Cooperative frequency modulation control method including network construction type energy storage and network following type energy storage

Abstract

The invention provides a cooperative frequency modulation control method including network construction type energy storage and network following type energy storage, and the method comprises the steps: constructing a simulation model which comprises a network construction type energy storage unit, a network following type energy storage unit, a synchronous generator and an AC load, obtaining a frequency deviation when the simulation model is subjected to frequency disturbance, judging whether the absolute value of the frequency deviation exceeds a threshold value or not, and if yes, determining that the absolute value of the frequency deviation exceeds the threshold value; and if the frequency deviation exceeds a set threshold value, respectively regulating and controlling the net-forming type energy storage unit and the net-following type energy storage unit, if the frequency deviation does not exceed the set threshold value, entering a next sampling period, and if the frequency deviation exceeds the set threshold value, controlling the energy storage units to charge and discharge according to the positive and negative of the frequency deviation. According to the invention, the virtual inertia support and the frequency autonomous support of the network construction type energy storage unit are fully exerted, the following network type energy storage unit quickly responds to the upper control signal, a better frequency support effect is achieved, and the following network type energy storage and the network construction type energy storage can be quickly and effectively controlled to cooperatively participate in system frequency adjustment.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission in power systems, and particularly to a coordinated frequency regulation control method including grid-forming energy storage and grid-following energy storage. Background Art

[0002] In recent years, with the large-scale integration of new energy into the grid through power electronic converters and the continuous access of extra-regional direct current, the power grid in China has gradually shown an electrification trend, resulting in the overall power system showing the characteristics of decreasing inertia and uneven distribution, greatly weakening the frequency regulation ability and frequency stability of the power system.

[0003] However, since new energy units do not have the rotational inertia of synchronous generators themselves, the new power system shows the characteristic of "low inertia". Coupled with the intermittency and volatility of the output of new energy units, the frequency stability of the power system is reduced.

[0004] Electrochemical energy storage is a high-quality frequency regulation resource. Applying grid-forming control technology to energy storage is an effective solution to improve the frequency stability in the inertia response stage. Transforming energy storage into grid-forming can improve the system inertia level and frequency support ability. However, when grid-forming energy storage is applied to frequency support, problems such as overcharging or over-discharging of SOC are likely to occur. Since grid-following energy storage is regulated by the upper-level system, most current studies only consider the coordinated cooperation between grid-following energy storages during frequency regulation or the influence of a single parameter on the control performance. With the increasing penetration rate of grid-forming energy storage, how to make good use of the advantages of the virtual inertia support and frequency support of grid-forming energy storage, and at the same time consider the influence of multiple parameters such as the SOC and active power margin of grid-following energy storage on the control performance, and realize the coordinated frequency regulation of grid-forming energy storage and traditional grid-following energy storage has been rarely studied.

[0005] Therefore, it is very necessary to design a coordinated frequency regulation control method including grid-forming energy storage and grid-following energy storage. Summary of the Invention

[0006] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a coordinated frequency regulation control method including grid-forming energy storage and grid-following energy storage.

[0007] To achieve the above purpose, the present invention provides the following solutions:

[0008] The present invention provides a coordinated frequency regulation control method including grid-forming energy storage and grid-following energy storage, comprising:

[0009] Constructing a simulation model including a grid-forming energy storage unit, a grid-following energy storage unit, a synchronous generator, and an AC load;

[0010] When the simulation model has a frequency disturbance, obtain the frequency deviation, and determine whether the absolute value of the frequency deviation exceeds a threshold. If it exceeds the set threshold, regulate the network-forming energy storage unit and the grid-following energy storage unit respectively. If it does not exceed the set threshold, enter the next sampling period;

[0011] Among them, if it exceeds the set threshold, control the charge and discharge of the energy storage unit according to the positive or negative of the frequency deviation.

[0012] Preferably, the regulation of the network-forming energy storage unit is as follows:

[0013] Adjust the virtual inertia parameter according to the state of charge of the battery of the network-forming energy storage unit. At the same time, in order to increase the frequency modulation effect, introduce the active power-frequency equation into the network-forming energy storage unit to participate in frequency support.

[0014] Preferably, adjusting the virtual inertia parameter according to the state of charge of the battery of the network-forming energy storage unit is as follows:

[0015] When the system frequency drops, there is:

[0016]

[0017] When the system frequency rises, there is:

[0018]

[0019] In the formula, J i is the virtual inertia parameter of the i-th network-forming energy storage in the system, J0 is the initial virtual inertia, K J is the virtual inertia adjustment coefficient, and SOC i is the state of charge of the i-th network-forming energy storage.

[0020] Preferably, introducing the active power-frequency equation into the network-forming energy storage unit to participate in frequency support is as follows:

[0021] Introducing the active power-frequency equation into the network-forming energy storage unit to participate in frequency support, the specific formula is:

[0022] P ref =P set +k ω (ω N -ω)

[0023] In the formula, P set is the set value of the active power.

[0024] Preferably, the regulation of the grid-following energy storage unit is as follows:

[0025] Since the grid-connected energy storage unit only participates in the primary frequency regulation of the system, the state of charge (SOC) of the battery and the adjustable active power margin of the converter are used as constraint conditions to allocate the active power of the grid-connected energy storage unit to participate in the system frequency regulation. Among them, let the number of grid-connected energy storage units be N, and the capacity of each energy storage battery be P N , the SOC of the i-th energy storage battery is SOC i , and SOC1 < SOC2 < … < SOC N , the active power initially generated by the i-th energy storage is P i , then the active power margin ΔP i of the i-th energy storage battery = |P N - P i |;

[0026] When the system active load suddenly increases and the system frequency drops, the power setting value of the grid-connected energy storage unit at this time is:

[0027] P set,Δf＜0 = K ΔP (K soc ΔP i + P i ) + K lim P max

[0028]

[0029] In the formula, K ΔP is the power margin constraint coefficient, K lim is the maximum power convention coefficient. When the power margin ΔP i = |P N - P i | is 0, indicating that the energy storage has no excess active power regulation margin, then K ΔP takes 0, K lim takes 1. At this time, the energy storage emits the maximum active power for primary frequency regulation. When the power margin ΔP i = |P N - P i | is not 0, then K ΔP takes 0.95, K lim takes 0. At this time, the grid-connected energy storage unit adjusts the power according to the SOC size to ensure that the energy storage with a larger SOC emits as much active power as possible;

[0030] When the system active load suddenly decreases and the system frequency rises, the power setting value of the grid-connected energy storage unit at this time is:

[0031] P set,Δf＞0 = K ΔP (K soc ΔP i + P i ) + Klim P max

[0032]

[0033] In the formula, K ΔP is the power margin constraint coefficient, and K lim is the maximum power convention coefficient. When the power margin ΔP i = |P N - P i | is 0, indicating that there is no redundant active power regulation margin for the energy storage, then K ΔP takes 0, and K lim takes -1. At this time, the energy storage absorbs the maximum active power for primary frequency modulation. When the power margin ΔP i = |P N - P i | is not 0, then K ΔP takes -0.95, and K lim takes 0. At this time, the grid-connected energy storage unit adjusts the power according to the SOC value, ensuring that the energy storage with a smaller SOC absorbs as much active power as possible.

[0034] According to the specific embodiments provided by the present invention, the following technical effects are disclosed by the present invention:

[0035] The present invention provides a coordinated frequency modulation control method including a grid-forming energy storage and a grid-connected energy storage. The method includes: constructing a simulation model including a grid-forming energy storage unit, a grid-connected energy storage unit, a synchronous generator, and an AC load. When a frequency disturbance occurs in the simulation model, obtaining the frequency deviation, and determining whether the absolute value of the frequency deviation exceeds a threshold. If it exceeds the set threshold, the grid-forming energy storage unit and the grid-connected energy storage unit are respectively regulated. If it does not exceed the set threshold, the next sampling period is entered. Among them, if it exceeds the set threshold, the charging and discharging of the energy storage unit are controlled according to the positive and negative of the frequency deviation. The present invention gives full play to the virtual inertia support and frequency independent support of the grid-forming energy storage unit. The grid-connected energy storage unit quickly responds to the upper-layer control signal, achieving a better frequency support effect, and can quickly and effectively control the coordinated participation of the grid-connected energy storage and the grid-forming energy storage in the system frequency regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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 in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1Schematic diagram of the dynamic response characteristic curve of a system with energy storage from being disturbed to the frequency returning to normal provided by an embodiment of the present invention;

[0038] Figure 2 Method block diagram provided by an embodiment of the present invention;

[0039] Figure 3 Topological structure diagram of a simulation system for a coordinated frequency regulation control method including network-forming and grid-following energy storage provided by an embodiment of the present invention;

[0040] Figure 4 Schematic diagram for comparing the simulated frequency regulation effects provided by an embodiment of the present invention;

[0041] Figure 5 Schematic diagram of the active power output of three energy storage units provided by an embodiment of the present invention;

[0042] Figure 6 Effect diagram of adjusting the virtual inertia coefficient of the network-forming energy storage unit provided by an embodiment of the present invention. Specific embodiments

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying 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 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 shall fall within the protection scope of the present invention.

[0044] The purpose of the present invention is to provide a coordinated frequency regulation control method including network-forming and grid-following energy storage, which gives full play to the virtual inertia support and frequency independent support of the network-forming energy storage unit. The grid-following energy storage unit quickly responds to the upper-layer control signal, achieving a better frequency support effect, and can quickly and effectively control the coordinated participation of the grid-following energy storage and the network-forming energy storage in the system frequency regulation.

[0045] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0046] Figure 1 The dynamic response characteristic curve of a system with energy storage from being disturbed to the frequency returning to normal provided by an embodiment of the present invention is described in detail as follows:

[0047] The process of the power system from the occurrence of a disturbance to the lowest point of the system frequency usually includes disturbance power distribution, inertia response, and primary frequency regulation processes. Among them, t0 is the disturbance moment, t1 is the moment when the governor operates, and t2 is the moment of the lowest frequency point;

[0048] The process by which the system prevents frequency from dropping and restores to normal frequency change can be roughly divided into the following stages:

[0049] At the starting stage of t0, the synchronous generator can automatically share the disturbance power and maintain the power balance of the system;

[0050] The stage of t0 - t1 is the inertia response stage. The remaining online generators convert their rotational kinetic energy (inertia) into actual power generation to maintain the power balance of the system. At this time, the grid-forming energy storage unit with virtual inertia can provide virtual inertia for the system to slow down the rate of system frequency reduction;

[0051] The stage of t1 - t2 is the stage where inertia response and primary frequency regulation act together. At the moment of t1, the governor acts to increase the mechanical power until the unbalanced power of the system is reduced to zero. At the moment of t2, the lowest frequency point is reached. In this stage, the grid-forming energy storage can perform independent frequency regulation according to the control characteristics, while the grid-following energy storage, due to being regulated by the upper layer, completes its power distribution based on the constraints of its SOC and active power margin, realizing the coordinated frequency regulation of the grid-following energy storage and the grid-forming energy storage;

[0052] The stage of t2 - t3 is other frequency response stages, and subsequent secondary frequency regulation and other frequency regulation measures are successively put into use.

[0053] Figure 2 The flowchart of the method provided by the embodiment of the present invention is as Figure 2 shown. The present invention provides a coordinated frequency regulation control method including a grid-forming energy storage and a grid-following energy storage, which includes:

[0054] Construct a simulation model including a grid-forming energy storage unit, a grid-following energy storage unit, a synchronous generator, and an AC load. Among them, the topological structure diagram of the simulation model is as Figure 3 shown;

[0055] When a frequency disturbance occurs in the simulation model, obtain the frequency deviation, and judge whether the absolute value of the frequency deviation exceeds the threshold. If it exceeds the set threshold, then regulate the grid-forming energy storage unit and the grid-following energy storage unit respectively. If it does not exceed the set threshold, then enter the next sampling period;

[0056] Among them, if it exceeds the set threshold, then control the charging and discharging of the energy storage unit according to the positive and negative of the frequency deviation (positive represents charging, and negative represents discharging).

[0057] The regulation of the grid-forming energy storage unit is specifically as follows:

[0058] If the absolute value of the frequency deviation exceeds the set threshold, during the inertial response stage, the network-forming energy storage provides virtual inertia support for the power grid relying on its control characteristics. To optimize the SOC (ensuring that the energy storage with a large SOC has a large virtual inertia when the system frequency drops to generate the most active power, and the energy storage with a small SOC has a large virtual inertia when the frequency rises to minimize power output), the virtual inertia parameter is adjusted according to the state of charge of the battery of the network-forming energy storage unit. At the same time, to enhance the frequency regulation effect, the active power-frequency equation is introduced for the network-forming energy storage unit to participate in frequency support.

[0059] The virtual inertia parameter is adjusted according to the state of charge of the battery of the network-forming energy storage unit, specifically as follows:

[0060] When the system frequency drops, there is:

[0061]

[0062] When the system frequency rises, there is:

[0063]

[0064] In the formula, J i is the virtual inertia parameter of the i-th network-forming energy storage in the system, J0 is the initial virtual inertia, K J is the virtual inertia adjustment coefficient, and SOC i is the state of charge of the i-th network-forming energy storage.

[0065] The active power-frequency equation is introduced for the network-forming energy storage unit to participate in frequency support, specifically as follows:

[0066] The active power-frequency equation is introduced for the network-forming energy storage unit to participate in frequency support, and the specific formula is:

[0067] P ref = P set + k ω (ω N - ω)

[0068] In the formula, P set is the set value of the active power.

[0069] The network-following energy storage units are regulated separately, specifically as follows:

[0070] Since the network-following energy storage units only participate in the primary frequency regulation of the system, the state of charge SOC of the battery and the adjustable active power margin of the converter are used as constraint conditions to allocate the active power of the network-following energy storage units to participate in the system frequency regulation. Among them, let the number of network-following energy storage units be N, the capacity of each energy storage battery be P N , the SOC of the i-th energy storage battery be SOC i , and SOC1 < SOC2 < … < SOCN , the active power initially generated by the i-th energy storage is P i , then the active power margin ΔP of the i-th energy storage battery i = |P N - P i |;

[0071] When the active power load of the system suddenly increases and the system frequency drops, the power setting value of the grid-connected energy storage unit at this time is:

[0072] P set,Δf＜0 = K ΔP (K soc ΔP i + P i ) + K lim P max

[0073]

[0074] In the formula, K ΔP is the power margin constraint coefficient, K lim is the maximum power convention coefficient. When the power margin ΔP i = |P N - P i | is 0, indicating that the energy storage has no redundant active power regulation margin, then K ΔP takes 0, K lim takes 1. At this time, the energy storage generates the maximum active power for primary frequency modulation. When the power margin ΔP i = |P N - P i | is not 0, then K ΔP takes 0.95, K lim takes 0. At this time, the grid-connected energy storage unit adjusts the power according to the SOC value to ensure that the energy storage with a large SOC generates as much active power as possible;

[0075] When the active power load of the system suddenly decreases and the system frequency rises, the power setting value of the grid-connected energy storage unit at this time is:

[0076] P set,Δf＞0 = K ΔP (K soc ΔP i + P i ) + K lim P max

[0077]

[0078] In the formula, K ΔP is the power margin constraint coefficient, K lim is the maximum power convention coefficient. When the power margin ΔP i= |P N -P i | being 0 indicates that there is no redundant active power regulation margin for energy storage, so K ΔP takes 0, and K lim takes -1 (positive and negative respectively represent discharging / charging). At this time, the energy storage absorbs the maximum active power for primary frequency regulation. When the power margin ΔP i = |P N -P i | is not 0, then K ΔP takes -0.95, and K lim takes 0. At this time, the grid-following energy storage unit adjusts the power according to the SOC value, ensuring that the energy storage with a smaller SOC absorbs as much active power as possible.

[0079] Based on the above method, the present invention also provides a coordinated frequency regulation control system including a grid-forming and a grid-following energy storage. The system includes a Simulink simulation system and a calculation module;

[0080] Among them, in the Simulink simulation system, a simulation model including a grid-forming energy storage unit, a grid-following energy storage unit, a synchronous generator, and an AC load is constructed;

[0081] In the Simulink simulation system, an active load disturbance is set, and the frequency from the start to the end of the simulation is collected based on the acquisition module in the Simulink simulation system. The difference between the rated frequency and the actually collected frequency is the frequency deviation, and the absolute value of the frequency deviation is |Δf|. It is judged whether the absolute value of the frequency deviation exceeds the set threshold;

[0082] The calculation module is used for the case where the absolute value of the frequency deviation exceeds the threshold. The grid-forming energy storage based on the virtual synchronous generator control provides virtual inertia for the system, and at the same time controls the dynamic adjustment of the virtual inertia parameters to adapt to the change of SOC. The active frequency droop control ensures that the grid-forming energy storage can provide autonomous frequency support. The grid-following energy storage optimizes the power distribution based on the state of charge SOC of the battery and the adjustable active power margin of the converter as constraints, realizing the coordinated frequency support of the grid-forming energy storage and the grid-following energy storage.

[0083] The present invention also gives a simulation example, which uses one grid-forming energy storage unit, two grid-following energy storage units, one synchronous generator, and an AC load. The simulation condition takes a 20% sudden increase in load as an example, and the simulation parameters are shown in Table 1;

[0084] Table 1 Main system parameters

[0085]

[0086]

[0087] Figure 4It shows the frequency modulation effect diagram of a coordinated frequency modulation control method for a power grid-forming and grid-following energy storage provided by the present invention. It can be seen that when the system frequency drops, the lowest point of the frequency drop using the frequency modulation control method provided by the present invention is significantly lifted.

[0088] Figure 5 It shows the active power output of a power grid-forming energy storage and two grid-following energy storages provided by an embodiment of the present invention under the condition of a 20% sudden increase in active load, which is described in detail as follows:

[0089] As Figure 5 shown, the power grid-forming energy storage responds quickly when the load suddenly increases at 8 s, and autonomously emits active power to support the system frequency drop; the initial active power of the grid-following energy storage unit 1 is 2 MW, and the initial SOC is relatively high at 85%. When the frequency drops, it emits about 4.5 MW of active power, controls it to emit more active power to support the system frequency drop, and resumes the initial output after the absolute value of the frequency deviation is less than the set threshold. The initial active power of the grid-following energy storage unit 2 is 5 MW, and its initial SOC is 40%. It controls it to emit less active power to avoid over-discharging of the SOC. When the frequency drops, it emits about 5.5 MW of active power, and resumes the initial output after the absolute value of the frequency deviation is less than the set threshold.

[0090] Figure 6 It shows the virtual inertia regulation process of the power grid-forming energy storage unit provided by an embodiment of the present invention when the frequency drops, which is described in detail as follows:

[0091] As Figure 6 shown, the initial virtual inertia of the power grid-forming energy storage is about 3.185 kg·m 2 , and when the system frequency drops, it ensures that the battery with a large SOC has a large virtual inertia when the system frequency drops, so as to emit the most active power.

[0092] Each embodiment in this specification is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0093] Specific examples are used in this article to elaborate on the principles and implementation methods of the present invention. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A coordinated frequency regulation control method for a power grid forming type and a grid following type energy storage, characterized in that, Including: Construct a simulation model including a network-forming energy storage unit, a grid-following energy storage unit, a synchronous generator, and an AC load; When a frequency disturbance occurs in the simulation model, obtain the frequency deviation, and judge whether the absolute value of the frequency deviation exceeds a threshold. If it exceeds the set threshold, adjust the network-forming energy storage unit and the grid-following energy storage unit respectively. If it does not exceed the set threshold, enter the next sampling period; Among them, if it exceeds the set threshold, control the charge and discharge of the energy storage unit according to the positive or negative of the frequency deviation.

2. The method according to claim 1, wherein Adjust the network-forming energy storage unit specifically as follows: Adjust the virtual inertia parameter according to the state of charge of the battery of the network-forming energy storage unit. At the same time, to increase the frequency modulation effect, introduce the active-power - frequency equation into the network-forming energy storage unit to participate in frequency support.

3. The method according to claim 2, characterized in that, Adjust the virtual inertia parameter according to the state of charge of the battery of the network-forming energy storage unit specifically as follows: When the system frequency drops, there is: When the system frequency rises, there is: Where J i is the virtual inertia parameter of the i-th network-forming energy storage in the system, J0 is the initial virtual inertia, and K J is the virtual inertia regulation coefficient, and SOC i is the state of charge of the i-th network-forming energy storage.

4. The method according to claim 3, wherein Introduce the active-power - frequency equation into the network-forming energy storage unit to participate in frequency support specifically as follows: Introduce the active-power - frequency equation into the network-forming energy storage unit to participate in frequency support, and the specific formula is: P ref = P set + k ω (ω N - ω) Where P set is the set value of the active power.

5. The method according to claim 4, wherein Adjust the grid-following energy storage unit respectively specifically as follows: Since the grid-following energy storage unit only participates in the primary frequency regulation of the system, the state of charge (SOC) of the battery and the adjustable active power margin of the converter are used as constraint conditions to allocate the active power of the grid-following energy storage unit to participate in the system frequency regulation. Among them, let the number of grid-following energy storage units be N, and the capacity of each energy storage battery be P N , the SOC of the i-th energy storage battery is SOC i , and SOC1 < SOC2 < … < SOC N , the active power initially generated by the i-th energy storage is P i , then the active power margin ΔP of the i-th energy storage battery i = |P N - P i |; When the system active load suddenly increases and the system frequency drops, the power set value of the grid-following energy storage unit at this time is: P set,Δf＜0 = K ΔP (K soc ΔP i + P i ) + K lim P max where K ΔP is the power margin constraint coefficient, and K lim is the maximum power convention coefficient. When the power margin ΔP i = |P N - P i | is 0, indicating that there is no redundant active power regulation margin for the energy storage, then K ΔP takes 0, and K lim takes 1. At this time, the energy storage emits the maximum active power for primary frequency modulation. When the power margin ΔP i = |P N - P i | is not 0, then K ΔP takes 0.95, and K lim takes 0. At this time, the grid-connected energy storage unit adjusts the power according to the SOC value, ensuring that the energy storage with a larger SOC emits as much active power as possible; When the system active load suddenly decreases and the system frequency rises, the power set value of the grid-following energy storage unit at this time is: P set,Δf＞0 = K ΔP (K soc ΔP i + P i ) + K lim P max Wherein, K ΔP is the power margin constraint coefficient, and K lim is the maximum power convention coefficient. When the power margin ΔP i = |P N - P i | is 0, indicating that there is no redundant active power regulation margin for the energy storage, then K ΔP takes 0, and K lim takes -1. At this time, the energy storage absorbs the maximum active power for primary frequency modulation. When the power margin ΔP i = |P N - P i | is not 0, then K ΔP takes -0.95, and K lim takes 0. At this time, the grid-connected energy storage unit adjusts the power according to the SOC value to ensure that the energy storage with a smaller SOC absorbs as much active power as possible.

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