based on the mechanical "admittance" model, a transfer function that can fully describe the active command input and grid disturbance response of the multi-GFVSG system is derived, and the power-frequency response characteristics of the multi-GFVSG grid-connected system are analyzed by using the transfer function, and a circuit substitution simulation model of the multi-GFVSG grid-connected system is built by replacing mechanical components with circuit system components, and the power-frequency response characteristics of the multi-GFVSG grid-connected system are verified by using the circuit substitution simulation results, thereby ensuring the feasibility of using the circuit simulation model to analyze the power-frequency response characteristics of the multi-GFVSG grid-connected system. The present invention has the advantages of accurately analyzing the power frequency response characteristics of the system without establishing a complex multi-GFVSG grid-connected system simulation model and having a small amount of calculation, and can be conveniently applied to the research on power frequency oscillation characteristic analysis and response performance optimization of the multi-GFVSG grid-connected system.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A simulation substitution method for a multi-network virtual synchronous machine grid-connected system includes the following steps:

[0011] Step 1, using the electromechanical analogy principle, the rotor motion equation of the grid-forming virtual synchronous machine (GFVSG) and the voltage and current equation of the RLC circuit are compared to obtain the analogy relationship between the mechanical elements and the circuit system elements;

[0012] Step 2: Based on the analogy relationship obtained in step 1, the power frequency small signal model of the GFVSG single-machine grid-connected mode is equivalent to a mechanical "admittance" two-terminal network including a current source and a first "admittance" and a second "admittance";

[0013] Step 3, considering the influence of grid impedance, the two-terminal networks of mechanical "admittance" obtained in step 2 are connected in sequence to obtain the mechanical "admittance" model of the multi-GFSVG grid-connected system;

[0014] Step 4: Based on the analogy between the mechanical elements and the circuit system elements obtained in step 1, the circuit system elements are used to build the mechanical "admittance" model of the multi-GFSVG grid-connected system obtained in step 3, and a circuit replacement simulation model of the multi-GFSVG grid-connected system is obtained.

[0015] Preferably, the rotor motion equation of the GFVSG in step 1 is:

[0016]

[0017] The voltage and current equations for the RLC circuit are:

[0018]

[0019] By comparison, the corresponding relationship between mechanical components and circuit system components is: ΔP ref Corresponding to i S , ΔP e Corresponding to i L , 1 / Dω0 corresponds to R, Jω0 corresponds to C, Δω corresponds to u, Δω c Corresponding to u c , 1 / K corresponds to L; where P ref is the active power instruction of GFVSG, P e is the active power of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, ω is the angular frequency of GFVSG, ω c is the angular frequency of the AC busbar at the common connection point, J is the virtual inertia parameter of GFVSG, K is the synchronous voltage coefficient of GFVSG, Δ represents the small disturbance at the equilibrium point, i S is the current source of the RLC circuit, i L is the inductor current of the RLC circuit, R is the parallel resistance of the RLC circuit, C is the parallel capacitance of the RLC circuit, u is the port voltage of the RC parallel branch in the RLC circuit, L is the series inductance of the RLC circuit, u c is the terminal voltage of the RLC circuit.

[0020] Preferably, the "admittance" in step 2 refers to the inverse of the impedance, and the current source of the mechanical "admittance" two-terminal network is ΔP after analogy in step 1 ref , the first "admittance" of the two-terminal network of mechanical "admittance" is the inverse Y of the equivalent impedance of Jω0 and 1 / Dω0 in parallel after analogy in step 1 a , the second "admittance" of the two-terminal network is the reciprocal Y of the 1 / K equivalent impedance after the analogy in step 1 b , Y a , Y b The expressions are:

[0021]

[0022] Wherein, J is the virtual inertia parameter of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, K is the synchronous voltage coefficient of GFVSG, and s is the Laplace operator.

[0023] Preferably, the grid impedance in step 3 adopts the "admittance" Yg Description, Y g The expression is:

[0024]

[0025] Among them, K g is the synchronous voltage coefficient of the power grid, and s is the Laplace operator.

[0026] Preferably, the circuit replacement simulation model of the multi-GFVSG grid-connected system in step 4 is S Alternative ΔP ref ,i L Alternative ΔP e , R replaces 1 / Dω0, C replaces Jω0, u replaces Δω, u c Substitution of Δω c , L replaces 1 / K, L g Replace 1 / K g Circuit replacement simulation model; where P ref is the active power instruction of GFVSG, P e is the active power of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, ω is the angular frequency of GFVSG, ω c is the angular frequency of the AC busbar at the common connection point, J is the virtual inertia parameter of GFVSG, K is the synchronous voltage coefficient of GFVSG, Δ represents the small disturbance at the equilibrium point, i S is the current source of the RLC circuit, i L is the inductor current of the RLC circuit, R is the parallel resistance of the RLC circuit, C is the parallel capacitance of the RLC circuit, u is the port voltage of the RC parallel branch in the RLC circuit, L is the series inductance of the RLC circuit, u c is the terminal voltage of the RLC circuit, L g is the series inductance of the grid.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention discloses a simulation substitution method for a multi-network type virtual synchronous machine grid-connected system. The method uses the electromechanical analogy principle to establish a mechanical "admittance" model of a multi-GFVSG grid-connected system, and then replaces mechanical components with circuit system components to build a circuit substitution simulation model of the multi-GFVSG grid-connected system. The present invention has the advantages of accurately analyzing the power frequency response characteristics of the system without establishing a complex multi-GFVSG grid-connected system simulation model and a small amount of calculation, and can be conveniently applied to the research on power frequency oscillation characteristic analysis and response performance optimization of the multi-GFVSG grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1It is a power frequency small signal model of a grid-connected virtual synchronous machine in a grid-connected mode according to an embodiment of the present invention.

[0030] Figure 2 1 is a topological diagram of an RLC circuit in an embodiment of the present invention.

[0031] Figure 3 It is a power-frequency equivalent two-terminal network of a meshed virtual synchronous machine system in an embodiment of the present invention.

[0032] Figure 4 It is a circuit replacement simulation model of the multi-network type virtual synchronous machine grid-connected system of the embodiment of the present invention.

[0033] Figure 5 It is the Bode diagram of the active command input response coefficient of the multi-network virtual synchronous machine grid-connected system under different parameters.

[0034] Figure 6 It is a simulation result diagram of a multi-network type virtual synchronous machine grid-connected system after adopting the present invention.

[0035] Figure 7 It is a comparison diagram of simulation waveforms before and after the multi-network type virtual synchronous machine grid-connected system adopts the present invention. DETAILED DESCRIPTION

[0036] The following specific implementation will be further described in conjunction with the above drawings, as follows:

[0037] See also Figure 1 The present invention proposes a simulation substitution method for a multi-network virtual synchronous machine grid-connected system, comprising the following steps:

[0038] Step 1: Using the electromechanical analogy principle, the rotor motion equation of the grid-type virtual synchronous machine (GFVSG) and Figure 2 By comparing the voltage and current equations of the RLC circuit shown, we can get the analogy between mechanical components and circuit system components;

[0039] Among them, the rotor motion equation of GFVSG is:

[0040]

[0041] The voltage and current equations for the RLC circuit are:

[0042]

[0043] By comparison, the corresponding relationship between mechanical components and circuit system components is: ΔP ref Corresponding to i S , ΔP e Corresponding to i L , 1 / Dω0 corresponds to R, Jω0 corresponds to C, Δω corresponds to u, Δωc Corresponding to u c , 1 / K corresponds to L; where P ref is the active power instruction of GFVSG, P e is the active power of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, ω is the angular frequency of GFVSG, ω c is the angular frequency of the AC busbar at the common connection point, J is the virtual inertia parameter of GFVSG, K is the synchronous voltage coefficient of GFVSG, Δ represents the small disturbance at the equilibrium point, i S is the current source of the RLC circuit, i L is the inductor current of the RLC circuit, R is the parallel resistance of the RLC circuit, C is the parallel capacitance of the RLC circuit, u is the port voltage of the RC parallel branch in the RLC circuit, L is the series inductance of the RLC circuit, u c is the terminal voltage of the RLC circuit.

[0044] Step 2: Based on the analogy relationship obtained in step 1, the power frequency small signal model of GFVSG single machine grid-connected mode is equivalent to Figure 3 The mechanical "admittance" two-terminal network shown includes a current source and first and second "admittances";

[0045] Among them, "admittance" refers to the reciprocal of impedance. The current source of the mechanical "admittance" two-terminal network is ΔP after the analogy in step 1. ref , the first "admittance" of the two-terminal network of mechanical "admittance" is the inverse Y of the equivalent impedance of Jω0 and 1 / Dω0 in parallel after analogy in step 1 a , the second "admittance" of the two-terminal network is the reciprocal Y of the 1 / K equivalent impedance after the analogy in step 1 b , Y a , Y b The expressions are:

[0046]

[0047] Wherein, J is the virtual inertia parameter of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, K is the synchronous voltage coefficient of GFVSG, and s is the Laplace operator.

[0048] Step 3, considering the influence of grid impedance, the two-terminal networks of mechanical "admittance" obtained in step 2 are connected in sequence to obtain the mechanical "admittance" model of the multi-GFSVG grid-connected system;

[0049] Among them, the grid impedance adopts "admittance" Y g Description, Y g The expression is:

[0050]

[0051] K g The calculation formula used is:

[0052]

[0053] Among them, K g is the synchronous voltage coefficient of the power grid, U PCC is the AC bus voltage amplitude at the common connection point, E is the output voltage amplitude of GFVSG, X g is the equivalent impedance of the power grid, s is the Laplace operator, ω c is the angular frequency of the AC bus at the common connection point, and Δ represents the small disturbance at the equilibrium point.

[0054] Step 4: Based on the analogy between the mechanical components and the circuit system components obtained in step 1, the circuit system components are used to build the mechanical "admittance" model of the multi-GFSVG grid-connected system obtained in step 3, and obtain Figure 4 The circuit replacement simulation model of the multi-GFSVG grid-connected system is shown.

[0055] Among them, the circuit replacement simulation model of the multi-GFVSG grid-connected system is based on i S Alternative ΔP ref ,i L Alternative ΔP e , R replaces 1 / Dω0, C replaces Jω0, u replaces Δω, u c Substitution of Δω c , L replaces 1 / K, L g Replace 1 / K g Circuit replacement simulation model; where P ref is the active power instruction of GFVSG, P e is the active power of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, ω is the angular frequency of GFVSG, ω c is the AC bus angular frequency at the common connection point, J is the virtual inertia parameter of GFVSG, K is the synchronous voltage coefficient of GFVSG, Δ represents the small disturbance at the equilibrium point, i S is the current source of the RLC circuit, i L is the inductor current of the RLC circuit, R is the parallel resistance of the RLC circuit, C is the parallel capacitance of the RLC circuit, u is the port voltage of the RC parallel branch in the RLC circuit, L is the series inductance of the RLC circuit, u c is the terminal voltage of the RLC circuit, L g is the series inductance of the grid, ω g is the grid angular frequency.

[0056] Example

[0057] In order to verify the correctness of the simulation substitution method of the multi-grid type virtual synchronous machine grid-connected system proposed in the present invention, the mechanical "admittance" model of the multi-grid type virtual synchronous machine (GFVSG) grid-connected system is used to derive the transfer function that can fully describe the active command input and grid disturbance response of the multi-GFVSG system, and perform frequency domain analysis to obtain the effects of different parameter changes on the power frequency oscillation characteristics and their changing laws of the multi-GFVSG grid-connected system. Then, the simulation substitution model of the multi-grid type virtual synchronous machine grid-connected system proposed in the present invention is used for time domain simulation analysis, and the simulation results are compared and verified with the frequency domain analysis results. Furthermore, the simulation results of the simulation substitution model of the multi-grid type virtual synchronous machine grid-connected system proposed in the present invention are compared and verified with the simulation results of the complete multi-GFVSG grid-connected system model. Specifically as follows:

[0058] In this embodiment, the differences between GFVSGs are ignored, and it is assumed that the GFVSGs have the same parameters, and the system line is set to be inductive. The relevant parameters are set as follows:

[0059] The rated capacity of GFVSG is 250kVA, and the grid angular frequency is ω g is 314.16 rad / s, the rated angular frequency ω0 is 314.16 rad / s, and the initial value of the virtual inertia parameter J is 6 kg·m 2 , AC bus voltage amplitude at the common connection point U PCC is 311V, the GFVSG output voltage amplitude E is 311V, and the transmission line equivalent inductance L line The initial value is 0.05mH, and the line equivalent impedance X≈L line The initial value of ω0 is 0.016Ω, and the equivalent inductance of the power grid is L G The initial value is 0.05mH, the equivalent impedance of the power grid is X g ≈L G The initial value of ω0 is 0.016Ω, and the virtual damping parameter D is 50.66J / rad.

[0060] In this embodiment, in order to obtain the power frequency oscillation characteristics and its variation law of the multi-GFVSG grid-connected system in subsequent analysis, the transfer function of active power is obtained through the mechanical "admittance" model of the multi-GFVSG grid-connected system:

[0061] according to Figure 1 The power frequency small signal model of the GFVSG in grid-connected mode shown in the figure has an active power that satisfies the following equation:

[0062] ΔP e =Φ(s)ΔP ref -Y p (s)Δω c (1)

[0063] In the formula

[0064] according to Figure 4 The multi-network virtual synchronous machine grid-connected system replacement simulation model of the embodiment of the present invention is shown. When n GFVSGs are connected to the grid at the same time in the system, the system node "admittance" matrix Y satisfies:

[0065]

[0066] For the mth GFVSG in the system, the corresponding non-zero elements in the “admittance” matrix should be:

[0067]

[0068] On the basis of establishing the "admittance" matrix of the examined system nodes, the active power expression of the mth grid-connected GFVSG is obtained as follows:

[0069]

[0070] Combining equations (1), (2), (3) and (4), the transfer function that fully describes the active power command input and grid disturbance response of the multi-GFVSG system is simplified as follows:

[0071]

[0072] in, || indicates parallel connection.

[0073] In this embodiment, in order to verify the correctness of the proposed simulation alternative method for a multi-network virtual synchronous machine grid-connected system, the Bode diagram of the first GFVSG active command input response coefficient M1(s) of the GFVSG output power transfer function under different parameters is drawn according to the frequency domain analysis method:

[0074] (1) Impact of the number of grid-connected GFVSGs n: 2, 4, and 6 GFVSGs are connected in sequence.

[0075] (2) Grid equivalent impedance X g ≈L G Impact of ω0: 4 GFVSGs are fixedly connected and the grid equivalent inductance L is changed in sequence G The values ​​are 0.05mH, 0.25mH, and 0.50mH.

[0076] (3) Influence of virtual inertia parameter J: Four GFVSGs were fixedly incorporated and the value of virtual inertia J was changed to 1 kg / m 2 , 6kg / m 2 , 12kg / m 2 .

[0077] (4) Line equivalent impedance X≈L line Impact of ω0: Four GFVSGs are fixedly connected and the equivalent inductance L of the transmission line is changed in sequence line The values ​​are 0.01mH, 0.05mH, and 0.1mH.

[0078] In this embodiment, in order to verify the correctness of the proposed simulation substitution method for a multi-network virtual synchronous machine grid-connected system, a simulation model of a multi-GFVSG grid-connected system using the present invention is built, and the active power instruction P of the first GFVSG in the multi-GFVSG grid-connected system is calculated. ref1 A 60kW step disturbance is applied, and the influence of different parameter changes on the active power response P1 of the first GFVSG is considered. Four time domain simulation conditions are set as follows:

[0079] The simulation condition 1 is set as: the impact of the number n of grid-connected GFVSGs, that is, 2, 4, and 6 GFVSGs are connected in sequence.

[0080] Set simulation condition 2 as: grid equivalent impedance X g ≈L G The influence of ω0, that is, the four GFVSGs are fixedly connected and the equivalent inductance L of the grid is changed in turn. G The values ​​are 0.05mH, 0.25mH, and 0.50mH.

[0081] Set simulation condition 3 as follows: the influence of virtual inertia parameter J, that is, four GFVSGs are fixedly incorporated, and the value of virtual inertia J is changed to 1kg / m 2 , 6kg / m 2 12kg / m 2 .

[0082] Set simulation condition 4 as: Line equivalent impedance X≈L line The influence of ω0, that is, the fixed connection of 4 GFVSGs, changes the equivalent inductance L of the transmission line in turn line The values ​​are 0.01mH, 0.05mH, and 0.1mH.

[0083] In this embodiment, in order to further verify the correctness of the proposed simulation substitution method for a multi-network type virtual synchronous machine grid-connected system, a simulation model of a multi-GFVSG grid-connected system before and after the present invention is built for simulation comparison and verification. The active power instruction P of the first GFVSG in the multi-GFVSG grid-connected system is compared with the active power instruction P of the first GFVSG in the multi-GFVSG grid-connected system. ref1 A 60kW step disturbance is applied, and the influence of different parameter changes on the active power response P1 of the first GFVSG is considered. Four time domain simulation comparison conditions are set up, as follows:

[0084] The simulation comparison condition 1 is set as: the impact of the number n of grid-connected GFVSGs, that is, 2, 4, and 6 GFVSGs are connected in sequence.

[0085] Set the simulation comparison condition 2 as: grid equivalent impedance X g ≈L G The influence of ω0, that is, the four GFVSGs are fixedly connected and the equivalent inductance L of the grid is changed in turn. G The values ​​are 0.05mH, 0.25mH and 0.50mH.

[0086] Simulation comparison condition 3 is set as follows: the influence of virtual inertia parameter J, that is, 4 GFVSGs are fixedly incorporated, and the value of virtual inertia J is changed to 1kg / m 2 , 6kg / m 2 and 12kg / m 2 .

[0087] Set the simulation comparison condition 1 as: line equivalent impedance X≈L line The influence of ω0, that is, the fixed connection of 4 GFVSGs, changes the equivalent inductance L of the transmission line in turn line The values ​​are 0.01mH, 0.05mH and 0.1mH.

[0088] According to the above frequency domain analysis, we can get Figure 5 The Bode diagram of the active input command response coefficient of the multi-network virtual synchronous machine grid-connected system under different parameters is shown in the figure. Among them, M1(s) represents the active input command response coefficient of the first GFVSG, n represents the number of GFVSGs connected to the grid, and X g Represents the equivalent impedance of the power grid, L G represents the equivalent inductance of the power grid, J represents the virtual inertia parameter of GFVSG, X represents the equivalent impedance of the line, L line Transmission line equivalent inductance, Figure 5 (a) is the Bode diagram of M1(s) of the multi-GFVSG grid-connected system when n changes, that is, Figure 5 In (a), the solid line, dashed line and dotted line represent the Bode diagram of M1(s) when n=2, n=4 and n=6, respectively. Figure 5 (b) is the M1(s) of the multi-GFVSG grid-connected system at L g The Bode diagram when the Figure 5 In (b), the solid line, dashed line and dotted line represent L G =0.05, L G =0.25 and L G =0.5, the Bode diagram of M1(s), Figure 5 (c) is the Bode diagram of M1(s) of the multi-GFVSG grid-connected system when J changes, that is, Figure 5In (c), the solid line, dashed line and dotted line represent the Bode diagram of M1(s) when J=1, J=6 and J=12, respectively. Figure 5 (d) is the Bode diagram of M1(s) of the multi-GFVSG grid-connected system when L changes, that is, Figure 5 In (d), the solid line, dashed line and dotted line represent L line =0.01, L line =0.05 and L line Bode plot of M1(s) when =0.1.

[0089] According to the above simulation conditions, we can get Figure 6 The simulation result diagram of the multi-network virtual synchronous machine grid-connected system after adopting the present invention is shown. Wherein, P1 represents the output active power of the first GFVSG, n represents the number of GFVSG grid-connected, X g Represents the equivalent impedance of the power grid, L G represents the equivalent inductance of the power grid, J represents the virtual inertia parameter of GFVSG, X represents the equivalent impedance of the line, L line represents the equivalent inductance of the transmission line, Figure 6 (a) is the simulation waveform of P1 when n changes after the multi-GFVSG grid-connected system adopts the present invention, Figure 6 (b) The multi-GFVSG grid-connected system adopts the present invention and P1 is at L G The simulation waveform when changing, Figure 6 (c) is the simulation waveform of P1 when J changes after the multi-GFVSG grid-connected system adopts the present invention, Figure 6 (d) The multi-GFVSG grid-connected system adopts the present invention after P1 is L line The simulation waveform when it changes, that is Figure 6 In (a), the solid line, dashed line and dotted line represent the simulation waveform of P1 when n=2, n=4 and n=6 respectively. Figure 6 In (b), the solid line, dashed line and dotted line represent L G =0.05, L G =0.25 and L G = 0.5, the simulation waveform of P1, Figure 6 In (c), the solid line, dashed line and dotted line represent the simulation waveform of P1 when J=1, J=6 and J=12 respectively. Figure 6 In (d), the solid line, dashed line and dotted line represent L line =0.01, L line =0.05 and L line The simulation waveform of P1 when =0.1.

[0090] According to the above simulation comparison conditions, we can get Figure 7The simulation waveform comparison diagram of the multi-network virtual synchronous machine grid-connected system before and after the present invention is adopted is shown. Wherein, P1 represents the output active power of the first GFVSG, n represents the number of GFVSG grid-connected, X g Represents the equivalent impedance of the power grid, L G represents the equivalent inductance of the power grid, J represents the virtual inertia parameter of GFVSG, X represents the equivalent impedance of the line, L line Equivalent inductance of a transmission line, the solid line represents the simulation waveform before the present invention is adopted, and the dotted line represents the simulation waveform after the present invention is adopted. Figure 7 (a) is a comparison of the simulation waveforms of P1 when n changes before and after the multi-GFVSG grid-connected system adopts the present invention, that is, Figure 7 In (a), the curves pointed to by n=2, n=4 and n=6 respectively represent the simulation waveform comparison of P1 when n=2, n=4 and n=6 before and after the multi-GFVSG grid-connected system adopts the present invention. Figure 7 (b) The multi-GFVSG grid-connected system adopts the present invention before and after P1 in L g The simulation waveform comparison when changing, that is Figure 7 (b) In G =0.05, L G =0.25 and L G = 0.5 respectively represent the curves of P1 in L before and after the multi-GFVSG grid-connected system adopts the present invention. G =0.05, L G =0.25 and L G =0.5 when the simulation waveform comparison, Figure 7 (c) is the comparison of the simulation waveforms of P1 when J changes before and after the multi-GFVSG grid-connected system adopts the present invention, that is, Figure 7 In (c), the curves pointed to by J=1, J=6 and J=12 respectively represent the simulation waveform comparison of P1 when J=1, J=6 and J=12 before and after the multi-GFVSG grid-connected system adopts the present invention. Figure 7 (d) The multi-GFVSG grid-connected system adopts the present invention before and after P1 in L line The simulation waveform comparison when changing, that is Figure 7 (d) In line =0.01, L line =0.05 and L line = 0.1 respectively represent the curves of P1 in L before and after the multi-GFVSG grid-connected system adopts the present invention. line =0.01, L line =0.05 and L line =0.1 when the simulation waveform is compared.

[0091] according to Figure 5 (a) It can be seen that when L G=0.05mH, J=6kg·m 2 , L line =0.05mH, the Bode diagram of coefficient M1(s) has two resonance peaks, and the resonance peak value decreases with the increase of the number of grid-connected GFVSGs n (2, 4, 6), and the bandwidth increases slightly. This means that there will be two oscillations of different frequencies in the system step response. With the increase of the number of grid-connected units n, the oscillation will gradually decrease and the response will be slightly faster.

[0092] according to Figure 5 (b) It can be seen that when n = 4 and J = 6 kg·m 2 , L line =0.05mH, the Bode diagram of coefficient M1(s) has two resonance peaks, and the resonance peak value increases with the equivalent inductance L of the power grid. G (0.05mH, 0.25mH, 0.5mH) increases, and the bandwidth decreases. This means that there will be two oscillations of different frequencies when the system step responds. As the equivalent inductance L G As the value increases, the oscillation will gradually decrease and the response will become slower.

[0093] according to Figure 5 (c) It can be seen that when n = 4, L G =0.05mH, L line =0.05mH, the Bode diagram of coefficient M1(s) has a resonance peak, and the resonance peak value increases with the virtual inertia parameter J(1kg·m 2 , 6kg·m 2 、12kg·m 2 ), and a new resonance peak is generated on the left side of the original resonance peak, and the bandwidth is reduced. This shows that when the system step response increases, the oscillation will gradually intensify and generate new resonance, and the response will slow down as the virtual inertia parameter J increases.

[0094] according to Figure 5 (d) It can be seen that when n = 4, L G =0.05mH, J=6kg·m 2 When the coefficient M1(s) is used, the Bode diagram has two resonance peaks. The resonance peak value increases with the equivalent inductance L of the transmission line. line The increase of (0.01mH, 0.05mH, 0.1mH) is slightly reduced, and the bandwidth is slightly reduced. This means that there will be two oscillations of different frequencies in the system step response. line As the value of increases, the oscillation decreases slightly and the response becomes slightly slower.

[0095] according to Figure 6 (a) It can be seen that when L G =0.05mH, J=6kg·m 2 , Lline =0.05mH, for P ref1 When a step disturbance of 60 kW is applied, the output power P1 has two oscillations of different frequencies. As the number of grid-connected GFVSGs n (2, 4, 6) increases, the oscillation amplitude decreases, and the response speed becomes slightly faster.

[0096] according to Figure 6 (b) It can be seen that when n = 4 and J = 6 kg·m 2 , L line =0.05mH, for P ref1 When a 60kW step disturbance is applied, the output power P1 has two oscillations of different frequencies. G The increase of (0.01mH, 0.05mH, 0.1mH) reduces the oscillation amplitude and the response speed becomes faster.

[0097] according to Figure 6 (c) It can be seen that when n = 4, L G =0.05mH, L line =0.05mH, for P ref1 When a 60kW step disturbance is applied, the output power P1 has two oscillations of different frequencies, which change with the virtual inertia parameter J (1kg·m 2 , 6kg·m 2 、12kg·m 2 ) increases, the oscillation becomes more violent, the oscillation amplitude increases, new frequency oscillations appear, and the response speed becomes slower.

[0098] according to Figure 6 (d) It can be seen that when n = 4, L G =0.05mH, J=6kg·m 2 , for P ref1 When a 60kW step disturbance is applied, the output power P1 has two oscillations of different frequencies. line The increase of (0.01mH, 0.05mH, 0.1mH) slightly reduces the oscillation amplitude and slows down the response speed.

[0099] Will Figure 6 (a) and Figure 5 After comparing the results of (a), it is not difficult to see that the present embodiment Figure 6 The simulation results of a multi-network virtual synchronous machine grid-connected system in (a) can be compared with Figure 5 The transfer function Bode diagram analysis results in (a) maintain a one-to-one correspondence, which fully reflects the correctness of the simulation substitution method for the multi-network type virtual synchronous machine grid-connected system proposed in the present invention.

[0100] Will Figure 6 (b) and Figure 5 After comparing the results of (b), it is not difficult to see that the present embodiment Figure 6 The simulation results of a multi-network virtual synchronous machine grid-connected system in (b) can be compared with Figure 5 The transfer function Bode diagram analysis results in (b) maintain a one-to-one correspondence, which fully reflects the correctness of the simulation substitution method for the multi-network type virtual synchronous machine grid-connected system proposed in the present invention.

[0101] Will Figure 6 (c) and Figure 5 After comparing the results of (c), it is not difficult to see that the present embodiment Figure 6 The simulation results of a multi-network virtual synchronous machine grid-connected system in (c) can be compared with Figure 5 The transfer function Bode diagram analysis results in (c) maintain a one-to-one correspondence, which fully reflects the correctness of the simulation substitution method for the multi-network type virtual synchronous machine grid-connected system proposed in the present invention.

[0102] Will Figure 6 (d) and Figure 5 After comparing the results of (d), it is not difficult to see that this embodiment Figure 6 The simulation results of a multi-network virtual synchronous machine grid-connected system in (d) can be compared with Figure 5 The transfer function Bode diagram analysis results in (d) maintain a one-to-one correspondence, which fully reflects the correctness of the simulation substitution method for the multi-network type virtual synchronous machine grid-connected system proposed in the present invention.

[0103] according to Figure 7 (a) It can be seen that when L G =0.05mH, J=6kg·m 2 , L line =0.05mH, for P ref1 When a 60kW step disturbance is applied and the number of grid-connected machines n changes, the results of the two simulation methods are consistent, which once again demonstrates the correctness of the simulation alternative method for a multi-grid type virtual synchronous machine grid-connected system proposed in the present invention.

[0104] according to Figure 6 (b) It can be seen that when n = 4 and J = 6 kg·m 2 , L line =0.05mH, for P refl When a 60kW step disturbance is applied, the grid equivalent inductance L G When , the results of the two simulation methods are consistent, which once again demonstrates the correctness of the simulation substitution method for the multi-network type virtual synchronous machine grid-connected system proposed in the present invention.

[0105] according to Figure 6 (c) It can be seen that when n = 4, LG =0.05mH, L line =0.05mH, for P ref1 When a 60kW step disturbance is applied, the results of the two simulation methods are consistent when the virtual inertia parameter J changes, which once again demonstrates the correctness of the simulation alternative method for the multi-configuration grid-connected virtual synchronous machine system proposed in the present invention.

[0106] according to Figure 6 (d) It can be seen that when n = 4, L G =0.05mH, J=6kg·m 2 When P ref1 When a 60kW step disturbance is applied, the equivalent inductance L of the transmission line is line When , the results of the two simulation methods are consistent, which once again demonstrates the correctness of the simulation substitution method for the multi-network type virtual synchronous machine grid-connected system proposed in the present invention.

[0107] The above description is a detailed description of the preferred feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modified changes completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A simulation substitution method for a multi-network virtual synchronous machine grid-connected system, characterized in that: The steps include: Step 1, using the electromechanical analogy principle, the rotor motion equation of the grid-forming virtual synchronous machine (GFVSG) and the voltage and current equation of the RLC circuit are compared to obtain the analogy relationship between the mechanical elements and the circuit system elements; Step 2: Based on the analogy relationship obtained in step 1, the power frequency small signal model in the GFVSG single-machine grid-connected mode is equivalent to a mechanical "admittance" two-terminal network including a current source and a first "admittance" and a second "admittance"; Step 3, considering the influence of grid impedance, the two-terminal networks of mechanical "admittance" obtained in step 2 are connected in sequence to obtain the mechanical "admittance" model of the multi-GFSVG grid-connected system; Step 4: Based on the analogy between the mechanical components and the circuit system components obtained in step 1, the circuit system components are used to build the mechanical "admittance" model of the multi-GFSVG grid-connected system obtained in step 3, and a circuit replacement simulation model of the multi-GFSVG grid-connected system is obtained.

2. The simulation substitution method of a multi-network virtual synchronous machine grid-connected system according to claim 1, characterized in that: The rotor motion equation of the GFVSG in step 1 is: The voltage and current equations for the RLC circuit are: By comparison, the corresponding relationship between mechanical components and circuit system components is: ΔP ref Corresponding to i S , ΔP e Corresponding to i L , 1 / Dω0 corresponds to R, Jω0 corresponds to C, Δω corresponds to u, Δω c Corresponding to u c , 1 / K corresponds to L; Among them, P ref is the active power instruction of GFVSG, P e is the active power of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, ω is the angular frequency of GFVSG, ω c is the angular frequency of the AC busbar at the common connection point, J is the virtual inertia parameter of GFVSG, K is the synchronous voltage coefficient of GFVSG, Δ represents the small disturbance at the equilibrium point, i S is the current source of the RLC circuit, i L is the inductor current of the RLC circuit, R is the parallel resistance of the RLC circuit, C is the parallel capacitance of the RLC circuit, u is the port voltage of the RC parallel branch in the RLC circuit, L is the series inductance of the RLC circuit, u c is the terminal voltage of the RLC circuit.

3. The simulation substitution method of a multi-network virtual synchronous machine grid-connected system according to claim 1, characterized in that: The "admittance" in step 2 refers to the reciprocal of impedance. The current source of the mechanical "admittance" two-terminal network is ΔP after analogy in step 1. ref , the first "admittance" of the two-terminal network of mechanical "admittance" is the inverse Y of the equivalent impedance of Jω0 and 1 / Dω0 in parallel after analogy in step 1 a , the second "admittance" of the two-terminal network of mechanical "admittance" is the inverse of the 1 / K equivalent impedance after the analogy in step 1, Y b , Y a , Y b The expressions are: Wherein, J is the virtual inertia parameter of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, K is the synchronous voltage coefficient of GFVSG, and s is the Laplace operator.

4. The simulation substitution method of a multi-network virtual synchronous machine grid-connected system according to claim 1, characterized in that: In step 3, the grid impedance adopts "admittance" Y g Description, Y g The expression is: Among them, K g is the synchronous voltage coefficient of the power grid, and s is the Laplace operator.

5. The simulation substitution method of a multi-network virtual synchronous machine grid-connected system according to claim 1, characterized in that: The circuit replacement simulation model of the multi-GFVSG grid-connected system in step 4 is S Alternative ΔP ref ,i L Alternative ΔP e , R replaces 1 / Dω0, C replaces Jω0, u replaces Δω, u c Substitution of Δω c , L replaces 1 / K, L g Replace 1 / K g Circuit replacement simulation model; Among them, P ref is the active power instruction of GFVSG, P e is the active power of GFVSG, D is the virtual damping parameter of GFVSG, ω0 is the rated angular frequency of GFVSG, ω is the angular frequency of GFVSG, ω c is the angular frequency of the AC busbar at the common connection point, J is the virtual inertia parameter of GFVSG, K is the synchronous voltage coefficient of GFVSG, Δ represents the small disturbance at the equilibrium point, i S is the current source of the RLC circuit, i L is the inductor current of the RLC circuit, R is the parallel resistance of the RLC circuit, C is the parallel capacitance of the RLC circuit, u is the port voltage of the RC parallel branch in the RLC circuit, L is the series inductance of the RLC circuit, u c is the terminal voltage of the RLC circuit, L g is the series inductance of the grid.

Images