A method and system for quantifying oscillation stability

Abstract

The present invention discloses an oscillation stability quantification method and system, which relate to the field of oscillation stability analysis. The method obtains sampling data; determines a control coefficient of an energy storage system according to a voltage source angular frequency, a voltage source synchronous angular frequency, and active power; determines a rotor motion variation of the grid-connected system according to an inertia parameter of a direct-drive wind turbine, a damping parameter of the direct-drive wind turbine, and a synchronous angular velocity of the grid-connected system; and determines quantitative parameters of the grid-connected system according to the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the rotor motion variation. The quantitative parameters include an oscillation frequency and a damping ratio. The quantitative parameters are used to characterize the oscillation stability of the grid-connected system. The present invention can realize quantitative analysis of oscillation stability.

Description

Technical Field

[0001] The present invention relates to the field of oscillation stability analysis, and in particular to an oscillation stability quantification method and system. Background Art

[0002] Promoting the development of new energy sources such as wind power and photovoltaics is a key direction for achieving sustainable renewable energy development. However, wind turbine converters decouple the active power output of wind turbines from system frequency. This prevents wind turbines from adjusting their active power output in response to changes in system frequency, reducing system inertia and frequency stability. In power systems with a high proportion of renewable energy, energy storage technology has emerged. Energy storage systems offer fast response times and can output active power to support system frequency, improving frequency stability. Therefore, vigorously developing energy storage is a must for the power industry.

[0003] However, while energy storage-based virtual inertia and virtual damping control can improve system frequency stability, they can also cause low-frequency oscillations, worsening the system's oscillation stability. Therefore, analyzing the impact of energy storage-based virtual inertia and virtual damping control on system oscillation stability is crucial. While scholars have primarily studied the mechanisms by which virtual inertia and virtual damping control influence system oscillation stability through methods such as damping torque analysis, they have not quantitatively analyzed the impact of energy storage-based virtual inertia and virtual damping control parameters on the oscillation damping ratio. Quantifying the impact of energy storage-based virtual inertia and virtual damping control on system oscillation stability requires further research. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for quantifying oscillation stability, which can perform quantitative analysis on oscillation stability.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for quantifying oscillation stability is provided, the method being used for a grid-connected system including energy storage;

[0007] The grid-connected system includes: a direct-drive wind turbine, a phase-locked loop control module, an energy storage system, and a voltage source; the direct-drive wind turbine and the energy storage system are both connected to the voltage source; the energy storage system is arranged on the grid-connected side of the direct-drive wind turbine; the energy storage system is used to provide inertia and damping to the direct-drive wind turbine; the phase-locked loop control module is arranged between the direct-drive wind turbine and the energy storage system;

[0008] The method comprises:

[0009] Acquire sampling data; the sampling data includes: voltage source angular frequency, voltage source synchronous angular frequency, inertia parameters of the direct-drive wind turbine, damping parameters of the direct-drive wind turbine, power angle variation of the grid-connected system, and active power of the energy storage system; the active power includes inertial support power of inertia and damping support power;

[0010] Determining a control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency and the active power; the control coefficient includes: an inertia control coefficient and a damping control coefficient;

[0011] Determining a rotor motion variation of the grid-connected system according to an inertia parameter of the direct-drive wind turbine, a damping parameter of the direct-drive wind turbine, and a power angle variation of the grid-connected system; the rotor motion variation includes: a mechanical power variation and an electromagnetic power variation;

[0012] The quantitative parameters of the grid-connected system are determined based on the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine and the rotor motion change; the quantitative parameters include: oscillation frequency and damping ratio; the quantitative parameters are used to characterize the oscillation stability of the grid-connected system.

[0013] Optionally, determining the control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency, and the active power specifically includes:

[0014] Determining the grid frequency of the phase-locked loop control module according to the voltage source angular frequency;

[0015] A control coefficient of the energy storage system is determined according to the voltage source synchronous angular frequency, the grid frequency and the active power.

[0016] Optionally, the calculation formula of the control coefficient is:

[0017]

[0018]

[0019] Where ΔP ESS1 is the inertial support power of inertia; ΔP ESS2 is the support power of the damping; J vir is the inertia control coefficient; D vir is the damping control coefficient; ω pll is the grid frequency of the phase-locked loop control module; ω s is the voltage source synchronous angular frequency; T f is the time constant of the low-pass filter; s is the frequency domain operator; K p_pll K is the proportional coefficient in the phase-locked loop control module; i_pllis the integral coefficient in the phase-locked loop control module; ω g is the angular frequency of the voltage source; Δω is the frequency increment.

[0020] Optionally, determining the quantitative parameters of the grid-connected system according to the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the rotor motion variation specifically includes:

[0021] determining the synchronous angular velocity of the grid-connected system according to the rotor motion variation;

[0022] A quantitative parameter of the grid-connected system is determined according to the control coefficient and the synchronous angular velocity.

[0023] Optionally, the calculation formula for the synchronous angular velocity of the grid-connected system is:

[0024]

[0025] Where ω0 is the synchronous angular velocity of the grid-connected system; Δω G is the change in angular velocity; Δδ G is the power angle change; ΔP mG is the change in mechanical power; ΔP eG is the change in electromagnetic power; D G is the damping parameter of the direct-drive wind turbine; J G is the inertia parameter of the direct-drive wind turbine.

[0026] Optionally, the calculation formula of the quantization parameter is:

[0027]

[0028] Among them, ω n is the oscillation frequency of the grid-connected system; ξ is the damping ratio of the grid-connected system; J G is the inertia parameter of the direct-drive wind turbine; D G is the damping parameter of the direct-drive wind turbine; J vir is the inertia control coefficient; D vir is the damping control coefficient; X ∑ is the line inductance of the grid-connected system; ω0 is the synchronous angular velocity of the grid-connected system.

[0029] An oscillation stability quantification system, comprising:

[0030] A data acquisition module for acquiring sampled data; the sampled data includes: voltage source angular frequency, voltage source synchronous angular frequency, inertia parameters of the direct-drive wind turbine, damping parameters of the direct-drive wind turbine, power angle variation of the grid-connected system, and active power of the energy storage system; the active power includes inertial support power of inertia and damping support power;

[0031] A support power determination module, configured to determine a control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency, and the active power; the control coefficient includes: an inertia control coefficient and a damping control coefficient;

[0032] a rotor motion variation determination module, configured to determine the rotor motion variation of the grid-connected system based on the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the power angle variation of the grid-connected system; the rotor motion variation includes: a mechanical power variation and an electromagnetic power variation;

[0033] A quantitative parameter determination module is used to determine the quantitative parameters of the grid-connected system based on the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine and the rotor motion change; the quantitative parameters include: oscillation frequency and damping ratio; the quantitative parameters are used to characterize the oscillation stability of the grid-connected system.

[0034] Optionally, the support power determination module specifically includes:

[0035] A grid frequency determination submodule, configured to determine the grid frequency of the phase-locked loop control module according to the voltage source angular frequency;

[0036] A processing submodule is used to determine a control coefficient of the energy storage system according to the voltage source synchronization angular frequency, the grid frequency and the active power.

[0037] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0038] The present invention provides an oscillation stability quantification method and system, which determines the control coefficient of an energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency and the active power; determines the rotor motion change of the grid-connected system according to the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine and the synchronous angular velocity of the grid-connected system; determines the quantitative parameters of the grid-connected system according to the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine and the rotor motion change, and the quantitative parameters are used to characterize the oscillation stability of the grid-connected system; it can be seen that the present invention obtains the quantitative relationship between the inertia and damping provided by the energy storage system and the oscillation damping ratio of the grid-connected system, thereby determining the quantitative parameters of the grid-connected system, and then determining the oscillation stability of the grid-connected system according to the quantitative parameters. Therefore, the present invention can realize the quantitative analysis of the oscillation stability, so that the oscillation frequency and damping ratio that affect the oscillation stability can be displayed through specific data expression, thereby making the analysis of the oscillation stability simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 A flow chart of a method for quantifying oscillation stability provided by an embodiment of the present invention;

[0041] Figure 2 A schematic diagram of a grid-connected system model provided by an embodiment of the present invention;

[0042] Figure 3 A schematic diagram of inertial damping control including a phase-locked loop control module provided in an embodiment of the present invention;

[0043] Figure 4 A schematic structural diagram of a grid-connected system provided in an embodiment of the present invention;

[0044] Figure 5 A structural diagram of an oscillation stability quantification system provided by an embodiment of the present invention;

[0045] Figure 6 A comparison diagram of oscillation mode simulations provided by an embodiment of the present invention;

[0046] Figure 7 A schematic diagram of the changes in the system oscillation mode provided by an embodiment of the present invention;

[0047] Figure 8 A schematic diagram of the change of the synchronous machine power angle provided by an embodiment of the present invention;

[0048] Figure 9 A schematic diagram of the structure of a four-machine two-zone system provided by an embodiment of the present invention;

[0049] Figure 10 A schematic diagram of the dynamic change of the oscillation mode λ1 provided in an embodiment of the present invention;

[0050] Figure 11 A schematic diagram of the dynamic change of the oscillation mode λ2 provided in an embodiment of the present invention;

[0051] Figure 12 A curve diagram showing the power angle difference between SG-1 and SG-2 provided in an embodiment of the present invention;

[0052] Figure 13 A power angle difference variation curve diagram between SG-3 and SG-4 provided in an embodiment of the present invention.

[0053] Explanation of symbols:

[0054] Data acquisition module-1, support power determination module-2, rotor motion change determination module-3, quantization parameter determination module-4. DETAILED DESCRIPTION

[0055] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0056] The purpose of the present invention is to provide a method and system for quantifying oscillation stability, which can perform quantitative analysis on oscillation stability.

[0057] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] Example 1

[0059] like Figure 1 As shown, an embodiment of the present invention provides an oscillation stability quantification method, which is used for a grid-connected system containing energy storage; the grid-connected system includes: a direct-drive wind unit, a phase-locked loop control module, an energy storage system and a voltage source; the direct-drive wind unit and the energy storage system are both connected to the voltage source; the energy storage system is arranged on the grid-connected side of the direct-drive wind unit; the energy storage system is used to provide inertia and damping to the direct-drive wind unit; a phase-locked loop control module is arranged between the direct-drive wind unit and the energy storage system.

[0060] The method comprises:

[0061] Step 100: Acquire sampling data; the sampling data includes: voltage source angular frequency, voltage source synchronous angular frequency, inertia parameters of the direct-drive wind turbine, damping parameters of the direct-drive wind turbine, power angle variation of the grid-connected system, and active power of the energy storage system; active power includes inertial support power of inertia and support power of damping.

[0062] Step 200: Determine the control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency and the active power; the control coefficient includes: an inertia control coefficient and a damping control coefficient.

[0063] Step 300: Determine the rotor motion variation of the grid-connected system based on the inertia parameters of the direct-drive wind turbine, the damping parameters of the direct-drive wind turbine, and the power angle variation of the grid-connected system; the rotor motion variation includes: mechanical power variation and electromagnetic power variation.

[0064] Step 400: Determine the quantitative parameters of the grid-connected system based on the control coefficient, the inertia parameters of the direct-drive wind turbine, the damping parameters of the direct-drive wind turbine, and the rotor motion variation. The quantitative parameters include oscillation frequency and damping ratio. The quantitative parameters are used to characterize the oscillation stability of the grid-connected system.

[0065] Furthermore, step 200: determining the control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency and the active power, specifically includes:

[0066] The grid frequency of the phase-locked loop control module is determined according to the voltage source angular frequency.

[0067] The control coefficient of the energy storage system is determined according to the voltage source synchronous angular frequency, grid frequency and active power.

[0068] Specifically, the calculation formula of the control coefficient is:

[0069]

[0070]

[0071] Where ΔP ESS1 is the inertial support power of inertia; ΔP ESS2 is the support power of the damping; J vir is the inertia control coefficient; D vir is the damping control coefficient; ω pll is the grid frequency of the phase-locked loop control module; ω s is the voltage source synchronous angular frequency; T f is the time constant of the low-pass filter; s is the frequency domain operator; K p_pll K is the proportional coefficient in the phase-locked loop control module; i_pll is the integral coefficient in the phase-locked loop control module; ω g is the angular frequency of the voltage source; Δω is the frequency increment.

[0072] Wherein, determining the quantitative parameters of the grid-connected system according to the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the rotor motion variation specifically includes:

[0073] The synchronous angular velocity of the grid-connected system is determined according to the rotor motion variation.

[0074] A quantitative parameter of the grid-connected system is determined according to the control coefficient and the synchronous angular velocity.

[0075] Specifically, the calculation formula for the synchronous angular velocity of the grid-connected system is:

[0076]

[0077] Where ω0 is the synchronous angular velocity of the grid-connected system; Δω G is the change in angular velocity; Δδ G is the power angle change; ΔP mG is the change in mechanical power; ΔP eG is the change in electromagnetic power; D G is the damping parameter of the direct-drive wind turbine; J G is the inertia parameter of the direct-drive wind turbine.

[0078] The calculation formula of the quantization parameter is:

[0079]

[0080] Among them, ω n is the oscillation frequency of the grid-connected system; ξ is the damping ratio of the grid-connected system; J G is the inertia parameter of the direct-drive wind turbine; D G is the damping parameter of the direct-drive wind turbine; J vir is the inertia control coefficient; D vir is the damping control coefficient; X ∑ is the line inductance of the grid-connected system; ω0 is the synchronous angular velocity of the grid-connected system.

[0081] In practical applications, the specific implementation steps of the oscillation stability quantification method provided in this embodiment may also be as follows:

[0082] Step 1: Establish a direct-drive wind turbine grid-connected system model with energy storage inertia and damping control. The established direct-drive wind turbine grid-connected system model with energy storage inertia and damping control is as follows: Figure 2 As shown, it includes direct-drive wind turbines and energy storage systems.

[0083] The energy storage system is installed on the grid-connected side of the direct-drive wind turbine, providing virtual inertia and virtual damping support. This provides inertia and damping, thereby improving the frequency stability of the grid-connected system while suppressing system oscillations. The direct-drive wind turbine model primarily includes a direct-drive permanent magnet generator, a generator-side converter, a grid-side converter, and their control systems. The energy storage system model includes the energy storage battery, converter, and its control equipment.

[0084] Figure 2 Medium V pmd 、V pmq are the d-axis and q-axis voltages on the side of the direct-drive wind turbine respectively; V cd 、V cq are the d-axis and q-axis voltages of the grid-side converter respectively; I wd , I wq are the d-axis and q-axis currents of the direct-drive wind turbine input to the wind turbine grid-connected node, P w , Q ware the active power and reactive power of the direct-drive wind turbine input to the wind turbine grid-connected node; L PMSG 、L ESS are the line inductance between the grid-side converter of the direct-drive wind turbine and the PCC point; C dc 、V dc are the DC capacitance and DC capacitance voltage of the direct-drive wind turbine respectively; C dc1 、V dc1 are the DC capacitance and DC capacitor voltage of the energy storage system respectively; V ESSd 、V ESSq are the d-axis and q-axis voltages of the grid-side converter respectively; I ESSd , I ESSq are the d-axis and q-axis currents input from the energy storage battery to the wind turbine grid-connected node, P ESS , Q ESS are the active power and reactive power input from the energy storage battery to the wind turbine grid-connected node; V gd 、V gq are the d-axis and q-axis voltages of PCC respectively.

[0085] Step 2: Propose an energy storage inertia damping control with a phase-locked loop control module and derive its mathematical model. In order to use the active power of the energy storage to provide inertia and damping for the wind turbine, a differential link of the system frequency is introduced to provide inertial support for the wind turbine. A frequency deviation is introduced to provide damping support for the wind turbine, so that the wind turbine has inertia damping characteristics similar to those of a synchronous machine. The system frequency adopts the angular frequency of the wind turbine's grid connection point.

[0086] In order to obtain the angular frequency of the wind turbine's grid connection point, a coordinate system with the grid connection point voltage positioned on the q axis is used for electrical quantity control. The angle between the dq rotating coordinate system and the xy synchronous coordinate system is represented by δ, which can be written as:

[0087]

[0088] Among them, ω pll is the grid frequency of the phase-locked loop control module, ω g is the grid angular frequency, that is, the voltage source angular frequency.

[0089] The abc / dq links satisfy:

[0090] u gabc sinδ=u gd

[0091] where u gabc is the voltage amplitude on the grid-connected side of the wind turbine; u gd is the d-axis voltage.

[0092] exist Figure 3 In the phase-locked loop, set:

[0093]

[0094] You will get:

[0095] ω pll =K i_pll x pll -K p_pll u gd

[0096] where x pll for u d The integral of K p_pll K is the proportional coefficient in the phase-locked loop control module; i_pll is the integral coefficient in the phase-locked loop control module.

[0097] according to Figure 3 The phase-locked loop control block diagram in the figure is shown in Figure 1. The transfer function of the phase-locked loop control module is derived as follows:

[0098] -u gabc sinδ·(K p_pll +K i_pll / s)=ω pll

[0099] δ=(ω pll -ω g ) / s

[0100] Since the present invention is concerned with small disturbance stability, u abc is approximately 1pu, and since δ is very small, sinδ≈δ, which gives

[0101]

[0102] Then the transfer function of the phase-locked loop control module can be obtained as:

[0103]

[0104] Where s is the frequency domain operator.

[0105] final, Figure 3 The corresponding energy storage inertial damping control strategy equation is as follows:

[0106]

[0107] Where ΔP ESS1 is the inertial support power of inertia; ΔP ESS2 is the support power of the damping; J vir is the inertia control coefficient; D vir is the damping control coefficient; ω pllis the grid frequency of the phase-locked loop control module; ω s is the voltage source synchronous angular frequency; ΔP ESS The active power provided by the energy storage system during the frequency change of the grid-connected system; T f is the time constant of the low-pass filter; s is the frequency domain operator; K p_pll K is the proportional coefficient in the phase-locked loop control module; i_pll is the integral coefficient in the phase-locked loop control module; ω g is the angular frequency of the voltage source; Δω is the frequency increment.

[0108] When a direct-drive wind turbine with energy storage type inertial control and damping control is added to a single-machine infinite system (i.e., a voltage source), the active power P output by the energy storage system is w_E Will affect the active power P of the synchronous machine eG , thus affecting the size of the dominant oscillation mode of the system. The structure of the direct-drive wind turbine grid-connected system with energy storage inertial control and virtual damping control is as follows: Figure 4 As shown. Where E∠δ G , V1∠δ1, V2∠0 are the terminal voltage of the synchronous machine, the grid connection point voltage of the wind-storage system, and the voltage of the infinite system (i.e., the voltage source) respectively; X1 is the line inductance between the synchronous machine and the grid connection point of the wind-storage system; X2 is the line inductance between the synchronous machine and the infinite system, and X2>>X1 is satisfied; P s It is the active power output from the sending system to the infinite system.

[0109] Step 3: Analyze the mathematical relationship between the oscillation frequency, oscillation damping ratio, and the inertia and damping of traditional synchronous machines in a single-machine infinite system;

[0110] First, for a single-machine infinite system, set the inertia parameter of the synchronous machine to J G , the damping parameter is D G , then the rotor motion equation of the synchronous machine is as follows:

[0111]

[0112] in:

[0113]

[0114] Combining them we can get:

[0115]

[0116]

[0117] Where ΔP mG , ΔP eG are the mechanical power variation and electromagnetic power variation of the synchronous machine respectively; ΔωG , Δδ G are the angular velocity change and power angle change of the synchronous machine respectively; ω0 is the synchronous angular velocity of the system; E and U are the voltages of the synchronous machine and the infinite system respectively; δ G(0) is the initial value of the synchronous machine power angle.

[0118] Thus, the low-frequency oscillation frequency ω of a single-machine infinite system can be calculated n and the damping ratio ξ:

[0119]

[0120] Step 4: Add energy storage type virtual inertia and virtual damping control to the single-machine infinite system containing direct-drive wind turbines. According to the rotor motion equation of the synchronous machine, the quantitative relationship between the virtual inertia, virtual damping control parameters and the system oscillation damping ratio is theoretically derived.

[0121] according to Figure 4 There is the expression:

[0122]

[0123] Since the added energy storage system converter control strategy sets the reactive power baseline value of the energy storage to 0, the voltage change caused by the reactive power control of the energy storage system is ignored when analyzing its impact on system oscillation stability. Linearizing the above equation yields:

[0124]

[0125] Eliminating Δδ1 from the above equation, we can obtain that after the single-machine infinite system is added to the wind-storage system, the change in the output active power of the synchronous machine is:

[0126]

[0127] Among them, δ G(0) , δ 1(0) They are the initial values of the power angle of the synchronous machine node and the wind turbine grid-connected node respectively.

[0128]

[0129] Since the sending end system is connected to the infinite system, δ G(0) ≈δ 1(0) ≈0, E≈V1≈V2=1, and X2>>X1, then X ∑ =X2+X1≈X2.

[0130]

[0131] but

[0132]

[0133] The active power output of the wind-storage system is obtained as follows:

[0134] ΔP w_E =-J vir sΔω G (s)-D vir Δω G (s)

[0135] Thus, the change of the active power output of the wind storage system ΔP can be further obtained w_E and synchronous machine power angle Δδ G The mathematical relationship between them is as follows:

[0136]

[0137] Therefore, the change in active power output of the wind-storage system ΔP w_E Under the influence of eG As follows:

[0138]

[0139] Then, the rotor motion equation of the synchronous machine under the influence of the wind storage system can be obtained:

[0140]

[0141] Therefore, when a direct-drive fan with energy storage inertial control and damping control is added to a single-machine infinite system, the oscillation frequency and damping ratio of the system are calculated as follows:

[0142]

[0143] According to the above formula, for a single-machine infinite system containing a direct-drive wind turbine, when energy storage inertia control and damping control strategies are added, the system's oscillation frequency will decrease accordingly, and the oscillation damping ratio will increase, thereby enhancing the system's oscillation stability. And if the system parameters are given: the direct-drive wind turbine unit inertia parameter J G and the damping parameter D G , inertia control coefficient J of energy storage converter vir and the damping control coefficient D vir , that is, the inertia control coefficient J vir and the damping control coefficient D vir ; Line inductance X between the sending end system and the infinite system ∑ , that is, the line inductance of the grid-connected system; then, the oscillation frequency and oscillation damping ratio of the grid-connected system composed of the voltage source containing the direct-drive wind turbine can be quantitatively calculated after adding the energy storage type inertial control and damping control. virand the damping control coefficient D vir Under certain conditions, the inertia parameter J of the synchronous machine is G The smaller it is, the more significantly the system's oscillation frequency decreases and the more significantly the system's oscillation damping increases, thereby significantly improving the system's oscillation stability.

[0144] Through the above steps, the impact of energy storage inertial control on grid oscillation stability can be quantitatively analyzed, and the oscillation damping ratio corresponding to different inertia and damping parameters can be accurately analyzed.

[0145] Example 2

[0146] like Figure 5 As shown, an embodiment of the present invention provides an oscillation stability quantification system, which includes: a data acquisition module 1, a support power determination module 2, a rotor motion change determination module 3, and a quantization parameter determination module 4.

[0147] Data acquisition module 1 is used to obtain sampled data; the sampled data includes: voltage source angular frequency, voltage source synchronous angular frequency, inertia parameters of the direct-drive wind turbine, damping parameters of the direct-drive wind turbine, power angle change of the grid-connected system and active power of the energy storage system; active power includes inertial support power of inertia and support power of damping.

[0148] The supporting power determination module 2 is used to determine the control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency and the active power; the control coefficient includes: inertia control coefficient and damping control coefficient.

[0149] The rotor motion variation determination module 3 is used to determine the rotor motion variation of the grid-connected system based on the inertia parameters of the direct-drive wind turbine, the damping parameters of the direct-drive wind turbine and the power angle variation of the grid-connected system; the rotor motion variation includes: mechanical power variation and electromagnetic power variation.

[0150] The quantitative parameter determination module 4 is used to determine the quantitative parameters of the grid-connected system based on the control coefficient and the rotor motion variation. The quantitative parameters include: oscillation frequency and damping ratio. The quantitative parameters are used to characterize the oscillation stability of the grid-connected system.

[0151] Specifically, the support power determination module 2 includes: a grid frequency determination submodule and a processing submodule.

[0152] The grid frequency determination submodule is used to determine the grid frequency of the phase-locked loop control module according to the voltage source angular frequency.

[0153] The processing submodule is used to determine the control coefficient of the energy storage system according to the voltage source synchronization angular frequency, the grid frequency and the active power.

[0154] In addition, the present invention also provides a simulation verification of the quantization parameters. Figure 4 For the system in [1], the inertia parameter is set to 6 and the damping parameter is set to 2. The dominant oscillation mode, oscillation frequency, and oscillation damping ratio of the grid-connected system are calculated when different values of the inertia control coefficient and the damping control coefficient are selected, and simulation verification is performed. Figure 6 This is a comparison chart of oscillation mode simulation. Figure 6 The comparison between the theoretical calculation value and the simulation value in the paper verifies the correctness of the quantitative analysis of the influence of energy storage type inertial damping control on the system oscillation stability. When the inertia control coefficient and damping control coefficient of the energy storage system are set to three cases respectively, the changes in the system oscillation mode and the synchronous machine power angle are shown in the figure below. Figure 7 and Figure 8 shown.

[0155] When the inertia control coefficient is increased, the closer the dominant oscillation mode is to the imaginary axis, the system's oscillation frequency gradually decreases, the system's damping ratio gradually decreases, and the system's small disturbance stability gradually weakens; when the damping control coefficient is increased, the farther the dominant oscillation mode is from the imaginary axis, the system's oscillation frequency remains unchanged, the system's damping ratio gradually increases, and the system's small disturbance stability gradually enhances; this is consistent with the theoretical analysis, verifying the correctness of the qualitative influence of energy storage-type inertial damping control on the system's oscillation stability.

[0156] Simultaneously increasing the inertia control coefficient and the damping control coefficient can gradually reduce the system's oscillation frequency, increase the oscillation damping ratio, and improve the system's oscillation stability. Energy storage-based inertia control and virtual damping control can improve system frequency stability while suppressing system oscillations. As the inertia control coefficient and the damping control coefficient increase, the power angle oscillation frequency gradually decreases and the oscillation damping ratio increases, enhancing the system's power angle stability.

[0157] Qualitative analysis of oscillation stability by inertial control and virtual damping control is verified based on a four-machine two-zone system. Figure 9 As shown. Among them, PMSG-1 represents the direct-drive wind turbine with serial number 1, PMSG-2 represents the direct-drive wind turbine with serial number 2, and SG-1 represents the synchronous machine with serial number 1; similarly, SG-2, SG-3 and SG-4 are synchronous machines with corresponding serial numbers. The inertia parameters of SG-1, SG-2, SG-3 and SG-4 are 6, and the damping parameter is 0.5. A direct-drive wind turbine PMSG-1 and PMSG-2 with additional energy storage inertia control and damping control are added to each of the two zones. The parameters of the direct-drive wind turbines are the same, and the dominant oscillation modes of the system are the oscillation mode λ1 between SG-1 and SG-2 and the oscillation mode λ2 between SG-3 and SG-4. Under three different conditions, the dynamic changes of λ1 and λ2 are as follows Figure 10 and Figure 11 shown.

[0158] By changing the inertia control coefficient and the damping control coefficient, the power angle difference curves of SG-1 and SG-2 and the power angle difference curves of SG-3 and SG-4 are plotted as follows: Figure 12 and Figure 13 shown.

[0159] As the inertia control coefficient and damping control coefficient increase, the system's oscillation stability gradually increases. This verifies the correctness of the qualitative analysis of the effects of energy storage-based inertia control and damping control on system oscillation stability in a multi-machine system, thereby validating the correctness of the proposed method for quantitative analysis of oscillation stability with energy storage-based virtual inertia control.

[0160] This paper first provides a model for the control of energy-storage virtual inertia and virtual damping for direct-drive wind turbines. It then adds energy-storage virtual inertia and virtual damping control to a single-unit infinite-energy system containing a direct-drive wind turbine. The quantitative relationship between the inertia control coefficient, the damping control coefficient, and the system's oscillation damping ratio is theoretically derived. Finally, based on examples of a single-unit infinite-energy system and a four-unit, two-zone system, eigenroot analysis and time-domain simulation analysis using MATLAB were performed to verify the correctness of the quantitative analysis proposed in this paper. This provides a method for quantifying oscillation stability with energy-storage virtual inertia control, enabling a more accurate quantitative analysis of the impact of virtual inertia control on oscillation stability.

[0161] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0162] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for quantifying oscillation stability, characterized in that: The method is used for a grid-connected system containing energy storage; The grid-connected system includes: a direct-drive wind turbine, a phase-locked loop control module, an energy storage system, and a voltage source; the direct-drive wind turbine and the energy storage system are both connected to the voltage source; the energy storage system is arranged on the grid-connected side of the direct-drive wind turbine; the energy storage system is used to provide inertia and damping to the direct-drive wind turbine; the phase-locked loop control module is arranged between the direct-drive wind turbine and the energy storage system; The method comprises: Acquire sampling data; the sampling data includes: voltage source angular frequency, voltage source synchronous angular frequency, inertia parameters of the direct-drive wind turbine, damping parameters of the direct-drive wind turbine, power angle variation of the grid-connected system, and active power of the energy storage system; the active power includes inertial support power of inertia and damping support power; Determining a control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency and the active power; the control coefficient includes: an inertia control coefficient and a damping control coefficient; Determining a rotor motion variation of the grid-connected system according to an inertia parameter of the direct-drive wind turbine, a damping parameter of the direct-drive wind turbine, and a power angle variation of the grid-connected system; the rotor motion variation includes: a mechanical power variation and an electromagnetic power variation; Determining quantitative parameters of the grid-connected system based on the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the rotor motion variation; the quantitative parameters include: oscillation frequency and damping ratio; the quantitative parameters are used to characterize the oscillation stability of the grid-connected system; The calculation formula of the control coefficient is: Where ΔP ESS1 is the inertial support power of inertia; ΔP ESS2 is the support power of the damping; J vir is the inertia control coefficient; D vir is the damping control coefficient; ω pll is the grid frequency of the phase-locked loop control module; ω s is the voltage source synchronous angular frequency; T f is the time constant of the low-pass filter; s is the frequency domain operator; K p_pll K is the proportional coefficient in the phase-locked loop control module; i_pll is the integral coefficient in the phase-locked loop control module; ω g is the angular frequency of the voltage source; Δω is the frequency increment.

2. The oscillation stability quantification method according to claim 1, characterized in that: Determining the control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency, and the active power specifically includes: Determining the grid frequency of the phase-locked loop control module according to the voltage source angular frequency; A control coefficient of the energy storage system is determined according to the voltage source synchronous angular frequency, the grid frequency and the active power.

3. The oscillation stability quantification method according to claim 1, characterized in that: Determining the quantitative parameters of the grid-connected system according to the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the rotor motion variation specifically includes: determining the synchronous angular velocity of the grid-connected system according to the rotor motion variation; A quantitative parameter of the grid-connected system is determined according to the control coefficient and the synchronous angular velocity.

4. The oscillation stability quantification method according to claim 3, characterized in that: The calculation formula of the synchronous angular velocity of the grid-connected system is: Where ω0 is the synchronous angular velocity of the grid-connected system; Δω G is the change in angular velocity; Δδ G is the power angle change; ΔP mG is the change in mechanical power; ΔP eG is the change in electromagnetic power; D G is the damping parameter of the direct-drive wind turbine; J G is the inertia parameter of the direct-drive wind turbine.

5. The oscillation stability quantification method according to claim 3, characterized in that: The calculation formula of the quantization parameter is: Among them, ω n is the oscillation frequency of the grid-connected system; ξ is the damping ratio of the grid-connected system; J G is the inertia parameter of the direct-drive wind turbine; D G is the damping parameter of the direct-drive wind turbine; J vir is the inertia control coefficient; D vir is the damping control coefficient; X ∑ is the line inductance of the grid-connected system; ω0 is the synchronous angular velocity of the grid-connected system.

6. An oscillation stability quantification system, characterized in that: The system comprises: A data acquisition module for acquiring sampled data; the sampled data includes: voltage source angular frequency, voltage source synchronous angular frequency, inertia parameters of the direct-drive wind turbine, damping parameters of the direct-drive wind turbine, power angle variation of the grid-connected system, and active power of the energy storage system; the active power includes inertial support power of inertia and damping support power; A support power determination module, configured to determine a control coefficient of the energy storage system according to the voltage source angular frequency, the voltage source synchronous angular frequency, and the active power; the control coefficient includes: an inertia control coefficient and a damping control coefficient; a rotor motion variation determination module, configured to determine the rotor motion variation of the grid-connected system based on the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the power angle variation of the grid-connected system; the rotor motion variation includes: a mechanical power variation and an electromagnetic power variation; a quantitative parameter determination module, configured to determine the quantitative parameters of the grid-connected system based on the control coefficient, the inertia parameter of the direct-drive wind turbine, the damping parameter of the direct-drive wind turbine, and the rotor motion variation; the quantitative parameters including: oscillation frequency and damping ratio; the quantitative parameters are used to characterize the oscillation stability of the grid-connected system; The calculation formula of the control coefficient is: Where ΔP ESS1 is the inertial support power of inertia; ΔP ESS2 is the support power of the damping; J vir is the inertia control coefficient; D vir is the damping control coefficient; ω pll is the grid frequency of the phase-locked loop control module; ω s is the voltage source synchronous angular frequency; T f is the time constant of the low-pass filter; s is the frequency domain operator; K p_pll K is the proportional coefficient in the phase-locked loop control module; i_pll is the integral coefficient in the phase-locked loop control module; ω g is the angular frequency of the voltage source; Δω is the frequency increment.

7. The oscillation stability quantification system according to claim 6, characterized in that: The support power determination module specifically includes: A grid frequency determination submodule, configured to determine the grid frequency of the phase-locked loop control module according to the voltage source angular frequency; A processing submodule is used to determine a control coefficient of the energy storage system according to the voltage source synchronization angular frequency, the grid frequency and the active power.

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