Energy storage method for novel power system

Abstract

The invention discloses an energy storage method for a novel power system, and relates to the technical field of energy transfer. Comprising the steps of obtaining system disturbance and system frequency lowest point frequency deviation according to a previous frequency event, and calculating synchronous machine system equivalent capacity and synchronous machine system equivalent difference of a power system based on a synchronous machine system equivalent model. Energy storage system frequency characteristic representation is obtained according to the requirement of a power grid for the maximum frequency deviation and the equivalent parameters of the synchronous machine system, the required energy storage system ESS capacity and adjustment difference are calculated based on an energy storage system equivalent model, and whether the synchronous machine system equivalent capacity and the synchronous machine system equivalent adjustment difference obtained through calculation meet conditions or not is checked; and selecting an energy storage system to store energy based on the steps and the actual condition of the power grid. Vs and delta s of the energy storage system can be quickly calculated, the frequency supporting capacity of the energy storage system can be quickly and accurately evaluated by a power grid, and a proper scheduling strategy is formulated.

Description

Technical Field

[0001] The present invention relates to the technical field of energy dispatching, and in particular to an energy storage method for a new power system. Background Technique

[0002] Under the strategic guidance of "carbon peak and carbon neutrality", in the construction of a new power system with new energy as the main body, the technology and industrial ecology of the power industry are facing major changes. However, due to the "zero inertia" characteristics of new energy power generation systems represented by wind power and photovoltaic power, as the proportion of new energy increases, the stability of the power system gradually weakens. With its resource endowments such as fast speed, flexibility, and adjustability, the energy storage system has increasingly become an important dispatching resource for the power grid. The energy storage system has both "source-load" characteristics and plays an important role in system frequency support.

[0003] For the energy storage system participating in frequency response, the capacity Vs and droop coefficient δs of the energy storage system become important indicators for evaluating its frequency support ability. However, most of the existing energy storage product designs are based on simulation analysis, which means that the energy storage system in a certain area is strictly coupled with the power grid characteristics of that area, and the design of energy storage parameters has not formed a standard theoretical system. Furthermore, the design based on the simulation analysis method is not universal. The classic SFR model based on the existing technology is essentially an equivalent of a reheating unit, so this model is only applicable to conventional thermal power reheating units and cannot meet the current situation of heterogeneous synchronous machine systems. At the same time, due to objective factors such as climate and geography, resources such as wind power and photovoltaic power have weak frequency support ability and weak flexibility. Therefore, currently, resources such as wind power and photovoltaic power generally do not actually participate in system frequency response; on the other hand, the frequency characteristic function after superimposing the new energy system is a high-order nonlinear function, which is difficult to solve accurately. Therefore, it is not conducive to the power grid to quickly evaluate the frequency support ability of the energy storage system.

[0004] Therefore, how to provide an energy storage method for a new power system to solve the difficulties existing in the prior art is an urgent problem for those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides an energy storage method for a new power system, which is beneficial to quickly and accurately evaluate the frequency support ability of the energy storage system.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An energy storage method for a new power system includes the following steps:

[0008] S1. Obtain system disturbances and the frequency deviation at the lowest point of the system frequency according to previous frequency events;

[0009] S2. Calculate the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system based on the equivalent model of the synchronous machine system;

[0010] S3. Obtain the frequency characteristic representation of the energy storage system according to the requirements of the power grid for the maximum frequency deviation and the equivalent parameters of the synchronous machine system;

[0011] S4. Calculate the required energy storage system ESS capacity and speed regulation based on the equivalent model of the energy storage system;

[0012] S5. Check whether the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system calculated in S2 meet the conditions;

[0013] S6. Select an energy storage system for energy storage based on the above steps and the actual situation of the power grid.

[0014] For the above method, optionally, in S2, the step response function of the system frequency is monotonically decreasing and convergent, and there is a first-order power-frequency transfer function when the frequency is at the lowest point. Let the minimum value of the function be equal to the lowest frequency point, then the power-frequency transfer function is the equivalent model of the synchronous machine system.

[0015] For the above method, optionally, the calculation expressions for the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system in the power system are:

[0016]

[0017] where, Δf nadir is the frequency deviation at the lowest point of the system frequency, Δf max1 is the maximum frequency deviation, ΔP d is the system disturbance, D is the equivalent damping coefficient of the system, f N is the system base frequency, V g is the equivalent capacity of the synchronous machine system, δ g is the equivalent speed regulation of the synchronous machine system.

[0018] For the above method, optionally, S3 includes calculating the frequency error E between the actual value and the proposed model at the time t nadir when it appears at the lowest point.

[0019] For the above method, optionally, the expressions for calculating the required energy storage system ESS capacity and speed regulation in S4 are:

[0020]

[0021] where, V s and δ s are the ESS capacity and speed regulation, Δf max is the allowable frequency deviation of the system.

[0022] For the above method, optionally, in S5, the inspection condition adopts the constraint condition of setting the equivalent model of the energy storage system, and the expression is:

[0023]

[0024] As can be seen from the above technical solutions, compared with the prior art, the present invention provides an energy storage method for a new power system, which has the following beneficial effects: By adopting the first-order system equivalent synchronous machine system and the frequency characteristics of the energy storage system, considering the rapidity of the energy storage system, ignoring the action dead zone and action delay of the energy storage system, and considering the actual power grid operation situation, ignoring the situation where wind turbines and photovoltaic units participate in frequency response. On this basis, the system frequency characteristics can be equivalent to a first-order system, and the V of the energy storage system can be quickly calculated s and δ s , which is beneficial for the power grid to quickly and accurately evaluate the frequency support ability of the energy storage system and formulate appropriate dispatching strategies. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0026] Figure 1 It is a flowchart of an energy storage method for a new power system disclosed by the present invention;

[0027] Figure 2 It is a schematic diagram of the equivalent model of the synchronous machine system disclosed by the present invention;

[0028] Figure 3 It is a schematic diagram of the equivalent model of the energy storage system disclosed by the present invention;

[0029] Figure 4 It is a flowchart of the energy storage system parameter calculation disclosed in the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] Referring to Figure 1 as shown, the present invention discloses an energy storage method for a new power system, including the following steps:

[0032] S1. Obtain the system disturbance and the frequency deviation at the lowest point of the system frequency according to the previous frequency events;

[0033] S2. Calculate the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system based on the equivalent model of the synchronous machine system;

[0034] S3. Obtain the frequency characteristic representation of the energy storage system according to the requirement of the maximum frequency deviation of the power grid and the equivalent parameters of the synchronous machine system;

[0035] S4. Calculate the required capacity and speed regulation of the energy storage system ESS based on the equivalent model of the energy storage system;

[0036] S5. Check whether the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system calculated in S2 meet the conditions;

[0037] S6. Select an energy storage system for energy storage based on the above steps and the actual situation of the power grid.

[0038] Further, referring to Figure 2 As shown, in S2, the step response function of the system frequency is monotonically decreasing and convergent. When the frequency is at the lowest point, there is a first-order power-frequency transfer function. Let the minimum value of the function be equal to the frequency at the lowest point, then the power-frequency transfer function is the equivalent model of the synchronous machine system. In the figure, H is the system inertia time constant.

[0039] Further, the dynamics of the system frequency can be expressed as:

[0040]

[0041] Solving the time-domain solution of the system frequency can obtain:

[0042]

[0043] where, Δf * (t) is the per-unit value of the system frequency change. It can be seen that Δf * (t) is a monotonically increasing function. Therefore, the maximum value of Δf * (t) can be expressed as:

[0044]

[0045] Furthermore, it can be known that the maximum system frequency deviation is directly related to the coefficient B, and B is determined by the product of V g and δ g . Therefore, when the maximum frequency deviation Δf max1 is equal to the frequency deviation at the lowest point of the system frequency Δf nadir , the product of V g and δ g can be calculated.

[0046] Furthermore, the equivalent capacity of the power system synchronous machine system and the calculation expression of the equivalent speed regulation of the synchronous machine system are as follows:

[0047]

[0048] Among them, Δf nadir is the frequency deviation at the lowest point of the system frequency, Δf max1 is the maximum frequency deviation, ΔP d is the system disturbance, D is the system equivalent damping coefficient, f N is the system base frequency, V g is the equivalent capacity of the synchronous machine system, and δ g is the equivalent speed regulation of the synchronous machine system.

[0049] Furthermore, S3 includes calculating the frequency error E between the actual value and the proposed model at the time t nadir when it appears at the lowest point.

[0050] Specifically, the calculation expression is:

[0051]

[0052] The maximum rate of change of system frequency RoCoF max can be expressed as:

[0053]

[0054] Assuming that the frequency continues to change at the rate of RoCoF max , then the time t nadir1 can be expressed as:

[0055]

[0056] Considering the response of the governor, the absolute value of the average rate of change of system frequency RoCoF will be less than RoCoF max , so the γ parameter is introduced to describe the relationship between t nadir1 and t nadir , and the expression is:

[0057] t nadir1 = γ·t nadir ,

[0058] where γ is a constant and γ ≤ 1. Therefore, the error E can be expressed as:

[0059]

[0060] Therefore, when t nadir1 is much smaller than t nadir , the error E is extremely small.

[0061] Further, based on Figure 2 the equivalent model of the synchronous machine system shown, the equivalent aggregated model of the distribution network energy storage is as Figure 3 shown. The calculation formulas for the required energy storage system ESS capacity and droop in S4 are as follows:

[0062]

[0063] wherein, V s and δ s are the ESS capacity and droop, and Δf max is the allowable frequency deviation of the system.

[0064] Further, in S5, the test condition adopts setting the constraint condition of the equivalent model of the energy storage system, and the expression is:

[0065]

[0066] Specifically, the droop of the energy storage system is greater than that of the synchronous machine system. When the energy storage system reaches 100% discharge intensity, the frequency deviation is 1 / (δ s ). Therefore, the sum of the outputs of the energy storage system and the synchronous machine system needs to be greater than the power disturbance. In addition, in order to maintain the maximum frequency deviation, 1 / (δ s ) needs to be greater than Δf * max .

[0067] In a specific embodiment, referring to Figure 4 shown, in order to maintain the stability of the power grid, the system frequency fault ΔP d usually can select the maximum frequency disturbance that has occurred in the history of this region. Due to different system operation modes, f nadir is also different when facing the same disturbance. Therefore, the lowest point of the maximum frequency disturbance that occurs under the small operation mode should be selected.

[0068] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A energy storage method for a new power system, characterized in that Including the following steps: S1. Obtain the system disturbance and the frequency deviation at the lowest point of the system frequency according to the previous frequency events; S2. Calculate the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system based on the equivalent model of the synchronous machine system; S3. Obtain the frequency characteristic representation of the energy storage system according to the requirement of the maximum frequency deviation of the power grid and the equivalent parameters of the synchronous machine system; S4. Calculate the required capacity and speed regulation of the energy storage system ESS based on the equivalent model of the energy storage system; S5. Check whether the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system calculated in S2 meet the conditions; S6. Select the energy storage system for energy storage based on the above steps and the actual situation of the power grid.

2. A method for energy storage for a new power system according to claim 1, wherein In S2, the step response function of the system frequency is monotonically decreasing and convergent. When the frequency is at the lowest point, there is a first-order power-frequency transfer function. Let the minimum value of the function be equal to the lowest point of the frequency, then the power-frequency transfer function is the equivalent model of the synchronous machine system.

3. A method for energy storage for a new power system according to claim 2, wherein The calculation expressions for the equivalent capacity of the synchronous machine system and the equivalent speed regulation of the synchronous machine system in the power system are: Among them, Δf nadir is the frequency deviation at the lowest point of the system frequency, Δf max1 is the maximum frequency deviation, ΔP d is the system disturbance, D is the equivalent damping coefficient of the system, f N is the reference frequency of the system, V g is the equivalent capacity of the synchronous machine system, δ g is the equivalent speed regulation of the synchronous machine system.

4. A method for energy storage for a new power system according to claim 1, wherein S3 includes calculating the frequency error E between the actual value and the proposed model at the time t when the lowest point appears. nadir ​ 5. A method for energy storage for a new power system according to claim 1, wherein The calculation expressions for the required capacity and speed regulation of the energy storage system ESS in S4 are: Among them, V s and δ s are the ESS capacity and droop, and Δf max is the allowable system frequency deviation.

6. A method for energy storage for a new power system according to claim 1, wherein In S5, the checking condition adopts the constraint condition of setting the equivalent model of the energy storage system, and the expression is:

Images