A method for analyzing the stability of a power grid containing multiple grid-connected converters

Abstract

The present invention relates to the field of electric power technology, and discloses a method for analyzing the stability of a power grid of a new energy unit containing multiple grid-connected converters, including: S1, taking into account the multi-time scale coupling characteristics of the new energy unit, constructing a Hamiltonian model of a control system of a grid-connected converter system port containing a high proportion of new energy units; S2, establishing a mathematical model of a single new energy unit, and applying a coherent equivalence criterion to construct an aggregation equivalence model of a new energy unit group composed of multiple new energy units; S3, deriving a stability criterion and a system parameter stability domain of a Hamiltonian model of a control system of a grid-connected converter system port containing a high proportion of new energy based on a passivity theory; S4, based on the established stability criterion, studying a stability improvement scheme of a Hamiltonian model of a control system of a grid-connected converter system port containing a high proportion of new energy from the perspective of control strategy improvement and parameter design. The present invention is conducive to ensuring that large-scale new energy is safely and reliably connected to the power grid.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a method for analyzing the stability of a power grid of a new energy unit containing multiple grid-connected converters. Background Art

[0002] The development of new energy power generation and grid connection technology has become a core part of my country's energy sustainable development strategy. Among them, wind power and photovoltaic power generation have received key development and support from the country due to their sustainability, flexibility and environmental friendliness, and related new energy power generation and grid connection projects have been successively built in various places.

[0003] In recent years, with the rapid development of new energy sites, the grid structure is undergoing significant changes. Most new energy power stations are located in remote areas and connected to the grid through long-distance transmission lines. Weak damping has become an inherent feature of the grid. The increasing proportion of new energy grid connection has also brought many new challenges to the safe and stable operation of the grid.

[0004] The impact of high-proportion renewable energy access on grid stability is becoming increasingly prominent. Currently, transient modeling and analysis of grids with high-proportion renewable energy mainly have the following problems: the impact mechanism of grid-connected converters of renewable energy units on transient stability of grids needs to be studied in depth. Since the interaction mechanism between multiple power electronic equipment and between them and the grid is not clear, even if a single grid-connected converter can operate stably, it is difficult to ensure the stable operation of complex power electronic systems (new energy units) containing multiple grid-connected converters. Therefore, it is necessary to study the impact mechanism of grid-connected converters on grid stability and quantitative analysis methods. Summary of the invention

[0005] The present invention provides a power grid stability analysis method for a new energy unit containing multiple grid-connected converters, proposes a system stability criterion and a stability domain estimation method based on the energy viewpoint, explores the influence of the grid-connected converter on the power grid stability, and provides theoretical guidance and application reference for the stable operation of the power grid.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for analyzing the stability of a power grid of a new energy generator set including multiple grid-connected converters, comprising:

[0008] S1. Establish the Hamiltonian function of the grid-connected converter system, take into account the multi-time scale coupling characteristics of the new energy units, and construct the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of new energy units;

[0009] S2. Establish a mathematical model of a single new energy unit, and apply the coherent equivalence criterion to construct an aggregated equivalence model of a new energy unit group consisting of multiple new energy units, so as to generate a general model suitable for different working conditions;

[0010] S3. Based on the Hamiltonian model of the control system of the ports of the grid-connected converter system containing a high proportion of new energy, further analyze the influence of different control loops under different working conditions of the aggregation equivalent model of the new energy unit group on the stability of the Hamiltonian model of the ports of the grid-connected converter system containing a high proportion of new energy, and derive the stability criterion and system parameter stability domain of the Hamiltonian model of the control system of the ports of the grid-connected converter system containing a high proportion of new energy based on the passivity theory, and explain the coupling characteristics and energy interaction mechanism of the multi-converter system through mathematical representation;

[0011] S4. Based on the established stability criterion, a solution to improve the stability of the Hamiltonian model of the control system of the port of the grid-connected converter system containing a high proportion of new energy is studied from the perspective of control strategy improvement and parameter design, so as to optimize the damping characteristics of the power grid.

[0012] As an optimization, the specific steps of S1 are:

[0013] S1.1. Considering the influence of different control loops, the Hamiltonian functions of the power loop, phase-locked loop, voltage loop and current loop are constructed from four time scales through physical model equivalence. The port Hamiltonian model of the control system of the grid-connected converter system for the control loops of the power loop, phase-locked loop, voltage loop and current loop is established by orthogonal decomposition and first integration method, and the dynamic response characteristics of the converter frequency and voltage under different control strategies and different time scales are analyzed.

[0014] As an optimization, in S2, different operating conditions in the general model applicable to different operating conditions include load mutation, weak power grid and power grid failure.

[0015] As an optimization, the specific steps of S2 are:

[0016] S2.1. Let a new energy unit be a new energy power generation unit, analyze the differences in dynamic characteristics of a new energy power generation unit under different working conditions, establish a full-order dynamic differential equation of the influencing factors affecting the dynamic characteristics of the new energy power generation unit, and construct a state space model of a single new energy power generation unit;

[0017] S2.2. Based on the dynamic behavior of renewable energy power generation units at multiple time scales, a reduced-order model of a single renewable energy power generation unit suitable for low-frequency oscillation analysis of power grid is constructed;

[0018] S2.3. According to Hamiltonian theory, a similarity criterion for dynamic characteristics of new energy units based on generalized Hamiltonian action is proposed, and the grouping index of multiple new energy units is determined. A fuzzy clustering algorithm is used to group and cluster the new energy units in the new energy station according to the grouping index of multiple new energy units, and the dynamic models of the new energy units in the same group are equivalently aggregated;

[0019] S2.4. Establish AGC and AVC control models for new energy stations, study the active frequency regulation characteristics and reactive voltage regulation characteristics of different types of new energy stations, construct external characteristic model equations for new energy stations, analyze the impact of the output characteristics of new energy stations on the grouping and clustering of new energy units in new energy stations, and establish a new energy unit aggregation equivalent model with dynamic equivalents of multiple new energy units.

[0020] As an optimization, the influencing factors include wind turbine tower shadow effect, phase-locked loop, virtual inertia control, and photovoltaic maximum power point tracking (MPPT).

[0021] As an optimization, in S3, different control loops under different working conditions include maximum power tracking control, low voltage ride-through control, phase-locked loop, DC voltage control, virtual inertia control, frequency / voltage droop control, and inner loop current control.

[0022] As an optimization, the specific steps of S3 are:

[0023] S3.1. Analyze the time scales of different control links and their corresponding characteristics;

[0024] S3.2. Analyze the influence of the coupling between the time scale controls responded by different control links on the Hamiltonian model of the grid-connected converter system port containing a high proportion of new energy, establish a full-order physical coupling model of the grid-connected converter, and then analyze the influence of different control loops on the dynamic behavior of the converter by applying voltage / frequency disturbance excitations of different time scales;

[0025] S3.3. Considering different working conditions, a mathematical model of multiple grid-connected converters is established, the interaction mechanism between the control responses of multiple grid-connected converters at different time scales is studied, and the influence of the number of grid-connected converters, the connection mode between the grid-connected converters, and the line parameters on the grid damping and stability are analyzed.

[0026] As an optimization, the specific steps of S4 are:

[0027] S4.1. Find the operation boundary and operation constraint of the grid-connected converter system for stable operation corresponding to the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of new energy;

[0028] S4.2. Based on the passivity theory, parameter optimization and control strategies for grid-connected converters under different operating conditions are proposed for the operating boundaries and operating constraints, and the optimal damping configuration is designed for the power grid.

[0029] As an optimization, the specific steps of S4.1 are:

[0030] S4.1.1. For a simple grid-connected converter system, study the influence mechanism of different control loops on the stability of the grid-connected converter system and the large signal stability analysis method based on Hamiltonian theory, establish the stable parameter space and operation boundary of the grid-connected converter system, and compare and analyze the changing law of the stable operation boundary of the grid-connected converter system under different time scales and different operating conditions;

[0031] S4.1.2. For complex grid-connected converter systems, based on the dissipative characteristics of the Hamiltonian system, the large signal stability criterion of the grid-connected converter system under multiple time scales is analyzed, and the constraints for the stable operation of the system are further derived. The stable parameter space containing multiple system parameters and its boundaries are calculated.

[0032] As an optimization, the specific steps of S4.2 are:

[0033] S4.2.1. Based on the grid's requirements for stability margin, propose an optimization design scheme for converter physical parameters, controller parameters, line structure and parameters from the perspective of grid parameter design;

[0034] S4.2.2. With the goal of improving the large-signal stability of the power grid, energy shaping, damping injection and virtual impedance advanced control methods are studied from the perspective of control strategy optimization, and the optimal damping configuration is designed for the power grid to ensure the passivity and robustness of the power grid.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] Due to the large number of power electronic equipment connected to the power grid, the dynamic coupling of multiple control loops of the power electronic converter itself leads to very complex dynamic characteristics of the new energy units. At present, performance testing and analysis are generally carried out on a single converter device, ignoring the interaction after multiple converters are connected to the grid, and lacking stability indicators and quantitative evaluation of grid-connected converters. The new energy unit stability evaluation method of the present invention can provide the necessary theoretical support for improving the stable operation level of a high-proportion new energy power grid, which is conducive to ensuring the safe and reliable access of large-scale new energy to the power grid, effectively reducing power outages caused by the connection of multiple converters to the grid of new energy units, and ensuring high-quality and reliable power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0038] Figure 1 The present invention provides a flow chart of a method for analyzing the stability of a power grid of a new energy generator set containing multiple grid-connected converters. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0040] Example 1

[0041] A grid stability analysis method for new energy units with multiple grid-connected converters. Aiming at the complex system formed by large-scale grid-connected new energy units, the equivalent modeling method of new energy units is studied based on the Hamiltonian action equivalence principle, and a dynamic equivalent model of new energy units suitable for grid stability analysis is constructed; at the same time, considering various working conditions such as load mutation, weak grid and grid fault, the stability analysis method of grid-connected converter is studied, and the stable parameter space and stable operation boundary of the system are established; the influence of different control loops on the stability of grid-connected converters is revealed, and the influence of factors such as the number of grid-connected converters, connection mode, and line parameters on the damping and stability of new energy systems is analyzed. On this basis, with the goal of improving the stability of the new energy grid-connected system, the control strategy and parameter optimization scheme of the grid-connected converter under different working conditions are proposed based on the passive control theory.

[0042] Before introducing the present invention, the theoretical or practical basis of the present invention is first introduced. In the present invention, one grid-connected converter corresponds to one new energy generator set.

[0043] 1. Homological equivalence criterion based on Hamiltonian action:

[0044] Hamiltonian mechanics is an important part of theoretical mechanics, which uses the energy form transformation of the dynamic system to characterize the changing trend of each state variable. By analogy between the physical quantities of the electrical system and the mechanical system, the concepts and theorems of Hamiltonian mechanics are applied to the three-phase inverter system, providing a basis for selecting the physical quantities used to determine the synchronization of the grid-connected inverter.

[0045] There are energy input and output and energy dissipation in the three-phase inverter system, which makes the three-phase inverter system exchange energy with the outside world. Therefore, the three-phase inverter system is a non-conservative system, and the minimum action equation it satisfies is:

[0046]

[0047] The three-phase inverter is a non-conservative system, and the Hamiltonian action S only represents the conversion relationship between electric energy and magnetic energy between the energy storage elements in the system. It cannot reflect the energy exchange between the three-phase inverter system and the outside, and cannot fully reflect the change trend of all state variables. Therefore, the generalized Hamiltonian action S is defined to comprehensively consider the energy exchange within the system and the energy exchange between the system and the outside, so that the minimum action equation it satisfies is the same as that of the conservative system.

[0048] 2. Port Hamiltonian modeling theory:

[0049] For a conservative mechanical system with n degrees of freedom, let q = (q1, L, q n ) T is the generalized coordinate, and p=(p1,L,p n ) T is the generalized momentum. In the 2n-dimensional phase space, if the energy function H(q,p) is used to represent the total energy of the system (including the kinetic energy and potential energy of the system), then H(q,p) can also be called the Hamiltonian function of the system. Therefore, the dynamics of the system can be described by the port Hamiltonian equation:

[0050]

[0051] In the formula, J(x) is called the structural matrix, which reflects the energy exchange characteristics of the system and is an antisymmetric matrix; R(x) is the damping matrix, which reflects the dissipation characteristics of the system and is a symmetric semi-positive definite matrix. In actual systems, R(x) is generally composed of energy-consuming elements.

[0052] 3. Passivity control theory:

[0053] Consider a nonlinear system

[0054]

[0055] Where x∈R n is the state vector; u∈R m and y∈R m are m-dimensional input vectors and output vectors; f(x) and h(x) are n-dimensional and m-dimensional function vectors respectively; g(x) is an n×m-dimensional function matrix. If for a given function s(u,y), there exists a semi-positive function V(x) such that for any input signal u∈R m The following are all true:

[0056]

[0057] Then the system is called dissipative, V(x) is called the energy storage function of the system, and inequality (4) is called the dissipative inequality. Dissipation is a generalization of the physical energy loss characteristics. If the system is guaranteed to be dissipative, then system (2) is called passive. Passivity is related to the external input and output signals of the system. The physical meaning of system dissipation is that the growth of system energy is always less than or equal to the sum of external energy injection, which shows that the movement process of the passive system is always accompanied by energy consumption.

[0058] like Figure 1 As shown, the specific steps of the present invention include:

[0059] S1. Establish the Hamiltonian function of the grid-connected converter system, take into account the multi-time scale coupling characteristics of the new energy units, and construct the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of new energy units.

[0060] In this embodiment, the specific steps of S1 are:

[0061] S1.1. Considering the influence of different control loops, the Hamiltonian functions of the power loop, phase-locked loop, voltage loop and current loop are constructed from four time scales through physical model equivalence. The port Hamiltonian model of the control system of the grid-connected converter system for the control loops of the power loop, phase-locked loop, voltage loop and current loop is established by orthogonal decomposition and first integration method, and the dynamic response characteristics of the converter frequency and voltage under different control strategies and different time scales are analyzed.

[0062] For the control system, the orthogonal decomposition and first integration method are used to construct its Hamiltonian energy function, and the port Hamiltonian models of each control loop such as power loop, phase-locked loop, voltage loop and current loop are established. The port Hamiltonian models of each link are integrated to form a complete mathematical expression of the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of new energy units, and the structural characteristics of the Hamiltonian model of the control system of the grid-connected converter system port under different control strategies and different time scales are analyzed.

[0063] S2. Establish a mathematical model of a single new energy unit, and apply the coherent equivalence criterion to construct an aggregated equivalence model of a group of new energy units to generate a universal model suitable for different operating conditions.

[0064] Considering various working conditions such as load mutation, weak power grid and power grid failure, and based on the dynamic behavior of renewable energy power generation units at multiple time scales, a reduced-order model of a single renewable energy power generation unit suitable for low-frequency oscillation analysis is constructed; according to Hamiltonian theory, a similarity criterion for unit dynamic characteristics based on generalized Hamiltonian action is proposed, and the grouping index of multiple units is determined; a fuzzy clustering algorithm is used to group and cluster renewable energy station units according to the grouping index, and the equivalent aggregation of dynamic models is performed. The impact of the output characteristics of renewable energy stations on unit grouping and clustering is analyzed, and a dynamic equivalent modeling method for large-scale renewable energy stations is established.

[0065] Specifically, in this embodiment, the specific steps of S2 are:

[0066] S2.1. Assume that a new energy unit is a new energy power generation unit, analyze the differences in dynamic characteristics of a new energy power generation unit under different working conditions, establish a full-order dynamic differential equation of the influencing factors affecting the dynamic characteristics of the new energy power generation unit, and construct a state space model of a single new energy power generation unit; in this embodiment, the influencing factors include the tower shadow effect of the wind turbine, the phase-locked loop, the virtual inertia control, and the photovoltaic maximum power tracking (MPPT).

[0067] S2.2. Based on the dynamic behavior of renewable energy power generation units at multiple time scales, a reduced-order model of a single renewable energy power generation unit suitable for low-frequency oscillation analysis of power grid is constructed;

[0068] S2.3. According to Hamiltonian theory, a similarity criterion for dynamic characteristics of new energy units based on generalized Hamiltonian action is proposed, and the grouping index of multiple new energy units is determined. Fuzzy clustering algorithm is used to cluster the new energy station units according to the grouping index of multiple new energy units, and the dynamic models of the new energy units in the same group are equivalently aggregated.

[0069] S2.4. Establish AGC and AVC control models for new energy stations, study the active frequency regulation characteristics and reactive voltage regulation characteristics of different types of new energy stations, construct external characteristic model equations for new energy stations, analyze the impact of new energy station output characteristics on the grouping and clustering of new energy station units, and establish a dynamic equivalent new energy unit aggregation equivalent model for large-scale new energy stations.

[0070] S3. Based on the Hamiltonian model of the control system of the ports of the grid-connected converter system containing a high proportion of renewable energy, further analyze the influence of different control loops (including but not limited to maximum power tracking control, low voltage ride-through control, phase-locked loop, DC voltage control, virtual inertia control, frequency / voltage droop control, inner loop current control) under different working conditions of the equivalent model of the aggregation of renewable energy units on the stability of the Hamiltonian model of the ports of the grid-connected converter system containing a high proportion of renewable energy, and derive the stability criterion and system parameter stability domain of the Hamiltonian model of the control system of the ports of the grid-connected converter system containing a high proportion of renewable energy based on the passivity theory, and explain the coupling characteristics and energy interaction mechanism of the multi-converter system through mathematical representation;

[0071] In this embodiment, the specific steps of S3 are:

[0072] S3.1. Analyze the time scales of different control links and their corresponding characteristics;

[0073] S3.2. Analyze the influence of the coupling between the time scale controls responded by different control links on the Hamiltonian model of the grid-connected converter system port containing a high proportion of renewable energy, establish a full-order physical coupling model of the grid-connected converter, and then analyze the influence of different control loops on the dynamic behavior of the converter by applying voltage / frequency disturbance excitations of different time scales;

[0074] S3.3. Considering different working conditions, a mathematical model of multiple grid-connected converters is established, the interaction mechanism between the control responses of multiple grid-connected converters at different time scales is studied, and the influence of the number of grid-connected converters, the connection mode between the grid-connected converters, and the line parameters on the grid damping and stability are analyzed.

[0075] S4. Based on the established stability criteria, the stability improvement scheme of the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of renewable energy is studied from the perspective of control strategy improvement and parameter design, so as to optimize the damping characteristics of the power grid.

[0076] With the goal of improving the stability of the grid-connected converter system, system optimization strategies under different working conditions are proposed based on the passivity theory. On the one hand, from the perspective of system parameter design, the optimization design scheme of the physical parameters, controller parameters, line structure and parameters of the grid-connected converter is studied. On the other hand, from the perspective of control strategy optimization, the optimization control method of the system under different working conditions is studied based on the passivity theory. According to the system's requirements for stability margin, advanced control methods based on energy perspectives such as energy shaping, damping injection and virtual impedance are used to design the optimal damping configuration and energy trajectory for the system to ensure the passivity and robustness of the system. The specific steps are as follows:

[0077] S4.1. Find the operation boundary and operation constraint of the grid-connected converter system for stable operation corresponding to the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of new energy;

[0078] S4.2. Based on the passivity theory, parameter optimization and control strategies of grid-connected converters under different operating conditions are proposed according to the operating boundaries and operating constraints, and the optimal damping configuration is designed for the power grid.

[0079] In this embodiment, the specific steps of S4.1 are:

[0080] S4.1.1. For simple grid-connected converter systems, study the impact mechanisms of different control loops on the stability of the grid-connected converter system and the large signal stability analysis method based on Hamiltonian theory, establish the stable parameter space and operating boundary of the grid-connected converter system, and compare and analyze the changing patterns of the stable operating boundary of the grid-connected converter system under different time scales and different operating conditions; the simple grid-connected converter system here refers to a grid-connected converter system with only one grid-connected converter or multiple grid-connected converters connected only in series or multiple grid-connected converters connected only in parallel.

[0081] S4.1.2. For complex grid-connected converter systems, according to the dissipative characteristics of Hamiltonian systems, the large signal stability criterion of the grid-connected converter system under multiple time scales is analyzed, and the constraints for the stable operation of the system are further derived, and the stable parameter space containing multiple system parameters and its boundaries are calculated. The complex grid-connected converter system here refers to a grid-connected converter system with multiple series-parallel grid-connected converters.

[0082] In this embodiment, the specific steps of S4.2 are:

[0083] S4.2.1. Based on the grid's requirements for stability margin, propose an optimization design scheme for converter physical parameters, controller parameters, line structure and parameters from the perspective of grid parameter design;

[0084] S4.2.2. With the goal of improving the large-signal stability of the power grid, energy shaping, damping injection and virtual impedance advanced control methods are studied from the perspective of control strategy optimization, and the optimal damping configuration is designed for the power grid to ensure the passivity and robustness of the power grid.

[0085] In order to improve the factors affecting the grid-connected converter system, this embodiment also takes into account the nonlinear factors of the new energy units.

[0086] Taking into account the influence of different topological structures and operating conditions of the converter system, the Hamiltonian energy function is constructed according to the physical characteristics of the energy storage elements and dissipative elements, and the port Hamiltonian model of the circuit system of the converter system port is established. The nonlinear dynamic response characteristics of the port Hamiltonian model of the circuit system of the converter system port containing new energy units are analyzed in detail.

[0087] Specifically, based on the nonlinear characteristics of the new energy units, a port Hamiltonian model of the circuit system of the grid-connected converter system is established to analyze the nonlinear dynamic response characteristics of the converter containing a high proportion of new energy units, and then the stability criterion and system parameter stability domain of the port Hamiltonian model of the circuit system of the grid-connected converter system containing a high proportion of new energy are derived based on the passivity theory; the stability criterion and system parameter stability domain are also the stable parameter space and operating boundary of the grid-connected converter system established by the large signal stability analysis method based on the Hamiltonian theory mentioned later. Find out the operating boundaries and operating constraints of the stable operation of the grid-connected converter system corresponding to the port Hamiltonian model of the circuit system of the grid-connected converter system containing a high proportion of renewable energy (that is, based on the large signal stability analysis method of Hamiltonian theory, establish the stable parameter space and operating boundaries of the grid-connected converter system); then based on the passivity theory, propose parameter optimization of the grid-connected converter under different working conditions for the operating boundaries and operating constraints, and design the optimal damping configuration for the power system. Specifically, according to the requirements of the power system for the stability margin, from the perspective of the parameter design of the power system, propose the optimization design scheme of the physical parameters, control parameters and line structure of the converter, and design the optimal damping configuration of the power system.

[0088] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for analyzing the stability of a power grid of a new energy unit containing multiple grid-connected converters, characterized in that: include: S1. Establish the Hamiltonian function of the grid-connected converter system, take into account the multi-time scale coupling characteristics of the new energy units, and construct the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of new energy units; S2. Establish a mathematical model of a single new energy unit, and apply the coherent equivalence criterion to construct an aggregated equivalence model of a new energy unit group consisting of multiple new energy units, so as to generate a general model suitable for different working conditions; S3. Based on the Hamiltonian model of the control system of the ports of the grid-connected converter system containing a high proportion of new energy, further analyze the influence of different control loops under different working conditions of the aggregation equivalent model of the new energy unit group on the stability of the Hamiltonian model of the ports of the grid-connected converter system containing a high proportion of new energy, and derive the stability criterion and system parameter stability domain of the Hamiltonian model of the control system of the ports of the grid-connected converter system containing a high proportion of new energy based on the passivity theory; The specific steps of S3 are: S3.

1. Analyze the time scales of different control links and their corresponding characteristics; S3.

2. Analyze the influence of the coupling between the time scale controls responded by different control links on the Hamiltonian model of the grid-connected converter system port containing a high proportion of new energy, establish a full-order physical coupling model of the grid-connected converter, and then analyze the influence of different control loops on the dynamic behavior of the converter by applying voltage / frequency disturbance excitations of different time scales; S3.

3. Considering different working conditions, establish a mathematical model of multiple grid-connected converters, study the interaction mechanism between the control responses of multiple grid-connected converters at different time scales, and analyze the impact of the number of grid-connected converters, the connection mode between grid-connected converters, and the line parameters on the grid damping and stability; S4. Based on the established stability criterion, a solution to improve the stability of the Hamiltonian model of the control system of the port of the grid-connected converter system containing a high proportion of new energy is studied from the perspective of control strategy improvement and parameter design, so as to optimize the damping characteristics of the power grid.

2. A method for analyzing the stability of a power grid of a new energy generator set containing multiple grid-connected converters according to claim 1, characterized in that: The specific steps of S1 are: S1.

1. Considering the influence of different control loops, the Hamiltonian functions of the power loop, phase-locked loop, voltage loop and current loop are constructed from four time scales through physical model equivalence. The port Hamiltonian model of the control system of the grid-connected converter system for the control loops of the power loop, phase-locked loop, voltage loop and current loop is established by orthogonal decomposition and first integration method, and the dynamic response characteristics of the converter frequency and voltage under different control strategies and different time scales are analyzed.

3. The method for analyzing the stability of a power grid of a new energy generator set containing multiple grid-connected converters according to claim 1, characterized in that: In S2, different operating conditions in the general model applicable to different operating conditions include load mutation, weak power grid and power grid failure.

4. A method for analyzing the stability of a power grid of a new energy unit containing multiple grid-connected converters according to claim 1 or 3, characterized in that: The specific steps of S2 are: S2.

1. Let a new energy unit be a new energy power generation unit, analyze the differences in dynamic characteristics of a new energy power generation unit under different working conditions, establish a full-order dynamic differential equation of the influencing factors affecting the dynamic characteristics of the new energy power generation unit, and construct a state space model of a single new energy power generation unit; S2.

2. Based on the dynamic behavior of renewable energy power generation units at multiple time scales, a reduced-order model of a single renewable energy power generation unit suitable for low-frequency oscillation analysis of power grid is constructed; S2.

3. According to Hamiltonian theory, a similarity criterion for dynamic characteristics of new energy units based on generalized Hamiltonian action is proposed, and the grouping index of multiple new energy units is determined. A fuzzy clustering algorithm is used to group and cluster the new energy units in the new energy station according to the grouping index of multiple new energy units, and the dynamic models of the new energy units in the same group are equivalently aggregated; S2.

4. Establish AGC and AVC control models for new energy stations, study the active frequency regulation characteristics and reactive voltage regulation characteristics of different types of new energy stations, construct external characteristic model equations for new energy stations, analyze the impact of the output characteristics of new energy stations on the grouping and clustering of new energy units in new energy stations, and establish a new energy unit aggregation equivalent model with dynamic equivalents of multiple new energy units.

5. The method for analyzing the stability of a power grid of a new energy generator set containing multiple grid-connected converters according to claim 4, characterized in that: The influencing factors include wind turbine tower shadow effect, phase-locked loop, virtual inertia control and photovoltaic maximum power point tracking.

6. The method for analyzing the stability of a power grid of a new energy generator set containing multiple grid-connected converters according to claim 1, characterized in that: In S3, different control loops under different working conditions include maximum power tracking control, low voltage ride-through control, phase-locked loop, DC voltage control, virtual inertia control, frequency / voltage droop control, and inner loop current control.

7. The method for analyzing the stability of a power grid of a new energy generator set containing multiple grid-connected converters according to claim 1, characterized in that: The specific steps of S4 are: S4.

1. Find the operation boundary and operation constraint of the grid-connected converter system for stable operation corresponding to the Hamiltonian model of the control system of the grid-connected converter system port containing a high proportion of new energy; S4.

2. Based on the passivity theory, parameter optimization and control strategies for grid-connected converters under different operating conditions are proposed for the operating boundaries and operating constraints, and the optimal damping configuration is designed for the power grid.

8. A method for analyzing the stability of a power grid of a new energy generator set containing multiple grid-connected converters according to claim 7, characterized in that: The specific steps of S4.1 are: S4.1.

1. For a simple grid-connected converter system, study the influence mechanism of different control loops on the stability of the grid-connected converter system and the large signal stability analysis method based on Hamiltonian theory, establish the stable parameter space and operation boundary of the grid-connected converter system, and compare and analyze the changing law of the stable operation boundary of the grid-connected converter system under different time scales and different operating conditions; S4.1.

2. For complex grid-connected converter systems, based on the dissipative characteristics of the Hamiltonian system, the large signal stability criterion of the grid-connected converter system under multiple time scales is analyzed, and the constraints for the stable operation of the system are further derived. The stable parameter space containing multiple system parameters and its boundaries are calculated.

9. A method for analyzing the stability of a power grid of a new energy unit containing multiple grid-connected converters according to claim 8, characterized in that: The specific steps of S4.2 are: S4.2.

1. Based on the grid's requirements for stability margin, propose an optimization design scheme for converter physical parameters, controller parameters, line structure and parameters from the perspective of grid parameter design; S4.2.

2. With the goal of improving the large-signal stability of the power grid, energy shaping, damping injection and virtual impedance advanced control methods are studied from the perspective of control strategy optimization, and the optimal damping configuration is designed for the power grid to ensure the passivity and robustness of the power grid.

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