Wind power plant and energy storage quasi-synchronous electromechanical grid frequency cooperative support control method and system

Abstract

The invention provides a wind power plant and energy storage quasi-synchronous generator power grid frequency cooperative support control method and system, and the method comprises the steps: carrying out the response remodeling of a wind power plant-wind power plant-flexible direct current-energy storage system to the power grid load change based on the power grid frequency response process of a conventional synchronous generator, and obtaining delta P in the response process; and based on the magnitude relationship between the delta P and the active power output of the energy storage system, frequency response control of the wind turbine generator and the energy storage system is coordinated. The power grid frequency response process of a traditional synchronous generator is decomposed, and frequency response control of a wind turbine generator and frequency response control of an energy storage system are utilized for cooperation, so that response of wind power and response of energy storage are integrated, characteristics similar to those of a power source of the traditional synchronous generator are embodied, and therefore the frequency stability of a power grid is enhanced; and the work of power grid dispatchers is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of power grid technology, and in particular to a method and system for coordinated support control of wind farm and energy storage quasi-synchronous machine grid frequency. Background Art

[0002] As my country's power system gradually shifts from traditional fossil energy to clean renewable energy, the characteristics of the power grid are also changing, which is reflected in the increased volatility of power sources, the reduced inertia of the power system, and the weakening of the equivalent power grid strength. In this context, the growing capacity of wind power (hundreds of MW to GW) not only replaces fossil energy, but also brings corresponding challenges. The replacement of synchronous generators by wind power without inertia reduces the overall inertia of the power grid and seriously affects the frequency stability of the power grid operation. If a new energy system with wind and solar power as the main power source is to be built, wind farms need to transform from follower power sources to dominant power sources, and to a certain extent, simulate synchronous generators, assume the obligation to establish the voltage of the power system and maintain the real-time energy balance of the system, and support the stability of the power grid frequency. Summary of the invention

[0003] In view of the defects in the prior art, the object of the present invention is to provide a method and system for coordinated support control of the frequency of a quasi-synchronous machine network of a wind farm and energy storage.

[0004] According to one aspect of the present invention, a method for coordinated support control of the frequency of a quasi-synchronous electromechanical network of a wind farm and energy storage is provided, comprising:

[0005] Based on the grid frequency response process of the synchronous generator, the response of the wind farm-flexible direct current-energy storage system to the grid load change is reshaped to obtain the actual additional power ΔP that the system needs to generate during the response reshaping process;

[0006] Based on the relationship between the additional power ΔP actually required by the system and the active output of the energy storage system, the frequency response of the wind turbine generator set and the energy storage system are cooperatively controlled.

[0007] Preferably, the grid frequency response process of the synchronous generator includes:

[0008] At time t1, the synchronous generator has two initial operating points, namely, initial active power P0 and initial frequency f0;

[0009] At time t1, a sudden load change occurs, and the active power suddenly changes from P0 to P1. At this time, the synchronous generator bears the sudden load power of P1-P0 according to the electrical distance to the load sudden change point; at the same time, the output frequency starts to decrease from f0;

[0010] During the time period t1-t2, multiple synchronous generators redistribute the load power according to the size of inertia, and the power angle oscillates. After the time point P2, the oscillation ends, the load power borne by each synchronous generator tends to be stable, and finally transitions to P3; P3 is determined by the frequency regulation coefficient of the load and the primary frequency regulation coefficient of the unit itself;

[0011] Time t3 is the time corresponding to P3. At this time, the output frequency is also stable at f3.

[0012] Preferably, the step of reshaping the response of the wind farm-flexible direct current-energy storage system to the change in grid load to obtain the additional power ΔP actually required by the system during the response reshaping process includes:

[0013] Detect the frequency change rate when the grid frequency changes beyond the dead zone;

[0014] Based on the frequency change rate and the virtual inertia of the wind farm-flexible direct current-energy storage system, the power that needs to be increased when the grid frequency changes beyond the dead zone is calculated;

[0015] Add the delay factor and obtain the actual additional power based on the calculated additional power.

[0016] The actual additional power required decreases as the frequency decreases until the final actual additional power required is obtained;

[0017] Enter the primary frequency modulation stage.

[0018] Preferably, the additional power required when the grid frequency changes beyond the dead zone is specifically:

[0019]

[0020] ΔP0 represents the additional power required by the virtual inertia calculation; H v Represents the virtual inertia coefficient, which is used to characterize the effect of frequency change on power change and is related to the number of submodules and the size of the submodule capacitance; ω g Represents the grid frequency, dω g / dt represents the change in grid frequency.

[0021] Preferably, the power actually required to be increased is specifically:

[0022]

[0023] ΔP represents the actual additional power required by the system; ΔP0 represents the additional power required based on the virtual inertia calculation, that is, the theoretical additional power required when the grid frequency changes beyond the dead zone; Represents a first-order inertia link, indicating the delay due to control, detection and filtering links; KPF Indicates the proportional coefficient between the frequency change and the active power change, also expressed as the primary frequency modulation coefficient; Δω g Represents the frequency change.

[0024] Preferably, the final actual additional power required is specifically:

[0025] ΔP=-K PF Δω g .

[0026] Preferably, the coordinated control of the frequency response of the wind turbine generator set and the energy storage system based on the relationship between the power ΔP actually required to be generated by the system and the active output of the energy storage system includes:

[0027] If the active output capacity of the energy storage system is greater than the additional power ΔP that the system actually needs to generate, all the power will be provided by the energy storage system.

[0028] Preferably, the coordinated control of the frequency response of the wind turbine generator set and the energy storage system based on the magnitude relationship between the ΔP and the active output of the energy storage system includes:

[0029] If the active output capacity of the energy storage system is less than ΔP, the wind turbine will provide the inertia response, and the energy storage system will make up the remaining power.

[0030] Preferably, if the energy storage system is still unable to compensate the active power output to ΔP after the wind turbine generator system provides an inertia response, the energy storage system outputs at maximum power.

[0031] According to a second aspect of the present invention, a quasi-synchronous electromechanical network frequency coordinated support control system for a wind farm and energy storage is provided, comprising:

[0032] Response reshaping module: Based on the grid frequency response process of the synchronous generator, the wind farm-flexible direct current-energy storage system is reshaped in response to grid load changes to obtain the actual additional power ΔP that the system needs to generate during the response reshaping process;

[0033] System response module: based on the relationship between the power ΔP actually required to be generated by the system and the active output of the energy storage system, coordinately controls the frequency response of the wind turbine and the energy storage system.

[0034] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0035] The method and system for coordinated support control of the frequency of a quasi-synchronous machine grid of a wind farm and energy storage in the embodiment of the present invention decomposes the grid frequency response process of a traditional synchronous generator, and coordinates the frequency response control of the wind turbine and the energy storage system respectively, so that the response of wind power and energy storage is integrated, reflecting characteristics similar to those of a traditional synchronous generator power supply, thereby enhancing the frequency stability of the grid and facilitating the work of grid dispatchers. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0037] Figure 1 It is a flow chart of a method for coordinated support control of the frequency of a quasi-synchronous power grid of a wind farm and energy storage in one embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the response process of a synchronous generator to a change in grid load in a preferred embodiment of the present invention; wherein (a) represents active power, and (b) represents frequency;

[0039] Figure 3 Schematic diagram of the response reshaping process of the wind farm-flexible direct current-energy storage system to the grid load change in a preferred embodiment of the present invention, wherein (a) represents active power and (b) represents frequency;

[0040] Figure 4 A single-line diagram of a simulation system in a specific embodiment of the present invention;

[0041] Figure 5 The present invention is a schematic diagram of the grid frequency response result of the simulation system in a specific embodiment of the present invention connected to the synchronous grid; wherein (a) represents the synchronous machine speed (grid frequency); (b) represents the bipolar DC voltage difference; (c) represents the wind farm frequency; (d) represents the output active power of wind farm 1; (e) represents the output active power of wind farm 1 energy storage; (f) represents the output active power of wind farm 2; (g) represents the output active power of wind farm 2 energy storage; (h) represents the active power of wind farm side converter 1; (i) represents the active power of wind farm side converter 2; (j) represents the active power of grid side converter 1; (k) represents the active power of grid side converter 2. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0043] In one embodiment of the present invention, a method for coordinated support control of the frequency of a quasi-synchronous power grid of a wind farm and energy storage is provided, such as Figure 1 As shown, the following steps are included:

[0044] Step 1: Based on the grid frequency response process of the synchronous generator, the wind farm-flexible direct current-energy storage system is reshaped in response to the grid load change, and the power ΔP actually required to be increased by the system during the response reshaping process is obtained;

[0045] Step 2: Based on the relationship between the additional power ΔP actually required by the system and the active output of the energy storage system, the frequency response of the wind turbine and the energy storage system are coordinated and controlled.

[0046] The above-mentioned embodiments can solve the problem that the wind farm and energy storage do not cooperate well when performing frequency response to the power grid and cannot simulate the response characteristics of the real synchronous generator.

[0047] In a preferred embodiment of the present invention, the grid frequency response process of the conventional synchronous generator is decomposed. Figure 2 As shown in Figure (a) and (b), they are respectively the active power and frequency response curves of a typical synchronous generator when the grid load suddenly increases. P0 and f0 are the initial working points of the synchronous generator. A sudden load change occurs at time t1. At this time, the synchronous generator bears the sudden load power of (P1-P0) according to the electrical distance to the load mutation point, and the output frequency begins to decrease. In the time period t1-t2, the load power will be redistributed among multiple synchronous generators according to the size of inertia, and a small power angle oscillation will occur. After time point P2, the oscillation ends, the load power borne by each unit tends to be stable, and finally transitions to P3, and P3 is determined by the frequency regulation coefficient of the load and the primary frequency regulation coefficient of the unit itself.

[0048] Based on the grid frequency response process of the traditional synchronous generator in the above embodiment, in another preferred implementation, the response of the wind farm-flexible direct current-energy storage system to the grid load change is reshaped. For the wind farm-flexible direct current-energy storage system, there is no need to simulate the output power fluctuation caused by the power angle oscillation during the period of P1-P2, but the response characteristics shown in Figure 3 (a) and Figure (b) can be adopted. Specifically:

[0049] When the grid frequency changes beyond the dead zone, the frequency change rate df / dt is detected, and the power that needs to be increased is calculated based on the virtual inertia of the wind farm-flexible direct current-energy storage system:

[0050]

[0051] Among them, ΔP0 represents the power that needs to be increased by calculating the virtual inertia; H v Represents the virtual inertia coefficient, which is used to characterize the effect of frequency change on power change and is related to the number of submodules and the size of the submodule capacitance; ω g Represents the grid frequency, dω g / dt represents the change in grid frequency. Since ω=2πf, the formula can be expressed as This establishes the relationship between the rate of change of grid frequency and the change in active power. Since 2π is a constant, ω is often used. g Replace f g Indicates the grid frequency.

[0052] Ideally, the additional power should be completed instantly, but in reality, due to the delay of control, detection and filtering, the actual power response will have a delay of about 100 ms. Then, set:

[0053]

[0054] In the formula, ΔP represents the actual additional power required by the system; ΔP0 represents the additional power required by the virtual inertia calculation, that is, the theoretical additional power required when the grid frequency changes beyond the dead zone; Represents a first-order inertia link, indicating the delay due to control, detection and filtering; K PF It indicates the proportional coefficient between the frequency change and the active power change, and can also be expressed as the primary frequency modulation coefficient; Δω g Represents the frequency change.

[0055] At this point, ΔP will continue to decrease as the frequency decreases until eventually:

[0056] ΔP=-K PF Δω g

[0057] Primary frequency regulation refers to the system adjusting active power to adapt to changes in system frequency. Due to physical factors (delays in control, detection, filtering, etc.), there is a deviation between the required additional power calculated by virtual inertia and the actual required additional power. Therefore, after the deviation is completely filtered out, the primary frequency regulation link will be entered. That is, when ΔP = -K PF Δω g Enter the primary frequency modulation stage.

[0058] Through the reshaping in the above embodiments, ΔP in the entire response process is obtained. In some preferred embodiments, if the active output capacity of the energy storage is greater than ΔP, all power can be provided by the energy storage. In other embodiments, if the active output capacity of the energy storage is less than ΔP, the wind turbine needs to provide an inertia response, and then the energy storage can make up the rest. Furthermore, if the energy storage still cannot make up the active output to ΔP after the wind turbine provides an inertia response, the energy storage can be output at maximum power.

[0059] Based on the same inventive concept, in other embodiments of the present invention, a quasi-synchronous electromechanical network frequency coordinated support control system for a wind farm and energy storage is provided, comprising:

[0060] Response reshaping module: Based on the grid frequency response process of the synchronous generator, the wind farm-flexible direct current-energy storage system is reshaped in response to grid load changes to obtain the actual additional power ΔP that the system needs to generate during the response reshaping process;

[0061] System response module: based on the relationship between the power ΔP actually required to be generated by the system and the active output of the energy storage system, coordinately controls the frequency response of the wind turbine and the energy storage system.

[0062] The modules / units in the above examples of the present invention may specifically refer to the implementation techniques of the corresponding steps of the method for coordinated frequency support control of a quasi-synchronous machine network of a wind farm and energy storage in the above embodiments, which will not be described in detail here.

[0063] In order to verify the feasibility and effectiveness of the quasi-synchronous machine grid frequency coordinated support control method of wind farm and energy storage proposed in the above embodiment, a specific embodiment of the present invention, based on the simulation system shown in 4, established a simulation model of a large-scale wind farm connected to the grid through a multi-terminal flexible direct current transmission system in PSCAD / EMTDC. Among them, the capacity of wind farm 1, wind farm side converter 1 and grid side converter 1 is 750MW, and the capacity of wind farm 2, wind farm side converter 2 and grid side converter 12 is 1500MW. The specific parameters of the system are shown in the following table:

[0064] Table 1 Parameters of converter station 1 on the wind farm side and converter station 1 on the grid side

[0065]

[0066] Table 2 Parameters of converter station 2 on wind farm side and converter station 2 on grid side

[0067]

[0068] Table 3 Line parameters

[0069]

[0070]

[0071] Table 4 Aggregation parameters of full-power wind turbines

[0072]

[0073] The grid-side converter 1 and the grid-side converter 2 are both connected to the same grid, which consists of a 20GW synchronous generator and a 5GW load. P Set to 1, K dc Set to 5, K W Set to 125, H v Set to 0.1s, and the active power setting is set to 375MW. K of the grid-side converter 2 P Set to 1, K dc Set to 10, K W Set to 250, H v The time interval is set to 0.1s, the active power setting is set to 750MW, and the energy storage system with a rated capacity of 15% is connected to the AC side of the sending-end converter. At the 15th second, the grid load suddenly increases by 1GW. The simulation results are as follows: Figure 5 As shown in Figures (a) to (k). It can be found that when the grid frequency changes, the frequency change can be accurately mapped in the two wind farm frequencies through the DC grid and the bipolar DC voltage difference. After the wind turbines detect the frequency change, the two wind farms can provide inertia response in real time. The support power provided by the wind farms can be evenly divided between the two grid-side converters in proportion and flow into the grid to damp the grid frequency change. After the inertia response ends, the energy storage system can also compensate for the reduced power of the wind turbine to avoid a secondary drop. In addition, through the reshaping of the energy storage system, the grid frequency response characteristics of the wind farm-flexible direct current grid-connected system can be made close to the response characteristics of the synchronous generator.

[0074] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A method for coordinated support control of the frequency of a quasi-synchronous electromechanical network of a wind farm and energy storage, characterized in that: include: Based on the grid frequency response process of the synchronous generator, the response of the wind farm-flexible direct current-energy storage system to the grid load change is reshaped to obtain the actual additional power ΔP that the system needs to generate during the response reshaping process; Based on the relationship between the additional power ΔP actually required by the system and the active output of the energy storage system, the frequency response of the wind turbine generator set and the energy storage system are cooperatively controlled.

2. A method for coordinated support control of wind farm and energy storage quasi-synchronous machine network frequency according to claim 1, characterized in that: The grid frequency response process of the synchronous generator includes: At time t1, the synchronous generator has two initial operating points, namely, initial active power P0 and initial frequency f0; At time t1, a sudden load change occurs, and the active power suddenly changes from P0 to P1. At this time, the synchronous generator bears the sudden load power of P1-P0 according to the electrical distance to the load sudden change point; at the same time, the output frequency starts to decrease from f0; During the time period t1-t2, multiple synchronous generators redistribute the load power according to the size of inertia, and the power angle oscillates. After the time point P2, the oscillation ends, the load power borne by each synchronous generator tends to be stable, and finally transitions to P3; P3 is determined by the frequency regulation coefficient of the load and the primary frequency regulation coefficient of the unit itself; Time t3 is the time corresponding to P3. At this time, the output frequency is also stable at f3.

3. The method for coordinated support control of the frequency of a wind farm and a quasi-synchronous electromechanical network of energy storage according to claim 1 is characterized in that: The step of reshaping the response of the wind farm-flexible direct current-energy storage system to the grid load change to obtain the additional power ΔP actually required by the system during the response reshaping process includes: Detect the frequency change rate when the grid frequency changes beyond the dead zone; Based on the frequency change rate and the virtual inertia of the wind farm-flexible direct current-energy storage system, the power that needs to be increased when the grid frequency changes beyond the dead zone is calculated; Add the delay factor and obtain the actual additional power based on the calculated additional power. The actual additional power required decreases as the frequency decreases until the final actual additional power required is obtained; Enter the primary frequency modulation stage.

4. A method for coordinated support control of wind farm and energy storage quasi-synchronous machine network frequency according to claim 3, characterized in that: The additional power required when the grid frequency changes beyond the dead zone is specifically: ΔP0 represents the additional power required by the virtual inertia calculation; H v Represents the virtual inertia coefficient, which is used to characterize the effect of frequency change on power change and is related to the number of submodules and the size of the submodule capacitance; ω g Represents the grid frequency, dω g / dt represents the change in grid frequency.

5. A method for coordinated support control of wind farm and energy storage quasi-synchronous machine network frequency according to claim 4, characterized in that: The actual additional power required is specifically: ΔP represents the actual additional power required by the system; ΔP0 represents the additional power required based on the virtual inertia calculation, that is, the theoretical additional power required when the grid frequency changes beyond the dead zone; Represents a first-order inertia link, indicating the delay due to control, detection and filtering links; K PF Indicates the proportional coefficient between the frequency change and the active power change, also expressed as the primary frequency modulation coefficient; Δω g Represents the frequency change.

6. A method for coordinated support control of wind farm and energy storage quasi-synchronous machine network frequency according to claim 5, characterized in that: The final actual additional power required is specifically: ΔP=-K PF Give g 。 7. A method for coordinated support control of wind farm and energy storage quasi-synchronous machine network frequency according to claim 1, characterized in that: The method of collaboratively controlling the frequency response of the wind turbine generator set and the energy storage system based on the relationship between the power ΔP actually required to be generated by the system and the active output of the energy storage system includes: If the active output capacity of the energy storage system is greater than the additional power ΔP that the system actually needs to generate, all the power will be provided by the energy storage system.

8. The method for coordinated support control of the frequency of a quasi-synchronous electromechanical network of a wind farm and energy storage according to claim 1 is characterized in that: The collaboratively controlling the frequency response of the wind turbine generator set and the energy storage system based on the magnitude relationship between the ΔP and the active output of the energy storage system includes: If the active output capacity of the energy storage system is less than ΔP, the wind turbine will provide the inertia response, and the energy storage system will make up the remaining power.

9. A method for coordinated support control of wind farm and energy storage quasi-synchronous machine network frequency according to claim 8, characterized in that: If the energy storage system still cannot compensate the active output to ΔP after the wind turbine provides inertia response, the energy storage system will output at maximum power.

10. A wind farm and energy storage quasi-synchronous machine network frequency coordinated support control system, characterized in that: include: Response reshaping module: Based on the grid frequency response process of the synchronous generator, the wind farm-flexible direct current-energy storage system is reshaped in response to grid load changes to obtain the actual additional power ΔP that the system needs to generate during the response reshaping process; System response module: based on the relationship between the power ΔP actually required to be generated by the system and the active output of the energy storage system, coordinately controls the frequency response of the wind turbine and the energy storage system.

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